Release 11.0 Documentation for ANSYS
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You use the Drop Test Set-up dialog box for inputting parameters for an ANSYS LS-DYNA analysis that uses the Drop Test Module (DTM). You access it by choosing Main Menu> Drop Test> Set Up.
The Drop Test Set-up dialog box consists of four tabbed “pages,” each of which contains a group of related DTM set-up information. The tabs, in order from left to right, are Basic, Velocity, Target, and Status. Each information group is logically arranged on a tab; the most basic and frequently addressed parameters appear on the first tab, with each of the next two tabs providing more advanced parameters. Most DTM analyses involve using the default settings for parameters on these two tabs. You do however have the option of modifying these parameters as needed. The Status tab displays the values currently set for acceleration due to gravity, initial translational and angular velocity, and the estimated time at the end of solution. This tab is located furthest to the right because you are encouraged to examine its contents as a final set up task, before committing the parameters to the ANSYS database (by clicking OK in the dialog box).
Once you are satisfied with the settings on the Basic tab, you do not need to progress through the remaining tabs unless you want to change some of the advanced parameters. As soon as you click OK on any tab of the dialog box, the settings are applied to the ANSYS database and the dialog box closes. The target is then created and loads are applied.
When you make changes to any tabbed page, your changes are applied to the ANSYS database only when you click OK to close the dialog box.
Use the Basic tab to specify the options described below.
Gravity -- Specify the magnitude of gravity.
Magnitude of g drop down list and text field: You have the option to select one of the standard values for gravity or type in a customized value. The values for gravity you can choose from the drop down list are:
zero (default)
386.4
32.2
9.81
9810
Any value that you choose must have units that are consistent with the units used in the model of the object being dropped. You only need to input the magnitude of gravity. The direction is assumed to be in the negative Y direction, referenced to the screen coordinates. The object's coordinate components of the gravity loading are imposed on the object internally by the DTM, using three separate EDLOAD commands just before the problem is solved.
Drop Height -- Specify values for the drop height and the height reference point.
Height field: (default = 0) You type the value of the drop height in units consistent with the units of length used in creating the object being dropped. The height is always measured along the Y axis (referenced to the screen coordinates) from the center of the top face of the target to some height reference point in the object.
Reference drop down list: You choose the reference point from the following options:
Lowest Object Point (default): Reference point is the point on the object with the minimum screen Y coordinate value. If this option is used, then the node on the object with the minimum Y coordinate value is the reference point. If there is more than one node at this Y coordinate, then one of them is chosen arbitrarily to be the reference point.
Object CG: Reference point is the object's center of gravity as calculated by ANSYS. If the center of gravity has been previously calculated for some other purpose, then the information is stored, and the calculation is not repeated.
If the analysis is set to begin near impact time (default), then you will notice that the separation between the center of the target and the reference point, measured along the screen Y axis, is not equal to the specified drop height. This is because the target is created so that there is only a small separation, which is the case just before impact. However, if the analysis is set to begin at drop time, the separation between the target and the reference point equals the drop height.
By default, the target is oriented such that its top face is normal to the screen Y axis. If the orientation of the target is modified from the default orientation (see Target Orientation in this User's Guide), the location of the center of the top face of the target at the time of the drop is not altered. Therefore, the definition of the drop height outlined above is not changed.
You should always define the drop height so that all nodes on the object are above the plane of the top face of the target prior to the drop.
Set Orientation -- Specify the orientation of the model with respect to the gravitational field.
Rotate button: You click this button to access the DTM Rotate dialog box, which allows you to dynamically rotate the object on the screen. This dialog box contains a Help button that you can click for more information.
Pick Nodes button: You click this button to access a picking dialog box, which allows you to define a vector either by picking two nodes, or by picking one node and having the object's center of gravity be the second node. The “up” direction is defined as the direction going from the first node that you pick to the second node that you pick. This dialog box contains a Help button that you can click for more information.
Solution Time -- Specify when the drop test analysis will start and how long it will run.
Start analysis near impact time radio button (default): You click this option to save computation time that would be expended as the object drops through the air. To use this option, the angular velocity must be zero. The velocity at the start of the analysis is calculated automatically assuming the object is a rigid body and there is no resistance due to the air. If an initial translational velocity is applied, it is taken into account in calculating the velocity at the start of the analysis.
Start analysis at drop time radio button: You click this option to include the entire time it takes for the object to drop from the specified height in the analysis. Although extra computation time is expended that is not directly involved with the drop test impact, this option accounts for rigid body rotation and is useful if you want to produce animations that include frames of the entire drop test, starting from when the object drops.
Run time after impact field: You type the time in seconds that you want the analysis to run after the object hits the target.
Number of Results Output -- Specify the number of times that the output is written to the results file and to the time-history file.
On Results file field: (default = 100) You type the number of times that the output is written to results file Jobname.RST. See the EDRST command for details.
On time history file field: (default = 1000) You type the number of times that the output is written to time-history file Jobname.HIS. See the EDHTIME command for details. Note here that a component containing the lowest point and the node closest to the object's center of gravity is automatically created for time-history postprocessing. You may define additional nodes. Refer to the EDHIST command for details.
OK: Applies the settings on the Drop Test Set-up dialog box to the ANSYS database and closes the dialog box.
Cancel: Cancels any changes that you have made on the Drop Test Set-up dialog box since the last time that you clicked the OK button.
Help: Displays this help topic.
Related Information -- For further information about the options on the Basic tab, see the following sections in this user's guide:
Use the Velocity tab to specify the object velocities, as described below.
Translational Velocity -- Specify the initial translational velocity of the object being dropped at the beginning of the drop time, even if the analysis is set to begin near impact. If you apply a translational velocity other than zero, and choose to start the analysis near impact time, the initial angular velocity must be zero. If these conditions are not met, ANSYS will automatically start the analysis at drop time, and it will automatically recreate the target.
Velocity relative to drop down list: You choose either object coordinate system or screen coordinate system (default). If you enter the velocity relative to the screen coordinate system, the components are resolved into the object coordinate system internally by the DTM.
X Component field: (default = 0) The X component of the translational velocity.
Y Component field: (default = 0) The Y component of the translational velocity.
Z Component field: (default = 0) The Z component of the translational velocity.
Angular Velocity -- Specify the initial angular velocity of the object being dropped. The angular velocity is about the object centroid in units of radians/(unit time). Applying an angular velocity other than zero is only valid when starting the analysis at drop time. ANSYS automatically sets this option when you choose Solve, and it automatically recreates the target to reflect this change.
Velocity relative to drop down list: You choose either object coordinate system (default) or screen coordinate system. If you enter the velocity relative to the screen coordinate system, the components are resolved into the object coordinate system internally by the DTM before being input on the EDVEL command.
X Component field (default = 0): The X component of the angular velocity.
Y Component field (default = 0): The Y component of the angular velocity.
Z Component field (default = 0): The Z component of the angular velocity.
OK: Applies the settings on the Drop Test Set-up dialog box to the ANSYS database and closes the dialog box.
Cancel: Cancels any changes that you have made on the Drop Test Set-up dialog box since the last time that you clicked the OK button.
Help: Displays this help topic.
Related Information -- For further information about the options on the Velocity tab, see the following sections in this user's guide:
When you choose the Target tab, the target is automatically created.
Also, use the Target tab to specify the options described below.
Dimensions -- Specify the target's position and size.
Center target using drop down list. You can change the position of the target by changing the location of the point on the center of the top face of the target in the screen X-Z plane. The point's Y coordinate is fixed when the drop height is specified. You can designate this point with one of the following options in the drop down list:
Lowest Object Point: (default) The lowest object point is the point on the object with the minimum screen Y coordinate value. If only a single node exists on the object at this point, then the screen X coordinate value of this node is used as the point's X coordinate, and the screen Z value is used as the point's Z value. If there is more than one node at the minimum Y point, then the X coordinate of the point is found by first selecting only those nodes located at the minimum Y point. Then, the point's X value is equal to the sum of the maximum and minimum screen X values in the selected set of nodes, divided by 2. Similarly, the point's Z value is equal to the sum of the maximum and minimum screen Z values in the selected set of nodes, divided by 2.
Object CG: The screen X value at the object center of gravity is used as the point's X value, and the screen Z value of the cg is used as the point's Z value.
Length scale factor field: (default = 1.0) You type a scale factor that changes the length of the target from the default length. The default length is determined by ANSYS, based on the overall dimensions of the object being dropped.
Thickness scale factor field: (default = 1.0) You type a scale factor that changes the thickness of the target from the default thickness. The default thickness is equal to 0.1 times the default length.
Orientation angle -- Specify the rotation of the target about the screen Z axis (normal to the screen and pointing toward you).
Rotation about screen Z field: (default = 0) You type the rotation angle in degrees about the screen Z axis.
The drop height loses its meaning when the normal to the target’s large faces is perpendicular to the screen Y axis. Therefore, if you modify the orientation so that the angle is greater than 89o or less than -89o with the screen Y axis, then the input is considered to be invalid. A warning is printed to the screen, and the target is returned to its previous orientation.
Material Properties -- Specify the material properties of the target. Material properties are used for a contact stiffness calculation and a time step calculation.
Young's Modulus field: (default = object's lowest Young's modulus) You type the target's Young's modulus in units consistent with the analysis.
Density field: (default = object's highest density) You type the target's density in units consistent with the analysis.
Poisson's Ratio field: (default = object's Poisson's ratio) You type the target's Poisson's ratio.
Contact -- Specify the contact friction coefficients described below.
Static friction coeff field: (default = 0.0) You type the static friction coefficient, which is FS as described in the Notes section of the EDCGEN command.
Dynamic friction coeff field: (default = 0.0) You type the dynamic friction coefficient, which is FD as described in the Notes section of the EDCGEN command.
Exponential decay coeff field: (default = 0.0) You type the exponential decay coefficient, which is DC as described in the Notes section of the EDCGEN command.
OK: Applies the settings on the Drop Test Set-up dialog box to the ANSYS database and closes the dialog box.
Cancel: Cancels any changes that you have made on the Drop Test Set-up dialog box since the last time that you clicked the OK button.
Help: Displays this help topic.
Related Information -- For further information about the options on the Target tab, see the following sections in this user's guide, except as noted:
Use the Status tab to check the values currently set for acceleration due to gravity, initial translational and rotational velocity, and the total time at the end of solution. One of the following statements is also displayed:
Successful set-up. Ready to drop. [black print] This statement indicates that all the current set-up data is acceptable and you can click OK to commit the settings.
Proceed with caution. See error messages. [yellow print] This statement indicates that some of the current set-up data could be problematic in enabling a solution, or is otherwise “non-standard” (for example, a zero entry detected for the value of gravity). You should examine the error messages in the ANSYS Output window to determine what is causing them to occur. Then, if necessary, change settings as appropriate and recheck the Status tab until the first message in black appears for problem situations. Click OK to commit the settings.
Unsuccessful set-up. See error messages. [red print] This statement indicates that the current set-up data has produced errors that are serious enough to prevent a solution. The target will not be created in this situation. You should examine the error messages in the ANSYS Output window to determine the causes of these problems. Then change settings as appropriate and recheck the Status tab until the first message in black appears. Click OK to commit the settings.
It is recommended that you check this information in the Status tab along with a view of the object and the target in the in the ANSYS Graphics window before you click OK in the Drop Test Set-up dialog box as this commits all the set up data to the ANSYS database.
Action Buttons
OK: Applies the settings on the Drop Test Set-up dialog box to the ANSYS database and closes the dialog box.
Cancel: Cancels any changes that you have made on the Drop Test Set-up dialog box since the last time that you clicked the OK button.
Help: Displays this help topic.
Related Information -- For further information about the options on the Status tab, see the following section in this user's guide:
