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1.
The development of a definitive predictive model that accurately accounts for the nonlinear hydrodynamics and structural response behavior observed in arrays of closely spaced risers on deep water structures will require a more detailed understanding of this fluid–structure interaction. Through the analysis and interpretation of data from model basin tests on single and paired tandem cylinder configurations this study is directed at uncovering the nature of some aspects of this nonlinear response behavior using an orthogonal third-order Volterra technique that can delineate between linear, quadratic and cubic nonlinear frequency dependent behavior. As part of the analysis procedure the data was organized in input–output pairs that would provide logical groupings of the measured quantities. The data pairs presented in this study include wave excitation and inline cylinder displacement, wave excitation and transverse cylinder displacement, wave excitation and inline reaction force, and, upstream cylinder and downstream cylinder response. This information is presented in terms of spectral and coherence plots. The single cylinder data is presented as a means to contrast the behavior of the tandem cylinders. Both configurations were analyzed at two different pretensions adding another dimension to this investigation. It is shown that although a primary variable such as displacement may be more easily measured, pretension and force measurements provide an important key to our understanding of this difficult problem. 相似文献
2.
Kyoung Kim Powers E. Ritz C. Miksad R. Fischer F. 《Oceanic Engineering, IEEE Journal of》1987,12(4):568-575
A quadratic system model based on Volterra series representation is utilized to model the nonlinear response of moored vessels subjected to random seas. The key idea is to represent the relationship between the incident sea wave (input) and corresponding sway response of the moored vessel (output) with a parallel combination of linear and quadratic transfer functions, and to estimate them by processing actual input and output data. Compared to previous approaches, we take the important step of removing the restriction that the random input must possess Gaussian statistics. The feasibility and validity of the approach is demonstrated by analyzing experimental data taken in model basin tests. We also describe some of the deleterious consequences of assuming Gaussian sea-wave excitation when in fact the excitation is non-Gaussian. 相似文献
3.
Shutang Zhu 《Ocean Engineering》1999,26(12):535
This paper presents a transfer function method (TFM) which can separate a regular wave field into incident and reflected waves based on the linear wave theory. The TFM uses specific transfer functions and corresponding convolution integrals to separate time series data measured in a combined partial standing wave system into incident and reflected waves. After this separation, estimation of the reflection coefficient becomes very easy. All manipulations have been performed in time domain. Furthermore, this method does not involve the calculation of wave heights and/or phase differences. The present method is demonstrated through numerical sample and physical model experiments carried out in a wave flume. Compared with other methods, the TFM gives much better estimates of the incident wave heights for physical model experiments in this study. 相似文献
4.
Analysis of dynamic effects relevant for the wear damage in hydraulic machines for wave energy conversion 总被引：1，自引：0，他引：1
The present paper deals with a mathematical model of a heaving-buoy Wave Energy Converter (WEC) equipped with high-pressure hydraulic power take-off machinery for energy conversion. This model is based on linear hydrodynamic theory, and a hybrid frequency-time domain model is used to study the dynamics of the heaving-body exposed to an irregular incident wave. For the power take-off system, end-stop devices are provided to protect the hydraulic machinery when the buoy is exposed to severe sea states. The model also takes into account the lubricated friction force and pressure drops of orifice flow through the valves in the hydraulic system. All the forces mentioned in the hydraulic power take-off machinery have non-linear features. A complete non-linear state space model for the WEC system is presented in this study.The WEC system was numerically simulated for different cylinder lengths under a fixed volume. The effect of fluid compressibility in the cylinder has been investigated in the mathematical model. High frequency oscillations (HFOs) caused by the compressibility of the fluid are displayed in the time series and in corresponding power spectra, and variation is shown for different cylinder sizes. Piston ring and cylinder bore wear damage is estimated by using Archard’s equation on the basis of the simulation results. A comparison of these results with a performance of an identical WEC system which neglects fluid compressibility has been done in this work. It shows that although the spectral power is small, HFO can make a large contribution to both the ring and cylinder bore wear. For the purpose of wear prediction, oscillations at or below the wave frequency and HFO may be equally important. 相似文献
5.
The wave runup caused by a vertical cylinder surging in regular waves is studied both experimentally and numerically. The so-called DualSPHysics Smoothed Particle Hydrodynamics (SPH) code is used for the 3-D numerical modelling. A wide range of cylinder sizes and wave conditions is investigated with results comparing favourably between the experimental and SPH model under both fixed and forced-surge conditions. The experimental and SPH results are further used to predict the maximum runup amplification, in particular the ratio of the runup caused by the surging cylinder to that of the fixed, over the phase difference between the incident wave and surge motion. This maximum runup ratio has been analysed for its dependence on factors such as wave steepness, wave scattering and surge amplitude. An empirical equation is proposed for predicting the maximum runup ratio from known incident wave and surge conditions. Comparison with results from linear solvers suggests that the linear solvers under-predict the full nonlinear runup by a factor of 1.3–1.5. 相似文献
6.
Surface water wave elevations and kinematics from four unidirectional irregular wave trains, with a Pierson and Moskowitz or JONSWAP random wave spectrum, were measured in the laboratory using resistance wave probes and a laser Doppler anemometer. The wave elevation data, velocity time series, extreme (largest) wave horizontal velocity profiles and extreme wave acceleration fields are compared with the predictions of a new wave kinematics model, named the hybrid wave model. Irregular waves are commonly viewed as the summation of many linear wave components of different frequencies, but more accurate predictions of downstream surface elevations (wave evolution) and wave kinematics are attained by considering the non-linear interactions among wave components. The hybrid wave model incorporates these non-linear wave component interactions, and its wave evolution predictions and kinematics estimates are compared with laboratory measurements in this study. Linear random wave theory, Wheeler stretching and linear extrapolation wave kinematic prediction techniques are also compared. Comparisons between measurements and hybrid wave model estimates demonstrate its improved capability to predict velocity and acceleration fields and wave evolution in two-dimensional irregular waves. 相似文献
7.
Based on historical wind fields in the Bohai Sea,a sequence of annual extremal wave heightsis produced with numerical wave models for deep-water and shallow water.The design wave heights withdifferent return periods for the nearest deep-water point and for the shallow water point are estimated onthe basis of P-Ⅲ type,Weibull distribution,and Gumbel distribution;and the corresponding values for theshallow water point are also estimated based on the HISWA model with the input of design wave heightsfor the nearest deep-water point.Comparisons between design wave heights for the shallow water point es-timated on the basis of both distribution functions are HISWA model show that the results from differentdistribution functions scatter considerably,and influenced strongly by return periods;however,the resultsfrom the HISWA model are convergent,that is,the influence of the design wave heights estimated with dif-ferent distribution functions for deep water is weakened,and the estimated values decrease for long 相似文献
8.
Matthew Browne Bruno Castelle Darrell Strauss Rodger Tomlinson Michael Blumenstein Chris Lane 《Coastal Engineering》2007
Estimation of swell conditions in coastal regions is important for a variety of public, government, and research applications. Driving a model of the near-shore wave transformation from an offshore global swell model such as NOAA WaveWatch3 is an economical means to arrive at swell size estimates at particular locations of interest. Recently, some work (e.g. Browne et al. [Browne, M., Strauss, D., Castelle, B., Blumenstein, M., Tomlinson, R., 2006. Local swell estimation and prediction from a global wind-wave model. IEEE Geoscience and Remote Sensing Letters 3 (4), 462–466.]) has examined an artificial neural network (ANN) based, empirical approach to wave estimation. Here, we provide a comprehensive evaluation of two data driven approaches to estimating waves near-shore (linear and ANN), and also contrast these with a more traditional spectral wave simulation model (SWAN). Performance was assessed on data gathered from a total of 17 near-shore locations, with heterogenous geography and bathymetry, around the continent of Australia over a 7 month period. It was found that the ANNs out-performed SWAN and the non-linear architecture consistently out-performed the linear method. Variability in performance and differential performance with regard to geographical location could largely be explained in terms of the underlying complexity of the local wave transformation. 相似文献
9.
《Coastal Engineering》2005,52(4):313-329
This study concerns the possible interrelationships of wave data among wave-measuring stations. This study uses wave records collected at Station Pi-Tou-Chiao (PTC) from 1983 to 1988, and at Station Keelung (KL) from 1983 to 1988. Depending upon the amount of consecutive data missing in the records, three methods were used to estimate their values. The methods used for data completion are: interpolation, ARMA model, and O'Carroll [O'Carroll, F.M., 1984. Weather modelling for offshore operations. The Statistician, 33, 161–169.] model. Using monthly transfer functions (TFs) between these two stations, the interrelationships of the significant wave heights measured at PTC and KL were estimated, and the records of the two measuring stations were set to have equal lengths. Assessments of the proposed methods were carried out by comparing the mean values, standard deviations, skewness, and kurtosis of both the completed and estimated wave records. The results indicate that the proposed methodologies can be used to fill in data gaps and to transfer data from one station to another—both of these methodologies are needed in the study of oceanographic time series. 相似文献
10.
《Coastal Engineering》2001,44(2):153-190
This paper summarizes the results of the European Union Marine Science and Technology (EU MAST) III project “Scour Around Coastal Structures” (SCARCOST). The summary is presented under three headings: (1) Introduction; (2) Flow and scour processes with the subheadings: flow and scour processes around vertical cylinders; flow and scour processes at detached breakwaters; flow and scour processes at submerged breakwaters; and the effect of turbulence on sediment transport; and (3) Sediment behaviour close to the structure with the subheadings: field measurement and analysis of wave-induced pore pressures and effective stresses around a bottom seated cylinder; non-linear soil modelling with respect to wave-induced pore pressures and gradients; wave-induced pressures on the bottom for non-linear coastal waves, including also wave kinematics; development of a numerical model (linear soil modelling) to calculate wave-induced pore pressures—the effect of liquefaction on sediment transport; penetration of blocks in non-consolidated fine soil; and cyclic stiffness of loose sand.The paper also includes a discussion of the role of scale effects in laboratory testing and the applicability of the results obtained in supporting engineering design. 相似文献
11.
Numerical simulation of non-linear regular and focused waves in an infinite water-depth 总被引：3，自引：0，他引：3
Inviscid three-dimensional free surface wave motions are simulated using a novel quadratic higher order boundary element model (HOBEM) based on potential theory for irrotational, incompressible fluid flow in an infinite water-depth. The free surface boundary conditions are fully non-linear. Based on the use of images, a channel Green function is developed and applied to the present model so that two lateral surfaces of an infinite-depth wave tank can be excluded from the calculation domain. In order to generate incident waves and dissipate outgoing waves, a non-reflective wave generator, composed of a series of vertically aligned point sources in the computational domain, is used in conjunction with upstream and downstream damping layers. Numerical experiments are carried out, with linear and fully non-linear, regular and focused waves. It can be seen from the results that the present approach is effective in generating a specified wave profile in an infinite water-depth without reflection at the open boundaries, and fully non-linear numerical simulations compare well with theoretical solutions. The present numerical technique is aimed at efficient modelling of the non-linear wave interactions with ocean structures in deep water. 相似文献
12.
Data on the acceleration of an oscillating cylinder in water are analysed by a Kalman extended filter. A hydrodynamical forcing model based upon Morison's equation appears to be reasonable and drag estimation appears simple using simulated data. Estimation based upon real data gives an average drag coefficient decreasing with the oscillation amplitude. An assymetric drag coefficient variation over the oscillation period is estimated. 相似文献
13.
A higher-order non-hydrostatic σ model is developed to simulate non-linear refraction–diffraction of water waves. To capture non-linear (or steep) waves, a 4th-order spatial discretization is utilized to approximate the large horizontal pressure gradient. A higher-order top-layer pressure treatment is further implemented to resolve wave propagation. The model's characteristics including linear wave dispersion and non-linearity are carefully examined. The accuracy of the present model using only two vertical layers is validated by laboratory data and the available results predicted by the non-linear Schrödinger equation, Boussinesq-type equations, the non-linear mild slope equation, and the Laplace equation. Features of harmonic generation as well as the influences of dispersion and non-linearity on wave energy transfer processes are discussed. 相似文献
14.
An approach for modelling of multipeaked directional wave spectra is proposed. For model identification, a numerical optimization technique that uses the random linear search algorithm is applied. This technique allows the fitting of spectral models to measured or hindcast data. The HIPOCAS hindcast data for North Atlantic are used for an application study. 相似文献
15.
A.J.H.M. Reniers M.J. Groenewegen K.C. Ewans S. Masterton G.S. Stelling J. Meek 《Coastal Engineering》2010
The accuracy of nearshore infragravity wave height model predictions has been investigated using a combination of the spectral short wave evolution model SWAN and a linear 1D SurfBeat model (IDSB). Data recorded by a wave rider located approximately 3.5 km from the coast at 18 m water depth have been used to construct the short wave frequency-directional spectra that are subsequently translated to approximately 8 m water depth with the third generation short wave model SWAN. Next the SWAN-computed frequency-directional spectra are used as input for IDSB to compute the infragravity response in the 0.01 Hz–0.05 Hz frequency range, generated by the transformation of the grouped short waves through the surf zone including bound long waves, leaky waves and edge waves at this depth. Comparison of the computed and measured infragravity waves in 8 m water depth shows an average skill of approximately 80%. Using data from a directional buoy located approximately 70 km offshore as input for the SWAN model results in an average infragravity prediction skill of 47%. This difference in skill is in a large part related to the under prediction of the short wave directional spreading by SWAN. Accounting for the spreading mismatch increases the skill to 70%. Directional analyses of the infragravity waves shows that outgoing infragravity wave heights at 8 m depth are generally over predicted during storm conditions suggesting that dissipation mechanisms in addition to bottom friction such as non-linear energy transfer and long wave breaking may be important. Provided that the infragravity wave reflection at the beach is close to unity and tidal water level modulations are modest, a relatively small computational effort allows for the generation of long-term infragravity data sets at intermediate water depths. These data can subsequently be analyzed to establish infragravity wave height design criteria for engineering facilities exposed to the open ocean, such as nearshore tanker offloading terminals at coastal locations. 相似文献
16.
The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements. 相似文献
18.
Kiho Kim Sung Bae Kim Powers E.J. Miksad R.W. Fischer F.J. 《Oceanic Engineering, IEEE Journal of》1994,19(2):183-192
This paper presents an adaptive second-order Volterra filter and its application to model-test data of a prototype tension leg platform (TLP). The least-squares approach of a second-order Volterra model and its adaptive filtering algorithm based on recursive least-squares are introduced. The second-order Volterra filter is applied to identify the linear and quadratically nonlinear relationship between irregular sea wave excitation and the surge response of a tension leg platform. Next, a deconvolution technique, based on the impulse invariance standard Z-transform, is utilized to recover the linear and quadratic forces exerted on the TLP 相似文献
19.
20.
A number of existing models for surface wave phase speeds (linear and non-linear, breaking and non-breaking waves) are reviewed and tested against phase speed data from a large-scale laboratory experiment. The results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non-linearity in phase speed based depth inversions. The analysis is focused on the surf zone, where depth inversion accuracies are known to degrade significantly. The collected data includes very high-resolution remote sensing video and surface elevation records from fixed, in-situ wave gages. Wave phase speeds are extracted from the remote sensing data using a feature tracking technique, and local wave amplitudes are determined from the wave gage records and used for comparisons to non-linear phase speed models and for non-linear depth inversions. A series of five different regular wave conditions with a range of non-linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation, which includes both non-linearity and dispersion effects, best matches the observed phase speeds across the domain and hence, improves surf zone depth estimation via depth inversions. Incorporating non-linearity into the phase speed model reduces errors to O(10%), which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion. Considering the controlled conditions and extensive ground truth, this appears to be a practical limit for phase speed-based depth inversions. Finally, a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions. However, increasing wave steepness degrades the sensitivity of this inversion method. 相似文献