Characteristics Of Hydrodynamic Forces Research Articles

Experimental Investigation of the Yaw Misalignment Effect on the Power Performance and System Loading of a Flapping‐Foil Hydrokinetic Turbine

ABSTRACTHydrokinetic turbines (HTs) extract power by utilizing hydrodynamic forces from flow energy. The surplus load not used for power generation acts as a system load and must be considered when designing the turbine. Additionally, due to the variability of the flow direction during tidal power generation, the effect of the yaw misalignment angle on the power generation performance and system loading is an important design consideration. This study investigates the characteristics of an experimental model of an HT that uses two flapping foils, at different yaw misalignment angles through circulating water tunnel experiments. Experimental results show that with a yaw angle change of 10°, the power performance decreases by approximately 10% and the load increases by about 30% compared to an aligned configuration. Notably, the load in the flow‐perpendicular direction was significant, with periodic changes due to repetitive up‐and‐down motions. Consequently, the hydrodynamic force characteristics of the HT differ from those of conventional rotary turbines, necessitating the development of a design method that fits these characteristics for the actual installation of flapping‐foil HTs at tidal current power generation sites.

Temporal and Spatial Variation Characteristics of Hydrodynamic Forces in Urban Shallow Lakes

To study the temporal and spatial variation characteristics of hydrodynamic forces in Rule Lake, a two-dimensional mathematical model of shallow water lake was established based on MIKE 21, and the flow field characteristics of Rule Lake under the action of topography, wind field and inflow were simulated and analyzed. The results show that the spatial and temporal heterogeneity of hydrodynamics in the Rule Lake area is obvious, the velocity in the lake area presents a gradient change characteristic of high in the west and low in the east, and the velocity in the middle of the lake area is greater than that in the bends of shorelines on both sides of the lake area; Under the driving of wind field, there is a reverse circulation area in the lake area. The existence of the circulation area can disturb the dead water area at the shoreline bend and improve the local water mobility; The flow velocity in summer and autumn is slightly higher than that in spring and winter. It is suggested that during the operation and maintenance period, attention should be paid to the fluidity of the water body in the southwest of the lake area, the change in water quality and the timely removal of floating garbage on the water surface.

Numerical investigation of the influence of surface wettability on water entry of spheres

The water-entry problem is a complex multiphase hydrodynamic problem that is directly related to many engineering applications and natural phenomena, such as torpedo airdrops, seaplane landings, and ship slamming. Therefore, studying the influence of the microscopic properties of the object surface on the macroscopic phenomenon during water entry is necessary. In this study, the volume of fluid model and continuum surface force models are coupled to establish a multiphase flow numerical method for the water entry of objects considering surface wettability. The effect of surface wettability on the evolution of the cavity, multiphase flow-field structure, and hydrodynamic force characteristics are analyzed in detail. The results show that the movement of liquid film formed on the surface of the sphere at the early stage is the key to the formation of the cavity. For hydrophobic spheres, the liquid film separates near the equator of the sphere, and air enters it to form a cavity. At the moment of pinch-off, the pressure in the lower cavity increases, which generates a force that pushes the sphere to accelerate the fall, and this force is higher for spheres with a smaller density ratio. The flow-field structure shows that both rotational and shear effects play a dominant role in the evolution of the flow field in the cavity. For hydrophilic spheres, the liquid film follows the contact line along the surface of the sphere and converges at the top to form an upward jet.

Hydrodynamic and radial force characteristics with design of a single-channel pump for wastewater treatment based on the similarity law

Single-channel pumps are widely employed for wastewater treatment in Korea. To render possible the application of this type of pump in other countries using different power frequencies, the present study applies the similarity law to redesign the impeller geometry of the single-channel pump optimized in a previous study. To this end, the numerical simulations are conducted using steady and unsteady Reynolds-averaged Navier–Stokes equations and a shear stress transport reattachment modification turbulence model. Numerical simulations are confirmed by an experiment based on the 11th API610 standard. At design flow rate condition, the novel pump model meets the design requirement with the minimum total head coefficient of 3.078. The distance between the center of the radial force and the origin of the new model is notably decreased in comparison with the reference model, especially at the design point with a reduction of 3.418 times. Moreover, the results of the unsteady radial force are consistent with those of the steady radial force. The pressure oscillations in the new model are likewise reduced compared to the reference model, particularly at several measuring points under design flow rate with pressure oscillations dropping from 8.5% and 10.1–5.3% and 1.2%, respectively. The non-uniform high-pressure region caused by the rotor-stator interaction at the outlet of the impeller is evidently suppressed in the new model. The new single-channel pump is feasible for new power frequency and performs better with low vibration and noise levels during the operation.

Hydrodynamic coefficients of a forced oscillating flexible pipe with energy competition model

The objective of this study is to reveal the characteristics of hydrodynamic force and coefficients undergoing vortex-induced vibration (VIV) of a flexible pipe in an oscillatory flow. The flexible pipe is forced to oscillate with different amplitudes and periods in the still water to simulate the equivalent oscillatory flow. Different from the traditional model, the hydrodynamic forces for the flexible pipe under the new energy competition force model in both in-line (IL) and cross-flow (CF) directions are divided into drag, excitation and added mass force. The identification methods of the hydrodynamic coefficients for the energy competition force model are then established. The detailed features of the hydrodynamic coefficients under the new force model in an oscillatory are illustrated. The distribution comparison of the two forces, i.e., drag force plays a role in energy dissipation and excitation force acts as energy input, explains the differences of the VIV response in magnitudes under different oscillatory flows. By summarizing the hydrodynamic coefficients, the drag and excitation coefficients are found to be inverse proportion to the Keulegan-Carpenter (KC) number. The independence of the added mass coefficients and KC number is revealed. On the basis of the observation, the empirical models for hydrodynamic coefficients are preliminarily proposed. The effects of the oscillatory flow on the hydrodynamics are established to be determined by the KC numbers under the same reduced velocity. The present investigations will provide a better guideline for developing flow-induced vibration prediction methods in future work.

Influences of floating ice on the vertical water entry process of a trans-media projectile at high speeds

It is of great significance to study the hydrodynamic process of trans-media projectiles passing through ice-water mixture at high speeds for the application of weapons in low-temperature environments of high-latitude water areas during the winter. Based on the volume of fluid (VOF) method and the Schnerr-Sauer cavitation model, the processes of a projectile vertically entering water (without floating ice) and passing through ice-water mixture without collision with ice at different initial high speeds were studied. The influences caused by the ice on the cavity evolution, flow field characteristics, hydrodynamic and ballistic characteristics were analyzed. The results showed that the floating ice alters the volume of air that is sucked into the cavity by hindering the diffusion and contraction movement of the liquid at the gas-liquid interface, changing the degree of cavitation and the formation and development modes of the cavity. It causes a different evolution of the cavity shape, delays the cavity closure, and affects the hydrodynamic force and ballistic characteristics of the projectile ultimately. With increasing velocity, the influence of ice on cavity shape reduces, however, on projectile ballistics, it enhances. The results can provide some theoretical references for further application research on trans-media weapons in floating ice environments.

Hydrodynamic force and attitude angle characteristics of a spinning stone impacting a free surface

This paper describes a numerical study of the hydrodynamics, pressure distribution, and attitude angle characteristics of spinning stones impacting a free surface. A numerical model is developed using the large-eddy simulation and volume-of-fluid techniques, and a wide range of cases are considered under different initial attack angles and spinning velocities. Three stages are defined according to the evolution of the vertical resultant force. For stones with a low spinning velocity and small attack angle, a high-pressure zone emerges at the bottom of the leading edge. Furthermore, the characteristics of the attack angle α and the roll angle φ are demonstrated and analyzed for different initial conditions. The results show that attack angle, roll angle, and vertical resultant force evolve differently for small attack angle compared with that for other initial attack angles, but a similar evolution law governs the attack angle and roll angle during the skipping process. Furthermore, the relations between amplitude and frequency of attitude angle oscillations and the initial attack angles and spinning velocities are presented.

받음각을 갖는 초공동 수중 운동체에서 발생하는 초월공동과 유체력 특성에 대한 수치적 연구

Recently, as the technology of the supercavitating underwater vehicle is improved, the necessity of research for maneuvering characteristics of the supercavitating underwater vehicle has emerged. In this study, as a preliminary step to analyzing the maneuverability of a supercavitating underwater vehicle, the characteristics of cavity shapes and hydrodynamic forces generated in a supercavitating underwater vehicle with an angle of attack were evaluated numerically. First, the geometry was designed by modifying the shape of the existing supercavitating underwater vehicle. The continuity and the Navier-stokes equations are numerically solved, and turbulent eddy viscosity is solved by the k-ωSST model. The results present the characteristics of cavity shape and the hydrodynamic forces of the designed geometry with an angle of attack.

Control of vortex-induced vibrations of the cylinder by using split-ter plates immersed in the cylinder wake at low Reynolds number

The vortex-induced vibrations of a cylinder with two plates symmetrically distributed along the centerline of the wake are studied by using the fluid-structure interaction simulations on the Arbitrary Lagrangian-Eulerian method. In this study, the different geo-metrical distribution parameters of the splitter plates and inflow velocities are taken into account. The physical mechanisms of vortex-induced vibration of the cylinder with symmetrical plates are revealed from the cylinder amplitude, hydrodynamic force characteristics, vortex shedding frequency, and flow pattern modification. The results show that the dynamic interaction between the vortex shed from the oscillation cylinder and plates is responsible for the wake stabilization mechanism, and the stable wake and the dynamic response reduction of the main cylinder can be achieved at a wide range of reduced velocities by placing sym-metrical sheets at suitable locations.

Study on Transient Fuel Hydrodynamic Force Characteristics of High-Speed Solenoid Valve for Common Rail Injector

The working process of the high-speed solenoid valve (HSV) of high-pressure common rail (CR) injector has the characteristics of electro-magnetic-mechanical-hydrodynamic multi-physical field coupling. However, most of the research work in this field is carried out without considering hydrodynamic environment of the HSV. Furthermore, the dynamic response characteristics of the transient fuel hydrodynamic force (TFHF) of the HSV should not be neglected. In this study, a three-dimensional finite element method is used to simulate the TFHF between the injector electromagnet and the armature. The results show that cavitation phenomena appears on the lower surface of the armature during the HSV opening process. The faster the armature moves up, the greater the cavitation intensity. Damping holes on the armature can reduce the TFHF acting on the upper surface of the armature; however, the armature structure with straight grooves and damping holes reduces the TFHF more evidently during the HSV opening and the inhibition effect of this structure on cavitation is more evident. The TFHF on the armature decreases with an increase in the depth of the coil groove. However, the selection of the groove depth should be considered together with the optimization of the electromagnetic force characteristics of the HSV.

Cavitation Characteristics and Hydrodynamic Radial Forces of a Reversible Pump–Turbine at Pump Mode

As the most critical part of a hydropower station, reversible pump–turbines (RPTs) are facing the trend of high parameterization (e.g., high head and high rotation speed) with the rapid development of hydropower, which may cause more detrimental cavitation-induced hydrodynamic forces. Considering that cavitation occurs more easily under pump mode than turbine mode for the RPT, the characteristics and generation mechanism of the hydrodynamic radial force induced by cavitation of a RPT model at pump mode are investigated by computational fluid dynamics and experimental methods. Combined with the shear stress transport (SST) turbulence model, the three-dimensional (3D) unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved to calculate the cavitation flow of the RPT at various cavitation states. The blade loading and the pressure pulsations of the pressure/suction surfaces of the blade are monitored from the inlet to the outlet. Results show that with the development of cavitation, increasing cavitation bubbles covering the blade surfaces lead to the decrease of the blade loading, weaken the regularity of the pressure fluctuation, and increase the amplitude of the pressure pulsation, especially the suction surface. Furthermore, the characteristics of hydrodynamic radial forces under various cavitation states are discussed, and it is found that the values of the hydrodynamic radial forces become larger and the alternating hydrodynamic radial forces are more remarkable with the development of cavitation. Meanwhile, the symmetry of the radial force of the impeller presents a slight change due to the rotor–stator interaction between impeller and guide vanes and the symmetrical structure of the guide vanes. Then, to explore the generation mechanism of the hydrodynamic radial forces, the frequency spectrum of the pressure pulsation and hydrodynamic radial forces are analyzed comparatively. It is found that the hydrodynamic radial forces are affected by the rotor–stator interaction in the initial stage of cavitation, whereas the influence of the pressure distribution of suction surface of the blade increases with the development of cavitation.

3D Numerical Investigation of Forces and Flow Field around the Semi-Submersible Platform in An Internal Solitary Wave

Characteristics of hydrodynamic forces and flow fields around the semi-submersible platform induced by the internal solitary wave (ISW) propagation were investigated in a 3D numerical wave tank. Good agreements between numerical results and experimental data of forces and torque on the platform were achieved. The hydrodynamic loads increased and decreased with the increases in the ISW amplitude and fluid depth ratio, respectively. The pressure mainly contributed to the force on the platform. The horizontal forces on bracings were negligible. Almost all the vertical forces on the platform were derived from those on pontoons. The horizontal force and torque on the platform increased with the increases in the angle between the platform symmetrical axis and the ISW propagation direction. The platform subjected the maximum vertical force when the angle was 0°. There were obvious velocity reductions around the platform during the ISW propagation, as visible vortexes shedding around the platform could be observed. Complexities of the distributions of flow fields around the platforms located at the 30°- and 60°-direction were greater than those around the platforms located at the 0°- and 90°-direction. Flow fields around the same kind components of each platform located at different angles were similar.

Numerical and experimental investigations on the hydrodynamic radial force of single-channel pumps

In order to clarify the generation mechanism and characteristics of hydrodynamic radial force in single-channel pumps, the transient flow in three single-channel pumps was analyzed by computational fluid dynamics (CFD). The three pumps had the identical impeller but with a spiral volute (model 1), a circular volute (model 2), and a torus (model 3). Experiments on pump performance were performed and high frequency pressure sensors were mounted in the spiral volute to measure pressure distribution in the volute of model 1. It indicates that the numerical results are approximately consistent with the experimental results. The radial force is mainly caused by the pressure acting on the blade. The impeller radial force in model 1 was the largest while the model 3 was the smallest, as it is not affected by rotor stator interaction, and rotor stator interaction plays a vital role in the shock load of pumps. The radial forces of different rotational speed were analyzed and indicated that Reynolds number has little influence on the radial force coefficient CF. The dominant frequency of the radial force on the impeller is the rotational frequency of impeller for all rotational speeds. Moreover, the amplitude of the radial force fluctuations increased with increasing flow rate in model 2, but the change was not obvious with the increasing of flow rate in model 3, while at lower flow rate the largest amplitude of the radial force fluctuations was presented in models 1.

Estimation of hydrodynamic forces acting on concrete blocks of toe protection works for coastal dikes by tsunami overflows

The extraordinary tsunami generated by the Great East Japan Earthquake in 2011 destroyed coastal protection facilities in the Tohoku region. After the catastrophe, landward toe protection works comprising concrete blocks were proposed at damaged coastal areas. However, the hydrodynamic behavior of the protection works against tsunami overflows has not been fully elucidated by earlier experimental studies. Therefore, this study investigated validity of three-dimensional (3-D) numerical simulations of tsunami flows over a simulated coastal dike with protection works of concrete block models. This study also presented a method of estimating the hydrodynamic forces acting on block models under the tsunami overflows. After conducting basic validation of the present numerical method, we compared experimentally obtained results of hydrodynamic forces to results obtained from simulations. Results show that the simulation data are qualitatively consistent with experimental data for the considered cases of overflow depths of four kinds. They also presented that the characteristics of hydrodynamic forces depend mainly on both the distance from the dike foundation and tsunami overflow depth. The salient finding is that the hydrodynamic forces are affected to a considerable degree by the irregularity of the block model arrangement or surface asperity of the protection works. The impulsive force of tsunami overflows at actual coasts will perturb concrete blocks placed in orderly rows at the original installation. Therefore, the landward toe protection works using concrete blocks necessitate supportive constructions to enhance their structural stability.

Hydrodynamic force investigation of a rigid cylinder under the coupling CF and IL motion

Extensive researches have been conducted to simulate the two-degree-of-freedom (2DOF) vortex induced vibration (VIV) of a cylinder during the past few decades. However, there are still very few publications in terms of the hydrodynamic force of a cylinder with 2DOF motion in cross-flow (CF) and in-line (IL) directions. This study employs the Reynolds-Average-Navier–Stokes (RANS) equations and shear stress transport (SST) k-ω turbulence model to investigate the hydrodynamic force characteristics. The numerical model is firstly validated based on the 2DOF VIV experiment of an elastically supported cylinder in the literature. The results indicate that the predicted displacement and hydrodynamic force are approximately harmonic, and are in reasonable agreement with the experimental data. By imposing harmonic motion on the cylinder in CF and IL directions with period ratio of 2, parametric analyses are carried out to simply broaden the understanding of the sensitivity of the hydrodynamic coefficients including force coefficient, excitation coefficient and added mass coefficient, to the motion-related parameters, such as the motion phase angle, non-dimensional amplitude and frequency. There would be a sudden change for the excitation coefficient and added mass coefficient at a certain motion phase angle approximately corresponding to the peak of the force coefficient. The varying trend of the hydrodynamic coefficient with non-dimensional amplitude is different from that obtained from one-degree-of-freedom (1DOF) forced vibration test in literatures, and is significantly related with the motion phase angle and non-dimensional frequency. The non-dimensional frequency seems to mainly affect the excitation coefficient, added mass coefficient and mean drag coefficient in the lock-in range.

Characteristics of hydrodynamic force acting on pots used in coastal and inland waters in Korea and Japan

Characteristics of hydrodynamic force acting on pots used in coastal and inland waters in Korea and Japan

Numerical solution for a ship-wave problem in a two-layer fluid using a double-model linearised interface condition

ABSTRACTShip performance in shallow water where the rigid bottom is covered by a mud layer is a crucial topic to be investigated. In such muddy areas, a two-layer fluid is stratified according to the properties of the sediments. The water–mud interface behaves similar to a sheet on which the internal waves propagate after the ship's passage. Therefore, for safe navigation, it is necessary to clearly understand the influence of the internal waves on the ship's hydrodynamic force characteristics. In this study, the steady wave-making problem of a ship in a two-layer fluid was solved using the Rankine source panel method. The boundary value problem was formulated using a newly proposed double-model linearised interface condition. After the present method was validated via a comparison with results of a Wigley hull solved by the author's existing method, it was applied to solve the ship-wave problem of KVLCC2. The unique changes in wave-making resistance, sinkage and trim according to the ship's speed and two-layer fluid conditions were evaluated.

Maneuverability of <i>C<sub>b</sub></i>-Series Full Hull Ships

Maneuvering simulations for full hull ships were conducted by the MMG model, which is one of a maneuvering simulation method, based on the hydrodynamic force characteristics obtained in the captive model tests presented in previous paper1), and compared with the free-running model test results. The purpose of this study is to investigate the applicability of the MMG model to the full hull ships with very large block coefficient. We found that the original formula for longitudinal velocity component to rudder (uR) in the MMG model is not well working in case that the block coefficient (Cb) is very large as Cb = 0:87. To settle the problem, an improved formula of uR proposed by Yoshimura et al.3) was used and it was confirmed that the formula can capture the behavior of the rudder normal force just after steering better. Turning and course keeping performances in fullscale ships become worse comparing to those in ship model due to the worse rudder force performance comes from smaller propeller load in fullscale. Although the level of the worse turning performance is not so serious in fullscale, there is a possibility that overshoot angle of zig-zag maneuvers is over the IMO regulation for the present ship with Cb = 0.87.

漩门湾不同类型湿地大型底栖动物群落特征比较研究

PDF HTML阅读 XML下载 导出引用 引用提醒 漩门湾不同类型湿地大型底栖动物群落特征比较研究 DOI: 10.5846/stxb201503310623 作者: 作者单位: 浙江师范大学生态研究所,浙江师范大学生态研究所,浙江师范大学生态研究所,浙江师范大学生态研究所,浙江师范大学生态研究所,浙江师范大学生态研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 浙江省自然科学基金项目（ZEO204） Variation in macrobenthic community characteristics among different types of wetlands in Xuanmen Bay Author: Affiliation: Institute of Ecology,Zhejiang Normal University,Institute of Ecology,Zhejiang Normal University,Institute of Ecology,Zhejiang Normal University,Institute of Ecology,Zhejiang Normal University,Institute of Ecology,Zhejiang Normal University,Institute of Ecology,Zhejiang Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为研究漩门湾围垦后自然滩涂湿地和不同利用方式人工湿地7种生境的大型底栖动物群落结构现状和受扰动情况，2010年10月至2012年7月在两个区域中进行了为期两周年8个季度的大型底栖动物调查，结果表明：两周年共获得大型底栖动物5门8纲41科63种；第一周年为47种，其中自然滩涂湿地41种，人工湿地14种；第二周年为58种，其中自然滩涂湿地50种，人工湿地10种，人工湿地的物种数明显少于自然滩涂湿地。采集到的物种以软体动物和节肢动物为主，分别为32种和23种，各占总物种数的50.00%和37.10%。两周年的年均栖息密度和年均生物量在生境间从高到低依次为，年均栖息密度第一周年HS > GT > HH > RL > SC > NY > SK，第二周年GT > HS > HH > SC > NY > RL > SK；年均生物量第一周为HS > RL > HH > GT > NY > SK > SC，第二周年是HS > HH > RL > GT > NY > SC > SK。3种大型底栖动物的生物多样性指数（Margalef丰富度指数（S）、Shannon-Wiener多样性指数（H’）、Pielou均匀度指数（J））分析表明，两周年7种生境3种多样性指数均处在不断的变化之中，人工湿地的Margalef丰富度指数（S）和Shannon-Wiener多样性指数（H’）相对于自然滩涂湿地偏低，而Pielou均匀度指数（J）人工湿地大于自然滩涂湿地。聚类和排序的结果表明，围垦使大型底栖动物的群落结构发生明显的变化。ABC曲线分析结果表明，自然滩涂湿地受到的干扰程度较轻，而人工湿地受到的干扰程度较大。围垦改变了潮滩高程、水动力、盐度、沉积物特性，再加上人类活动的影响，这些因素是造成底栖动物群落结构及生物多样性变化的主要原因，围垦结束后的生态修复十分必要。 Abstract:In order to study the structure of the macrobenthic community in the coastal and artificial wetlands in Xuanmen Bay, samples in different seasons were collected in seven habitats from two types of wetlands from October 2010 to July 2012. We identified 63 macrobenthic species in total, belonging to 41 Families, 8 Classes, and 5 Phyla. In the first year, 47 species were found, of which 41 were identified in the coastal wetlands and 14 in the artificial wetlands. In the second year, 58 species were found, including 50 in the coastal wetlands and 10 in the artificial wetlands. The total number of species in the artificial wetlands was significantly lower compared to that in the coastal wetlands. The two dominant species belonged to mollusks and arthropods, and accounted for 50.00% and 37.10%, of the species total respectively. In two years, 5 species were identified in the coastal wetland and the average number of dominant species was 4.50, whereas in the artificial wetlands, 8 species were identified, with the average number of dominant ones being 3.25. The two-year average density and biomass values for the macrobenthos ranked from highest to the lowest were as follows for the first year:density values were HS > GT > HH > RL > SC > NY > SK, and GT > HS > HH > SC > NY > RL > SK, whereas biomass values were HS > RL > HH > GT > NY > SK > SC and HS > HH > RL > GT > NY > SC > SK. In two years, three species diversity measurements (the Margalef richness index (S), the Shannon-Wiener diversity index (H'), and the Pielou evenness index (J)) were in a state of constant change in 7 different habitats. Compared with the values obtained for the coastal wetlands, S and H' in the artificial wetlands were lower. Over two years, three species diversity measurements in the coastal wetlands three habitats (HH,GT,HS) was the second year higher than the first year, while in the artificial wetlands, three species diversity measurements in the NY habitat was the second year higher than the first year, other three habitats (SC,SK,RL) was the first year higher than the second year. Based on the results of the two-way ANOVA analysis of the diversity of the three species, we found that S in 7 of the habitats was significantly distinct (F6,6=7.62, P<0.01). However, in different years the index showed no significant changes (F1,6=0.44, P>0.05). Additionally H' in various habitats and multiple years revealed no significant differences. The J in distinct habitats and years also showed no significant differences. The hierarchical cluster analysis and non-metric multidimensional scaling (MDS) showed that community structure was divided into two groups:SC,SK, NY, and RL in the artificial wetland, and GT, HS, and HH in the coastal wetlands, which indicated that the community structure had been changed greatly because of land reclamation. From the ABC curve analysis, we theorized that the coastal wetland was affected by slight disturbances and the artificial wetland was influenced by dramatic disturbances. Reclamation changes the tidal flat elevation, hydrodynamic force, salinity and tidal flat sediment characteristics. These factors, including human activities, were pivotal to obtain an understanding of variations in macrobenthic communities. Therefore, the ecological restoration projects after reclamation are essential. 参考文献 相似文献 引证文献

Oscillatory flow regimes around four cylinders in a square arrangement under small and conditions

Sinusoidally oscillatory flow around four circular cylinders in an in-line square arrangement is numerically investigated at Keulegan–Carpenter numbers ($\mathit{KC}$) ranging from 1 to 12 and at Reynolds numbers ($\mathit{Re}$) from 20 to 200. A set of flow patterns is observed and classified based on known oscillatory flow regimes around a single cylinder. These include six types of reflection symmetry regimes to the axis of flow oscillation, two types of spatio-temporal symmetry regimes and a series of symmetry-breaking flow patterns. In general, at small gap distances, the four structures behave more like a single body, and the flow fields therefore resemble those around a single cylinder with a large effective cylinder diameter. With increasing gap distance, flow structures around each individual cylinder in the array start to influence the overall flow patterns, and the flow field shows a variety of symmetry and asymmetry patterns as a result of vortex and shear layer interactions. The characteristics of hydrodynamic forces on individual cylinders as well as on the cylinder group are also examined. It is found that the hydrodynamic forces respond in a similar manner to the flow field to the cylinder proximity and wake interference.