Mehran Koohgilani

Optimum Design of Fibre Orientation in Composite Laminate Plates for Out-Plane Stresses

Previous studies have shown that composite fibre orientations can be optimised for specific load cases such as longitudinal or in-plane loading. However, the methodologies utilised in these studies cannot be used for general analysis of such problems. In this research, an extra term is added to the optimisation penalty function in order to consider the transverse shear effect. This modified penalty function leads to a new methodology whereby the thickness of laminated composite plate is minimized by optimising the fibre orientations for different load cases. Therefore, the effect of transverse shear forces is considered in this study. Simulated annealing (SA) is used to search for the optimal design. This optimisation algorithm has been shown to be reliable as it is not based on the starting point, and it can escape from the local optimum points. In this research, the Tsai-Wu failure and maximum stress criteria for composite laminate are chosen. By applying two failure criteria at the same time the results are more reliable. Experimentally generated results show a very good agreement with the numerical results, validating the simulated model used. Finally, to validate the methodology the numerical results are compared to the results of previous research with specific loading.

Determination of the static pressure loads on a marine composite panel from strain measurements utilising artificial neural networks

One of the first steps in marine structural design is to calculate the wave-induced loads and load combinations. In contrast with both the hydrostatic loads and the self-weight loads which can be evaluated with a high degree of confidence, it is more difficult to measure the in-service hydrodynamic loads generated by sea waves. Direct pressure load measurement techniques can currently provide only data at finite locations while classical analytical techniques require knowledge of all the parameters that influence the load and that each parameter is studied independently. Therefore, a novel technique is required to overcome these limitations by providing a method of measuring the pressure load over large areas with relatively few sensors and minimal data collection. This paper reports research undertaken to develop an inverse problem approach utilising an artificial neural network for measurement of the pressure loads experienced by marine structures. The suitability and performance of utilising an artificial neural network for quantifying the pressure load applied to a marine structure is presented. It was found that the artificial neural network was able to estimate accurately the pressure loads applied to up to 12 locations on the structure. It is concluded that the inverse problem approach can be used to estimate the applied loads on the marine structure in real time from strain measurements.

A semi-analytical model for deflection analysis of laminated plates with the Newton-Kantorovich-Quadrature method

A semi-analytical approach for analysis of laminated plates with general boundary conditions under a general distribution of loads is developed. The non-linear equations are solved by the Newton-Kantorovich-Quadrature (NKQ) method which is a combination of well-known Newton-Kantorovich method and the Quadrature method. This method attempts to solve a sequence of linear integral equations. The convergence of the proposed method is compared with other semi-analytical methods. The validation of the method is explored through various numerical examples and the results compared with finite element method (FEM) and experimental tests. Good agreement between the NKQ model, FEM and experimental results are shown to validate the model.

In-Service Transient Load Measurement on a Large Composite Panel

Current practices to estimate the pressure loads on the hull of small high-speed craft in a seaway are based on determination of the wave loads by applying rules and standards which itself relies either on often conservative methods, leading to a craft that is heavier and slower than it could be otherwise. There are rather large uncertainties in the wave load predictions for ships mainly caused by not necessarily sufficient theoretical basis of the calculation methods. Direct pressure measurement techniques can only provide data at each transducer location and classical analytical techniques require a large amount of experimental data to be collected to relate pressure to the structures response. The evaluation of wave generated hydrodynamic loads is less reliable as the dynamic nature of the loading as well as transient effects such as slamming and green water on deck still demands more investigations. Therefore, a novel technique is required to overcome these limitations by providing a method of measuring the pressure load with relatively few sensors and minimal data collection. This paper reports on research undertaken to develop an inverse problem approach utilising an Artificial Neural Network (ANN) for quantification of in-service, transient loads in real-time acting on the craft from the craft’s structural response (strain response to load). This study investigates suitability and performance of utilising ANN as an inverse problem approach to estimate impact loads applied to up to 13 locations on the structure in real-time from 16 strain measurements.

Sensor Optimisation for in-Service Load Measurement of a Large Composite Panel under Small Displacement

Current methods to estimate the behaviour of composite structures are based on trial and error or oversimplification. Normally the nonlinearities in these structures are neglected and in order to cover this inadequacy in design of composite structures, an overestimate safety factor is used. These methods are often conservative and leading to the heavier structures. A novel technique employs Artificial Neural Network (ANN) as an inverse problem approach to estimate the pressure loads experienced by marine structures applied on a composite marine panel from the strain measurements. This can be used in real-time to provide an accurate load history for a marine structure without requiring knowledge of the material properties or component geometry. It is proposed that the ANN methodology, with further research and development, could be utilised for the quantification of in-service, transient loads in real-time acting on the craft from the craft’s structural response (strain response to load). However, to fully evaluate this methodology for load monitoring of marine structures further research and development is required such as sensor optimisation. The number of sensors should be minimised to reduce the time to train the system, cost and weight. This study investigates the number of sensors required for accurate load estimation by optimising the method.

A Semi-Analytical Model for Buckling of Laminated Plates with the NKQ Method

A semi-analytical approach for analysis of laminated plates with general boundary conditions under a general distribution of loads is developed. The non-linear equations are solved by the Newton-Kantorovich-Quadrature (NKQ) method which is a combination of well-known Newton-Kantorovich method and the Quadrature method. This method attempts to solve a sequence of linear integral equations. In this paper this method is used to propose a semi-analytical model for buckling of laminated plates. The convergence of the proposed method is investigated and the validation of the method is explored through numerical examples and the results compared with finite element method (FEM). There is a good agreement between the NKQ model and FEM results.

HIGH PERFORMANCE ROPES FOR CATENARY MOORING

The paper describes the criteria for selection of ropes for catenary mooring systems and discusses the alternative solutions for a modern catenary mooring system. The mechanical properties of high performance synthetic fibre ropes, namely aramid, HMPE and LCP, are analyzed. These materials are attractive for applications requiring high stiffness, high tenacity and low density. Advantages and limitations of these ropes, relative to the medium performance fibre ropes, such as nylon and polyester, and steel wire ropes, is also discussed in the light of the requirements for mooring applications.