oasys ls-dyna training courses
TRANSCRIPT
LS-DYNA ENVIRONMENT
Seat Belt Fitting
Oasys LS-DYNA TRAINING COURSES
Revision 3.0 2019
© Arup 2019 All Rights Reserved
Do Not Copy Without Permission
LS-DYNA ENVIRONMENT
Set Current Layer
• Prior to the seatbelt creation process it is important to select the ‘current
layer’ in PRIMER.
• This dictates which include file the seatbelt will be created in.
• There are several ways to set the current layer:
– Right-clicking an entity from the model window and ‘Set current layer’.
– From the INCLUDE panel (right-clicking an include and ‘Make current layer’).
– From the part tree (right-clicking an include and ‘Make current layer’).
LS-DYNA ENVIRONMENT
Seatbelt Definition
• A functioning seatbelt is not a single LS-DYNA entity, rather it is a
collection of LS-DYNA elements and properties which together define a
seatbelt system.
• To aid the user, PRIMER has a seatbelt tools menu:
LS-DYNA ENVIRONMENT
Seatbelt Definition
• Note: a seatbelt definition is a PRIMER construct and as such it is not
saved within *KEYWORD and *END, like regular LS-DYNA data.
• Instead, similar to a dummy tree, the data is saved post-*END in a form
that PRIMER can read:
LS-DYNA stops reading data here.
PRIMER seatbelt data.
It is important that this data is not accidently
deleted as the seatbelt definition will be lost.
LS-DYNA ENVIRONMENT
Belt Fitting
• Read the simple seat and dummy
model belt_fitting.key into PRIMER
LS-DYNA ENVIRONMENT
Belt Fitting
• Tools => Safety => Seatbelts
• This menu allows you to define and
modify a seatbelt definition
• Seatbelts => 1.Define; to start creating
a seatbelt definition
LS-DYNA ENVIRONMENT
Belt Fitting
• Seatbelts => Create
• Select the model in which we want to
create the seatbelt definition (Model 1)
and give the Seatbelt definition an ID
and name.
• Press Apply
LS-DYNA ENVIRONMENT
Belt Fitting
• Now we need to select the parts
around which the seatbelt is to be fitted
• Press Part.. and select the parts
shown in red below
• Press Apply
LS-DYNA ENVIRONMENT
Belt Fitting
• Next we need to define a path for the seatbelt
• Seatbelts => 2.Fit
• Press Define path
• At this point a large options panel will also appear.
Ignore it for now; it will be discussed in detail later.
Ignore for now.
LS-DYNA ENVIRONMENT
Belt Fitting
• We now have to select a number of points to
define the seatbelt path, by picking nodes.
• Starting from retractor and travelling towards
the end/anchor point, simply select nodes
from the model
• As the points are selected they appear as
coordinates in the Seatbelt Menu
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LS-DYNA ENVIRONMENT
Belt Fitting
• Next we need to define some of the points to
be fixed so that they won’t move during the
seatbelt fitting (the end points are
automatically fixed).
• Press on the ‘U’ for the relevant point and
select ‘F: Fixed’
• These can be changed by right-clicking the
entries in the ‘Fix’ column.
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LS-DYNA ENVIRONMENT
Belt Fitting
• It is possible for PRIMER to add
DATABASE_CROSS_SECTION requests at points
along the belt.
• This is done by additionally selecting the ‘X’ option
from the point fixity drop down (a little x will appear).
• Some points (e.g. sliprings) require the cross-
sections to be offset from point.
• The offsets can be controlled ‘X-Sect Offsets’ menu:
LS-DYNA ENVIRONMENT
Belt Fitting
• The belt path shape can be tweaked via ‘Modify
coords’ and ‘Control twist’:
• Modifying coords allows the user to drag the points
along the x, y and z axis using the left, middle and
right mouse buttons respectively.
• For example the hip points needs lifting in Z to avoid
an initial penetration with the hip:
LS-DYNA ENVIRONMENT
Belt Fitting
• The belt path shape can be tweaked via ‘Modify
coords’ and ‘Control twist’:
• Control twist allows the user to rotate the belt at each
point.
• For example the buckle slipring needs to be rotated
to avoid a belt-to-belt clash:
LS-DYNA ENVIRONMENT
Belt Fitting
• The panel also contains tools to translate/rotate/scale and reflect the entire
belt path as one:
• Sometimes, for complex routing additional points may be required to generate
the desired path.
• New points can be created before or after existing points or at intermediate
locations along the belt:
• In general, fewer points are better to avoid over constraining the fit process.
LS-DYNA ENVIRONMENT
Belt Fitting
• Once complete the path define and tweak
• Press Save to store this path
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LS-DYNA ENVIRONMENT
Belt Fitting
• Press Dimens; This opens the window in which
we can define the dimensions of the seatbelt
• Width = 40mm
• Thickness = 3mm (to help prevent contact penetration)
• Length = 25mm
• #rows = 2 (number elements across the width of the belt)
• Press Done
LS-DYNA ENVIRONMENT
• Press Fitting Params to control the fitting process.
• The defaults should work satisfactorily in most case.
• But sometimes still need to change some:
– Tol: Make larger to force looser fitting;
– Curve: Make this angle smaller to avoid sharply
belt, e.g. at torso/upper leg region
– Friction: Set a reasonable value
• Press Done
LS-DYNA ENVIRONMENT
Belt Fitting
• Press Fit; To fit the seatbelt to the dummy
• This is an iterative process so you may need
to press the button a couple of times (2-3) to
get a good fit between the belt and dummy
• When you a happy with the fit press Accept
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LS-DYNA ENVIRONMENT
Belt Fitting
• Next we need to create the seatbelt mesh
• Seatbelts=>3.Mesh
• First we need to define the seatbelt
element properties
• Sbelt props – is used to define the
properties for the 1D *Element_Seatbelt
• Shell props – is used to define the
properties for the 2D *Element_Shells
This option allows you to define the node to be used
at this end / fixed point on this section of the belt
instead of letting PRIMER generate a new node.
This is used to fix the end of the belt to the vehicle
structure. However this shouldn’t be used if a slipring,
retractor or pre-tensioner are to be created at this
point on the belt.
LS-DYNA ENVIRONMENT
Belt Fitting
• The old (pre v14) display can be accessed by toggling the O/N button
• The 5 mesh types as the showing:
1 2 3
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LS-DYNA ENVIRONMENT
Belt Fitting
• Define the part into which the
*Element_Seatbelts are to be created
• Specify a Slack Length for the
elements if required
Use Part 100
LS-DYNA ENVIRONMENT
Belt Fitting
• Define the part into which the
*Element_Shells are to be created
Use Part 101
LS-DYNA ENVIRONMENT
Belt Fitting
• The belt is split up into sections that run between the end and fixed points
(in this model we have 3 sections)
• For each of these section we need to define
how we want the belt to be meshed
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LS-DYNA ENVIRONMENT
Belt Fitting
• There are Three options to chose from
1. *Element_Seatbelt 1d
2. *Element_Seatbelt 2d
3. *Element_Shell only
4. *Element_Seatbelt 1d at each end and
*Element Shell in the middle
5. *Element_Seatbelt 2d at each end and
*Element Shell in the middle
• Only the sections that are in contact with
the dummy need to be meshed with shell
elements
(use Option 2 ,3,4or 5)
• Elements connecting to a slipring or
retractor need to be *Element_Seatbelt.
(use Option 1,2 ,4or 5)
LS-DYNA ENVIRONMENT
Belt Fitting
• The first section isn’t in contact with the
dummy so it doesn’t need to be meshed
using any shell elements
• Press the Arrow button to move onto the
next section
LS-DYNA ENVIRONMENT
Belt Fitting
• The second section is in contact with the dummy
need to be meshed using some shell elements
• It also needs to go through sliprings at either end so
it need to meshed as a mixture of seatbelt and shell
elements
• Typically 3 to 4 seatbelt elements at the ends are
need to allow for them to flow through the slipring
LS-DYNA ENVIRONMENT
Belt Fitting
• The third section is in contact with the dummy need to be meshed using some shell elements
• It also needs to go through a slipring at one end so it should be meshed as a mixture of seatbelt and shell elements
• Once the belt is no longer in contact with the dummy is doesn’t need to be meshed as shell elements
LS-DYNA ENVIRONMENT
Belt Fitting
• Now press Generate to create the mesh
• A window will come up detailing the
elements that will be created
• Press OK and PRIMER will create the
elements
LS-DYNA ENVIRONMENT
Belt Fitting
• Next we need to define the contact
between the belt and the dummy.
• Seatbelts => 4.Contact
• We can create two contacts– *Contact_Automatic_Node_to Surface
between the node on the belt elements
and the dummy
– *Contact_Automatic_Surface_to_Surface
between the shell elements and the
dummy
• Typical only the contact between
the shell elements and the dummy
is created.
• The dummy side of the contact will
only include those parts selected at
the start of the seatbelt definition
• Press Create button to make the
relevant contacts
LS-DYNA ENVIRONMENT
Belt Fitting
• We have now finished seatbelt definition.
Tips on avoiding Initial Penetrations when fitting the seatbelt
• Add a factor to the true thickness of the belt elements
– i.e. enter a large than real thickness in the seatbelt Dimens window (see Slide 9)
– In the analysis, high belt forces & penetration may cause you to thicken the contact surface
anyway).
• Avoid too many pushes of the FIT button
– About 2 - 3 times should be enough
– use visual inspection to check the fit rather than just pressing the button a lot of times.
• Try a different path, or moving the existing points.
• As a last resort, move the penetrating nodes with ORIENT.
LS-DYNA ENVIRONMENT
Seat Belt Editing/Re-Fitting
LS-DYNA ENVIRONMENT
Editing a Definition
• The strength of using PRIMER seatbelt definitions is how easily they can be
modified.
• In the previous example the belt was created using shell elements and 1D
seatbelt elements.
• This can easily be changed by re-entering the seatbelt panel and reopening
the ‘Mesh’ menu.
• For example, to change the belt to entirely 2D seatbelt elements it is simply
a case of toggling the type for each segment:
2D properties (Section is shell,
Material is seatbelt)were not entered
previously so must be input now.
LS-DYNA ENVIRONMENT
Editing a Definition
• Once the mesh has been modified and any required data input the user
must click ‘Generate’ as before:
• This time PRIMER will ask the user what they would like to do with the
entities from the previous mesh.
• In the majority of cases the user should REUSE the existing mesh (to save
re-entering retractor/slipring data)
• When prompted, delete the redundant data by clicking ‘Delete sel’ (and
Continue).
LS-DYNA ENVIRONMENT
Editing a Definition
• The mesh/belt has now been updated and the model can be saved.
• Primer will give a summary popup of the new belt contents.
Note: after editing a seatbelt it may be necessary to clean up
empty sets.
This can be done using the Remove->Cleanup function.
LS-DYNA ENVIRONMENT
• Available from Version 9.3 RC2
• Works only if belt was initially fitted in
Primer.
• If using a belt model created in previous
versions of Primer, check carefully for
redundant seatbelt elements attached to
retractor and/or sliprings after the first
re-fitting of the belt in 9.3 RC2. You may
find it necessary to re-create the belt
definition in Primer 9.3 RC2 for this
feature to work properly.
Belt re-fit
LS-DYNA ENVIRONMENT
• After repositioning dummy and seat…
• … Use Seatbelt=>Auto-refit
• Try this using your model in “front low”
position, then “seat-dummy base”
Belt re-fit
LS-DYNA ENVIRONMENT
• Belt automatically re-fitted and remeshed
• Primer uses the same meshing parameters and element types as the initial belt mesh
• In 9.3 RC2 the node and element labels are not preserved. You might want to renumber them later.
Belt re-fit
LS-DYNA ENVIRONMENT
Seat Belt Related Items
LS-DYNA ENVIRONMENT
*Mat_Seatbelt (B01)
This material model is used for *Element_Seatbelt parts.
• MID – Material ID
• MPUL – Mass per unit length
• LLCID – Load curve for belt loading (Force vs Engineering Strain)
Take the material stress-strain curve and multiply by the belt cross sectional area.
• ULCIN – Unload curve for belt loading (Force vs Engineering Strain). Same as loading curve for elastic behaviour
• LMIN – Minimum Length, Used to determine when an element goes in or out of a retractor, or through a slipring
(typically about 1.5 - 5mm)
• CSE – Optional compressive stress elimination option which applies to shell elements only (default 0.0):
EQ.0.0: eliminate compressive stresses in shell fabric
EQ.1.0: do not eliminate compressive stresses. This option should not be used if retractors and
slip rings are present in the model.
EQ.2.0: whether or not compressive stress is eliminated is decided by LS-DYNA automatically,
recommended for shell belt. (2D seatblet)
LS-DYNA ENVIRONMENT
2D SHELL Material
This material model is used for *Element_Shell part.
*SECTION_SHELL with ELFORM 5/ELFORM9
LS-DYNA ENVIRONMENT
Seatbelt Related Items
• Slipring elements - allow seatbelt elements to pass though the fixed points on the belt path as the belt loaded by the dummy. The friction of the belt passing through and a lockup time can be defined on the input card.
• Retractor elements – represent the belt spool. Retractors allow belt to be paid out in 2 states: unlocked and locked. Pay out force in the unlocked state is lower then in the locked state
• Pretensioner – represents a pyrotechnic or spring type device to pull in the belt after a signal is received from the sensor. There is no pretensioner element – the user defines the pretensioner properties and associates it with the retractor
• Load limiter – Limits the maximum force that can be exerted on the occupant by the belt. This is usually modelled separately using a spring element,
LS-DYNA ENVIRONMENT
Sliprings (*Element_Seatbelt_Slipring)
The Slipring element is fixed to the vehicle structure and allows seatbelt elements to flow through it
• SBSRID – Slipring Element ID
• SBID1 – ID of *Element_Seatbelt on one side of the slipring
• SBID2 – ID of *Element_Seatbelt on the other side of the slipring
• FC – Dynamic Friction coefficient
• SBRNID – Slipring Node ID (fixing node attached to the vehicle structure)
• LTIM – Lock up time
• FCS – Optional Static Friction coefficient
• ONID – Optional orientation node ID.
LS-DYNA ENVIRONMENT
Sliprings (*Element_Seatbelt_Slipring)
The Slipring element is fixed to the vehicle structure and allows seatbelt elements to flow through it
• SBSRID – Slipring Element ID
• SBID1 – ID of *Element_Seatbelt on one side of the slipring
• SBID2 – ID of *Element_Seatbelt on the other side of the slipring
• FC – Dynamic Friction coefficient
• SBRNID – Slipring Node ID (fixing node attached to the vehicle structure)
• LTIM – Lock up time
• FCS – Optional Static Friction coefficient
LS-DYNA ENVIRONMENT
All nodes inside this
area are coincident
Sliprings (*Element_Seatbelt_Slipring)
Seatbelt Element 1
(SBID1)
Seatbelt Element 2
(SBID2)
• Seatbelt Element 1 and Seatbelt Element 2 share the same node
• The Slipring fixing node (SBRNID) is coincident with but not connected to the node on Seatbelt
Element 1 and Seatbelt Element 2
• Typically the slipring fixing node is on the structure of the vehicle or connected to it with a
constraint (e.g. Nodal Rigid Body)
Slipring Fixing Node
(SBRNID)
LS-DYNA ENVIRONMENT
•Frictional sliding of belt over slipring can be
specified as a function of two angles from
LS971 R4
Sliprings (*Element_Seatbelt_Slipring)
DLT
锁止锁舌
LS-DYNA ENVIRONMENT
Sliprings (*Element_Seatbelt_Slipring)
• If K is undefined, the limiting force ratio is taken as 𝑒FC×𝜃. If K is defined, the maximum
force ratio is computed as
𝑒FC×𝜃(1+K×𝛼2)
•where alpha is the angle shown in Figure 17-21. If FUNCID is specified, the coefficients
FC, FCS, and K are not used. The function is defined using the *DEFINE_FUNCTION
keyword input. This function is a function of three variables, and the ratio is given by
evaluating
𝑇2/𝑇1= FUNC(FCT, 𝜃, 𝛼)
•where FCT is the instantaneous friction coefficient at time 𝑡. For example, the default
behavior can be obtained using the function definition (assuming FCT has a value of
0.025 and the function ID is unity)
*DEFINE_FUNCTION
1,
f(fct,theta,alpha) = exp(0.025*theta)
Behavior like default option can be obtained with (K=0.1):
*DEFINE_FUNCTION
1,
f(fct,theta,alpha) = exp(0.025*theta*(1.+0.1*alpha*alpha))
LS-DYNA ENVIRONMENT
Retractor (*Element_Seatbelt_Retractor)
The Retractor element has two states: unlocked and locked.
– When unlocked the seatbelt elements at paid out or taken in at a constant fixed
tension
– When locked the belt is paid out according to the user defined force-pull out
relationship
• switching from unlocked to locked is controlled by the sensors referred to on the
Retractor card.
A number of seatbelt elements can be pre-stored inside the retractor to be paid out
during the analysis. These elements can be automatically created for you by
PRIMER when you create the retractor element.
– The elements are all zero length and the nodes are coincident with the retractor
node
– On the *Element_Seatbelt card the SBRID variable is set to the retractor element ID
LS-DYNA ENVIRONMENT
Retractor (*Element_Seatbelt_Retractor)
• SBRID – Retractor Element ID
• SBRNID – Retractor Node ID (fixing node attached to the vehicle structure)
• SBID – ID of *Element_Seatbelt connected to the retractor
• SID1 – SID4 – Sensor IDs that control when the retractor should lock
LS-DYNA ENVIRONMENT
Retractor (*Element_Seatbelt_Retractor)
• TDEL – Time delay after sensor firing before locking the retractor
• PULL – Length of belt to pay out between time delay and locking
• LLCID – Load curve for loading (Force vs Pull Out Length)
• ULCID – Load curve for unloading (Force vs Pull Out Length)
• LFED – Element Feed Length
LS-DYNA ENVIRONMENT
Retractor (*Element_Seatbelt_Retractor)
Seatbelt Element
(SBID)
Retractor Fixing
Node (SBRNID)
Seatbelt Element Inside
the Retractor
(created by PRIMER)
All nodes inside this
area are coincident
•The Retractor fixing node (SBRNID) is coincident with but not connected to the nodes of the
seatbelt element (SBID) and all the seatbelt elements stored in the retractor
•A least one sensor must be referred to.. If the retractor should start the analysis locked then
use a time base (SBTYP = 3) sensor and set the Time = 0.0sec
LS-DYNA ENVIRONMENT
Retractor Example
• Autoliv
http://www.autoliv.com/ProductsAndInnovations/PassiveSafetySystems/Pages/Seatbelts/Pretensioners.aspx
LS-DYNA ENVIRONMENT
Pretensioner (*Element_Seatbelt_Pretensioner)
The pretensioner element can behave in a
number of different ways depending on which
type (SBPRTY) is specified on the element
card.
• Type 1 & 5 – represent pyrotechnic devices that
spin the spool of the retractor
• Type 2 & 3 – represent pre-loaded springs /
torsion bars (using discrete elements)
• Type 4, 6 & 7 – allow a particular force behaviour
to be defined
LS-DYNA ENVIRONMENT
Pretensioner (*Element_Seatbelt_Pretensioner)
• Type 1 & 5 pretensioners effectively shift the retractor force vs. pull out
curve by the pull-in on the pretensioner pull in vs. time curve at that time.
• E.g. at time t, retractor pull out = 5mm, therefore force without pretensioner
= F1. With pretensioner, pull in at time t = 20mm, therefore force applied by
retractor is F2 (equivalent to 25mm pull-out)
5mm
F1
Pull-out
Forc
e
t
20mm
Time
Pu
ll in
25mm
F2
LS-DYNA ENVIRONMENT
Pretensioner (*Element_Seatbelt_Pretensioner)
• Type 4 allows the pretensioner force to be defined by a force vs.
time relationship.
• Once curves cross, the retractor curve is used to define to force
Pretensioner force
LS-DYNA ENVIRONMENT
Pretensioner Example
• TRW
http://www.trw.com/occupant_safety_systems/seat_belts/pretensioning
LS-DYNA ENVIRONMENT
Load Limiter
A load limiter is typically modelled using an elastoplastic spring (*MAT_S03)
between the retractor and the vehicle structure. A cylindrical joint is also
need to prevent the retractor from drifting.
Retractor
Retractor fixing node connected to the rigid
part using a *Constrained_Extra_Node
Small Rigid Part (2x2 shell elements)
Vehicle Structure
Cylindrical Joint with
stiffness spring
F
dHigh elastic stiffness (K)
Yield force (FY) = load limit
Low tangent stiffness (KT)
LS-DYNA ENVIRONMENT
2D Seatbelts
• SEATBELT SHELL ELEMENTS
• Seatbelt shell elements can be defined from ls971 R4
– Defined on *ELEMENT_SEATBELT card.
• Works with:
– Sliprings
– Retractors
• Needs a regular mesh.
*ELEMENT_SEATBELT
$# eid pid n 1 n 2 sbrid slen n3 n4
200001 1003 936692 909127 0 0.0000E+00 909128 936693
200002 1003 909127 926692 0 0.0000E+00 926693 909128
200003 1003 936693 909128 0 0.0000E+00 909129 936694
200004 1003 909128 926693 0 0.0000E+00 926694 909129
200005 1003 936694 909129 0 0.0000E+00 909130 936695
200006 1003 909129 926694 0 0.0000E+00 926695 909130
200007 1003 936695 909130 0 0.0000E+00 909131 936696
200008 1003 909130 926695 0 0.0000E+00 926696 909131
200009 1003 936696 909131 0 0.0000E+00 909132 936697
200010 1003 909131 926696 0 0.0000E+00 926697 909132
LS-DYNA ENVIRONMENT
2D Seatbelts
• Primer automatically creates required data for shell seatbelts:
– SHELL_SEATBELT
– EDGSET in SECTION_SHELL
– Node sets for SLIPRINGs and RETRACTOR
LS-DYNA ENVIRONMENT
2D Seatbelts
• For the Sliprings, sketch the Node Set –
SBRNID and Shell Sets SBID1 and SBID2.
• Check how the structure nodes in the set
SBRNID are attached to the vehicle structure,
using “J”.
2D Seatbelt slipring
Structure node picked
by user
1D Seatbelt slipring
Structure node SBRNID
picked by user
Belt element
SBID2Belt element
SBID1
Belt node created by
Primer, coincident with
structure node Set SBRNID: Set of nodes created
by Primer, coincident with belt
nodes and connected to structure
by NRB or C_EXTRA_NODES
“Shell”
Set
SBID2
Structure node SBRNID
picked by user
LS-DYNA ENVIRONMENT
2D Seatbelts
• The 1D seatbelt retractors reference a single “mouth” element
• For the 2D seatbelts, Primer automatically creates a Set SBID, as
required. Sketch the set.
2D Seatbelt retractor
1D Seatbelt retractor
Structure node SBRNID picked
by user
“Mouth” belt
element SBIDBelt node created
by Primer
coincident with
structure node
Set SBRNID: Nodes coincident
with belt nodes created by
Primer and connected to
structure by NRB or
C_EXTRA_NODES
Set
SBID
Structure node
picked by user
LS-DYNA ENVIRONMENT
Contact Information
UK:
Arup
The Arup Campus
Blythe Valley Park
Solihull, West Midlands
B90 8AE
UK
T +44 (0)121 213 3399
F +44 (0)121 213 3302
For more information please contact the following:
www.arup.com/dyna
China:
Arup
39/F-41/F Huai Hai Plaza
Huai Hai Road (M)
Shanghai
China 200031
T +86 21 311 88875
F +86 21 311 88882
India:
nHance Engineering Solutions Pvt. Ltd (Arup)
Ananth Info Park
HiTec City
Madhapur
Hyderabad - 500081
India
T +91 (0) 40 44369797 / 8