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1.
A series of model tests were performed to investigate the behavior of vertical pressure imposed on the bottom of a trench. The tests were conducted in two phases to generate soil arching due to soil deformation: (1) the backfilling phase and (2) the lowering-bottom phase. First, the backfilling phase was performed by filling sand into the trench, in which soil deformation was developed due to selfcompaction by the weight of the sand. The lowering-bottom phase was then conducted by lowering the bottom plate of the trench to induce additional soil deformation. The behavior of the vertical pressure acting on the bottom of the trench during the backfilling phase can simulate that of the vertical pressure imposed on the bottom of buried rigid pipes. The behaviors of buried flexible pipes could be observed during the lowering-bottom phase, in which both the minimum and the maximum vertical pressures could be obtained according to the induced soil deformation. A novel method for predicting the vertical pressures in each phase was proposed. The agreements between the predictions by the proposed method and the experimental results were demonstrated. 相似文献
2.
随着新能源等新兴产业的高速发展,金属矿产资源需求激增,国内外争相发展深海采矿技术。基于竖轴漩涡的水动力特性,设计了一种带有4个切向射流喷嘴的吸盘式水力集矿装置,提出应用切向射流在集矿装置内诱导生成竖轴漩涡的新集矿方法。开展水力集矿模型试验,研究竖轴漩涡集矿流场流速分布特征;分析低、中、高3种旋流度流态下,集矿流量对矿粒运动轨迹和采集率的影响。结果表明：矿粒起动轨迹随着旋流度的增加,逐渐从混乱无序转向明显的圆周运动;在特定集矿流态下,矿粒采集率随集矿流量的增加不断提高;当矿粒采集率超过90%时,集矿流量需求随着旋流度的增加而减小。通过采矿车原理样机水池测试,初步验证了集矿装置的集矿性能,可为集矿装备的设计研发与论证提供借鉴。 相似文献
3.
近壁圆柱绕流问题在海底悬跨管道的研究中具有重要的意义。在绕流阻力、升力以及海底土壤的耦合作用下,海底管道所发生的移位、悬跨等现象对于海底管道的安全运行构成了很大的威胁。正确预测各种绕流条件下管流之间的作用力是保证油气管道安全的首要任务。海底管道在极端海洋环境条件下的管、流相互作用为高雷诺数绕流问题,处于高雷诺数下的绕流模拟比处于低雷诺数下的绕流模拟要复杂很多,它需要更精细的网格以及合适的湍流模型。此文对处于悬跨状态下的海底管道进行数值研究,给出不同间隙比下海流绕流海底管道的流场结构形态,分析了间隙比对绕流阻力和绕流升力的影响,为进一步研究海底悬跨管道的受力和变形提供载荷边界数据。 相似文献
4.
《Applied Ocean Research》1997,19(2):113-140
The effect of breaking and steep non-breaking waves on a vertical pile such as found in minimal caisson structures in the Gulf of Mexico shallow water environment was studied in a wave tank testing. The waves generated were both regular and irregular. The irregular waves were of Bretschneider type. In some tests current was combined in the direction of waves. Specially steep waves in the recorded wave profile were chosen for the analysis of wave forces. It was observed that the forces on the caisson at the wave frequency due to breaking waves were no higher in general than those in nonbreaking steep waves. The drag coefficients in waves alone were much higher than those in a combined wave-current field. The wave-current drag coefficients approached those found in the steady current alone. 相似文献
5.
Nguyen Ba Thuy Katsutoshi Tanimoto Norio Tanaka Kenji Harada Kosuke Iimura 《Ocean Engineering》2009,36(15-16):1258-1269
The objective of this study is to investigate the effects of an open gap, such as a road, in a coastal forest on tsunami run-up. A numerical model based on two-dimensional nonlinear long-wave equations was developed to account for the effects of drag and turbulence induced shear forces due to the presence of vegetation. Experiments were conducted on a forest simulated with vertical cylinders by changing the gap width. The numerical model was validated in good agreement with the experimental results. The numerical model was then applied to a wide forest of Pandanus odoratissimus, a tree species that is a dominant coastal vegetation on a sand dune in South and Southeast Asia. The effect of vertical stand characteristics of P. odoratissimus with aerial roots was considered on the drag resistance. A straight open gap perpendicular to the shoreline was used to investigate the effect of gap width. As the gap width increases, the flow velocity at the end of the open gap first increases, reaches a maximum, and then decreases, while the run-up height increases monotonously. The maximum velocity in the present condition is 1.7 times the maximum velocity without a coastal forest. The effects of different gap arrangements in the forest on tsunami run-up were also investigated in this paper. The flow velocity at the end of an open gap can be reduced by a staggered arrangement. 相似文献
6.
网箱浮架是我国深水养殖的重要设施装备,其水动力特性直接关系其工作稳定性。文章针对3层桁架式海洋网箱浮架建立有限元模型,采用流固耦合方法对17级台风正面来流条件下的网箱浮架水动力特性展开模拟计算,并对比分析有无网衣时网箱浮架水动力特性的变化规律。结果表明：在台风正面来流的情况下,网箱浮架的饵料舱侧向支撑点、上层步道板连接管迎浪侧和中层承力结构交叉点是应力集中的主要区域;当浮架悬挂网衣结构时,其垂荡距离减小,但纵摇程度加剧,即网衣结构有利于浮架结构在垂直方向上的稳定,但增加其纵摇运动强度;当悬挂网衣结构时,由于浮架在垂直方向上更为稳定,其饵料舱侧向支撑点、上层步道板连接管迎浪侧的最大应力分别降低5.1%和3.2%,中层承力结构交叉点的最大应力变化不明显,而迎浪侧中下层连接管的最大应力降低8.7%。 相似文献
7.
SWAN模型中不同风拖曳力系数对风浪模拟的影响 总被引：1，自引：1，他引：0
本文以荷兰哈灵水道海域为实验区域,通过敏感性实验,研究了在14 m/s、31.5 m/s和50 m/s（分别代表一般大风、强热带风暴和强台风的极端条件）定常风速下SWAN模型中不同风拖曳力系数对风浪模拟的影响程度。结果表明,对于近岸浅水区域（水深小于20 m）,风拖曳力系数计算方案的选择对有效波高影响较小,而且当风速增加到一定程度后,波浪破碎成为影响波高值的主要因素;对于深水区域（水深大于30 m）,一般大风条件下风拖曳力系数计算方案的选择对有效波高影响仍然较小,随着风速的继续增大,风拖曳力系数计算方案的选择对有效波高的影响逐渐显著。对于平均周期,风拖曳力系数计算方案的选择和风速的改变对其影响均较小,而由水深变浅导致的波浪破碎对其影响较为显著。根据敏感性实验结果,本文对SWAN模型中风拖曳力系数计算方案的选择做出如下建议:计算近岸浅水区域风浪场或深水区域一般大风条件风浪场时,其风拖曳力系数可以直接采用模型默认选项;而对于深水区域更大风速条件,可首先采用模型默认选项试算,然后结合当地海域实测波浪资料进行修正。 相似文献
8.
We present a numerical study on the hydrodynamic performance of undulation NACA0012 foil in the near wake of D-section cylinder. Computations are conducted using unsteady incompressible Navier-Stokes equations with a moving adaptive mesh based on laminar flow. Investigations are focused on the effect of distance ratio between foil tip and centre of cylinder (L/D≤2.0) on the thrust/drag performance of foil and cylinder at various foil undulation frequency (St). We found that, foil thrust coefficient (Ct) increases considerably with the appearance of cylinder and an optimal distance exists at which Ct reaches maxima. The maximum increment is about eleven times that of its counterpart of single foil, which is obtained at St=0.23 and L/D=0.5. Our results for the cylinder drag coefficient (Cd) observed the existence of optimal parametric map, combined with various gap ratios and foil frequencies. With these parameters, insertion of an undulation foil can significantly lead to the drag reduction indicating that undulating foil could work efficiently as a passive vortex control device for cylinder drag reduction. 相似文献
9.
王欣欣 M. Robinson SWIFT Tobias DEWHURST Igor TSUKROV Barbaros CELIKKOL Carter NEWELL 《海洋工程》2015,29(3):431-444
To investigate the dynamics of submersible mussel rafts, the finite element program Aqua-FE?, developed by the University of New Hampshire (UNH), was applied to rafts moored at the surface and submerged. The submerged configuration is used to reduce wave forcing and to avoid contact with floating ice during winters in northern waters. Each raft consists of three pontoons connected by a grid framework. Rafts are intended to support densely spaced mussel ropes hung from the framework. When submerged, the pontoons are flooded, and the raft is held vertically by floats attached by lines. The computer models were developed in Aqua-FE? to simulate the effects of waves and current. They were validated by comparison with wave tank results by use of a 1/10 scale raft physical model. Comparisons showed good agreement for the important heave (vertical) and pitch (rotational) motions, though there was a tendency towards conservative results for wave and current drag. Full-scale simulations of surface and submerged single raft and two rafts connected in tandem were performed. Submerged raft wave response was found to be reduced relative to that at the surface for both the single and two-raft configurations. In particular, the vertical motion of mussel rope connection points was significantly reduced by submergence, resulting in reduced potential for mussel drop-off. For example, the maximum vertical velocities of mussel rope attachment points in the submerged two raft case were 7%?20% of the corresponding velocities when at the surface. 相似文献
10.
《Coastal Engineering》2001,42(1):1-16
Vanes are essentially flat vertical flow guiding structures. In the beach protection application vanes are placed, inshore of the breaking zone, in the upper part of the vertical water column and with a predefined angle of attack to the design wave orthogonal. They are thus subjected to a generally inshore-directed flow, which induces a lift, and drag force on the vane. These forces, in turn, induce a flow that counteracts the wave-induced longshore current, thus decreasing the longshore current velocity, which facilitates sediment deposition. Two experiments were conducted in a small-scale wave basin with the purpose of investigating the vane function. Both experiments were conducted with a movable bed that formed a crenulate-shaped bay between two headland structures. The first experiment showed that the vanes created a salient upstream of the vanes. This result is also supported by initial prototype results. The second experiment showed that the longshore velocity was reduced upstream of the vane and that the bulk of the velocity reduction took place in the nearshore part of the breaking zone. The main flow feature is identified as a large horizontal vortex inshore of the vane. 相似文献
11.
作为海上浮式结构物的一种新型锚固基础,动力锚具有自安装、不受水深影响、适用范围广的特点。在动力锚的基础上研发的组合动力锚结合了动力锚自安装和板锚法向受荷的特点,具有安装快速、适用多种类型海床、承载效率高等性质。组合动力锚在水中自由下落时的水动力学特性（下落速度、方向稳定性等）会受到锚链、尾翼宽度和助推器质量等因素影响。若下落速度过小或方向稳定性过差,则会影响锚的安装成功率。采用计算流体动力学方法模拟流体对锚的冲击和锚在水中自由下落过程,以优化组合动力锚的尾翼尺寸;其次研究锚链作用力和助推器质量对组合动力锚下落速度和偏角的影响规律。计算结果表明：组合动力锚的拖曳阻力系数为0.45左右,尾翼宽度最优尺寸为翼板宽度的1.25倍。连接在锚眼处的锚链会减小组合动力锚的下落速度并加剧锚的偏转,需综合锚的下落速度和偏角来确定锚在水中下落高度。 相似文献
12.
Estimation of wave induced loadings on subsea pipelines involves the evaluation of the hydrodynamic coefficients of drag, inertia, vertical inertia and lift. These coefficients vary with the methodology adopted and the order of wave theory used to compute the water particle kinematics. This paper presents a new and simple method to determine the hydrodynamic coefficients for subsea pipelines in the drag and inertial flow regime. The results are reported for three relative clearances of a pipeline model from the simulated ocean floor. 相似文献
13.
The concept of micro-bubble ejection is emerging as an attractive method for viscous drag reduction for high speed craft. Most of the drag reduction literature presents results for micro-bubble ejection above/below horizontal surfaces. Nevertheless, modern high-speed hull forms are slender with vertical surfaces. This paper presents results of model tests with micro-bubble ejection to the vertical sides of a high speed model with a non-wetting coating. The coating yielded drag reduction of 4–6% and micro-bubbles with coating reduced overall drag by 4–11%. The local coefficient of friction with micro-bubbles is analyzed and found comparable to vertical flat plate results of [Madavan et al., 1984]. 相似文献
14.
This paper investigates the high frequency behaviours and magnetic anisotropy of rapidly solidified FINEMET (Fe73.5Si13.5B9Nb3Cu1) alloy ribbons annealed in an applied magnetic field. It finds that the ribbons annealed with the applied magnetic field show much higher resonance frequencies and have even higher permeability at higher frequencies than the samples annealed without the magnetic field and the non-annealed ribbons. M?ssbauer spectroscopy had been employed to study the spatial distribution of the magnetic moments of five selected FINEMET alloy ribbons in different heat-treated conditions. The results show that an easy plane has been established after annealling in the magnetic field, while for the other ribbons this effect is not significant. Hence, the relationship between magnetic field annealing and high frequency property has been bridged by the bianisotropic theory. 相似文献
15.
A scale model of a flexible circular net with different weights attached to the bottom was tested in a flume tank. Global forces and net deformation were measured for different steady current velocities. Three different sizes of bottom weights were used in the tests. The results from these tests are presented and discussed with the emphasis on the dependency between the forces and the geometry. Comparison is also made to empirical based formulas for calculation of drag and lift forces on net structures. Findings show that i) the forces on, and deformation of a flexible net structure are mutually highly dependent on each other; ii) estimates of global forces on a flexible net structure calculated using simple drag formulas derived from stiff net panel experiments give large errors when compared to experimental measurements; iii) numerical models taking into account the dependency between force and deformation should be used to obtain accurate estimates of forces on flexible net structures; and iv) the forces on a flexible net structure are dependent on Reynolds number, and their dependency are similar to that of a regular cylinder. 相似文献
16.
The present paper proposes a numerical model to determine horizontal and vertical components of the hydrodynamic forces on a slender submarine pipeline lying at the sea bed and exposed to non-linear waves plus a current. The new model is an extension of the Wake II type model, originally proposed for sinusoidal waves (Soedigdo et al., 1999) and for combined sinusoidal waves and currents (Sabag et al., 2000), to the case of periodic or random waves, even with a superimposed current. The Wake II type model takes into account the wake effects on the kinematic field and the time variation of drag and lift hydrodynamic coefficients. The proposed extension is based on an evolutional analysis carried out for each half period of the free stream horizontal velocity at the pipeline. An analytical expression of the wake velocity is developed starting from the Navier–Stokes and the boundary layer equations. The time variation of the drag and lift hydrodynamic coefficients is obtained using a Gaussian integration of the start-up function. A reduced scale laboratory investigation in a large wave flume has been conducted in order to calibrate the empirical parameters involved in the proposed model. Different wave and current conditions have been considered and measurements of free stream horizontal velocities and dynamic pressures on a bottom-mounted pipeline have been conducted. The comparison between experimental and numerical hydrodynamic forces shows the accuracy of the new model in evaluating the time variation of peaks and phase shifts of the horizontal and vertical wave and current induced forces. 相似文献
17.
The longline is modelled using lumped masses and tension-only springs including structural damping. The mussel culture is modelled as cylinders attached to the main line and the equations are formulated for the coupled dynamics of the main line, buoys and mussel socks using Kane's formalism. Surface waves are described by Stokes’ second-order wave theory. The hydrodynamic loads are applied via a Morison's equation approach using the instantaneous relative velocities and accelerations between the fluid field, the longline and the attached buoys and mussel masses. The algorithm is presented and the equations are solved using the Runge–Kutta routine “ode45” in MATLAB. Outputs include position, orientation and velocity of all components and tension in all line segments. The numerical model may be used to predict the dynamics of longline systems using drag coefficients determined from field measurements. We expect that the results will be useful for checking and optimizing shellfish aquaculture designs prior to installation and for modifying existing designs to safeguard against failure. 相似文献
18.
This paper reports experimental measurements of the hydrodynamics forces acting on a low drag submersible. The model was manufactured using standard, cost-effective methods without undue attention paid to the roughness or waviness of the model's surface. It was seen, using flow visualisation techniques, that the laminar boundary layer extended over 70% of the vehicle length; furthermore, no separation of the flow was seen over the remaining 30% of the body. Hydrodynamic forces were measured, and a significant reduction in drag was found compared with standard turbulent submersible shapes. The low drag performance was quite resilient to changes in incidence, showing a large drag “bucket” for angles of incidence between ± 4°. With the addition of a set of cruciform fins at the rear of the body, incorporating control surfaces, it was found that for a centre of gravity position forward of 41.3% of the body length, the vehicle would be statically stable both stick-free and stick-fixed. Finally, using a pitot tube wake rake the velocity profile of the boundary layer at the propeller location was found to be that of an attached, turbulent boundary layer closely matching a
power law. The importance of full interference measurement tests to allow for the support strut effects is clearly demonstrated. 相似文献
19.
20.
The spectral properties of nonlinear drag forces of random waves on vertical circular cylinders are analyzed in this paper by means of nonlinear spectral analysis. The analysis provides basic parameters for estimation of the characteristic drag forces. Numerical computation is also performed for the investigation of the effects of nonlinearity of the drag forces.The results indicate that the wave drag forces calculated by linear wave theory are larger than those calculated by the third order Stokes wave theory for given waves. The difference between them increases with wave height. The wave drag forces calculated by use of hnear approximation are about 5% smaller than their actual values when measured in the peak values of spectral densities. This will result in a safety problem for the design of offshore structures. Therefore, the nonlinear effect of wave drag forces should be taken into comidemtion in design and application of important offshore structures. 相似文献