Nj Woodman

Vulnerability of structural systems

Abstract A structure is vulnerable if relatively small damage leads to disproportionately large consequences. A structure which is unacceptably vulnerable in any one way is not acceptably robust. A theory of structural vulnerability has been previously reported by the authors. The purpose of the theory is to identify particular failure scenarios by analysing the connectivity of the structural form. In this paper vulnerability theory is applied to three-dimensional frames and, in a preliminary way, to structural dynamics which is crucially important in assessing impact damage in for example progressive collapse. The concepts are illustrated through examples. The vulnerable failure scenarios may then be examined by conventional response analysis and/or by systems reliability theory and risk assessment. The theory is also applicable to structural damage assessment or for assessing structures under unforeseen terrorist attack.

Vulnerability of 3-dimensional trusses

Abstract A system is robust if it can withstand arbitrary damage. There are many practical ways to design in robustness but there is yet no accepted theory of robustness. One insight into the lack of robustness is gained if it were possible to identify how a system is vulnerable. This insight is in the form of ‘a theory of structural vulnerability’ developed at the University of Bristol for 2-dimensional structures [Lu Z, Yu Y, Woodman NJ, Blockley DI. A theory of structural vulnerability. The structural engineer 1999:77(18):17–24]. It is a theory of form and connectivity the purpose of which is to identify weak links within a structure. In this paper further development of the theory and its application to 3-dimensional structures is presented. Algorithms for implementing the theory are described and illustrated through three examples.

The risk of vulnerable failure

There is, as yet, no generally accepted theory of structural robustness or of its corollary, structural vulnerability. The theory of structural vulnerability developed at the University of Bristol is a theory of form that seeks to identify failure scenarios where small damage can lead to disproportionate consequences. In this paper the previously reported theory is combined with a standard response analysis to produce a measure of structural risk which includes the chance of a vulnerable loss of functionality. A simple example of a pin jointed structure is presented.

VULNERABILITY OF SYSTEMS

Abstract A system is vulnerable if any damage from any source produces consequences that are disproportionately large in comparison with that damage. Conversely a system is not robust if it cannot withstand arbitrary damage. Reliability theory is not sufficient for robust safety. In this paper, we propose a contribution to a general theory of vulnerability that is a theory of form and connectivity. The purpose is to identify weak links. This preliminary theory can be applied to a wide range of systems including structures, water pipe works, traffic flows and organisations and is potentially of use for safety management and to reduce the risk of overlooking vulnerable failure scenarios.

An object-oriented structure for transient dynamics on concurrent computers

Abstract This paper describes the deep knowledge encoded into sets of objects so that their aggregated behaviour simulates the dynamics of some physical systems. The details of the mathematical models used to date and their application to a number of standard numerical experiments are presented. A multi-time step scheme is given for cases where different time steps have to be used in different parts of a discretized model. Poincare sections of the chaotic response of a multi-degree of freedom system indicates that complex large scale simulation can be carried out in this way. The natural parallelism of the method ensures good performance on concurrent architectures. Implementations on snared memory, distributed memory machines based on transputers, and the fine grained connection machine are described.

Structural dynamic analysis on a connection machine

Abstract The Interacting Objects Process Model is a naturally parallel way of representing processes based on a ‘connectionist’ approach. It provides powerful new opportunities for the modelling of complex systems including flexible local behaviour models, interrogation methods similar to those used in artificial intelligence and self monitoring methods for more effective reliability management. The development of the IOPM for structural dynamic analysis using the massively parallel Connection Machine CM-200 is reported here. Examples include idealised systems of springs and masses and continuum structural systems using finite element relations. The performance compared to that of the IOPM on a sequential machine is analysed.

QUALITATIVE QUERYING OF PHYSICAL PROCESS SIMULATIONS

Abstract The preliminary design of a query system for the computer simulation of physical processes is presented. Most engineering simulations produce vast amounts of quantitative data. It often requires special training to interpret the data and many of them may not be directly relevant to a particular decision. Human beings usually find qualitative explanations easier to absorb than large quantities of detail. The query system described in the paper is a preliminary to the production of an interrogation system which can provide both qualitative answers and explanations. In the first part of the system, natural language queries are transformed into standard query types using a neural net. In the second part qualitative replies are formed from neural nets which are trained by data from the simulation. An object oriented hierarchy which facilitates the mappings of quantitative data into qualitative attributes is presented. The development of a more detailed and sophisticated explanation system is also disc...

Structural dynamic analysis using the interacting objects process model

Abstract The Interacting Objects Process Model (IOPM) is an object-oriented approach to software design. The IOPM is naturally parallel and presents powerful new opportunities for the modelling of complex physical processes including flexible local behaviour models, interrogation methods similar to those used in artificial intelligence and self monitoring methods for more effective reliability management. The development of the IOPM for linear/nonlinear continuum problems in structural dynamics is presented. Finite element knowledge is used to model stiffness and mass properties but the approach differs from conventional finite element programming in that no assembly of matrices is required and behaviour can be monitored at a local level.

Qualitative analysis of non-linear dynamical systems

Developments in non-linear dynamics have shown that a variety of non-linear deterministic systems with no random inputs can produce random-like or chaotic motions. However, much computational effort is required to identify and analyse chaotic behaviour. We present a powerful methodology to simulate and extract the qualitative behaviour of non-linear systems on a massively parallel Connection Machine. As an example, a simple physical system is analysed to show the effectiveness of the scheme. It is shown that such an analysis is important for designing robust structures.