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1
Mockutė, Agota, Enzo Marino, Claudio Lugni, and Claudio Borri. "Comparison of Nonlinear Wave-Loading Models on Rigid Cylinders in Regular Waves." Energies 12, no. 21 (October 23, 2019): 4022. http://dx.doi.org/10.3390/en12214022.
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Monopiles able to support very large offshore wind turbines are slender structures susceptible to nonlinear resonant phenomena. With the aim to better understand and model the wave-loading on these structures in very steep waves where ringing occurs and the numerical wave-loading models tend to lose validity, this study investigates the distinct influences of nonlinearities in the wave kinematics and in the hydrodynamic loading models. Six wave kinematics from linear to fully nonlinear are modelled in combination with four hydrodynamic loading models from three theories, assessing the effects of both types of nonlinearities and the wave conditions where each type has stronger influence. The main findings include that the nonlinearities in the wave kinematics have stronger influence in the intermediate water depth, while the choice of the hydrodynamic loading model has larger influence in deep water. Moreover, finite-depth FNV theory captures the loading in the widest range of wave and cylinder conditions. The areas of worst prediction by the numerical models were found to be the largest steepness and wave numbers for second harmonic, as well as the vicinity of the wave-breaking limit, especially for the third harmonic. The main cause is the non-monotonic growth of the experimental loading with increasing steepness due to flow separation, which leads to increasing numerical overpredictions since the numerical wave-loading models increase monotonically.
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Pitchforth, D. J., T. J. Rogers, U. T. Tygesen, and E. J. Cross. "Grey-box models for wave loading prediction." Mechanical Systems and Signal Processing 159 (October 2021): 107741. http://dx.doi.org/10.1016/j.ymssp.2021.107741.
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Ahmad, Sayyid Zainal Abidin Syed, Mohd Khairi Abu Husain, Noor Irza Mohd Zaki, Mohd Hairil Mohd, and Gholamhossein Najafian. "Comparison of Various Spectral Models for the Prediction of the 100-Year Design Wave Height." MATEC Web of Conferences 203 (2018): 01020. http://dx.doi.org/10.1051/matecconf/201820301020.
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Offshore structures are exposed to random wave loading in the ocean environment, and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. In most cases, the dominant load on offshore structures is due to wind-generated random waves where the ocean surface elevation is defined using appropriate ocean wave energy spectra. Several spectral models have been proposed to describe a particular sea state that is used in the design of offshore structures. These models are derived from analysis of observed ocean waves and are thus empirical in nature. The spectral models popular in the offshore industry include Pierson-Moskowitz spectrum and JONSWAP spectrum. While the offshore industry recognizes that different methods of simulating ocean surface elevation lead to different estimation of design wave height, no systematic investigation has been conducted. Hence, the aim of this study is to investigate the effects of predicting the 100-year responses from various wave spectrum models. In this paper, the Monte Carlo time simulation (MCTS) procedure has been used to compare the magnitude of the 100-year extreme responses derived from different spectral models. Additionally, the linear random wave theory (LRWT) was implemented to simulate the offshore structural responses due to random wave loading. The models have been tested for three different environmental conditions represented by Hs = 15m, 10m and 5m respectively. The accuracy of the predictions of the 100-year responses from Pierson-Moskowitz and JONSWAP spectrums will then be investigated.
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Lindt, John W. van de, Rakesh Gupta, Daniel T. Cox, and Jebediah S. Wilson. "Wave Impact Study on a Residential Building." Journal of Disaster Research 4, no. 6 (December 1, 2009): 419–26. http://dx.doi.org/10.20965/jdr.2009.p0419.
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Recent natural disasters around the world including both tsunamis and hurricanes, have highlighted the inability of wood buildings to withstand wave and surge loading during these extreme events. Little is known about the interaction between coastal residential light-frame wood buildings and wave and surge loading because often little is left of the buildings. This leaves minimal opportunity for forensic investigations. This paper summarizes the results of a study whose objective was to begin to better understand the interaction between North American style residential structures and wave loading. To do this, one-sixth scale residential building models typical of North American coastal construction, were subjected to tsunami wave bores generated from waves of heights varying from 10 cm to 60 cm. The lateral force produced by the wave bores were, as expected, found to vary nonlinearly with parent wave height.
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Raovic, Nevena, Otto Anker Nielsen, and Carlo Giacomo Prato Carlo Giacomo Prato. "DYNAMIC QUEUING TRANSMISSION MODEL FOR DYNAMIC NETWORK LOADING." Transport 32, no. 2 (July 13, 2015): 146–59. http://dx.doi.org/10.3846/16484142.2015.1062417.
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This paper presents a new macroscopic multi-class dynamic network loading model called Dynamic Queuing Transmission Model (DQTM). The model utilizes ‘good’ properties of the Dynamic Queuing Model (DQM) and the Link Transmission Model (LTM) by offering a DQM consistent with the kinematic wave theory and allowing for the representation of multiple vehicle classes, queue spillbacks and shock waves. The model assumes that a link is split into a moving part plus a queuing part, and p that traffic dynamics are given by a triangular fundamental diagram. A case-study is investigated and the DQTM is compared with single-class LTM, single-class DQM and multi-class DQM. Under the model assumptions, single-class models indicate that the LTM and the DQTM give similar results and that the shock wave property is properly included in the DQTM, while the multi-class models show substantially different travel times for two vehicle classes. Moreover, the results show that the travel time will be underestimated without considering the shock wave property.
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Fox, Colin, and Tim G. Haskell. "Ocean wave speed in the Antarctic marginal ice zone." Annals of Glaciology 33 (2001): 350–54. http://dx.doi.org/10.3189/172756401781818941.
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AbstractThe propagation of ocean waves in the marginal ice zone (MIZ) is investigated with the aim of determining whether the loading and scattering of waves by ice floes is significant. Measurements made using instrumented ice floes in the MIZ north of the Ross Sea, Antarctica, during June 1998 are used to determine the frequency-wavelength relationship for propagating ocean waves in that region. This measured-dispersion equation is related to the effective large-scale properties of the MIZ that occur in models for wave propagation and scattering. We present the measured wave speeds to enable estimation of the parameters in these models.
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Robertson, Amy, and Lu Wang. "OC6 Phase Ib: Floating Wind Component Experiment for Difference-Frequency Hydrodynamic Load Validation." Energies 14, no. 19 (October 8, 2021): 6417. http://dx.doi.org/10.3390/en14196417.
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A new validation campaign was conducted at the W2 Harold Alfond Ocean Engineering Laboratory at the University of Maine to investigate the hydrodynamic loading on floating offshore wind substructures, with a focus on the low-frequency contributions that tend to drive extreme and fatigue loading in semisubmersible designs. A component-level approach was taken to examine the hydrodynamic loads on individual parts of the semisubmersible in isolation and then in the presence of other members to assess the change in hydrodynamic loading. A variety of wave conditions were investigated, including bichromatic waves, to provide a direct assessment of difference-frequency wave loading. An assessment of the impact of wave uncertainty on the loading was performed, with the goal of enabling validation with this dataset of numerical models with different levels of fidelity. The dataset is openly available for public use and can be downloaded from the U.S. Department of Energy Data Archive and Portal.
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Bouyssy, V., and R. Rackwitz. "Polynomial Approximation of Morison Wave Loading." Journal of Offshore Mechanics and Arctic Engineering 119, no. 1 (February 1, 1997): 30–36. http://dx.doi.org/10.1115/1.2829042.
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For offshore structures with slender elements, the modeling of random wave loads by the Morison equation yields an equation of motion which has no analytical solution for response moments except in a few limiting cases. If polynomial approximations of the Morison drag loads are introduced, some procedures are available to obtain the stationary moments of the approximate response. If the response process is fitted by non-Gaussian models such as proposed by Winterstein (1988), the first four statistical moments of the response are necessary. The paper investigates how many terms should be included in the polynomial approximation of the Morison drag loading to accurately estimate the first four response moments. It is shown that a cubic approximation of the drag loading is necessary to accurately predict the response variance for any excitation. For the fit of the first four response moments, at least a fifth-order approximation appears necessary.
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Beltman, W. M., E. N. Burcsu, J. E. Shepherd, and L. Zuhal. "The Structural Response of Cylindrical Shells to Internal Shock Loading." Journal of Pressure Vessel Technology 121, no. 3 (August 1, 1999): 315–22. http://dx.doi.org/10.1115/1.2883709.
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The internal shock loading of cylindrical shells can be represented as a step load advancing at constant speed. Several analytical models are available to calculate the structural response of shells to this type of loading. These models show that the speed of the shock wave is an important parameter. In fact, for a linear model of a shell of infinite length, the amplitude of the radial deflection becomes unbounded when the speed of the shock wave is equal to a critical velocity. It is evident that simple (static) design formulas are no longer accurate in this case. The present paper deals with a numerical and experimental study on the structural response of a thin aluminum cylindrical shell to shock loading. Transient finite element calculations were carried out for a range of shock speeds. The results were compared to experimental results obtained with the GALCIT 6-in. shock tube facility. Both the experimental and the numerical results show an increase in amplitude near the critical velocity, as predicted by simple steady-state models for shells of infinite length. However, the finite length of the shell results in some transient phenomena. These phenomena are related to the reflection of structural waves and the development of the deflection profile when the shock wave enters the shell.
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Bloom, Frederick. "Constitutive Models for Wave Propagation in Soils." Applied Mechanics Reviews 59, no. 3 (May 1, 2006): 146–75. http://dx.doi.org/10.1115/1.2177685.
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A survey is provided of the various constitutive models that have been used to study the phenomena of wave propagation in soils. While different material models have been proposed for the response of soils, it is now generally understood that no single model may be used over the entire range of pressures which are typically studied. The constitutive models reviewed in this paper include a number of effective stress and multiphase models, the volume distribution function model, and various versions of the P−α model. Also discussed are classical elastic-plastic models, models possessing different elastic constants in loading and unloading, variable modulus models, and capped elastic-plastic models.
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Elosta, Hany, Shan Huang, and Atilla Incecik. "Wave loading fatigue reliability and uncertainty analyses for geotechnical pipeline models." Ships and Offshore Structures 9, no. 4 (October 22, 2013): 450–63. http://dx.doi.org/10.1080/17445302.2013.834168.
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Najafian, G. "Probability models for offshore structural response due to Morison wave loading." Ocean Engineering 34, no. 17-18 (December 2007): 2289–99. http://dx.doi.org/10.1016/j.oceaneng.2007.05.013.
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Prikazchikov, Danila A. "Asymptotic Formulation for the Rayleigh Wave on a Nonlocally Elastic Half-Space." Vibration 6, no. 1 (January 7, 2023): 57–64. http://dx.doi.org/10.3390/vibration6010005.
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This paper deals with the Rayleigh wave, propagating on a nonlocally elastic, linearly isotropic half-space, excited by a prescribed surface loading. The consideration develops the methodology of hyperbolic–elliptic models for Rayleigh and Rayleigh-type waves, and relies on the effective boundary conditions formulated recently, accounting for the crucial contributions of the nonlocal boundary layer. A slow-time perturbation scheme is established, leading to the reduced model for the Rayleigh wave field, comprised of a singularly perturbed hyperbolic equation for the longitudinal wave potential on the surface, acting as a boundary condition for the elliptic equation governing the decay over the interior. An equivalent alternative formulation involving a pseudo-differential operator acting on the loading terms, with parametric dependence on the depth coordinate, is also presented.
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Shoaib, M., and L. Kari. "Discrete Element Simulation of Elastoplastic Shock Wave Propagation in Spherical Particles." Advances in Acoustics and Vibration 2011 (August 9, 2011): 1–9. http://dx.doi.org/10.1155/2011/123695.
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Elastoplastic shock wave propagation in a one-dimensional assembly of spherical metal particles is presented by extending well-established quasistatic compaction models. The compaction process is modeled by a discrete element method while using elastic and plastic loading, elastic unloading, and adhesion at contacts with typical dynamic loading parameters. Of particular interest is to study the development of the elastoplastic shock wave, its propagation, and reflection during entire loading process. Simulation results yield information on contact behavior, velocity, and deformation of particles during dynamic loading. Effects of shock wave propagation on loading parameters are also discussed. The elastoplastic shock propagation in granular material has many practical applications including the high-velocity compaction of particulate material.
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Badshah, Eid, Amjad Naseer, Muhammad Ashraf, Feroz Shah, and Kareem Akhtar. "Review of Blast Loading Models, Masonry Response, and Mitigation." Shock and Vibration 2017 (2017): 1–15. http://dx.doi.org/10.1155/2017/6708341.
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Different models for prediction of blast loading, response of masonry structure against blast load, and various mitigation strategies are discussed. Variation of peak positive incident pressure with scale distance in free field spherical burst and surface burst scenarios, proposed by different researchers, is presented and compared. The variation is found significant in the region of small scaled distances. Blast wave parameters in urban environment have been found different from the free field scenario. Effects of geometry, boundary conditions, and material properties on response of masonry buildings were found significant. Different mitigation strategies such as blast wall, landscaping, architecture, and retrofitting techniques are presented.
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Raby, A. C., A. Antonini, A. Pappas, D. T. Dassanayake, J. M. W. Brownjohn, and D. D'Ayala. "Wolf Rock lighthouse: past developments and future survivability under wave loading." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2155 (August 19, 2019): 20190027. http://dx.doi.org/10.1098/rsta.2019.0027.
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Lighthouses situated on exposed rocky outcrops warn mariners of the dangers that lurk beneath the waves. They were first constructed when approaches to wave loading and structural response were relatively unsophisticated, essentially learning from previous failures. Here, we chart the evolution of lighthouses on the Wolf Rock, situated between Land's End and the Isles of Scilly in the UK. The first empirical approaches are described, followed by design aspects of the present tower, informed by innovations developed on other rocky outcrops. We focus on a particular development associated with the automation of lighthouses: the helideck platform. The design concept is described and the structure then scrutinized for future survivability, using the latest structural modelling techniques of the entire lighthouse and helideck. Model validation data were obtained through a complex logistical field operation and experimental modal analysis. Extreme wave loading for the model required the identification of the 250-year return period wave using a Bayesian method with informative prior distributions, for two different scenarios (2017 and 2067). The structural models predict responses of the helideck to wave loading which is characterized by differential displacements of 0.093 m (2017) and 0.115 m (2067) with associated high tension forces and plastic strain. This article is part of the theme issue ‘Environmental loading of heritage structures’.
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Liu, Jie, Jian Lin Li, Ying Xia Li, Shan Shan Yang, Ji Fang Zhou, and Chao Feng Zhang. "Studies on Related ms Magnitude Rate Models in Triangular Wave Unloading Section of Calcium Medium-Fine Sandstone." Advanced Materials Research 152-153 (October 2010): 164–70. http://dx.doi.org/10.4028/www.scientific.net/amr.152-153.164.
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Specific to the improvement in the present research of mechanical response under cyclic loading, this paper, taking the calcareous middle- coarse sandstone as the research subject and the RMT-150C experimental system in which data is recoded by ms magnitude as the platform, develops several related models concerning the unloading rate of triangle waves. The unloading process is divided into lag time segment and non-lag time segment, with criterions and related parameters provided as well. The term apparent elastic modulus is defined. The test data analysis shows that there exist a linear relationship between the apparent modulus and instant vertical force before load damage in non-lag time segment. On the preceding basis, a rate-dependent model of triangular wave un-installation section in non-lag time segment is established. Due to the inability of the loading equipment to accurately input the triangle wave, the average loading rate is amended and a constant term is added into it. The model is proved to be reliable, as the predicted value of the deformation rate and the stress strain curve coincides with measured value. At the same time, the impact of the lag time is pointed out quantitatively and a predication model of lag time segment is set up.
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Li, Jingru, Sheng Li, and Zhongjian Miao. "Investigations on the Complex Band Diagram of Flexural Wave through the Fluid-Loaded Phononic Plate." Applied Sciences 12, no. 23 (December 3, 2022): 12386. http://dx.doi.org/10.3390/app122312386.
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This paper investigates the complex band diagram of flexural waves in the phononic plate with semi-infinite heavy fluid loading. The system under examination is a square plate lattice with two-dimensional periodicity immersed in a fluid domain with infinite height. The numerical models based on the wave field transformation and the Galerkin method combined with the finite element discretization technique are developed to investigate the real and imaginary parts of the dispersion relation of flexural waves propagating through the phononic plate incorporating the fluid-loading effects. A perfect agreement is found between the location and width of stop bands from the real band diagram and the attenuation diagram, which supports the validity of the numerical models. Moreover, the complex band diagram is verified by the transverse vibration transmittance of the finite phononic plate. The results demonstrate that the external fluid loading is able to adjust the location, bandwidth, and decaying level as well as affect the degree of attenuation anisotropy of the complete and directional band gaps.
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Jeng, Dong-Sheng, Xiaoxiao Wang, and Chia-Cheng Tsai. "Meshless Model for Wave-Induced Oscillatory Seabed Response around a Submerged Breakwater Due to Regular and Irregular Wave Loading." Journal of Marine Science and Engineering 9, no. 1 (December 24, 2020): 15. http://dx.doi.org/10.3390/jmse9010015.
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The evaluation of wave-induced seabed stability around a submerged breakwater is particularly important for coastal engineers involved in design of the foundation of breakwaters. Unlike previous studies, a mesh-free model is developed to investigate the dynamic soil response around a submerged breakwater in this study. Both regular and irregular wave loadings are considered. The present model was validated against the previous experimental data and theoretical models for both regular and irregular waves. Parametric study shows the regular wave-induced liquefaction depth increases as wave period and wave height increase. The seabed is more likely to be liquefied with a low degree of saturation and soil permeability. A similar trend of the effects of wave and seabed characteristics on the irregular wave-induced soil response is found in the numerical examples.
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Yao, Shujian, Nan Zhao, Zhigang Jiang, Duo Zhang, and Fangyun Lu. "Dynamic Response of Steel Box Girder under Internal Blast Loading." Advances in Civil Engineering 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/9676298.
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This paper aims at investigating the dynamic response of the steel box girder under internal blast loads through experiments and numerical study. Two blast experiments of steel box models under internal explosion were conducted, and then, the numerical methods are introduced and validated. The dynamic response process and propagation of the internal shock wave of a steel box girder under internal blast loading were investigated. The results show that the propagation of the internal shock wave is very complicated. A multi-impact effect is observed since the shock waves are restricted by the box. In addition, the failure modes and the influence of blast position as well as explosive mass were discussed. The holistic failure mode is observed as local failure, and there are two failure modes for the steel box girder's components, large plastic deformation and rupture. The damage features are closely related to the explosive position, and the enhanced shock wave in the corner of the girder will cause severe damage. With the increasing TNT mass, the crack diameter and the deformation degree are all increased. The longitudinal stiffeners restrict the damage to develop in the transverse direction while increase the crack diameter along the stiffener direction.
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Chaplin, J. R., K. Subbiah, and M. Irani. "Loading on a Vertical Cylinder in Multidirectional Waves." Journal of Offshore Mechanics and Arctic Engineering 117, no. 3 (August 1, 1995): 151–58. http://dx.doi.org/10.1115/1.2827083.
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This paper presents laboratory measurements of local and total loading on an isolated vertical cylinder in irregular unidirectional and multidirectional waves. Maximum Keulegan-Carpenter numbers in individual waves were about 16, and maximum Reynolds numbers about 3 × 104. It is shown that in these conditions, existing theoretical and numerical models underestimate the reduction in loading on a cylinder due to wave spreading. Besides the changes that are predicted when Morison’s equation is used with constant coefficients, there are hydrodynamic influences that contribute further force reductions. Comparisons with Dean’s (1977) hybrid approach suggest that in the present conditions these reductions are in the region of 3 and 6 percent for a spreading function cos2s θ, with s = 8 and s = 2, respectively. Larger reductions can be expected at higher Keulegan-Carpenter numbers, though scale effects are likely to become more important in the drag-dominated regime.
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Bezuijen, A., J. Wouters, and C. Laustrup. "BLOCK REVETMENT DESIGN WITH PHYS. AND NUM. MODELS." Coastal Engineering Proceedings 1, no. 21 (January 29, 1988): 160. http://dx.doi.org/10.9753/icce.v21.160.
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A combination of a physical model and numerical models has been used in the design of a block revetment for the Danish North Sea coast. The wave pressure loading on the revetment during design conditions was investigated in a physical scale model. The measured wave pressures were used as a boundary condition for the numerical models. Solutions for the flow equations through the coverlayer, filter layer and subsoil were then obtained in the numerical models, taking into account the influence of turbulence. With these solutions the stability of the coverlayer and subsoil was evaluated. The paper presents a description of the various models and information about the design of the revetment.
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SWANTEK, A. B., and J. M. AUSTIN. "Collapse of void arrays under stress wave loading." Journal of Fluid Mechanics 649 (April 13, 2010): 399–427. http://dx.doi.org/10.1017/s0022112009993545.
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The interaction of an array of voids collapsing after passage of a stress wave is studied as a model problem relevant to porous materials, for example, to energy localization leading to hotspot formation in energetic materials. Dynamic experiments are designed to illuminate the hydrodynamic processes of collapsing void interactions for eventual input into device-scale initiation models. We examine a stress wave loading representative of accidental mechanical insult, for which the wave passage length scale is comparable with the void and inter-void length scales. A single void, two-void linear array, and a four-void staggered array are studied. Diagnostic techniques include high-speed imaging of cylindrical void collapse and the first particle image velocimetry measurements in the surrounding material. Voids exhibit an asymmetrical collapse process, with the formation of a high-speed internal jet. Volume and diameter versus time data for single void collapse under stress wave loading are compared with literature results for single voids under shock-wave loading. The internal volume history does not fall on a straight line and is in agreement with simulations, but in contrast to existing linear experimental data fits. The velocity field induced in the surrounding material is measured to quantify a region of influence at selected stages of single void collapse. In the case of multiple voids, the stress wave diffracts in response to the presence of the upstream void, affecting the loading condition on the downstream voids. Both collapse-inhibiting (shielding) and collapse-triggering effects are observed.
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Foda, Mostafa A., Adrian W. K. Law, and Jo Y. H. Chang. "WAVE-INDUCED BREAKOUT OF HALF-BURIED MARINE PIPES." Coastal Engineering Proceedings 1, no. 21 (January 29, 1988): 109. http://dx.doi.org/10.9753/icce.v21.109.
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An experimental study is conducted in order to identify the major physical processes leading to the breakout of half-buried submarine pipelines from the seafloor under ocean wave action. Both the hydrodynamic loading on the exposed surface of the pipe, as well as the resulting displacement history of the pipe, were recorded and analyzed in order to identify the critical pipe-soil-wave conditions for the detachment of the pipe from the seabed. The paper also examines the balance of the pipe under the combined lift and drag loading from the water wave. An experimental breakout force-time power law is obtained and compared to available theoretical breakout models.
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Syed Ahmad, Sayyid Zainal Abidin, Mohd Khairi Abu Husain, Noor Irza Mohd Zaki, Nurul ‘Azizah Mukhlas, and Gholamhossein Najafian. "An Improved Version of ETS-Regression Models in Calculating the Fixed Offshore Platform Responses." Journal of Marine Science and Engineering 10, no. 11 (November 11, 2022): 1727. http://dx.doi.org/10.3390/jmse10111727.
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An offshore structural design should accurately calculate wave loads and structural responses acting on slender cylinders. The hydrodynamic drag-dominated force was always challenging, hence the hydrodynamic wave loading became a complex solution; it led to a nonlinear relation between the wave force and responses caused by the diffracted and radiated waves, which was included in Morison’s equation. For more consistency in the structural assessment, the linearised drag–inertia force was considered in model development, such as an improved version of the efficient time simulation regression (ETS-Reg) procedure that was introduced. The study aimed to improve the prediction of structural responses using the predetermined linear, polynomial, and cubic regression models. These simulations were performed focusing on high sea state conditions without wave-induced current effects. In order to evaluate the level of accuracy, the recent ETS-Reg models were compared and validated using the Monte Carlo time simulation (MCTS) method. An amended ETS-Reg model, known as the ETS-RegLR model, was also compared with the previous results obtained using the conventional ETS-Reg models (ETS-RegSE), leading to better structural response calculations.
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Braun, Moritz, Alfons Dörner, Kane F. ter Veer, Tom Willems, Marc Seidel, Hayo Hendrikse, Knut V. Høyland, Claas Fischer, and Sören Ehlers. "Development of Combined Load Spectra for Offshore Structures Subjected to Wind, Wave, and Ice Loading." Energies 15, no. 2 (January 13, 2022): 559. http://dx.doi.org/10.3390/en15020559.
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Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.
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Yuan, L., Tao Xu, and Q. Xu. "Spallation of Concrete under Dynamic Loading: Mesh Size Effect." Applied Mechanics and Materials 50-51 (February 2011): 929–33. http://dx.doi.org/10.4028/www.scientific.net/amm.50-51.929.
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Spallation of concrete under dynamic loading has been the hot issue of concern about civil engineering structures and protective engineering. In the present paper, the principle of propagation of stress wave and the induced spallation process along a one-dimensional bar and the RFPA-Dynamics code which considers the heterogeneity of the concrete materials are briefly introduced. In order to numerically investigate the effect of mesh size of numerical model on the computational results, the failure process of concrete with three mesh sizes under dynamic loads was numerically simulated using RFPA-Dynamics code. Numerical simulations show that the failure patterns of concrete with different mesh sizes under dynamic stress waves are different. It is found that for the numerical models with the same mechanical parameters, the smaller mesh size of the numerical model is, the longer propagation of stress wave delay, the smaller the compressive stress is, thus the greater the tensile stress is, and the number of cracks is increasing, in general, rupture is more serious. The accuracy of mesh is little to improve when the number of the grid increases to a certain value.
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Liang, Minzu, Xiangyu Li, Yuliang Lin, and Fangyun Lu. "Compaction Wave Propagation in Layered Cellular Materials Under Air-Blast." International Journal of Applied Mechanics 11, no. 01 (January 2019): 1950003. http://dx.doi.org/10.1142/s1758825119500030.
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The propagation of compaction waves in layered cellular material subjected to air-blast is analyzed to examine the mechanism of compaction wave and reveal the phenomena that develop at the interface between the cellular layers. Similar to the previous studies of cellular materials under dynamic loading, the topology of cellular materials is neglected and homogeneous properties are assumed. The rigid-perfectly plastic-locking (R-PP-L) material idealization and the simple shock theory are employed to analyze the compaction situations. Analytical solutions for compaction wave propagation of double-layer cellular materials with two gradient-arrangements under air-blast loading have been worked out. The densification wave occurs at the blast end and then gradually propagates to the distal end for layers’ densities increase in the propagation direction (positive gradient). While compaction waves simultaneously form in both layers and propagate to the distal end in the same direction for the negative gradient. The finite element (FE) models using the Voronoi technique are carried out with practical aluminum foam to verify the predictions of the theoretical analysis. The potential of layered cellular materials to design efficient structural components under air-blast load is discussed, which would outperform their corresponding single counterpart with equal mass.
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Liu, Tian Hua, and Shang Jiu Meng. "Computer Simulation of Pore-Water Pressure." Advanced Materials Research 852 (January 2014): 613–18. http://dx.doi.org/10.4028/www.scientific.net/amr.852.613.
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An appropriate analysis of pore pressure models under irregular loading effects is provided. the model is based on liquefaction test with the constant amplitude loading and pore pressure model, based on the accumulated principle of residual pore pressure, using the differential method: superposition method and optimization method. Using constant amplitude loading liquefied test, and artificial modulation irregular load liquefied test and earthquake wave input dynamic triaxial liquefied test on model, the system has been tested, the result displayed: (1) the model can better simulate the results of constant amplitude loading liquefied test; (2) the model can better describe the trend on artificial modulation irregular load liquefied test results (3) the model can describe pore-pressure growth law under earthquake wave, and also can better analysis on differential pore-pressure under different type of earthquake wave (4) the model has less parameters, can analysis of pore-pressure in real time, easy to use.
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Santamarina, J. C., and G. Cascante. "Stress anisotropy and wave propagation: a micromechanical view." Canadian Geotechnical Journal 33, no. 5 (November 6, 1996): 770–82. http://dx.doi.org/10.1139/t96-102-323.
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Wave propagation is a constant-fabric macrophenomenon, suitable to microinterpretation. Both velocity and attenuation characterize state, including inherent and stress-induced anisotropy. The purpose of this research is to study the effect of isotropic and deviatoric stresses on wave propagation in particulate materials at low strains and to interpret results at the microlevel. A resonant-column device was midified to allow for the application of axial extension and axial compression deviatoric loading. The fixed-free boundary condition of the sample was maintained. Data for round, hard-grained sand show that shear wave velocity and attenuation are primarily dependent on the mean stress on the polarization plane, with minimal effect of the deviatoric component, in agreement with prior observations at stress ratios less than 23. Attenuation is strongly correlated with the mean stress in the polarization plane and the level of shear strain. Damping does not vanish at low strains, contrary to predictions based on hysteretic behaviour; hence, other loss mechanisms must take place at low strains. Low-strain wave parameters are adequately corrected for mid-strain using modified hyperbolic models. Measured velocity and damping trends during isotropic and anisotropic loading qualitatively agree with predictions based on regular arrays. Key words: mechanical waves, resonant column, damping, shear modulus, stress anisotropy, random vibration.
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Patil, Sandeep, Rahul Murkute, Nima Shirafkan, and Bernd Markert. "Deformation of Stacked Metallic Sheets by Shock Wave Loading." Metals 8, no. 9 (August 29, 2018): 679. http://dx.doi.org/10.3390/met8090679.
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The focus of the present work is to develop a deep understanding of deformation of stacked metal sheets with a series of different sequences by using shock wave loading. Here, experimental and numerical investigations of deformation of a single metal sheet of 1.5-mm and the stack of three metal sheets of 0.5-mm thickness of aluminum (Al), copper (Cu) and brass (Br) material were carried out. In the shock wave experiments, helium was used as the driving gas to produce a strong shock wave. Finite elements method (FEM) simulations on 3D-computational models were performed with explicit dynamic analysis, and Johnson-Cook material model was used. The obtained results from experiments of the outer diameter, thickness distribution, and dome height were analyzed and compared with the numerical simulations, and both the results are in excellent agreement. Moreover, for the same pressure load, due to lower inter-metallic friction in the stacked sheets compared to a cohesive property of the single sheet, an excellent deformation of stacked metallic sheets was observed. The results of this work indicated that the shock wave-forming process is a feasible technique for mass production of stacked metallic sheets as well as fabricating a hierarchical composite structure, which provides higher formability and smooth thickness distribution compared to a single material.
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Sun, Ze, Mengchun Bian, Jun Ding, Jiarui Liu, Haicheng Zhang, and Daolin Xu. "Study on the Wind and Wave Environmental Conditions of the Xisha Islands in the South China Sea." Journal of Marine Science and Engineering 10, no. 10 (October 9, 2022): 1459. http://dx.doi.org/10.3390/jmse10101459.
Full textAbstract:
Wind and waves are the main factors of environmental loading on ships and offshore structures. Thus, detailed understanding of wind and wave conditions can improve the design and maintenance of these structures. This paper developed a validated long-term wind and wave hindcast database covering the recent 32 years from 1988 to 2019. The spatial distribution of wind and wave characteristics for the whole Xisha Islands’ domain were analyzed. Frequency and directional distributions of wind speeds and significant wave heights were investigated at several locations around typical islands. Extreme value models were used to estimate the wind speed for 100-year return levels, whereas environmental contour approaches were utilized to establish the extreme sea-state parameters for 50- and 100-year return periods. It was found that the Weibull distribution was better fitted to the significant wave heights of the Xuande Atoll’s sites in the open sea, while the exponential Weibull distribution provided a better fit at the Yongle Atoll’s sites where waves are sheltered.
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Westcott, Gregory, Annette R. Grilli, Stephan Grilli, James T. Kirby, and Fengyan Shi. "INDIVIDUAL WAVE EFFECTS ON COASTAL STRUCTURE DAMAGE DURING WINDSTORMS." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 14. http://dx.doi.org/10.9753/icce.v36.structures.14.
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In hazard assessment studies that evaluate the damage caused to coastal structures by windstorm-generated surge and waves, the standard approach has been to estimate structural loading by applying phase-averaged wave propagation models (e.g., SWAN, STWAVE) and storm surge models (e.g., ADCIRC), coupled or not with each other. Bare-earth “Digital Elevation Models†(DEMs) have typically been used as a basis for model grid development, with sometimes empirical adjustments being made to beach profiles or dune crest levels to account for storm-induced erosion. In recent work, the latter approach has been improved by including real time morphodynamic changes in simulations, using models such as XBeach (e.g., Schambach 2017; Schambach et al., 2017), which are still based on the wave action conservation equation, including semi-empirical parameterizations of wave breaking and many formulations based on linear wave theory (e.g., phase/group velocity, radiation stresses,…), as well as low-order wave-wave interaction terms. Finally, structural damage has typically been estimated based on empirical damage curves, developed based on field surveys, that use flow depth and controlling wave crest height as inputs (e.g., Grilli et al., 2017). Neglected in this modeling approach, however, are dynamic set-up and runup effects, as well as strongly nonlinear wave interactions that occur near and in the surf and swash zones.
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Erofeev, Vladimir I., Sergey I. Gerasimov, and Alexey O. Malkhanov. "Nonlinear Spatial Localized Strain Waves." EPJ Web of Conferences 183 (2018): 02030. http://dx.doi.org/10.1051/epjconf/201818302030.
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A possible way of study of single waves in solids is discussed. The soliton is one of these waves without shape and parameters varying. Soliton deformation parameters are connected with the elastic moduli of the third order that allows defining values of these moduli by means of the measured solitondeformation parameters in various type waveguides made of the same material. The conditions under which a soliton can exist in a rod are analytically determined. For simultaneous excitation of loading in several wave guides two new energetic photosensitive structures (the mixtures are given) initiated by means of short light impulses of noncoherent light sources are proposed. Conditions of excitation of the waves on the basis of multipoint optical initiation loading impulses are described. As a technique for registration the shadowgraph visualization is proposed. It is discussed, how the problem connected to the use of energetic initiation structures consisting in the power background illumination can be solved. The shadow scheme with the use of a tiny dot explosive light source (Tbr ~41 kK) allows to carry out modelling experiments on research of slabbing actions, jet formations, fluffings, hydrodynamic instability during shock-wave loading of investigated samples, which makes it attractive for determination of parameters in equations-of-state for investigated materials, creation of numerical models and their validation. Some examples showing basic possibility of application of the declared techniques are included.
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Severa, Libor. "Behaviour of the peach under underwater shock wave loading." Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis 56, no. 4 (2008): 151–60. http://dx.doi.org/10.11118/actaun200856040151.
Full textAbstract:
The paper concerns with the experimental and numerical study of the peach (Red Haven) at underwater shock wave loading. The behaviour of the peach skin as well as peach stone can be described in terms of elasticity. Following experiments have been performed: tensile testing of the skin (exocarp) specimens at constant elongation at strain rate 0.01 s−1, compression test of the mesocarp specimens at different strain rates corresponding to quasi – static loading, compression test of the mesocarp specimens at the high rates of strain (about 1000 s−1), and compression test of the whole peach stone at strain rate corresponding to quasi – static loading. The model of the peach has been suggested. The model is used for the numerical simulation, which was performed on the software LS DYNA 3D finite element code. Pressure wave propagation in the water has been studied and following quantities evaluated: pressure on the peach surface, displacement, and surface velocity. Two different models (Maxwell and Kelvin) have been used. The results of this simulation show some agreement with results of the observation (undamaged peach skin). The numerical simulation also gives an insight on the details of the loading, which was recently tested as a tool of fruit treatment. It has been shown that undewater shock wave treatment of peaches can lead to their softening.
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Clifton, R. J. "Stress Wave Propagation, Dynamic Material Response, and Quantitative Non-Destructive Evaluation." Applied Mechanics Reviews 38, no. 10 (October 1, 1985): 1276–78. http://dx.doi.org/10.1115/1.3143690.
Full textAbstract:
Stress wave propagation is of fundamental importance in modern technology because it provides the primary means for the nondestructive examination of defects and in-homogeneities in opaque materials and the only means for studying the response of materials under the dynamic loading conditions associated with impact and explosions. Advances in such diverse technologies as nuclear reactor safety, integrated circuit inspection, and armor penetration depend strongly on advances in the modeling of the propagation of stress waves and in the improved characterization of the dynamic response of materials. Stress waves play a central role in a wide range of geotechnical and geophysical applications including reservoir exploration, earthquake monitoring, and the prediction of ground motion due to earthquakes and blast loading. Because of the inherent complexity of stress waves in solids (i.e., three wave speeds, anisotropy, and inhomogeneity), as well as the importance of nonlinearity in applications involving intense loading, progress in the modeling of stress wave phenomena depends critically on large scale computations. Increased availability of supercomputers provides an excellent opportunity for advances in the modeling of three dimensional phenomena, including such complicating features as anisotropy, inhomogeneity, defects, nonlinearity, and sliding interfaces. Research is needed on accurate and efficient algorithms for these calculations and for acoustic imaging which requires algorithms for inverse problems in which the size and shape of defects, as well as variations in density and in elastic moduli, are to be obtained by probing the region of interest with ultrasonic waves. Improved characterization of the sources and receivers of ultrasound is essential for reliable determination of the required geometrical features and material properties. Improved understanding of the dynamic inelastic response of materials is crucial to realizing the full benefits of the emerging computational power. Strain rate sensitivity, shear strain localization, crack propagation, twinning, and phase transformations are all aspects of mechanical response that need to be modeled in many dynamic loading applications. Basic experiments on these aspects of material behavior combined with computer simulation of the experiments should lead to significant progress in understanding the underlying mechanisms and, thereby, to improved models for use in computations.
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He, Guanghua, Binyang Xie, Wei Wang, Shuang Liu, and Penglin Jing. "Ship Loading Influence on the Slamming Impact of Typical Sections of an S-175 Container Ship." Journal of Marine Science and Engineering 8, no. 3 (March 3, 2020): 163. http://dx.doi.org/10.3390/jmse8030163.
Full textAbstract:
This paper investigates the influence of ship-loading condition on slamming during water entry. Three typical sections of the S-175 container ship, namely the bow, parallel middle body and stern, under three different loading conditions are studied. Full-sized models are established and simulated by commercial software LS-DYNA based on the explicit finite element method (FEM) using the arbitrary Lagrangian–Eulerian (ALE) algorithm. At first, validation is carried out by simulating the Wave Induced Loads on Ships Joint Industry Project II (WILS JIP-II) ship section entering the water and by verifying that the response is in good agreement with published experimental data. Then, nine different cases with three typical sections of the container ship and three different loadings, including the no-load (lightship weight), half-load and full-load weights of the ship, are investigated. Finally, the influence of the ship loading and sectional shape on the water impacts is analyzed and discussed. The present study is useful for the analysis of loading effects on ship slamming at the early stage of ship design.
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Balomenos, Georgios P., and Jamie E. Padgett. "EFFECTS OF WAVE LOADING CONDITIONS ON THE FRAGILITY OF PILE-SUPPORTED WHARVES/PIERS." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 29. http://dx.doi.org/10.9753/icce.v36.structures.29.
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Pile-supported wharves/piers are often subjected to extreme forces caused by coastal hazards. For instance, hurricanes Katrina (2005) and Wilma (2005) caused significant structural damage to pile-supported piers (Gutierrez et al. 2006) and wharves (Bardi et al. 2007), respectively. The problem becomes more pressing as the hazard exposure of these structures evolves with sea level rise caused by climate change (Lamberti et al. 2011). Thus, in light of gaps in the risk assessment of these structures in hurricane prone regions, Balomenos and Padgett (2018a) proposed the first probabilistic framework for developing analytical fragility models for pile-supported wharves/piers vulnerable to hurricane-induced storm surge and waves. Then, Balomenos and Padgett (2018b) adopted this framework to provide an initial exploration into the sensitivity of the fragility estimate to epistemic uncertainties in the wave load model. However, considering that the wave period may have a significant variation at or near the coast based on reported periods during hurricanes Katrina and Rita (Dietrich et al. 2011), this study further explores the influence of hazard parameter variation on the resulting failure probability of these structures, while propagating uncertainties in other parameters such as concrete compressive strength, deck thickness, etc.
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Zhao, W., and F. M. Burdekin. "Dynamic Structural Integrity Assessment for Offshore Structures." Journal of Offshore Mechanics and Arctic Engineering 126, no. 4 (November 1, 2004): 358–63. http://dx.doi.org/10.1115/1.1710872.
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The paper initially presents the results of a dynamic structural integrity assessment for fracture of cracked plate and tubular members under sinusoidal loading at different frequencies. The behavior of cracked members and joints in an offshore structure under wave loading (Stokes 5th order or gridded wave) is then examined. Global structural dynamic analyses of a whole offshore jacket were carried out as the first step, then, a set of sub-models of joints was selected from chosen locations and modeled with through thickness cracks under the loading extracted from the global analysis. The sub-model dynamic results were analyzed to obtain the fracture response in terms of variation of crack tip opening displacement (CTOD). Related values of K, J and their rates were also calculated. These results are used to give guidance on methods for design and assessment of structural integrity under dynamic loading.
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Jin, Dingyi, Xiaoliang Deng, and Wenyang Liu. "Eulerian peridynamic modeling of microjetting from a grooved aluminum sample under shock loading." Journal of Applied Physics 131, no. 10 (March 14, 2022): 105108. http://dx.doi.org/10.1063/5.0078121.
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The micro jetting from a grooved aluminum surface under impact loading is investigated by using Eulerian peridynamics (PD). The simulation results are compared with the published experimental data and the spike velocity model, exhibiting qualitative agreement. The governing mechanism accounting for the formation of micro jetting is elucidated from the perspective of the shock wave interaction with the surface groove. The PD simulation results indicate that the incident shock wave induces progressive groove collapse along the direction of shock wave propagation. The rarefaction waves reflected from the groove edges cause the variation of the velocity vector of PD material points, leading to the material points above and below the symmetric axis of the groove converging toward the symmetric axis and colliding with each other. Then, those collided material points are driven by the incident shock wave propagating along the horizontal symmetric axis and eventually ejected from the groove. The effects of the groove dimensions and the impact velocity on the spike velocity and the ejected mass are discussed. The results show that spike velocity decreases with an increasing groove angle but increases with increasing impact velocity. Furthermore, the ejected mass increases with increasing impact velocity. However, when the depth of the surface groove is fixed and the groove angle increases, the ejected mass first increases and then decreases with the turning point at ∼120°. As the depth of the surface groove increases, the ejected mass increases. The simulation results provide a mechanistic understanding of the micro jetting phenomena and instructive guidance for developing better ejecta models.
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Rabault, Jean, Graig Sutherland, Atle Jensen, Kai H. Christensen, and Aleksey Marchenko. "Experiments on wave propagation in grease ice: combined wave gauges and particle image velocimetry measurements." Journal of Fluid Mechanics 864 (February 13, 2019): 876–98. http://dx.doi.org/10.1017/jfm.2019.16.
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Water wave attenuation by grease ice is a key mechanism for the polar regions, as waves in ice influence many phenomena such as ice drift, ice breaking and ice formation. However, the models presented so far in the literature are limited in a number of regards, and more insights are required from either laboratory experiments or fieldwork for these models to be validated and improved. Unfortunately, performing detailed measurements of wave propagation in grease ice, either in the field or in the laboratory, is challenging. As a consequence, laboratory data are relatively scarce, and often consist of only a couple of wave elevation measurements along the length of the wave tank. We present combined measurements of wave elevation using an array of ultrasonic probes, and water kinematics using particle image velocimetry (PIV), in a small-scale wave tank experiment. Experiments are performed over a wider frequency range than has been previously investigated. The wave elevation measurements are used to compute the wavenumber and exponential damping coefficient. In contrast to a previous study in grease ice, we find that the wavenumber is consistent with the mass loading model, i.e. it increases compared with the open water case. Wave attenuation is compared with a series of one-layer models, and we show that they satisfactorily describe the viscous damping occurring. PIV data are also consistent with exponential wave amplitude attenuation, and a proper orthogonal decomposition analysis reveals the existence of mean flows under the ice that are a consequence of the displacement and packing of the ice induced by the gradient in the wave-induced stress. Finally, we show that the dynamics of grease ice can generate eddy structures that inject eddy viscosity into the water under the grease ice, which would lead to enhanced mixing and participating in energy dissipation.
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Katalinić, Marko, and Joško Parunov. "Comprehensive Wind and Wave Statistics and Extreme Values for Design and Analysis of Marine Structures in the Adriatic Sea." Journal of Marine Science and Engineering 9, no. 5 (May 12, 2021): 522. http://dx.doi.org/10.3390/jmse9050522.
Full textAbstract:
Wind and waves present the main causes of environmental loading on seagoing ships and offshore structures. Thus, its detailed understanding can improve the design and maintenance of these structures. Wind and wave statistical models are developed based on the WorldWaves database for the Adriatic Sea: for the entire Adriatic Sea as a whole, divided into three regions and for 39 uniformly spaced locations across the offshore Adriatic. Model parameters are fitted and presented for each case, following the conditional modelling approach, i.e., the marginal distribution of significant wave height and conditional distribution of peak period and wind speed. Extreme significant wave heights were evaluated for 20-, 50- and 100-year return periods. The presented data provide a consistent and comprehensive description of metocean (wind and wave) climate in the Adriatic Sea that can serve as input for almost all kind of analyses of ships and offshore structures.
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Castillo, Carmen, Rafael Molina, Rebeca Gómez, and Enrique Castillo. "A STATISTICAL MODEL FOR DAMAGE ACCUMULATION IN BREAKWATERS." Coastal Engineering Proceedings 1, no. 32 (February 1, 2011): 19. http://dx.doi.org/10.9753/icce.v32.posters.19.
Full textAbstract:
Rehabilitation and maintenance studies are a great concern for Port Authorities and other Administrations.
For a complete risk analysis, probability of failure due to instability of the armour layer must be analyzed and therefore a knowledge on its deterioration rate is needed.
Breakwater armour stability is highly variable and difficult to quantify for many variables are involved in the problem.
Breakwater armour stability is stochastic in nature as both loading and armour conditions are. There is uncertainty in armour placing and shape and in loading by waves and water level.
Dimensionality, compatibility conditions and the central limit theorem are suggested to be considered for building consistent statistical models reproducing random breakwater damage progression due to general random wave actions.
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Wang, Lu, Amy Robertson, Jason Jonkman, and Yi-Hsiang Yu. "Uncertainty Assessment of CFD Investigation of the Nonlinear Difference-Frequency Wave Loads on a Semisubmersible FOWT Platform." Sustainability 13, no. 1 (December 23, 2020): 64. http://dx.doi.org/10.3390/su13010064.
Full textAbstract:
Current mid-fidelity modeling approaches for floating offshore wind turbines (FOWTs) have been found to underpredict the nonlinear, low-frequency wave excitation and the response of semisubmersible FOWTs. To examine the cause of this underprediction, the OC6 project is using computational fluid dynamics (CFD) tools to investigate the wave loads on the OC5-DeepCwind semisubmersible, with a focus on the nonlinear difference-frequency excitation. This paper focuses on assessing the uncertainty of the CFD predictions from simulations of the semisubmersible in a fixed condition under bichromatic wave loading and on establishing confidence in the results for use in improving mid-fidelity models. The uncertainty for the nonlinear wave excitation is found to be acceptable but larger than that for the wave-frequency excitation, with the spatial discretization error being the dominant contributor. Further, unwanted free waves at the difference frequency have been identified in the CFD solution. A wave-splitting and wave load-correction procedure are presented to remove the contamination from the free waves in the results. A preliminary comparison to second-order potential-flow theory shows that the CFD model predicted significantly higher difference-frequency wave excitations, especially in surge, suggesting that the CFD results can be used to better calibrate the mid-fidelity tools.
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Ellefsen, Karl J., and David L. Wright. "Radiation pattern of a borehole radar antenna." GEOPHYSICS 70, no. 1 (January 2005): K1—K11. http://dx.doi.org/10.1190/1.1852779.
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The finite-difference time-domain method was used to simulate radar waves that were generated by a transmitting antenna inside a borehole. The simulations were of four different models that included features such as a water-filled borehole and an antenna with resistive loading. For each model, radiation patterns for the far-field region were calculated. The radiation patterns show that the amplitude of the radar wave was strongly affected by its frequency, the water-filled borehole, the resistive loading of the antenna, and the external metal parts of the antenna (e.g., the cable head and the battery pack). For the models with a water-filled borehole, their normalized radiation patterns were practically identical to the normalized radiation pattern of a finite-length electric dipole when the wavelength in the formation was significantly greater than the total length of the radiating elements of the model antenna. The minimum wavelength at which this criterion was satisfied depended upon the features of the antenna, especially its external metal parts.
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Liang, Minzu, Xiangyu Li, Yuliang Lin, Kefan Zhang, and Fangyun Lu. "Dynamic Compressive Behaviors of Two-Layer Graded Aluminum Foams under Blast Loading." Materials 12, no. 9 (May 3, 2019): 1445. http://dx.doi.org/10.3390/ma12091445.
Full textAbstract:
Experimental and numerical analyses were carried out to reveal the behaviors of two-layer graded aluminum foam materials for their dynamic compaction under blast loading. Blast experiments were conducted to investigate the deformation and densification wave formation of two-layer graded foams with positive and negative gradients. The shape of the stress waveform changed during the propagation process, and the time of edge rising was extended. Finite element models of two-layer graded aluminum foam were developed using the periodic Voronoi technique. Numerical analysis was performed to simulate deformation, energy absorption, and transmitted impulse of the two-layer graded aluminum foams by the software ABAQUS/Explicit. The deformation patterns were presented to provide insights into the influences of the foam gradient on compaction wave mechanisms. Results showed that the densification wave occurred at the blast end and then gradually propagated to the distal end for the positive gradient; however, compaction waves simultaneously formed in both layers and propagated to the distal end in the same direction for the negative gradient. The energy absorption and impulse transfer were examined to capture the effect of the blast pressure and the material gradient. The greater the foam gradient, the more energy dissipated and the more impulse transmitted. The absorbed energy and transferred impulse are conflicting objectives for the blast resistance capability of aluminum foam materials with different gradient distributions. The results could help in understanding the performance and mechanisms of two-layer graded aluminum foam materials under blast loading and provide a guideline for effective design of energy-absorbing materials and structures.
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Wendt, Nielsen, Yu, Bingham, Eskilsson, Kramer, Babarit, et al. "Ocean Energy Systems Wave Energy Modelling Task: Modelling, Verification and Validation of Wave Energy Converters." Journal of Marine Science and Engineering 7, no. 11 (October 25, 2019): 379. http://dx.doi.org/10.3390/jmse7110379.
Full textAbstract:
The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.
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Wang, F., P. Zhang, Z. Sun, Z. Jiang, and Q. Zhang. "REFINE OF REGIONAL OCEAN TIDE MODEL USING GPS DATA." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3 (April 30, 2018): 1685–88. http://dx.doi.org/10.5194/isprs-archives-xlii-3-1685-2018.
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Due to lack of regional data constraints, all global ocean tide models are not accuracy enough in offshore areas around China, also the displacements predicted by different models are not consistency. The ocean tide loading effects have become a major source of error in the high precision GPS positioning. It is important for high precision GPS applications to build an appropriate regional ocean tide model. We first process the four offshore GPS tracking station’s observation data which located in Guangdong province of China by using PPP aproach to get the time series. Then use the spectral inversion method to acquire eigenvalues of the Ocean Tidal Loading. We get the estimated value of not only ~12hour period tide wave (M2, S2, N2, K2) but also ~24hour period tide wave (O1, K1, P1, Q1) which has not been got in presious studies. The contrast test shows that GPS estimation value of M2, K1 is consistent with the result of five famous glocal ocean load tide models, but S2, N2, K2, O1, P1, Q1 is obviously larger.
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Alati, Natale, Giuseppe Failla, and Felice Arena. "Seismic analysis of offshore wind turbines on bottom-fixed support structures." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2035 (February 28, 2015): 20140086. http://dx.doi.org/10.1098/rsta.2014.0086.
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This study investigates the seismic response of a horizontal axis wind turbine on two bottom-fixed support structures for transitional water depths (30–60 m), a tripod and a jacket, both resting on pile foundations. Fully coupled, nonlinear time-domain simulations on full system models are carried out under combined wind–wave–earthquake loadings, for different load cases, considering fixed and flexible foundation models. It is shown that earthquake loading may cause a significant increase of stress resultant demands, even for moderate peak ground accelerations, and that fully coupled nonlinear time-domain simulations on full system models are essential to capture relevant information on the moment demand in the rotor blades, which cannot be predicted by analyses on simplified models allowed by existing standards. A comparison with some typical design load cases substantiates the need for an accurate seismic assessment in sites at risk from earthquakes.
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Wu, Zhiwen, Canrong Xie, Guoxiong Mei, and Hongyuan Dong. "Dynamic analysis of parametrically excited marine riser under simultaneous stochastic waves and vortex." Advances in Structural Engineering 22, no. 1 (June 29, 2018): 268–83. http://dx.doi.org/10.1177/1369433218783968.
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This study investigates the dynamic analysis of parametrically excited marine riser under simultaneous stochastic waves and vortex. A general analysis considers the parametric excitation resulting from platform motion, ocean wave loading directly on the rise, and vortex-shedding excitation due to flow bypassing the risers. Stochastic wave force and vortex excitation acting on the riser in the time domain is formulated by the stochastic phase spectrum method and derived by the linear-wave theory using a Pierson–Moskowitz wave spectrum to simulate real sea conditions. A derived parametrically excited top tensioned riser model subjected to simultaneous stochastic waves and vortex excitations is proposed. The efficacy of the present method is assessed by solutions obtained from other existing methods and experimental data of two test models. The present method is evaluated by solutions computed from existing methods and experimental data of two test models, and a general good agreement of the analyses between the proposed approach and other methods is observed. The availability of resonance, parametric stability, energy distribution and transfer, and the sensitivity of key parameters estimated by single-frequency and multi-frequency excitation are compared and discussed. Comparing with the results obtained from the harmonic excitation method, the present method can be used to make more reasonable and accurate calculations of the dynamic response of risers operating in real sea conditions.