MPC184单元——Revolute joint定义_饮马长江

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MPC184单元——Revolute joint定义

(2012-05-22 15:14:15)

分类： ANSYS

http://s8/middle/82b52627hc09ad19613f7&690joint定义" TITLE="MPC184单元——Revolute joint定义" />
et,2,mpc184
keyopt,2,1,6 !define a two-node revolute joint element.
keyopt,2,4,1 !element is a z-axis revolute joint with the local e₃ axis as the revolute axis.
!!!A local Cartesian coordinate system must be specified at the first node, I, of the element. The specification of the second local coordinate system at node J is optional. If the local coordinate system is not specified at node J, then the local coordinate system at node J is assumed to be the same as that at node I.

MPC184 Revolute Joint Input Summary
1 Nodes i,j NOTE: For a grounded joint element, specify either node I or node J in the element definition and leave the other node(the grounded node)blank. For example: E,,j or E,i,.
2 DOFs--ux uy uz rotx roty rotz
3 Real Constants--None
4 Material Properties use the join label on the TB command to define stiffness, damping, and coulomb friction behavior.
5 Surface load--none
6 Body Loads--Temperatures T(I),T(J)
7 Element Loads

Rotations --

ROTX (KEYOPT(4) = 0)

ROTZ (KEYOPT(4) = 1)

Angular velocities --

OMGX (KEYOPT(4) = 0)

OMGZ (KEYOPT(4) = 1)

Angular accelerations --

DMGX (KEYOPT(4) = 0)

DMGZ (KEYOPT(4) = 1)

Moments --

MX (KEYOPT(4) = 0)

MZ (KEYOPT(4) = 1)

8 Special Features

Large deflection

Linear perturbation

9 KEYOPT(1)

Element behavior:

6 -- Revolute joint element

10 KEYOPT(4)

Element configuration:

0 -- x-axis revolute joint with local 1 direction as the revolute axis.

1 -- z-axis revolute joint with local 3 direction as the revolute axis.
--------------------------------------------------------------------------------------------------
Connecting Bodies to Joints

Other than in idealized geometry (such as that shown in Figure 2.1), an MPC184 joint element is defined by one or two nodes in space and requires special modeling techniques to connect the joint to the body appropriately.

Figure 2.14 shows a 3-D model of a pinned joint where the geometry of the joint (the pin) is explicitly modeled. To perform a multibody analysis, the pin geometry is ignored and the behavior replaced by the appropriate MPC184 joint element.

http://s9/middle/82b52627hc09bae8f2a58&690joint定义" TITLE="MPC184单元——Revolute joint定义" />

Figure 2.15 shows the meshed model including the revolute joint. To connect the bodies to the joint, you must use either elements (such as beams) or constraint equations. The easiest way to do so is to use contact elements to create surface-based constraints (multipoint constraints, or MPCs), as follows:

Define a pilot node at one end of the joint. The pilot node connects the joint to the rest of the body.
Select the nodes on the surface of the body that you want to connect to this pilot node.
Create contact surface elements on this surface. By sharing the same real constant number (REAL,N ), MPCs between the surface nodes and the pilot node are generated during the solution.

http://s8/middle/82b52627hc09bb39ed277&690joint定义" TITLE="MPC184单元——Revolute joint定义" />

Figure 2.16 shows the contact elements and Figure 2.17 shows the MPCs (constraint equations) created during the solution for the lower body.

Create the pilot node using the TARGE170 element--setting KEYOPT(2) = 1 so as not to allow the program to constrain any DOFs--and issuing the TSHAP,PILO command.

If you mesh the body with elements having no midside nodes (such as SOLID185), use CONTA173 as the element type for the surface mesh. For elements with midside nodes (such as SOLID186 or SOLID187), use CONTA174. Set the following element key options to create the necessary constraints:

KEYOPT(2) = 2	Constraint (MPC) option.
KEYOPT(4) = 2	Generate rigid MPC constraints.
KEYOPT(12) = 5	Bonded behavior between the pilot node and the contact surface.

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http://s8/middle/82b52627hc09bbbf63477&690joint定义" TITLE="MPC184单元——Revolute joint定义" />

Instead of the rigid option, you can also choose a flexible (force-distributed or RBE3-type) constraint option by setting KEYOPT(4) = 1. The following figures illustrate the difference in behaviors:
http://s9/middle/82b52627hc09bbfedcf28&690joint定义" TITLE="MPC184单元——Revolute joint定义" />

Following is a typical command sequence for connecting bodies to joints:

! Step 1: Define a pilot node at the joint node

et,59,170 ! type ID=59 is an available ID

keyopt,59,2,1 ! do not allow program to constrain DOFs

real,59 ! real ID=59 is an available ID

tshap,pilot

e,9536 ! “9536” is the joint node

! Step 2: Select the nodes of the corresponding surface

csys,15 ! CS at center of pin

nsel,s,loc,x,15 ! nodes at r=15

! Step 3: Create the contact elements on the surface

et,60,173

keyopt,60,2,2 ! constraint (MPC) option

keyopt,60,4,2 ! rigid MPC

keyopt,60,12,5 ! bonded always contact

type,60

real,59 ! same real ID: this connects the pilot

! to this surface

esurf ! generate the contact elements on the surface

nsel,all

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