CAE-Companion-2018-2019

Engineering WISSEN CAE

forces, reaction moments, internal forces, stress „ „ natural frequencies „ „ results from frequency response analysis (amplitudes, phases, velocities and accelerations), acoustic measures (surface velocities, sound pressure) „ „ thermal values (temperature, internal or reaction heat flux) „ „ and any combination of those For the optimization process a large variety of standard manufacturing methods can be chosen from a library. These include techniques like casting, stamping, drilling, turning, etc. After topology optimization, an automatic validation of the resulting design proposal – eventually with subse- quent shape optimization – or a direct transfer into CAD Systems can be performed. The use of topology optimization in the early stage of the development process reduces the number of development cycles and helps to cut costs. Shape Optimization Shape optimization allows for specific detail improvements of existing designs. In general often small, but significant changes in the shape (i.e. outer contour) of the component lead to major reduc- tions of local hotspots like stresses, damage, strains and contact pressures. Shape modifications can be performed by: „ „ changing geometric parameters like radii and dimensions „ „ morphing (simple transformations like zooming, linear distortion or translation) of specified areas „ „ modification by means of shape basis vectors (combined changes of several coupled surface handles, similar to previous) „ „ non parametric shape modifications by moving all surface nodes of a specified area independently

modifications provided by a finite set of parameters do not offer enough degrees of freedom. For significant improve- ments the full shape flexibility of non parametric methods is required. The non-parametric shape modifications (offered by software like, e.g. SIMULIA Tosca Structure.shape) are performed automatically in interaction with the FEM simulation where each surface node can be displaced independently. Objective and constraint values for non parametric shape optimization can be chosen amongst others from: „ „ volume, mass, center of gravity, moments of inertia

„ „ stress, strain, including plastic strain „ „ compliance, displacements, rotations „ „ natural frequencies „ „ fatigue values

Generally in only 5-10 iterations significant improvements can be achieved. The changes can be very sensitive to the simulation result, i.e. slightly different values can gener- ate very different contours.

Figure 4: Shape optimization of an exhaust manifold – reduction of plastic strains under consideration of thermomechanical loads (images courtesy FEV GmbH) Thus to ensure high quality results and use the full optimi- zation potential the FE-solver must provide reliable, realistic results as input for the optimization: „ „ Mesh smoothing distributes shape changes at the surface to the inner elements to achievehomogenousmeshquality. „ „ The use of realistic models including contact, non-linear (eventually user) materials and geometric non linearities guarantee that the optimization task is performed based on the real and no surrogate component. „ „ Approved high quality analysis software (even user codes) and direct coupling with fatigue simulation provide verified results. Finally, a large variety of geometric andmanufacturing restrictions has to be applied during the optimization to keep important properties for the already detailed design.

Figure 3: Methods for shape optimization based on parameters, morphing and non-parametric approaches Parameter variation often does not provide effective solutions for the removal of stress hotspots as the shape

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