Modelling and measurement of backscattering from partially water-filled cylindrical shells

The backscattering from partially water-filled cylindrical shells has been studied using finite element (FE) analysis and experimental measurements for low to medium frequencies, corresponding to 2 < ka < 30 (where a is the shell outer radius). For a partially-filled shell, filled to three quarters of the inner diameter, backscattering has been investigated numerically as a function of the elevation angle of the incident wave, and in particular as the wave direction changes from horizontal to vertical. Comparisons with fully air-filled and fully water-filled shells indicate that the shell resembles the former when the wave is incident from above and the latter when the wave is incident horizontally. The experiments were performed in a reservoir, using horizontal incidence and wideband Ricker pulses generated by a parametric array. The short duration of the Ricker pulses made it possible to observe a number of returns after the specular return for a shell with a high filling fraction; these included contributions due to S0 waves generated at the front and back walls of the shell, and the back wall return. Inversion of the FE model data enabled the expected waveforms to be predicted; the measurements were in very good agreement with the prediction

Finite element modelling of transportation tunnels

The aim of this thesis is to determine the ground deformation and stress distribution around highway tunnels at various stages of excavation and for several support conditions using finite element modelling techniques. When ground is excavated and material removed the subsequent redistribution of stress in the remaining surrounding material needs to be treated by one of three methods. These are the gravity difference method, the stress reversal technique and the relaxation approach. The first two methods were chosen for the simulation of excavation in this study. The tunnel data are in the form of the dimensions of the tunnel, heights of the rock layers, details of the shotcrete lining and tunnel support systems. A pre-processing program was written to transform this information into a finite element mesh in a format suitable for use by PAFEC-FE software. This enables different tunnel models and meshes to be produced with minimum error and time. The lack of adequate post-processing facilities available in PAFEC-FE dictated that computer programs needed to be written in order to reformat the textual output files and process the mesh stress and displacement outputs for graphical display using UNIRAS. In this way repeated use could be made of PAFEC-FE without time-consuming and error-prone manual retrieval of data. The tunnels were modelled at various stages of excavation and with such support provided at those stages as to allow the computed displacements to be compared with measurements made on highway tunnels in Turkey. The stresses generated in the tunnel supports and surrounding ground were also calculated to enable the possibility of damage or failure of the support structure or ground to be assessed and the selection of an optimal support system. Insertion of a support system into the model has a marginal effect on the development of rock strength around an excavation boundary

The Mechanical Properties of Carbon Fibre With Glass Fibre Hybrid Reinforced Plastics

Merged with duplicate record 10026.1/2475 on 15.03.2017 by CS (TIS)Fibre composite hybrid materials are generally plastics reinforced with two different fibre species. The combination of these three materials (in this thesis they are carbon fibres, glass fibres and polyester resin) allows a balance to be achieved between the properties of the two monofibre composites. Over the fifteen years since the introduction of continuous carbon fibre as a reinforcement, there has been considerable speculation about the "hybrid effect", a synergistic strengthening of reinforced plastics with two fibres when compared with the strength predicted from a weighted average from the component composites. A new equation is presented which predicts the extent of the hybrid effect. Experiments with a variety of carbon-glass hybrids were undertaken to examine the validity of the theory and the effect of the degree of inter-mixing of the fibres. The classification and quantification of the hybrid microstructures was examined with a view to crosscorrelation of the intimacy of mixing and the strength. Mechanical tests were monitored with acoustic emission counting and acoustic emission amplitude distribution equipment. Some specimens were subjected to one thermal cycle to liquid nitrogen temperature prior to testing. Fracture surfaces were examined in the scanning electron microscope. Numerical analysis by finite element methods was attempted. A constant strain triangular element was used initially, but in the later analyses the PAFEC anisotropic isoparametric quadrilateral elements were used. The system was adapted so that a \Ir singularity could be modelled, and post processor software was written to allow nodal averaging of the stresses and the presentation of this data graphically as stress contour maps

Finite element modelling and testing of filament-wound orthotropic components

Existing software for CNC filament winding of fibre reinforced plastics has been linked to typical finite element codes by automating the generation of finite element models of filament wound components. The algorithms required for this process have been created and encoded as computer programs. The program FILFEM I generates models of components manufactured using the CADFIL I CAD/CAM system for the filament winding of axisymmetric components. The suite of programs named FILFEM II achieves the same objective for non-axisymmetric components manufactured using CADFIL II although its method of operation is quite different from that of FILFEM I. FILFEM I has been tested by automatically generating models of a pinched cylindrical filament-wound tube manufactured from glass-reinforced polyester resin. The results from these models generally compared well with results obtained from experiments and from an analytical solution extended by the author from work by Calladine. However, the validity of a comparison with experiment depends upon the accuracy of the material properties assumed in the analyses. The material property values required for the analyses were investigated experimentally. Tests based upon pinched rings and a modified split-disc method are described together with more conventional tests of material properties. A method is presented for the determination of unidirectional material properties from the experimentally-measured properties of laminates. Difficulties in obtaining consistent results were attributed to problems with the quality of the specimens, inadequacies in the orthotropic model of material behaviour, and to material damage occurring during the experiments. In order to provide a test component for FILFEM II, a number of filament wound elbows were manufactured although some problems with winding quality remain. The fibre paths files used in manufacturing the elbows were used to test the operation of FILFEM II and further work including experimental verification is proposed

Finite element modelling and testing of filament-wound orthotropic components

Existing software for CNC filament winding of fibre reinforced plastics has been linked to typical finite element codes by automating the generation of finite element models of filament wound components. The algorithms required for this process have been created and encoded as computer programs. The program FILFEM I generates models of components manufactured using the CADFIL I CAD/CAM system for the filament winding of axisymmetric components. The suite of programs named FILFEM II achieves the same objective for non-axisymmetric components manufactured using CADFIL II although its method of operation is quite different from that of FILFEM I. FILFEM I has been tested by automatically generating models of a pinched cylindrical filament-wound tube manufactured from glass-reinforced polyester resin. The results from these models generally compared well with results obtained from experiments and from an analytical solution extended by the author from work by Calladine. However, the validity of a comparison with experiment depends upon the accuracy of the material properties assumed in the analyses. The material property values required for the analyses were investigated experimentally. Tests based upon pinched rings and a modified split-disc method are described together with more conventional tests of material properties. A method is presented for the determination of unidirectional material properties from the experimentally-measured properties of laminates. Difficulties in obtaining consistent results were attributed to problems with the quality of the specimens, inadequacies in the orthotropic model of material behaviour, and to material damage occurring during the experiments. In order to provide a test component for FILFEM II, a number of filament wound elbows were manufactured although some problems with winding quality remain. The fibre paths files used in manufacturing the elbows were used to test the operation of FILFEM II and further work including experimental verification is proposed

Fluid-structure interaction of submerged shells

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A general three-dimensional hydroelasticity theory for the evaluation of responses has been adapted to formulate hydrodynamic coefficients for submerged shell-type structures. The derivation of the theory has been presented and is placed in context with other methods of analysis. The ability of this form of analysis to offer an insight into the physical behaviour of practical systems is demonstrated. The influence of external boundaries and fluid viscosity was considered separately using a flexible cylinder as the model. When the surrounding fluid is water, viscosity was assessed to be significant for slender structural members and flexible pipes and in situations where the clearance to an outer casing was slight. To validate the three-dimensional hydroelasticity theory, predictions of resonance frequencies and mode shapes were compared, with measured data from trials undertaken in enclosed tanks. These data exhibited differences due to the position of the test structures in relation to free and fixed boundaries. The rationale of the testing programme and practical considerations of instrumentation, capture and storage of data are described in detail. At first sight a relatively unsophisticated analytical method appeared to offer better correlation with the measured data than the hydroelastic solution. This impression was mistaken, the agreement was merely fortuitous as only the hydroelastic approach is capable of reproducing-the trends recorded in the experiments. The significance of an accurate dynamic analysis using finite elements and the influence of physical factors such as buoyancy on the predicted results are also examined

Computational Aspects of Heat Transfer in Structures

Techniques for the computation of heat transfer and associated phenomena in complex structures are examined with an emphasis on reentry flight vehicle structures. Analysis methods, computer programs, thermal analysis of large space structures and high speed vehicles, and the impact of computer systems are addressed

Dynamic impact testing and computer simulation of wheelchair tiedown and occupant restraint systems (WTORS).

Occupant Restraint Systems (ORS) have been widely used in Public Service Vehicles (PSVs). A Wheelchair Tiedown and Occupant Restraint System (WTORS) has been developed to provide effective occupant protection for disabled people who are seated in wheelchairs. An international laboratory study had been conducted to produce a compliance test protocol that included specification of the sled deceleration versus time history and the crash pulse corridor. Currently effort at the international level is being focused through the International Standards Organisation (ISO) to produce standards for WTORS and transportable wheelchairs. Dynamic sled testing of WTORS was conducted in Middlesex University Road Safety Engineering Laboratory (MURSEL) to develop a test protocol in a WTORS System. This research has been concerned with the effects to which the occupant of a wheelchair secured by a WTORS is subjected in a frontal impact. Both occupant Forward Facing Frontal (FFF) and Rearward Facing Frontal (RFF) impact configurations have been considered. A Surrogate wheelchair with a tiedown restraint System, a Surrogate occupant restraint System, and an Anthropomorphic Test Dummy (ATD) were used to facilitate highly controlled tests. Production wheelchairs were also crash tested to validate the response of the Surrogate System. A 48 km/h-20g crash pulse falling within the ISO standard crash pulse corridor was specified. The Crash Victim Simulation (CVS), one of the computer modelling methods, and Finite Element Analysis (FEA) models were designed to study the dynamic response of a restrained wheelchair and its occupant in a crash environment. Two CVS computer packages: MADYMO®, DYNAMAN® and one of FEA programs: PAFEC were used in WTORS models to predict the occupant response during impacts and hence provide data to optimise future system design. A modelling protocol for WTORS was developed based on the results of ninety (90) sled tests of WTORS Surrogate system and forty (40) dynamic tests of production wheelchairs. To illustrate the potential of these models the results of simulations were validated by sled tests. A random effects Statistical method was used to quantify the results. The load-time histories were also traced to qualify the test and model results. A literature review highlighted twenty years of wheelchair crash research. The correlation between computer model and experimental results was made more accurately. The modelling technique of interconnection of FEA models into CVS program was also introduced. The velocity profile and the natural frequency of WTORS analysis were used to explain why the wheelchair and dummy experienced acceleration amplifications relative to the sled. The shoulder belt load at floor-mounted configuration was found to be higher than that at B pillar configuration. Energy principles were also applied to show why more compliant wheelchair tiedown Systems subjected restraints to a less severe crash environment. A decomposition of forces using the computer model showed why quasi-static analysis is insufficient in WTORS design. It is concluded that the B pillar anchorage of the occupant diagonal strap is superior to the floor-mounted configuration

Finite element analysis of a continuum undergoing large plastic deformation

In today's society there is a need for engineers to design to the limit of materials, with which they are working, because of industrial demands for more competative designs. This thesis describes the work carried out to investigate the concept of the finite element method, to gain insight into the theory behind it and to apply this knowledge in developing a computer program to simulate the load mechanisms and boundary conditions, particularly to the ring structure under large elasticplastic deformation. Finite element is a method of mathematically modelling a component for stress analysis. It requires large quantities of data which are manipulated by matrix techniques to obtain results. The use of the computer is therefore essential to save time on a complex component. The finite element program developed in this work is based on a twodimensional plane elasticity analysis using constant strain triangular elements. Yield is based on Von-Mises' criterion, plastic flow on Prandtl-Reuss relationship and the formulation includes linear strain hardening. The formulation of the elasticplastic matrix is based on the initial stress method. The equipment for the experimental work was designed and this included the modification of the hydraulic system of the press machine, the base of testing and the measurement system. Experimental work was carried out on the ring structure under three different types of loading conditions: 1. between two knife-edges; 2. between two rigid parallel surfaces; 3. between two rigid parallel surfaces and two lateral walls with a gap. A comparison was made between the output data from the E.P. Program, which was developed in the current work, and the commercial packages. The results of this comparison are in reasonable agreement with each other. A comparison was also carried out between the experimental results and the theoretically predicted results, and reasonable agreement was obtained