The activities involved in the design process can be classified largely as two types：synthesis and analysis．As illustrated in Fig. 10-1，the initial design activities（such as identification of the design need，formulation of design specifications，feasibility study with collecting relevant design information，and design conceptualization）are part of the synthesis subprocess．That is，the result of the synthesis subprocess is a conceptual design of the prospective product in the form of a sketch or a layout drawing that shows the relationships among the various product components[2]．The major financial commitments needed to realize the product idea are made and the functionality of the product is determined during this phase of the cycle．Most of the information generated and handled in the synthesis subprocess is qualitative and consequently is hard to capture in a computer system．
Once the conceptual design has been developed，the analysis subprocess begins with analysis and optimization of the design．An analysis model is derived first because the analysis subprocess is applied to the model rather than the design itself．Despite the rapid growth in the power and availability of computers in engineering，the abstraction of analysis model will still be with us for the foreseeable future．The analysis model is obtained by removing from the design unnecessary details，reducing dimensions，and recognizing and employing symmetry．Dimensional reduction，for example，implies that a thin sheet of material is represented by an equivalent surface with a thickness attribute or that a long slender region is represented by a line having cross-sectional properties．Bodies with symmetries in their geometry and loading are usually analyzed by considering a portion of the model．In fact，you have already practiced this abstraction process naturally when you analyzed a structure in an elementary mechanics class．
Once a design has been completed，after optimization or some tradeoff decisions，the design evaluation phase begins．Prototypes may be built for this purpose．The new technology called rapid prototyping is becoming popular for constructing prototypes．This technology enables the construction of a prototype by deposition layers from the bottom to the top．Thus it enables the construction of the prototype directly from its design because it requires basically the cross-sectional data of the product．If the design evaluation on the prototype indicates that the design is unsatisfactory，the process described is repeated with a new design．
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設計過程所涉及的活動大體上分為兩類綜合和分析。如圖10-1所示，原始設計活動，如設計需求的認定，設計規格說明的規劃，根據收集的相關設計信息進行可行性研究以及設計概念化等，都屬綜合子過程部分；即綜合子過程的結果是各個產品部件間的關系以草圖或布局圖的形式來表示的所期望產品的概念設計。用于實現該產品理念的主要財政承諾和產品功能都在產品周期的這一階段確定。在綜合子過程中產生和處理的大多數信息是定性的，因此在計算機系統中很難得到。
一旦概念設計形成，分析子過程就開始對設計進行分析和優化。首先要導出一個分析模型，因為分析子過程適用于該模型而非設計本身。盡管在工程上，計算機的能力和可用性迅速提高，但對分析模型的抽象依然會在可預見的未來仍有待人去完成。分析模型可從設計中去除不必要的細節，縮小尺寸和識別并使用對稱性。例如：尺寸縮小表示一張薄的材料由具有厚度屬性的等效曲面來代表，或一個細長區域由具有截面特性的線段來表示。在幾何和負荷上具有對稱性的物體通常用模型的某一部分進行分析。實際上，在初等機械課程上對一個結構進行分析時，早就實踐過這種自然的抽象過程。
一旦設計完成，在經過優化或一些權衡制定之后，就開始了設計評價階段。為此目的可進行原型制作。一種用于構建原型稱之為原型速成的新技術現已非常普及。這種技術可通過從底到頂層層地構建原型，由于它可以根據設計直接構建原型，因此它只需要產品的截面數據即可。如果在原型上的設計評價表明這種設計不盡人意，那么，就以新的設計重復進行上述過程。
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