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1
Md, Noar Nor. "Wave impacts on rectangular structures". Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/6609.
Testo completoAbstract (sommario):
There is a good deal of uncertainty and sensitivity in the results for wave impact. In a practical situation, many parameters such as the wave climate will not be known with any accuracy especially the frequency and severity of wave breaking. Even if the wave spectrum is known, this is usually recorded offshore, requiring same sort of (linear) transfer function to estimate the wave climate at the seawall. What is more, the higher spectral moments will generally be unknown. Wave breaking, according to linear wave theory, is known to depend on the wave spectrum, see Srokosz (1986) and Greenhow (1989). Not only is the wave climate unknown, but the aeration of the water will also be subject to uncertainty. This affects rather dramatically the speed of sound in the water/bubble mixture and hence the value of the acoustic pressure that acts as a maximum cutoff for pressure calculated by any incompressible model. The results are also highly sensitive to the angle of alignment of the wave front and seawall. Here we consider the worst case scenario of perfect alignment. Given the above, it seems sensible to exploit the simple pressure impulse model used in this thesis. Thus Cooker (1990) proposed using the pressure impulse P(x, y) that is the time integral of the pressure over the duration of the impact. This results in a simplified, but much more stable, model of wave impact on the coastal structures, and forms the basis of this thesis, as follows: Chapter 1 is an overview about this topic, a brief summary of the work which will follow and a summary of the contribution of this thesis. Chapter 2 gives a literature review of wave impact, theoretically and experimentally. The topics covered include total impulse, moment impulse and overtopping. A summary of the present state of the theory and Cooker’s model is also presented in Chapter 2. In Chapter 3 and Chapter 4, we extend the work of Greenhow (2006). He studied the berm and ditch problems, see Chapter 3, and the missing block problem in Chapter 4, and solved the problems by using a basis function method. I solve these problems in nondimensionlised variables by using a hybrid collocation method in Chapter 3 and by using the same method as Greenhow (2006) in Chapter 4. The works are extended by calculating the total impulse and moment impulse, and the maximum pressure arising from the wave impact for each problem. These quantities will be very helpful from a practical point of view for engineers and designers of seawalls. The mathematical equations governing the fluid motion and its boundary conditions are presented. The deck problem together with the mathematical formulation and boundary conditions for the problem is presented in Chapters 5 and 6 by using a hybrid collocation method. For this case, the basis function method fails due to hyperbolic terms in these formulations growing exponentially. The formulations also include a secular term, not present in Cooker’s formulation. For Chapter 5, the wave hits the wall in a horizontal direction and for Chapter 6, the wave hits beneath the deck in a vertical direction. These problems are important for offshore structures where providing adequate freeboard for decks contributes very significantly to the cost of the structure. Chapter 7 looks at what happens when we have a vertical baffle. The mathematical formulation and the boundary conditions for four cases of baffles which have different positions are presented in this chapter. We use a basis function method to solve the mathematical formulation, and total impulse and moment impulse are investigated for each problem. These problems are not, perhaps, very relevant to coastal structures. However, they are pertinent to wave impacts in sloshing tanks where baffles are used to detune the natural tank frequencies away from environmental driving frequencies (e.g ship roll due to wave action) and to damp the oscillations by shedding vortices. They also provide useful information for the design of oscillating water column wave energy devices. Finally, conclusions from the research and recommendations for future work are presented in Chapter 8.
2
Katsidoniotaki, Eirini. "Extreme wave conditions and the impact on wave energy converters". Licentiate thesis, Uppsala universitet, Elektricitetslära, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-441043.
Testo completoAbstract (sommario):
The amount of energy enclosed in ocean waves has been classified as one of the most promising renewable energy sources. Nowadays, different wave energy conversion (WEC) systems are being investigated, but only a few concepts have been operated in a sea environment. One of the largest challenges is to guarantee the offshore survivability of the devices in extreme wave conditions. However, there are large uncertainties related to the prediction of extreme wave loads on WECs. Highfidelity computational fluid dynamics (CFD) simulations can resolve nonlinear hydrodynamic effects associated with wave-structure interaction (WSI). This thesis explores the point-absorbing WEC developed by Uppsala University in extreme wave conditions. The dynamic response and the forces on key components (mooring line, buoy, generator's end-stop spring) of the device are studied and compared. The high nonlinear phenomena accompany the steep and high waves, i.e., breaking behavior, slamming loads can be well-captured by the highfidelity CFD simulations. A commonly used methodology for extreme waves selection, recommended by technical specifications and guidelines, is the environmental contour approach. The 100-year contour in Hamboldt Bay site in California and the 50-year contour in the Dowsing site, outside the UK, are utilized to extract the extreme waves examined in the present thesis. Popular methodologies and data from different sources (observational and hindcast data) are examined for the environmental contour generation providing useful insights. Moreover, two popular approaches for the numerical representation of the extreme sea states, either as focused wave or as equivalent regular wave, were examined and compared. A midfidelity model of the WEC is successfully verified, as the utilization of lower fidelity tools in the design stage would reduce the computational cost. Last but not least, in CFD simulations the computational grid is sensitive in large motions, something often occurs during extreme-WSI. The solution of this issue for the open source CFD software OpenFOAM is provided here.
3
Topliss, Margaret E. "Water wave impact on structures". Thesis, University of Bristol, 1994. http://hdl.handle.net/1983/2fa7ba69-7867-4cd0-8b3a-de4de97f98db.
Testo completo
4
Wood, Deborah Jane. "Pressure-impulse impact problems and plunging wave jet impact". Thesis, University of Bristol, 1997. http://hdl.handle.net/1983/c3dbd4c5-5082-4c71-a16e-3daa969e22ee.
Testo completo
5
Cox, Simon John. "Pressure impulses caused by wave impact". Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266731.
Testo completo
6
Abdolmaleki, Kourosh. "Modelling of wave impact on offshore structures". University of Western Australia. School of Mechanical Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0055.
Testo completoAbstract (sommario):
[Truncated abstract] The hydrodynamics of wave impact on offshore structures is not well understood. Wave impacts often involve large deformations of water free-surface. Therefore, a wave impact problem is usually combined with a free-surface problem. The complexity is expanded when the body exposed to a wave impact is allowed to move. The nonlinear interactions between a moving body and fluid is a complicated process that has been a dilemma in the engineering design of offshore and coastal structures for a long time. This thesis used experimental and numerical means to develop further understanding of the wave impact problems as well as to create a numerical tool suitable for simulation of such problems. The study included the consideration of moving boundaries in order to include the coupled interactions of the body and fluid. The thesis is organized into two experimental and numerical parts. There is a lack of benchmarking experimental data for studying fluid-structure interactions with moving boundaries. In the experimental part of this research, novel experiments were, therefore, designed and performed that were useful for validation of the numerical developments. By considering a dynamical system with only one degree of freedom, the complexity of the experiments performed was minimal. The setup included a plate that was attached to the bottom of a flume via a hinge and tethered by two springs from the top one at each side. The experiments modelled fluid-structure interactions in three subsets. The first subset studied a highly nonlinear decay test, which resembled a harsh wave impact (or slam) incident. The second subset included waves overtopping on the vertically restrained plate. In the third subset, the plate was free to oscillate and was excited by the same waves. The wave overtopping the plate resembled the physics of the green water on fixed and moving structures. An analytical solution based on linear potential theory was provided for comparison with experimental results. ... In simulation of the nonlinear decay test, the SPH results captured the frequency variation in plate oscillations, which indicated that the radiation forces (added mass and damping forces) were calculated satisfactorily. In simulation of the nonlinear waves, the waves progressed in the flume similar to the physical experiments and the total energy of the system was conserved with an error of 0.025% of the total initial energy. The wave-plate interactions were successfully modelled by SPH. The simulations included wave run-up and shipping of water for fixed and oscillating plate cases. The effects of the plate oscillations on the flow regime are also discussed in detail. The combination of experimental and numerical investigation provided further understanding of wave impact problems. The novel design of the experiments extended the study to moving boundaries in small scale. The use of SPH eliminated the difficulties of dealing with free-surface problems so that the focus of study could be placed on the impact forces on fixed and moving bodies.
7
Abraham, Aliza Opila. "Extreme wave impact on a flexible plate". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104117.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 99-102).
This thesis describes the use of a combination of various visual techniques to characterize the flow-structure interaction of a breaking wave impacting a flexible vertically mounted plate. Several experiments were conducted on a simulated dam break in which water was rapidly released from a reservoir to generate a wave, which impinged on a cantilevered stainless steel plate downstream. Two high speed cameras collected data on the water and the plate simultaneously. Manual tracking of the wave front and Particle Image Velocimetry (PIV) were used to gather water height, wave speed, crest speed, vorticity, and particle speed, which were used to determine the pressure exerted by the water on the plate. An algorithm was written to track the edge of the plate to find plate deflection over time. The dynamic beam bending equation was used to find the forces experienced by the plate, which were compared to the pressure results. A series of waves of different heights and breaking locations were tested, controlled by the ratio of the height of water initially in the tank and the height of water in the dam break reservoir, for two different plate locations. The properties of the wave varied depending on these parameters, as did the deflection of the plate. The plate deformed more and the recorded velocities in the wave were higher when the depth ratio decreased and when the plate was moved farther from the reservoir. These results shed light on the effect of breaking wave impacts on offshore structures and ship hulls, taking into account the elasticity of these structures. They also provide a test case for future numerical fluid-structure interaction simulation techniques.
by Aliza Opila Abraham.
S.M.
8
Schöpfer, Philipp. "Non-linear Wave Impact on Monopile Structures". Thesis, KTH, Lättkonstruktioner, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-203342.
Testo completoAbstract (sommario):
This Master Thesis deals with non-linear wave impacts on monopile structures by introducing a potential flow solver named OceanWave3D (OCW3D) for simulating free surface waves and their kinematics under engineering consideration. A comparison to Rambøll’s analytical tool WAVGEN is conducted with the aim of providing distinct recommendations on the application and suitability of both programs for the monopile design. As WAVGEN applies common wave theories it is able to generate single waves in linear or non-linear form but only linear irregular sea states. In contrary, OCW3D includes both the non-linearity of the wave shape and the randomness of the water surface, resulting in a fully non-linear sea state due to the numerical solution. The obtained wave kinematics from both tools are read by a finite-element software which converts water particle velocities into wave loads. In order to reveal differences between both approaches an ultimate limit strength analysis of the foundation is performed, implementing wave kinematics by either WAVGEN or OCW3D. Here, the conventional approach with WAVGEN includes the principle of an embedded stream function wave into a linear irregular sea state to somewhat cover the non-linearity of the wave profile and the arbitrary surface elevation. As a result, the structural analysis yields a maximum overturning moment (OTM) which can be clearly affiliated to the inserted extreme wave represented by the stream function wave. On the other hand, the new approach with OCW3D generates a fully non-linear sea state in a numerical wave tank although without influencing the maximum wave. The already more realistic wave simulation by OCW3D is improved by activating a breaking filter which dissipates the energy of waves which would not exist in reality due to breaking. Multiple realisations give indications whether the non-linear sea state solution produces a single wave that exceeds the embedded stream function wave and the respective structural response. The final results in some cases confirm a greater OTM with OCW3D due to more aggressive and non-linear wave kinematics although the wave height of the embedded stream function wave is not surpassed. However, considering the most realistic wave and kinematics after a certain distance along the numerical wave tank when the breaking filter has removed all the excess energy a saving of almost 4.0 % in the structural response with OCW3D is reached. Additionally, the work has provided an unprecedented validation of Rambøll’s engineering procedure of defining an embedded stream function, i.e. this commonly used approach delivers representative wave loads compared to actual wave impacts induced by non-linear sea states.
9
Rimal, Nischal. "Impact Localization Using Lamb Wave and Spiral FSAT". University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1388672483.
Testo completo
10
Bradshaw, Douglas Robert Saunders. "Linear wave propagation in traumatic brain injury". Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341646.
Testo completo
11
Greenwood, Charles. "The impact of large scale wave energy converter farms on the regional wave climate". Thesis, University of the Highlands and Islands, 2016. https://pure.uhi.ac.uk/portal/en/studentthesis/the-impact-of-large-scale-wave-energy-converter-farms-on-the-regional-wave-climate(e734db00-2108-48f9-b162-a1fc85ef61d6).html.
Testo completo
12
Musa, Abu Bakar. "Wave motion and impact effects in viscoelastic rods". Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/10799.
Testo completoAbstract (sommario):
Two separate problems are to be investigated in this thesis. The first problem is the propagation of waves through a short rod (or slug) of viscoelastic material. The second problem is the study of impact of a short viscoelastic rod (or slug) on a stationary semi-infinite viscoelastic. rod. The viscoelastic materials are modelled as standard linear solids which involve 3 material parameters and the motion is treated. as one-dimensional. For the first study, a viscoelastic slug is placed between two semi-infinite elastic rods and a wave initiated in the first rod is transmitted through the slug into the second rod. The objective is to relate the transmitted signal to the material parameters of the slug. We solve the governing system of partial differential equations using the Laplace transform and we examine the propagating velocity discontinuity using discontinuity analysis and the limit theorem of the Laplace transform. We then approximate the solution of the propagating disturbance using the regular perturbation method. We invert the Laplace transformed solution numerically to obtain the transmitted signal for several viscosity time constants and ratios of acoustic impedances. We compare the results obtained using the above techniques. In the second problem, we first model the impact and solve the governing system of partial differential equations in the Laplace transform domain. Then we examine the propagating stress and velocity discontinuities using discontinuity analysis. We approximate the solutions of the propagating stress and velocity using the regular and multiple scales perturbation methods. In this problem, we first consider the slug is elastic and the rod is viscoelastic. Secondly, we consider the slug is viscoelastic and the rod is elastic and thirdly, we consider both materials are viscoelastic. Numerically we invert the Laplace transformed solutions for the interface stress and interface velocity for several viscosity time constants and ratios of acoustic impedances to determine whether the slug and the rod part company or remain in contact. Then we compare the results obtained using the discontinuity analysis, regular and multiple scales perturbation methods.
13
Yang, Yongqian. "Impact of Patchy Vegetation on Wave and Runup Dynamics". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/72278.
Testo completoAbstract (sommario):
Coastal regions are vulnerable to various natural processes, ranging from normal waves to extreme events. Given the flourishing development and large population along coastlines, various measures have been taken to mitigate the water-induced damage. Nature-based coastal protection, especially vegetation, has attracted unprecedented studies over the past two decades. To enhance understanding of this subject, this dissertation evaluates the impact of patchy vegetation on wave and runup dynamics along coastlines. Selecting from a prototype in Dalehite Cove, Galveston Bay, TX, results from a Boussinesq model (COULWAVE) showed patchy vegetation reduced up to 75% mean shoreward current in the mound-channel wetland systems. These vegetation patches also reduced the primary circulation around mounds, with a power-form relation between circulation size and various parameters (i.e., bathymetry, incident wave and vegetated roughness). Substituting spectral waves for regular waves in the similar wetlands, more energy was transferred into the higher frequencies. The impact of patchy vegetation on wave energy was frequency- and space-dependent, with increased energy observed in specific harmonics and locations. Comparison with unvegetated horizontal bathymetry demonstrated that mound-channel bathymetry was the dominant factor in transferring and dissipating wave energy, while vegetation patches added a fair contribution. As for extreme events, such as tsunamis, laboratory experiments and numerical simulations were conducted to assess the effectiveness of patchy vegetation with various roughness levels, spacings and sizes. Overall, vegetation patches reduced the most destructive loads onshore by up to 80%. Within-patch roughness variation only caused uncertainty on the hydrodynamics around the seaward patches, while the mitigation of extreme loads was not undermined. A logarithmic relation was observed between the protected area from extreme loads and the vegetated coverage. These findings will fill the knowledge gap of hydrodynamics in the presence patchy vegetation, and improve the engineering practice of coastal protection using nature-based infrastructure.Ph. D.
14
Tan, Loh Teng Young. "Assessments of wave-structure interactions for an oscillating wave surge converter using CFD". Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/12230.
Testo completoAbstract (sommario):
This thesis is concerned with the use of the open source computational fluid dynamics (CFD) software package, OpenFOAM® for predicting and analysing the behaviour of a near-shore oscillating wave surge converter (OWSC), when subject to various types of ocean wave conditions in a numerical wave tank (NWT). OpenFOAM® which utilises a Finite Volume Method (FVM) is used to solve the incompressible, Reynolds Averaged Navier-Stokes (RANS) equations for a two-phase fluid, based on a Volume of Fluid (VOF) phase-fraction approach to capture the interface between the air and water phases. Preliminary studies on classic wave-structure interaction benchmark cases, involving a fixed and a vertically oscillating semi-immersed horizontal cylinder are carried out. The gradual transition of the linear to non-linear behaviour of the horizontal and vertical forces induced on a fixed cylinder when subject to various regular waves, and the amplitude ratios of the surface waves elevations generated by the prescribed oscillatory motion of the cylinder, are shown to provide good overall agreement within the limitations of the relevant theory and the experimental data in the literature. The OWSC is modelled with the inclusion of a Power Take-Off (PTO) system, using a linear damping restraint, and simulated in two-dimensional (2D) and three-dimensional (3D) setups. The 2D and 3D numerical results, such as the surface wave elevations, flap angular velocity, PTO torque and flap angular displacement, compare well with one another and with the experimental data for operational regular head-on and oblique wave conditions. Small discrepancies between numerical results and experimental data are likely to be caused by non-linear behaviour of the PTO system. Pressure distributions on the flap surfaces and forces induced on the flap and hinge of the OWSC for various wave conditions are also presented. The effects between 2D and 3D wave-structure interactions become more significant when subject to large waves that break during impact. Comparison between the full scale and 1:24 scale numerical results of the OWSC shows no significant evidence of viscous and scaling effects. The validated 2D OWSC model is also subject to embedded focused waves, to predict the worse possible scenario of wave loading in extreme wave conditions. The delay of the focus event breaking is shown to affect the slamming behaviour for the larger focus event wave heights. Incorporation of a focused wave at different phase positions within a background of regular waves reveals that the focus event wave height has little effect on the peak tangential force on the flap during the slamming event, when a PTO cut-off mechanism is implemented to prevent excessive torque surges. In contrast, the peak radial force on the flap and the maximum resultant force on the hinge appear to respond more sensitively to the focus event wave height. It has been demonstrated that OpenFOAM® is able to provide a comprehensive understanding of the complex hydrodynamic analysis and prediction of highly non-linear wave-structure interactions for an OWSC, which give useful guidance and confidence to WEC developers on the design considerations relevant to the OWSC systems.
15
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.
Testo completo
16
Khan, Md Mahfujul H. "Understanding Impact Load Wave Transmission Performance of Elastic Metamaterials". University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1479146177020136.
Testo completo
17
Siddiq, Kashif. "The impact of oscillator phase noise on the design of millimetre-wave continuous wave radar systems". Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760876.
Testo completoAbstract (sommario):
This PhD thesis focuses on quantifying the impact of oscillator phase noise on the design of MMW CW radar systems with the goal of optimising the system to achieve better target detection and tracking. Phase noise in the transmitters of radar systems is known to distort the target response by broadening the linewidth and raising the noise floor of radar systems when a strong scatterer is present in the scene, hence degrading the detection and tracking performance. The situation is worse when multiple large scatterers are present, as the noise sidebands of all scatterers superimpose causing small targets, like pedestrians, to disappear in the phase noise sidebands. Some of the phase noise is cancelled at short ranges in coherent radars but the cancellation is not effective at long ranges. This research presents the design of phase noise reduction techniques. Phase noise modelling at the system level is presented to elaborate the methods of minimising the impact of phase noise. It will be shown that the frequency synthesiser is the most significant phase noise contributor. The design and implementation of a low phase noise signal source is presented. Both linear and non-linear phase noise models are used and developed further in order to meet the radar optimisation goals. An elaborate relationship of the phase spectrum with the RF spectrum of an oscillator is presented. The idea of coherence time is used as a tool for the selection of radar signal sources, and a novel derivation of the minimum bound on the transmitter phase noise level presented to prevent excessive distortion of target spectra. A new phase noise model is developed for the analog-to-digital conversion process using an independent sampling clock. The case of a sampling clock derived from the transmitter's reference oscillator will also be discussed. The models aid the selection of an appropriate sampling clock for a given radar application. A novel method of characterising the phase noise statistics using the integer and the fractional Brownian motion models will be presented. Models for the lineshape and the linewidth of the RF spectrum are dealt with in detail by reviewing the existing models in the literature. These analyses aid in assessing the fundamental resolution capability of radar systems in terms of the phase noise processes. A novel analysis of the RF spectrum of a signal impaired with random-walk phase noise is detailed, and it is shown that the RF spectrum exhibits time-dispersion and satellite peaks. It is shown that the success of the proposed work depends on techniques for careful measurement, analysis, and mitigation of the various noise processes.
18
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.
Testo completoAbstract (sommario):
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.
19
Zhou, Weiyu. "Crash-impact behavior of graphite/epoxy composite sine wave webs". Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/12226.
Testo completo
20
Smith, Helen Claire Margaret. "Modelling for resource and environmental impact assessments of wave farms". Thesis, University of Exeter, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445738.
Testo completo
21
Dahlsten, Hilda. "Life Cycle Assessment of Electricity from Wave Power". Thesis, Institutionen för energi och teknik, SLU, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-162582.
Testo completoAbstract (sommario):
The use of ocean wave energy for electricity production has considerable potential, though it has proven to be difficult. A technology utilizing the heaving (up-and-down) motions of the waves was conceived at Uppsala University in the early 2000´s, and is being further developed for commercial use by Seabased Industry AB. The purpose of this master´s degree project was to increase the knowledge of the environmental performance of Seabased´s wave energy conversion concept and identifying possible areas of improvement. This was done by conducting a life cycle assessment (LCA) of a hypothetical prototype wave power plant. All flows of materials, energy, emissions and waste were calculated for all stages of a wave power plant´s life cycle. The potential environmental impact of these flows was then assessed, using the following impact categories: • Emission of greenhouse gases • Emission of ozone depleting gases • Emission of acidifying gases • Emission of gases that contribute to the forming of ground-level ozone • Emission of substances to water contributing to oxygen depletion (eutrophication) • Energy use (renewable and non-renewable) • Water use The methodology used was that prescribed by the ISO standard for Environmental Product Declarations (EPD) and further defined by the International EPD Programme.The potential environmental impact was calculated per kWh of wave power electricity delivered to the grid. The main result of the study is that the potential environmental impact of a wave power plant mainly stems from the manufacturing phase. In particular, the production of steel parts makes a large contribution to the overall results. Future wave power plant designs are expected to be considerably more material efficient, meaning that there are large possibilities to improve the environmental performance of this technology.
22
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.
Testo completo
23
Menday, Roger. "The forced vibration of a partially delaminated beam". Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/27082.
Testo completoAbstract (sommario):
The forced vibration of a partially delaminated structure such as an aircraft wing can result in catastrophic crack growth. In order to look at the underlying mechanism of the dynamics and failure of the material, a simplified model of a cantilever beam with a single delamination at its free end is considered. We investigate a number of aspects of this system, using mathematical models to gain insight into its behaviour.
24
Tabatabaee, Ghomi Mohammad. "Impact wave process modeling and optimization in high energy rate explosive welding". Licentiate thesis, Mälardalen University, School of Sustainable Development of Society and Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-6663.
Testo completoAbstract (sommario):
Impact waves are used in many different industries and are classified according to whether they cause plastic or elastic deformations. In the plastic deformation mode, these waves can be used to produce special electrical joints. In the elastic deformation mode, they can be used to detect leakage or to measure the thickness of pipes. Both modes have applications in offshore technology. In this thesis the application of impact waves in the plastic deformation mode and explosive welding are discussed. In the explosive welding (EXW) process a high velocity oblique impact produced by a carefully controlled explosion occurs between two or more metals. The high velocity impact causes the metals to behave like fluids temporarily and weld together. This process occurs in a short time with a high rate of energy.
EXW is a well known method for joining different metals together. It is a multidisciplinary research area and covers a wide range of science and technology areas including wave theory, fluid dynamics, materials science, manufacturing and modeling. Many of the important results in EXW research are obtained from experimentation.
This thesis is mainly based on experimental work. However, it begins with a review of the fundamental theory and mechanisms of explosive welding and the different steps of a successful welding operation. Many different EXW tests are done on horizontal and vertical surfaces with unequal surface areas, and on curved surfaces and pipes. The remainder of the thesis evaluates the results of these experiments, measures the main parameters, and shows the results of simulations to verify the experimental results. The thesis ends with a number of suggestions for improving and optimizing the EXW process. One of these improvements is a model for joining metallic plates with unequal surface areas. An Al-Cu joint based on this model is used in the ALMAHDI aluminum factory, a large company in southern Iran that produces more than 200,000 tons of aluminum per year. Improved methods are also suggested for joining curved surfaces. These methods may have extensive applications in pipelines in oil and gas industries, especially in underwater pipes.
Impact vågor används i många olika branscher och klassificeras enligt de deformationer de orsakat: elastiska och plastiska deformationer. I plastisk deformation mode, dessa vågor skulle kunna användas för att framställa särskild elektrisk lederna. I deformationen läge, de skulle kunna användas för att upptäcka läckage eller mäta tjockleken på rören. Båda har tillämpningar inom offshore-teknik. I denna avhandling tillämpningen av effekterna vågor i plastisk deformation mode och explosiva svetsning diskuteras. I den explosiva svetsning (EXW) process hög hastighet sned effekt som produceras av en noggrant kontrollerad explosion uppstår mellan två eller flera metaller. Den höga hastigheten effekt gör att metaller gå ihop samtidigt som beter sig som vätskor. Denna process sker i en kort tid med hög energi.
EXW är en känd metod för att gå med olika metaller tillsammans. Det är ett tvärvetenskapligt forskningsområde och omfattar ett brett spektrum av naturvetenskap och teknik, inklusive våg teori, vätskor dynamik, materialvetenskap, tillverkning och modellering. Många av de viktiga resultat i EXW forskning har erhållits från experiment.
Denna uppsats bygger främst på experimentella verk. Det kommer dock att börja med en genomgång av grundläggande teori och mekanism av explosiva svetsning och de olika stegen i en lyckad welding operation. Då många olika EXW tester göras på horisontella och vertikala ytor med icke lika ytor och på krökta ytor och ledningar. Utvärdering av resultaten, som mäter de viktigaste parametrarna, som utför vissa simuleringar för att verifiera experimentella resultat och några förslag för att förbättra och optimera EXW process utgör de andra delarna av uppsatsen. En av dessa förbättringar är en modell för att gå med metalliska plattor med icke-lika ytor. En Al-Cu gemensamt bygger på denna modell används i ALMAHDI aluminium fabrik, ett stort företag i södra Iran att produktionen är mer än 200000 ton per år. Dessutom en del andra förbättrade metoder föreslås för att gå med krökta ytor. Dessa metoder kan få omfattande tillämpningar inom olje-och gasindustrin som rörledningar, särskilt under rören.
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Winsor, Fraser N. "Methods for removing inertial force from measured wave impact force signals". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0021/MQ55546.pdf.
Testo completo
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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/.
Testo completo
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Aziz, Asim. "Impact dynamic rupture modelling of solids for shock wave lithotripsy simulation". Thesis, Glasgow Caledonian University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.688271.
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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.
Testo completoAbstract (sommario):
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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Kim, Ji-Eun. ""Korean wave" in China : its impact on the South Korean-Chinese relations". Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39363.
Testo completoAbstract (sommario):
The “Korean Wave” refers to the love of South Korean cultural products. The wave has started in East Asia and swept over Southeast Asia. More recently, it has even landed in the Middle East and part of Europe. In particular, this thesis looks at the Korean Wave in the context of China, where the Korean Wave first started and the term was coined. It aims to answer the following research questions: 1) To what extent the Korean pop culture has influenced the public sentiment in China? 2) How the government and political leaders have responded to the Korean Wave in China? In response, it is argued that Korean soap-operas, in particular, have boosted the Chinese public’s interest in Korea and created positive national images of Korea. This effect can be explained by the Korean media and government’s active support and the timely development of the internet. However, the high-level response to the phenomenon has also reflected the Chinese government’s concern over foreign cultural imports and their unwillingness to utilize the Korean Wave as a tool of promoting South Korea-China relations. Finally, this thesis also argues that the Korean Wave has a potential to become the cornerstone of “soap-opera diplomacy” based on the cultural familiarity that could improve the declining state to state bilateral relations.
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Villegas, Ruiz Eloy Ángel. "Wave aberrations in ophthalmic progressive power lenses and impact on visual quality". Doctoral thesis, Universidad de Murcia, 2009. http://hdl.handle.net/10803/10843.
Testo completoAbstract (sommario):
Las lentes progresivas (LP) para gafas es una solución muy extendida para la presbicia, ya que proporcionan una visión continua a todas las distancias debido a un cambio progresivo de potencia. En este trabajo se han medido las aberraciones de frente de onda espacialmente resueltas y la calidad visual en estas lentes. Además del astigmatismo que aumenta periféricamente, también se han encontrado pequeños valores de aberraciones de tercer orden, coma y trefoil, que producen un bajo deterioro de la calidad óptica y visual. El logaritmo de métricas sobre la PSF del sistema lente con ojo son las que mejor predicen la agudeza visual. Durante la primera semana de adaptación, no se aprecia una mejora significativa de la agudeza visual a través de distintas zonas de las LPs. Al comparar diferentes LPs, las aberraciones, principalmente el astigmatismo, se comporta como un colchón de agua, que se puede mover pero no eliminar.Progressive lenses (PL) are designed to provide continuous vision at all distances by means a progressive change in spherical power from upper to lower zones. In this thesis, we measure the spatially resolved aberrations and the visual quality of PLs. In addition to astigmatism, third order aberrations, coma and trefoil, are also found in the PLs, but the impact of these aberrations on visual performance is limited. The logarithm of metrics on the PSF of the entire system eye plus PL are the parameters that best predict the visual acuity. There is not a significant improvement of visual acuity through the different zones of the PLs during the first week of adaptation. The current designs of PLs are somehow similar to a waterbed, with the aberrations, mainly astigmatism, being the water: they can be moved but they cannot be eliminated.
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Martínez, Asensio Adrián. "Impact of large-scale atmospheric variability on sea level and wave climate". Doctoral thesis, Universitat de les Illes Balears, 2015. http://hdl.handle.net/10803/371456.
Testo completoAbstract (sommario):
This thesis aims at quantitatively characterizing the recent (last few decades) and future climate variability of marine climate in the Western Mediterranean Sea and the North Atlantic Ocean. Namely it focuses on sea level and wind-waves, as these are the variables with a larger potential impact on coastal ecosystems and infrastructures. We first use buoy and altimetry data to calibrate a 50-year wind-wave hindcast over the Western Mediterranean in order to obtain the best characterization of the wave climate over that region. The minimization of the differences with respect to observations through a non-linear transformation of the Empirical Orthogonal Functions of the modelled fields results in an improvement of the hindcast, according to a validation test carried out with independent observations. We then focus on the relationship between the large scale atmospheric forcing and our target variables. Namely we quantify and explore the cause-effect relations between the major modes of atmospheric variability over the North Atlantic and Europe, i.e. the North Atlantic Oscillation, the East Atlantic pattern, the East Atlantic Western Russian pattern and the Scandinavian pattern, and both the Mediterranean sea level and the North Atlantic wave climate. To do so, we use data from different sets of observations and numerical models, including tide gauges, wave buoys, altimetry, hydrography and numerical simulations. Our results point to the North Atlantic Oscillation as the mode with the largest impact on both, Mediterranean sea level (due to the local and remote influence on its atmospheric component) and the North Atlantic wave climate (due to its effect on both the wind-sea and swell components). Other climate indices have smaller but still meaningful contributions; e.g. the East Atlantic pattern plays a significant role in the wave climate variability through its impact on the swell component. Finally, we explore the performance of statistical models to project the future wave climate over the North Atlantic under global warming scenarios, including the large scale climate modes as predictors together with other variables such as atmospheric pressure and wind speed. Notably, we highlight that the use of wind speed as statistical predictor is essential to reproduce the dynamically projected long-term trends.Esta tesis caracteriza cuantitativamente la variabilidad climática reciente (las últimas décadas) y futura del clima marino en el Mar Mediterráneo y en el Océano Atlántico Norte. Concretamente, se centra en el nivel del mar y en el oleaje, ya que éstas son las variables con un mayor impacto potencial en ecosistemas e infraestructuras costeras. En primer lugar, utilizamos datos de boyas y altimetría para calibrar un hindcast de oleaje de 50 años en el Mediterráneo Occidental, con el objetivo de obtener la mejor caracterización climática del oleaje sobre esta región. La minimización de las diferencias con respecto a las observaciones a través de una transformación no lineal de las Funciones Empíricas Ortogonales de los campos modelados se traduce en una mejora del hindcast, de acuerdo al test de validación llevado a cabo con observaciones independientes. Luego nos centramos en las relaciones entre el forzamiento atmosférico de gran escala y nuestras variables de interés. En concreto, cuantificamos y exploramos las relaciones causa-efecto entre los modos de variabilidad atmosférica más importantes del Atlántico Norte y Europa (la Oscilación del Atlántico Norte, el patrón del Atlántico Oriental, el patrón del Atlántico Oriental/Rusia Occidental y el patrón Escandinavo) y el nivel del mar del Mediterráneo y el oleaje del Atlántico Norte. Para ello, usamos datos de diferentes conjuntos de observaciones y modelos numéricos, incluyendo mareógrafos, boyas de oleaje, altimetría, hidrografía y simulaciones numéricas. Nuestros resultados señalan la Oscilación del Atlántico Norte como el modo de mayor impacto, tanto en el nivel del mar del Mediterráneo (debido a la influencia local y remota en su componente atmosférica) como en el oleaje del Atlántico Norte (debido a su efecto en las componentes de mar de viento y de mar de fondo). Otros índices climáticos tienen contribuciones más pequeñas pero todavía significativas; e.g. el patrón del Atlántico Oriental juega un papel importante en la variabilidad del oleaje a través de su impacto en la componente de mar de fondo. Finalmente, exploramos la capacidad de los modelos estadísticos de proyectar el clima futuro del oleaje sobre el Atlántico Norte bajo escenarios de calentamiento global, incluyendo los modos climáticos de gran escala como predictores junto con otras variables como la presión atmosférica y la velocidad del viento. En particular, destacamos que el uso de la velocidad del viento como predictor estadístico es esencial para reproducir las tendencias a largo plazo proyectadas de por los modelos dinámicos.
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Walters, Mark Bernhardt James. "An experimental study into impact wave propagation in cross ply composite plates". Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/34719.
Testo completoAbstract (sommario):
To gain insight into the problem of impact on to composite materials this work has examined experimentally the characteristics of stress waves propagating through a multi layered plate due to a surface impact. Theoretical and numerical techniques have been developed for an impulsive line load acting on the upper surface of a four layer cross ply plate. These resolve the surface and inter lamina disturbances caused by the passing stress waves due to a normal line impulse onto a plate. The objective of this work was to examine the wave propagation in a cross ply plate with experimental techniques and compare the wave characteristics with the analytical predictions. To detect the passing of the stress waves on the surfaces and at the ply interfaces a piezo electric sensor was developed using polarized homopolymer of vinylidene fluoride (PVDF) film. The responses collected from surfaces and mid plane of the impacted plate were dominated by the low frequency contribution of the impact, so the high frequency shear wave responses were extracted with digital filters. The experimental results presented show that when the limiting wave velocity in the plate was that of a Rayleigh type surface wave the largest disturbance in the plate occurred on the upper surface of the plate, and that when the limiting wave velocity in the plate was that in an internal shear wave and the largest disturbance occurred at the mid plane of the plate. These results demonstrated that the presence or absence of shear waves could be resolved experimentally at the surfaces and ply interfaces of a multi layered material. A good correlation was seen between the experimental results and the analytical results which provided some verification for the analysis method.
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Protic, Serena. "The impact of fourth wave feminism: Using social media as a feminist resource". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Cerca il testo completoAbstract (sommario):
There is little doubt that the Internet, and especially social media, has revolutionised our lives, transforming the way in which we communicate (Liveperson 2017), read the news (Pew Research Center 2016), shop and conduct business (Deloitte 2015), work (Zetterstrom 2012) and even find love (Pew Research Center 2015).
The Internet has had an impact on feminism as well, revolutionising the way feminists participate in political and cultural activism and contributing to the creation of a fourth feminist wave. Thanks to the Internet, virtually anybody who has access to it can become an activist and fight for the movement from the comfort of their home, whether by contributing to the creation of an online archive, signing petitions, supporting boycott movements or sharing their experiences on a blog (Cochrane 2013). But what is the real impact of the Internet on the way activists operate? Will it replace grassroots activism with time, or is it contributing to the development of new strategies, which will cooperate with existing methods, in an effort to collectively change the culture we are living in? This study suggests the unfolding of a new, fourth feminist wave, analyses the contribution of the Internet to fourth wave feminism and explores the potential of online activism as a tool to combat misogyny.
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Mishra, Vijay. "Impact of Hurricanes on Structures - A Performance Based Engineering View". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3251.
Testo completoAbstract (sommario):
The magnitude of damage caused to the United States (US) coast due to hurricanes has increased significantly in the last decade. During the period 2004-2005, the US experienced seven of the costliest hurricanes in the country's history (NWS TPC-5, 2007) leading to an estimated loss of ~ $158 billion. The present method for predicting hurricane losses, HAZUS (HAZard US), is solely based on hurricane hazard and damage caused to building envelopes only and not to structural systems (Vickery et al., 2006). This method does not take into account an intermediate step that allows for better damage estimates, which is structural response to the hazards that in turn can be mapped to the damage. The focus of this study was to quantify the uncertainty in response of structures to the hurricane hazards associated with hurricanes from performance based engineering perspective. The study enumerates hazards associated with hurricanes events. The hazards considered can be quantified using a variety of measures, such as wind speed intensities, wave and surge heights. These hazards are quantified in terms of structural loads and are then applied to a structural system. Following that, structural analysis was performed to estimate the response from the structural system for given loads. All the possible responses are measured and they are fitted with suitable probability distribution to estimate the probability of a response. The response measured then can be used to understand the performance of a given structure under the various hurricane loads. Dynamic vs. static analysis was performed and results were compared. This will answer a few questions like, if there is any need to do both static and dynamic analysis and how hurricane loads affect the structural material models. This being an exploratory study, available resources, research, and models were used. For generation of annual or extreme values of hazard, various available wind speed, storm surge, and wave height models were studied and evaluated. The wind field model by Batts et al. (1980) was selected for generation of annual wind speed data. For calculation of maximum storm surge height, the Sea, Lake Overland Surges from Hurricane (SLOSH, Jelesnianski et al., 1992) program was used. Wave data was acquired from a National Oceanic and Atmospheric Administration (NOAA) database. The (extreme or annual) wind speed, surge height, and wave height generated were then fitted by suitable probability distributions to find the realizations of hazards and their probabilities. The distribution properties were calculated, correlations between the data were established, and a joint probability distribution function (PDF) of the parameters (wind speed, wave height, and storm surge) was generated. Once the joint distribution of extreme loads was established, the next step was to measure the dynamic response of the structural system to these hazards. To measure the structural response, a finite element model of three-story concrete frame were constructed. Time histories of wind load were generated from wind net pressure coefficients recorded in a wind tunnel test (Main and Fritz, 2006). Wave load time histories were generated using laboratory basin test (Hawke's et al., 1993) wave height time history data and were converted into wave loads using Bernoulli's equation. Surge height was treated as a hydrostatic load in this analysis. These load time histories were then applied to the finite element model and response was measured. Response of the structural system was measured in terms of the mean and maximum displacements recorded at specific nodes of model. Response was calculated for loads having constant mean wind speed and surge/wave and different time histories. The dominant frequency in the wind load time histories was closer to the natural frequency of the structural model used than the dominant frequency in the wave height time histories. Trends in the response for various combinations of mean wind speed, wave height, and surge heights were analyzed. It was observed that responses are amplified with increase in the mean wind speed. Less response was measured for change in mean surge/wave height as the tributary area for wave forces was less compared to wind force. No increase in dynamic amplification factor was observed for increase in force time histories case.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering MS
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Tabatabaee, Ghomi Mohammad. "MODELLING AND SIMULATION OF ELASTIC & PLASTIC BEHAVIOUR OF PROPAGATING IMPACT WAVE : Impact- echo and Explosive welding process development". Doctoral thesis, Mälardalens högskola, Akademin för hållbar samhälls- och teknikutveckling, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-13332.
Testo completoAbstract (sommario):
A force that is applied dynamically in a short period of time is called an impact force (shock wave). Due to the concentrated application of force on a small area in a fraction of a second, unique applications have emerged that other types of loadings are not capable of performing. Explosions, an impact of a hammer, impact of waves on a shore wall, or the collision of two automobiles are examples where impact waves occur. In this research the effects of impact on solid materials and the motion of stress waves due to the impact are studied and some of their industrial applications are described. The primary objective of this work is further development of some elastic and plastic impact wave methods, aiming to reduce the energy consumption of explosive welding (EXW) as well as the cost of NDT technologies. Many numerical simulations and a vast amount of experimental work were employed to reach this goal. The impact wave creates elastic deformations that move the particles of the body. In this research we focused on dimensional measurement by calculating the time of wave travel between the source of energy and a discontinuity in the part studied. The impact echo (IE) method can be used for determining the location and extent of all kinds of flaws, such as cracks, de-lamination, holes and de-bonding in concrete structures, columns and hollow cylinders with different cross-sections and materials. In the present study, simulation of the impact-echo method was carried out numerically using direct and indirect methods. In the direct method a steel ball directly impacts on the upper surface of a concrete plate-like structure, whereas in the indirect method the impact impulse transmits to the concrete plate via a steel bar, in order to adapt the method for situations where there is no access to the plate being measured. In each method a two-dimensional finite element analysis (in axisymmetric geometry) was performed for the thickness measurement of concrete plates using the LS-DYNA program. Numerical results are presented for different values of plate thickness and different projectile speeds for both the direct and the indirect method and the indirect results are validated by comparison with the results obtained by the direct method. The method was validated against experimental measurements. A high energy impact wave produces plastic deformations in metals. In this research explosive welding was studied as an application of high energy impact waves. A new method for joining different, non-compatible metals (Al and Cu-based materials) was introduced. This method may be extended for use in offshore applications. Many 3-D numerical simulations were performed using the ABAQUS explicit commercial software. The model was validated against experimental measurements. The outcome of this research work could be summarized as follows: a) Introducing an indirect IE method in NDT technology for thickness measurement in particularly inaccessible structures. b) Introducing a new, grooved method in EXW technology to join surfaces made of different materials, in particular Al-Cu joints. The results could be employed to reduce the energy consumption and cost associated with EXW and IE technologies. The methodology can be used in many other applications in all kinds of process industries.
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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.
Testo completoAbstract (sommario):
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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Wolters, G. "Characteristics of wave impact induced pressure pulse propagation into cracks of coastal structures". Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419521.
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Mousavi, Saed. "Identification of Viscoelastic Materials by Use of Wave Propagation Methods". Doctoral thesis, Uppsala universitet, Hållfasthetslära, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8324.
Testo completoAbstract (sommario):
Complex moduli and Poisson’s ratio have been estimated using extensional and torsional wave experiments. The data were used for assessment of linearity and isotropy of two polymers, polymethyl methacrylate (PMMA) and polypropylene (PP). The responses of both materials were found to be close to linear and isotropic. A statistical analysis of different estimation approaches for complex modulus and Poisson’s ratio was conducted. It was shown that a joint estimation of complex modulus and Poisson’s ratio improves the estimated results. Considerable improvement was achieved in the frequency range 5-15 kHz for Poisson’s ratio. A non-equilibrium split Hopkinson pressure bar (SHPB) procedure for identification of complex modulus has been developed. Two simplified procedures were also established. Both overestimated the magnitude of the complex modulus. The complex modulus of PP was identified using PMMA and aluminium bars, and the estimated complex modulus was in good agreement with published results. The procedure was found to be accurate regardless of the specimen size or the specimen-to-bar impedance ratio. The procedure was also used to analyze the mechanical response of four compacted pharmaceutical tablet materials. A Debye-like relaxation was observed for all tested materials. Utilizing SHPB effectively requires knowledge about the impact process that is normally used for excitation. Therefore the impact between a cylindrical striker and a long cylindrical bar of viscoelastic material was studied theoretically and experimentally. Strains measured at three locations along a PMMA bar impacted by strikers of the same material agreed well with the theoretical results. A method for identification of complex shear modulus from measured shear strains on a disc subjected to a transient torque at its centre has been established. The two-dimensional wave solutions used are exact in the sense of three-dimensional theory. The results from experimental tests with different load amplitudes and durations agree well with each other.
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Robertson, A. W. "The impact of wind on a balsam fir wave forest at Spirity Cove, Newfoundland". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233583.
Testo completo
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Li, Guojing. "Development of a wireless instrumented projectile for impact testing based on elastic wave reduction". Diss., Connect to online resource - MSU authorized users, 2008.
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Samtleben, Nadja, e Ch Jacobi. "Impact of intermittent gravity wave activity on the middle atmospheric circulation during boreal winter". Universität Leipzig, 2018. https://ul.qucosa.de/id/qucosa%3A31793.
Testo completoAbstract (sommario):
Simulations of the circulation in the middle atmosphere during northern winter performed with a nonlinear, mechanistic, global circulation model show that the upper mesospheric jet is greatly overestimated and also the position with respect to latitude and height does not correspond to observations. Apart from that also the winter wind reversal in the mesopause region, evoked by breaking gravity waves (GWs), is located too low around 80km, but is observed to be usually around 100 km. These discrepancies are planned to be eliminated by modifying the distribution of GW amplitudes driving the GW parameterization. This distribution is currently based on potential GW energy data derived from GPS radio occultation measurements and has to be replaced by a distribution based on momentum flux estimates applying
midfrequency approximation. The results show a weaker mesospheric jet more realistically tilted towards lower latitudes with height. Also the meridional circulation extending from the summer to the winter pole decelerates and less GWs are propagating into the mesosphere. By additionally varying the GW amplitudes in magnitude and time, the wind reversal is shifted upwards and the mesospheric jet is slowed down.Simulationen der Zirkulation der mittleren Atmosphäre während des nordhemisphärischen Winters unter Verwendung eines nicht-linearen mechanistischen globalen Zirkulationsmodells ergaben beim Vergleich mit Messungen, dass der simulierte, mesosphärische Jet stark überschätzt wird und dessen Position von den Beobachtungen abweicht. Die in der Mesopausenregion einsetzende Windumkehr, hervorgerufen durch brechende Schwerewellen, befindet sich in etwa 80 km anstatt in 100 km. Diese Diskrepanzen sollen eliminiert werden. Hierfür wird die Verteilung der Schwerewellenamplituden, die die Schwerewellenparametrisierung innerhalb des Modells antreibt, am oberen Rand der Troposphäre modifiziert. Diese basiert derzeit auf global beobachteten, zonal gemittelten Daten der potentiellen Energie von Schwerewellen abgeleitet aus GPS Radiookkultationsmessungen und soll durch eine auf Impulsflüssen basierende Verteilung ersetzt werden. Das Modellexperiment zeigt, dass der mesosphärische Jet mit der Höhe in Richtung niedriger Breiten geneigt ist und abgebremst wird. Zudem schwächt die Meridionalzirkulation vom Sommer- zum Winterpol leicht ab und weniger Schwerewellen dringen bis in die Mesosphäre vor. Zusätzlich wird durch zeitliche und unterschiedlich starke Variation der Schwerewellenamplitude die Windumkehr verlagert und der mesosphärische Jet abgebremst.
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Reid, Terry Vincent. "A Computational Approach For Investigating Unsteady Turbine Heat Transfer Due To Shock Wave Impact". Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/25983.
Testo completoAbstract (sommario):
The effects of shock wave impact on unsteady turbine heat transfer are investigated. A numerical approach is developed to simulate the flow physics present in a previously performed unsteady wind tunnel experiment.
The windtunnel experiment included unheated and heated flows over a cascade of highly loaded turbine blades. After the flow over the blades was established, a single shock with a pressure ratio of 1.1 was introduced into the wind tunnel test section. A single blade was equipped with pressure transducers and heat flux microsensors. As the shock wave strikes the blade, time resolved pressure, temperature, and heat transfer data were recorded.Ph. D.
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Mackenzie, Graeme Douglas. "The shallow crustal structure of the Chicxulub impact crater from surface wave dispersion studies". Thesis, University of Leicester, 1999. http://hdl.handle.net/2381/30436.
Testo completoAbstract (sommario):
A surface wave dispersion study has been conducted on high frequency (0.5-5 Hz) crustal Rayleigh waves propagating across the 65 Ma. Chicxulub impact structure in Mexico. These were recorded on a 20 station seismic array deployed along 4 radial arms across the region and originated from nearby quarries within the array. Events originating from the same quarry were stacked prior to the application of a multiple filter technique to produce group velocity dispersion curves. Using a genetic algorithm several one-dimensional shear wave velocity-depth models have then been obtained through the optimisation of the fundamental and higher mode dispersion curves. The models provide information on the velocity structure of the upper few kilometres of the crust and suggest an infilling of the crater from the crater rim inwards. An inverted velocity gradient is modelled over the upper few hundred metres across most of the region with the exception of a central radial area. This inverted velocity zone may be connected to dolomitization during a late Miocene regression. The base of the Tertiary sequence is modelled at c. 1-1.5 km depth and shows increased velocities compared to the overlying sediments. This velocity increase may imply some form of hydrothermal alteration of the sediments caused by a thermal blanket effect created by the underlying crater breccia and melt. Immediately below the Tertiary sediments a c. 200 m thick low velocity zone is interpreted as a layer of suevitic impact breccia. Models obtained at c. 35-45 km radius from the crater centre are consistent with the existence of a peak ring as a topographic high above the crater floor. The results from the velocity models provide fresh information on the sedimentation of the region and some constraints on the crater morphology.
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Monges, Arnaud C. "Impact of the Madden-Julian oscillation over tropical South America During Austral summer". Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/25784.
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Haikonen, Kalle. "Underwater radiated noise from Point Absorbing Wave Energy Converters : Noise Characteristics and Possible Environmental Effects". Doctoral thesis, Uppsala universitet, Elektricitetslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-235016.
Testo completoAbstract (sommario):
The conversion of wave energy into electrical energy has the potential to become a clean and sustainable form of renewable energy conversion. However, like all forms of energy conversion it will inevitably have an impact on the marine environment, although not in the form of emissions of hazardous substances (gases, oils or chemicals associated with anticorrosion). Possible environmental issues associated with wave energy conversion include electromagnetic fields, alteration of sedimentation and hydrologic regimes and underwater radiated noise. Underwater noise has the potential to propagate over long distances and thus have the potential to disturb marine organisms far away from the noise source. There is great variation in the ability to perceive sound between marine organisms, one sound that is clearly audible to one species can be completely inaudible to another. Thus, to be able to determine potential environmental impact from WECs associated with underwater noise, the noise radiated from the WECs must be known. This thesis presents results from studies on the underwater radiated noise from four different full-scale WECs in the Lysekil Wave Power Project. Hydrophones were used to measure the underwater radiated noise from operating point absorbing linear WECs. The main purpose was to study the radiated noise from the operating WECs with emphasis on characteristics such as spectrum levels, Sound Pressure Level (SPL), noise duration and repetition rate. This to be able to determine the origin of the noise and if possible, implement design changes to minimize radiated noise. The results identified two main operational noises (transients with the bulk of the energy in frequencies <1 kHz). The SPL of the radiated noise fluctuated significantly, depending on wave height. Broadband SPLrms of the measurements ranged between ~110 dB and ~140 dB re 1 µPa and SPLpeak of specific noises ranges between ~140 and ~180 dB re µPa. Audibility was estimated range from 1km to 15 km depending critically on species and on assumptions of propagation loss. The noise is not expected to have any negative effects on behaviour or mask any signals, unless in the vicinity (<150m) of the WECs in significant wave heights. No physical damage, even in close vicinity are expected on either fish or marine mammals. Having the aim to have as little impact on the environment a possible, these studies are important. This way precautions can be implemented early in the technical development of this kind of renewable energy converters. The benefits from the WECs the Lysekil wave power project are believed to outweigh possible environmental impacts due to underwater radiated noise.Vid avhandlingens tryckläggning upptäcktes inte att tidpunkt för disputation var fel.
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Bramberger, Martina [Verfasser], e Markus [Akademischer Betreuer] Rapp. "Mountain wave impact on flight conditions of high-flying aircraft / Martina Bramberger ; Betreuer: Markus Rapp". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1188564285/34.
Testo completo
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Weeks, Hoi Ping. "The molecular and cellular impact of wave interactions on the aggressiveness of PC-3 cells". Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/70578/.
Testo completoAbstract (sommario):
The metastatic spread of cancer cells to distant sites in the body accounts for the majority of cancer-related death and significantly decreases patient survival. Whilst cell migration is a physiologically important process, when uncontrolled, it can be a contributing factor to the metastatic phenotype. Actin polymerisation enables the dynamic restructuring of the cytoskeleton which is fundamental to cell migration and is stimulated by the Arp (actin-related protein) 2/3 protein complex which in turn is activated by members of the WAVE (WASP Verprolin homologous protein) family. WAVE1 and 3 expression was targeted separately in the PC-3 cell line utilising ribozyme transgene transfection. In vitro experiments revealed a reduction in cell growth and invasion following WAVE1 or 3 knockdown in PC-3 cells. These experiments were also repeated with small molecule inhibitors targeting the Arp2/3 complex, ROCK and N-WASP independently. This inhibitor work implicates Arp2/3 as a facilitator of cell proliferation through which WAVE regulates. Inhibition of Arp2/3, ROCK or N-WASP in WAVE1 knockdown cells increased cell invasion which may be attributed to the regulatory role of WAVE3 on MMP activity. Co-localisation of WAVE1 and 3 with ARP2 and ROCK-I was observed in PC-3 cells whilst this affect was abolished with WAVE1 or 3 knockdown. Furthermore, WAVE3 and WAVE1 knockdown affected ARP2 and ROCK-II tyrosine phosphorylation, respectively. These results suggest WAVE1 and 3 proteins are involved in several metastatic traits that characterise PC-3 cells. Furthermore, the contribution of WAVE in the networks that influence these traits may also involve association with Arp2/3 complex, ROCK-I and –II and N-WASP. Additionally, it sheds light on the similarities between these two related proteins and also highlights their subtle distinctions in PC-3 cells. The data outlined here provides justification to futher explore WAVE1 and 3 as potential contributors of prostate cancer progression.
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Nikulin, Grigory. "Impact of Rossby waves on ozone distribution and dynamics of the stratosphere and troposphere". Doctoral thesis, Kiruna : Swedish institute of Space Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-596.
Testo completo
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Yang, Mijia. "IMPACT MECHANICS OF ELASTIC AND ELASTIC-PLASTIC SANDWICH STRUCTURES". University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1142444606.
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Langhamer, Olivia. "Wave energy conversion and the marine environment : Colonization patterns and habitat dynamics". Doctoral thesis, Uppsala universitet, Elektricitetslära, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-107193.
Testo completoAbstract (sommario):
A wave energy park has been established on the Swedish west coast outside Lysekil and pioneer work about its interactions with the marine environment has been conducted. So far, little is known about the effects of offshore energy installations on the marine environment, and this thesis assists in minimizing environmental risks as well as in enhancing potential positive effects on the marine environment. The Lysekil research site is situated about two kilometres offshore and has been under development since 2005. During this time 26 “environmental devices”, without generators, consisting of a steel buoy attached via a wire to a foundation on 25 m depth have been placed out for ecological studies on macrofauna in surrounding sediments and on colonization of the foundations and the buoys. Sediment samples to examine macrofauna in the seabed have been taken during five seasons. Biomass, abundance and diversity of infauna in the test site were generally low, but higher than in a nearby control site. The species composition was typical for the area and depth. In addition to sediment analysis, the effect of wave power concrete foundations on the marine environment has been investigated by scuba diving. The surface orientation and its effect on colonization by sessile organisms was examined on the first five foundations, placed out in 2005, and observations of habitat use by fish and crustaceans were made. The results show a succession of colonization over time (three years of investigation) with a higher cover by sessile organisms on vertical surfaces. Mobile fauna abundance on and around the foundations was generally low. Three months after the deployment of the 21 new foundations in 2007, assemblages of mobile organisms were examined visually. Also here, mobile species exhibit a low density, but still higher than on surrounding soft bottoms. The edible crab used artificial holes in the foundations frequently. The foundations were placed in two different clusters, north and south, and the degree to which early recruits covered the foundations and the succession of epibenthic communities were documented during two years. Sessile organisms colonized the northern foundations more rapidly, producing a higher diversity which suggests that the placement of wave energy devices affects colonization patterns. Biofouling on buoys was examined and blue mussels, Mytilus edulis, dominated with a cover about 90%. Wave exposed buoys were particularly favoured by M. edulis which there had a higher biomass and larger shells compared to those on sheltered buoys. Biofouling on wave power buoys, independent whether these had a cylindrical or toroidal shape, was insufficient to markedly affect their energy production. Finally, the thesis incorporates a review describing wave power projects in general pointing out the need of future research on for instance no-take zones, marine bioacoustics and electromagnetic fields. The main conclusions are that large-scale renewable wave energy conversion will cause ecological impact primarily by adding new hard substrate to an area but not by harming organisms or decreasing biodiversity within wave power parks.