Bojan Dolšak

Finite element mesh design expert system

The paper presents a consultative rule-based expert system for finite element mesh design. The aim of the expert system presented is to propose the appropriate type of the finite elements and determine the resolution values for the finite element mesh to be used for the analysis. The extensive knowledge base, comprising about 1900 rules, was built mainly by the use of machine learning (ML) techniques. Several examples will confirm that an expert system shell written in Prolog enables efficient use of the knowledge base and adequate communication between the system and the user. The system has the ability to explain the inference process. Thus, it can also be used as a teaching tool for inexperienced users—students. The results of the experimental use of the system are encouraging and can be used as guidelines for further developments and improvements of the system.

Comparison of subjective comfort ratings between anatomically shaped and cylindrical handles

Most authors have provided diameter recommendations for cylindrical handle design in order to increase performance, avoid discomfort, and reduce the risk of cumulative trauma disorders. None of the studies has investigated the importance of determining the correct handle shape on the subjective comfort ratings, which could further improve the handles ergonomics. Therefore, new methods based on a virtual hand model in its optimal power grasp posture have been developed in order to obtain customised handles with best fits for targeted subjects. Cylindrical and anatomically shaped handles were evaluated covering ten subjects by means of an extensive subjective comfort questionnaire. The results suggest large impact of the handle shape on the perceived subjective comfort ratings. Anatomically shaped handles were rated as being considerably more comfortable than cylindrical handles for almost all the subjective comfort predictors. They showed that handle shapes based on optimal power grasp postures can improve subjective comfort ratings, thus maximising performance. Future research should consider real conditions, since the comfort ratings can vary based on the specific task and by the tool selected for the task.

Intelligent decision support for structural design analysis

Abstract Many comprehensive composite computer-aided design systems with special analysis tools have been developed in order to make the product development process more effective. However, these computer-aided tools still concentrate mainly on the numerical aspects of analysis whilst, in most of cases, they fail to provide any kind of expert advice during the decision-making process. It is obvious that the existing computer tools in this field need to be extended in order to reach a higher level of performance by adding some intelligent behaviour. This paper discusses a framework for intelligent decision support for structural design analysis using a finite element method. The intelligent environment presented is composed of several knowledge-based modules in order to address some major bottlenecks within the analysis-based design improvement process. The prototypes of four intelligent modules are presented within this context. These are: an intelligent module for supporting some initial decisions within the design analysis process, an intelligent module for finite elements’ selection, an intelligent module for finite element mesh design, and an intelligent module for supporting the results’ interpretation process. According to the feedbacks of those experts who participated in the evaluation process, these prototypes could be applied as useful supporting tools for inexperienced designers in design practice, as shown in certain examples presented in this paper.

Intelligent FEA-based design improvement

Structural analysis using the finite element method is an integrate part of the design process for many components. Finite element analysis is the most extensively used numerical analysis in mechanical engineering practice and is incorporated into many computer-aided design systems. The existing commercial software is very helpful when supporting realisation of the analysis process but still fails to provide adequate support during the post-processing phase. The results of analysis should be studied and decisions made regarding the designs suitability with respect to its engineering specifications. In general, design changes are indispensable and designers need help to design them properly. The prototype of an intelligent rule-based consultative system is being developed by the authors to provide such advice when considering a description of the design structures critical area. This system is encoded in Prolog. It can deal with the results of prior strain-stress or thermal analysis. It presents a short list of proposed design changes that should be taken into account when improving the design.

Recommendations for tool-handle material choice based on finite element analysis

Huge areas of work are still done manually and require the usages of different powered and non-powered hand tools. In order to increase the user performance, satisfaction, and lower the risk of acute and cumulative trauma disorders, several researchers have investigated the sizes and shapes of tool-handles. However, only a few authors have investigated tool-handles materials for further optimising them. Therefore, as presented in this paper, we have utilised a finite-element method for simulating human fingertip whilst grasping tool-handles. We modelled and simulated steel and ethylene propylene diene monomer (EPDM) rubber as homogeneous tool-handle materials and two composites consisting of EPDM rubber and EPDM foam, and also EPDM rubber and PU foam. The simulated finger force was set to obtain characteristic contact pressures of 20xa0kPa, 40xa0kPa, 80xa0kPa, and 100xa0kPa. Numerical tests have shown that EPDM rubber lowers the contact pressure just slightly. On the other hand, both composites showed significant reduction in contact pressure that could lower the risks of acute and cumulative trauma disorders which are pressure-dependent. Based on the results, it is also evident that a composite containing PU foam with a more evident and flat plateau deformed less at lower strain rates and deformed more when the plateau was reached, in comparison to the composite with EPDM foam. It was shown that hyper-elastic foam materials, which take into account the non-linear behaviour of fingertip soft tissue, can lower the contact pressure whilst maintaining low deformation rate of the tool-handle material for maintaining sufficient rate of stability of the hand tool in the hands. Lower contact pressure also lowers the risk of acute and cumulative trauma disorders, and increases comfort whilst maintaining performance.

Knowledge-Based System for Supporting the Design of a Plate-Press

This paper presents a knowledge-based system capable of giving the designer quality support when making decisions from the aspect of modeling the reinforcement of a plate-press within a position of maximum compressive load, and by choosing suitable material for the plate. Based on the selected combination of reinforcement and material, this system acquaints the user with the size and position of the largest comparative stress, and the greatest nodal displacement in the load-direction. This system operates based on the implemented knowledge of experts in the execution of design, material selection, and numerical analysis based on the finite-element method (FEM), which was written with the help of parameters within the knowledge-base of the CATIA V5 CAD -system. Using this system gives the user an opportunity to reach conclusions that are crucial for designing a plate-press or pressure-loaded die-elements, in general. The results reveal that the system can dramatically shorten design time and improve design quality in comparison to manual design process.

A knowledge base for finite element mesh design

Abstract The finite element method (FEM) is the most successful numerical method, that is used extensively by engineers to analyse stresses and deformations in physical structures. These structures should be represented as a finite element mesh. Defining an appropriate geometric mesh model that ensures low approximation errors and avoids unnecessary computational overheads is a very difficult and time consuming task. It is the major bottleneck in the FEM analysis process. The inductive logic programming system GOLEM has been employed to construct the rules for deciding about the appropriate mesh resolution. Five cylindrical mesh models have been used as a source of training examples. The evaluation of the resulting knowledge base shows that conditions in the domain are well represented by the rules, which specify the required number of the finite elements on the edges of the structures to be analysed using FEM. A comparison between the results obtained by this knowledge base and conventional mesh generation techniques confirms that the application of inductive logic programming is an effective approach to solving the problem of mesh design.

Mesh generation expert system for engineering analysis with FEM

Abstract The finite element method is used extensively by engineers and modeling scientists to analyze deformations and stresses in physical structures. These structures are represented quantitatively as finite collections of elements. The displacement of each element is computed using algebraic equations. In order to design a numerical model of a physical structure it is necessary to decide the appropriate resolution for modeling each component part. Considerable expertise is required in choosing these resolution values. A too fine mesh leads to unnecessary computational overheads when executing the model. A too coarse mesh produces intolerable approximation errors. In this paper we demonstrate that rules for deciding on appropriate resolution values can be inductively constructed from expert provided examples. The Inductive Logic Programming algorithm Golem is employed for this purpose.

Human cognition as an intelligent decision support system for plastic products' design

Engineering work is a complex task mainly supported by computer aids. This paper highlights its deficiencies when the designer cannot obtain any expert recommendations or guidelines from the computers program regarding a decision-making process such as material selection. Particular products development design process, within a well-known enterprise from the white goods industry is presented and supported by a case study. The advantages and disadvantages are set out, and any potential benefits gained from using an intelligent decision support system for plastic products design are introduced. The proposed decision support system contains human cognition within the field of design knowledge and special domain knowledge expertise regarding plastics supported by design methodology called Design for Manufacturing (DFM).

Justification for a 2D versus 3D fingertip finite element model during static contact simulations

Abstract The biomechanical response of a human hand during contact with various products has not been investigated in details yet. It has been shown that excessive contact pressure on the soft tissue can result in discomfort, pain and also cumulative traumatic disorders. This manuscript explores the benefits and limitations of a simplified two-dimensional vs. an anatomically correct three-dimensional finite element model of a human fingertip. Most authors still use 2D FE fingertip models due to their simplicity and reduced computational costs. However we show that an anatomically correct 3D FE fingertip model can provide additional insight into the biomechanical behaviour. The use of 2D fingertip FE models is justified when observing peak contact pressure values as well as displacement during the contact for the given studied cross-section. On the other hand, an anatomically correct 3D FE fingertip model provides a contact pressure distribution, which reflects the fingertip’s anatomy.