The Javelin Technologies Blog

So you have just received a file from your customer in the IGES format and when you open it up, you notice that its size has been scaled up by around 25. The issue is that you were expecting the units to be in mm but the file is stored in inches. One way would be to simply scale the entire model by a factor of 1/25.4 but what if this is an IGES assembly and has multiple parts. I am sure you will find some way to scale everything and put the things back together again.

Here is a simple technique that you can use to correct the units stored within the IGES document. IGES documents are stored as simple ASCII documents so you will need a text editor (I use notepad++ rather notepad because it can handle very large file sizes).

When you open the iges file, the first few lines are the iges header and contain the metadata including the units. Look for the following unit indicator, possibly in the 3^rd or 4^th line of the document: 2HIN, 4HINCH, 2HMM, 2HFT, 2HMI, 1HM, 2HKM, 3HMIL, 2HUM, 2HCM, 3HUIN. Once you locate this, the entry just before this entry, will be another unit indicator which is an integer between 1 to 11. Both these indicators have to be consistent so if you change one, you have to change the other one as well. Here is a table of units for the iges header.

Once you have edited the two unit indicators in the iges file, you can save the document. Open it in SolidWorks and you will see that the size has been scaled to the units you want.

Example, an IGES file originally marked as inches

,,22HI-DEAS Master Series 7,33H/scratch/dobobd/iges/Example2.igs,,31HI-DG      1
EAS Master Series 7:      IGES,32,38,6,308,1,2HIN,1.0D0,2,2HMM,1,0.0D0, G      2
13H990208.103851,.01D0,100.0D0,12HYourNameHere,15HYourCompanyHere,11,0, G      3
13H990208.103851,;                                                      G      4

The units changed in the header to be mm

,,22HI-DEAS Master Series 7,33H/scratch/dobobd/iges/Example2.igs,,31HI-DG      1
EAS Master Series 7:      IGES,32,38,6,308,2,2HMM,1.0D0,2,2HMM,1,0.0D0, G      2
13H990208.103851,.01D0,100.0D0,12HYourNameHere,15HYourCompanyHere,11,0, G      3
13H990208.103851,;                                                      G      4

SolidWorks 2013 adds a new post-processing capability which allows the user to view the results on selected entities. These entities could be either bodies or faces.

To view the plot on a selected entities, open the plot PropertyManager and, under Advanced Options, select Show Plot on selected entities. You can select faces or bodies to view results on.

Watch the video below to see how to use this new feature:

Perhaps the best enhancement for simulation studies added in SolidWorks Simulation 2013 is the submodeling capability. For studies with a large number of bodies, this feature allows the users to improve results at critical areas without having to rerun the analysis in the entire model. It can allow mesh refinement for a selected portion of the model and rerun analysis only in the selected region. This feature can act as a huge time saver.

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You can display the mesh and results of shells using a 3D representation of shell bodies. There is a new option to display the thickness of shells in result plots (stress, displacement, and strain) and when viewing the mesh.

To view the results on a 3D representation of shell bodies, in a Stress Plot, Displacement Plot, or Strain Plot Property Manager, under Advanced Options, select Render shell thickness in 3D (slower).

The shell thickness displayed in the plots is the value defined in the Shell Definition Property Manager. The orientation of thickness is displayed with relation to the midsurface of the shell, as defined by the offset value (Shell Definition Property Manager).

For stress plots, results for the top and bottom shell faces are shown. Results are linearly interpolated across the shell thickness. When probing stress plots, both the top and bottom shell values are displayed.

Imagine a manhole cover in a pressure vessel that needs to be bolted to a flange in the pressure vessel. This usually requires a number of bolts to hold the two pieces together. Furthermore, same type of bolts may be present in the assembly at various locations. Imagine having to define all these bolt connectors for a simulation. I am sure this is going to give nightmares to people trying to simulate multiple bolts using SolidWorks Simulation.

You will be happy to learn that SolidWorks Simulation has a smart feature which could reduce the effort in the definition of these bolt connectors.

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For large problems, solid elements can often take a long time to mesh and solve. For thin bodies with constant thickness, we can replace the solid elements with shell elements which will significantly speed up the process of both meshing and solution.

For bodies which are geometrically symmetric and are loaded symmetrically about a plane, the symmetry condition can also be used to speed up the analysis. The built-in symmetry condition of SolidWorks can only be applied on faces, however when shell elements are cut on a plane, the produce symmetry about edges and not faces. The symmetry condition can then be created manually using the reference geometry condition. In applying this condition, we need to restrict any displacements along the plane of symmetry and at the same time we need to restrict the out of plane rotations. (Shell elements have 6 dof compared to solids which have only 3 dof).

The table below highlights the symmetry condition in the three principle planes.

When performing design studies in SolidWorks, you can typically link the dimensions within the model to design study parameters and then vary those dimensions to undertake design studies or design optimizations.

If you use shell elements in an analysis then the thickness of the shell is defined within the simulation setup and is not part of the model itself. To perform a design study on the thickness of the shell, the thickness needs to be linked to a simulation parameter. To define this parameter, the Link Value option within the shell definition property manager can be used. Once the link value option is selected, a Parameters dialog box pops up. This can then be used to define a “Simulation Parameter” and linking this parameter to the thickness definition of the shell. Once the parameter is appropriately linked, it appears in the parameters list in the design study variable view window.

SolidWorks simulation provides two options to solve the set of FEA algebraic equations; iterative or direct solution methods.

The iterative solver, FFEPlus, uses approximate techniques to solve the problem. It assumes a solution and then calculates the associated errors. The iterations continue until the errors become acceptable.

The direct solver, Direct Sparse, solves the set of equations directly without any approximations and hence there are no errors associated with the solution process. There will still be discretization errors which are present both in iterative or direct solvers.

A solver may be selected changing the study properties from the study feature tree. Read More »

I see a number of people trying to create simple simulation studies and then comparing the results to hand calculations of well known problems. Although this is a good practice to gain confidence in the results obtained by SolidWorks, at times it is tedious and time consuming process. SolidWorks already contains an extensive library of simulation validation problems. It contains both verification problems and NAFEMS Benchmarks. The verification problems compare results of SolidWorks Simulation studies to known analytical solutions while the NAFEMS benchmark problems demonstrate the accuracy of SolidWorks Simulation software by comparing results to other software.

The Validation Library can be found under the SolidWorks Simulation help menu.

My SolidWorks Simulation 2013 pick of the day is the new functionality for obtaining beam joint reactions. Now it is possible to list reaction forces and reaction moments at beam joints that have fixed translations or rotations.

After the simulation is completed, right click on Results and choose the List Result Forces. Now you can pick the joints you want to view the reaction forces on. The reaction forces and moments will be displayed in call outs on the screen with a graphical representation on the joint.

Watch the video below to see this feature in action.