SECTION 10 CAR DESIGN S10-1 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation

SECTION 10 CAR DESIGN S10-2 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation

SECTION 10 CAR DESIGN S10-3 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Topics covered in this case study: u Groups and Lists u 0-D Elements u Rigid Elements

SECTION 10 CAR DESIGN S10-4 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Problem Description u We have inherited a PATRAN database of a vehicle body- in-white. u We are tasked with breaking the model down into manageable sections so that the we can: l refine the mesh further l apply properties to the elements l breakout components for detailed analysis l control the post processing of different components u We are required to add a mass representation of the engine and spring stiffnesses of the shock absorbers.

SECTION 10 CAR DESIGN S10-5 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation

SECTION 10 CAR DESIGN S10-6 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n What is a Group? u Any subset of model u A collection of entities n Why use more than just the Default Group? u Separate groups for geometry & finite elements u Isolate Subsets when working with large models

SECTION 10 CAR DESIGN S10-7 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Allows geometric and FE entities to be divided into separate groups for various modeling and post-processing tasks n A group named default_group is created automatically when a new database is created n Groups become permanent members of the database n Name of current group is displayed as part of Viewport banner

SECTION 10 CAR DESIGN S10-8 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Current u Group into which newly created entities are placed u Only one group may be current at a time n Target u Group that will be acted upon u Translate entities from the Target Group to the Current Group u Modify the appearance of the Target Group n Posted u Group is displayed in a viewport u A group may be posted to more than one viewport u More than one group may be posted to a viewport

SECTION 10 CAR DESIGN S10-9 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n First step: Create two groups. The first contains only geometry and the second only finite element entities. u Create groups rapidly using canned selection options u Make groups visible by posting

SECTION 10 CAR DESIGN S10-10 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Click on the Group menu Group/Create form: Enter New Group Name Check the Posted box - this will ensure the new group formed is visible (ie posted) Check the Unpost All Other Groups box -this will ensure all other groups are invisible (unposted) -In Group Contents, select the Add All Geometry option

SECTION 10 CAR DESIGN S10-11 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Enter New Group Name as geom and Apply A group named geom, containing only the geometry entities, is now formed. In this case only some of the construction surfaces and a plane are present in the database Note default_group which contains ALL the database entities is unposted

SECTION 10 CAR DESIGN S10-12 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Repeat the process and now the viewport contains the new group mesh created by using the Group Contents option: Add All FEM Note that the groups default_group and geom are listed now in Existing Group Names

SECTION 10 CAR DESIGN S10-13 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Using the option Group/Post we can select any of the groups to be visible in the viewport. To select a single group as in this case, click on the group named geom from the list and then hit Apply. We can also select all groups, the current group or no groups using the options on the menu.

SECTION 10 CAR DESIGN S10-14 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation To post both geom and mesh groups at the same time: Click on geom and hold the Shift key and click on mesh. This method is ideal for a long list of groups. To pick selectively use the Ctrl key.

SECTION 10 CAR DESIGN S10-15 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Second step: Create two more groups. The first contains the roof mesh only and the second contains only the front windscreen. u defining the current group u controlling the entity picking u controlling the viewport display of the group u modifying the group

SECTION 10 CAR DESIGN S10-16 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Choose a view that will allow a us to pick all the roof entities. New Group Name is roof Check Make Current Check Unpost All Other Groups Choose Option: Add Entity Selection This allows us to make the selection by clicking and dragging in the viewport.

SECTION 10 CAR DESIGN S10-17 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The selected entities are now highlighted. Now hit Apply The group will be created. It will be made current, which means any new entities created will be added to it. All other groups will be unposted.

SECTION 10 CAR DESIGN S10-18 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation We have the roof region, but it has extra entities. Need a strategy for cleanly eliminating these. First we change our Picking Preference from default – Enclose centroid to Enclose any Portion

SECTION 10 CAR DESIGN S10-19 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Next use Group/Modify The Target Group is roof as that is what we want to modify. The Member List shows us what is in the group at present. We wish to select entities to put into the Member List to Add/Remove set. Then we will apply the -Remove- option.

SECTION 10 CAR DESIGN S10-20 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Now we are ready to pick the entities to remove. Select Polygonal Picking from the Selection bar, and set the Picking Preference so that entities we just touch will be picked. That makes the selection very simple now. Hit OK to complete the action.

SECTION 10 CAR DESIGN S10-21 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The group roof is now finished. However it can be irritating when working with groups because the viewport will snap to a view that fits each group posted or created. To disable this use Preferences/Graphics and uncheck Auto Extend

SECTION 10 CAR DESIGN S10-22 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Repeat the same procedure as the group roof to create another group called f_screen

SECTION 10 CAR DESIGN S10-23 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Post both roof and f_screen groups together. Use Ctrl key to select.

SECTION 10 CAR DESIGN S10-24 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Third step: We will look at more powerful ways to create and manipulate groups. We will create groups containing entities belonging to the B pillar of the car. We now introduce methods for: u Using Lists to help create groups

SECTION 10 CAR DESIGN S10-25 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The B pillar is defined as shown. We want to get the nodes and elements for this component into a group. B Pillar

SECTION 10 CAR DESIGN S10-26 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation To help us define the group we first build a local coordinate system which has its y axis running up the B Pillar. Use Create/Coord/Axis Axis: Axis 1 and 2 And pick 3 Nodes.

SECTION 10 CAR DESIGN S10-27 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Patran LISTS u We will use a LIST method to create the B Pillar group. u A list is a set of entities which are brought together in a single temporary set. u The list is created by selecting either an Attribute or Association that its entities will have in common. u After creation, the entities in the list can be used to create or add to a group. u In our case the Attribute will be a distance from the xy plane of coordinate frame 6.

SECTION 10 CAR DESIGN S10-28 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Objective: All nodes in the region +/- 2.5 in around the xy plane of Coord 6 will be put into a temporary list.

SECTION 10 CAR DESIGN S10-29 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Under Tools: Select List/Create Select FEM/Node/Attribute Attribute is Coord Value Refer. Coord Frame is 6 Check z axis Use default tolerance of.005 Choose the between option –2.5 to 2.5 Choose Target List A

SECTION 10 CAR DESIGN S10-30 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation List box List A will now pop up and will contain a list of all the nodes that meet the criterion set. If we select Add to Group then we have a further option in the List Save menu to choose a Group to add the entities into. This can be an existing group or a new as yet undefined group. We define a new group b_pillar

SECTION 10 CAR DESIGN S10-31 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Post the b_pillar group

SECTION 10 CAR DESIGN S10-32 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Clear List A box and create a new list that includes all the elements associated to the nodes in the b_pillar group. Use FEM/Element/Association Select Nodes Select Target List A Apply Choose Add To Group and select b_pillar

SECTION 10 CAR DESIGN S10-33 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The resulting of adding the List A contents is shown. The group can be cleaned up as before using Group/Modify to remove unwanted elements.

SECTION 10 CAR DESIGN S10-34 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Fourth step: We will look at more powerful ways to create and manipulate groups. We will break the entities in the car into three sectors We now introduce methods for: u Moving or copying entities between groups u Performing boolean operations using Lists to create groups

SECTION 10 CAR DESIGN S10-35 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation First we create an empty group called sector1 by defining no entities in the group. We make this group current and unpost all the other groups.

SECTION 10 CAR DESIGN S10-36 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation We now use Group: Move/Copy to copy the elements from f_screen group to sector1 group. Note how we can choose what entities we wish to operate on. Element : Node 96: :

SECTION 10 CAR DESIGN S10-37 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Post the f_screen, b_pillar, and roof groups together.

SECTION 10 CAR DESIGN S10-38 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Include all the posted entities in a new group called sector2 by using Add Entity Selection

SECTION 10 CAR DESIGN S10-39 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n To summarize, we have two main groups now: Sector1 Sector2 We want to create a third group which contains all of the mesh except for those entities in Sector2.

SECTION 10 CAR DESIGN S10-40 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Clear List A and create a new list A containing elements associated with the sector2 group. We use Association by Group.

SECTION 10 CAR DESIGN S10-41 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Fill List B with elements associated with the group mesh.

SECTION 10 CAR DESIGN S10-42 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Use the List/Boolean function to create a third list ; Listc List B contains the whole mesh. List A contains the mesh in sector2. Use Boolean B-A Add the elements in the Listc to a new group called sector3.

SECTION 10 CAR DESIGN S10-43 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Post the sector3 group. Note that the sector3 group could have been created using the Group/Create/Boolean option

SECTION 10 CAR DESIGN S10-44 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n We deviate from the Car example to look at a very powerful function of Groups: u To Create new entities l We have created a 1 x 1 surface and meshed it using global edge length of 0.1 l We created a group called mesh that contains only the finite element entities and a similar geometry group called geom l We now wish to create further regions of geometry and mesh using the Group Options

SECTION 10 CAR DESIGN S10-45 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create and post a group called combo that contains all of the entities in the model. We can do this directly or by assembling the mesh and geom groups

SECTION 10 CAR DESIGN S10-46 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Using Group/Transform/Translate We now translate the group combo to form a new group called combo2.

SECTION 10 CAR DESIGN S10-47 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation We have a further option to Transform any Loads and Boundary Conditions and/or Material and Physical Properties that are associated with the selected group The Translation Vector we have used here is the edge of the plate. It is convenient to use the Tip and base point method.

SECTION 10 CAR DESIGN S10-48 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The translation is completed and the new entities are in the current group combo2 combo combo2

SECTION 10 CAR DESIGN S10-49 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation EXERCISE Perform Workshop 11 Spacecraft Fairing in your exercise workbook.

SECTION 10 CAR DESIGN S10-50 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n We now look at the general class of elements termed 0D. This includes the following: u Spring Elements – used to model bolts, connections etc. u Mass Elements – used to simulate lumped mass.

SECTION 10 CAR DESIGN S10-51 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Spring Elements u CELAS1, CELAS2, CELAS3, CELAS4, CBUSH u The CELASi elements are connected by two degrees of freedom - one at each grid/ground connection point. u The CBUSH elements connects from 1 to 6 degrees of freedom between two GRID points. u Force components: axial force P or moment M Displacement components:axial translation u or rotation

SECTION 10 CAR DESIGN S10-52 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u CELAS1Connects two points, which may be grid points, scalar points, or both, with reference to a property entry. u CELAS2Connects two points, which may be grid points, scalar points or both, without reference to a property entry u CELAS3Connects only scalar points with reference to a property entry ( Not Supported in Patran) u CELAS4Connects only scalar points without reference to property entry ( Not Supported in Patran) u CBUSHConnects two GRID points. Avoids the grounding problem inherent in CELASi elements (when mis-used). May connect 1 to 6 dof.

SECTION 10 CAR DESIGN S10-53 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The CBUSH is the recommended form for scalar springs. l It avoids the potential grounding which may occur when two non-coincident points are connected. l The CELASi elements simply insert terms directly into the stiffness matrix without considering geometry or displacement coordinate systems. l The CBUSH correctly accounts for the effects of geometry and displacement coordinate systems.

SECTION 10 CAR DESIGN S10-54 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The CBUSH - Defines a generalized spring-and- damper structural element that may be nonlinear or frequency dependent.

SECTION 10 CAR DESIGN S10-55 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The CBUSH u Field Contents l EIDElement identification number. (Integer > 0) l PIDProperty identification number of a PBUSH entry. (Integer > 0; Default =EID) l GA, GBGrid points identification number of connections points. (Integer > 0)

SECTION 10 CAR DESIGN S10-56 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The CBUSH l XiComponent of orientation vector, from GA, in the displacement coordinate system at GA. l GOAlternate method to supply orientation vector using grid point GO. Direction is from GA to GO l CIDElement coordinate system identification. A 0 means the basic coordinate system. If CID is blank, then the element coordinate system is determined from GO or Xi.

SECTION 10 CAR DESIGN S10-57 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The CBUSH l SLocation of spring-damper (Real; Default =0.5) l OCID Coordinate system identification of spring- damper offset. (Integer; Default=-1 which means element coordinate system) l S1, S2, S3 Components of spring-damper offset in the OCID coordinate system if OCID 0

SECTION 10 CAR DESIGN S10-58 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The PBUSH - Defines the nominal property values for a generalized spring-and-damper structural element u Field Contents l PIDProperty identification number. (Integer > 0) l "K"Flag indicating that next 1 to 6 fields are stiffness values. (Character) l KiNominal stiffness values in directions 1 through 6. (Real; Default=0.0)

SECTION 10 CAR DESIGN S10-59 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The PBUSH - Defines the nominal property values for a generalized spring-and-damper structural element u Field Contents l "B"Flag indicating that the next 1 to 6 fields are force-per-velocity damping. (Character) l BiNominal damping coefficient in units of force per unit velocity. (Real; Default=0.0)

SECTION 10 CAR DESIGN S10-60 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The PBUSH - Defines the nominal property values for a generalized spring-and-damper structural element u Field Contents l "GE"Flag indicating that the next fields is structural damping. (Character) l GE1Nominal Structural damping constant. (Real;Default=0.0)

SECTION 10 CAR DESIGN S10-61 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The PBUSH - Defines the nominal property values for a generalized spring-and-damper structural element u Field Contents l "RCV"Flag indicating that the next 1 to 4 fields are stress or strain coefficients. (Character) l SAStress recovery coefficient in the translational component numbers 1 through 3. (Real, Default=1.0) l STStress recovery coefficient in the rotational component numbers 4 through 6. (Real; Default=1.0) l EAStrain recovery coefficient in the translational components. (Real; Default=1.0) l ETStrain recovery coefficient in the rotational components. (Real; Default=1.0)

SECTION 10 CAR DESIGN S10-62 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Rear Suspension n Zero Dimensional Elements u We want to add the rear suspension to the car model. We will do this using, in turn: l CELAS elements l BUSH elements

SECTION 10 CAR DESIGN S10-63 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation If the suspension is connected to another component then we need to define a pair of grids to form end B of the springs.

SECTION 10 CAR DESIGN S10-64 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create each suspension element directly using Create/Element/Edit Use Bar2 generic MSC.Patran Topology.

SECTION 10 CAR DESIGN S10-65 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create the suspension element properties using Create/1D/Spring Provide a Property Set Name Pick the elements using Select Members Use the element selector El El 17582

SECTION 10 CAR DESIGN S10-66 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation From the main form select Input Properties On the CELAS1 form: Input Spring Constant Select the DOFs using the String List: here we use UY Note: In general, springs should always be created between coincident nodes. A spring connecting two nodes separated by a distance can cause grounding problems.

SECTION 10 CAR DESIGN S10-67 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation $ Elements and Element Properties for region : rear_susp PELAS $ Pset: "rear_susp" will be imported as: "pelas.12" CELAS CELAS n Zero Dimensional Elements u The CELAS1 and PELAS cards are shown u The Cross Reference from the CELAS1s to the PELAS is via PID 12 u Both ends of the spring have DOF 2 (the y direction) u Ky = 1e6 lbf/in

SECTION 10 CAR DESIGN S10-68 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u If CELAS2 is desired, select Write Properties on Element Entries in the Patran Analysis Translation Parameters form:

SECTION 10 CAR DESIGN S10-69 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u Stiffness in multiple directions: l The Suspension has only the Uy direction stiffness defined so far. l If we want to apply stiffness in all 6 degrees of freedom we will need to define 6 elements for each suspension component, connected between the same grids. We will end up with 6 CELAS1 elements per suspension component. l Setting up this number of elements is tedious and is one of the reasons to use a CBUSH element instead.

SECTION 10 CAR DESIGN S10-70 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u Zero Length Springs: l The concept of length in a spring is misleading and in general it is bad practice to put in a finite length. They are strictly 0D elements even though we create them via generic Patran Bar2 elements. l There are two alternatives in our case: l A Spring between two coincident grids l A Grounded Spring l When creating the Spring between coincident grids we create the zero length Bar2 element and property exactly as shown before, except being careful to select the coincident grids properly.

SECTION 10 CAR DESIGN S10-71 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u Zero Length Springs: l The grounded spring is created by defining a 0D element in Patran and then associating Grounded Spring Properties. By definition only one grid is needed.

SECTION 10 CAR DESIGN S10-72 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The Bush Element: l As described in the theory section the CBUSH element is much preferred when defining a finite length spring. Length now has a physical meaning and geometry is taken into account properly. l However we still classify it as a 0D element. l The CBUSH can be defined as having coincident grids, or grounded with a single grid. But we need to define an orientation vector to define the direction of the stiffness terms l We repeat the suspension example now …

SECTION 10 CAR DESIGN S10-73 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create each suspension element as before Create/Element/Edit Use Bar2 generic MSC.Patran Topology

SECTION 10 CAR DESIGN S10-74 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create the suspension element properties using Create/1D/Bush Provide a Property Set Name Pick the elements using Select Members Use the element selector El El 17582

SECTION 10 CAR DESIGN S10-75 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation String List From the main form select Input Properties On the Bush form: Input Bush Orientation Input Spring Constants 1 to 6 as required

SECTION 10 CAR DESIGN S10-76 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Bush Element We define the Orientation by using the orientation vector method. The CID method can be used when the two grid points are coincident. The direction of the stiffness terms is then defined. Note only translational stiffness is defined.

SECTION 10 CAR DESIGN S10-77 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Elements u The CBUSH and PBUSH cards are shown. u The Cross Reference from the CBUSHs to the PBUSH is via PID 12. u The Stiffnesses are defined on the PBUSH card via the K flag and the orientation is defined by the vector

SECTION 10 CAR DESIGN S10-78 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Mass Elements u Mass elements are used when mass properties of a structural component are idealized at a single grid point. u They are used in dynamic analysis and static analysis where inertia loading are used. u Only 3 mass elements are created by MSC.Patran: l CONM2 – a simple lumped mass definition l CONM1 – a more complex mass definition l CMASS1 – a scalar mass definition u Of these the CONM2 is the most commonly used.

SECTION 10 CAR DESIGN S10-79 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Mass Elements u We will now represent the engine block in the car via a CONM2 element. u This is a very typical example where we do not want to model the engine block in detail, but want to have the correct mass and inertia terms included. u We have a tet mesh of the block, so we can use that to find lumped mass properties.

SECTION 10 CAR DESIGN S10-80 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The tet mesh of the block

SECTION 10 CAR DESIGN S10-81 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Select Tools Mass Properties… Show/3D Define the region using a previously defined group block Check Plot Principal Axes

SECTION 10 CAR DESIGN S10-82 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The Principal Axes are plotted.

SECTION 10 CAR DESIGN S10-83 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The cg is reported relative to Coord 0 in this case. Coord 9 has been created at the cg. M =.8412 I11 = I22 = I33 = CG = [34.24,24.91,-30.0] (Mass density values)

SECTION 10 CAR DESIGN S10-84 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation First we create a grid at the origin of the block as reported.

SECTION 10 CAR DESIGN S10-85 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Now we create a Point Element at this grid. A triangle confirms the element position.

SECTION 10 CAR DESIGN S10-86 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation In Properties Create/0D/Mass Input Property Set Name Choose Lumped Option Select Members (use the point element selection pick). Input Properties for CONM2 as reported previously.

SECTION 10 CAR DESIGN S10-87 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation $ Elements and Element Properties for region : block_mass CONM n Zero Dimensional Mass Elements u The CONM2 element is shown below with M, I11, I22, I33 completed.

SECTION 10 CAR DESIGN S10-88 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Mass Elements u The other options for creating Mass properties from point elements are shown:

SECTION 10 CAR DESIGN S10-89 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Zero Dimensional Mass Elements u If generic bar2 elements are used then a CMASS1 element with 2 grids is created.

SECTION 10 CAR DESIGN S10-90 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Offset 20,0,0 in Coord 0 from grid Mass 200 n Zero Dimensional Mass Elements u A very common application is to offset a CONM2 element. The setup is shown below:

SECTION 10 CAR DESIGN S10-91 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Rigid Elements u A very useful set of elements are defined as Rigid Elements. They are most commonly used as general connection elements, where we do not wish to model the connections in detail. u The most common Rigid Elements are: l RBE2 - one independent node and multiple dependant nodes. l RBE3 – one dependent node and multiple independent nodes.

SECTION 10 CAR DESIGN S10-92 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation connections engine n Rigid Elements – the RBE2 u Consider the engine mass we have just created. We need to connect it into the bulkhead structure, but we have a lumped mass idealization and we do not wish to model the detail of the connections.

SECTION 10 CAR DESIGN S10-93 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation lumped mass idealization n Rigid Elements – the RBE2 u We will connect the lumped mass to the attachment points via an RBE2 element.

SECTION 10 CAR DESIGN S10-94 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create/MPC/RBE2 Define Terms Switch off Auto Execute Check Create Dependent Select only DOFs Ux thru Rz Pick Node List and hit Enter

SECTION 10 CAR DESIGN S10-95 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation The Dependent Terms box will be populated Select Create Independent Select Node List – pick the node at the engine mass Hit Enter The Independent Terms will be filled in

SECTION 10 CAR DESIGN S10-96 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Hit Cancel in the sub-form Hit Apply in the main form The RBE2 will be shown

SECTION 10 CAR DESIGN S10-97 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n The spider we have formed will now form an infinitely rigid connection between the CONM2 at its grid and the other four connecting grids.

SECTION 10 CAR DESIGN S10-98 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n Rigid Elements – the RBE3 n Sometimes a rigid spider is not appropriate: u Connecting a mass to a flexible backing structure, such as a satellite platform. u Connecting a beam element to a shell structure, such as a fuselage idealization. n In these cases we use an RBE3 element, which looks identical, but now the body of the spider is the dependent grid. The feet are the independent grids. n The dependent grid moves as an average of the independent grids. It forms a soft connection.

SECTION 10 CAR DESIGN S10-99 NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation Create/MPC/RBE3 The procedure is the same as before except that the mass grid is dependent. The connection grids are independent and only choose DOFs Ux to Uz.

SECTION 10 CAR DESIGN S NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation n The engine mass will now move as the average of the connection grids. n The connections and the bulkhead will not be stiffened by the presence of the RBE3.

SECTION 10 CAR DESIGN S NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation EXERCISE Perform Workshop 12 RBE2 vs. RBE3 in your exercise workbook.

SECTION 10 CAR DESIGN S NAS120, Section 10, May 2006 Copyright 2006 MSC.Software Corporation