Sarayut Nonsiri

Modelling, Evaluation and Simulation during the Early Design Stages: Toward the Development of an Approach Limiting the Need for Specific Knowledge

The early stages of the design process are keys in the development of products and services. Nevertheless, they are marked by multiple constraints imposed on them, such as, most notably, a limited amount of time available for modelling and evaluating ideas and concepts. The present article develops an approach for modelling, and simulating initial design solutions during these critical early stages. The final objective is to minimize the amount of prerequisite knowledge a designer should have on the artefact being designed in order to propose, develop, and evaluate early models. First, the current work analyses the conditions necessary to develop a modelling and comparison environment for early design solutions. This is done through mathematical considerations of the design process. In a second part, the work proposes a modelling and simulation approach and develops the machinery behind it. The approach integrates and maps a series of normalized semantic descriptions of functions, generic engineering components and variables, a set of elementary laws associated with these components, and a set of elementary base units. All these elements are used to refine and guide the modelling process. This process is uses the Vaschy-Buckingham theorem followed by an approximation of the generic law describing the general behaviour of elementary components. This combination leads to an approximated model of the behaviour of the studied artefact. The model is further developed by implementing the behaviour in a system dynamics tool using two basic bricks of the system dynamics language, converters and flows. In a final part, the approach is illustrated through the case study of a beam structure.

Model-based approach for change propagation analysis in requirements

The need for support related to the complexity management of systems engineering problems, specifically for requirements management and changes is especially necessary during the early stages of the systems engineering process. Indeed, these stages have a tremendous impact on the overall outcome of a project. If not anticipated at early stages, changes in requirements are leading to changes in the design and in the later implementation stages, resulting in an unexpected increase in costs (monetary, time, etc.). The framework proposed in this article for requirements change prediction consists of a three steps process. First, requirements are modeled using SysML with predefined relationships. Second, all the relationships between requirements in the SysML model are transformed into an adjacency matrix also named DSM. A higher order Dependency Structure Matrix is applied; this matrix-based methodology allows support in the prediction of which requirements will be affected after a change in a specific requirement. Third, the change propagation path is visualized. Using this framework, it is possible to predict the possible propagation of changes in requirements. In addition, it is also possible to identify the requirements that can be reused. This can help to save the time and cost for developing a new system.

Impact analysis of graph-based requirements models using PageRank algorithm

Managing requirements changes of complex systems and the potential impact of such changes represents a big issue for companies. Currently, commercial modelers propose tools for analyzing the direct impact of requirements changes on system design or code but the analysis of requirement change on other requirements remains seldom studied. This paper proposes an approach for the impact analysis of changes in requirements combined with a ranking of importance of requirements in graph based requirements network. Warshall algorithm is used in this paper for performing the impact analysis. Along with this approach, PageRank algorithm is used for ranking requirements according to their importance. Requirements hierarchy and their textual description of importance are considered as input for calculating their impact as well as their importance within the network of requirements. This combination of Warshall and PageRank algorithms provide significant results for helping designers in decision-making process of modifying requirements for future design versions.

Systematic Search for Design Contradictions in Systems’ Architecture: Toward a Computer Aided Analysis

Time pressure imposed to the engineering design process is one fundamental constraint pushing engineers to rush into known solutions, to avoid analysing properly the environment of a design problem, to avoid modelling design problems and to take decision based on isolated evidences. Early phases in particular have to be kept short despite the large impact of decisions taken at this stage. Significant efforts are currently spent within different engineering communities to develop a model-based design approach adapted to conceptual stages. Developing such type of models is also challenging due to the fuzziness of the information and due to the complexity of the concepts and processes manipulated at this stage. Currently few support tools are really capable of really supporting an analysis of the early design concepts and architectures. Simultaneously the approach should be fast, easy to use and should provide a real added-value to efficiently support the decision and the design process. The present article is presenting a framework based on a progressive transformation of the design concepts. The final material generated by this transformation process is an oriented graph with different types of classified variables. This graph can be processed as described in the article to automatically exhibit the conflicts or contradictions present in the design concept architecture. The article is proposing two main contributions which are a real move toward model development at conceptual stage and the possibility to process those models to detect solution weaknesses. The discussion is presenting further developments and possibilities associated with this method.

A Combined Design Structure Matrix (DSM) and Discrete Differential Evolution (DDE) Approach for Scheduling and Organizing System Development Tasks Modelled using SysML

During a system engineering process there are an important number of tasks that need to be organized, mapped together and recursively considered. The tasks that are mapped together are exchanging different flows of information and material. In this type of iterative processes, significant savings in term of development time can be made by providing a method that is optimizing the amount of feedbacks and iterations to the minimal level simply required for the successful development of the system. Task scheduling in a system engineering process can become extremely complex. Nevertheless it is a crucial step of the early stages of the systems engineering process for time-to-market, cost-efficiency and quality reasons. In this article, the authors are proposing to combine a computational approach (Discrete Differential Evolution) with Model Based Systems Engineering (MBSE) for minimizing iterations and reducing lead-time development. The present article is contributing to recent research works using Design Structure Matrixes (DSM) and computational methods for visualizing and analyzing systems engineering processes. The paper is proposing a framework integrating a model-based approach and a DSM based analysis of the process architecture to assist system engineers in organizing and scheduling tasks. As a result, this framework allows engineers to automatically populate DSMs generated from MBSE models developed in SysML. A specific stereotype is proposed to represent system development tasks in SysML. The sequencing of the engineering tasks is optimized with the application of a Discrete Differential Evolution algorithm (DDE) taking into account the different constraints. The practical use of the proposed framework is demonstrated on the case study of a mobile robot developed for the Eurobot competition. The article also discusses the possibility to use the current framework to analyze the impact of requirement changes on the scheduling of development tasks.

Graph Based Representation and Analyses for Conceptual Stages

What is the fundamental similarity between investing in stock of a company, because you like the products of this company, and selecting a design concept, because you have been impressed by the esthetic quality of the presentation made by the team developing the concept?Except that both decisions are based on a surface analysis of the situations, they both reflect a fundamental human’s cognitive feature. Human brain is profoundly trying to minimize the efforts required to solve a cognitive task and is using when possible an automatic mode relying on recognition, memory, and causality. This mode is even used in some occasion without the engineer being conscious of it. Such type of tendencies are naturally pushing engineers to rush into known solutions, to avoid analyzing the context of a design problem, to avoid modelling design problems and to take decision based on isolated evidences. Those behaviors are familiar to experience teachers and engineers. This tendency is magnified by the time pressure imposed to the engineering design process. Early phases in particular have to be kept short despite the large impact of decisions taken at this stage. Few support tools are capable of supporting a deep analysis of the early design conditions and problems regarding the fuzziness and complexity of the early stage. The present article is hypothesizing that the natural ability of humans to deal with cause-effects relations push toward the massive usage of causal graphs analysis during the design process and specifically during the early phases. A global framework based on graphs is presented in this paper to efficiently support the early stages. The approach used to generate graphs, to analyze them and to support creativity based on the analysis is forming the central contribution of this paper.Copyright

A Discrete Differential Evolution Algorithm for Product Development Scheduling

The scheduling of the design activities in product development process is a crucial step in early stages in order to achieve the project in time and cost-effective manner. In complex product development process, many dependency relationships or feedback loop could exist between design activities with multiple technical domains. Sequencing the design activities is a decision making process in order to reduce these feedback loops, and therefore, reduce amount of required information flows between activities. In recent years, methods for sequencing the design activities in design process have been proposed in order to reduce lead-time development and cost. The purpose of this research work is to present a methodology for design process sequencing in product development project by using Design Structure Matrix (DSM) for visualization a complex process and Discrete Differential Evolution (DDE) for sequencing the design tasks. The tests performed in this article have shown that this approach provides very competitive results in term of the quality of obtained solutions when compared to Genetic algorithms (GA). In additional it is a simple, effective and easy to use since the amount of control parameters to set is reduced.Copyright

An Early Modeling and Simulation Approach for Fast Evaluation of Early Design Concepts

Being able to quickly model and simulate very early design solutions in the design process is an important practical issue for engineering designers. Early design is characterized by the small amount of quantitative data available at the beginning of the development process. The task is becoming cumbersome for engineers when in addition they do not possess extensive knowledge of the domain of interest. In this context, traditional modeling and simulation methods are disqualified for supporting the early engineering design choices because they require too much details and precise quantitative information. The approach considered in this article to supply the deficiency of traditional modeling methods is combining three domains of physics and mathematics: qualitative physics, dimensional analysis and graph-based representation. The present article develops the general framework which is emerging from this combination. The authors develop the framework to the fast modeling and simulation of an air bearing. The structure of the article is the following, first the basis of the modeling and simulation method are briefly presented. In a second step the entire approach is developed on the case of an air bearing concept with the goal of making the presentation as pedagogical as possible. A causal ordering heuristic is used and combined with the topology of the concept to test. This is gradually leading to a causal graph which is transformed into a flow graph that can be simulated in system dynamics simulation tools. A new and easy approach to discover the laws governing the system dynamic model is also explained. Finally the model is simulated and analyzed.As a result, the method presented in this article offers several advantages: 1- it can be supported by a dedicated computer aided approach, 2- it brings simulation capabilities at very early design stage level where it is seldom present.© 2012 ASME