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Support Forum, Can anyone help me better understand the definition of Compliance and why we would use it in our models either as a constraint or as an objective function? Should the value of the constraint be a 0 to 1 value or any larger number? Compliance I know is designated as Strain Energy...am I the one choosing the units for that value? Is it better used as a constraint or an objective? If I want to use it in a dual thermal/structural loading model, should I use compliance/temperature as the constraint/objective? I'm really just looking for more help on this. My supervisor is asking a lot of questions about it and I don't have many answers. Any help is greatly appreciated! Thanks. Dylan Stelzer
Hi, This should (hopefully) be a quick Q&A. I have a surface (2-D meshed shell elements) and would like to apply a force constraint to the nodes on the mesh of this surface. My only wish is that the vector of the force constraint be perpendicular to the surface (like constant compression or tension at all points of the surface). Does anyone have experience in this? I was told equations might be where to start but I'm not entirely sure how to utilize that as I'm fairly new into exploring anything other than constant loads. I've attached an image file for better reference of the surface. Thanks! Dylan Stelzer
editied: Hi, I deleted the original question because it was ill-posed. The question was: How does the Volume Constraint work and how the understanding of it can help to better interpret optimization results. Here is what I learned after a conversation with Mr Grasmannsdorf from Altair: Volume Constraint means you want OptiStruct to calculate for example the stiffest (minimum compliance) structure with a certain volume fraction (VF), for arguments sake let's say 25% of the original volume of your design space. The VF references a virtual volume for the calculations, not your actual structure's volume! This is a bit confusing at first, because the help defines the VF as total volume at current iteration divided by the initial design volume. However the "volume at current iteration" is a virtual volume!!! Similar to the Young's Modulus, the virtual volume is a function of the element density. V_virtual_i = V_element_i * density Therefore the virtual volume is the integral over the design domain of the density values. The volume constraint then is V_virtual <= VF * Initial Volume ---- What's the meaning of this? The integral can be satisfied by either many elements with small density values or a lesser amount of elements with higher density values. The density value of the elements is updated via the strain energy during the iterations. Due to the optimization's surge for a maximum stiffness, the optimization solution strives to higher density values hence trying to eliminate elements with lower density values. For the interpretation best-practice has show that all elements above a density value of circa 0,3 corresponds to the desired VF of the structure. The exact density threshold for the VF depends on the amount of intermediate densities in the solution a therefore varies a little. I hope the helped you to understand how the volume constraint worked and helps you to a better understanding of topology optimizations Regards Hauke