A Formal Approach to Handling Conflicts in Multiattribute Group Decision Making

The Hypothetical Equivalents and Inequivalents Method (HEIM) has been developed to support decision making in multiattribute problems where one decision maker is making the decision. In this paper HEIM is modified to support group decision making in multiattribute problems, resulting in the Group Hypothetical Equivalents and Inequivalents Method (G-HEIM). Instead of aggregating attribute weights or overall alternative values from each individual as is common in other group decision methods, G-HEIM operates by aggregating individual preferences. It is recognized that in group decision making, common preferences among group members can rarely be guaranteed, unless individual freedom is greatly limited. G-HEIM instead allows individuals to freely express preferences over a number of hypothetical alternatives and then explores the level of conflict or differences from the aggregated group preferences. The relationship between the level of conflicting preferences and the usability of the resulting decision is also directly studied using the G-HEIM. An automotive selection example is used to illustrate the approach.

An Efficient Weighting Update Method to Achieve Acceptable Consistency Deviation in Analytical Target Cascading

Weighting coefficients are used in Analytical Target Cascading (ATC) at each element of the hierarchy to express the relative importance of matching targets passed from the parent element and maintaining consistency of linking variables and consistency with designs achieved by subsystem child elements. Proper selection of weight values is crucial when the top level targets are unattainable, for example when “stretch” targets are used. In this case, strict design consistency cannot be achieved with finite weights; however, it is possible to achieve arbitrarily small inconsistencies. This article presents an iterative method for finding weighting coefficients that achieve solutions within user-specified inconsistency tolerances and demonstrates its effectiveness with several examples. The method also led to reduced computational time in the demonstration examples.

Trim Loop Closure for Enhanced CAD Interoperability

The transfer of design data among different CAD systems or subsequent downstream analysis applications is critically important to the acceleration of the product development cycle. Since each vendor has its own proprietary native file format, this transfer of data among differing systems is difficult at best. International standards such as IGES and STEP have evolved to address this challenge, but they are generally not sufficiently explicit. Each vendor writes its own “flavor” of the standard that other applications may not understand. This paper bridges a gap between disparate systems by developing a strategy to assess the completeness and robustness of models represented in IGES or STEP format, and a technique to either repair the representation or add missing information so that a downstream application can properly interpret it. The method ensures that the receiving system gets a full and accurate NURBS-based representation: the original surface, the corresponding full complement of model space trim curves, and the corresponding full complement of parameter space trim curves. With all the information present, the downstream system is more likely to receive the information it requires to interpret the model.

Design for Project Change Management: Part 2 — Attribute Design

This research introduces a new systematic approach to identify the optimal design configuration and attributes to minimize the potential construction project changes. The second part of this paper focuses on the attribute design aspect. In this research, the potential changes of design attribute values are modeled by probability distribution functions. Attribute values of the design whose construction tasks are least sensitive to the changes of these attribute values are identified based upon Taguchi Method. In addition, estimation of the potential project change cost due to the potential design attribute value changes is also discussed. Case studies in pipeline engineering design and construction have been conducted to show the effectiveness of the introduced approach.

DRed and Design Folders: A Way of Capturing, Storing and Passing On Knowledge Generated During Design Projects

This paper describes a software tool called DRed (the Design Rationale editor), that allows engineering designers to record their design rationale (DR) at the time of its generation and deliberation. DRed is one of many proposed derivatives of the venerable IBIS concept, but by contrast with other tools of this type, practicing designers appear surprisingly willing to use it. DRed allows the issues addressed, options considered, and associated arguments for and against, to be captured graphically. The software, despite still being essentially a research prototype, is already in use on high profile design projects in an international aerospace company, including the presentation of results of design work to external customers. The paper compares DRed with other IBIS-derived software tools, to explain how it addresses problems that seem to have made them unsuitable for routine use by designers. In addition to the capture and presentation of the DR itself, the set of linked DR graphs can be used to provide a map of the contents of an electronic Design Folder, containing all the documents created by an individual or team during a design project. The structure of the knowledge model instantiated in such a Design Folder is described. By reprising a design case study published at the DTM 2003 conference, concerning the design of a Mobile Arm Support (MAS), the DRed knowledge model is compared with the previously proposed Design Data Model (DDM), to show how it addresses the shortcomings identified in the DDM. Finally the methodology and results of the preliminary evaluation of the use of DRed by aerospace designers are presented.

The Role of Constraints and Human Interaction in Evolving MEMS Designs: Microresonator Case Study

In this paper we review the current state of automated MEMS synthesis with a focus on generative methods. We use the design of a MEMS resonator as a case study and explore the role that geometric constraints and human interaction play in a computer-aided MEMS design system based on genetic algorithms.

Fully Free-Form Deformation Features (δ-F4) Incorporating Discontinuities

To limit low-level manipulations of free-form surfaces, the concept of Fully Free Form Deformation Features (δ-F4) have been introduced. They correspond to shapes obtained by deformation of a surface area according to specified geometric constraints. In our work, we mainly focused on those features aimed at enforcing the visual effect of the so-called character lines, extensively used by designers to specify the shape of an object. Therefore, in the proposed approach, 3D lines are used to drive surface deformation over specified areas. Depending on the wished shape and reflection light effects, the insertion of character lines may generate surface tangency discontinuities. In CAD systems, such kind of discontinuities is generally created by a decomposition of the initial surface into several patches. This process can be tedious and very complex, depending on the shape of the deformation area and the desired surface continuity. Here, a method is proposed to create discontinuities on a surface, using the trimming properties of surfaces. The corresponding deformation features produce the resulting surface in a single modification step and handle simultaneously more constraints than current CAD systems. The principle of the proposed approach is based on arbitrary shaped discontinuities in the parameter domain of the surface to allow the surface exhibiting geometric discontinuities at user-prescribed points or along lines. The proposed approach is illustrated with examples obtained using our prototype software.

Integrating Freeform and Feature-Based Fitting Methods

Reverse engineering (RE) is the process of defining and instantiating a model based on the measurements taken from an exemplar object. Traditional RE is costly, requiring extensive time from a domain expert using calipers and/or coordinate measurement machines to create new design drawings/CAD models. Increasingly RE is becoming more automated via the use of mechanized sensing devices and general purpose surface fitting software. This work demonstrates the ability to reverse-engineer parts by combining feature-based techniques with freeform surface fitting to produce more accurate and appropriate CAD models than previously possible.

Optimization of Chemical Etching Process in Niobium Cavities

Superconducting niobium cavities are important components of linear accelerators. Buffered chemical polishing (bcp) on the inner surface of the cavity is a standard procedure to improve its performance. The quality of bcp, however, has not been optimized well in terms of the uniformity of surface smoothness. A finite element computational fluid dynamics (cfd) model was developed to simulate the chemical etching process inside the cavity. The analysis confirmed the observation of other researchers that the sections closer to the axis of the cavity received more etching than other regions. A baffle was used by lanl personnel to direct the flow of the etching fluid toward the walls of the cavity. A new baffle design was tined using optimization techniques. The redesigned baffle significantly improves the performance of the etching process. To verify these results an experimental setup for flow visualization was created. The setup consists of a high speed, high resolution ccd camera. The camera is positioned by a computer-controlled traversing mechanism. A dye injecting arrangement is used for tracking the fluid path. Experimental results are in general agreement with computational findings.

Assessing Product Architecture Costing: Product Life Cycles, Allocation Rules, and Cost Models

Product families and product platforms have been suggested as design strategies to serve heterogeneous markets via mass customization. Numerous, individual cost advantages of these strategies have been identified for various life cycle processes such as product design, manufacturing, or inventory. However, these advantages do not always occur simultaneously, and sometimes even counteract each other. To develop a better understanding of these phenomena, this paper investigates the cost implications of the underlying design decision: the product architecture choice. The investigation includes factors such as product life cycle phases, allocation rules, and cost models, all of which impact the cost analysis results. Based on this investigation, directions for future research on product architecture costing are provided.