David Begg

On simultaneous optimization of smart structures – Part II: Algorithms and examples

Five algorithms for the simultaneous optimal design of smart structural systems are presented. These algorithms are developed based on sequential mathematical programming and guided random search techniques, being applied to multidisciplinary optimization in which both structural layout and controller parameters are involved. A method to prevent singularities when updating the structural layout is suggested. Two adaptive trusses are optimised and comparison is made for the different optimal schemes on the basis of iteration histories and major results achieved. All of the five algorithms are shown efficient in improving the trusss performance with respect to robustness and controllability. The results show that the greatest improvement in all the performance indicators is achieved using a genetic algorithm, whilst the most efficient scheme is seen to be a novel hybrid combining sequential linear programming with simulated annealing.

On simultaneous optimisation of smart structures – Part I: Theory

The emerging space missions not only support the idea of smart structures but also call for fast development and application of advanced structures having highly distributed sensors (analogous to a nervous system) and actuators (muscle-like materials) to yield structural functionality and distributed control function. A major concern of the development of the smart system is how to make the multidisciplinary system work efficiently and optimally. This problem is considered in the present paper. The optimal control, sensitivity analysis and integrated optimisation of such a multidisciplinary system is presented. In particular the structural shape and topology are used as design variables, as augmenting the traditional optimal design concept for smart structures and leading to a relatively new field with a high potential for innovation. Discussion of the major problem solving methodologies is also presented to address the truly simultaneous optimisation of smart structures.

Adaptive search in discrete limit analysis problems

Abstract The limit analysis of a segmental arch is considered. A collapse work rate minimisation problem is formulated, with constraints on the minimisation that incorporate a mesh description of geometric compatibility based on Kirchhoff’s network laws. A single quadratic objective function and a set of linear constraint equations are used to perform a limit analysis that considers both rotational and frictional failures in the arch. For comparison with a tested linear optimisation technique for arch analysis, the quadratic objective function is reduced to a linear function, and a Genetic Algorithm (GA) is adopted for the solution method. Ordinal ranking is based on the geometric suitability and energy requirements of a collapse mechanism. The solution set is then driven towards efficiency by the GA. The GA uses a roulette wheel selection mechanism based on the fitness of an individual to select parents for subsequent generations. Goals are dynamically redefined as the optimal solutions in a population improve. A conventionally challenging problem shows the solving efficiency of the GA formulation.

Masonry arch collapse loads and mechanisms by heuristically seeded genetic algorithm

A novel method of initialising and applying genetic algorithms to the limit analysis problem of masonry arch collapse mode identification is described. The method of encoding an individual uses half the resources (with no accompanying loss of information) in comparison with a simple genetic algorithm (SGA) implementation. The new genetic algorithm (GA) uses a set of heuristic rules to seed the initial population and control subsequent genetic operations (mutation and reproduction). The heuristics developed are seen to be applicable to different sized problems. The heuristic GA (HGA) results are compared with simple GA results and are shown to be significantly more efficient. The heuristic GA finds better solutions than the simple GA after far less iteration and with smaller populations. Several conventionally challenging problems illustrate the solving efficiency of the heuristically initialised genetic algorithm formulation.

Sensitivity analysis of smart structures

Abstract The simultaneous optimal design of adaptive structural systems has been formulated as a multi-objective programming problem with the structural variables and controller parameters as design variables. To construct a well-behaved algorithm for the solution of a problem of such complexity, accurate sensitivity information is essential. The purpose of this paper is to systematically evaluate the analytical expressions for the design gradients of the various objectives and constraints with respect to the continuous design variables. Kleinmans Lemma and Bellmans expansion are employed in the derivation, and as a result, the gradient of quadratic performance criterion with respect to the open-loop plant matrix is obtained. This result provides, along with previous results obtained by others, a complete sensitivity package for smart structural control and optimisation. With this sensitivity information, a truly simultaneous optimisation of a smart structure could be possible. Numerical results are presented as verification of the analytical derivations.

Algorithms for Optimal Design of Smart Structural Systems

Simultaneous optimal design of smart structural systems is considered in this article. A major augmentation to this multidisciplinary optimization problem is optimal structural layout design in terms of shape and topology. Four algorithms, namely, guided random search techniques, sequential mathematical programming, and their mixtures, are presented and used for the problem solving. A method to prevent singularities when updating structural layout is also suggested. Design variable linking schemes are used to reduce the number of design variables and give reasonable optimal results. Two examples are solved. Comparison of the algorithms on the basis of achieved improvements in system energy, control effort, robustness, and controllability is made.

An atomic force microscopy study of the effect of tensile loading and elevated temperature on polyvinylidene fluoride from flexible oil pipelines

Flexible pipelines and risers have been used for more than 20 years for the transport of oil and gas in the petroleum industry. In the current study, a phase II polyvinylidene fluoride based pipeline material was subjected to varying degrees of tensile deformation, and microtomed sections were examined by atomic force microscopy (AFM) in order to investigate the resulting topographic changes. The effects of annealing at 100 and 130°C on the maximum load and on topography were also studied. Annealing at 130°C for varying lengths of time gave an increase in the maximum load which was found to be dependent upon crystallization kinetics. AFM studies showed ridges running perpendicular to the loading axis, which are attributed to flow lines resulting from the extrusion process. In annealed samples these ridges were closer together than in unannealed samples. The ridges were absent in quenched samples, but they gradually reappeared after storage at room temperature. These observations were further verified by transmission electron microscopy studies.

Effects of hook shape and cement replacement materials on pullout behaviour of steel fibres

The purpose of this study is to investigate the effect of hook shape and material of high tensile strength hooked end steel fibres and the impact of cement replacement materials on pullout behaviour of steel fibres from cementitious composites. The cement replacements which have been used in this research included silica fume, pulverised fuel ash, limestone filler and ground granulated blast-furnace slag. In total, more than 800 samples have been manufactured for experimental research on compressive strength and pullout behaviour of hooked end steel fibres from cementitious matrices. The effects of parameters such as water/binder ratio, cement replacement content, age of sample, hooked end shape and tensile strength of fibre on fibre–matrix pullout behaviour were determined. The results of tests and analysis indicate that hook shape, tensile strength of fibre and silica fume affect the maximum pullout force and ground granulated blast-furnace slag can significantly improve the residual pullout energy which would be useful for the optimisation of steel fibre reinforced concrete. The outcome of this research may be useful to widen the potential applications of the material across civil engineering.

The influence of infill wall topology and seismic characteristics on the response and damage distribution in frame structures

This paper identifies the effects of infill wall existence and arrangement in the seismic response of frame structures utilising the global structural damage index after Park/Ang () and the maximum interstorey drift ratio (MISDR) to express structural seismic response. Five different infill wall topologies of a 10-storey frame structure have been selected and analysed presenting an improved damage distribution model for infill wall bearing frames, hence promoting the use of nonstructural elements as a means of improving frame structural seismic behaviour and highlighting important aspects of structural response, demonstrating the suitability of such element implementation beyond their intended architectural scope.