Week 4

PRE-PROCESSING OF VARING THICKNESS OF BOTTLE CAP BY ANSA

OBJECTIVE:

• The main objective for this project is to obtain topologoical clen up,mid surface of varing or different thickness followed by Meshing the model which should satisfy the Qualiy Criteria.

ABSTRACT:

In this project we are going to see difference in thickness of the model,and how we are going to obtain the mid surface for the particular geometry and assigning different PID.

Performing the first step of CAE process(pre-processing) in ANSA.

METHODOLOGY:

• Import geometry
• checking errors
• topological clean up
• Extracting mid surface for different thickness
• Assining different PID for each part
• Meshing the component for given Quality criteria.

PROCEDURE:

• After opening ANSA,import the model from file command.

• This is the model we can see when we import the geometry into ANSA interface.
• Now check for any errors in the geometry.
• If errors are present,fix the errors automatically and manually.

(a) (b)

• In the above two images (a) image shows that the model has many errors.
• In (b) image we can see that the model has no errors,which are fixed by automatic and manual method.

Why to fix Errors: We have to fix the errors of the geometry because if the are any gaps or cracks and unwanted surfaces,there will be not good mesh flow in the model which is our main objective.To perform a good mesh flow we need to check and fix the errors.

METHODS OF MIDSURFACE:

• OFFSET
• MIDDLE

OFFSET:This method is used when there is non uniform thickness in the model.Measure the thickness of the part and and give offset half of the thickness.If the colour is Gray then take Negative sign,if the colour is gold do not take any negative as gold colour is negative in ANSA.

MIDDLE:This method is used when there are identical surfaced in the model.Select one side of the surface which is red coulour the select green colour which is another side and select the thickness which is of blue colour.Middle method can be use for only identical parts.

(a) (b)

• In the above (a) image as the surface is uniform,we can do middle method.But as there are identical parts on both sides it is advised to do offset method.
• In the above (b) image as there are many identical surfaces we can select at a time by middle multi and can obtain midsurface at a time for identical surfaces.

ASSIGN PID:

• After obtining midsurface assign PID for each and every part seperatly.
• This is because,when there are many surfaces in the model and having varing thickness it is preferable to assign different PID,which we be easy for user to assign thickness for different surfaces.

• As we can see in the above image,different PIDS have been assigned for different faces.Which will be easy for the user to observe that midsurface have been assigned correctly or not and to assign thickness.

NOTE:In some cases when two faces of different thickness are joined by the third face,the thickness should be taken as shown

• In the above image we can see three different PID are assigned for three faces.
• If we consider CREAM colour face as PID 1,GREY colour as PID 2,then VOILET colour face is taken as the average of PID 1 and PID 2
• PID 1=1.529
• PID 2=1.278
• Average PID=(p1+p2)/2 0r Average thickness=(t1+t2)/2
• Avg pid=(1.529=1.2785)/2
• Avg pid=1.028
• Therefore,the thickness should be assigned for middle face is 1.028,which is taken as average of two different thickness.

MID SURFACE FOR THREADS:

• To extract mid surface for threads we nedd to create middle curve for lines of same plane.

• After selecting the curves lines do middle click in the mouse or press Enter,a purple colour curve appears in the middle of the threads.
• If this not appears,turn on the curves option which is in the bottom right of ANSA interface.
• Do fine for middle curve miltiple times which will be in a correct shape to extrace midsurface.

• In the above image we can see a purple colour curve between two lines.
• Now project that curve to the mid surface of the faces which is extracted.
• After that,create a new face by selecting purple colour curve and the projected cure on the mid surface,then we can see the midsurface of the threads.

• We can observe that the midsurface for the threads is done.

MID SURFACE FOR ROTATING PARTS:

• In the model we can see that there are fins,which are at same distance for the model in 360 degree.
• It will be difficult for us to take midsurface for each and every fins.
• To do that we need to extract mid surface for one fine and do transform to other fins in 360 degree which will save our time and energy.

NOTE:In order to extract midsurface for the rotating fins,we need to create a two points(which defines line) such that they exist at the centre of the model.

• To create a point,go to poins-COG select diameter(we can take outer circle),then one point is created,do same by selecting inner circle to define another point.

• For identical FINS we can create midsurface for selecting middle option,in this case mid surface is extraced for one identical part.

TRANSFORM:

• To transform the middle surface of fins in 360 degree,go to transorm option.
• Select the entity which needs to be transformed.
• NOw do middle click and select rotate.
• If we have to make mid surface for 10 steps we need to do it for 9,because already we have done one
• In our model we have two sets od fins,one is of 16 and other is of 36 in members.
• For both fins the procedure is same.
• In x bar we need to select one point,then automatially ANSA will take y and z co-ordinates.
• Same manner select second point for dx.
• For angle,if we have 16 fins we need to do it for 15 so angle will be 360/15.
• If we are doing for 36,the angle will be 360/35.

• In this manner we can extracr mid surface for rotating fins.

TOTAL MIDSURFACE OF THE MODEL:

ORIENTATION:

• Make sure to do orient,always prefere grey colour on the outer side of the model because in ANSA grey is a positive and Gold is negative.

QUALITY CRITERIA:

• The Quality criteria which should be followed is given below.

• In Quality criteria enter the above parameters which should be followed.
• In Quality parameters,make your target lenght as 1.

MESHING:

• To do meshing,select lenght as 1 for this model.
• For better meshing do meshing individually for each part.
• Do re-construct for each part after meshing.

Rules OF MESHING:

• Meshing should be done for each part.
• No trias should be connected to the edges.
• No trias should be near to each other.
• No rotating quads should be present.

• After meshing we can see there are so many off elemnts which are not supporting Quality criteria.
• This can be rectified my reconstruct and by smoothing or even by manual method.

• Above image we can see that every part is meshed,as there are no unmeshed parts.
• And mesh flow is also good.

SOLVING OF MESH:

• There are trias near to each other,we acn solve it by doing split option and smooth it.

• In the above image trias are very near so we can do split it by split option in forward direction and smoot it.

PASTE:

• In paste we can move tria in backward direction.

• By paste option we can move tria back.
• the image shown,where we can see white colour and yellow colour points.
• white colour are for 1 series and yellow colour are for 2 series of pasting.
• While pasting make sure parametric paste should be COG.

OFF ELEMENTS:

• After meshing every part,and doing some mesh cleaning,we can find some off elements are present.
• When there is OFF element in the model then that particular element is failing for Quality criteria.

WHY ELEMENTS ARE FAILING FOR QUALITY CRITERIA:

CASE 1

• Some elements fail for QC because,if there is a TRIPLE con and double con which we should not remove in the Geometry then the element fail for QC.

• In the above images we can see that element is failing for minimum lenght,because there is a TRIPLE con and Double con which are very near to eachother,
• In topo mode we can see that clearly.If we try to remove Double con then there will be change in Geometry which is not acceptable.

CASE 2

• In the above images the mesh is failing for SKEWNESS.
• In left image we can see that two faces are having different thickness as well as PID.
• We cannot join two pids as they are of different thickness.
• So in this case the element is failing for thickness.

GOOD MESH FLOW:

• The above image represents good mesh flow of the model,because
• No trias near to each other.
• no trias are on the edges.
• No rotating Quad.

• The model in Topo mode and Mesh mode in same view.

DRAW SHELL AS SOLID:

• After completing of the mesh make sure to tick draw shell as solid in Quality criteria.In which our model will look like as below.

• Here we can see that our model has assigned thickness with good mesh flow and midsurface is extracted correctly.

LEARNING OUTCOMES:

• Able to fix topological errors.
• Can do mid surface for the model having different thickness.
• Able to assign PID for each and every part.
• Able to do midsurface by both offset and middle method.
• Able to take thickness of sharing faces.
• Can fix Mesh parameters qith QC.

CONCLUSION:

From this model,we can know that assigning varing thickness of any model is same.The procedure should be followed is same for all 2d shell elements.If some elements fail for Quality criteria which are changing the geometry,we can accept that element.The majority of the model should accept Quality criteria.Keeping in mind the geometry should not change at any cost.

LINK OF THE PROJECT: https://drive.google.com/file/d/1JNVwGJjDreFfqHLmF9C__VnFs3xW55Dj/view?usp=sharing