Aylmer L Johnson
University of Cambridge, Department of Engineering, Faculty Member
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In the undergraduate engineering course at the University of Cambridge six graphics terminals are being used to teach 500 undergraduates by packages and routines especially designed for unsupervised operation by men in their first and... more
In the undergraduate engineering course at the University of Cambridge six graphics terminals are being used to teach 500 undergraduates by packages and routines especially designed for unsupervised operation by men in their first and second years. Topics covered include closed-loop control systems, slider mechanisms, projection theory, intersection of surfaces, elastic and plastic collapse and vibrating systems. Ordinary display facilities are also available for use by undergraduates, research students and teaching staff. The terminals are installed in the students’ drawing office directly alongside the normal drawing boards and are in full-time use. The choice of a flat bed plotter and teleprinter as a terminal has been proved wise for teaching and economy. Gradual expansion into other areas of teaching and research is taking place, and the introduction of CAD methods, not as a separate subject but as an integral part of the normal Cambridge Engineering degree course, is proceeding smoothly and with enthusiasm from teaching staff and undergraduates alike.
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ABSTRACT The software package Dymola, which implements the new, vendor-independent standard modelling language Modelica, exemplifies the emerging generation of object-oriented modelling and simulation tools. This paper shows how, in... more
ABSTRACT The software package Dymola, which implements the new, vendor-independent standard modelling language Modelica, exemplifies the emerging generation of object-oriented modelling and simulation tools. This paper shows how, in addition to its simulation capabilities, it may be used as an embodiment design tool, to automatically size a design assembled from a library of generic parametric components. The example used is a miniature model aircraft diesel engine. To this end, the component classes contain extra algebraic equations for calculating the overload factor (or its reciprocal, the safety factor) for all the different failure modes, such as buckling or tensile yield. Thus, the simulation results contain the maximum overload or the minimum safety factor for each failure mode, along with the critical instant and the device state at which it occurs. The Dymola “Initial Conditions Calculation” function, controlled by a simple software script, may then be used to perform automatic component sizing. Each component is minimised in mass, subject to a chosen safety factor against failure, over a given operating cycle. Whilst the example is in the realm of mechanical design, it must be emphasised that the approach is equally applicable to the electrical or mechatronic domains, indeed to any design problem requiring numerical constraint satisfaction
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A matrix-based method is presented for calculating velocities and accelerations in two- and three-dimensional mechanisms. The method involves no symbolic manipulation or differentiation and is comparatively simple to implement as a... more
A matrix-based method is presented for calculating velocities and accelerations in two- and three-dimensional mechanisms. The method involves no symbolic manipulation or differentiation and is comparatively simple to implement as a computer algorithm, in that the same arithmetic process is used regardless of the configuration of the mechanism, and regardless of its complexity. The quantity of computation varies linearly with the number of moving parts in the mechanism.
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<jats:title>Abstract</jats:title> <jats:p>Many designs fail because one or more checks are not done, or are done too late during the design process. A functional modelling system is presented, which provides systematic... more
<jats:title>Abstract</jats:title> <jats:p>Many designs fail because one or more checks are not done, or are done too late during the design process. A functional modelling system is presented, which provides systematic design checking at early design phases by means of constraint satisfaction. However, problems can occur if the design to be checked involves too many constraints.</jats:p> <jats:p>This paper presents some extended research, which establishes a knowledge hierarchy for managing the mathematical constraints, so that the computer can process large designs. A case study of fastening joint design using this hierarchy is discussed.</jats:p>
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The feasible solution space for a mechanical engineering design is determined by the variables and constraints involved in the design. Although constraint satisfaction programs can be used to find individual solutions in this space, their... more
The feasible solution space for a mechanical engineering design is determined by the variables and constraints involved in the design. Although constraint satisfaction programs can be used to find individual solutions in this space, their search strategies become very inefficient if the search space is much larger than the solution space. The user then cannot be sure whether a prolonged unsuccessful search is due to this inherent inefficiency, or because no solution space actually exists. In addition, such programs provide no information about the amount by which a satisfactory design solution can be adjusted without violating any constraints. This paper presents the implementation of a computer program which utilises a domain propagation algorithm to estimate the feasible design space. The theoretical descriptions of domain propagation and the algorithm are also discussed. Case studies show that this program enhances the efficiency and robustness of the constraint-based design proc...
PurposeThis paper aims to explore the information needs and information-seeking behaviours of the new generation of engineering designers. A survey study is used to approach what their information needs are, how these needs change during... more
PurposeThis paper aims to explore the information needs and information-seeking behaviours of the new generation of engineering designers. A survey study is used to approach what their information needs are, how these needs change during an engineering design project and how their information-seeking behaviours have been influenced by the newly developed information technologies (ITs). Through an in-depth analysis of the survey results, the key functions have been identified for the next-generation management systems.Design/methodology/approachThe paper first proposed four hypotheses on the information needs and information-seeking behaviours of young engineers. Then, a survey study was undertaken to understand their information usage in terms of the information needs and information-seeking behaviours during a complete engineering design process. Through analysing the survey results, several findings were obtained and on this basis, further comparisons were made to discuss and eval...
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In the global market of air transport, integration of products and services is now seen as being necessary for the long-term success of engine manufacturers. This paper describes research stimulated by a fundamental shift that is... more
In the global market of air transport, integration of products and services is now seen as being necessary for the long-term success of engine manufacturers. This paper describes research stimulated by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defence purposes, away from the selling of products to the provision of services. Our collaborating aerospace company now offers TotalCare TM contracts, under which it leases engines to airlines while remaining responsible for their maintenance. The aims of our ongoing research are to: (1) understand the current flows of in-service information to designers; (2) understand the in-service information requirements of designers; (3) develop, based on this understanding, the most appropriate theories and methods to support designers in their new task. The work presented in this paper aims at understanding the use of in-service information in a design task by examining the executed desi...
This research is triggered by the emerging 'power by the hour'® paradigm, in which aero engines are effectively leased to airlines, with the manufacturing company remaining responsible for their maintenance and repair throughout... more
This research is triggered by the emerging 'power by the hour'® paradigm, in which aero engines are effectively leased to airlines, with the manufacturing company remaining responsible for their maintenance and repair throughout their service life. By incorporating knowledge about the performance of existing products into the design phase of new products, it is hoped to tackle some of the in-service problems at the design stage. In the aerospace sector, it is standard design practice to utilise the experience gained from past projects, but that from in-service has not been given sufficient attention. In this context, the aims of our ongoing research are: (1) to understand the current flows of in-service information to designers; (2) to understand the in-service information requirements of designers; (3) to develop the most appropriate theories and methods to support designers in their new task of creating engines which will perform reliably and economically throughout their ...
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This paper shows how, by harnessing recent technological advances in the field of ObjectOrientedPhysical Systems Modelling [7], much greater ease of use, rigour and computationalefficiency in design constraint management can be achieved... more
This paper shows how, by harnessing recent technological advances in the field of ObjectOrientedPhysical Systems Modelling [7], much greater ease of use, rigour and computationalefficiency in design constraint management can be achieved [1]. Additionally, this approachprovides "virtual prototype" animated dynamic models of the resulting design artefacts, forsubsequent evaluation and optimisation. These have built-in design constraint checking,ensuring that at every instant
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A new type of computerized design aid is described, which raises the need to carry out the simple preliminary static analysis of articulated assemblies of rigid bodies by computer; and a matrix-based method is presented for doing this.... more
A new type of computerized design aid is described, which raises the need to carry out the simple preliminary static analysis of articulated assemblies of rigid bodies by computer; and a matrix-based method is presented for doing this. This method also forms the basis for a new approach to the kinematic analysis of such assemblies, which in turn provides the inertia (D’Alembert) forces for the static analysis.
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ABSTRACT In the context of collaborative product development, new requirements need to be accommodated for Virtual Prototyping Simulation (VPS), such as distributed processing and the integration of models created using different tools or... more
ABSTRACT In the context of collaborative product development, new requirements need to be accommodated for Virtual Prototyping Simulation (VPS), such as distributed processing and the integration of models created using different tools or languages. Existing solutions focus mainly on the implementation of distributed processing, but this paper explores the issues of combining different models (some of which may be proprietary) developed in different software environments. In this paper, we discuss several approaches for developing VPS, and suggest how it can best be integrated into the design process. An approach is developed to improve collaborative work in a VPS development by combining disparate computational models. Specifically, a system framework is proposed to separate the system-level modeling from the computational infrastructure. The implementation of a simple prototype demonstrates that such a paradigm is viable and thus provides a new means for distributed VPS development.
This research is triggered by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defence purposes, away from the selling of products to the provision of services. Under the emerging... more
This research is triggered by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defence purposes, away from the selling of products to the provision of services. Under the emerging 'power by the hour' paradigm, aero engines are effectively leased to the airlines, with the manufacturing company remaining responsible for their maintenance and repair throughout their service life. This has triggered a major re-assessment of the design of aero engines to reduce their overall life-cycle costs, while maintaining performance efficiency. The important aims of our ongoing research are: firstly to understand the current flows of in-service information to designers; secondly to understand the information requirements of designers about in-service issues; thirdly to develop the most appropriate theories and methods to support designers in their new task. This paper presents the results of the initial phase of an ongoing research pr...
In the global market of air transport, integration of products and services is now seen as being necessary for the long-term success of engine manufacturers. This paper describes research stimulated by a fundamental shift that is... more
In the global market of air transport, integration of products and services is now seen as being necessary for the long-term success of engine manufacturers. This paper describes research stimulated by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defence purposes, away from the selling of products to the provision of services. Our collaborating aerospace company now offers TotalCare TM contracts, under which it leases engines to airlines while remaining responsible for their maintenance. The aims of our ongoing research are to: (1) understand the current flows of in-service information to designers; (2) understand the in-service information requirements of designers; (3) develop, based on this understanding, the most appropriate theories and methods to support designers in their new task. The work presented in this paper aims at understanding the use of in-service information in a design task by examining the executed desi...
This research is triggered by the emerging 'power by the hour'® paradigm, in which aero engines are effectively leased to airlines, with the manufacturing company remaining responsible for their maintenance and repair throughout... more
This research is triggered by the emerging 'power by the hour'® paradigm, in which aero engines are effectively leased to airlines, with the manufacturing company remaining responsible for their maintenance and repair throughout their service life. By incorporating knowledge about the performance of existing products into the design phase of new products, it is hoped to tackle some of the in-service problems at the design stage. In the aerospace sector, it is standard design practice to utilise the experience gained from past projects, but that from in-service has not been given sufficient attention. In this context, the aims of our ongoing research are: (1) to understand the current flows of in-service information to designers; (2) to understand the in-service information requirements of designers; (3) to develop the most appropriate theories and methods to support designers in their new task of creating engines which will perform reliably and economically throughout their ...
The software package Dymola, which implements the new, vendor-independent standard modelling language Modelica, exemplifies the emerging generation of object-oriented modelling and simulation tools. This paper shows how, in addition to... more
The software package Dymola, which implements the new, vendor-independent standard modelling language Modelica, exemplifies the emerging generation of object-oriented modelling and simulation tools. This paper shows how, in addition to its simulation capabilities, it may be used as an embodiment design tool, to automatically size a design assembled from a library of generic parametric components. The example used is a miniature model aircraft diesel engine. To this end, the component classes contain extra algebraic equations for calculating the overload factor (or its reciprocal, the safety factor) for all the different failure modes, such as buckling or tensile yield. Thus, the simulation results contain the maximum overload or the minimum safety factor for each failure mode, along with the critical instant and the device state at which it occurs. The Dymola “Initial Conditions Calculation” function, controlled by a simple software script, may then be used to perform automatic comp...
This research was undertaken in an aerospace company, which manufactures aero engines and also offers contracts, under which it remains responsible for the maintenance of engines. These contracts allow the company to collect far more data... more
This research was undertaken in an aerospace company, which manufactures aero engines and also offers contracts, under which it remains responsible for the maintenance of engines. These contracts allow the company to collect far more data about the in-service performance of their engines than was previously available. This paper aims at understanding what parts of this in-service information are accessed when components or systems of existing aero engines need to be redesigned, because they have not performed as expected in service. In an attempt to address this aim, five case studies involving the redesign of components of an aero engine are examined. The redesign is based on the in-service experience of the existing components. The findings provide an understanding of the different types of information, and in particular the types of in-service information, accessed by designers in a redesign task.
ABSTRACT The developments of recent years in computer hardware have resulted in rapid advances in the capabilities of Computer-aided Design: but continued hardware development alone is not enough to ensure similar progress in the future.... more
ABSTRACT The developments of recent years in computer hardware have resulted in rapid advances in the capabilities of Computer-aided Design: but continued hardware development alone is not enough to ensure similar progress in the future. In order to grow further, CAD must move further into the design process itself, which raises the need for a language whereby designers and computers can ‘discuss’ a design when it is still at the conceptual stage. The Engineering Design Centre at Cambridge University has now made substantive progress in this area: this paper summarises the progress made to date, and describes how some of the issues which have been raised are currently being tackled.
... early development of a modeller called DUCT, now widely used in the pattern-making industry, prospective ... of split lines and draw angles rather than leaving such details to the patternmaker. ... necessary to insist that the... more
... early development of a modeller called DUCT, now widely used in the pattern-making industry, prospective ... of split lines and draw angles rather than leaving such details to the patternmaker. ... necessary to insist that the computer processes these concepts in an 'intelligent' way 2 ...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
A matrix-based method is presented for calculating velocities and accelerations in two- and three-dimensional mechanisms. The method involves no symbolic manipulation or differentiation and is comparatively simple to implement as a... more
A matrix-based method is presented for calculating velocities and accelerations in two- and three-dimensional mechanisms. The method involves no symbolic manipulation or differentiation and is comparatively simple to implement as a computer algorithm, in that the same arithmetic process is used regardless of the configuration of the mechanism, and regardless of its complexity. The quantity of computation varies linearly with the number of moving parts in the mechanism.
Research Interests:
This article describes the research stimulated by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defense purposes, away from the selling of products to the provision of services.... more
This article describes the research stimulated by a fundamental shift that is occurring in the manufacture and marketing of aero engines for commercial and defense purposes, away from the selling of products to the provision of services. This research was undertaken in an aerospace company, which designs and manufactures aero engines and also offers contracts, under which it remains responsible for the maintenance of engines. These contracts allow the company to collect far more data about the in-service performance of their engines than was previously available. This article aims at identifying what parts of this in-service information are required when components or systems of existing engines need to be redesigned because they have not performed as expected in service. In addition, this article aims at understanding how designers use this in-service information in a redesign task. In an attempt to address these aims, we analyzed five case studies involving redesign of components or systems of an existing engine. The findings show that the in-service information accessed by the designers mainly contains the undesired physical actions (e.g., deterioration mechanisms, deterioration effects, etc.) and the causal chains of these undesired physical actions. We identified a pattern in the designers' actions regarding the use of these causal chains. The designers have generated several solutions that utilize these causal chains seen in the in-service information. The findings provide a sound basis for developing tools and methods to support designers in effectively satisfying their in-service information requirements in a redesign task.
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The design and development of complex engineering systems generally encompasses multi-disciplinary knowledge and entails systematic analysis at an early design stage. A paradigm known as collaborative simulation is introduced to address... more
The design and development of complex engineering systems generally encompasses multi-disciplinary knowledge and entails systematic analysis at an early design stage. A paradigm known as collaborative simulation is introduced to address this characteristic: that is, decomposing the system into manageable subsystems and incorporating them at simulation run-time. However, many key limitations still remain in current collaborative simulation solutions, especially in the modern context of distributive and collaborative design. Our motivation in this research is to develop such a tool that can support the effective deployment and dynamic integration of simulation models distributed on the Internet. As a major implementation technology in industry, Web services have advantages such as modularized system structure and universally available computing capability. We propose a service-oriented approach that treats a collaborative simulation system as loosely-coupled components, e.g. simulation models and simulation management, all of which are wrapped as independent Web services. A prototype system is developed, based on which a simple case study is looked at. It is evidenced in this work that Web services and service-oriented architecture have great potential in developing engineering software tools.