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A high-precision hydrodynamic model coupled with the hydrological habitat suitability model to reveal estuarine vegetation distribution

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Journal of Hydrodynamics 2022年第3期34卷 451-466页

作者： Qiao-feng Ma Shu-xiu Liang Zhao-chen Sun Wen-hao Hou Xin-yue Hu Rui-jin Zhang state Key laboratory of coastal and offshore engineering Dalian University of TechnologyDalian116024China School of Marine Science and Environment engineering Dalian Ocean UniversityDalian116023China Operational Oceanographic Institution Dalian Ocean UniversityDalian116023China

In this paper,based on the finite volume method,a high-precision hydrodynamic model coupled with the habitat suitability model is established,and the computational efficiency of the coupled model is improved by a graphics processing unit(GPU)-accelerated technology.The coupled model is used to solve the problem of the non-conservation of mass that may be caused by the nearshore hydrodynamic model in the processing of wetting and drying,while avoiding the unphysical high velocities at the wetting and drying boundaries.The coupled model is applied to simulate the high-precision hydrodynamic process of the Liao River estuary(LRE)and the hydrological habitat suitability of the estuarine vegetation(Suaeda heteroptera)growing in the LRE.The simulated values of the hydrological variables(the water level,the water depth,the current velocity and direction)are highly consistent with the measured values.The root mean square errors(RMSE)of the hydrological variables are 0.10m,0.12m/s and 17.24°,respectively.Furthermore,the simulated combined suitability index(CSI)distribution of Suaeda heteroptera(S.heteroptera)matches with the distribution of S.heteroptera obtained from the high-resolution remote sensing satellite images during the same time period.The ratio of the simulated weighted usable area(WUA)of S.heteroptera to the area obtained from the remote sensing satellite images during the same period is 81.9%.This study reveals the phenomenon that the distribution of S.heteroptera in the LRE is highly correlated with the high-precision hydrodynamic processes,and provides a scientific basis and a valuable reference for the conservation and the restoration of the estuarine vegetation.

关键词： High-precision hydrodynamic model habitat suitability model conversation of mass weighted usable area vegetation distribution

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Probabilistic seismic hazard analysis in Nepal

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Earthquake engineering and engineering Vibration 2013年第4期12卷 577-586页

作者： Thapa Dilli Ram Wang Guoxin state Key laboratory of coastal and offshore engineering Dalian University of Technology

The seismic ground motion hazard for Nepal has been estimated using a probabilistic approach. A catalogue of earthquakes has been compiled for Nepal and the surrounding region （latitude 26% N and 31.7% N and longitude 79° E and 90° E） from 1255 to 2011. The distribution of catalogued earthquakes, together with available geological and tectonic information were used to delineate twenty-three seismic source seismic source information and probabilistic earthquake hazard prediction relationship, peak ground accelerations （PGAs） have zones in Nepal and the surrounding region. By using the parameters in conjunction with a selected ground motion been calculated at bedrock level with 63%, 10%, and 2% probability of exceedance in 50 years. The estimated PGA values are in the range of 0.07-0.16 g, 0.21 0.62 g, and 0.38-1.1 g for 63%, 10%, and 2% probability of exceedance in 50 years, respectively. The resulting ground motion maps show different characteristics of PGA distribution, i.e., high hazard in the far-western and eastern sections, and low hazard in southern Nepal. The quantified PGA values at bedrock level provide information for microzonation studies in different parts of the country.

关键词： seismic hazard assessment peak ground acceleration earthquake Nepal Himalaya

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Experimental Study of Nonlinear Behaviors of A Free-Floating Body in Waves

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China Ocean engineering 2016年第3期30卷 421-430页

作者：贺铭任冰邱大洪 state Key laboratory of coastal and offshore engineering Dalian University of Technology

Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.

关键词： floating body nonlinear wave motion trajectory drift speed oscillation period

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Adaptive element free Galerkin method applied to analysis of earthquake induced liquefaction

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Earthquake engineering and engineering Vibration 2008年第2期7卷 217-224页

作者：荚颖唐小微栾茂田杨庆 state Key laboratory of coastal and offshore engineering Dalian University of Technology

An automatically adaptive element free method is presented to analyze the seismic response of liquefiable soils. The method is based on the element free Galerkin method （EFGM） and the fission procedure that is part of h-refinement, indicated by error estimation. In the proposed method, a posteriori error estimate procedure that depends on the energy norm of stress and the T-Belytschko （TB） stress recovery scheme is incorporated. The effective cyclic elasto-plastic constitutive model is used to describe the nonlinear behavior of the saturated soil. The governing equations are established by u-p formulation. The proposed method can effectively avoid the volumetric locking due to large deformation that usually occurs in numerical computations using the finite element method （FEM）. The efficiency of the proposed method is demonstrated by evaluating the seismic response of an embankment and comparing it to results obtained through FEM. It is shown that the proposed method provides an accurate seismic analysis of saturated soil that includes the effects of liquefaction .

关键词： adaptive element-free Galerkin method soil liquefaction large deformation error estimation seismic response

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Hydrodynamic Analysis of Elastic Floating Collars in Random Waves

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China Ocean engineering 2015年第3期29卷 341-356页

作者：白晓东赵云鹏董国海李玉成 state Key laboratory of coastal and offshore engineering Dalian University of Technology

As the main load-bearing component of fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a mathematical method is developed to study the motions and elastic deformations of elastic floating collars in random waves. The irregular wave is simulated by the random phase method and the statistical approach and Fourier transfer are applied to analyze the elastic response in both time and frequency domains. The governing equations of motions are established by Newton＇s second law, and the governing equations of deformations are obtained based on curved beam theory and modal superposition method. In order to validate the numerical model of the floating collar attacked by random waves, a series of physical model tests are conducted. Good relationship between numerical simulation and experimental observations is obtained. The numerical results indicate that the transfer function of out-of-plane and in-plane deformations increase with the increasing of wave frequency. In the frequency range between 0.6 Hz and 1.1 Hz, a linear relationship exists between the wave elevations and the deformations. The average phase difference between the wave elevation and out-of-plane deformation is 60° with waves leading and the phase between the wave elevation and in-plane deformation is 10° with waves lagging. In addition, the effect of fish net on the elastic response is analyzed. The results suggest that the deformation of the floating collar with fish net is a little larger than that without net.

关键词： floating collars random waves hydrodynamic characteristics in-plane and out-of-plane deformation net effect

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A Study of the Stability Properties in Simulation of Wave Propagation with SPH Method

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China Ocean engineering 2017年第2期31卷 173-181页

作者： CHANG Jiang LIU Shu-xue LI Jin-xuan state Key laboratory of coastal and offshore engineering Dalian University of Technology

When ordinary Smoothed Particle Hydrodynamics （SPH） method is used to simulate wave propagation in a wave tank, it is usually observed that the wave height decays and the wave length elongates along the direction of wave propagation. Accompanied with this phenomenon, the pressure under water decays either and shows a big oscillation simultaneously. The reason is the natural potential tensile instability of modeling water motion with ordinary SPH which is caused by particle negative stress in the computation. I＇o deal with the problems, a new sextic kernel function is proposed to reduce this instability. An appropriate smooth length is given and its computation criterion is also suggested. At the same time, a new kind dynamic boundary condition is introduced. Based on these improvements, the new SPH method named stability improved SPH （SISPH） can simulate the wave propagation well. Both the water surface and pressure can be well expressed and the oscillation of pressure is nearly eliminated. Compared with other improved methods, SISPH can truly reveal the physical reality without bringing some new problems in a simple way.

关键词： wave propagation SPH method instability sextic kernel function SISPH

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Investigation on A Resistance-Type Porosity Model and the Experimental Coefficients

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China Ocean engineering 2019年第4期33卷 468-476页

作者： ZHAO Pei-hong SUN Da-peng WU Hao state Key laboratory of coastal and offshore engineering Dalian University of Technology

The mathematical model based on the Volume-Averaged/Reynolds-Averaged Navier Stokes (VARANS) equations has been adopted in recent years to generally simulate the interaction between waves and porous structures. However, it is still hard to determine the two experimental coefficients (α and β) included in VARANS equations. In the present study, VARANS equation is adopted to describe the flow inside and outside the porous structures uniformly, with applying the volume averaged k ε model to simulate the turbulence effect. A new calibration method is used to evaluate the accuracy of numerical simulation of wave motion on porous seabed with different coefficients, by taking the wave damping rate as an index. The calibration is achieved by completing a simulation matrix on two calibration cases. A region can be found in the parameter space to produce a lower error, which means that the simulation results are better consistent with the experimental results.

关键词： porous media VARANS equations wave damping rate perforated caisson rubble-mound foundation

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Failure Pressure Analysis of Corroded Moderate-to-High Strength Pipelines

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China Ocean engineering 2016年第1期30卷 69-82页

作者：苏晨亮李昕周晶 state Key laboratory of coastal and offshore engineering Dalian University of Technology

Based on the elastic-plastic, large-deformation finite element method, burst capacity of steel pipeline with longitudinal corrosion defect subjected to internal pressure is studied. The appropriate stress-based criterion is used to predict the failure pressure of finite element model of corroded pipeline under internal pressure. By considering the pipe steel grades and geometries of corrosion defects, a series of finite element analyses is conducted. The effects of corrosion depth, length and width on burst capacity are also discussed. A specific failure pressure solution for the assessment of corrosion defects in moderate-to-high strength pipeline is proposed on the base of numerical results. The failure pressures predicted by the proposed method are in better agreement with the experimental results than the results by the other methods.

关键词： steel pipeline stress-based criteria failure pressure effect of corrosion width

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Study on Volume Variation and Stability of Riverbed in the Yangtze Estuary

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China Ocean engineering 2023年第3期37卷 433-446页

作者： DING Lei JIAO Jian TONG Chao-feng WANG Yi-fei CHEN Ben SUN Jie-ying DOU Xi-ping Key laboratory of Port Waterway and Sedimentation Engineering of MOTNanjing Hydraulic Research InstituteNanjing 210029China College of Harbour Coastal and Offshore EngineeringHohai UniversityNanjing 210098China state Key laboratory of Hydraulics and Mountain River engineering Sichuan UniversityChengdu 610065China

In recent years,regional floods and typhoons have occurred in the Yangtze Estuary.Changing dynamic conditions and dramatic reduction of sediment discharge in the basin are affecting the dynamic equilibrium pattern of the Yangtze Estuary.Based on the field measurement data and theoretical derivation,this paper analyzed the changing process of runoff-sediment discharge into the sea after the operation of the Three Gorges Project(TGP),and the tidal dynamics and sediment variation characteristics of the Yangtze Estuary.The erosion of South Branch mainly occurs in the channel below-10 m contour,and the riverbed volume below contours 0 m and-10 m has a good correlation with the sediment discharge of Datong Station in the previous year.On this basis,the ratio of the horizontal distance from the starting point to the section centroid below the average water level(B_c)and the water depth at the section centroid(H_c)was proposed to describe the change of the section shape.The relationships between the water-diverting ratio,the sediment-diverting ratio and the water-diverting angle,the conditions of runoff and sediment discharge from the upper reach and the characteristics of the riverway section were established,and the theoretical calculation equations of the water-diverting ratio,the sediment-diverting ratio and the diverting angle of each bifurcation were also established.

关键词： Yangtze Estuary volume variation section shape riverbed stability

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laboratory Study of the Nonlinear Transformation of Irregular Waves over A Mild Slope

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China Ocean engineering 2014年第4期28卷 489-500页

作者：于博马玉祥马小舟董国海 state Key laboratory of coastal and offshore engineering Dalian University of Technology

This paper considers the nonlinear transformation of irregular waves propagating over a mild slope （1：40）. Two cases of irregular waves, which are mechanically generated based on JONSWAP spectra, are used for this purpose. The results indicate that the wave heights obey the Rayleigh distribution at the offshore location; however, in the shoaling region, the heights of the largest waves are underestimated by the theoretical distributions. In the surf zone, the wave heights can be approximated by the composite Weibull distribution. In addition, the nonlinear phase coupling within the irregular waves is investigated by the wavelet-based bicoherence. The bicoherence spectra reflect that the number of frequency modes participating in the phase coupling increases with the decreasing water depth, as does the degree of phase coupling. After the incipient breaking, even though the degree of phase coupling decreases, a great number of higher harmonic wave modes are also involved in nonlinear interactions. Moreover, the summed bicoherence indicates that the frequency mode related to the strongest local nonlinear interactions shifts to higher harmonics with the decreasing water depth.

关键词： irregular waves shallow water nonlinear interactions wave height distribution wavelet bicoherence

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