Shear Flow Dispersion Under Wave and Current

The longitudinal dispersion of solute in open channel flow with short period progressive waves is investigated. The waves induce second order drift velocity in the direction of propagation and enhance the mixing process in concurrent direction. The 1-D wave-period-averaged dispersion equation is derived and an expression for the wave-current induced longitudinal dispersion coefficient (WCLDC) is proposed based on Fischer's expression (1979) for dispersion in unidirectional flow. The result shows that the effect of waves on dispersion is mainly due to the cross-sectional variation of the drift velocity. Furthermore, to obtain a more practical expression of the WCLDC, the longitudinal dispersion coefficient due to Seo and Cheong (1998) is modified to incluee the effect of drift velocity. Laboratory experiments have been conducted to verify the proposed expression. The experimental results, together with dimensional analysis, show that the wave effect can be reflected by the ratio between the wave amplitude and wave period. A comparative study between the cases with and without waves demonstrates that the magnitude of the longitudinal dispersion coefficient is increased under the presence of waves.     

Research on Characteristics of Density Current Under the Action of Waves

In this paper,the characteristics of density current under the action of waves are describedwith the help of flume experiment and theoretical analysis.The study shows that turbid water under the ac-tion of the waves can present three types of motion,i.e.significant stratification,fragile stratification andstrong mixing.The motion of turbid water presents significant stratification when(H/D)/△ρ/ρ~(1/2)≤4.5,generally this state is known as density current.The formulas of motionvelocity,thickness,and discharge of density current moving on horizontal bottom are derived by use of ba-sic equations such as momemtum equation,equation of energy conservation and continuity equation offluid.The time-average velocity and the thickness of density current under the action of waves have a rela-tionship with such parameters as relative density(△ρ/ρ),wave height(H),and water depth(D).Whenthese parameters are determined,the time-average thickness and motion velocity of density current are al-so determined.The relat     

Analysis on Interface Shear Stress of Thermally Insulated Ocean Pipelines Under Installation

1.IntroductionMost of the crude oil producedfromoffshore China has a highcontent of wax,which makesthe oilagglomerate at hightemperature.Heat preservation measures,therefore,must be adopted to maintainthe temperature higher thanthe oil’s pour point,sotha…     

Numerical Modeling of Water Wave Interaction with A Soft Mud Bed

A vertical 2-D numerical model is presented for simulating the interaction between water waves and a soft mud bed. Taking into aceotmt nonlinear theology, a semi-empirical theological model is applied to this water-mud model, reflecting the combined visco-elasto-plastic properties of soft mud under such oscillatory external forces as water waves. In order to increase the resolution of the flow in the neighborhood of both sides of the inter-surface, a logarithmic grid in the vertical direction is employed for numerical treatment. Model verifications are given through comparisons between the calculated and the measured mud mass transport velocities as well as wave height changes.     

New Interpretation of Dependence of Wind Stress on Wave State

Based on observations from buoys, it is found that the wave age is well correlated with the nondimensional wave height, and this correlation is best described by a 3/5-power law. This similarity law is valid in the cases of wind waves as well as swells under natural sea states. On the basis of the 3/5-power law combined with the well-known 3/2-power law, it is shown that the wave-induced wind stress increases rapidly with wave age, indicating that the traditional observations or analytic techniques have only given the turbulent Reynolds stress induced by short wind waves, but excluded the long-wave-induced wind stress. The latter constitutes a small fraction to the total wind stress when the wave age is smaller than 1.0. The increase of sea-surface roughness with wave age can be attributed to wave breaking.     

Numerical Modeling of Wave and Current Interaction in the Tidal Inlet Area

This paper investigates the phenomena of wave refraction and diffraction in the slowly varying topography, as well as the current deflection due to wave actions. A numerical model is developed based on depth integrated mean continuity equation and momentum equations, and a 3rd-order wave equation which governs the wave diffraction, refraction and interaction with current. Examples to examine the above model are given comparing with the laboratory data or the numerical results of other researchers. An example simulating the inlet area shows the interesting velocity field which may be used as a pioneer to further study on the nearshore hydrodynamics and sedimentation.     

Study on Measurement Methods of Multi-Directional Waves—Wave Gauge Array Method

- Measuring multi-directional waves with the wave gauge array is one of the fundamental and easily realised methods. In this paper, the wave gauge array is described and the effects of the gauge spacing, the array orientations, etc. of the three array arrangements, i. e., linear array, T-type array and pentagon array, on the resolution of the directional spreading of waves, are investigated experimentally. This study can be used as a reference in the experimental study and the field measurement of directional waves.     

Computation of Wave, Tide and Wind Current for the South China Sea Under Tropical Cyclones

Based on the third-generation oceanic wave prediction model (WAVEWATCH Ⅲ) ,the third-generation nearshore wave calculation model (SWAN) and the mathematical tide, tidal current and cyclone current model, which have been improved, interconnected and expanded, a coupled model of offshore wave, tide and sea current under tropical cyclone surges in the South China Sea has been established. The coupled model is driven by the tropical cyclone field containing the background wind field. In order to test the hindcasting effect of the mathematical model, a comparison has been made between the calculated results and the observational results of waves of 15 cyclone cases, water levels and current velocities of the of 7 cyclones. The results of verification indicate that the calculated and observed results are basically identical.     

Experimental Study on Silt Incipient Motion Under Wave Action

Experiments on silt incipient motion under wave action were carried out.Under wave action,for different wave periods,water depths and bulk densities of silt,the shear stress or height of waves for incipient motion was determined,and a relation between the shear stress and bulk density of silt was established.Results indicate that the critical shear stress depends on the structure of the silt itself,related to the tightness between the grains(or bulk density).Exterior condition is only an external cause of silt incipient motion,and the critical shear stress for the incipient motion is the token of exterior condition.     

Effect of Wave Groups on Wave Run-up

-The effect of wave group on wave run-up on a slope dike is mainly discussed in this paper. Two simulating methods of wave group and their applications in laboratory are introduced. Synthesizing the research results of wave run-up on a slope dike, the effect of wave group on wave run-up on a slope dike in coastal protection engineering is studied as the main point.     

Analytical Research on Wave Diffraction on Arc-Shaped Bottom-Mounted Perforated Breakwaters

An analytical method is developed to study wave diffraction on arc-shaped and bottom-mounted perforated breakwaters.The breakwater is assumed to be rigid,thin,vertical,immovable and located in water of constant depth.The fluid domain is divided into two regions by imaginary interface.The velocity potential in each region is expanded by eigenfunctions.By satisfying the continuity of pressure and normal velocity across the imaginary fluid interface,a set of linear algebraic equations can be obtained to determine the unknown coefficients of eigenfunctions.Numerical results,in the form of contour maps of the relative wave amplitude around the breakwater,are presented for a range of wave and breakwater parameters.Results show that the wave diffraction on the arc-shaped and bottom-mounted perforated breakwater is related to the incident wavelength and the porosity of the breakwater.The porosity of the perforated breakwater may have great effect on the diffracted field.     

Wave Refraction-Diffraction in the Presence of a Current

-Wave refraction-diffraction due to a large ocean structure and topography in the presence of a 'current are studied numerically. The mathematical model is the mild-slope equation developed by Kirby (1984). This equation is solved using a finite and boundary element method. The physical domain is devid-ed into two regions: a slowly varying topography region and a constant water depth region. For waves propagating in the constant water depth region, without current interfering, the mild- slope equation is then reduced to the Helmholtz equation which is solved by boundary element method. In varying topography region, this equation will be solved by finite element method. Conservation of mass and energy flux of the fluid between these two regions is required for composition of these two numerical methods. The numerical scheme proposed here is capable of dealing with water wave problems of different water depths with the main characters of these two methods.     

Vibrating-Rocking Motion of Caisson Breakwater Under Breaking Wave Impact

The possible motions of a caisson breakwater under dynamic load excitation include vibrating, vibrating-sliding and vibrating-rocking motions. The models of vibrating motion and vibrating-sliding motion have been proposed in an early paper. In this paper, a model of vibrating-rocking motion of caisson breakwaters under breaking wave impact is presented, which can be used to simulate the histories of vibrating-rocking motion of caisson breakwaters. The effect of rocking motion on the displacement, rotation, sliding force and overturning moment of breakwaters is investigated. In case the overturning moment exceeds the stability moment of a caisson, the caisson may only rock. The caisson overturns only in case the rocking angle exceeds the critical angle. It is shown that the sliding force and overturning moment of breakwaters can be reduced effectively due to the rocking motion. It is proposed that some rocking motion should be allowed in breakwater design.     

Numerical Simulation of Wave Interaction with Perforated Caisson Breakwaters

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The Mechanism Analysis of Seafloor Silt Liquefaction Under Wave Loading

The sediment in Chengbei area of the Huanghe (Yellow River) subaqueous delta is the object of a reseach project in this article. The accumulating and dissipating effects following the change of time are considered first in the study area and the distributing curves of excess pore water pressure along with time and depth in the soil stratum are gained; the possibility of silt liquefaction is evaluated using the computing values and the affecting depth of liquefaction is given. This paper quantitatively analyzes the dynamic response of seafloor soil under the cyclic loading of waves and makes an inquiry into the instable mechanism of soil.     

Dynamic Response Behaviors of Upright Breakwaters Under Breaking Wave Impact

- The dynamic response behaviors of upright breakwaters under broken wave impact are analysed based on the mass-damper-spring dynamic system model. The effects of the mass, damping, stiffness, natural period, and impulse duration (or oscillation period) on the translation, rotation, sliding force, overturning moment, and corresponding dynamic amplifying factors are studied. It is concluded that the ampli-ying factors only depend on the ratio of the system natural period to impulse duration (or oscillation period) under a certain damping ratio. Moreover, the equivalent static approach to breakwater design is also discussed.     

Shear Failure of a Clamped Dented Tubular Beam Under Lateral Impact

- The shear failure of a rigid-plastic dented clamped tubular beam under the lateral impact of a mass is investigated. Both the denting and the impact point are in the middle span of the beam. It is assumed that denting does not spread during the shear sliding. Numerical results show that the axial force and lateral deflection of the beam are very small at the moment of the occurence of shear failure, which means that the finite deformation effect can be neglected in the shear failure analysis. Also, some aspects of the initial impact energy are investigated.     

The Behavior of Reinforced Concrete Members Under Combined Torsion and Shear

- The behavior of the reinforced concrete members subjected to combined torsion and shear is studied in this paper. Based on the skew bending failure pattern observed in tests, and according to the gradual increase in strain on the concrete surface, a nonlinear full range analysis is performed for predicting the torque-twist relationship of members under combined torsion and shear for the ratio of torsion to shear is chosen bigger than 0.5 (T/ V b> 0.5). The test results are compared with the theoretical predictions.     

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 waves 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.     

Vibrating-Sliding Motion of Caisson Breakwaters Under Various Breaking Wave Impact Forces

Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is used to simulate the vi-brating-sliding motion of the caisson under various types of breaking wave impact forces, i.e., single peak impact force, double peak impact force, and shock-damping oscillation impact force. The effects of various breaking wave impacts and the sliding motion on the dynamic response behaviors of caisson breakwaters are investigated and the calculation of relevant system parameters is discussed. It is shown that the dynamic responses of the caisson are significantly different under different types of breaking wave impact forces even when the amplitudes of impact forces are equal. The amplitude of dynamic response of the caisson is lower under single peak impact excitation than that under double peak impact or shock-damping oscillation impact excitation. Though the disp