NONLINEAR DYNAMICS RESPONSE OF CASING PIPE UNDER COMBINED WAVE-CURRENT

The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison’s nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin’s method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.

Research on Current Situation,Symptoms and Protection Technological Measures of Ancient Trees in Surging Waves Pavilion,China

The paper had studied growth situation and disease symptoms of ancient trees in Surging Waves Pavilion.There were 14 ancient trees belonging to 10 genera of 9 families,with tree age of 120-260 years.These trees had been well protected generally.There were 9 ancient trees growing well,occupying 64.29%,which were Ginkgo biloba,Cupressus funebris Endl.,Podocarpus macrophyllus,Zelkova schneideriana Hand.-Mazz,Cinnamomum camphora(L.)Presl,Buxus sinica,and Wisteria sinensis(Sims)Sweet.There were 5 ancient trees needing to be protected preferentially,occupying 35.71%,including Ligustrum lucidum,Osmanthus fragrans and Pterocarya stenoptera.The disease symptoms were trunk rot and hollow structure.Based on these symptoms,the paper had proposed protective measures for Ligustrum lucidum and Osmanthus fragrans:① enclosing eroding holes on the trunk;② clearing up eroded woodiness on the surface of trunk,disinfecting and applying anti-corrosion protectants;③ filling eroded holes of the trunk.Protective measures for Pterocarya stenoptera included:① clearing up the inner part and interior walls;② disinfecting the inside and interior walls of holes;③ applying anti-corrosion protectants.

Magnetic Current Stimulated by Strain Wave in One-dimensional Ferromagnetic Bar

应变波通过铁磁性杆件时，由于压磁效应，可以激发出不均匀的磁流．本文用实验证实了这种现象，而且给出了一维杆件中的磁流产生电场的计算方法和模拟结果．运用磁流理论得到的分析结果与实验结果基本一致．

Numerical Simulation of Spatial Lag Between Wave Breaking Point and Location of Maximum Wave-Induced Current

A quasi three-dimensional numerical model of wave-driven coastal currents with the effects of surface rollers is developed for the study of the spatial lag between the location of the maximum wave-induced current and the wave breaking point. The governing equations are derived from Navier-Stokes equations and solved by the hybrid method combining the fractional step finite different method in the horizontal plane with a Galerkin finite element method in the vertical direc- tion. The surface rollers effects are considered through incorporating the creation and evolution of the roller area into the free surface shear stress. An energy equation facilitates the computation process which transfers the wave breaking energy dissipation to the surface roller energy. The wave driver model is a phase-averaged wave model based on the wave action balance equation. Two sets of laboratory experiments producing breaking waves that generated longshore currents on a planar beach am used to evaluate the model＇s performance. The present wave-driven coastal current model with the roller effect in the surface shear stress term can produce satisfactory results by increasing the wave-induced nearshore current velocity inside the surf zone and shifting the location of the maximum longshore current velocity landward.

Numerical Simulation for Refraction-Diffraction of Waves in Water of Slowly Varying Current and Topography

A new numerical finite difference iteration method for refraction-diffraction of waves ia water of slowly varying current and topography is developed in this paper. And corresponding theoretical model including the dissipation term is briefly described, together with some analysis and comparison of computational results of the model with measurements in a hydraulic scale model (Berkhoff et al., 1982). An example of practical use of the method is given, showing that the present model is useful to engineering practice.

Numerical study of wave and longshore current interaction

Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole (2001) and Reniers and Battjes (1997) were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious.

Longshore currents of regular waves on different beaches

The experiment and numerical computations of longshore currents produced by regularwaves on the two beaches with the slopes of 1:100 and 1:40 are made. The cross-shore distributions of longshore current velocities and wave heights are given and the influences of wave heights, wave periods and beach slopes on the longshore currents are discussed. The discussion is also made for the influences of different eddy viscosity coefficients on the numerical results of longshore current velocities.

Longshore Currents of Random Waves on Different Plane Beaches

Model tests and numerical calculation of longshore currents and wave heights produced by irregular waves on two beaches with slopes of 1:100 and 1:40 are studied. The cross-shore distributions of longshore current velocities and wave heights are given and the influences of wave heights, wave periods, and beach slopes on longshore currents are discussed. The discussion is also made on the influences of different eddy viscosity coefficients on the numerical results of longshore current velocities.

Mooring Tension and Motion Characteristics of A Submerged Fish Reef with Net in Waves and Currents Using Numerical Analysis

A numerical model was used to analyze the motion response and mooring tension of a submerged fish reef system. The system included a net attached to a rigid structure suspended up from the bottom with a single, high tension mooring by fixed flotation. The analysis was performed by using a Morison equation type finite element model configured with truss elements. Input forcing parameters into the model consisted of both regular and irregular waves, with and without a steady current. Heave, surge and pitch dynamic calculations of the reef structure were made. Tension response results of the attached mooring line were also computed. Results were analyzed in both the time and frequency domain in which appropriate, linear transfer functions were calculated. The influence of the current was more evident in the tension and heave motion response data. This is most likely the result of the large buoyancy characteristics of the reef structure and the length of the mooting cable. Maximum mooting component tension was found to be 13.9 kN and occurred when the reef was subjected to irregular waves with a co-linear current of 1.0 m/s velocity. The results also showed that the system had little damping （in heave） with damped natural periods of 2.8 s. This combination of system characteristics promotes a possible resonating situation in typical open sea conditions with similar wave periods.

A possible mechanism of current in medium under electromagnetic wave

In this paper a possible mechanism of current in medium is presented. Comparison between this current and the magnetization current was made. Expression for this current was derived. This work is helpful to understanding the interaction between medium and electromagnetic wave.

Effect of Rectangle Wave Pulse Current on Solidification Structure of ZA27 Alloy

The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The restdts show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current. Imposed pulse current could induce the solidification system to oscillate. The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of dusters in melt, the oscillating state of melt on the surface of dusters, the active energy of atom diffusion , the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work. Rectangle wave pulse current involves rich harmonic waves ; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.

Numerical study of seabed response and liquefaction around a jacket support offshore wind turbine foundation under combined wave and current loading

The seabed instability induced by the transient liquefaction when exposed to wave-current may threaten the safety of offshore structures.In this study,the Reynolds-averaged Navier-Stokes(RANS)equations with the k-e turbulence model were used to imitate the fluid dynamics,and Biot's poro-elastic theory was used to simulate the transient seabed response.An in-house solver(porous-fluid-seabed-structure interactions-field operation and manipulation)integrating the flow model and seabed model with the finite volume method was developed.The present model was confirmed with published experimental results and then used to analyze the dynamic process of the fluid-seabed-structure interactions as well as seafloor liquefaction around the jacket foundation under wave-current loading.The simulated results showed that the depth and range for the liquefaction area around the jacket foundation tended to increase at first and then declined as the wave propagated forward in the absence of current.In addition,the results demonstrated that the liquefaction depth under current and wave in the same orientation was greater than that without current.It is worth mentioning that the downstream piles were more prone to liquefaction than the upstream piles when the forward current existed.

Wave Breaking Phenomena of Irregular Waves Combined with Opposing Current

Experimental study and theoretical analysis show that the critical value of relative wave height (H / d)b given by Goda and the critical wave steepness (H / L)b given by Michell and Miche can be adopted as the spilling breaking indices of regular waves. According to the same principle, a systematic theoretical analysis and experiment of irregular wave have been done by the authors in order to solve the breaking problem of irregular waves. It is indicated that the authors' method for determining wave breaking of regular waves can also be used for irregular waves.

Modeling of random wave transformation with strong wave-induced coastal currents

The propagation and transformation of multi-directional and uni-directional random waves over a coast with complicated bathymetric and geometric features are studied experimentally and numerically. Laboratory investigation indicates that wave energy convergence and divergence cause strong coastal currents to develop and inversely modify the wave fields. A coastal spectral wave model, based on the wave action balance equation with diffraction effect （WABED）, is used to simulate the transformation of random waves over the complicated bathymetry. The diffraction effect in the wave model is derived from a parabolic approximation of wave theory, and the mean energy dissipation rate per unit horizontal area due to wave breaking is parameterized by the bore-based formulation with a breaker index of 0.73. The numerically simulated wave field without considering coastal currents is different from that of experiments, whereas model results considering currents clearly reproduce the intensification of wave height in front of concave shorelines.

Effect of oceanic current on typhoon-wave modeling in the East China Sea

We use the WAVEWATCH-III model to quantify the effect of oceanic current on typhoon-wave modeling in the East-China-Sea（ECS）.Typhoons Jelawat and Saomai in the autumn of 2000 are hindcasted.The oceanic currents in the ECS are mainly constituted of Kuroshio and typhoon-generated currents.The results show distinguishable differences in wave height and wave period under the typhoon conditions.The oceanic current causes the maximum differences,of up to a 0.5 m significant wave height and a 1 s mean wave period.Comparisons between typhoons Jelawat and Saomai show the dependence of the current effect on the typhoon characteristics.

Wave-current bottom shear stresses and sediment re-suspension in the mouth bar of the Modaomen Estuary during the dry season

On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.

Wave Scattering by Double Slotted Barriers in A Steady Current:Experiments

The adoption of slotted breakwaters can be an ideal option in the protection of very large near-shore floating struc-trees that may extend offshore to a considerable water depth. In this paper, we experimently investigated the behaviour of wave transmission and reflection coefficients of double slotted barriers in the presence of a steady opposing current. The experimental results show that opposing currents have only minor effects on wave reflection, but can significantly reduce the wave transmission through double slotted barriers. The experimental results suggest that coastal currents should be taken into consideration for an economical design of slotted breakwaters.

Electromagnetic backscattering from one-dimensional drifting fractal sea surface Ⅰ：Wave–current coupled model

To study the electromagnetic backscattering from a one-dimensional drifting fractal sea surface,a fractal sea surface wave–current model is derived,based on the mechanism of wave–current interactions.The numerical results show the effect of the ocean current on the wave.Wave amplitude decreases,wavelength and kurtosis of wave height increase,spectrum intensity decreases and shifts towards lower frequencies when the current occurs parallel to the direction of the ocean wave.By comparison,wave amplitude increases,wavelength and kurtosis of wave height decrease,spectrum intensity increases and shifts towards higher frequencies if the current is in the opposite direction to the direction of ocean wave.The wave–current interaction effect of the ocean current is much stronger than that of the nonlinear wave–wave interaction.The kurtosis of the nonlinear fractal ocean surface is larger than that of linear fractal ocean surface.The effect of the current on skewness of the probability distribution function is negligible.Therefore,the ocean wave spectrum is notably changed by the surface current and the change should be detectable in the electromagnetic backscattering signal.

WAVE CURRENT FORCE COEFFICIENTS ON INCLINED CYLINDER AND A NEW ESTIMATION METHOD

Based on the review of present force coefficients estimation methods, a new method in the frequency domain, revised cross-spectrum estimation method, is presented in this paper. Some experiments on the wave-current force on inclined cylinders are also described and the wave current force coefficients are estimated by the revised cross-spectrum estimation method. From the results, it is found that the wave and current directions have some regular effect on the coefficients. According to the results, some empirical formulas are obtained for converting the wave-current force coefficients on inclined cylinders into a unified coefficient. Comparisons show that the unified coefficients are in good agreement with other results.

Study on scour around vertical large-size cylinder base due to combined action of wave and current

Based on the mechanism of local scour around vertical large-sized cylinder due to combined action of wave and current,the sour morphology,scour process and the maximum scour depth around the cylinders are studied experimentally.The influence of various ocean environmental parameters on local scour around the cylinder is considered in physical model test.The experimental results indicate that the principal effect factors on the scour in fine-sand seabed are wave height,wavelength,current velocity,ratio of diameter to wavelength and ratio of depth to wavelength when the ratio of cylinder diameter to wavelength is from 0.2 to 0.8.In this paper,dimensional analysis theory is utilized to establish a theoretical equation for forecasting maximum scour depth around large-sized round cylinder base due to the combined action of wave and current.The results computed with the theoretical equation are compared with the experimental results,and found to be in good consistency.The results in this studies can be used to estimate the maximum sour depth around analogous structures.