What Type of Elements Should I Use for Fast and Accurate Results?
The core of Finite Element Analysis (FEA) is breaking down your parts into individual pieces (or finite elements) to be able to solve your analysis. Using the correct type of elements and applying mesh properly is very important to the results of the simulation. This article will cover the type of elements to use while other articles like this meshing guide covers the element meshing process.
The three main element types are Shells, Beams, and Solids. As a rule of thumb, parts that are thin with a single thickness should be set up as Shell Elements, parts that are long and slender with a single profile should be set up as Beam Elements, and all other parts should be setup as Solid Elements. The main goal is to apply the right kind of element to get accurate results without waiting a long time for the problem to solve. Following this procedure will allow you to reduce long solve times while still getting accurate results.
Beam Elements
Beam Elements are the simplest type of elements and therefore, if applied correctly, can save the most solve time while still getting accurate results. Beam Elements can be used when the part is long and slender with a constant cross section. This is often the case for structural applications. The criteria to consider a beam long and slender is the ratio of the length of the beam and the largest dimension of its cross section should be greater than 10. For example, in the images below both beams meet the criteria of having a constant cross section but the slenderness ratio for one would be 120/5 = 24 and therefore pass the greater than 10 criteria while the other beam would have a slenderness ratio of 20/5 = 4 and not pass this criteria.
If the parts were created using SOLIDWORKS Weldments, then when you make a new study the parts will automatically come into the analysis as Beam Elements. To change a Solid Element to a Beam Element or a Beam Element to a Solid Element you can right click the part in the Simulation Feature Tree and select the applicable option “Treat as Beam…” or “Treat as Solid” option.
Shell Elements
Shell elements are the next simplest type of elements and can be used on thin parts with a constant thickness. This criteria is often true for sheet metal parts but can also apply in many other circumstances. The criteria to determine if a part is thin enough to be considered a shell element is similar to the Beam elements mentioned in the previous section. Take the characteristic length of the part and divide it by the thickness of the part. If this ratio is greater than 20 then it can be characterized as a thin shell part, if the ratio is between 5 and 20, it can be characterized as a thick shell part, if it is below 5 then you should treat the body as a solid element.
To demonstrate the time savings that shell elements can provide, below are pictures of the same pulley meshed with shell elements and again meshed with Solid elements. To get accurate bending stresses on thin parts using solid elements, it is generally recommended to have the mesh small enough to have at least 2 high solid quality elements through the thickness of the part. In this case, the number of needed elements goes from about 15,000 elements with using Shell Elements to about 2 million elements with using Solid Elements! The number of elements directly corresponds to the amount of time that it will take to solve the study.
To apply shell elements to parts, the easiest method is to create the parts using sheet metal functionality in the SOLIDWORKS CAD modeling environment and then SOLIDWORKS Simulation will automate the process of defining the Shell Elements in the simulation study. However, Solid Elements can be changed to Shell Elements by right clicking the body in the Simulation Feature Manager Tree and selecting “Define Shell by Selected Faces” and filling out the property manager to define the shell element.
Solid Elements
Solid Elements are the most common type of element but are also the most resource intensive elements to use for parts with a high aspect-ratio shape. If your parts don’t meet the criteria for beam or shell elements, you should use solid elements. Most bodies will come into your simulation studies as Solid Elements, but you can change a Beam or Shell Element back to Solid Element by right-clicking the body and selecting “Treat as Solid”. Solid elements can represent practically any geometry and do not carry the inherent geometry simplifications used by beam or shell elements. Solid elements will always give you the most accurate geometric representation and stress results, but for large and complex models it may not be possible to solve with solid elements at a sufficient resolution.
Conclusion
Solid Elements are the most common type of element but are also the most resource intensive elements to use for parts with a high aspect-ratio shape. If your parts don’t meet the criteria for beam or shell elements, you should use solid elements. Most bodies will come into your simulation studies as Solid Elements, but you can change a Beam or Shell Element back to Solid Element by right-clicking the body and selecting “Treat as Solid”. Solid elements can represent practically any geometry and do not carry the inherent geometry simplifications used by beam or shell elements. Solid elements will always give you the most accurate geometric representation and stress results, but for large and complex models it may not be possible to solve with solid elements at a sufficient resolution.