On the interaction of a solitary wave and a submerged dike

The unsteady, two-dimensional Navier–Stokes equations and the exact free surface boundary conditions were solved to study the interaction of a solitary wave and a submerged dike. A piston-type wavemaker was set up in the computational domain to produce the incident solitary waves. The incident wave and the associated boundary layer flow in a wave tank with a flat bed were compared with the analytical solutions to verify the accuracy of this numerical scheme. Effects of the incident wave height and the size of the dike on the wave transformation, the flow fields, and the drag forces on the dike were discussed. Our numerical results showed that even though the induced local shear stress on the top surface of the dike is large at some particular locations, the resultant pressure drag is much larger than the friction drag. The primary vortex generated at the lee side of the dike and the secondary vortex at the right toe of the dike may scour the bottom and cause a severe problem for the dike.     

Wave motion over a breakwater system of a horizontal plate and a vertical porous wall

A two-dimensional analytical solution is presented to study the reflection and transmission of linear water waves propagating past a submerged horizontal plate and through a vertical porous wall. The velocity potential in each fluid domain is formulated using three sets of orthogonal eigenfunctions and the unknown coefficients are determined from the matching conditions. Wave elevations and hydrodynamic forces acting on the porous wall are computed. Reflection and transmission coefficients are presented to examine the performance of the breakwater system. The present analytical solutions are found in fairly good agreement with the available laboratory data. The results indicate that the plate length, the porous-effect, the gap between plate and porous wall, and the submerged depth of the plate all show a significant influence on the reflected and transmitted wave fields. It is also interesting to note that the submerged plate plays an important role in reducing the transmitted wave height, especially for long incident waves.     

Runup of solitary waves on a straight and a composite beach

Particle Image Velocimetry (PIV) and wave gauges have been used to investigate the runup of solitary waves at two different beaches. The first beach is straight with an inclination of 10°, whereas the second is a composite beach with a change in the 10° inclination to 4° at a vertex point above the equilibrium water level. Comparison with numerical simulations using a Navier–Stokes solver with zero viscosity has been performed for the composite beach. Four different amplitudes of incoming solitary waves are investigated.Measurements of the runup show that the composite beach gives a lower runup compared to the straight beach. Furthermore, the composite beach experiences a longer duration of the rundown compared to the straight beach. This is at least partially assumed to be a result of scaling effects, since the fluid above the vertex creates a relatively thinner runup tongue compared to the straight beach scenario.The appearance of a stagnation point at the beach boundary is clearly visible in both the PIV results and the numerical simulation. This stagnation point is originating at the lowermost part of the beach, and is moving upwards with time. It is found that the stagnation point moves faster upwards for the straight beach than for the composite beach. Further, the stagnation point is moving even faster in the numerical simulation, suggesting that the velocity with which the stagnation point moves is influenced by viscous scaling effects.Finally, the numerical simulation seems to capture the physics of the flow well, despite differences in the phase compared to the PIV results. This applies to both the flow field and the surface elevations.     

Vibrations of a rectangular orthotropic plate with a free edge: a comparison of analytical and numerical results

Transverse vibrations of a rectangular orthotropic plate with a free edge while the others are supported according to four different combinations of boundary conditions are considered in the present paper. The presence of a concentrated mass is also taken into account. In view of the difficulty of satisfying exactly the natural boundary conditions at the free edge, the fundamental frequency of vibration is determined by means of the optimized Rayleigh-Ritz method and a pseudo-Fourier expansion which contains, in its argument, the optimization parameters γ_i. The results are in excellent agreement with those obtained by means of a finite element algorithmic procedure.     

Comparison between a U-OWC and a conventional OWC

With an additional vertical duct at the wave-beaten side, an OWC is expected to give some much better performances. This is, essentially, due to two reasons. First, an OWC with the additional vertical duct (U-OWC) has an eigenperiod greater than the eigenperiod of a conventional OWC. Second, the amplitude of the pressure fluctuations on the opening of a U-OWC is greater than the amplitude of the pressure fluctuations on the opening of a conventional OWC (the greater the smaller the wave period is). For the first reason, a U-OWC can give performances better than those of a conventional OWC both with swells and large wind waves. For the second reason, a U-OWC can give performances better than those of a conventional OWC also with small wind waves.     

鞘氨醇杆菌产微生物絮凝剂的组成及絮凝特性

首次发现从青岛市团岛污水处理厂的活性污泥中分离得到的嗜温鞘氨醇杆菌(Sphingobacterium thalpophilum)产生絮凝剂,研究了该菌株所产絮凝剂的理化性质和絮凝特性。结果表明,该菌所产絮凝剂MBFQ-7是1种酸性多糖,主要由葡萄糖、甘露糖、阿拉伯糖、葡萄糖醛酸和半乳糖组成。絮凝实验表明,当微生物絮凝剂用量为7~8 mg/L,pH=3~7,温度20~80℃时,MBFQ-7具有较高的絮凝活性。     

Characteristics of a Cup Anemometer and a Procedure of Measuring the Wind Velocity

On the basis of the data of laboratory, model, and field investigation of the characteristics of a proposed cup anemometer, we obtain the following results: the distance constant is equal to 0.32 m with a mean-square deviation of 0.05 m, which is smaller than for the other anemometers of this type by an order of magnitude, the dynamic characteristics of the anemometer are linear for typical conditions of atmospheric turbulence, the variance and spectrum of noises (as a result of transformation of pulsed signals at the output of the anemometer) are described by universal functions with known parameters, the transmission bandwidth is approximately equal to 2 Hz for wind velocities lower than 5 m/sec and up to 5 Hz for higher wind velocities, and the errors of measurements of the mean wind velocity and the characteristics of the longitudinal component of velocity are approximately equal to 1 and 3%, respectively. The dimensions and weight of the anemometer are quite small, which enables one to perform long-term measurements of the characteristics of wind velocity for all types of platforms within broad ranges of hydrometeorological conditions.     

Wave response of a spar buoy with and without a damping plate

Report on a computer analysis of wave response of a spar buoy that has been operated successfully in the Mediterranean over the past ten years, to find out how the presence of a large horizontal plate at the bottom affects its wave response. The calculations show that the addition of a damping plate decreases have response for short waves but increases the response for very long waves.     

Respiration rates of copepod larvae and a ciliate from a tropical sea

The respiration rates of copepod larvae and a ciliate (Placus sp.) from a tropical sea were measured with an oxygen electrode method. The general range of body size of these animals was 40–161m (diameter equivalent to a sphere), and the respiration rate measured was 0.00076–0.00176l O₂ (animal)^–1h^–1 (or 2.02–9.05l O₂ (mg wet weight)^–1h^–1) at 25.5–29.2C. There was no marked difference observed between the respiration rates of copepod larvae and the ciliate. The respiration rates obtained here are relatively higher than the rates of other similar sized protozoans found in the literature, but lower than the rate extrapolated from larger planktonic copepods in tropical seas.The present results and other information available on microzooplankton biomass suggest that microzooplankton respiration is of near equal importance to that of net zooplankton in the study of energy flow through tropical, pelagic ecosystems.     

Fine Structure of a Stratified Flow around a Fixed and Slow-Moving Wedge

The dynamics of the establishment and spatial structure of flows of a continuously stratified fluid around a fixed and slow-moving horizontal wedge are studied using direct numerical simulation based on the fundamental system of inhomogeneous fluid mechanics equations. Large-scale components (eddies, internal waves, and the wake) and fine-structure components are isolated in the flow patterns in near and away from the obstacle. The mechanism of formation of the propulsive force generating the self-motion of a free body at a neutral-buoyancy horizon is determined. The dependence of the flow parameters on the shape of the obstacle is shown. The transformation of the medium perturbation field at the beginning of the induced slow movement of the wedge at the neutral-buoyancy horizon is traced. The complex structures of fields of different physical quantities and their gradients are visualized. The intrinsic temporal and spatial scales of the flow components are identified.     

Towing dynamics of a liferaft and fast rescue craft in a surface wave

The equations of motion for the coupled dynamics of a small liferaft and fast rescue craft in a surface wave are formulated in two dimensions using the methods of Kane and Levinson [1985. Dynamics: Theory and Applications. McGraw-Hill Inc., New York]. It is assumed that the motion normal to the wave surface is small and can be neglected, i.e. the bodies move along the propagating wave profile. The bodies are small so that wave diffraction and reflection are negligible. A Stokes second order wave is used and the wave forces are applied using Morison's equation for a body in accelerated flow. Wind loads are similarly modelled using drag coefficients. The equations are solved numerically using the Runge–Kutta routine “ode45” of MATLAB^®. The numerical model provides guidelines for predicting the tow loads and motions of small craft in severe sea states.     

两层流体中矩形箱浮体的附加质量和阻尼系数

研究了两层流体中矩形箱浮体的辐射问题。基于特征函数匹配理论,针对矩形箱浮体的三种振荡运动模式(横荡、垂荡和横摇),建立两层流体中矩形箱浮体辐射势的求解方法,导出矩形箱浮体附加质量和阻尼系数的计算公式。对所建立的求解模型进行了数值计算分析,结果表明在矩形箱浮体的某个振荡频率范围内,流体的分层效应对其附加质量和阻尼系数有显著影响的。     

Laboratory modeling of the structure of a thermal bar and related circulation in a basin with a sloping bottom

Development of a thermal bar in a laboratory flume with an inclined bottom (3.7°–12°) under the conditions of cooling/heating of the water with a temperature close to that of the maximal density is studied. The structure of the temperature field and currents during different stages of the circulation is examined: (i) formation of an along-slope gravity current, (ii) generation of a subsurface jet, and (iii) transformation of one type of the circulation into another at passing the temperature of the maximum density. The “fall” and “spring” types of the thermal bar are shown to be dynamically equivalent: the transport of the near-shore waters to the deepwater part, which is driven by the buoyancy flux rather than by the heat flux across the surface, transforms stage (i) into stage (ii), while the opposite (on-shore) flow is generated in the intermediate layers. A comparison of the results with the field and laboratory data published allows us to suggest that the propagation of the thermal bar front in the “fast” stage can be considered as the development of a convective jet with its velocity U ～ h ^3/4, which is proportional to the growing thickness of the upper layer h affected by the heating/cooling processes     

Hadley and Rossby regimes in a simple model of convection of a rotating fluid

This paper analyzes the properties of solutions to the equations describing the motion of a stratified fluid in the class of velocity and temperature fields linear in coordinates. For an ideal fluid, these equations, on the one hand, are exact for the corresponding hydrodynamic problem and, on the other hand, are identical to the equations of motion for a heavy top. In a conservative case, the equations of motion of a top share common solutions with the equations of geophysical fluid dynamics and reproduce motions similar to those existing in the theory of the large-scale atmospheric circulation. This study considers the effects of viscosity and heat conduction in the fluid, which are, in a sense, similar to the effect of friction in the case of a top. The influence of deflections of the vectors of gravity and external rotation from their standard directions for a plane-parallel atmosphere is also considered. The regimes of motions that are described by the starting equations and approximations commonly used to model the atmospheric general circulation (the quasi-geostrophic approximation) are analyzed. It is shown that these equations correctly describe the Hadley and Rossby circulation regimes and transitions between them that are observed in numerical and laboratory experiments. Particular attention is given to the consistency between different regimes of the exact equations and their quasi-geostrophic approximations, which is manifested for small Rossby numbers and is generally absent for large Rossby numbers. The asymptotic behaviors of the curves of transition between the Hadley and Rossby regimes under the conditions of breaking the external symmetry of flows are obtained. These asymptotics explain the corresponding transition boundaries for the regimes observed in the known experiments in annuluses.     

The persistence and mobility of a light crude oil in a Sandy beach

The weathering of a very light crude oil (a condensate) in a sandy beach in Nova Scotia has been studied by following changes in its detailed chemical composition.Evaporation was the dominant weathering process in supratidal sand. After 4 months all oil components more volatile than n-C₁₆ had disappeared; concentrations of compounds less volatile than n-C₁₈ did not change. In the surface sand of the upper intertidal zone evaporation was much slower, with C₈ hydrocarbons still present after 3 months. Dissolution was also important in this environment with aromatic components up to the C₁-naphthalenes being removed in the first month. In subsurface (5–10 cm) sand from this zone and in both surface and subsurface samples from the middle intertidal zone, no loss of volatiles occurred over a 6-month period. Preferential Dissolution was significant in these environments, but was neither as rapid nor as extensive as in the surface sand of the upper intertidal zone. Observed dissolution rates were at least ten times slower than those predicted using equilibrium solubilities and pore water exchange rates.The mobility of the condensate through beach sand was dependent on the oil/sand ratio. At low concentrations, bulk oil movement was insignificant, but, at higher concentrations, movement was rapid, independent of interstitial water flow and exclusively upwards. Only at higher concentrations was appreciable oil free in the sand interstices where it was subject to this buoyancy transport mechanism.     

Diffraction by a hard truncated wedge and a strip

A method of formulating the scattered acoustical field for certain types of hard bodies through the use of well-known exact solutions for the simple semi-infinite wedge and/or corner is presented. The method yields a representation of the total sound field for all frequencies and satisfying all boundary conditions. Relevant hard-wedge solutions for harmonic line sources and for plane waves are reviewed. Such solutions, which are rigorous, represent the total sound field as a superposition of directional line sources and sinks at the wedge vertex. A method of representing multiple scatter from combinations of wedges, allowing the explicit solution of the case of a truncated wedge, is introduced. This method uses the classic self-consistent algorithm for multiple scatter, together with a rigorous representation of vertex-diffracted fields     

Wave height transformation and set-up between a submerged permeable breakwater and a seawall

In this study,we investigated wave transformation and wave set-up between a submerged permeable breakwater and a seawall.Modified time-dependent mild-slope equations,which involve parameters of the porous medium,were used to calculate the wave height transformation and the mean water level change around a submerged breakwater.The numerical solution is verified with experimental data.The simulated results show that modulations of the wave profile and wave set-up are clearly observed between the submerged breakwater and the seawall.In contrast to cases without a seawall,the node or pseudo-node of wave height evolution can be found between the submerged breakwater and the seawall.Higher wave set-up occurs if the nodal or pseudo-nodal point appears near the submerged breakwater.We also examined the influence of the porosity and friction factor of the submerged permeable breakwater on wave transformation and set-up.     

Interaction between a synoptic eddy and a Rossby wave

The behaviour of an isolated synoptic eddy on the -plane in the field of a plane Rossby wave is reported. As is shown, the eddy exchanges its energy intensively with Rossby waves having zero frequency in the frame of axes moving with the eddy. If the Rossby wave has an amplitude exceeding some critical value, a transition from average translational eddy motion along the meridian to oscillations in the vicinity of the equilibrium latitude is possible.Translated by Mikhail M. Trufanov. UDK 551.465.535:551.466.