MESHING THE PRESSURE VALVE WITH DIFFERENT ELEMENT SIZE USING ANSA

OBJECTIVE

To mesh the given pressure valve model using ANSA with various element size of

• 15mm
• 7mm
• 2mm

TOOLS USED DURING THE PROCESS

• Not function
• ! Not function
• All function
• Lock function
• Invert function
• Coons (Under Surface)
• Intersect (Under Faces)
• Loop function
• Feature Area

PROCEDURE

1. STEPS TO OPEN A FILE IN ANSA

• Click on File
• Select Open
• Select File (FORMAT .igs/SLDPRT .ansa etc.)
• Click Open
• A translator window appears CLICK OK

As the part gets opened in ANSA, firstly it is in wire mode and in entity mode, for desirable visualization we have to change it to shadow mode (It is the visualisation of the part in solid 3D) and the ENT Mode to PID Mode. As we change it to PID Mode we need to change the colour of the edges in model for desirable visualization as for this we need to follow the following steps:

Steps To Change The Colour Of The Edges In The Model

• Go to Quality criteria option (F11)
• Select the tab Presentation Parameter
• Under visualisation option select Draw CONS in PID
• Click Apply then click on ok.(Now the edges will be in yellow colour ).

Checking The Geometry of the Model

• Goto checks option
• Select Geometry
• An information box will appear
• Click on execute to see the error though it should show no geometrical error for perfect meshing. But a lot of topological errors were detected we need to fix them for proper meshing.

2. CLEANING UP OF THE TOPOLOGICAL ERRORS IN THE OUTER SURFACE GEOMETRY

• Enter in PID mode for desired view, in PID drop down menu select PID Region. As PID Region allows us to show the geometry in same PID.
• We started with PID Walls of the valve and locked its view using Lock function in which a lot of topological errors were diagnosed also many holes and surfaces were absent.

FIG.1 VALVE TOPOLOGICAL ERRORS

STEPS TO GET THE SURFACES, HOLES ERRORS FIXED

• Under TOPO
• GOTO SURFACE
• Select COONS
• Select all the edges of the hole using left mouse click
• Middle click will preview the desired surface
• Click OK

STEPS TO GET COMPLEX HOLES ERRORS FIXED

• UNDER FACES OPTION
• SELECT DELETE
• SELECT the surface which has the error and has to be rectified using left mouse click.
• After delete GOTO SURFACE OPTION and Select COONS
• Select all the edges of the holes, middle mouse click to preview the desired rectified surface
• Click OK, the geometrically desired surface is created.

TO DELETE UNNECCESARY HOT POINTS FROM THE GEOMETRY

• In TOPO Mode
• Goto Hot Points
• Select Delete
• Use left mouse click to drag to draw a box around the irrelevant Hot points in the geometry
• The unnecessary extra Hot Points are deleted

FIG. 2 RECTIFIED GEOMETRY OF OUTER SURFACE

NOTE

• For complex holes in the geometry use cross hatches which will help in differentiating the different surface from one another also each surface has its own cross hatch.
• Missing surfaces can be detected by red cons.

3. CLEANING UP OF THE TOPOLOGICAL ERRORS IN THE INNER SURFACE GEOMETRY

• As the geometry clean-up for outer surface is completely done we will again select the PID Region option for the inner surface which include seal and the spring geometry and lock the inner surface geometry view using lock option.

FIG. 3 TOPOLOGICAL ERRORS IN THE INNER SURFACE

STEPS FOR INTERSECT TOOL

As the geometry of spring and the valve are intersecting each other we need to go for a Boolean operation in which we need to intersect both the surfaces together for valid geometry.

• Under FACES sub-menu
• GOTO Intersect tool
• Select the first face (for e.g. valve seal) using left mouse click
• Select the second face (for e.g. spring) using left mouse click
• Middle mouse click to intersect both the surfaces.

DELETING THE INTERNAL SPRING OF THE VALVE

• Inside the valve seal , we need to delete all irrelevant internal part of the spring, which will give you the view of spring and the seal valve are intersected.
• Use delete option from upper menu to delete the unnecessary part of internal spring.

FIG.4 RECTIFIED GEOMETRY OF INNER SURFACE

NOTE

• If there are no connection between the two intersected part it will show in two different PIDs.
• At last when we will select PID Region we will find complete part of the valve seal and valve spring will be selected at once, which shows that they are converted into single PID Region.
• CLICK on !- option
• SELECT PID Region
• The entire valve spring and the valve seal gets selected.

LOOP FUNCTION

The surface of Inlet, Outlet and the External bottom casing are made using the loop function.

Loop function enable us to select the closed loop of the geometry at a single click .

STEPS FOR CREATING SURFACE USING LOOP FUNCTION

• Under Topology
• Goto Surface menu
• Select Coons
• Select Loop
• As the loop is selected make a left click on the closed loop cons of the holes where the surface is to be created.
• At one click the closed loop will be selected and the new desired surface will preview.
• Click OK the new surface is created.

After finishing the geometry clean-up completely, we need to assign the PID for all the parts of the geometry

STEPS FOR ASSIGNING PID TO EACH PART OF GEOMETRY

To assign the property to the model we need to select TOPO MODE (upper right of the menu tool box)

• Go to TOPO MODE
• Under Faces sub-menu
• Select SET PID OPTION
• Select Faces/shell
• Go to below tool bar and select CROSS HATCHES option it enables diagonals of the model
• Left click on cross hatches then middle click of your mouse
• A shell property help box will appear
• Select new option tab , a box will appear, create a New ID name of the specific part (for ex. INLET)
• Click ok then in shell property help box double click on New ID (INLET) to assign it to the specific part of the model.
• Same procedure will be followed for each of the parts of the mode.

FIG. 5 ASSIGNING OF PID

NOTE

As the valve seal and valve spring is converted into single PID so we have to use Feature Area option as it will select only the object which is at some feature angle. (for e.g. spring is at some angle to the valve seal)

STEPS TO ASSIGN PID FOR SPRING USING FEATURE AREA OPTION

• Goto SET PID
• FEATURE AREA OPTON
• Select Faces/shell
• Corner are selected by entity manually.
• Left click on cross hatches then middle click of your mouse
• A shell property help box will appear
• Select new option tab , a box will appear, create a New ID name of the specific part (for ex. SPRING)
• Click ok then in shell property help box double click on New ID (SPRING) to assign it to the specific part of the model.

FIG. 6 PID ASSIGNED FOR SPRING

READY FOR MESHING

As there are no geometrical errors present in the model and the properties are also assigned to the model so it is ready for the meshing, steps for meshing is as follows:

For meshing the model we need to go to MESH MODULE (upper right of the menu tool box)

• Select Mesh module
• Under Perimeters sub-menu
• Select length (To decide the length of mesh discretization )
• By left click draw a box around the valve, all points of the valve will get Selected
• Click middle button of mouse a length parameter box will appear , insert the numeric value 2mm.
• Click OK .

Now we will start with meshing

• Select Mesh module
• Under Mesh Generation
• Select Spot Mesh by clicking left mouse button
• Rightside below one Option List drop down menu will appear with element type select tria
• By using left mouse button draw a box around the valve model
• Click middle mouse button
• Mesh will be generated.

FIG. 7 MESHED PRESSURE VALVE

NOTE

To change the element size, again follow the above steps only the numeric values in the length option will be changed. (i.e. 15mm,7mm )

OBSERVATION

Bigger elements size provides coarser srface and inaccurate results, usually smaller element size provides less skewness as well as smoother mesh with better mesh quality as compared to bigger element size, and can provide us with accurate results, but the computing time gets significant as well, so as in our project we need to mesh the valve with 15mm, 7mm, 2mm respectively.

FIG. 8 MESHED VALVE WITH ELEMENT SIZE 15mm

During 15mm mesh we witnessed the meshed surface was too coarse with high skewness as the mesh length was too high 15mm so there was a large jumps in the surface between adjacent cells, so this mesh length is not desirable due to numerous of errors this mesh length will provide us inaccurate result.

FIG. 9 MESHED VALVE WITH ELEMENT SIZE 07mm

During 7mm mesh we saw somewhat same errors as compare to the 15mm mesh as 7mm mesh length is also higher so similar errors were being faced during meshing with 7mm , as in this the mesh is not smooth though its coarse, high skewness could be witnessed due to which it has very poor mesh quality.

FIG. 10 MESHED VALVE WITH ELEMENT SIZE 02mm

During 2mm mesh the results was better. The values of ‘off’ were quite less. As the mesh was smooth with low skewness ,there was a gradual change in element size which is desirable and also it has better mesh quality. It provided us with more accurate results.

CONCLUSION

Element size with 2mm is the best option for meshing the valve because, during 2mm mesh the results are better than as compared to the 15mm and 7mm element size the values of ‘off’ are also quite less as compared to the ‘off’ shown for 15mm and 7mm element size. As in this element size the mesh is smooth with low skewness ,there was a gradual change in element size which is desirable and better mesh quality is witnessed as compared to the 15mm and 7mm element size. We attained more accurate results than the results of 15mm and 7mm element size.

FIG.11 THE BEST OPTION FOR MESHING PRESSURE VALVE IS ELEMENT SIZE OF 2mm