Georg Thimm

Paradigm shift: unified and associative feature-based concurrent and collaborative engineering

With widely used concurrent and collaborative engineering technologies, the validity and consistency of product information become important. In order to establish the state of the art, this paper reviews emerging concurrent and collaborative engineering approaches and emphasizes on the integration of different application systems across product life cycle management (PLM) stages. It is revealed that checking product information validity is difficult for the current computer-aided systems because engineering intent is at best partially represented in product models. It is also not easy to maintain the consistency among related product models because information associations are not established. The purpose of this review is to identify and analyze research issues with respect to information integration and sharing for future concurrent and collaborative engineering. A new paradigm of research from the angle of feature unification and association for product modeling and manufacturing is subsequently proposed.

Towards unified modelling of product life-cycles

This paper presents the potential of modelling a products life-cycle using the Unified Modelling Language (UML). The potential benefits and limitations are discussed. An example of a vacuum cleaner is cited in support of this approach. Model consistency across the various life cycle stages of the product is of major concern and an algorithm for constraint management is proposed and prospective research directions highlighted.

Systematic prediction of crystal structures

A generally applicable and systematic prediction of crystal structures and their properties has been an important goal of crystallography and materials science. Here we present such a general and systematic approach. This approach is based on a combination of graph theory with quantum mechanics. As an application, structures, properties and relative stabilities of small hypothetical carbon polymorphs with up to six atoms per unit cell are presented

Unified Feature Modeling Scheme for the Integration of CAD and CAx

AbstractIn concurrent engineering, it is difficult to organize product information in an interconnected and consistent way due to complicated interrelations and proprietary data formats. This paper proposes an information representation scheme which accentuates feature association and feature unification. Feature association establishes persistent relations among different features constituents while feature unification provides a generic format for different application features. A unified feature defines common attributes and methods of all the supported application features. Feature relations are identified in application, feature and feature constituent levels for controlling the consistency among different application feature models.

Change propagation algorithm in a unified feature modeling scheme

Product lifecycle stages are inter-related and mutually constraining. Due to the sequential nature of the product development processes, some constraints or conflicts may emerge in a later stage and require modifications to the decisions made in earlier stages. The iterations between stages are hence unavoidable and must be managed carefully to maintain the consistency, integrity and validity of product information models. Due to the inter- or intra-stage relations, a chain of changes is very likely to occur as the consequence of an initial change. Modeling and maintaining these relations are important in collaborative engineering to evolve the state of the whole product model in a consistent manner. This paper introduces a new method of modeling associative engineering relations in a unified feature modeling scheme and elaborates a change propagation algorithm for the information consistency control among multiple applications of product lifecycle stages. The algorithm is established on a JTMS-based dependency network. Two case studies are used to illustrate the proposed dependency network and change propagation algorithm.

Associations in a Unified Feature Modeling Scheme

Features allow one to associate human knowledge and product geometry. The authors proposed, in earlier publications, a unified feature modeling scheme with the aim to maintain the integrity and consistency of a product model. Different application feature models within and across different product life-cycle stages are integrated, and especially, nongeometric relations (besides geometric ones) are handled. In this paper, as an improvement to the previous work, two types of associations are introduced: sharing and dependency. In the context of conceptual and detail design stages, these associations are described and the implementation is discussed in detail.

Agent-based composable simulation for virtual prototyping of fluid power system

This paper proposes an agent-based composable simulation framework to address the challenges of integration, composability, distributed coordination, and interaction for the development of a virtual prototype of fluid power system. The approach proposed represents each virtual hydraulic component by a domain agent (DA). The agents are then gathered into a multi-agent system, which models the hydraulic system as a whole. The virtual prototyping evaluation depends on the communication and collaboration of multiple agents. A case study shows that agent-based composable simulation can predict the overall system performance. A prototype implementation of the proposed system is presented in this paper.

Knowledge-Based Reasoning in a Unified Feature Modeling Scheme

Feature-based modeling is an accepted approach to include high-level geometric information in product models as well as to facilitate a parameterized and constraint-based product development process. Moreover, features are suitable as an intermediate layer between a product’s knowledge model and its geometry model for effective and efficient information management. To achieve this, traditional feature technology must be extended to align with the approach of knowledge-based reasoning. In this paper, based on a previously proposed unified feature modeling scheme, feature definitions are extended to support knowledge-based reasoning. In addition, a communication mechanism between the knowledge-based system and the feature model is established. The methods to embed and use knowledge for information consistency control are described.

Prediction of a nanoporous sp2-carbon framework structure by combining graph theory with quantum mechanics

Abstract A nanoporous carbon framework structure is predicted by combining graph theoretical approaches and density functional calculations. Bond lengths in this polymorph, with all atoms sp 2 -hybridised, are in good agreement with typical C–C and CC bond lengths, bond angles are close to 120°, and it is 0.36 eV/atom less stable than diamond. The electronic structure suggests it is a quasi-one-dimensional metal with anisotropic electronic properties and a spectroscopic signature. The compound has a high bulk modulus of 234(1) GPa but a density similar to that of graphite and amorphous carbon. Changes in the lattice parameters on compression are strongly anisotropic.

Optimal process plans for manufacturing and tolerance charting

Abstract A graph theoretical approach is presented that permits the calculation of optimal process plans from datum hierarchy trees, which are elegant representations of tolerance charts. The theory is developed for a cost function that minimizes machine and datum changes. Restrictions on the sequence of machining operations arising from technical constraints or the layout of a group cell are taken into account. The process plans are optimal with respect to a specified datum hierarchy tree, manufacturing constraints and cost function. It is shown that the number of possible plans for real industrial trees is very large, and therefore this kind of optimization is beyond the ability of a human process planner. Trial runs with industrial parts indicate that optimization can be performed by a computer within a time period that is acceptable for industrial use.