A knowledge based expert system for moulded part design

In today's competitive market many consumer products are designed with complex curved shapes to meet customers' demands for styling and ergonomics. These styled products are commonly manufactured using moulding processes because they can produce a wide range of freeform shapes at relatively low cost. However, although injection moulding and metal casting allow a great deal of design freedom they also make significant demands on the designer to ensure that parts are designed with due regard for manufacturability. This paper describes a knowledge based moulding advisor that has been developed to provide design for moulding advice to designers during the design process. The main contributions of the research are the development of a hierarchical knowledge representation to allow moulding advice to be generated at different levels of detail and the integration of the expert system with a geometric part description extracted from a Computer Aided Design (CAD) solid model. A demonstrator for the manufacturing advisor has been implemented using the expert system shell CLIPS and integrated with CAD using feature recognition. The moulding advisor is able to generate tailored design for moulding advice for a range of manufacturing processes and materials and evaluate the manufacturability of a designed part at the feature level. The paper provides a case study for a simple moulded test part

Set-based approach to passenger aircraft family design

Presented is a method for the design of passenger aircraft families. Existing point-based methods found in the literature employ sequential approaches in which a single design solution is selected early and is then iteratively modified until all requirements are satisfied. The challenge with such approaches is that the design is driven toward a solution that, although promising to the optimizer, may be infeasible due to factors not considered by the models. The proposed method generates multiple solutions at the outset. Then, the infeasible solutions are discarded gradually through constraint satisfaction and set intersection. The method has been evaluated through a notional example of a three-member aircraft family design. The conclusion is that point-based design is still seen as preferable for incremental (conventional) designs based on a wealth of validated empirical methods, whereas the proposed approach, although resource-intensive, is seen as more suited to innovative designs

An investigation into efficient multiple command order picking in high bay narrow aisle warehouses

With the increasing tempo of business, order picking efficiency becomes of increasing importance. The aim of this research is to find ways of increasing order picking efficiency by decreasing travel time of the picking cycle.Finding the optimal (shortest) order picking tour can be equated to the task of finding a solution to the Travelling Salesman Problem (TSP). This is notoriously difficult to solve in reasonable time when conventional computers are used. A number of heuristic algorithms have been developed for solving the TSP, some of these have been specially adapted for multiple command order picking. In this previous work the stacker crane's shuttle was assumed to travel with constant velocities in the horizontal and vertical directions. In this research it is shown that this assumption leads to creating suboptimal tours. The contribution of the error is analytically derived and its magnitude estimated by a simulation experiment. In previous work it has been shown that the shape of the zones in class based storage affects the travel time for single and dual command order picking. In this research, for the first time, the interaction between class based storage and multiple command order picking is investigated. Three types of zone configurations are modelled and then investigated using simulation in a factorial experiment. The results from the experiment indicate that the zone shape does affect the optimal solution.The new zone configurations are tested in a case study against existing configurations in a distribution warehouse of Volkswagen - Audi (VAG-UK). This showed that overall improvement in travel time of the new configurations was significant. Computer simulation was used to estimate the individual contribution from zoning and tour construction

Design exploration for engineering design optimisation : an aircraft conceptual perspective

Most of the efforts in optimisation so far have been focused on the development of novel or the improvement of existing numerical methods for an effective computation of optimal solutions. Particular attention has been put on balancing multiple conflicting objectives, handling the interaction between different disciplines, reducing computational cost and managing uncertainty. Nonetheless, specific issues of this design methodology still remain to be properly addressed. In this research, attention is concentrated on advancing engineering optimisation as a tool for design exploration. The work is put in the context of conceptual aircraft design. The overall aim of the present research is to develop a methodology that allows the designer to effectively conduct an exploration and analysis of alternative design solutions via a set of methods that can be used separately or conjointly. The initial part of the thesis introduces two novel methods for assisting the formulation of an optimisation problem, which generally is assumed to be given a priori. Nonetheless, the correctness of the optimisation statement, which is not addressed by established optimisation methods, turns out to be decisive for the feasible design set determination. The designer is thus provided with an adaptive formulation of functional and designvariable constraints, which allows the exploration of further promising solutions initially not contained in the feasible design set. Meaningless results or the loss of important solutions can therefore be partially avoided. In a second instance, attention is focused on the visualisation needs for design exploration. A suitable visualisation methodology has been developed to make the large multidimensional results of complex design optimisation procedures fully readable and explanatory. This is achieved by integrating advanced visualisation techniques which provide the designer with diverse perspectives of the data under study and allow him/her to conduct a number of analysis tasks on it, without the need to be an expert in numerical optimisation methods. Last, but not least, a methodology to address conceptual design change problems is proposed. The decision-maker is enabled to formally state the new design requirements and priorities introduced by the conceptual change via an adequate problem reformulation. All the data previously collected can thus be re-used and exploited to drive an effective exploration of alternative design solutions through design space regions of interest. The evaluation of the proposed methodologies has been carried out with a number of test cases. Analytical examples have been used for the assessment of effectiveness, whereas codes representative of aircraft sizing procedures have been adopted to evaluate the methodologies functionality. A visualisation user interface prototype has also been developed for demonstration and evaluation purposes.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Computational design process modeling

In the conceptual design phase, relatively simple equations and functions (or compiled code) are used to describe the aircraft and to perform trade-off studies. The latter require an optimal execution sequence in order to reduce computational cost and design time, respectively. The focus of this paper is the dynamic derivation of the optimal computational plan for each study so that the designer could focus on designing the aircraft rather than managing the process flow. Two methodologies, the Design Structure Matrix (DSM) and the Incidence Matrix are used for the computational process modeling. The incidence matrix describes the relationship between variables and equations/models. The DSM has been used to express the dependency relationships between the models and also, after manipulation, to produce the solution process. The designer specifies the independent (known) variables first. Then the variable flow is modeled using the Incidence Matrix Method (IMM). It determines how data flows through the models, and also identifies any strongly connected components (SCCs). The second step is to rearrange all equations/models hierarchically in order to reduce the feedback loops in each of the identified SCCs. This is achieved by the application of a genetic-based algorithm. Subsequently all SCCs and noncoupled models are assembled into a macro model which forms a global DSM. The global DSM is further rearranged to obtain an upper triangular matrix which defines the final model execution sequence. A simple aircraft sizing example is presented to illustrate the proposed method and algorithm. Advantages of the method include improved efficiency and the ability to deal with both algebraic and numerical models as well as with multiple outputs per model

Efficient method for variance-based sensitivity analysis

Presented is an efficient method for variance-based sensitivity analysis. It provides a general approach to transforming a sensitivity problem into one uncertainty propagation process, so that various existing approximation techniques (for uncertainty propagation) can be applied to speed up the computation. In this paper, formulations are deduced to implement the proposed approach with one specific technique named Univariate Reduced Quadrature (URQ). This implementation was evaluated with a number of numerical test-cases. Comparison with the traditional (benchmark) Monte Carlo approach demonstrated the accuracy and efficiency of the proposed method, which performs particularly well on the linear models, and reasonably well on most non-linear models. The current limitations with regard to non-linearity are mainly due to the limitations of the URQ method used

Computational workflow management for conceptual design of complex systems : an air-vehicle design perspective

The decisions taken during the aircraft conceptual design stage are of paramount importance since these commit up to eighty percent of the product life cycle costs. Thus in order to obtain a sound baseline which can then be passed on to the subsequent design phases, various studies ought to be carried out during this stage. These include trade-off analysis and multidisciplinary optimisation performed on computational processes assembled from hundreds of relatively simple mathematical models describing the underlying physics and other relevant characteristics of the aircraft. However, the growing complexity of aircraft design in recent years has prompted engineers to substitute the conventional algebraic equations with compiled software programs (referred to as models in this thesis) which still retain the mathematical models, but allow for a controlled expansion and manipulation of the computational system. This tendency has posed the research question of how to dynamically assemble and solve a system of non-linear models. In this context, the objective of the present research has been to develop methods which significantly increase the flexibility and efficiency with which the designer is able to operate on large scale computational multidisciplinary systems at the conceptual design stage. In order to achieve this objective a novel computational process modelling method has been developed for generating computational plans for a system of non-linear models. The computational process modelling was subdivided into variable flow modelling, decomposition and sequencing. A novel method named Incidence Matrix Method (IMM) was developed for variable flow modelling, which is the process of identifying the data flow between the models based on a given set of input variables. This method has the advantage of rapidly producing feasible variable flow models, for a system of models with multiple outputs. In addition, criteria were derived for choosing the optimal variable flow model which would lead to faster convergence of the system. Cont/d.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

STPA enabled safety assessment in the architecting of complex systems

STPA is a hazard assessment technique that represents systems as hierarchical control structures composed of feedback control loops. Existing computational support focuses on creating the diagrams that depict these hierarchies. However, the elements in the loops and the signals exchanged must be determined manually. This impedes safety assessment, thus reducing the number of designs that can potentially be explored. Furthermore, the manual approach does not guarantee the correct update of the architecture with changes resulting from safety assessment, which can make the architecture inconsistent with the safety assessment. To overcome these limitations, proposed for the first time are two methods that automate the creation of: (1) hierarchical control structures and (2) detailed control loops. The methods create STPA models by analysing the architecture, which is modelled as a graph. The concept is illustrated with a representative example of a wheel brake system. The resulting models are compared with those obtained manually by the authors of STPA. The automation is shown to significantly reduce the required time and effort. It was also found to ensure consistency among the safety analysis and the architecture definition as it requires safety features to be included in the architecture before being considered in STPA analysis

An assumption network-based approach to support margin allocation and management

Presented is an approach to support margin allocation and management via a graph-theoretical network of assumptions. In contrast to the document-centric approach, the network captures assumptions dependencies, and enables an algorithmic process supporting margin allocation and management. Ultimately, this methodology is intended to assist decision-makers in managing assumptions and examining their impact on an architecture. Explicitly linking margins to assumptions allows to support mitigating their risk of invalidity. The approach is demonstrated with a conceptual aircraft design exampl