[19] developed a systematic representation of the work transforma

[19] developed a systematic representation of the work transformation matrix method, with a discrete state-space description kinase inhibitors of signaling pathways of the development

process. With this representation, the dynamics of the development process can be easily investigated and predicted, using well-established discrete system analysis and control synthesis techniques. In addition, Ong et al. [20] developed nonhomogenous and homogenous state-space concepts, where the nonhomogenous one monitored and controlled the stability and the convergence rate of development tasks and at the same time predicted the number of development iterations; the homogenous one did not consider external disturbances and its response was only due to initial conditions. Xiao et al. [21] put forward a model for solving coupled task sets based on resource leveling strategy.

However, it is hypothesized that once resources allocated to coupled task sets are ascertained, then, in all iterations’ process, they no longer change. It does not exactly accord with the real product development process. So, the authors [22] further proposed an approach to analyze development iteration based on feedback control theory in a dynamic environment. Firstly, the uncertain factors, such as task durations, output branches of tasks, and resource allocations, existing in product development were discussed. Secondly, a satisfaction degree-based feedback control approach is put forward. This approach includes two scenarios: identifying of a satisfaction degree and monitoring and controlling of iteration process. In the end, an example of a

crane development was provided to illustrate the analysis and disposing process. Different from the above research, we propose a method to solve coupled task sets combined with tearing approach and inner iteration technology in this paper. Its obvious advantages lie in identifying invalid iteration process and further analyzing its effects on time and cost of the whole product development process. 3. Modeling Design Iteration Based on Tearing Approach and Inner Iteration Technology 3.1. The Limitations of Classic WTM Model for Identifying Design Iteration In the classic WTM model, the entries either in every row or in every column of WTM sum to less than one so as to assure that doing one unit of work in some task during an iteration will create less than one unit of work for that task at a future stage. Cilengitide Such design and development process will converge. However, in real-world product design and development process, some unexpected situations may occur. For example, there is no technically feasible solution to the given specifications or the designers are not willing to compromise to reach a solution, which represents that the corresponding design process will not converge and the entries either in every row or in every column of WTM sum to more than one. Figure 1 denotes this situation. As can be seen from it the entries in the first column sum to 1.1(i.e., 0.4 + 0.

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