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Modifying Springs and Dampers

The information for springs and dampers is stored in text files found in their respective folders in

the database. Spring force is calculated by the following as shown in the help file on linear

springs:

Spring Force = - K*(DM(I,J) - OffsetCalc)

where:

• K - The linear stiffness defined in the spring property file.

• DM - The instantaneous distance between the I and J coordinate references.

• OffsetCalc - Depends on the free length defined in the spring property file and in the

spring install methods.

The I and J coordinate references are positions defined in the model that relay displacement

information into the spring force equation. OffseCalc is a value used to reconcile differences in

free length, preload and the design position of the spring attachments depending on the

installation method used.

The information below is for the default front springs for the FSAE model. The information can

be modified here, however ADAMS provides the Curve Manager for easier editing and more

functionality. You can use the data for your springs and dampers to modify existing property

files.

Warning: Remember to change your working directory before you begin this lesson. If you do not,

Adams may not work correctly. Also remember to move everything you wish to keep from the working

directory before you log off. See the Opening Files tutorial for more information.

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The springs can be modified at the subsystem level or the assembly level. For springs you can

specify the free length, installation type, and the spring rate. Below is the FSAE full vehicle

assembly. To modify the springs or dampers right click on the spring-damper assembly. You

can then select Modify for either the spring or damper.

Selecting Spring:> Modify opens the following dialag box. Here you have the option to select

another spring property file, adjust the installation type, and open the property file in the Curve

Manager. This spring installation is set to preload with the desired preload entered.

Installation

Type

Opens File in

Curve

Lets you write comments

about the file

Opens the property file

in the information

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Below is the spring property file for the text file shown previously. The curve manager provides

tools for creating models for your spring or damper. To work in standard units click

Settings>Units.

Select the desired units in the Set File Window that appears and click OK.

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To model linear springs you can change the spring rate by entering the slope and settin the spring

limits. Below the spring rate has been set to 450 lb/in, the limits have been set to -2 inches to +2

inches and the free length is set to 4.5 inches.

When you have modified the property file using the curve manager you can save the file as a

new property file or save using the original file name. The default place to save a new file is the

default writable database. When you create a new property file and want to use that file in the

current model you must select the new property file under the Modify Spring window. Below is

the previous spring with the rate of 450 lb/in.

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There are three installation methods provided to apply the spring model to the vehicle. You can

specify the spring preload, installed length or use the hadpoints for installation. For more on

these methods see the help file link below. In the Preload method you specify the spring force at

the design position. In the Installed Length method you specify the the spring length at the

design position. The Use Hardpoints uses the distance between the I and J coordinat references

as the spring length at the design postion. For clarification and visual aids see the help file.

ADAMS_Car/Working with Components/Forces/Springs/About Linear Springs

The property file for the default front damper for the FSAE model is shown below. The usual

header and units information are shown. The Force vs. Velocity curve is defined by a two-

dimensional spline defined by the points under [CURVE].

Installation

Types

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To see the Force vs. Velocity curve right click the spring/damper part assembly and select

Modify>Damper, as done previously with the spring.

Damper

Property

File

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Select the Curve Manager to see the curve. Notice the points are interpolated using a 2-D spline.

You can edit the curve by changing the slope, limits and number of points to the left of the

graph. In the plot view shown below the data from the property file are shown as hotpoints. The

hotpoints, shown with red circles, can be changed by moving them vertically but not

horizontally.

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The data can also be seen in tabular form for editing. Select View>Table to edit the data by

changing existing values or, inserting or deleting rows of data.

The default location for the curve manager to save is the default writable database. When you

create a new property file and want to use that file in the current model you must select the new

file under the Modify Spring/Damper window.

Warning: Remember to change your working directory before you begin this lesson. If you do not,

Adams may not work correctly. Also remember to move everything you wish to keep from the working

directory before you log off. See the Opening Files tutorial for more information.