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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Structural behaviour of glued laminated timber beams reinforced by compressed wood

Anshari, Buan January 2012 (has links)
As an engineered wood product, glued laminated timber (Glulam) is produced to minimise several natural weaknesses such as knots and non-uniform strength in order to enhance its stiffness and load carrying capacity. Many reinforcement methods have been tested, with promising results in increasing the strength and stiffness of beam. Recently, with increasing concern on environmental protection there is a growing trend in construction to use as many natural materials as possible. Therefore, conventional types of reinforcement using metals and/or synthetic materials do not fit well with this trend. A new approach to strengthen Glulam beams using pure natural materials has been established through this research. Glulam beams were strengthened by inserting compressed wood (CW) blocks into the pre-cut rectangular holes on the top of the beams. This practice was to make use of moisture-dependent swelling nature of the compressed wood. As a result, a pre-camber was produced in the mid-span of the beam reinforced. Significant initial tensile and compressive stresses were generated at both the top and the bottom extreme fibres of the beam, respectively. Material tests have been done to investigate material properties of compressed Japanese cedar with different compression ratios. Structural tests were undertaken for short and long Glulam beams strengthened by CW blocks after gained the pre-camber. 3-D finite element models have also been developed by using commercial code ABAQUS to simulate the pre-stressing behaviour of Glulam beams reinforced using compressed wood blocks. The finite element models were used to simulate the structural behaviour of the pre-stressed beams subjected to subsequent destructive bending tests. All computer models developed were validated against corresponding experimental results of the free moisture-dependent swelling, pre-stressing processes and the destructive tests for both the short and long beams. Reasonably good correlation was obtained in terms of the free swelling, the pre-camber, initial stress state of the Glulam beams reinforced and load-deflection relationships. Using validated computer models, parametric studies were further carried out to provide design information for such a reinforcing technique. The results have indicated that the reinforcing techniques using compressed wood blocks are very effective means to enhance the initial stiffness, bending strength and load carrying capacity of Glulam beams. The technology is ready to be applied in practice.

Model structure selection in powertrain calibration and control

Li, Zongyan January 2012 (has links)
This thesis develops and investigates the application of novel identification and structure identification techniques for I.C. engine systems. The legislated demand for reduced vehicle fuel consumption and emissions indicates that improved model-based dynamical engine calibration and control methods are required in place of the existing static set-point based mapping methods currently used in industry. The choice of structure of any dynamical engine model has significant consequences for the accuracy and the calibration/optimization time of engine systems. This thesis primarily addresses the issue of this structure selection. Linear models are well understood and relatively easy to implement however the modern I.C. engine is a highly nonlinear system which restricts the use of linear structures. Further the newer technologies required to achieve demanding fuel consumption and emission targets are increasingly more complex and nonlinear. The selection of appropriate nonlinear model regressor terms presents a combinatorial explosion problem which must be solved for accurate engine system modelling. In this thesis, two systematic nonlinear model structure selection techniques, namely stepwise regression with F-statistics and orthogonal least squares method with error reduction ratio, are accordingly investigated. SISO algebraic NARMAX engine models are then established in simulation studies with these methods and demonstrate the effectiveness of the approach. The thesis also investigates the development and application of multi-modelling techniques and the expansion of the model structure selection techniques to the identification of the local models terms within the multi-model structures for the engine. Based on the en- gine operating regions, novel multi-model networks can be established and several alternative multi-modelling techniques, such as LOLIMOT, Neural Network, Gaussian and log-sigmoid function weighted multi-models, for the multi-model engine system identification are explored and compared. An experimental validation of the methods is given by a black box identification of SISO engine models which are developed purely from the experimental engine test data sets. The results demonstrate that the multi-model structure selection techniques can be successfully applied on the engine systems, and that the multi-modelling techniques give good model accuracy and that good modelling efficiency can also be achieved. The outcome is a set of techniques for the efficient development of accurate nonlinear black-box models which can be acquired from experimental dynamometer test-bed data which should assist in the dynamic control of future advanced technology engine systems.

The energy-absorbing behaviour of novel aerospace composite structures

Zhou, Jin January 2015 (has links)
The aim of this research is to investigate the structural response of PVC foam based sandwich structures, composite reinforced foam cores and fibre metal laminates (FMLs) subjected to quasi-static and dynamic loading conditions. It also includes the investigation of the mechanical properties and energy-absorbing characteristics of the novel hybrid materials and structures for their potential use in aerospace and a wide range of engineering applications. Firstly,a series of experimental tests have been undertaken to obtain the mechanical properties of all constituent materials and structural behavior of the composite structures, which are used to develop and validate numerical models. The material tests carried out include (1) tension properties of composite laminates and aluminium alloys, (2) compression of PVC foams, carbon and glass fibre rods and tubes, and fibre metal laminates in the edge wise and flat wise, (3) shear and bending of PVC foams, (4) Hopkinson Bar, (5) quasi-static and dynamic crushing of composite reinforced foams, and (6) projectile impact on fibre reinforced laminates, aluminium alloy panels, PVC foam based sandwich panels and fibre metal laminates. The corresponding failure modes are obtained to validate the numerical predictions. In addition, perforation energy and specific energy absorptions of various composite structures investigated are evaluated. Moreover, the rate-sensitivity of FMLs based on glass fibre reinforced epoxy and three aluminium alloys has been investigated though a series of quasi-static and impact perforation tests on multilayer configurations ranging from a simple 2/1 lay-up to a 5/4 stacking sequence. FMLs based on a combination of the composite and metal constituents exhibit a low degree of rate-sensitivity, with the impact perforation energy increasing slightly in passing from quasi-static to dynamic rates of loading. Then, finite element (FE) models are developed using the commercial code Abaqus/Explicit to simulate the impact response of PVC foam sandwich structures. The agreement between the numerical predictions and the experimental results is very good across the range of the structures and configurations investigated. The FE models have produced accurate predictions of the impact load-displacement responses, the perforation energies and the failure characteristics recorded. The analyses are used to estimate the energy absorbed by the skins and the core during the perforation process. The validated FE models are also used to investigate the effect of oblique loading and to study the impact response of sandwich panels on an aqueous environment and subjected to a pressure differential (equivalent to flying at an altitude of 10000 m). The modelling has been further undertaken on the low velocity impact response of the sandwich structures based on graded or composite reinforced PVC foam cores, with reasonably good correlation to the corresponding experimental results. Consequently, a series of finite element analyses have been conducted to investigate the influence of varying foam density, rod diameter, rod length and fibre type on the energy-absorbing characteristics of the reinforced foams. Perforation energies, impact resistance performance and unit cost of the structures have been evaluated. Furthermore, the low velocity impact response of fibre metal laminates has been studied numerically. Here, the composite layer in FMLs is modelled using the modified 3D Hashin’s failure criteria, which are implemented into the main programme through a user-defined subroutine, whilst aluminium alloys are modelled using Johnson-Cook plasticity and the corresponding damage criterion. A large number of simulations have been undertaken to cover FMLs with all stacking sequences and alloy types studied, which are compared with the experimental results in terms of the load-displacement trace and failure modes, with very good correlation. Similar modelling work has been carried out on the aluminium layer and composite layer individually. The energy to perforate the various FMLs is plotted and fitted on a single curve that can be used to predict the perforation energies of other configurations. The dynamic characteristics of the composite structures through a series experimental tests and numerical predictions investigated in this project can be used in the design of lightweight composite structures for energy-absorbing applications.

Optimal dynamic calibration methods for powertrain controllers

Ostrowski, Kamil January 2015 (has links)
Emission legislation for passenger cars has become more stringent and the increasing demand for reduced fuel consumption has resulted in the introduction of complex new engine and after-treatment technologies involving significantly more control parameters. Vehicle manufacturers employ a time consuming engine parameter calibration process to optimise vehicle performance through the development of engine management system control maps. The traditional static calibration methods require an exponential increase in calibration time with additional calibration parameters and control objectives. To address this issue, this thesis develops and investigates a novel Inverse Optimal Behaviour Based Dynamic Calibration methodology and its application to diesel engines. This multi-stage methodology is based on dynamic black-box modelling and dynamic system optimisation. Firstly the engine behaviour is characterized by black-box models, based on data obtained in a rapid data collection process, for accurate dynamic representation of a subject engine. Then constrained dynamic optimisation is employed to find the optimal input-output behaviour. Finally the optimal input-output behaviour is used to identify feedforward dynamic controllers. The current study applies the methodology to an industrial state-of-the-art WAVERT model of a 1.5 litre Turbo EU6.1 Diesel engine acting as a virtual engine. The approach directly yields a feedforward controller in a nonlinear polynomial structure which can either be directly implemented in the engine-management system or converted to a dynamic or static look-up table format. The results indicate that the methodology is superior to the conventional static calibration approach in both computing efficiency and control performance. A low-cost Transient Testing Platform is presented in this work to carry out transient data collection experiments on a steady-state dynamometer with application to non-linear engine and emissions modelling using State Space Neural Networks. This modelling technique is shown to be superior to the polynomial models and achieves similar performance to non-linear autoregressive with exogenous input neural (NARMAX) network models. Numerical Dynamic Programming is investigated in a simplified engine calibration problem for a virtual engine to potentially improve the dynamic calibration optimisation stage. In a second study the novel dynamic calibration methodology is applied to the airpath control of a 3.0L Jaguar Land Rover (JLR) turbocharged Diesel engine utilizing a direct optimisation approach and State Space Neural Network models. A complete experimental application of the methodology is demonstrated in a vehicle where the vehicle-implemented calibration is obtained in a one-shot process solely from data obtained from the fast dynamic dynamometer testing. The results obtained demonstrate the potential of this methodology for the rapid development of efficient dynamic feedforward controllers based on limited data from the engine test bed.

Development of a new Euler-Lagrange model for the prediction of scour around offshore structures

Li, Yaru January 2015 (has links)
Numerical modelling of scour around offshore structures is still a challenging research topic for engineers and scientists due to the complex flow-structure-seabed interactions. In comparison to single-phase models and Eulerian models with Exner equation, a multiphase approach has advantages in interpreting the flow-particle and particle-particle interactions. In the present study, an Euler-Lagrange multiphase approach is adopted to develop a new scour model in order to simulate the air-water-sediment interplay simultaneously while being computationally efficient. The model is able to represent free-surface flow with a mobile bed, which is often critical for realistic scour modelling. Based on the open source computational fluid dynamics (CFD) software package OpenFOAM®, the model solves the Navier-Stokes equations on an Eulerian computational grid. The sediment particles are traced using the multiphase particle-in-cell (MP-PIC) method in a Lagrangian approach. The drag force from the fluid, body forces and inter-particle stresses as well as the interphase momentum transfer are all accounted for in the model. The model system is calibrated using several simple test cases, including a falling particle and steady flow passing isolated blocks, to identify optimal parameters for model operation. The model is then validated against available experimental data on a steady current around a vertical cylinder and sand suspension under oscillatory sheet flow, amongst other tests, with satisfactory agreement. Application of the model against laboratory experiments includes benchmark scour cases underneath a horizontal pipeline under currents and waves, respectively. The tunnel erosion and lee-wake erosion stages are captured well by the model. The scour prediction matches with the measurements. In addition, the onset of scour is reproduced vigorously without any additional numerical assumptions or approximations. The model's capability to resolve the scour process and reveal the mechanisms involved is presented well.

Intelligent synthesis of nanoparticles

Krishnadasan, Siva Haran January 2008 (has links)
No description available.

Development of 3D skin models for the detection of human melanoma using phosphorescence lifetime imaging microscopy

Raza, Ahtasham January 2015 (has links)
Solid tumours display varied oxygen levels and this characteristic can be exploited to develop new methodologies for detection. MCTS provides a useful model that mimic in vivo tumour microenvironment with varied metabolic gradient (oxygen, pH, glucose and ATP). Emission quenching of phosphorescence compounds by O2 is becoming a wide spread approach for sensing oxygen by optical method within biological model. The approach depends on the correlation of the lifetime of the phosphorescent probe with O2 pressure. The aim is to study the cell penetration and oxygen measurement potential of a novel phosphorescent PtLsCl probe in 2D and 3D biological models using a high resolution 1 and 2-photon emission Phosphorescence Lifetime Imaging Microscopy (PLIM). Quantitative analysis of fluorescence emission intensity and lifetime within cellular compartment showed preferred accumulation of PtLsCl in nucleoli of cells. Immunohistology experiments by Hypoxyprobe™ suggested hypoxia within MCTSs were dependent upon culture condition of MCTS (i.e. size and culture days). Thereafter, emission lifetime detected by 1 or 2-photon PLIM showed marked differences across the 3D MCTS and the variation in lifetime was dependent upon culture condition (size and culture days) of MCTS, suggesting varied oxygen concentration. The distribution of emission lifetime of PtLsCl in whole spheroids ranged from 0 to 12 microseconds with phosphorescence lifetime imaging revealing three distinct lifetime-related oxygen areas. Thereafter, emission lifetime of PtLsCl in the whole melanoma tissue engineered model was analysed. Distribution emission ranged from 0 to 13 microseconds, with phosphorescence lifetime imaging revealing three distinct areas – 1) a normal stromal region of 0 to 4.0 μsec; 2) a spheroid border 4.0 to 6.0 μsec and 3) an inner core of MCTS 6.0 to 13.0 μsec. A marked deviation in lifetime of PtLsCl across the melanoma tissue engineered model clearly demarcated tumour area within normal stroma. It is proposed that the depletion of O2 is known to increase the emission lifetime of the PtLsCl label described herein, and PtLsCl incorporated with 1 or 2 PE-PLIM system demonstrated an excellent potential for high-resolution mapping of oxygen concentration in multi-cellular tissue models. Furthermore, both 1 and 2P-PLIM of a highly sensitive PtLsCl label has shown the potential to detect changes in partial O2 pressure and related response (e.g. necrosis).

Modelling evoked local field potentials : an investigation into balanced synaptic excitation and inhibition

Luo, Jingjing January 2014 (has links)
No description available.

Modelling, analysis and forecasting of deep sea oxygen isotope variations response to orbital forcing

Condrea, Eliza Patricia January 2014 (has links)
No description available.

Synthesis, characterisation and properties of lithium pyrophosphate materials for lithium battery applications

Hsiao, Kuang-Che January 2014 (has links)
No description available.

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