Dissertations / Theses: 'Wave loading'

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Nerenberg, Jeffery G. "Blast wave loading of polymeric foams." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0024/MQ50647.pdf.

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Westphalen, Jan. "Extreme wave loading on offshore wave energy devices using CFD." Thesis, University of Plymouth, 2011. http://hdl.handle.net/10026.1/2878.

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Two commercial Navier-Stokes solvers are applied to wave-wave and wave-structure interaction problems leading to the final application of simulating a single float of the wave energy converter (WEC) Manchester Bobber in extreme waves and a fixed section of the Pelamis in regular waves. First the two software packages CFX and STAR CCM+ are validated against measured results from physical tank tests concerning the interaction of 3 non-linear focused wave groups of different steepness (Ning et al. 2007). The agreement for all of these cases is very good and could even be improved from first order to second order wave setup at the wavemaker. However, in preliminary regular wave tests, the damping of the waves is identified to be an issue, which is the reason for focusing the waves and placing the structures in the following experiments approximately one wavelength behind the wavemaker. The interaction of fixed vertical and horizontal cylinders in regular waves are simulated concerning the forces on the structures (Kriebel 1998, Dixon et al. 1979). For the horizontal cylinder non-linear force oscillations of double the wave frequency could be modelled in good agreement with physical tank data, where linearised models failed. For the vertical cylinder the problem of the secondary load cycle due to a backward-breaking wave behind the cylinder is of special interest (Stansberg 1997, Chaplin et al. 1997). Here, the horizontal forces on a slender cylinder with a diameter approximately equal to the wave height are simulated successfully. Furthermore, the highly non-linear wave run-up in front of the cylinder is resolved well in the numerical approach. The next set of simulations includes rigid body motion. Here, the forced oscillations of a cone shaped body near the still water surface is simulated. These results are compared with test data published by Drake et al. (2008). For these cases the non-linearity of the experiments is discussed by comparing the sum and differences of the force and surface elevation time histories for a set of simulations with opposite excursion of the cone. The hydrodynamic forces on the cone surface are resolved in very good agreement. The solution of the surface elevation close to the cone surface is also resolved reasonably well. After having validated the codes for fixed wave-structure interaction problems and forced motion, the CFD methods are finally applied to problems relevant to the survivability of WECs. First a single float in waves is modelled. This challenging case combines the extreme wave setup with a floating body problem in one and two degrees of freedom including the interaction of the float inertia with the inertia of a separate mass attached to it. The vertical translations of the float are compared with physical tank tests by Stallard et al. (2008). This case clearly demonstrates the capabilities and challenges in using CFD to simulate WECs. When representing the pulley and counterweight system by a simplified external body force rather than the full setup, the calculated translations of the float agreed better with the measured results from the physical tank test. Furthermore the codes are used to simulate a single fixed section of the Pelamis device in regular waves. The surface elevations close to the device are discussed and the forces acting on different strips on the structure are presented.

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Gustafsson, Egil. "Extreme loading and fatigue analysis of a wave energy device." Thesis, KTH, Marina system, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-198506.

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Wave energy is one of the possible solutions for meeting the future energy demand in a clean and sustainable way. Extracting large amounts of energy, a wave energy device would be subjected to extreme and fatigue loads from the waves. Designing such a device, a trade off needs to be done between making a device that is strong enough to withstand the loads and on the same time not too heavy making it inefficient and too costly. Having good estimations of extreme and fatigue loads are therefore critical when designing an efficient wave energy device. This thesis has aimed to create a tool that can be used between the already existing hydrodynamic and solid mechanic models available at CorPower Oceean. The goal has been that the tool shall extract the extreme and fatigue loads from the hydrodynamic model and format them in a way so that they can be used in the solid mechanical model. Four different tools have been created and compared for calculating fatigue using amplitude and spectral methods, where the amplitude methods also are able to estimate extreme loads. The fatigue tools have been evaluated against each other in a simple example showing that the estimated accumulated fatigue damage can be decreased by using several variables. An application of the tools has been done on a critical sub system of the wave energy device developed by CorPower Ocean. Where in this application critical points against extreme loading and fatigue have been localized. A new design has been suggested based on the strength analysis from the first one. Increasing the number of variables and using the tools developed in this thesis can significantly improve the fatigue damage estimations of the system. What fatigue method to use depends on the details for each case.

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Williams, Duncan Paul. "Scattering by wave-bearing surfaces under fluid loading." Thesis, University of Nottingham, 1999. http://eprints.nottingham.ac.uk/14370/.

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Wave-bearing surfaces and compressible fluids are often adjacent, the subsequent interactions are of substantial interest in structural acoustics, acoustic microscopy, seismology and many other fields. Here we take a broad view and discuss a variety of problems, both time harmonic and transient, which are amenable to exact solution. These in turn highlight physical effects and can additionally form the basis of asymptotic solutions. In structural acoustics the interaction of plate waves with defects is Cl major source of underwater noise. A model problem of two semi-infinite elastic plates (made of different material) joined in a variety of ways is considered for obliquely incident flexural plate waves. Asymptotic results for 'light' and 'heavy' fluid loading are extracted. In addition reciprocity and power flow relations, besides being of independent interest, provide a useful check on the results. There are many closely related problems involving a fluid loaded elastic solid. The situation here is somewhat similar, but often more complicated, due to the number of waves that an elastic solid supports, mode conversion at interfaces, and interfacial waves. We first address the scattering effects of low frequency waves by very small interfacial defects, that is, small relative to a typical wavelength. In this limit, and in related water wave or acoustic work, matched asymptotic expansions are used. An important aspect, that has not been noticed before, is the natural separation that occurs in the inner problem into fluid and solid pieces. A matching argument may now be used to give a useful physical interpretation of these defects and far field directivity patterns show the distinctive beaming that occurs along the Rayleigh angles in the light fluid loading limit. In many areas of interest embedded defects are imaged by pulses and we therefore require a transient analysis. In this case our problem involves a combination of compressional and shear source loadings beneath a fluid-solid interface. The exact solution is found and a full asymptotic analysis of this solution is performed with an emphasis upon wavefront expansions and leaky waves, and in particular, for 'light' and 'moderate' fluid loading. In some situations, when the sources are near the interface, a pseudo-compressional wavefront is generated and the limit as the loading approaches the interface is investigated. These non-geometric wave arrivals may be important in seismology and elastic wave studies related to the non-destructive evaluation of structures. This study is generalised to investigate the dynamic stress loading of subsurface cracks in either homogeneous or non-homogeneous media. An iterative method of solution based on physical considerations is developed and quantities of interest such as the scattered displacement fields and the stress intensity factors are determined. The problems considered here are ideally suited to analysis by transform methods and the Wiener-Hopf and Cagniard-de Hoop techniques.

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周奮鵬 and Fun-pang Chau. "Numerical methods in wave loading of large offshore structures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1985. http://hub.hku.hk/bib/B31206797.

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Hull, P. "Wave impact loading and its effects on blockwork structures." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246333.

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Chau, Fun-pang. "Numerical methods in wave loading of large offshore structures /." [Hong Kong] : University of Hong Kong, 1985. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12315916.

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Kozlowski, Tomasz. "Wave-Induced Loading of Submerged Core-Loc Armour Units." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/41870.

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This study investigates the relationship between wave-induced hydrodynamics and the resulting loading on Core-Loc concrete armour units below the still water level in a breakwater structure. Physical modelling experiments were performed at the National Research Council in Ottawa in which a 3D-printed 12 cm Core-Loc armour unit was instrumented and fixed in place within a rubble mound structure. Testing featured simultaneous measurement of force on this instrumented unit, pressure head at the base of the unit, and flow velocities below the SWL. Two main scenarios were tested, the isolated unit and fully armoured scenarios, under a range of regular waves and irregular sea states. Analysis of force development on the instrumented unit indicates that maximum slope-normal forces (both into and away from the structure) are associated with extremes in pressure head above the instrumented unit, while slope-parallel force extremes (both upslope and downslope) occur at times of the fastest change in water level. These loadings are consistent with Morison’s equation and imply drag dominance in the slope-parallel direction and inertia dominance in the slope-normal direction. Significant differences in forces were observed between isolated (no neighbouring units) and embedded (with neighbouring units) armour unit test cases. The presence of the armour layer significantly increased the normal force exerted on the unit and reduced the parallel force. Irregular sea state testing shows force peaks following normal distribution. Analysis of flow above the armour layer showed that force, flow velocity and flow acceleration are symmetrical in the slope-parallel direction, but largely asymmetrical in the slope-normal direction, with the flow velocity and force on the unit in particular experiencing large asymmetries. Wave height analysis indicated that each wave height follows a similar force development pattern with a magnitude proportional to wave height. Wave period analysis showed the formation of small secondary waves as the period increases. Wave steepness affected the peak force loading of the instrumented unit in a mostly linear fashion up to the critical Iribarren number.

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Smith, Robert H. "Energy absorption of sine wave beams subjected to axial impact loading." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1181251105/.

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Xu, Li. "Breaking wave slap loading on FPSO bows and shallow water cylinders." Thesis, University of Strathclyde, 2006. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25258.

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In 1989 the Schiehallion FPSO suffered bow damage from a steep fronted wave slap and the uncertainty in how to design for this type of loading became a concern to the oil industry and the regulators. The aim of this study is to research the insight of breaking wave impact on the bow of ship-type offshore structures experimentally and develop a methodology on how to design this type of loading. Steep wave impact pressures and the structural dynamic response on FPSO (shipshaped Floating oil Production Storage and Offloading vessel) bows are studied using 1180 scale instrumented models and time domain simulation with the funding from HSE and BP, a grant from EPSRC, associated in-kind industrial contributions, a University/Departmental Scholarship and an IMarEST Scholarship. This work has increased the understanding of the nature of the breaking waves that can cause large slap forces that are important for the design of offshore floating structures (and should also be relevant to ship design). Methods of generating model scale wave groups that should produce approximately the 1 in 3 hour maximum loads, when large waves break in unidirectional sea states prescribed by Hs and Tz, have been developed. These methods have been extended to spread seas and also to a 'partial' breaking wave in less steep seas, but no testing has taken place in spread seas or the longer period seas. In addition an empirical relationship has been determined that represents the steepening of a wave front based on the underlying linear wave. The forces and pressures from these waves have been measured on 1180 scale models of the Schiehallion FPSO and Loch Rannoch shuttle tanker. A time history simulation method of bow loading in random seas has been developed. It uses the wave front steepening relationship derived from the tests and a relatively simple slap force prediction based on velocity times rate of change of added mass. Incident wave pressure effects (with a non-linear correction) and added mass times acceleration forces are also included. Simple slam coefficient type formula has also been derived for easy application. The formula accounts for the effect of the size of the loaded area on the average pressure and the rise and decay times of the average pressure and, hence, the dynamic amplification of the response at the bow. The above experimental and theoretical work has considerably advanced the quantitative understanding of bow slap. Quantitatively we have some confidence in the most probable maximum slap force predictions in: long-crested seas with sea state steepnesses around 1114 - 1115 and when no air is trapped.

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Mai, Trí Cao. "On the role of aeration, elasticity and wave-structure interaction on hydrodynamic impact loading." Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/9884.

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Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The big research question is how the aeration of water and the elasticity of the structural section affect loading during severe environmental conditions. A further question is how the scattered waves from ships and offshore structures, the mooring line force and the structural response, which are known to affect local load and contribute to global load, will be affected by wave-structure interaction of a ship or offshore structure under non-breaking wave conditions. Three different experiments were undertaken in this study to try to answer these questions: (i) slamming impacts of a square flat rigid/elastic plate, which represents a plate section of the bottom or bow of ship structure, onto pure and aerated water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical rigid/elastic wall in pure and aerated water, where the wall represents a plate section of a hull; and (iii) wave-structure interactions of different FPSO-shaped models, where the models were fixed or taut moored. The experiments were carried out at Plymouth University’s COAST Laboratory. Spatial impact pressure distributions on the square plate have been characterised under different impact velocities. It was found that the impact pressures and force in pure water were proportional to the square of impact velocity. There was a significant reduction in both the maximum impact pressure and force for slamming in aerated water compared to that in pure water. An exponential relationship of the maximum force and the void fraction is proposed and its coefficients are found from drop test in this study. There was also a significant reduction in the first phase of the pressure and force impulse for slamming into aerated water compared with pure water. On the truncated wall, aeration also significantly reduced peak wave loads (both pressure and force) but impulses were not reduced by very much. For the case considered here, elasticity of the impact plate has a significant effect on the impact loads, though only at high impact velocities; here the impact loads were considerably reduced with increasing elasticity. Wave loading on the truncated wall was found to reduce with increasing elasticity of the wall for all investigated breaking wave types: high aeration, flip-through and slightly breaking wave impacts. In particular, impact pressure decreases with increasing elasticity of the wall under flip-through wave impact. As elasticity increases, the impulse of the first positive phase of pressure and force decreases significantly. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts. Scattered waves were generated from the interaction of focused wave groups with an FPSO model. The results show that close to the bow of the FPSO model, the highest amplitude scattered waves are observed with the most compact model, and the third- and fourth-harmonics are significantly larger than the incident bound harmonic components. At the locations close to the stern, the linear harmonic was found to increase as the model length was decreased, although the nonlinear harmonics were similar for all three tested lengths, and the second- and third-harmonics were strongest with the medium length model. The nonlinear scattered waves increased with increasing wave steepness and a second pulse was evident in the higher-order scattered wave fields for the fixed and free floating models. In addition, the higher harmonics of the mooring line force, and the heave and pitch motions all increased with increasing wave steepness. Incident wave angles of 0 (head-on), 10 and 20 degrees were experimentally investigated in this study. As the incident wave angle between the waves and the long axis of the vessel was increased from 0 to 20 degrees, the third- and fourth-harmonic scattered waves reduced on the upstream side. These third- and fourth-harmonic diffracted waves are important in assessing wave run-up and loading for offshore structure design and ringing-type structural response in fixed and taut moored structures. The second-, third- and fourth-harmonics of the mooring line force, and the heave and pitch motions decreased as the incident wave angle increased from 0 to 20 degrees.

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Omidvar, Pourya. "Wave loading on bodies in the free surface using smoothed particle hydrodynamics (SPH)." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/wave-loading-on-bodies-in-the-free-surface-using-smoothed-particle-hydrodynamics-sph(9d744522-6ecf-4496-a784-4ab08292e344).html.

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This thesis investigates wave loading on bodies in the free surface using smoothed particle hydrodynamics (SPH). This includes wave loading on fixed bodies, waves generated by heaving bodies in still water and the heave response of a body in waves, representing a wave energy device. SPH is a flexible Lagrangian technique for CFD simulations, which in principle applies to steep and breaking waves without special treatment allowing us to simulate highly nonlinear and potentially violent flows encountered in a real sea. However few detailed tests have been undertaken even with small amplitude waves.This research uses the open-source SPH code SPHysics. First two forms of SPH formulation, standard SPH with artificial viscosity and SPH-Arbitrary Lagrange Euler (ALE) with a Riemann solver, are used to simulate progressive waves in a 2-D tank. The SPH-ALE formulation with a symplectic time integration scheme and cubic spline kernel is found to model progressive waves with negligible dissipation whereas with the standard SPH formulation waves decay markedly along the tank. We then consider two well-defined test cases in two dimensions: progressive waves interacting with a fixed cylinder and waves generated by a heaving semi-immersed cylinder. To reduce computer time in a simple manner a variable particle mass distribution is tested with fine resolution near the body and coarse resolution further away, while maintaining a uniform kernel size. A mass ratio of 1:4 proved effective but increasing to 1:16 caused particle clumping and instability. For wave loading on a half-submerged cylinder the agreement with the experimental data of Dixon et al. (1979) for the root mean square force is within 2%. For more submerged cases, the results show some discrepancy, but this was also found with other modelling approaches. For the heaving cylinder, SPH results for the far field wave amplitude and vertical force on the cylinder show good agreement with the data of Yu and Ursell (1961). The variable mass distribution leads to a computer run time speedup of nearly 200% in these cases on a single CPU. The results of the vertical force and wave amplitude are shown to be quite sensitive to the value of the slope limiter in the Riemann solver for the 2-D heaving cylinder problem. A heaving 2-D wedge or 3-D cone whose oscillatory vertical motion is prescribed as the elevation of a focused wave group is a precise test case for numerical free-surface schemes. We consider two forms of repulsive boundary condition (Monaghan & Kos, 1999, and Rogers et al., 2008) and particle boundary force (Kajtar and Monaghan, 2009) for the 2-D wedge case, comparing the result with the experimental data of Drake et al. (2009). The repulsive boundary condition was more effective than the particle boundary force method. Variable particle mass with different kernel sizes was then tested for 2-D problems for mass ratios of 1:4, 1:16 and 1:4:16 with satisfactory results without particle clumping and instability. For the 3-D cone case, SPH reproduces the experimental results very closely for the lower frequency tested where there is no separation from the bottom surface of the body but for the higher frequencies the magnitudes of force minima were underestimated. The mass ratios of 1:8 and 1:8:27 in two and three nested regions are tested for the 3-D cone problem where a computer run time speedup of nearly 500% is achieved on 16 processors for the mass ratio of 1:8.Finally, the floating body of a heaving wave energy device known as the Manchester Bobber is modelled in extreme waves without power take-off. The results for a single float are in approximate agreement with the experiment.

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Banfi, Davide. "A field and laboratory study on the dynamic response of the Eddystone lighthouse to wave loading." Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/11607.

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Because little was known about how the masonry lighthouses constructed during the 19th century at exposed locations around the British Isles were responding to wave action, the dynamic response of the Eddystone lighthouse under wave impacts was investigated. Like other so called 'rock lighthouses', the Eddystone lighthouse was built on top of a steep reef at a site that is fully submerged at most states of the tide. Consequently, the structure is exposed to loading by unbroken, breaking and broken waves. When the breaking occurs, wave loading leads to complex phenomena that cannot be described theoretically due to the unknown mixture of air and water involved during the wave-structure interaction. In addition, breaking waves are generally distinguished from unbroken and broken wave due to the fact that they cause impulsive loads. As a consequence, the load effects on the structural response require a dynamic analysis. In this investigation the dynamic response of the Eddystone lighthouse is investigated both in the field and by means of a small-scale model mounted in a laboratory wave channel. In particular, field data obtained by the use of geophones, cameras and a wave buoy are presented together with wave loading information obtained during the laboratory tests under controlled conditions. More than 3000 structural events were recorded during the exceptional sequence of winter storms that hit the South-West of England in 2013/2014. The geophone signals, which provide the structural response in terms of velocity data, are differentiated and integrated in order to obtain accelerations and displacements respectively. Dynamic responses show different behaviours and higher structural frequencies, which are related to more impulsive loads, tend to exhibit a predominant sharp peak in velocity time histories. As a consequence, the structural responses have been classified into four types depending on differences of ratio peaks in the time histories and spectra. Field video images indicate that higher structural frequencies are usually associated with loads caused by plunging waves that break on or just in front of the structure. However, higher structural velocities and accelerations do not necessarily lead to the largest displacements of around a tenth of mm. Thus, while the impulsive nature of the structural response depends on the type of wave impact, the magnitude of the structural deflections is strongly affected by both elevation of the wave force on the structure and impact duration, as suggested by structural numerical simulations and laboratory tests respectively. The latter demonstrate how the limited water depth strongly affects the wave loading. In particular, only small plunging waves are able to break on or near the structure and larger waves that break further away can impose a greater overall impulse due to the longer duration of the load. As a consequence of the depth limited conditions, broken waves can generate significant deflections in the case of the Eddystone lighthouse. However, maximum accelerations of about 0.1g are related to larger plunging waves that are still able to hit the lighthouse with a plunging jet. When compared to the Iribarren number, the dimensionless irregular momentum flux proposed by Hughes is found to be a better indicator concerning the occurrence of the structural response types. This is explained by the fact that the Iribarren number does not to take into account the effects of the wide tidal range at the Eddystone reef, which has a strong influence on the location of the breaking point with respect to the lighthouse. Finally, maximum run up were not able to rise up to the top of the lighthouse model during the laboratory tests, despite this having been observed in the field. As a consequence, the particular configuration of the Eddystone reef and the wind could have a considerable bearing and exceptional values of the run up, greater than 40 m, cannot be excluded in the field.

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Crawford, Adam Randolph. "Measurement and analysis of wave loading on a full scale coastal structure." Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/837.

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The aim of this investigation was to measure and analyse wave loading on a full scale coastal structure in order to validate current breakwater design methods and to improve understanding of the physical processes involved. A range of new, robust field measurement instrumentation was developed and deployed at the chosen field site, the Alderney Breakwater in the Channel Islands. The instrumentation deployed in this particularly harsh wave loading environment included an array of wave loading pressure sensors together with co-located void fraction gauges, which were used to measure the percentage air entrained within the seawater. Wave data was measured by means of a sea bed array of six pressure sensors which were logged using an underwater data logger. Data from the instrumentation mounted on the breakwater wall was logged with a high specification remote data logger. Both the instrumentation and the data acquisition equipment were developed and adapted specifically for this investigation and as a result over 150 high quality data sets were recorded at very high logging rates, which allowed field data analysis at an unprecedented level. New calibration and data processing methods were developed for the analysis of this novel set of data records. Due to the meticulous planning, instrument development, data acquisition development, and deployment the data collected is, to the best of the Author's knowledge, the highest quality wave loading field data collected to date. The wave conditions measured at the site were used as inputs to three commonly used design methods for vertical coastal structures, which were used to estimate the maximum wave loading pressures over the height of the structure. The pressures and forces predicted by the models were contrasted with measured values and it was found that the Goda method (1985) predicted the events with a high degree of accuracy provided that the waves were not breaking directly onto the structure. When waves did break onto the structure high magnitude, short duration pressures were frequently measured which sometimes also acted over a very small spatial area. There was a large degree of temporal and spatial variability in the high magnitude breaking wave pressures and they were not accurately predicted by any of the models. The relationship between wave momentum flux and wave loading impulse was investigated both on a record by record basis and using a wave by wave analysis. For the Alderney field site a consistent relationship was found between the wave momentum flux and wave loading impulse, which could be used to estimate the wave loading impulse and duration for known wave input conditions. Features of interest were also identified from temporal comparisons of individual co-located pressure and aeration traces, including negative pressures and a negative correlation between air content and pressure over short time scales.

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Lambert, Luke. "Efficient probabilistic structural response prediction for aircraft turbulence and offshore wave loading." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2010819/.

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This thesis takes an interdisciplinary approach to the problem of the aleatory uncertainty manifest in the design of engineering structures that are subject to random loading, with specific application to continuous gust loading on aircraft and wave loading on offshore structures. The main focus is on aircraft gust loading because this is the area in which more significant progress is made. A review of the literature on gust loading is carried out to evaluate the sufficiency of existing methods and the possibility of a unified certification model is discussed. In order to obtain reliable probabilistic design loads using conventional stochastic simulation techniques, a large number of simulations are required to derive probability distributions that have adequately low sampling variability in the area of interest. A novel method, called the Efficient Threshold Upcrossing method, is developed that reduces the required number of simulations by at least 2 orders of magnitude. The method is initially developed for the efficient derivation of short-term offshore structural response statistics and is subsequently applied to the modelling of aircraft response to continuous turbulence. The ETU method was successfully extended to take into account long-term statistics of nonlinear aircraft response and it was shown that reliable design exceedance curves can be obtained by as little as 4\% of the computational cost of the conventional method. The current methods for the computation of design loads for nonlinear aircraft are limited to discrete, `1~-~cosine' gust encounters as the continuous turbulence models are only applicable to linear aircraft response. However, the most significant outcome of this thesis is that this is no longer the case, because the ETU method provides a way to calculate nonlinear response statistics in the time domain at a significantly lower computational cost. Mathematical models of a simple offshore structure, and both linear and nonlinear aircraft, are developed and a more robust technique is introduced for simulating patches of continuous turbulence. These models, which have the ability to generate random inputs, are used to derive response probability distributions for each of the test structures. The results obtained by applying the new approaches to these data sets show that they offer a marked improvement in performance.

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Lloyd, Alan. "Performance of reinforced concrete columns under shock tube induced shock wave loading." Thesis, University of Ottawa (Canada), 2010. http://hdl.handle.net/10393/28510.

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Recent events including deliberate attacks and accidental explosions have highlighted the need for greater research in structural response to blast loading. One of the primary research focuses has been on the prevention of progressive collapse of structures. The response of vertical load transferring members, such as columns, is of particular importance to progressive collapse prevention. In order to understand and predict the behaviour of the global structure during and after a blast loading event, a greater understanding of column behaviour must be developed. Currently there is a limited amount of experimental test data available on the response of reinforced concrete columns exposed to blast loads. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 14 half scale reinforced concrete columns were constructed and tested under blast pressures. The columns were designed according to Canadian Standard Association (CSA) Standard A23.3 for the "Design of Concrete Structures" (2006) standard as first story columns for both seismic and non-seismic regions. Axial load was applied to levels similar to what can be expected in actual structures. The columns were exposed to various pressure-impulse combinations which resulted in a range of column response. Comparisons are made between seismically designed and detailed columns and those that represent non-seismic gravity load columns in terms of displacement under similar shockwave loading. In addition, numerical analyses were conducted using single degree of freedom dynamic analysis. The numerical analysis accounts for the loss of axial load observed with horizontal displacement, strain rate effects on material strengths, the formation of plastic hinges in the column near the supports and at mid-height and the corresponding change in resistance and the response mode shape. The numerical analysis is validated with the experimental results and proven to accurately predict displacement of reinforced concrete columns under shock wave loading. The results indicate that an equivalent single degree of freedom model may be used to determine the response of a column under air blast induced shock loading if proper displacement-resistance models that account for material strength increase factors and change in axial load are used.

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Saalehi, Ahmad. "Quadtree-based finite element modelling of laminar separated flow past a cylinder." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308908.

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Olsson, Daniel. "Numerical simulations of energy absorbing boundaries for elastic wave propagation in thick concrete structures subjected to impact loading." Thesis, Umeå universitet, Institutionen för fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-58015.

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As many of the world’s nuclear power plants are near the end of their supposed life span a need arise to assess the components crucial to the safety of these plants. One of these crucial components is the concrete reactor confinement; to assess its condition, non-destructive testing (NDT) is an attractive method. Traditional testing of concrete structures has comprised of drilling out a sample and performing stress tests on it, but because of the radioactive environment inside the containment this method is far from ideal. NDT is of course possible to use at any structure but at reactor containments the benefits from not creating holes in the structure are prominent; NDT is also an attractive option from an esthetical point of view because it leaves the structure intact. The NDT method pertaining to this study is the impact echo method which comprise of applying a force on the structure, usually a hammer blow, and measuring the response with a receiver. The impact will excite waves propagating in the structure which gives rise to Lamb modes. Lamb modes are structural oscillations of the wall and it is the frequency of these modes that are used to determine the thickness of the wall. The elastic properties of the structure can in turn be obtained by measuring the velocities of the waves propagation. It is also possible to use the impact echo method to detect irregularities in the structure such as cracks or delamination. To simulate the dynamics of a system using NDT numerical methods such as finite element modeling (FEM) is often used. The purpose of this study is to assess the possibility to utilize absorbing layers using increasing damping (ALID) in models to reduce the computational time of FEM analyses. ALIDs are used at the edges to simulate an infinite system and are thus supposed to cancel out incoming waves to prevent unwanted reflection from the edges. The models in this study have all pertained to two dimensional plates utilizing infinitesimal strain theory; the decrease in computational time is significant when using ALIDs and for three dimensional models it would be even more so. The ALIDs are specified by length and maximum mass proportional Rayleigh damping (CMmax), in this study three different lengths are tested, 0.5, 1.5 and 4.5 m for CMmax ranging from 103 to 2*105 Ns/m. The damping is increased with increasing distance into the ALID with specified maximum value at the back edge. However, it should be noted that the increase in damping causes difference in impedance between elements and if this difference is too large it will cause reflections of waves at the boundary between the elements. The ALID must thus be defined so that it sufficiently cancels out the wave without causing unwanted reflections due to impedance differences. The conclusion is that the 0.5 m long ALID does not provide good results for any choice of maximum mass proportional Rayleigh damping. Both the 1.5 and 4.5 m long ALIDs are, however, concluded to be applicable; the 1.5 m ALID having 2*104 < CMmax <5*104 Ns/m and the 4.5 m ALID having 5*103 < CMmax < 104 Ns/m are choices that have shown promise in the performed simulations. The hope is that the results obtained in this study will aid in the development of numerical analysis techniques for NDT methods that can be used in the construction of new reactor confinements and/or maintenance of existing reactor confinements and other thick concrete structures.
Många av världens kärnkraftverk närmar sig slutet på sin beräknade livslängd och ett behov uppstår då att kunna utvärdera de komponenter som är väsentliga för säkerheten på dessa verk. Reaktoromslutningen i betong är en av dessa komponenter och oförstörande provning (NDT) är en attraktiv metod för att bedöma dess tillstånd. Traditionellt har utvärdering av betongkonstruktioner bestått av stresstester på borrprover men p.g.a. den radioaktiva miljön på insidan av omslutningen är denna metod ej att föredra. NDT är självklart möjligt att använda på allsköns betongkonstruktioner då det ger både konstruktionsmässiga och estetiska fördelar. NDT metoden som rör denna studie kallas impact echo och går ut på att man med en hammare slår till en punkt på väggen och mäter responsen en bit därifrån. Lasten ger upphov till vågor i form av deformation som propagerar i väggen och dessa ger i sin tur upphov till Lamb moder. Lamb moderna är strukturella oscillationer av väggen och genom att studera dess frekvenser kan väggens tjocklek bestämmas. Elastiska egenskaper i väggen erhålls utifrån de olika vågornas propageringshastigheter. Impact echo metoden kan även användas för att finna strukturella oegentligheter inuti väggen så som sprickor och delaminering. För att utföra numeriska simuleringar av dynamiska system med NDT-metoder är finita elementmetoden (FEM) användbar. Syftet med denna studie är att bedöma vilka möjligheter som finns för att implementera absorberande ränder med ökande dämpning (ALID) i datamodeller för att minska beräkningstiden av FEM-analyser. ALID används vid kanterna för att simulera ett oändligt system, dess uppgift är att dämpa bort inkommande vågor så att dessa ej reflekteras tillbaka och stör mätningarna. Samtliga modeller i denna studie är två-dimensionella med antagen oändligt liten spänning i normalriktningen. Vinsten i beräkningstid av att använda ALID är stor och ökar ytterligare om modellen utökas till tre dimensioner. Ett ALID definieras genom dess längd och maximala massproportionerlig Rayleigh-dämpning (CMmax). I denna rapport har längderna 0.5, 1.5 and 4.5 m använts med CMmax i intervallet från 103 till 2*105 Ns/m. Dämpningen ökar med ökat avstånd in i ALID med det specificerade maxvärdet vid den bakre kanten. Det bör noteras att skillnad i dämpning mellan element leder till skillnad i impedans; reflektioner av vågorna uppstår vid övergång från ett element med lägre impedans till ett med högre impedans. Ett ALID måste således vara definierat så att det dämpar bort tillräckligt av de inkommande vågorna utan att oönskade reflektioner i ALID uppstår. Studien pekar på att ett 0.5 m långt ALID inte åstadkommer önskvärda resultat för något av valen för CMmax som använts i denna rapport. Både det 1.5 och 4.5 m långa ALID har däremot get bra resultat; ett 1.5 m långt ALID bör ha 2*104 < CMmax <5*104 Ns/m och ett 4.5 m långt ALID 5*103 < CMmax < 104 Ns/m. Förhoppningen med studien är att resultaten skall underlätta utvecklingen av NDT-metoder som kan användas vid konstruktion och underhåll av reaktoromslutningar och andra tjocka betongkonstruktioner.

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19

Ahmad, Sahrim Haji. "High strain-rate behaviour of polymers using blast-wave and impact loading methods." Thesis, Loughborough University, 1988. https://dspace.lboro.ac.uk/2134/7496.

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20

Miyamoto, Junji. "The dynamics of liquefied sand under wave loading with applications to nearshore engineering." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/138475.

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21

Caputo, Piermodesto. "Hydrodynamic loading and structural dynamic assessment of offshore concrete lighthouse." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.

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Historic rock-mounted lighthouses play a vital role in the safe navigation around perilous reefs. Their longevity is threatened by the battering of waves which may be set to increase with climate change. The protection of this historic heritage needs the identification of both structural dynamic parameters (natural frequencies and shape modes), and of the worst-cases wave load combination, able to affect that natural frequencies. This dissertation was developed during a period of five months at University of Plymouth, along with the researching team of the project STORMLAMP. The project is divided in three parts; the first involving a meteocean analysis, developed by means of peak over threshold technique, aimed to address realistically a test campaign held afterwards. The second, focused on the dynamic analysis of the Dubh Artach lighthouse and was developed by means of a Matlab toolbox provided to the group by Prof. Brownjohn from Exeter University, partner of the project as well. It is aimed on one hand to detect the dynamic properties of the structure and, on the other hand, to recognize eventual directionality in the structural response. The third phase was held at Plymouth University laboratory “COAST”. During this phase, a laboratory campaign, involving more than 100 tests, allowed to perform a parametric analysis aimed to identify the parameters, of an extreme wave, that influence more the impact force and that the wave exerts on the structure. To extract impact time history, force signals were decomposed by means of Empirical mode decomposition and Duhamel integral algorithms. Image analysis, moreover, allowed to locate run-up caused by those waves upon a steel cylinder and to integrate a study of the run-up as well. The analysis led to several considerations useful on one hand for the prediction of the worst-case loading of the Dubh Artach lighthouse and, on the other hand, for the introduction of the NewWave theory for the design of coastal structures.

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22

Matemu, Christian Hillary. "Development of a One-Way Coupled Diffraction/Trapped Air Model for Predicting Wave Loading on Bridge Superstructure Under Water Wave Attack." UNF Digital Commons, 2018. https://digitalcommons.unf.edu/etd/823.

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In recent years, a number of researchers have applied various computational methods to study wind wave and tsunami forcing on bridge superstructure problems. Usually, these computational analyses rely upon application of computational fluid dynamic (CFD) codes. While CFD models may provide reasonable results, their disadvantage is that they tend to be computationally expensive. During this study, an alternative computational method was explored in which a previously-developed diffraction model was combined with a previously-developed trapped air model under worst-case wave loading conditions (i.e. when the water surface was at the same elevation as the bottom bridge chord elevation). The governing equations were solved using a finite difference algorithm in MATLAB for the case where the bridge was impacted by a single wave in two dimensions. Resultant inertial and drag water forces were computed by integrating water pressure contacting the bridge superstructure in the horizontal and vertical directions, while resultant trapped air forces (high-frequency oscillatory forces or sometimes called “slamming forces” in the literature) were computed by integrating air pressure along the bottom of the bridge deck in the vertical direction. The trapped air model was also used to compute the buoyancy force on the bridge due to trapped air. Results were compared with data from experiments that were conducted at the University of Florida in 2009. Results were in good agreement when a length-scale coefficient associated with the trapped air model was properly calibrated. The computational time associated with the model was only approximately one hour per bridge configuration, which would appear to be a significant improvement when compared with other computational technique

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23

Burrell, Russell P. "Performance of Steel Fibre Reinforced Concrete Columns under Shock Tube Induced Shock Wave Loading." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23516.

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It is important to ensure that vulnerable structures (federal and provincial offices, military structures, embassies, etc) are blast resistant to safeguard life and critical infrastructure. In the wake of recent malicious attacks and accidental explosions, it is becoming increasingly important to ensure that columns in structures are properly detailed to provide the ductility and continuity necessary to prevent progressive collapse. Research has shown that steel fibre reinforced concrete (SFRC) can enhance many of the properties of concrete, including improved post-cracking tensile capacity, enhanced shear resistance, and increased ductility. The enhanced properties of SFRC make it an ideal candidate for use in the blast resistant design of structures. There is limited research on the behaviour of SFRC under high strain rates, including impact and blast loading, and some of this data is conflicting, with some researchers showing that the additional ductility normally evident in SFRC is absent or reduced at high strain loading. On the other hand, other data indicates that SFRC can improve toughness and energy-absorption capacity under extreme loading conditions. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 13 half-scale steel fibre reinforced concrete columns, 8 with normal strength steel fibre reinforced concrete (SFRC) and 5 with an ultra high performance fibre reinforced concrete (UHPFRC), were constructed and tested under simulated blast pressures. The columns were designed according to CSA A23.3 standards for both seismic and non-seismic regions, using various fibre amounts and types. Each column was exposed to similar shock wave loads in order to provide direct comparisons between seismic and non-seismically detailed columns, amount of steel fibres, type of steel fibres, and type of concrete. The dynamic response of the columns tested in the experimental program is predicted by generating dynamic load-deformation resistance functions for SFRC and UHPFRC columns and using single degree of freedom dynamic analysis software, RCBlast. The analytical results are compared to experimental data, and shown to accurately predict the maximum mid-span displacements of the fibre reinforced concrete columns under shock wave loading.

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24

Corwin, Michael Thomas. "Inductively Loading a Half Width Leaky Wave Antenna to Control the Main Beam Direction." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1342464210.

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25

Rodriguez, Marcos. "The nonlinear wave loading and dynamic response of a freely-floating two-dimensional box." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/31524.

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This thesis concerns the nonlinear loading and dynamic response of a rectangular box in two dimensions. A fully-nonlinear potential flow model and a series of experimental procedures are employed to describe the nonlinearities governing the floating-body behaviour. Adopting this twin-track approach, nonlinear forcing components are found to make major contributions to both the excitation problem and the motion response. Two main sources of nonlinearity are established: a first associated with higher-order wave-structure interactions, and a second associated with viscous dissipation. The main advance of the present work lies in the quantification of the relative influence of these two sources. The first source, prevalent in steep wave conditions, is particularly significant in the diffraction regime and leads to significant excitation force amplifications. In deep water, these nonlinearities are primarily driven by interactions between the incident and the reflected wave components. The second source, due to viscosity, plays a minor role in the excitation problem, but has a major influence on the motion response. Viscous effects are critically important when the structure exhibits large motions, particularly at resonance. The relative importance of both types of nonlinearity is discussed in regular waves, focused wave groups and random seas. The first two cases are included to gain a clear physical description of the problem, whilst the random sea states are chosen to relate to practical ocean conditions. Experimental data is provided for sea states comprising in excess of 150,000 individual waves, presenting one of the most substantial data sets of this kind to date. In considering this random sea data, the two sources of nonlinearity are found to approximately balance in heave, with a load amplification due to wave-structure interactions and a motion reduction due to viscous dissipation. In roll, viscous dissipation dominates the overall response. Setting the work into its wider context, practical engineering approaches are also offered. A time-domain simulation, building upon a linear hydrodynamic description and a quadratic Morison's type drag term, is generally found to lead to a good agreement with the experimental data. An approach of this type is computationally very efficient, and hence suitable to day-to-day engineering practice.

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Berggren, Magnus. "Wave study Seaflex mooring system : Wave study to illuminate how first and second order wave force transfer to and affects the loading of flexible Seaflex mooring system." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-148136.

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When constructing a marina, one must consider many factors for calculating the mooring forces transferred to the mooring system of the docks. The forces transferred from waves is of course one of the most important. The wave induced forces may be described in different orders, the first-order wave forces from the frequency domain and the second-order wave forces determined from a wave field of different standing waves acting together. All floating objects are subjected to these wave forces, but for different mooring systems the transferred mooring force may vary. To describe the need for different calculations depending on the mooring system, a comparison to a spring system is made for both a Seaflex hawser and a guided pile system, which illustrates a significant difference in transferred mooring load. This is due to the hysteresis giving a low spring constant to the Seaflex hawser, which in turn transfers very little of the frequency induced first-order forces to the mooring system. This gives the conclusion that different methods for scaling the Seaflex mooring system is needed, since the first-order wave forces are not as significant than for a semi-rigid mooring system.

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27

Storhaug, Gaute. "Experimental investigation of wave induced vibrations and their effect on the fatigue loading of ships." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1521.

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This thesis represents an attempt to reveal and explain the mysterious excitation sources which cause global wave induced vibrations of ships. The wave induced vibrations of the hull girder are referred to as springing when they are associated with a resonance phenomenon, and whipping when they are caused by a transient impact loading. Both phenomena excite the governing vertical 2-node mode and possibly higher order modes, and consequently increase the fatigue and extreme loading of the hull girder. These effects are currently disregarded in conventional ship design. The thesis focuses on the additional fatigue damage on large blunt ships.

The study was initiated by conducting an extensive literature study and by organizing an international workshop. The literature indicated that wave induced vibrations should be expected on any ship type, but full scale documentation (and model tests) was mainly related to blunt ships. While the theoretical investigation of whipping mostly focused on slender vessels with pronounced bow flare, full scale measurements indicated that whipping could be just as important for blunt as for slender ships. Moreover, all estimates dealing with the fatigue damage due to wave induced vibration based on full scale measurements before the year of 2000 were nonconservative due to crude simplifications. The literature on the actual importance of the additional fatigue contribution is therefore scarce.

The workshop was devoted to the wave induced vibrations measured onboard a 300m iron ore carrier. Full scale measurements in ballast condition were compared with numerical predictions from four state-of-the-art hydroelastic programs. The predicted response was unreliable, and the programs in general underestimated the vibration level. The excitation source was either inaccurately described or lacking. The prediction of sea state parameters and high frequency tail behavior of the wave spectra based on wave radars without proper setting and calibration was also questioned. The measurements showed that vibrations in ballast condition were larger than in the cargo condition, the vibration was more correlated with wind speed than wave height, head seas caused higher vibration levels than following seas, the vibration level towards beam seas decayed only slightly, and the damping ratio was apparently linear and about 0.5%. The additional vibration damage constituted 44% of the total measured fatigue loading in deck amidships in the North Atlantic iron ore trade, with prevailing head seas encountered in ballast condition.

Four hypotheses, which may contribute to explain the high vibration levels, were formulated. They include the effect of the steady wave field and the interaction with the unsteady wave field, amplification of short incident waves due to bow reflection, bow impacts including the exit phase and sum frequency excitation due to the bow reflection. The first three features were included in a simplified program to get an idea of the relative importance. The estimates indicated that the stem flare whipping was insignificant in ballast condition, but contributed in cargo condition. The whipping was found to be sensitive to speed. Simplified theory was employed to predict the speed reduction, which was about 5kn in 5m significant wave height. The estimated speed reduction was in fair agreement with full scale measurements of the iron ore carrier.

Extensive model tests of a large 4-segmented model of an iron ore carrier were carried out. Two loading conditions with three bow shapes were considered in regular and irregular waves at different speeds. By increasing the forward trim, the increased stem flare whipping was again confirmed to be of less importance than the reduced bottom forces in ballast condition. The bow reflection, causing sum frequency excitation, was confirmed to be important both in ballast and cargo condition. It was less sensitive to speed than linear springing. The second order transfer function amplitude displayed a bichromatic sum frequency springing (at resonance), which was almost constant independent of the frequency difference. The nondimensional monochromatic sum frequency springing response was even higher. The sum frequency pressure was mainly confined to the bow area. Surprisingly, for the sharp triangular bow with vertical stem designed to remove the sum frequency effect, the effect was still pronounced, although smaller. The reflection of incident waves did still occur.

In irregular head sea states in ballast condition whipping occurred often due to bottom bilge (flare) impacts, starting with the first vibration cycle in hogging. This was also observed in cargo condition, and evident in full scale. This confirmed that the exit phase, which was often inaccurately represented or lacking in numerical codes, was rather important. Flat bottom slamming was observed at realistic speeds, but the vibratory response was not significantly increased. Stern slamming did not give any significant vibration at realistic forward speeds.

The fatigue assessment showed that the relative importance of the vibration damage was reduced for increasing peak period, and secondly that it increased for increasing wave heights due to nonlinearities. All three bows displayed a similar behavior. For the sharp bow, the additional fatigue damage was reduced significantly in steep and moderate to small sea states, but the long term vibration damage was less affected. The effect of the bulb appeared to be small. The contribution of the vibration damage was reduced significantly with speed. For a representative North Atlantic iron ore trade with head sea in ballast and following sea in cargo condition the vibration damage reduced from 51% at full speed to 19% at realistic speeds. This was less than measured in full scale, but the damping ratio of 1-3.5% in model tests was too high, and the wave damage in following seas in cargo condition was represented by head sea states (to high wave damage due to too high encounter frequency). Furthermore, the contribution from vibration damage was observed to increase in less harsh environment from 19% in the North Atlantic to 26% in similarWorld Wide trade. This may also be representative for the effect of routing. The dominating wave and vibration damage came from sea states with a significant wave height of 5m. This was in agreement with full scale results. In ballast condition, the nonlinear sum frequency springing appeared to be more important than the linear springing, and the total springing seemed to be of equivalent importance as the whipping process, which was mainly caused by bottom bilge (flare) impacts. All three effects should be incorporated in numerical tools.

In full scale, the vibration response reached an apparently constant level as a function of wave height in both ballast and cargo condition in head seas. This behaviour could be explained by the speed reduction in higher sea states. The vibration level in cargo condition was 60-70% of the level in ballast condition. Although common knowledge implies that larger ships may experience higher springing levels due to a lower eigenfrequency, a slightly smaller ore carrier displayed a higher contribution from the vibration damage (57%) in the same trade, explained by about 1m smaller draft. Moreover, the strengthening of the larger ship resulted in a 10% increase of the 2-node eigenfrequency. The subsequent measurements confirmed that an increased hull girder stiffness was not an effective means to reduce the relative importance of the vibration damage.

The relative importance of the excitation sources causing wave induced vibration may differ considerably for a slender compared to a blunt vessel. Therefore, full scale measurements on a 300m container vessel were briefly evaluated. The damping ratio was almost twice as high as for several blunt ships, possibly due to significant contribution from the container stacks. The reduced relative importance of the vibration damage with increasing wave height for the iron ore carrier in full scale was opposite to the trend obtained for the container vessel. Less speed reduction in higher sea states was confirmed, and the whipping process was apparently relatively more important for the container vessel. Both for the blunt and slender ship of roughly 300m length, the total fatigue damage due to vibration was of similar importance as the conventional wave frequency damage. The contribution to fatigue damage from wave induced vibrations should be accounted for, for ships operating in harsh environment with limited effect of routing, especially when they are optimized with respect to minium steel weight.

The four hypotheses were all relevant in relation to wave induced vibrations on blunt ships. Further numerical investigation should focus on the sum frequency springing caused by bow reflection and the whipping impacts at the bow quarter. The wave amplification, steady wave elevation and the exit phase must be properly incorporated. When it comes to design by testing, an optimized model size must be selected (wall interaction versus short wave quality). The speed must be selected in combination with sea state. The wave quality must be monitored, and a realistic damping ratio should be confirmed prior to testing. For the purpose of investigating sum frequency excitation, a large restrained bow model tested in higher waves may be utilized to reduce uncertainties in the small measured pressures.

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28

Mockute, Agota [Verfasser]. "Suitability of Wave Loading Models for Offshore Wind Turbine Monopiles in Rough Seas / Agota Mockute." Düren : Shaker, 2020. http://d-nb.info/1217164081/34.

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Mockutė, Agota [Verfasser]. "Suitability of Wave Loading Models for Offshore Wind Turbine Monopiles in Rough Seas / Agota Mockute." Düren : Shaker, 2020. http://nbn-resolving.de/urn:nbn:de:101:1-2020090605232739927321.

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30

McWilliam, S. "Response statistics under the action of first and second order wave forces and wind gust loading." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240898.

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31

Douglas, Steven. "Numerical Modeling of Extreme Hydrodynamic Loading and Pneumatic Long Wave Generation: Application of a Multiphase Fluid Model." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/34076.

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In this study, a three-dimensional two-phase (air and water) numerical solver is applied to investigate free surface flows. The first component aims to improve the overall understanding of the underlying physical mechanisms that occur during the interaction between turbulent hydraulic bores and simple structures. Data collected during large-scale physical experiments based on generating dam-break waves in a horizontal rectangular channel is used for comparing to the numerical results. An extensive sensitivity analysis on numerical parameters including spatial discretization and turbulence models is presented. Quantitative comparisons of numerical and experimental time series of water surface elevations, pressure, and net streamwise force exerted on the structure are used to validate the model. In the in-depth analysis, it is demonstrated that the model is able to simulate the pertinent aspects of the flow behaviour that occur during the interaction with good agreement. The numerical impulsive force generated at initial impact shows excellent agreement with the experimental results, particularly for the larger magnitudes bores considered. Since the numerical model treats the air as an incompressible media, the level of agreement observed between the experimental and numerical results suggests that the compressibility of the air in the leading edge of the bore during the physical testing had no significant effect on the measured impulsive force. The two-phase model was also able to capture the occurrence of a second transient spike in the force exerted on the structure when the initial runup collapsed back onto the incoming flow, trapping a pocket of air in the process. The model was further applied to investigate the effect of an initially quiescent layer of water in the downstream channel section on bore propagation characteristics and the subsequent interaction with the structure. It is demonstrated that for small nonzero values of initial downstream depth a substantial increase in bore depth occurs. However, further increases in the downstream depth did not appear have any significant effects. For the greatest downstream depth simulated, a considerable reduction in the hydrodynamic force is observed as a result of a more rapid closing of the wake that develops on the leeside of the structure. The second component of the study applies the same numerical solver to investigate a novel long wave generation technique for producing laboratory-scale tsunami waves. The concept is based on removing the air from the inside of a tank with a submerged outlet at the upstream end of the basin and releasing the water in a controlled manner. A similar procedure as described above was used to calibrate the numerical parameters to experimentally-measured wave heights and periods. To model the influence of the pneumatic valves mounted on top of the upstream chamber, time-varying pressure boundary conditions are developed to regulate and control the pressure inside the tank. Quantitative and qualitative comparisons of the numerical and experimental results show good agreement and a high potential for the solver to be used for similar investigations. An analysis is performed to improve the existing understanding of the wave formation process. The model is also applied to modify test configurations that influence the waveform for which the results may be used to aid in making operating decisions for future tests or in the design of similar wave generating devices.

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32

Aryawan, Iwan Darajat. "Development of analysis methods for the assessment of hull girder loading and strength of a turret moored FPSO." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327278.

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33

Chun, Sangeon. "Nonlinear Fluid-Structure Interaction in a Flexible Shelter under Blast Loading." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29849.

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Recently, numerous flexible structures have been employed in various fields of industry. Loading conditions sustained by these flexible structures are often not described well enough for engineering analyses even though these conditions are important. Here, a flexible tent with an interior Collective Protection System, which is subjected to an explosion, is analyzed. The tent protects personnel from biological and chemical agents with a pressurized liner inside the tent as an environmental barrier. Field tests showed unexpected damage to the liner, and most of the damage occurred on tent's leeward side. To solve this problem, various tests and analyses have been performed, involving material characteristics of the liner, canvas, and zip seals, modeling of the blast loading over the tent and inside the tent, and structural response of the tent to the blast loading as collaborative research works with others. It was found that the blast loading and the structural response can not be analyzed separately due to the interaction between the flexible structure and the dynamic pressure loading. In this dissertation, the dynamic loadings imposed on both the interior and the exterior sides of the tent structure due to the airblasts and the resulting dynamic responses were studied. First, the blast loadings were obtained by a newly proposed theoretical method of analytical/empirical models which was developed into a FORTRAN program. Then, a numerical method of an iterative Fluid-Structure Interaction using Computational Fluid Dynamics and Computational Structural Dynamics was employed to simulate the blast wave propagation inside and outside the flexible structure and to calculate the dynamic loads on it. All the results were compared with the field test data conducted by the Air Force Research Laboratory. The experimental pressure data were gathered from pressure gauges attached to the tent surfaces at different locations. The comparison showed that the proposed methods can be a good design tool to analyze the loading conditions for rigid or flexible structures under explosive loads. In particular, the causes of the failure of the liner on the leeward were explained. Also, the results showed that the effect of fluid-structure interaction should be considered in the pressure load calculation on the structure where the structural deflection rate can influence the solution of the flow field surrounding the structure.
Ph. D.

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34

Bullington, Amber L. "Thermal loading and modal frequency degeneracy in optical resonators for the Laser Interferometer Gravitational-Wave Observatory (LIGO) /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

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35

Abu, Husain Mohd Khairi. "Efficient (simulation) methods for derivation of probabilistic properties of offshore structural response due to random wave loading." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569889.

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Offshore structures are subject to a wide variety of environmental loads (such as wind, wave and current) all of which exhibit a high degree of statistical uncertainty. The dominant load, however, is normally due to wind-generated random waves. Probabilistic procedures can account for these uncertainties by establishing the statistical properties of loads and responses and hence are necessary for risk-based assessment of these structures. The major obstacle in establishing the probabilistic properties of the response is the nonlinearity of the wave load mechanism and/or the structural system which leads to non-Gaussian distribution for response. The problem is further compounded by current and by intermittent loading on members in the splash zone, which have a significant effect on the statistical properties of response. The most versatile and the most reliable technique for predicting the statistical properties of the response of an offshore structure to random wave loading is the time simulation technique. However, this technique requires very long simulations in order to reduce the sampling variability to acceptable levels. If this technique can be speeded up, then it would be an ideal technique because it does not suffer from any of the inadequacies of the alternative methods and is applicable to all different types of structures. This research is concerned with reducing the computational demand of the conventional time simulation (CTS) method. To this end, a more efficient version of the time simulation technique (ETS) has been introduced which divides the simulated response extreme values into a number of groups based on the magnitude of the extreme values of their associated surface elevation or linear response records. The probability distribution of extreme responses for each group is then calculated individually based on a relatively small number of simulations, and then the total probability theorem is used to derive the probability distribution of response extreme values. In this study, the probability distribution of response extreme values together with the 100-year responses from the ETS models have been compared with corresponding distributions and lOO-year responses from the CTS procedure to examine the accuracy and the efficiency of the efficient time simulation technique. Overall, four different structures, three different sea states and three different current situations have been investigated. This was necessary to ensure that the conclusions of this study are valid for a broad range of conditions. The ETS technique was found to be many times more efficient than the CTS method.

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36

Sui, T., C. Zhang, D.-S. Jeng, Yakun Guo, J. Zheng, W. Zhang, and J. Shi. "Wave-induced seabed residual response and liquefaction around a mono-pile foundation with various embedded depth." Elsevier, 2018. http://hdl.handle.net/10454/17990.

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Yes
Wave-induced seabed instability caused by the residual liquefaction of seabed may threaten the safety of an offshore foundation. Most previous studies have focused on the structure that sits on the seabed surface (e.g., breakwater and pipeline), a few studies investigate the structure embedded into the seabed (e.g. a mono-pile). In this study, by considering the inertial terms of pore fluid and soil skeleton, a three-dimensional (3D) integrated model for the wave-induced seabed residual response around a mono-pile is developed. The model is validated with five experimental tests available in the literature. The proposed model is then applied to investigate the spatial and temporal pattern of pore pressure accumulation as well as the 3D liquefaction zone around a mono-pile. The numerical simulation shows that the residual pore pressure in front of a pile is larger than that at the rear, and the seabed residual response would be underestimated if the inertial terms of pore fluid and soil skeleton are neglected. The result also shows that the maximum residual liquefaction depth will increase with the increase of the embedded depth of the pile.
This work was supported by the Fundamental Research Funds for the Central Universities [2017B15814], the International Postdoctoral Exchange Fellowship Program [20170014], National Science Foundation for Distinguished Young Scholars [Grant No. 51425901], Fundamental Research Funds for the Central Universities (2017B21514), Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province (2018SS02), Natural Science Foundation of Jiangsu Province [Grant No. BK20161509] and Open Foundation of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University [Project No: 2016491011].

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37

Lee, Keejoo. "A ceramic damage model for analyses of multi-layered ceramic-core sandwich panels under blast wave pressure loading." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2589.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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38

Najafian, G. "Local hydrodynamic force coefficients from field data and probabilistic analysis of offshore structures exposed to random wave loading." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317214.

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39

Host, Nicholas K. "Realization of a Low Cost Low Complexity Traveling Wave Antenna." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1420038529.

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40

Jain, Jayesh R. "Homogenization Based Damage Models for Monotonic and Cyclic Loading in 3D Composite Materials." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1230431496.

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41

Kowalczyk, Piotr Jozef. "Validation and application of advanced soil constitutive models in numerical modelling of soil and soil-structure interaction under seismic loading." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/275675.

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This thesis presents validation and application of advanced soil constitutive models in cases of seismic loading conditions. Firstly, results of three advanced soil constitutive models are compared with examples of shear stack experimental data for free field response in dry sand for shear and compression wave propagation. Higher harmonic generation in acceleration records, observed in experimental works, is shown to be possibly the result of soil nonlinearity and fast elastic unloading waves. This finding is shown to have high importance on structural response, real earthquake records and reliability of conventionally employed numerical tools. Finally, short study of free field response in saturated soil reveals similar findings on higher harmonic generation. Secondly, two advanced soil constitutive models are used, and their performance is assessed based on examples of experimental data on piles in dry sand in order to validate the ability of the constitutive models to simulate seismic soil-structure interaction. The validation includes various experimental configurations and input motions. The discussion on the results focuses on constitutive and numerical modelling aspects. Some improvements in the formulations of the models are suggested based on the detailed investigation. Finally, the application of one of the advanced soil constitutive models is shown in regard to temporary natural frequency wandering observed in structures subjected to earthquakes. Results show that pore pressure generated during seismic events causes changes in soil stiffness, thus affecting the natural frequency of the structure during and just after the seismic event. Parametric studies present how soil permeability, soil density, input motion or a type of structure may affect the structural natural frequency and time for its return to the initial value. In addition, a time history with an aftershock is analysed to investigate the difference in structural response during the earthquake and the aftershock.

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42

Kitchen, Ryan L. "Improving Steering Module Efficiency for Incremental Loading Finite Element Numeric Models." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1248.pdf.

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43

Shoaib, Muhammad. "Discrete element simulation of elasto-plastic shock waves in high-velocity compaction." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-31144.

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Elasto-plastic shock waves in high-velocity compaction of spherical metal particles are the focus of this thesis which consists of four papers (A-D). The compaction process is modeled by a discrete element method while using elastic and plastic loading, elastic unloading and adhesion at contacts. Paper A investigates the dynamic compaction of a one-dimensional chain of homogenous particles. The development of the elasto-plastic shock waves, its propagation and influence on the compaction process are examined. Simulations yield information on the contact behavior, velocity of the particle and its deformation during dynamic compaction. Effects of changing loading parameters on the compaction process are also discussed. Paper B addresses the non-homogeneity in a chain having; particles of different sizes and materials, voids between the particles and particles with/without adhesion between them. Simulations show transmission and reflection of elasto-plastic shock wave during compaction process. The particle deformation during incident and reflected shocks and particle velocity fluctuations due to voids between particles are simulated. The effects of adhesion on particles separation during unloading stage are also discussed. Paper C develops a simulation model for a high-velocity compaction process with auxiliary pistons, known as relaxation assists, in a compaction assembly. The simulation results reveals that the relaxation assists offer; smooth compaction during loading stage, prevention of the particle separation during unloading stage and conversion of higher kinetic energy of hammer into particles deformation. Furthermore, the influence of various loading elements on compaction process is investigates. These results support the findings of experimental work. Paper D further extends the one-dimensional case of Paper A and B into two-dimensional assembly of particles while adding friction between particles and between particles and container walls. Three particular cases are investigated including closely packed hexagonal, loosely packed random and a non-homogenous assembly of particles of various sizes and materials. Consistent with the one-dimensional case, primary interest is the linking of particle deformation with the elasto-plastic shock wave propagation. Simulations yield information on particle deformation during shock propagation and change in overall particles compaction with the velocity of the hammer. The force exerted by particles on the container walls and rearrangement of the loosely packed particles during dynamic loading are also investigated. Finally, the effects of presence of friction and adhesion on both overall particles deformation and compaction process are simulated.
QC 20110311

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44

Mikucka, Vita. "Dynamic problems for interface cracks under harmonic loading." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228606.

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This thesis is devoted to solution of the two-dimensional elastodynamic problem for a cracked bimaterial loaded by harmonic waves. The system of boundary integral equations for displacements and tractions at the interface is obtained from Somigliana identity with the allowance for the contact interaction of the opposite crack faces. Full expressions of the integral kernels derived by the consecutive differentiation of the Green's displacement tensor are given. Due to the contact that takes place between the faces of the crack under the applied external loading, the resulting process is a steady-state periodic, but not a harmonic one. Thus, components of the stress-strain state are expanded into exponential Fourier series. The collocation method with a piecewise constant approximation on each linear continuous boundary element is used for the numerical solution. The problem is solved using the iterative algorithm. The solution is refined during the iteration process until the distribution of physical values satisfies the imposed constraints. The results are obtained for the interface crack subject to normal tension-compression, normal shear, or oblique tension-compression waves with different values of the angle of the wave incidence and the wide range of the dimensionless wave number. The distributions of the normal and tangential components of the contact forces and displacement discontinuities on the surface of the crack are investigated. The stress intensity factors are computed and analyzed for various values of the wave frequency, the friction coefficient, and material properties. The maximal stress intensity factors at the trailing crack tip differ from the SIF values at the leading crack tip showing non-symmetry of solution with respect the space and time variables. It is concluded that the crack closure and friction effect change the solution both qualitatively and quantitatively, as the difference between comparable results can achieve 30-50%.

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45

Bailey, J. S. L. "Experimentally verified fluid loading models for slender horizontal cylinders in waves." Thesis, University of Sussex, 2000. http://sro.sussex.ac.uk/id/eprint/737/.

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This thesis reports on research work aimed at improving methods for predicting the fluid loading on fixed- and compliant offshore structures in waves. In focusing on slender member fluid-interaction models, the limitations and uncertainties associated with the widely-used Morison equation are examined. An improved empirical model has been developed and tested extensively alongside the Morison equation, using real experimental data. This improved model gives a better representation of the frequency dependency of the fluid-loading coefficients: this is particularly important in compliant motion conditions where the so-called relative velocity concept still needs to be verified under carefully controlled experimental conditions. The model is based entirely on the use of linear wave kinematics, thus simplifying calibration in irregular conditions and avoiding the need for a consistent non-linear wave theory (which is still lacking). By appropriate adaptation the improved model can also be extended to include amplitude dependency in the loading coefficients. The Improved Model has been developed through an analysis of experimental data. For this purpose the experimental work was focused on a horizontal cylinder, at model scale, located in a wave tank at the University of Sussex. The fluid loading experienced by a fixed cylinder, in both regular and irregular waves conditions, was measured and examined in detail. In addition, a comprehensive study of the loading on compliant cylinders, in both regular and irregular waves, was undertaken. Extensive use was made of appropriate parameter estimation techniques with initial attention (using simulated data) given to their accuracy for use with noisy experimental measurements. The effects of subtle (but undesirable) tank characteristics were also carefully taken into account. The study shows that, for fixed horizontal cylinders, benefits can be clearly identified in using the improved model, with frequency dependent coefficients, over the frequency dependent Morison equation. Moreover, the study shows that the relative velocity concept is more appropriate for use with the improved model than with the Morison model.

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46

Balech, Jean. "Análise da transferência de carga em estacas cravadas em argila mole à partir de provas de carga dinâmica de energia crescente." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/18/18132/tde-25062018-134808/.

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A utilização de métodos de análise apoiados na Teoria da Equação da Onda, a partir da instrumentação de medidas dinâmicas, como controle do comportamento de estacas, tem evoluído continuamente nos últimos anos. Após importantes considerações sobre a prova de carga dinâmica de energia crescente e o mecanismo de transferência de carga, procedem-se análises CAPWAP em um caso real de obra com o objetivo de analisar o comportamento do sistema estaca-solo perante a aplicação de níveis crescentes de energia. São apresentados nesta dissertação, os resultados do comportamento de vários sistemas isolados estaca-solo em maciço de argila mole, submetidos à prova de carga dinâmica de energia crescente. São feitas análises de: transferência de carga, atrito lateral local, quake da ponta, tensões dinâmicas e correlação entre prova de carga estática e dinâmica.
The use of analysis methods to control pile behavior employing the Stress-Wave Theory from results of dynamic pile driving measurements has evolved in recent years. After important considerations about the increasing energy dynamic loading test and the load transfer mechanism, CAPWAP analyses are proceed in a pilework with objective of analyzing the behavior of the pile-soil system before the application of growing levels of energy. Therefore, they are presented in this dissertation, the results of the behavior of several isolated pile-soil systems in soft clay formation, submitted to the dynamic loading test of growing energy. Among the analyses, load transfer diagrams, local friction, quake, dynamic tensions, and the correlation between static and dynamic loading test are presented.

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47

Carbol, Ladislav. "Měření akustických vlastností stavebních materiálů pomocí pseudonáhodné sekvence." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-355599.

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The thesis deals with research of pulse compression of the acoustic signal in terms of applications in civil engineering. Based on the study and analysis of these methods, automated measuring equipment for non-destructive testing with pseudorandom sequence of maximum length and automated signal analysis, have been designed and implemented. In a single test cycle are obtained three parameters that characterize the linear and nonlinear behavior of the sample. A nonlinear parameter, Time of Flight of ultrasonic wave in the sample is further in the work compared with the conventional pulse measuring, and spectral analysis is compared with the method impact-echo. Functionality and optimization of the testing method was performed on a total of three sets of test pieces made of various building materials. The experiments proved simple result interpretation, and high sensitivity to structural damage associated with temperature loading. The results were correlated with conventional nondestructive methods and by destructive testing was measured change in compressive strength and flexural strength. This work also includes continual measurement of fundamental frequency influenced by moisture on a mortar sample. Use of pulse compression signal is in the civil engineering quite unusual. Only in recent years this topic is discussed in scientific articles with increasing frequency. Great potential lies in the association of three test methods into a single. Beneficial is high test speed and measurement reproducibility, but also theoretical possibility of testing massive test elements.

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48

Ahmad, Saad. "Modeling the Discharge Loading of Radio Frequency Excited CO2 Slab lasers." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/1081.

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"RF excited CO2 lasers are widely used in industry. They provide relatively high power discharge levels while maintaining compactness, simplicity, and durability with respect to other competing laser technologies. To attain high power levels in the range of 5-10 KW, lasers with large electrode areas have to be designed. Unfortunately, due to the large electrode length requirements, transmission line effects make the discharge loading nonlinear, adversely affecting the efficiency of the CO2 laser. A standard approach to linearize the discharge loading is to introduce shunt inductors across the length of the electrodes in an effort to counter the capacitive nature of the discharge behavior. This thesis investigates and improves the theoretical models found in the literature in an effort to predict the discharge non-uniformity and allow for multiple shunt inductors installation. Specifically, we discuss the coupling of a CO2 laser discharge model with an electrical circuit solving scheme and how it can be characterized as one dimensional (1-D) and two dimensional (2-D) systems. The 1-D system is modeled using transmission line (TL) theory, where as the 2-D system is modeled using a finite difference time domain (FDTD) scheme. All our models were implemented in standard MATLAB code and the results are compared with those found in the literature with the goal to analyze and ascertain model limitations."

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49

Demir, Osman Koray. "Assessment Of Hand-type Hammer Drill Bits Under Percussive Loading." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608282/index.pdf.

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The task of a drill bit in percussive drilling is to transport the initial kinetic energy of the hammer to the workpiece in terms of stress waves. The efficiency of this transportation and the stresses that the drill bit is exposed to during the process is dependent on the nature of the stress waves. In hand-type hammer drilling, changing dimensions of the bit means changing conditions for the propagation and interaction of the stress waves. In this study, using finite element method, wave propagation and interaction in hand-type hammer drill bits is investigated with respect to drill bit dimensions. The main aim is to assess the effect of length and thickness on the efficiency and stress history of a hand-type drill bit. The results are evaluated in regard to workpiece hardness, which is a factor changing the effect of dimensions. In addition, chiseling test, which is used to prove bits under percussive loading, is carried out to detect differences between thin and thick drill bits, and the results are explained with the help of finite element simulations. Conclusions are drawn revealing the efficiency and stress history of drill bits under percussive loading with respect to thickness, length and workpiece hardness. Finally, it is seen that the real-life results of chiseling test are in agreement with the simulation results.

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50

Arshad, Naheed. "The response of a baffled plate to plane waves, with light and heavy fluid loading." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394279.

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Dissertations / Theses on the topic 'Wave loading'

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