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The quest to diversify the renewable energy producing systems has led to the development of wave energy converters. To get to a viable commercial wave energy converter system it is very crucial to have a levelized cost to energy for the system. This is done driving forward the system level optimization and upgradation for the whole wave energy converter. In this thesis, the focus was the support for the development of a full scaled composite pretension cylinder. Different predictive models were identified and studied to characterize the effects due to the cyclic reciprocating contacts on the composite pretension cylinder. The results of which, gave an early input to move forward towards more accurate testing leading to the development of a test rig. The test rig once developed could provide with the long term required data so that the actual composite pretension cylinder be designed and integrated onto the wave energy converter. / Strävan efter att diversifiera de system som producerar förnybar energi har lett till utvecklingen av vågenergiomvandlare. För att komma till ett livskraftigt kommersiellt vågenergiomvandlingssystem är det mycket viktigt att ha en nivåiserad energikostnad för systemet. Detta görs för att förbättra systemnivåoptimeringen och uppgraderingen för hela vågenergiomvandlaren. I denna avhandling var fokus stödet för utvecklingen av en fullskalad komposit förspänningscylinder. Olika prediktiva modeller identifierades och studerades för att karakterisera effekterna på grund av de cykliska fram- och återgående kontakterna på den sammansatta förspänningscylindern. Resultaten gav en tidig input för att gå vidare mot mer exakta tester, vilket ledde till utvecklingen av en testrigg. Den testrigg som en gång utvecklats kan ge långsiktigt erforderliga data så att den faktiska sammansatta förspänningscylindern kan utformas och integreras i vågenergiomvandlaren.

Discussed is a numerical and experimental characterization of the response of small-scale fiber-reinforced composite cylinders constructed to represent a fuselage design whereby the crown and keel consist of one laminate stacking sequence and the two sides consist of another laminate stacking sequence. This construction is referred to as a segmented cylinder. The response to uniform axial endshortening is discussed. Numerical solutions for the nonlinear prebuckling, buckling, and postbuckling responses are compared to experimental results. Focus is directed at the investigation of two specific cylinder configurations, referred to as axially-stiff and circumferentially-stiff cylinders. Small-scale cylinders, each having a nominal radius of 5 in., were fabricated on a mandrel by splicing adjacent segments together to form 0.5 in. overlaps. Finite-element models of both cylinder configurations, including the overlap regions, are developed using the STAGS finite-element code. Perfectly circular cylinder models are considered, as are models which include the measured geometry of the specimens as an imperfection. Prebuckling predictions show that the segmented cylinder response is characterized by the existence of circumferential displacement, and an axial boundary layer accompanied by circumferential gradients in radial displacement. Experimental measurements, taken with strain gages and displacement transducers, confirm these numerical findings. As the endshortening approaches the critical, or buckling, values, the response of the cylinders is characterized by wrinkling in the axial direction. In the axially-stiff cylinder, the crown and keel segments wrinkle, while in the circumferentially-stiff cylinder the side segments wrinkle. Experimental images taken from Moire interferometry show this response in the circumferentially-stiff cylinder. Four methods are used to predict the buckling values of endshortening and load for both cylinders, and the four values are in good agreement. The experimentally-measured buckling conditions, however, show that the models overpredict buckling values. For the axially-stiff cylinder, the difference could be due to the fact material failure not included in the model plays a role in the cylinder response. For the circumferentially-stiff cylinder, the difference is definitely due to material failure characteristics not included in the model. The predicted postbuckling response of the segmented cylinders is shown to be dominated by the existence of inward dimples in some or all of the segments. For the axially-stiff cylinder, the as-predicted dimpled crown and keel configuration is observed in the experiment but at a load 12 percent below predicted values. For the circumferentially-stiff cylinder material failure in the linear prebuckling range of response triggered buckling that resembled the predicted circumferential rings of dimples, but at a load 31 percent below predictions. Finally, it is shown that the effect of including the measured imperfections in the model has little observable effect on the circumferentially-stiff cylinder. For the axially-stiff cylinder the inclusion of the imperfections is found to effect the transition from buckling to postbuckling, but ultimately has little effect on postbuckling deformations. / Ph. D.

The initiation and propagation of adiabatic shear bands is analyzed numerically for an impulsively loaded thick-walled steel tube. A circumferential V-notch located at the outer surface of the center of the tube provides a stress concentration. The material is modeled as strain hardening, strain-rate hardening and thermal softening. The dynamic loading conditions considered are pure torsion, axial pressure combined with torsion, and internal pressure combined with torsion. Because of the stress concentration, a shear band will first initiate in an element adjoining the notch tip and propagate radially inwards through the thickness of the tube. The speed of propagation and the amount of energy required to drive a shear band through the material are calculated. The effects of the pressure preload and the depth of the notch are studied. Also, the influence of thermal softening is investigated by modeling it after a relation proposed by Zhou et al. <i>[Vita removed July 18, 2008 CK/GMc 2/2/2012]<i> / Master of Science

A three-dimensional, nonlinear dynamic analysis is conducted on a fully submerged, rigid, solid cylinder to be used as a breakwater. The breakwater could potentially be used as a single cylinder to protect small structures. Alternatively, multiple cylinders could be positioned in series to protect shorelines, harbors, or moored vessels from destructive incident water waves. The cylinder is positioned with its axis horizontal and is moored to the seafloor with four symmetrically placed massless mooring lines connected at the ends of the cylinder. The mooring lines are modeled as both linearly elastic ("regular") springs and compressionless springs. All six degrees of freedom of the structure are considered. The breakwater is modeled in air with a net buoyant force acting through the cylinder's center of gravity. The six "dry" natural frequencies of the structure are computed. Both linear and nonlinear free vibrations of the structure are considered. Linear damping is used to model the fluid and mooring damping effects. Normal and oblique harmonic wave forces at various frequencies and amplitudes are applied to the cylinder. The effects of the forcing amplitude and frequency, and the coefficient of damping, on the motion of the breakwater are studied. The results show that more erratic behavior occurs for the breakwater with compressionless springs, mainly due to the development of snap loads in the mooring lines. / Master of Science

An analytical and experimental investigation of the response of composite cylinders of elliptical cross-section to axial compression and internal pressure loadings is discussed. Nine eight-ply graphite-epoxy elliptical cylinders, three layups for each of three cross sectional aspect ratios, are specifically examined. The lay-ups studied are a quasi-isotropic (±45/0/90)_g, an axially-stiff (±45/0₂)_g, and a circumferentially-stiff (±45/90₂)_g. The elliptical cross sections studied are characterized by semi-minor axis (b) to semi-major axis (a) ratios of b/a = 0.70, 0.85, and 1.00 (circular). The cross sections are obtained by holding the semi-major axis constant for all cross sections, and only varying the semi-minor axis. The nominal semi-major axis for all specimens was 5.00 in. (127 mm), and all specimens were cut to the same length, which provided a length-to-radius ratio of 2.9 for the circular cylinders. For the elliptical cross section cylinders, the length to- radius ratios, L/R(s), ranged from two to slightly greater than six, where R(s) is the function describing the circumferential variation of the radius. A geometrically nonlinear special-purpose analysis, based on Donnell’s nonlinear shell equations, is developed to study the prebuckling responses of geometrically perfect cylinders. In this analysis the circumferentially-varying radius of curvature of the cylinder is expanded in a cosine series. While elliptical sections are studied here, it should be noted that such an expansion will accommodate any cross section with at least two axes of symmetry. The displacements are likewise expanded in a harmonic series using the Kantorovich method. The total potential energy, written in terms of the displacements, is then integrated over the circumferential coordinate. The variational process then yields the governing Euler-Lagrange equations and boundary conditions. This process has been automated using the symbolic manipulation package Mathematica ©. The resulting nonlinear ordinary differential equations are then integrated via the finite difference method. A geometrically nonlinear finite element analysis is also utilized to compare with the prebuckling solutions of the special-purpose analysis and to study the prebuckling and buckling responses of geometrically imperfect cylinders. The imperfect cylinder geometries are represented by an analytical approximation of the measured shape imperfections. An accompanying experimental program is carried out to provide a means for comparison between the real and theoretical systems using a test fixture specifically designed for the present investigation to allow for both axial compression and internal pressurization. A description of the test fixture is included. Three types of tests were run on each specimen: (1) low internal pressure with no axial end displacement, (2) low internal pressure with a low level compressive axial displacement and, (3) compressive axial displacement to failure, with no internal pressure. The experimental data from these tests are compared to predictions for both perfect and imperfect cylinder geometries. Prebuckling results are presented in the form of displacement and strain profiles for each of the three sets of load conditions. Buckling loads are also compared to predicted values based upon classical estimates as well as linear and nonlinear finite element results which include initial shape imperfections. Lastly, the postbuckling and failure characteristics observed during the tests are described. / Ph. D.

This thesis examines the flow around bluff bodies placed at the floodplain edge in a compound, open channel. The floodplain edge location is associated with a strong shear layer between lower velocity floodplain flow and high velocity flow in the main channel. The drag force exerted by a bluff body is dependant on the way in which the flow separates around the body and subsequently recovers but the drag coefficients typically used to represent the effects of bluff bodies are based on experiments on bodies in geometrically simple channels. The differences induced in the wake structures and therefore in the drag coefficients of bluff bodies when they are placed in the shear layer at the floodplain edge are little understood. In this study, experimental data is gathered that allows direct comparison of the wakes of identical bluff bodies, both emergent (surface-piercing) and submerged, in simple and compound open channels. For the compound channel scenarios, for both single and multiple block arrangements, turbulence data is also reported. These results are augmented using a computational model based on the solution of the 3D Reynolds Averaged Navier Stokes equations, using a non-linear turbulence model. The results show that the changes induced in the wake structures due to their location at the floodplain edge of the compound channel can have a significant effect on the drag coefficient. For the emergent bodies, the proximity of the deep main channel flow is shown to impact in a complex manner upon the processes of reattachment and re-separation, changing the formation of vorticity in the wake. For the submerged bodies, this is complicated by asymmetry in the same processes on the block top. For both body types, separation on the main channel side results in the creation of a strong axial circulation at the floodplain edge and the decay of the wake is asymmetrically affected by the differing behaviour of the turbulence on the two sides.

<p>Continuously throughout the process of developing Engine Control Units (ECU), the ECU and its control functions need to be dimensioned and tested for the engine itself. Since interaction between an ECU and a physical engine is both expensive and inflexible, software models of the engine are often used instead. One such test system, where an ECU interacts with software models, is called Hardware-in-the-Loop (HiL). This thesis describes a model constructed to facilitate implementation on a HiL testbed. </p><p>The model, derived in Matlab/Simulink, is a Cylinder-by-Cylinder Engine Model (CCEM) reconstructing the angle synchronous torque of a diesel engine. To validate the model, it has been parameterised for the DaimlerChrysler engine OM646, a straight turbocharged four cylinder diesel engine, and tested towards measured data from a Mercedes-Benz C220 test vehicle. Due to hardware related problems, validation could only be performed for low engine speeds where the model shows good results. Future work around this theme ought to include further validation of the model as well as implementation on HiL.</p>

Continuously throughout the process of developing Engine Control Units (ECU), the ECU and its control functions need to be dimensioned and tested for the engine itself. Since interaction between an ECU and a physical engine is both expensive and inflexible, software models of the engine are often used instead. One such test system, where an ECU interacts with software models, is called Hardware-in-the-Loop (HiL). This thesis describes a model constructed to facilitate implementation on a HiL testbed. The model, derived in Matlab/Simulink, is a Cylinder-by-Cylinder Engine Model (CCEM) reconstructing the angle synchronous torque of a diesel engine. To validate the model, it has been parameterised for the DaimlerChrysler engine OM646, a straight turbocharged four cylinder diesel engine, and tested towards measured data from a Mercedes-Benz C220 test vehicle. Due to hardware related problems, validation could only be performed for low engine speeds where the model shows good results. Future work around this theme ought to include further validation of the model as well as implementation on HiL.