unigraphics nx7.5 - thermal and flow analysis

11/1/2011

SIEMENS

PLM THERMAL AND FLOW ANALYSIS

NX7.5 CAST | Nguyễn Thế Quang Dũng

[NX7.5 CAST] - THERMAL AND FLOW ANALYSIS 1

Nguyễn Thế Quang Dũng NX-PLM 2011年 11月 5 日

Thermal and Flow Analysis Estimated time to complete this course: 2–3 hours

This course introduces you to the following thermal and flow analysis modules within the Advanced

Simulation application:

NX Thermal

NX Flow

NX Thermal and Flow

NX Electronic Systems Cooling

NX Space Systems Thermal

Setup information

Part folder: simulation

NX role: Advanced with full menus

System preparation

NX Thermal analysis

1. Introduction

NX Thermal is an NX Advanced Simulation application that you can use to model steady-state or

transient thermal analysis for any product or system.

Create your simulation using these types of tools:



Boundary conditions, modeling, and simulation objects — To specify loads, constraints, and

other objects that characterize a specific portion of the model. Although assigned to

geometric features of the model (points, edges, faces, or solid bodies), boundary conditions

are ultimately applied to the elements by the solver.

Solution definition tools — To set controls and specify solver parameters that govern the

entire model. They are always applied to the solution as a whole, not to specific elements or

geometry.

Modifying the model

To change geometry, access the idealized part using the Part Navigator and the Modeling application.

A part update applies the change to the idealized part and marks the mesh for update.

Mesh changes in the Finite Element model (FEM) are automatically propagated to the Simulation.

You can override the mesh collector properties, defined in the FEM file, by using Edit Attributes

Overrides, or an Override Set simulation object in in the Simulation file.

You can access and modify any simulation entity using the Simulation Navigator. Selecting an object

highlights the corresponding elements or graphics symbols in the graphics window. You can also

copy or clone any boundary condition or solution.

Modeling conduction

The thermal solver uses a finite volume formulation for modeling heat conduction between elements

that share nodes, provided that:

Thermal conductivity and specific heat properties are defined for the elements. Specific heat

is required only for transient analyses.

2D elements have thickness physical property defined.

1D elements have a beam section defined.

0D elements have a mass and diameter defined.

Modeling convection

You can model convection implicitly using boundary conditions provided that you define a

Convection to Environment constraint on:

Faces of 3D solids

2D elements

1D elements with cross area defined

0D elements with diameter defined

You can use different types according to the phenomena modeled.

Convection to Environment

Use this option when you know either the Convection Coefficient or Parameter and Exponent

and the fluid temperature.

Free Convection to Environment

Use this option when you want to use a specific free convection correlation (example: hot air

rising).



Forced Convection to Environment

Use this option when you want to use a specific forced convection correlation (example: fans).

Both in transient and steady state solves, the solver calculates a single convection coefficient value

for the entire convecting surface based on the characteristic information you specify.

Convection can also be explicitly model using a coupled NX Thermal and Flow solution by

simulating the fluid volume and the embedded volumes and surfaces in a model.

Modeling radiation

The software simulates radiation based on view factors between radiating elements. The solver

calculates black body view factors between all radiation elements. To calculate radiative

conductances, it combines these factors with thermo-optical properties, which you define for every

radiating element.

For surfaces that do not obey the gray body approximation, ray-traced view factors can be calculated

instead of black body view factors.

You can calculate radiation between surfaces defined by:

Faces of 3D solid elements.

The top and/or bottom of 2D shell elements based on the orientation of the element normals

that you specify.

The implied surface of 1D beam elements based on the section properties you define.

The implied surface of 0D concentrated mass elements based on the diameters you specify.

If you want an element or group of elements to participate in radiation exchange, you must apply

Thermo-Optical Properties and define a Radiation simulation object to calculate view factors

between these elements.

2. Workflow and file structure

Step Task Application and file type

1. Create or import the model.

Modeling

part file (.prt)

2. Simplify the model using NX Modeling and Advanced

Simulation commands.

Modeling and Advanced

Simulation

idealized part file (_i.prt)

3. Define materials, physical properties, and thermo-optical

properties.

Advanced Simulation

FEM file (.fem)

4.

Mesh the model and define mesh collectors to organize

meshes and assign physical properties.

Associate all FEMs to their corresponding parts when using

an assembly FEM.

Advanced Simulation

FEM file (.fem)

Assembly FEM file




(.afm)

5.

Define solution options and solver parameters.

Define loads, constraints, and other special boundary

conditions.

Solve and review solution messages.

Advanced Simulation

Simulation file (.sim)

6.

Review and display results using post-processing tools.

Refresh results to obtain additional results sets.

Advanced Simulation


3. Defining element and model properties

Physical properties

Physical properties define characteristics of your part that are not being explicitly modeled. Use the

properties in the Physical Properties Manager dialog box to describe the physical qualities and

characteristics of an element, such as thickness, layer stack definition, and others.

You can define physical properties to specify:

A spherical Concentrated Mass with a diameter and mass that you specify for 0D elements.

For example, you can model the effect of rivets in a riveted plate under thermal loads by

creating 0D elements at the appropriate locations and then assigning a concentrated mass to

them. You can also use 0D elements to model the mass of liquid inside a soda can without

modeling the liquid volume as a 3D mesh.

A linear uniformly varying Non-Structural Mass in Mass per Length units, for 1D Beam

elements. Use this to add additional capacitance to 1D elements.

A Thickness value, or a Non-Structural Mass value in mass per area units, for Thin Shell

collectors of 2D Shell elements. Use the Non-Structural Mass to add weight without

explicitly modeling geometry and meshing elements for it. For example, material inserts and

surface coatings.

A Layer Definition for a Multi-Layer Shell Uniform collector type definition for 2D shell

elements, in which you specify the Total Thickness and the Number of Layers.

Use this property to model multiple layers with detailed through-plane conduction and

conduction.

A layer Stack Definition for a Multi-Layer Shell Non-Uniform collector type definition for

2D shell elements, in which you define a layer stack with multiple Layer modeling objects.

Each layer can have defined different materials, thickness, and thermo-optical properties.

Use this property to model conductive or radiative heat transfer through the physical layers of

a sandwich material construction. For example, you can use Multi-Layer Shell Non-Uniform

to model accurate heat transfer through composite materials.

When you define a physical property in the active FEM file, you assign it to a mesh collector. The

meshes and their elements are assigned to the mesh collector inherit those physical properties.



Modeling objects

Use modeling objects to define particular properties for specific entities or for the whole model. You

can create or modify modeling objects from the Modeling Objects Manager or from the solution,

simulation objects, loads, and constraint dialog boxes.

Some NX Thermal modeling objects include:

Ablation-Charing

Active Heater Controller

Duct Head Loss

Layer

Thermo-Optical Properties / Thermo-Optical Properties — Advanced

Thermostat

Thermo-optical properties

Use the Thermo-Optical Properties or Thermo-Optical Properties — Advanced modeling objects to

define Emissivity, which is required for all radiation modeling.

Absorptivity is required to model radiative heat transfer in the solar band. To model specular and

transmissive effects, you can also define a Thermo-Optical Properties — Advanced modeling object

with values for:

Specular Reflectivity

Transmissivity

Index of Refraction

You can model radiation in different bands defining corresponding thermo-optical properties in a

Thermo-Optical Properties — Advanced modeling object, and choosing one of the following two

types:

Select Gray to define constant or temperature varying values for infrared Emissivity and a

value for Absorptivity when want to define properties in the solar spectrum.

Select Non-Gray — Wavelength Dependent to define wavelength dependent values of non-

gray Emissivity, Specular Reflectivity and Transmissivity.

Emissivity and absorptivity values can be constant or defined in function of a Bidirectional

Reflectance Distribution Function (BRDF). Specular Reflectivity and Transmissivity can be defined

in terms of direction of incidence and angle of incidence.

Note: When you define Thermo-Optical Properties or Thermo-Optical Properties — Advanced for a 2D mesh,

you should always first check the element normals to identify the top and bottom sides of the mesh.

4. Defining boundary conditions

Define appropriate thermal loads and constraints to simulate your model.

Boundary condition Description

Thermal Loads Lets you define known heat sources in your model. You can define thermal




loads over geometry or elements as:

A Heat Load

An area-based Heat Flux

A volumetric Heat Generation

Temperature Lets you specify a known temperature for the geometry or elements that you

select, regardless of heat flow. This temperature can be constant, time

varying, or spatially distributed.

Convection to

Environment

Implicitly models natural and forced convection based on a heat transfer

coefficient or standard correlation.

You specify the known heat Convection Coefficient value or the Correlation

and the Characteristic Information.

Simple Radiation to

Environment

Models area-dependent radiation of surfaces with known emissivities and

view factors to a radiative environment temperature.

You can specify a value for Emissivity and View Factor from zero to one.

For more information on all simulation objects see the Advanced Simulation online help.

Boundary Conditions → Solver Specific Simulation Objects→ Solver Specific Simulation Objects

→ NX Thermal and Flow, NX Electronic Systems Cooling, and NX Space Systems Thermal .

5. Defining thermal couplings

Use the Thermal Couplings family of simulation objects to model:

Heat transfer between the surfaces of solid objects or components that are physically or

thermally in contact.

Create generalized conductances defined by a coefficient.

The use of thermal couplings can ease meshing tasks and reduce model size and complexity during

the solution.

Heat paths can be modeled within the model defining:

Conduction using a Thermal Coupling simulation object.

Radiation using a Thermal Coupling — Radiation simulation object

Conduction and radiation for a perfect contact using a Surface-to-Surface Contact

simulation object.

Convection using a Thermal Coupling — Convection simulation object.

One way or user-specified conduction using a Thermal Coupling — Advanced

simulation object.



A complete description on how to manually calculate thermal coupling values is available in the

online help.

Conducting heat paths

You usually create a Thermal Coupling between parallel surfaces. If you create thermal couplings

between non-parallel surfaces and edges, you introduce inaccuracies. The farther the two surfaces are

from parallel, the greater the inaccuracy.

You define thermal couplings between:

The faces of 3D meshed bodies

Faces meshed with 2D elements

Polygon edges or curves meshed with 1D elements

Points meshed with 0D elements.

Most geometry/mesh combinations are supported. The software uses the area of the primary region

and the direction of the surfaces normals to calculate the magnitude of the heat path, as shown in the

table.

Select Heat Transfer Calculation Area

Face of polygon body meshed with 3D

elements

Polygon face surface area

Polygon face meshed with 2D elements Polygon face surface area

Curve or polygon edge meshed with 1D

elements

Length of polygon edge x perimeter of the associated beam

cross section

Mesh point meshed with 0D element Surface of a sphere of the 0D element's diameter

Radiating heat paths

The Thermal Coupling — Radiation simulation object models simple radiation between close

parallel surfaces, or between objects at great distances. It does this by creating radiative heat paths

(radiative conductances) between elements with view factors greater than 0.

The Thermal Coupling — Radiation simulation object calculates radiative heat transfer q:

q=σ x GBVF x ε1 x A1 (T12 + T2

2) (T1 +T2)

You define either of the following:

Element emissivities

Gray Body View Factor

Effective Emissivity (Emissivity * Gray Body View Factor)

Where

σ is the Stefan-Boltzmann constant.

GBVF is the specified gray body view factor.

ε1 is the emissivity of the primary elements.

A1 is the area of overlap of the primary element with the secondary element.

T1 is the absolute temperature of the primary elements.



T2 is the absolute temperature of the secondary elements.

6. About radiation enclosures and view factors

View Factors

A view factor represents the fraction of radiative energy that is emitted from one entity and arrives to

a second entity. The thermal solver uses view factors to compute radiative heat transfer.

Two parallel surfaces in close proximity have a view factor that tends to unity. Two surfaces that are

nearly co-planar have a view factor that tends to zero.

View factor calculation

Enclosures

An enclosure divides the space into compartments on which view factors for a radiation requests are

calculated. View factor calculation is expensive in terms of machine resources, therefore defining

radiation enclosures saves solution time.

For radiation requests with transmissivity thermo-optical properties defined, the solver will

automatically track rays that go through elements.

You can indicate that an enclosure radiates to ambient. In this case the solver will create radiative

conductances from a point at a very large distance outside the model to elements of the enclosure

visible to the point.



Heatsource

2D mesh A

Thermo-Optical Properties:

Top (blue arrows)

2D mesh B


Top (blue arrows) and

Bottom (green arrows)

Enclosure 1 Enclosure 2

Radiation heat is exchanged from:

Heatsource to mesh B.

Mesh A to mesh B.

Heatsource

2D mesh A


Top (blue arrows)

2D mesh B


Top (blue arrows)


Radiation heat is exchanged only from the heatsource to mesh

B because thermo-optical properties are not defined on the

bottom side of the 2D elements.

To model radiation to environment the elements of mesh A

must have bottom thermo-optical properties.

Radiation simulation object

Use a Radiation simulation object to create view factor calculation requests for enclosures

comprised of selected geometry or elements.

To simulate radiation exchange you must define:

Entities with Thermo-Optical Properties with a specified value for emissivity and/or

absorptivity.

A Radiation simulation object. You can create one of these types of radiation requests:

o All Radiation to let the thermal solver detect enclosures.

o Enclosure Radiation where you define the relevant enclosures by selecting entities

with the top and/or bottom thermo-optical properties defined.

The solver can use one of these techniques as the black body view factor calculation method:

Hemicube Rendering — This technique uses your computer's graphics card to calculate view

factors quickly and accurately. You can only use this option if your computer's graphics card

supports the Open Graphics Library (OGL) standard.



Deterministic — This is an analytical approach that uses a ray casting algorithm, which

calculates the black body view factors based on the mathematical definition of view factor or

form factor.

Monte Carlo — This technique determines view factors as part of the radiative exchange

calculation. It uses a ray casting algorithm with statistical sampling to evaluate the radiative

exchange in an enclosure.

7. Solar and radiative heating

Solar Heating

Use a Solar Heating simulation object to model heating of objects on the surface of the earth due

to sun incidence. This command calculates direct solar view factors for selected elements at a fixed

sun position or at calculation points along the sun's trajectory. Solar view factors are the direct view

of an element to the solar source, which is treated as a distant point source. You can model multiple

solar sources to simulate multi-directional heating of elements in a multiple heat source system.

Solar Heating is useful, for example, for modeling the thermal effects of the sun on exterior

equipment, buildings, and installations.

To define a Solar Heating simulation object:

Define a Thermo-Optical Properties – Advanced modeling object with a value for

Absorptivity under the Solar Properties group, for all elements included in the Solar Heating

simulation object.

Note

To specify a value for Absorptivity under the Solar Properties group, you must select the

Define Solar Properties (radiative source spectrum) check box in the Thermo-Optical

Properties – Advanced dialog box.

Create a Radiation simulation object that includes all affected elements to account for the

radiative heat that is diffusely reflected to and from the elements.

The options on the Model Orientation tab of the Solar Heating Space dialog box let you position the

model in relation to the sun to determine how the sun strikes it. The options available in this tab

depend on the method you select from the Orientation Method list. Some examples inlcude:

Latitude — The options in the Planet Vectors and Solar Vectors group let you define two

vectors to orient the model in relation to the Earth or selected planet. These two vectors

cannot be parallel to each other. Often, they are perpendicular to each other.

Sun Planet Vectors — You can use Specify Field to specify a series of time varying vectors

to model the position of the sun with respect to the global coordinate system by specifying

point sets in Cartesian or Spherical coordinates.

Radiative Heating

You define a Radiative Heating simulation object to model the radiative thermal effects of heat

sources such as electrical heater elements, engine and exhaust systems, lasers, or any object in the

model that emits significant and known quantities of radiative energy.



Create a Radiative Heating simulation object to define selected elements in your model as diffusely

or collimated radiating heat sources. The software then calculates the direct heat flux view factors to

other elements per heat source that you define.

With Radiative Heating:

You can define the energy to radiate in solar, infrared, or any other spectral distribution.

You can define a spectral distribution of the energy by specifying the Source Temperature of

the emitting surfaces or by specifying intensity, expressed as a fraction of the entire energy

emitted, as a function of wavelength.

Diffuse reflection and absorption of the incident radiative energy throughout the enclosure is

automatically computed, provided that you also create a Radiation simulation object.

Ray tracing is used for specular or transmissive surfaces.

Heat flux view factors are calculated from the radiative source elements to the elements of

the illuminated objects. If any of the illuminated elements have specular or diffuse properties,

rays will be traced from those elements. Diffuse reflections are also computed from the

illuminated elements, provided you also create an Enclosure Radiation type of Radiation

simulation object.

For loads applied to 2D or 1D geometry, you can specify how the load varies spatially over the area

of the 2D geometry or length of the 1D geometry.

8. Other simulation objects

Articulation

You can account for the motion of a spacecraft's moveable appendages, such as solar panels,

antennas, robotic systems, and optical platforms, in your thermal model to provide an accurate

picture of the heating cycles.

Use an Articulation simulation object to model the transient thermal effects of the movement of

selected elements in the model. The thermal solver uses the displacements of the articulation

sequence to calculate:

Time-varying radiative conductances

View factors at each location

Heat loads (including radiative and solar heating)

Varying conductances of thermal couplings

Shadowing of elements

To define the movement of the selected elements in your model, you use an Articulation simulation

object in conjunction with:

A Joint type modeling object to model the translation or rotation of the moving elements.

A Joint-Orbital Tracker type modeling object to link the rotation of the moving elements to

defined orbits.

Options in the Articulation Parameters group on the Transient Setup tab of the Solution dialog box

let you control the start and end times for the articulation as well as the calculation interval. You can

also choose to match the orbital start and end times and calculation interval that you may have

previously defined.



You can view an animated display or the articulating motion in post-processing. The animated model

accurately displays all the rotations and translations of its articulated parts, including compound

articulations.

Other simulation objects


Duct Flow Boundary

Conditions

Lets you model duct flow networks such as pipes and HVAC

systems.

Joule Heating Lets you model the heating generated due in an electrical circuit

defining a currents and voltages.

Peltier Cooler Lets you model the effect of a thermo electrical cooler generated by a

current or a voltage.

9. Solving the model

Solution options

You can set simulation options in the Solution dialog box. The most commonly used settings are

located on the Solution Details and the Ambient Conditions tabs. You should always review the

settings on the other tabs when they apply to the model you are solving.

For steady state solutions setting expected values for the solution on the Initial Conditions tab may

save analysis time.

For a transient analysis, you must specify a Start Time and an End Time in the Transient

Setup tab, and review the other settings. You can set global initial boundary conditions in the

Initial Conditions tab.

For a large model, deselecting the options for unneeded results types on the Results Options

tab can improve processing time and reduce the size of the results file.

Refreshing results

After you run a solution you can request additional results sets not included in the Results Option tab

of the Solution dialog box.

In the Results Options tab expand the Control group, click on Refresh Results, and follow the

instructions given by the interface.

Performing a restart

You usually restart an analysis in the following situations:



A steady state analysis has reached its iteration limit but has not converged yet.

A transient analysis has been run and you wish to continue the analysis over a new end time.

You have stopped a steady state or transient analysis and wish to continue the run.

You want re run your model with different properties but want to reuse information already

calculated. For example you want to change an object's emissivity but reuse previously

calculated view factors.

To perform a simulation restart use the options available in the Restart tab of the Solution dialog box.

Solver Parameters

Use Solver Parameters to control time step, convergence, speed calculation time, or to adjust the

solver for unusual modeling situations. For example you must set an appropriate time step for natural

convection problems.

After every solution, you should verify the convergence of the model. Review the message files for

global heat balance and mass balance for flow problems. Investigate warnings and check the view

factor sums for radiation problems.

Solving

When you select Solve , the solver generates an input file, then automatically begins processing.

An Information window displays model check results.

The Analysis Job Monitor dialog box lists the solve status for single or multiple runs.

The Solution Monitor displays all errors, warnings, and information messages from the

module currently executing.

o Click Inspect to scroll and check current solution status. These messages are also

available after the solution is completed.

o Click Stop to halt the current solution and discard the results. Restarting is not

possible.

o Click Pause to stop solution and recover results for post processing. In complex

models pause the solution to inspect the results after a few iterations, verify its

integrity, and continue the run. Continue the solve using the Restart tab at the Solution

dialog box.

10. Mapping overview

NX Thermal allows results transfer from a source model to another solver.

Temperature mapping

Temperature mapping creates associations between the element's centroid on the thermal

model to the closest element on the target model.

If the nodes do not match, temperatures are interpolated using the element's CG.



General considerations

The FEM global coordinate system from target model must be the same as in the source

model.

Both models should be geometrically congruent but do not need to have the same mesh.

Mapped temperatures are written in a result file (*.bun).

Temperature results mapped in to an structural analysis displaying deformation results

11. Suggested activity

In this activity, you perform the thermal radiation analysis of a oven.

Launch the Heat transfer analysis of an oven activity.

For more information, use the Command Finder to search for an icon or command.

NX Flow analysis

1. Introduction

NX Flow is an NX Advanced Simulation application that you can use to model steady-state or

transient fluid flow for any product or system.








geometry.



Modifying the model









Modeling fluid flow

The flow solver is an implicit code that uses a conservative finite volume formulation to solve the

Reynolds Averaged Navier-Stokes (RANS) equations describing fluid flow.

All elements you include in a flow solution must be 3D elements for which you assign the following

fluid material properties.

Mass density

Dynamic Viscosity

Thermal conductivity and specific heat

Coefficient of thermal expansion

Gas constant

For coupled solutions, the solver automatically simulates convection for fluid elements that touch

solid walls, or where you define Flow Surface simulation objects. Convection properties can be

tailored where appropriate.




Modeling

part file (.prt)




Simulation



properties.

Advanced Simulation

FEM file (.fem)

4.

Mesh the model and define mesh collectors to organize meshes

and assign physical properties.

Consider using a Fluid Domain meshing (discussed later in this

lesson) before meshing the flow model.

Advanced Simulation

FEM file (.fem)

Assembly FEM file

(.afm)




Associate all FEMs to their corresponding parts when using an

assembly FEM.

5.



conditions.


Advanced Simulation


6.



Advanced Simulation


3. Creating a fluid volume

While the solid mesh for a design part occupies the part itself, the fluid mesh occupies the void

between the bodies.

Because the void itself is not a body, you must create a solid body to occupy the void, You create the

solid body in the Modeling application then mesh this body with 3D fluid elements with the NX

meshing tools or using Fluid Domain simulation object in the FEM or Simulation files

respectively.

Electronics fan and heatsink

Extracted fluid volume of the electronics fan and heatsink

You can model the geometry of the fluid inside an assembly or a part with a complex internal cavity.

You can also model multiple fluids in a single model, provided no mixing takes place.

You can create a fluid volume using one of these methods:



Define a sketch representing the 2D shape of a regular fluid volume and then Extrude and/or

Revolve the sketch. Use this technique if you know the shape and dimensions of the fluid

volume.

Use Boolean operations to create the fluid volumes. You create a solid representing the

enclosed space and select the Unite, Subtract, or Intersect to modify the shape of the volume

based on the intersecting solid component geometry. Use this technique if you want to create

this fluid volume for single use in an analysis and if you are not interested in maintaining

links for geometry updates.

Create the enclosed fluid volume as a separate part file and component in your assembly file

structure using the WAVE Geometry Linker command. This command copies an instance of

the geometry of the inner volume and the components from the assembly part file. You then

modify the contour to represent the fluid volume by using the Delete Face command (on the

Synchronous Modeling toolbar). Use this technique if you want to maintain a link to the

geometry of assembly components to allow for geometry updates.


Modeling objects




Some NX Flow modeling objects include:

External Conditions

Fan Speed Controller

Non-Newtonian Fluid

Planer Head Loss

Scalar




Thermal Loads

Lets you define known heat sources in your model. You can define thermal


A Heat Load




select, regardless of heat flow. This temperature can be constant, time varying,

or spatially distributed.

Flow Boundary

Condition

Models flow boundary conditions, like inlet, outlet, opening, internal, and

recirculation fans.






6. Fluid domain and fluid surface meshing

When you create a flow model, you must specify a fluid volume for the mesh. You must create the

3D mesh using:

NX meshing tools in the FEM file.

A Fluid Domain simulation object.

Within the same model, you can combine both approaches to mesh adjacent fluid volumes. The flow

solver automatically connects adjacent fluid volumes when their polygon bodies share faces.

When you use the Fluid Domain simulation object:

The solver automatically detects solid bodies that are not part of the fluid domain but obstruct

the flow and meshes around them.

The solver automatically detects any changes to the arrangement of obstructions in the

overall volume when you re-solve and accounts for them

You can create boundary layer meshes. Boundary layer meshes are inherently more accurate

when modeling boundary layer effects.

Fluid flow around a train using boundary layer fluid domain

You can create two types of Fluid Domain simulation objects:

The Fluid Mesh type defines a mesh for general fluid volumes.



The Fluid Surface Mesh type lets you modify a Fluid Domain mesh by defining the surface

mesh size and boundary layer mesh parameters.

You cannot view a Fluid Domain mesh in the simulation or FEM file automatically or change its

display properties during flow model creation. However, you can inspect the Fluid Domain mesh in

the Post-Processing Navigator by reviewing:

Element size

Element skewness

Element aspect ratio

7. Flow boundary conditions

The Flow Boundary Condition simulation object models:

Devices that move the fluid, such as fans or pumps.

The known movement of the entire model through a stationary fluid. An example is the

analysis of air flowing around a moving object.

Openings in the boundary of the fluid domain through which fluid enters or exits at a

specified pressure, such as a vent or other passive opening.

To obtain good results, you must specify a sufficiently dense 3D flow mesh adjoining a Flow

Boundary Condition. For accurate modeling, the solver needs at least three fluid elements across the

face of any flow boundary condition.

The following are the basic Flow Boundary Condition types:



Inlet / Outlet

Models the flow of fluids in or out of the flow

domain at a known rate. The boundary

condition must lie on the free faces of models.

Outlet fan face lying on the free faces of 3D

fluid elements

Opening

Models openings that allow fluid to flow into or

out of the flow domain. The direction of the

flow is determined by to the solution. The

boundary condition must lie on the free faces of

models.

Opening faces adjacent to free faces of 3D

fluid elements

Internal Fan

Models a fan inside a flow domain where an

outlet direction must be specified. The boundary

condition must lie in an internal face with

matching nodes on either sides. Ensure this by

using mesh matting conditions on these faces.

Two internal fan faces in an electronics

card cage



Recirculation Loop

Models the extraction and the subsequent return

of fluid from and to the flow model. The


models.

Extract face and return face lying on the

free faces of fluid elements

Other flow boundary conditions

You can also use other flow boundary conditions to model special scenarios in your model:


Moving Frame of

Reference

Lets you model the effect of rotating machinery or watercraft on the

surrounding fluid.

For example you can use this simulation object to model rotating fans.

Mixing Plane Lets you interface two or more fluid regions with different flow conditions.

For example, you can use a Mixing Plane simulation object when you want

to interface a rotating flow region with a non rotating flow region.

Particle Injection Lets you track the location of particles injected to the fluid with specific size

and mass properties.

Screen Lets you model two dimensional openings that direct and impede the fluid

flow from moving within the fluid domain.

Supersonic Inlet Lets you model the fluid entering the domain at velocities over Mach 1.

Symmetry Plane Lets you define a plane about which a fluid volume is symmetrical.

8. Flow surfaces

You define a Flow Surface simulation object to model:

3D obstructions in a fluid volume using a simplified 2D geometry representation of the

original part.

Specific wall function characteristics.

Specific convection properties.



A rotating or translating surface in shear (moving wall).

For the selected faces, a Flow Surface overrides the default Friction and Convection Parameters

options on the 3D Flow tab in the Solution dialog box.

When you solve the model, the solver:

Establishes heat paths (conductances) from the surfaces and obstructions to adjacent 3D fluid

elements.

Opens the 3D flow mesh at the embedded Flow Surface, and models friction on both sides of

the Flow Surface.

Temperature sectioned contours of a shell mesh.

The shell models a heatsink inside a fluid domain.

9. Flow blockages

You can use flow blockages to model 3D obstructions in a fluid volume using a simplified geometry

representation of the original part.

A Flow Blockage simulation object provides a resistance to flow either completely diverting the

flow or to let the flow pass through with a slight drop in pressure.

Catalytic converter geometry

You can create three types of Flow Blockage:



Solid — Models a 3D obstruction with solid material properties that blocks the 3D flow and

is usually defined to exchange heat with the fluid by convection at its polygon faces. You can

also model surface friction.

Catalytic converter fluid flow with half side solid blockage Porous – Isotropic — Models an obstruction with fluid material properties, which equally

impedes the flow with the same resistance values in every direction but does not entirely

block the flow.

Catalytic converter fluid flow with half side isotropic blockage Porous – Orthotropic — Models an obstruction with fluid material properties, which impedes

the flow in three orthogonal directions with a different resistance value in each direction but

does not entirely block the flow.

Catalytic converter fluid flow with half side orthotropic blockage


Solution options







save analysis time.






Turbulence Models

The flow solver uses the Reynolds-Averaged Navier Stokes (RANS) methods to solve for turbulence.

You set the Turbulence Model for your flow analysis on the Solution Details page of the Solution

dialog box.

In the flow solver, you have the following options to model turbulence:

Fixed Viscosity

Defines uniform turbulence levels throughout the model, therefore it can be inaccurate and

should only be used for an initial study.

Mixing Length

Ideal for validated applications or quick initial analyses during early design stages.

κ-ε

It is widely used in the industry, and is more accurate than the Fixed Viscosity or Mixing

Length models, however it must be used with wall functions.

Not ideal for large pressure gradients, flow separation, or free shear flow.

κ-ω

Allows integration through the viscous sublayer. No wall functions are required.

Better predicts large pressure gradients.

Shear Stress Transport (SST)

Is a combination of the κ-ω and the κ-ε models. It behaves as the κ-ω formulation in the inner

parts of the boundary layer, and as a κ-ε model in the free stream.

It is a better model for adverse pressure gradients and separating flow.

This model is computationally expensive.

Refreshing results
















Solver Parameters







Solving









possible.




dialog box.


NX Flow allows results transfer from a source model to another solver.

Flow forces mapping

Flow mapping associates the face of the fluid element source model to the closest nodes on

the target model.



Static pressure and shear stress results are mapped to vector forces generated by the fluid on

the surface of the target model.



model.


Mapped flow forces are written in a result file (*.bun).

Pressure results mapped in to an structural analysis displaying deformation results


In this activity, you perform a flow analysis of fluid passing through a valve.

Launch the Flow analysis of a valve activity.

Electronic Systems Cooling and coupled thermal flow

1. Introduction

NX Electronic Systems Cooling is an NX Advanced Simulation application that you can use to

model the cooling and thermal management for electronic systems.








geometry.

Modifying the model











Modeling conduction








Modeling convection



Faces of 3D solids

2D elements









rising).





Convection can also be explicitly model using a coupled NX Thermal and Flow solution by

simulating the fluid volume and the embedded volumes and surfaces in a model.



Modeling radiation




radiating element.






that you specify.






Modeling fluid flow

The flow solver is an implicit code that uses a conservative finite volume formulation to solve the

Reynolds Averaged Navier-Stokes (RANS) equations describing fluid flow.

All elements you include in a flow solution must be 3D elements for which you assign the following

fluid material properties.

Mass density

Dynamic Viscosity

Thermal conductivity and specific heat

Coefficient of thermal expansion

Gas constant

For coupled solutions, the solver automatically simulates convection for fluid elements that touch

solid walls, or where you define Flow Surface simulation objects. Convection properties can be

tailored where appropriate.




Modeling

part file (.prt)




Simulation






properties.

Advanced Simulation

FEM file (.fem)

4.

Mesh the model and define mesh collectors to organize

meshes and assign physical properties.

Associate all FEMs to their corresponding parts when using

an assembly FEM.

Advanced Simulation

FEM file (.fem)

Assembly FEM file

(.afm)

5.



conditions.


Advanced Simulation


6.



Advanced Simulation


3. Creating a fluid volume

While the solid mesh for a design part occupies the part itself, the fluid mesh occupies the void

between the bodies.

Because the void itself is not a body, you must create a solid body to occupy the void, You create the

solid body in the Modeling application then mesh this body with 3D fluid elements with the NX

meshing tools or using Fluid Domain simulation object in the FEM or Simulation files

respectively.



Electronics fan and heatsink

Extracted fluid volume of the electronics fan and heatsink

You can model the geometry of the fluid inside an assembly or a part with a complex internal cavity.

You can also model multiple fluids in a single model, provided no mixing takes place.

You can create a fluid volume using one of these methods:

Define a sketch representing the 2D shape of a regular fluid volume and then Extrude and/or

Revolve the sketch. Use this technique if you know the shape and dimensions of the fluid

volume.

Use Boolean operations to create the fluid volumes. You create a solid representing the

enclosed space and select the Unite, Subtract, or Intersect to modify the shape of the volume

based on the intersecting solid component geometry. Use this technique if you want to create

this fluid volume for single use in an analysis and if you are not interested in maintaining

links for geometry updates.

Create the enclosed fluid volume as a separate part file and component in your assembly file

structure using the WAVE Geometry Linker command. This command copies an instance of

the geometry of the inner volume and the components from the assembly part file. You then

modify the contour to represent the fluid volume by using the Delete Face command (on the

Synchronous Modeling toolbar). Use this technique if you want to maintain a link to the

geometry of assembly components to allow for geometry updates.


Physical properties

















surface coatings.




conduction.






to model accurate heat transfer through composite materials.



Modeling objects




Some NX Electronic Systems Cooling modeling objects include:

External Conditions

Fan Speed Controller

Non-Newtonian Fluid

Planer Head Loss

Scalar






A Heat Load






Convection to Implicitly models natural and forced convection based on a heat transfer




Environment coefficient or standard correlation.

You specify the known heat Convection Coefficient value or the Correlation

and the Characteristic Information.

Simple Radiation to

Environment




Flow Boundary

Condition

Models flow boundary conditions, like inlet, outlet, opening, internal, and

recirculation fans.










the solution.





simulation object.



simulation object.


online help.














table.



elements




elements


cross section








2) (T1 +T2)





Where







7. Fluid domain and fluid surface meshing

When you create a flow model, you must specify a fluid volume for the mesh. You must create the

3D mesh using:

NX meshing tools in the FEM file.



A Fluid Domain simulation object.

Within the same model, you can combine both approaches to mesh adjacent fluid volumes. The flow

solver automatically connects adjacent fluid volumes when their polygon bodies share faces.

When you use the Fluid Domain simulation object:

The solver automatically detects solid bodies that are not part of the fluid domain but obstruct

the flow and meshes around them.

The solver automatically detects any changes to the arrangement of obstructions in the

overall volume when you re-solve and accounts for them

You can create boundary layer meshes. Boundary layer meshes are inherently more accurate

when modeling boundary layer effects.

Fluid flow around a train using boundary layer fluid domain

You can create two types of Fluid Domain simulation objects:

The Fluid Mesh type defines a mesh for general fluid volumes.

The Fluid Surface Mesh type lets you modify a Fluid Domain mesh by defining the surface

mesh size and boundary layer mesh parameters.

You cannot view a Fluid Domain mesh in the simulation or FEM file automatically or change its

display properties during flow model creation. However, you can inspect the Fluid Domain mesh in

the Post-Processing Navigator by reviewing:

Element size

Element skewness

Element aspect ratio



8. Flow boundary conditions

The Flow Boundary Condition simulation object models:

Devices that move the fluid, such as fans or pumps.

The known movement of the entire model through a stationary fluid. An example is the

analysis of air flowing around a moving object.

Openings in the boundary of the fluid domain through which fluid enters or exits at a

specified pressure, such as a vent or other passive opening.

To obtain good results, you must specify a sufficiently dense 3D flow mesh adjoining a Flow

Boundary Condition. For accurate modeling, the solver needs at least three fluid elements across the

face of any flow boundary condition.

The following are the basic Flow Boundary Condition types:



Inlet / Outlet

Models the flow of fluids in or out of the flow

domain at a known rate. The boundary

condition must lie on the free faces of models.

Outlet fan face lying on the free faces of 3D

fluid elements

Opening

Models openings that allow fluid to flow into or

out of the flow domain. The direction of the

flow is determined by to the solution. The


models.

Opening faces adjacent to free faces of 3D

fluid elements

Internal Fan

Models a fan inside a flow domain where an

outlet direction must be specified. The boundary

condition must lie in an internal face with

matching nodes on either sides. Ensure this by

using mesh matting conditions on these faces.

Two internal fan faces in an electronics

card cage



Recirculation Loop

Models the extraction and the subsequent return

of fluid from and to the flow model. The


models.

Extract face and return face lying on the

free faces of fluid elements

Other flow boundary conditions

You can also use other flow boundary conditions to model special scenarios in your model:


Moving Frame of

Reference

Lets you model the effect of rotating machinery or watercraft on the

surrounding fluid.

For example you can use this simulation object to model rotating fans.

Mixing Plane Lets you interface two or more fluid regions with different flow conditions.

For example, you can use a Mixing Plane simulation object when you want

to interface a rotating flow region with a non rotating flow region.

Particle Injection Lets you track the location of particles injected to the fluid with specific size

and mass properties.

Screen Lets you model two dimensional openings that direct and impede the fluid

flow from moving within the fluid domain.

Supersonic Inlet Lets you model the fluid entering the domain at velocities over Mach 1.

Symmetry Plane Lets you define a plane about which a fluid volume is symmetrical.

9. Flow surfaces

You define a Flow Surface simulation object to model:

3D obstructions in a fluid volume using a simplified 2D geometry representation of the

original part.

Specific wall function characteristics.

Specific convection properties.



A rotating or translating surface in shear (moving wall).

For the selected faces, a Flow Surface overrides the default Friction and Convection Parameters

options on the 3D Flow tab in the Solution dialog box.

When you solve the model, the solver:

Establishes heat paths (conductances) from the surfaces and obstructions to adjacent 3D fluid

elements.

Opens the 3D flow mesh at the embedded Flow Surface, and models friction on both sides of

the Flow Surface.

Temperature sectioned contours of a shell mesh.

The shell models a heatsink inside a fluid domain.


Articulation

You can account for the motion of a spacecraft's moveable appendages, such as solar panels,

antennas, robotic systems, and optical platforms, in your thermal model to provide an accurate

picture of the heating cycles.















defined orbits.




previously defined.



articulations.



Duct Flow Boundary

Conditions


systems.






Solution options





save analysis time.




For a 3D flow analysis with complex flow, settings on the 3D Flow tab can improve meshing,

accuracy, and convergence.





Turbulence Models

The flow solver uses the Reynolds-Averaged Navier Stokes (RANS) methods to solve for turbulence.

You set the Turbulence Model for your flow analysis on the Solution Details page of the Solution

dialog box.

In the flow solver, you have the following options to model turbulence:

Fixed Viscosity

Defines uniform turbulence levels throughout the model, therefore it can be inaccurate and

should only be used for an initial study.

Mixing Length

Ideal for validated applications or quick initial analyses during early design stages.

κ-ε

It is widely used in the industry, and is more accurate than the Fixed Viscosity or Mixing

Length models, however it must be used with wall functions.

Not ideal for large pressure gradients, flow separation, or free shear flow.

κ-ω

Allows integration through the viscous sublayer. No wall functions are required.

Better predicts large pressure gradients.

Shear Stress Transport (SST)

Is a combination of the κ-ω and the κ-ε models. It behaves as the κ-ω formulation in the inner

parts of the boundary layer, and as a κ-ε model in the free stream.

It is a better model for adverse pressure gradients and separating flow.

This model is computationally expensive.

Refreshing results
















Solver Parameters







Solving









possible.




dialog box.


NX Electronic Systems Cooling allows results transfer from a source model to another solver.

Temperature mapping




Flow forces mapping

Flow mapping associates the face of the fluid element source model to the closest nodes on

the target model.

Static pressure and shear stress results are mapped to vector forces generated by the fluid on

the surface of the target model.





model.


Mapped temperatures or flow forces are written in a result file (*.bun).


Pressure results mapped in to an structural analysis displaying deformation results


In this activity, you analyze the effects of component-induced thermal loads on a

computer power supply with printed circuit board assemblies. The activity also

simulates the effect of a forced-air cooling system on the power supply and its

thermal interaction with the electronic components.

Launch the Electronic Systems Cooling analysis activity.

Space Systems Thermal

1. Introduction

NX Space Systems Thermal is an NX Advanced Simulation application that you can use to model

heat transfer for spacecraft, and their systems and components.




Boundary conditions, modeling, and simulation objects — To specify orbits, articulations,

loads, constraints, and other objects that characterize a specific portion of the model.

Although assigned to geometric features of the model (points, edges, faces, or solid bodies),

boundary conditions are ultimately applied to the elements by the solver.



geometry.

Modifying the model



With NX Space Systems Thermal you can also create a mesh with no underlaying geometry using

Primitives.







Modeling the space thermal environment

With the commands available in NX Space Systems Thermal, you can define the:

Orbit, attitude, and articulations of a spacecraft.

Orbital maneuvers.

The celestial body being orbited or specify a body with particular conditions.

The software:

Creates an explicit model of the celestial body to calculate radiative heating for each element

in the spacecraft.

Uses the view factors (calculated when you define a Radiation simulation object) to

determine the distribution and absorption of radiative flux.

Models eclipses by controlling the direct solar incidence. Heating effects due to planet

radiation is still considered.

Models the specular and transmissive effects for different spectra.

Computes element shadowing to an accuracy that you specify.

After you define the orbit you can use the Orbit Visualizer command to display an animation of the

spacecraft in the simulated orbit.

You can define multiple orbital maneuvers (slews) or different orbit sections in the same simulation,

however in the Orbit Visualizer only the parent orbit will be displayed.

You define orbital maneuvers by defining one parent orbit and multiple child orbits. You must

ensure that the orbit sections of each orbit match in time and space.



Modeling conduction








Modeling convection



Faces of 3D solids

2D elements









rising).





Modeling radiation






radiating element.






that you specify.









Modeling

part file (.prt)




Simulation

idealized part file

(_i.prt)


properties.

Advanced Simulation

FEM file (.fem)

4.

Mesh the model and define mesh collectors to organize meshes

and assign physical properties.

Use mesh primitives to define a simplified model with no

underlying geometry (using Insert→ Primitive).

Associate all FEMs to their corresponding parts when using an

assembly FEM.

Advanced Simulation

FEM file (.fem)

Assembly FEM file

(.afm)

5.



conditions.


Advanced Simulation


6.



Advanced Simulation




3. Creating meshes using primitives volumes

You can define a mesh:

On geometry created in the Modeling application or imported from other CAD modeling

packages.

Using primitives in the FEM file to create structured 2D or 3D meshes based on a simple

geometric form type. You must specify the size, location, and orientation based on an

associated coordinate system, and mesh density of the elements.

You can define primitives by:

Points — Allow you to specify three-dimensional coordinates to define key points to provide

the shape information of the primitive.

Parameters — Allow you to define the primitive in relation to the X, Y, and Z-axes of a

coordinate system using angular and linear values.

You can position the primitive with respect to the global coordinate system by translating or rotating

the primitive's origin. You can define a primitive mesh and define a mesh collector to assign material,

physical, and thermo-optical properties to it. Alternatively, you can define a mesh collector first and

then assign the primitive mesh you create to it.

When you create a primitive with 2D elements, the top side of each 2D element faces a specific

direction by default, depending on the type of primitive.

With three-dimensional primitives, such as the Box Primitive or Sphere Primitive, the top

sides of the associated 2D elements face outward, away from the primitive.

With two-dimensional primitives, such as the Rectangle Primitive or Disc Primitive that you

create by specifying parameters, the top sides of the associated 2D elements face the +Z

direction.

With two-dimensional primitives, such as the Rectangle Primitive or Disc Primitive, that you

create by selecting points, the top sides of the associated 2D elements are determined by the

right hand rule, using the sequence P1, P2, P3 to define a rotation.

Note

3D elements have no top or bottom side, so the rules do not apply to primitives created with these

elements (example: Solid Brick Primitive, Solid Cylinder Primitive).




Physical properties















surface coatings.




conduction.






to model accurate heat transfer through Multi-Layer Insulation (MLI) material used to cover

spacecraft.



Modeling objects




Some NX Space Systems Thermal modeling objects include:

Ablation-Charing

Active Heater Controller

Duct Head Loss

Joint

Joint — Orbital Tracker

Layer



Monte Carlo Settings

Orbit

Thermo-Optical Properties / Thermo-Optical Properties — Advanced

Thermostat

Thermo-optical properties

Use the Thermo-Optical Properties or Thermo-Optical Properties — Advanced modeling objects to

define Emissivity, which is required for all radiation modeling.

Absorptivity is required to model radiative heat transfer in the solar band. To model specular and

transmissive effects, you can also define a Thermo-Optical Properties — Advanced modeling object

with values for:

Specular Reflectivity

Transmissivity

Index of Refraction

You can model radiation in different bands defining corresponding thermo-optical properties in a

Thermo-Optical Properties — Advanced modeling object, and choosing one of the following two

types:

Select Gray to define constant or temperature varying values for infrared Emissivity and a

value for Absorptivity when want to define properties in the solar spectrum.

Select Non-Gray — Wavelength Dependent to define wavelength dependent values of non-

gray Emissivity, Specular Reflectivity and Transmissivity.

Emissivity and absorptivity values can be constant or defined in function of a Bidirectional

Reflectance Distribution Function (BRDF). Specular Reflectivity and Transmissivity can be defined

in terms of direction of incidence and angle of incidence.

Note

When you define Thermo-Optical Properties or Thermo-Optical Properties — Advanced for a 2D

mesh, you should always first check the element normals to identify the top and bottom sides of the

mesh.






A Heat Load









Simple Radiation to

Environment













the solution.





simulation object.



simulation object.


online help.














table.



elements




elements


cross section








2) (T1 +T2)





Where







7. About radiation enclosures and view factors

View Factors

A view factor represents the fraction of radiative energy that is emitted from one entity and arrives to

a second entity. The thermal solver uses view factors to compute radiative heat transfer.

Two parallel surfaces in close proximity have a view factor that tends to unity. Two surfaces that are

nearly co-planar have a view factor that tends to zero.



View factor calculation

Enclosures

An enclosure divides the space into compartments on which view factors for a radiation requests are

calculated. View factor calculation is expensive in terms of machine resources, therefore defining

radiation enclosures saves solution time.

For radiation requests with transmissivity thermo-optical properties defined, the solver will

automatically track rays that go through elements.

You can indicate that an enclosure radiates to ambient. In this case the solver will create radiative

conductances from a point at a very large distance outside the model to elements of the enclosure

visible to the point.



Heatsource

2D mesh A


Top (blue arrows)

2D mesh B


Top (blue arrows) and

Bottom (green arrows)


Radiation heat is exchanged from:

Heatsource to mesh B.

Mesh A to mesh B.

Heatsource

2D mesh A


Top (blue arrows)

2D mesh B


Top (blue arrows)


Radiation heat is exchanged only from the heatsource to mesh

B because thermo-optical properties are not defined on the

bottom side of the 2D elements.

To model radiation to environment the elements of mesh A

must have bottom thermo-optical properties.

Radiation simulation object

Use a Radiation simulation object to create view factor calculation requests for enclosures

comprised of selected geometry or elements.

To simulate radiation exchange you must define:

Entities with Thermo-Optical Properties with a specified value for emissivity and/or

absorptivity.

A Radiation simulation object. You can create one of these types of radiation requests:

o All Radiation to let the thermal solver detect enclosures.

o Enclosure Radiation where you define the relevant enclosures by selecting entities

with the top and/or bottom thermo-optical properties defined.

The solver can use one of these techniques as the black body view factor calculation method:

Hemicube Rendering — This technique uses your computer's graphics card to calculate view

factors quickly and accurately. You can only use this option if your computer's graphics card

supports the Open Graphics Library (OGL) standard.



Deterministic — This is an analytical approach that uses a ray casting algorithm, which

calculates the black body view factors based on the mathematical definition of view factor or

form factor.

Monte Carlo — This technique determines view factors as part of the radiative exchange

calculation. It uses a ray casting algorithm with statistical sampling to evaluate the radiative

exchange in an enclosure. This technique is useful when:

o You want to model the effect of partial illumination of elements.

o You define bi-directional reflectance distribution functions (BRDFs) and scattering

coefficients in the Thermo-Optical Properties – Advanced modeling object that you

have assigned to a mesh collector to model diffuse reflection and transmission.

Specular reflection is the perfect reflection of radiation from a surface, in which a ray from a single

incoming direction is reflected into a single outgoing direction. The law of reflection describes such

behavior. Specular reflections are not included in radiation interchange unless you specifically

request them. To include specular reflections you must:

Define values for Specular Reflectivity and Transmissivity in the Thermo-Optical Properties

– Advanced modeling object that you define and assign to your specular surface.

Clear the Ignore specular and transparent effects for radiation request calculations check box

in the Radiation Parameters page of the Solver Parameters dialog box.

8. Defining orbital heating

Use an Orbital Heating simulation object to model spacecraft, their systems, and components

which undergo varying solar, albedo, and infrared heating in space using the orbit modeling

capabilities of Space Systems Thermal.

You can define an orbit as a complete segment or partial orbit segments. You can also concatenate

the segments to model orbital maneuvers. To do this, you must create multiple Orbital Heating

simulation objects with each orbit segment defined by a different Orbit modeling object.

The Orbital Heating simulation object requests solar, Albedo, and planet view factor calculations for

a spacecraft in a defined orbit. This radiation request takes into consideration, eclipses, movement of

appendages, spacecraft rotation, and spinning. A radiosity approach is used to determine the

reflection and absorption of the incident flux throughout the model. You can recover temperatures,

orbital view factors, and heat fluxes for post processing and visualization.

To define an Orbital Heating simulation object:

Define a Thermo-Optical Properties – Advanced modeling object, for all elements on which

you define an Orbital Heating simulation object. You must specify a value for Absorptivity

under the Solar Properties group of the Thermo-Optical Properties – Advanced dialog box.

Define an Orbit modeling object, and any necessary articulations.

Tip

To preview a defined orbit prior to solving the model, click Display in the Orbital Heating dialog box.

To read a text summary of the defined orbital heating simulation object, click Information.



9. Defining orbits

Use an Orbit modeling object to define the orbit, calculation positions, spacecraft attitude, sun, and

planet characteristics. Use an Orbit modeling object in conjunction with an Orbital Heating

simulation object to simulate the thermal effects of an orbit.

Orbital parameters

The options on the Orbit Parameters tab let you define the orbital parameters or select a predefined

orbit.

For the Geostationary and Geosynchronous orbit types, the Orbit Parameters tab is inactive.

This is because only one geostationary or geosynchronous orbit is defined for each planet.

For Planet Earth, some special classical Orbit Types are already partially defined:

o Sun-synchronous

o Shuttle

o Molniya

Sun planet characteristics

The options on the Sun Planet Characteristics tab let you define the planet size, period, gravity, and

Albedo fluxes for the planet. The options also define the time of year and solar flux. The software

provides reasonable default values for the selected planet. Solar flux values should always be

verified.

Spacecraft orientation

To define spacecraft orientation you must define two non-parallel vectors on the model. Associate

the vectors with two spatial direction options selected from the Aim at list and the Align with lists in

the Orientation Options group on the Spacecraft Attitude tab. During the orbital simulation, the

solver adjusts spacecraft orientation at each calculation position.

If you are modeling a spacecraft that spins to control attitude, you can specify this by defining

Rotation Parameters and/or Spinning Parameters on the Spacecraft Attitude tab.



Spacecraft positions

The options on the Calculation Positions page let you specify:

Whether the orbit you are specifying is a Full Orbit or a Partial Orbit.

The angular interval between two calculation points.

The solver calculates black body, solar, earth and Albedo view factors and resulting heat loads at

each calculation position on the orbit. All calculation positions are referenced from the start angle,

the spacecraft position at the beginning of the transient analysis.

Regardless of any intermediate calculations you specify, the software calculates results at both the

initial position of the spacecraft and the last defined position of the spacecraft. These two calculation

positions are respectively 0° and 360° from the start angle for a full orbit, or the start angle and the

end angle for a partial orbit.

The software defines four additional calculation positions when solving orbits with eclipse. Two are

located at the start of the eclipse region and two at its end to capture the rapid heat flux variation that

occurs in these regions.

10. Solar heating

Solar Heating Space

Use a Solar Heating Space simulation object to model heating of objects on the surface of a

planet due to sun incidence. This command calculates direct solar view factors for selected elements

at a fixed sun position or at calculation points along the sun's trajectory. Solar view factors are the

direct view of an element to the solar source, which is treated as a distant point source. You can

model multiple solar sources to simulate multi-directional heating of elements in a multi-star system.

Solar Heating Space is useful, for example, for modeling the thermal effects of the sun on exterior

equipment, buildings, and installations.

To define a Solar Heating Space simulation object:

Define a Thermo-Optical Properties – Advanced modeling object with a value for

Absorptivity under the Solar Properties group, for all elements included in the Solar Heating

simulation object.

Note

To specify a value for Absorptivity under the Solar Properties group, you must select the

Define Solar Properties (radiative source spectrum) check box in the Thermo-Optical

Properties – Advanced dialog box.

Create a Radiation simulation object that includes all affected elements to account for the

radiative heat that is diffusely reflected to and from the elements.

The options on the Model Orientation tab of the Solar Heating Space dialog box let you position the

model in relation to the sun to determine how the sun strikes it. The options available in this tab

depend on the method you select from the Orientation Method list. Some examples inlcude:



Latitude — The options in the Planet Vectors and Solar Vectors group let you define two

vectors to orient the model in relation to the Earth or selected planet. These two vectors

cannot be parallel to each other. Often, they are perpendicular to each other.

Sun Planet Vectors — You can use Specify Field to specify a series of time varying vectors

to model the position of the sun with respect to the global coordinate system by specifying

point sets in Cartesian or Spherical coordinates.

Radiative Heating

You define a Radiative Heating simulation object to model the radiative thermal effects of heat

sources such as electrical heater elements, engine and exhaust systems, lasers, or any object in the

model that emits significant and known quantities of radiative energy.

Create a Radiative Heating simulation object to define selected elements in your model as diffusely

or collimated radiating heat sources. The software then calculates the direct heat flux view factors to

other elements per heat source that you define.

With Radiative Heating:

You can define the energy to radiate in solar, infrared, or any other spectral distribution.

You can define a spectral distribution of the energy by specifying the Source Temperature of

the emitting surfaces or by specifying intensity, expressed as a fraction of the entire energy

emitted, as a function of wavelength.

Diffuse reflection and absorption of the incident radiative energy throughout the enclosure is

automatically computed, provided that you also create a Radiation simulation object.

Ray tracing is used for specular or transmissive surfaces.

Heat flux view factors are calculated from the radiative source elements to the elements of

the illuminated objects. If any of the illuminated elements have specular or diffuse properties,

rays will be traced from those elements. Diffuse reflections are also computed from the

illuminated elements, provided you also create an Enclosure Radiation type of Radiation

simulation object.

For loads applied to 2D or 1D geometry, you can specify how the load varies spatially over the area

of the 2D geometry or length of the 1D geometry.


Articulation

You can account for the motion of a parts in your assembly, such as solar panels, antennas, robotic

systems, and optical platforms, in your thermal model to provide an accurate picture of the heating

cycles.















defined orbits.




previously defined.



articulations.



Duct Flow Boundary

Conditions


systems.






Solution options





save analysis time.






For orbital analysis, you can define a periodic convergence by specifying the End Time as

Based on Cyclic Criterion or Based on Orbit Period.



Refreshing results














Solver Parameters







Solving









possible.






dialog box.


NX Space Systems Thermal allows results transfer from a source model to another solver.

Temperature mapping






model.


Mapped temperatures are written in a result file (*.bun).



In this activity, you analyze transient thermal effects of orbital heating on a

spacecraft.

The model simulates a spacecraft in low Earth orbit exposed to direct solar

heating, Earth IR and Albedo.

Launch the Space Systems Thermal analysis activity.



Activities

1. Activity: Heat transfer analysis of an oven

Estimated time to complete: 15–20 minutes

You will learn how to:

Setup radiation options, analyze and troubleshoot a material properties problem.

Analyze and correct reflection issues.

Eliminate all warnings and verify results.

Launch the Heat transfer analysis of an oven activity.

2. Activity: Flow analysis of a valve



Create a new part from Parasolid geometry.

Extract the interior valve volume.



Define the flow boundary conditions.

Solve the model and display the flow results.

Launch the Flow analysis of a valve activity.

3. Activity: Coupled thermal and flow analysis of a power

supply



Define a fluid domain mesh.

Define thermal and flow boundary conditions.

Define thermal couplings.

Analyze the thermal and flow results.

Launch the Electronic Systems Cooling analysis activity.



4. Activity: Space Systems Thermal analysis



Define 2D and 1D meshes on the satellite geometry.

Create thermal coupling boundary conditions.

Define a radiation enclosure.

Create an orbital heating boundary condition and display its orbit.

Run the analysis and view results.

Launch the Space Systems Thermal analysis activity.



5. Activity: Mapping the heat distribution of an I-beam on a

structural analysis



Create a mapping solution on the target model.

Obtain the temperature results for a specific time step and set up an

structural analysis in NX Nastran.

Launch the Mapping activity.

Contents Thermal and Flow Analysis .............................................................................................................................. 1

Setup information ........................................................................................................................................ 1

NX Thermal analysis ......................................................................................................................................... 1

1. Introduction ............................................................................................................................................. 1

Modifying the model .................................................................................................................................... 2

Modeling conduction ................................................................................................................................... 2

Modeling convection ................................................................................................................................... 2

Modeling radiation....................................................................................................................................... 3

2. Workflow and file structure ..................................................................................................................... 3

3. Defining element and model properties .................................................................................................. 4

Physical properties ....................................................................................................................................... 4

Modeling objects ......................................................................................................................................... 5

Thermo-optical properties ........................................................................................................................... 5

4. Defining boundary conditions .................................................................................................................. 5

5. Defining thermal couplings ...................................................................................................................... 6

Conducting heat paths ................................................................................................................................. 7



Radiating heat paths .................................................................................................................................... 7

6. About radiation enclosures and view factors .......................................................................................... 8

View Factors ................................................................................................................................................. 8

Enclosures .................................................................................................................................................... 8

Radiation simulation object ......................................................................................................................... 9

7. Solar and radiative heating .................................................................................................................... 10

Solar Heating .............................................................................................................................................. 10

Radiative Heating ....................................................................................................................................... 10

8. Other simulation objects........................................................................................................................ 11

Articulation ................................................................................................................................................ 11

Other simulation objects............................................................................................................................ 12

9. Solving the model .................................................................................................................................. 12

Solution options ......................................................................................................................................... 12

Refreshing results ...................................................................................................................................... 12

Performing a restart ................................................................................................................................... 12

Solver Parameters ...................................................................................................................................... 13

Solving ........................................................................................................................................................ 13

10. Mapping overview ............................................................................................................................. 13

11. Suggested activity .............................................................................................................................. 14

NX Flow analysis ............................................................................................................................................ 14

1. Introduction ........................................................................................................................................... 14

Modifying the model .................................................................................................................................. 15

Modeling fluid flow .................................................................................................................................... 15

2. Workflow and file structure ................................................................................................................... 15

3. Creating a fluid volume .......................................................................................................................... 16

4. Defining element and model properties ................................................................................................ 17

Modeling objects ....................................................................................................................................... 17

5. Defining boundary conditions ................................................................................................................ 17

6. Fluid domain and fluid surface meshing ................................................................................................ 18

7. Flow boundary conditions...................................................................................................................... 19

Other flow boundary conditions ................................................................................................................ 21

8. Flow surfaces ......................................................................................................................................... 21

9. Flow blockages ....................................................................................................................................... 22

10. Solving the model .............................................................................................................................. 23


Turbulence Models .................................................................................................................................... 24






Solving ........................................................................................................................................................ 25



Electronic Systems Cooling and coupled thermal flow ................................................................................. 26

1. Introduction ........................................................................................................................................... 26


Modeling conduction ................................................................................................................................. 27

Modeling convection ................................................................................................................................. 27

Modeling radiation..................................................................................................................................... 28

Modeling fluid flow .................................................................................................................................... 28


3. Creating a fluid volume .......................................................................................................................... 29


Physical properties ..................................................................................................................................... 30



6. Defining thermal couplings .................................................................................................................... 32

Conducting heat paths ............................................................................................................................... 32

Radiating heat paths .................................................................................................................................. 33

7. Fluid domain and fluid surface meshing ................................................................................................ 33

8. Flow boundary conditions...................................................................................................................... 35

Other flow boundary conditions ................................................................................................................ 37

9. Flow surfaces ......................................................................................................................................... 37

10. Other simulation objects.................................................................................................................... 38

Articulation ................................................................................................................................................ 38




Turbulence Models .................................................................................................................................... 40




Solving ........................................................................................................................................................ 41





Space Systems Thermal ................................................................................................................................. 42

1. Introduction ........................................................................................................................................... 42


Modeling the space thermal environment ................................................................................................ 43

Modeling conduction ................................................................................................................................. 44

Modeling convection ................................................................................................................................. 44

Modeling radiation..................................................................................................................................... 44


3. Creating meshes using primitives volumes ............................................................................................ 46


Physical properties ..................................................................................................................................... 47


Thermo-optical properties ......................................................................................................................... 48


6. Defining thermal couplings .................................................................................................................... 49

Conducting heat paths ............................................................................................................................... 49

Radiating heat paths .................................................................................................................................. 50

7. About radiation enclosures and view factors ........................................................................................ 50

View Factors ............................................................................................................................................... 50

Enclosures .................................................................................................................................................. 51

Radiation simulation object ....................................................................................................................... 52

8. Defining orbital heating ......................................................................................................................... 53

9. Defining orbits ........................................................................................................................................ 54

Orbital parameters ..................................................................................................................................... 54

Sun planet characteristics .......................................................................................................................... 54

Spacecraft orientation ............................................................................................................................... 54

Spacecraft positions ................................................................................................................................... 55

10. Solar heating ...................................................................................................................................... 55

Solar Heating Space ................................................................................................................................... 55

Radiative Heating ....................................................................................................................................... 56

11. Other simulation objects.................................................................................................................... 56

Articulation ................................................................................................................................................ 56









Solving ........................................................................................................................................................ 58



Activities ........................................................................................................................................................ 60

1. Activity: Heat transfer analysis of an oven ............................................................................................ 60

2. Activity: Flow analysis of a valve ............................................................................................................ 60

3. Activity: Coupled thermal and flow analysis of a power supply ............................................................ 61

4. Activity: Space Systems Thermal analysis .............................................................................................. 62

5. Activity: Mapping the heat distribution of an I-beam on a structural analysis ..................................... 63

unigraphics nx7.5 - thermal and flow analysis

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