The integration of optimization techniques with Finite Element Analysis(FEA) and CAD is having pronounced effects on the product design process.This integration has the power to reduce design costs by shifting the burden from the engineer to the computer.Furthermore,the mathematical rigor of a properly implemented optimization tool can add confidence to the design process.Generally,an optimization method controls a series of applications,including CAD software as well as FEA automatic solid meshers and analysis processors.This combination allows for shape optimizations on CAD parts or assemblies under a wide range of physical scenarios including mechanical and thermal effects.
Modern optimization methods perform shape optimizations on components generated within a choice of CAD packages.Ideally,there is seamless data exchange via direct memory transfer between the CAD and FEA applications without the need for file translation.Furthermore,if associativity between the CAD and FEA software exists,any changes made in the CAD geometry are immediately reflected in the FEA model.In the approach taken by ALGOR,the design optimization process begins before the FEA model is generated.The user simply selects which dimension in the CAD model needs to be optimized and the design criterion,which may include maximum stresses,temperatures or frequencies.The analysis process appropriate for the design criterion,and,if necessary without any humen intervention,the CAD geometry is updated.Care is taken such that the FEA model is also updated using the principle of associativity,which implies that constraints and loads are preserved from the prior analysis.The new FEA model,including a new high-quality solid mesh,is now analyzed,and the results are again compared with the design criterion.This process is repeated until the design criterion is satisfied.Fig.7.1 shows the procedure of shape optimization.
如今，綜合運用機械設(shè)計方法、有限元分析方法和計算機輔助設(shè)計技術(shù)進(jìn)行產(chǎn)品設(shè)計過程產(chǎn)生了深遠(yuǎn)的影響。這種綜合運用的手段將工程師身上的設(shè)計重?fù)?dān)交由計算機完成，因而降低了產(chǎn)品的設(shè)計成本。此外，正確運用優(yōu)化設(shè)計中嚴(yán)謹(jǐn)?shù)臄?shù)學(xué)推理也可以提高產(chǎn)品的設(shè)計的可靠性。優(yōu)化方法決定了產(chǎn)品設(shè)計過程中的精度問題，包括CAD軟件建模的準(zhǔn)確度，有限元分析中網(wǎng)格劃分的正確度以及分析處理器的計算精度等，這種方法能夠在考慮機械，熱等許多實際情況的影響下，對CAD系統(tǒng)構(gòu)建的零部件、裝配體的結(jié)構(gòu)進(jìn)行優(yōu)化。
現(xiàn)代優(yōu)化設(shè)計技術(shù)能夠?qū)AD軟件構(gòu)建的零件結(jié)構(gòu)進(jìn)行優(yōu)化。從優(yōu)化設(shè)計理論的角度上說，CAD格式的文件和FEA格式的文件之間不需要任何的格式轉(zhuǎn)換，就可以實現(xiàn)數(shù)據(jù)的無縫交換。這時這兩個文件之間存在關(guān)聯(lián)性，對CAD文件所做的任何修改在相應(yīng)的FEA文件中都能反映出來。例如，在使用有限元分析軟件ALGOR對某零部件或裝配體計算時，根本不需要建立其有限元模型就可以進(jìn)行優(yōu)化設(shè)計。用戶只要挑選出零部件或裝配體CAD模型中需要優(yōu)化的幾何尺寸，確定相應(yīng)的設(shè)計準(zhǔn)則（如最大應(yīng)力、最高溫度和最大頻率），然后運行相應(yīng)的分析計算過程，該軟件通過計算、比較，就可以完成CAD模型的結(jié)構(gòu)優(yōu)化，并且整個過程通常不需要使用者參與。需要注意的是，CAD與FEA格式文件之間的關(guān)聯(lián)性使得FEA模型更新了，但約束和施加的載荷保持不變，因此需要對更新過后的有限元模型進(jìn)行計算，對整個過程不斷重復(fù)迭代，直到最終的計算結(jié)果滿足設(shè)計要求為止。圖7.1所示的是零部件形狀優(yōu)化流程圖。