EXTRACTION OF MIDDLE SURFACE AND APPLYING MESH ,1D (BAR,BEAM,ROD) ON BRACKET

AIM : 

1. Extraction of midsurface on the given component
2. Mesh generation on extracted mid surface
3. creating 1D elements(BAR,BEAM,ROD) on the component with according to the given DOF,and crossection and applying mass and spring connections.

PROCEDURE: 

• CREATING MID SURFACE

As the name MIDSURFACE itself says that it is a surface which lies middle in between two surfaces.the purpose of midsurface is that say for an example if the given 3D cad component which have a thickness of less than 5mm if we create 3D mesh on it with tetra or hexa,the number of nodes and elements are going to increase since its a 3d model which inturns increase the storage space requires to store the data and it also prolongs the processing time for analyzing,so to avoid this midsurface is created where we can represent the enitire 3D model by a surface and create a shell element on it (shell elements are 2D representation of 3d elements hexa and tetra).now we proceed with creation of midsurfacing by importing the cad model

Since the given model is in .IGES file format before importing it we need to select the suitable format in FILE TYPE menu.

After importing the CAD model if it is in wireframe mode turn it into shaded view to see the component.the points at the perimeters which shows up after importing the model helps to meaure the dimensions of the model,for now we can hide the fixed points in the model if we need.picture below shows the imported bracket model.

now we proceed with midsurafing the model for that we select MIDSURFACE button under GEOMETRY tab.there is a button shows auto-midsurface which created midsurface in one click if the component is uniform and have non-variable thickness,if in case the cad component is having variable thickness we can choose other options under the midsurface toolbar.

we select the upper component to create the midsurface.here we can see the created midsurface is exactly in the middle in between the two planes and it is aligned in proper manner since the model is uniform and looks fine without any variable thickness.it is not able to create a mid if the cad model or the component we select is having non-uniform or variable thickness.

once after the midsrface is created, a component with name "Middle surface" is created under MODEL VIEW tab. if we create other midsurface for the the below bracket component both the above and below midsurfaces are going to combined and become one component which is not recommended. so it is better to create a seperate compoinent for other midsurface for that we create a new blank component in model view or we can duplicate the parallel bracket.by duplicating only the name and properties are assigned later then we can input its own properties and assign the midsurface for that duplicated component,so that the middle surfaces wont be combined into one and we can work on seperately.

for assigning or moving the midsurface to the component we created theres a tool named TOOL-ORGANISE by clicking shift+f11 then by changing element to surfaces click the destination component to move the new middle surface.here in the below picture two midsurfaces are created and organised seperately

• DEPLOYING THE MESH ON MIDSURFACE

Before creating mesh we need to create washer split near the holes in the model as we know that mesh elements will be poorly organised at circular edges and if we can create a washer split we can resolve the issue by arranging the nodes and eliminating any trias occuring at the circular sections.for creating washer split we choose GEOM-QUICKEDIT-WASHER SPLIT option and by selecting the circular edges we can create washer split around it as shown below

now we can proceed deploying the mesh on mid surface by selecting 2D-AUTOMESH and choosing the element size as required and select the surfaces to create the mesh.after meshing is check the mesh elements at circular edges where we created washer split.if there are any trias present along the edges we can organise the nodes around the perimeter of the circle by making the nodes even so that all the trias can be deleted and mesh will be proper. the difference is demonstrated as shown below.

• Assigning material

The next step is proceeded with assigning the material for the components.for that we create steel material by selecting the specified card image as MAT1.

• Assigning properties

now we assign properies to the material since there are two brackets we create two properties because we assign different thickness to those two brackets.here the two properies are created with names BRACKET-1 and BRACKET-2 so that we can assign them without confusion between the names.

The below images shows MATERIAL and PROPERTIES are assigned to the BACKET-1COMPONENT and similarly we do this to the other component as well.

• Creating 1D elements(bar,beam,rod,rbe2,rbe3,spring)

Creating RBE2 element with translational dof:

RBE (Rigid Body Elements) are the most simple of 1D elements and simply connect two ormore nodes together.In the case of an RBE2, one node serves as the Independent and the other(s) theDependant node(s). The Dependant node(s) simply “follow” the motion of the Independentnode in the Degrees of Freedom that have been linked. These elements are useful to simplyrepresent welds or to tie together two dissimilar meshes. One word of caution though isthatRBE2 elements, as they rigidly link nodes together, can induce a stiffness to the model that may not be desired.

now we create a rbe2 element on a circle by creating the nodes. the load which is going to act from one to other node is exactly equal since its a one element . so we create multiple nodes around the circle so that it distribute the any load uniformly around the node when applied.

to create the node 1D-RIGID and click on the nodes by choosing independent tab as calculate node and dependent tab as nodes by path. as it says nodes by path when we click the nodes it creates the other nodes around the circular path,later that we select dof as spcified for rbe2 rod element which is translational dof so uncheck the first 3 so that it restricts rotational and gives only translational dof to the element.finally after the selections with middle click rbe2 elemnt is created as shown below.

similarly by following the same steps we create rbe3 elements at other holes with specified dof given in the challenge as given below

• CREATING ROD(BOX DIMENSION),BEAM(I-section),BAR(X-SECTION)

 To create bar,beam,rod of required crossection and dimensions we select HYPERBEAM VIEW in top menu bar of hypermesh
 

this will take you to hyperbeam workspace where we going to create the elements that we need to attach it to the brackets

1.first a rod element is created by rightclicking on entities panel there we can see a create option under that we select standard section-hypermesh-thinwalled box.after creating the dimensions are specified with required input values as shown below

after creating the bar element we follow the same procedure but this time we create beam of I-crossection

now the beam of I crossection is created with specified dimensions and thicknesses as given in the challenge which is shown in below picture.

Bar of X(CROSS)-crossection is created with specified dimensions and thicknesses as given in the challenge which is shown in below picture

After creating all the beam section elements we return back to hypermesh model workspace and create properties for BAR,ROD,BEAM and assign these created models in BEAM SECTION menu as shown below.

first we create properties with same names as bar,beam and rod under the section of properties tab and then we allocate their respective beam elements as pictured below

the same process is repeated for other beam sections as well.then we update the properties under 1D section of bars and rod.the process for updating the elements is by choosing update option and clicking the elements we created before which are connected between the rbe2 and rbe3 elements by specifying the element type and nodes which is shown below.

propert-BAR

element type-CBAR is choosen and we click the cbar element we need to update as shown below.this procedure os same for the following rod and beam.

now,we apply mass of magnitude 10 with RBE2 link at D&E circular sections by selecting 1D-MASSES amnd choosing the nodes where rbe2 is present at the D and E circular hole.

thre final step is to create a spring connection at F edges for that we choose 1D-SPRINGS-CREATE-choose node at top and bottom brackets and by clicking on create we can make a spring connection on either sides of the bracket as shown below.

The final model with all the elements,loads and spring connection is created and shown below.since the elements can be seen as a line only we choose the option "1D detailed element representation"to see the crossections of elemets and the thickness of brackets surfaces can be seen by enabling "2D detailed elemet representation"

CONCLUSION:

• Extracted midsurface on the given component
• Generated mesh on the extracted midsurface
• created 1D elements(BAR,BEAM,ROD) on the component with according to the given DOF,and crossection and applying mass and spring connections.