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Two coaxial vertical cylinders-one is a riding hollow cylinder and the other a solid cylinder of greater radius at some distance above an impermeable horizontal bottom,were considered.This problem of diffraction by these two cylinders,which were considered as idealization of a buoy and a circular plate,can be considered as a wave energy device.The wave energy that is created and transferred by this device can be appropriately used in many applications in lieu of conventional energy.Method of separation of variables was used to obtain the analytical expressions for the diffracted potentials in four clearly identified regions.By applying the appropriate matching conditions along the three virtual boundaries between the regions,a system of linear equations was obtained,which was solved for the unknown coefficients.The potentials allowed us to obtain the exciting forces acting on both cylinders.Sets of exciting forces were obtained for different radii of the cylinders and for different gaps between the cylinders.It was observed that changes in radius and the gap had significant effect on the forces.It was found that mostly the exciting forces were significant only at lower frequencies.The exciting forces almost vanished at higher frequencies.The problem was also investigated for the base case of no plate arrangement,i.e.,the case having only the floating cylinder tethered to the sea-bed.Comparison of forces for both arrangements was carried out.In order to take care of the radiation of the cylinders due to surge motion,the corresponding added mass and the damping coefficients for both cylinders were also computed.All the results were depicted graphically and compared with available results. 相似文献
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In this paper a 3D numerical model was developed to study the complicated interaction between waves and a set of tandem fixed cylinders.The fluid was considered to be inviscid and irrotational.Therefore,the Helmholtz equation was used as a governing equation.The boundary element method(BEM) was adopted to discretize the relevant equations.Open boundaries were used in far fields of the study domain.Linear waves were generated and propagated towards tandem fixed cylinders to estimate the forces applied on them.Special attention was paid to consideration of the effect on varying non-dimensional cylinder radius and distance between cylinders,ka and kd on forces and trapped modes.The middle cylinder wave forces and trapped modes in a set of nine tandem cylinders were validated utilizing analytical data.The comparisons confirm the accuracy of the model.The results of the inline wave force estimation on n tandem cylinders show that the critical cylinder in the row is the middle one for odd numbers of cylinders.Furthermore the results show that the critical trapped mode effect occurs for normalized cylinder radiuses close to 0.5 and 1.0.Finally the force estimation for n tandem cylinders confirms that force amplitude of the middle cylinder versus normalized separation distance fluctuates about that of a single cylinder. 相似文献
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The vortex-induced vibrations (VIV) of two flexible circular cylinders in a tandem configuration were studied numerically for spacing ratios ranging from 6 to 18 and the reduced velocities ranging from 2.35 to 12.59. The VIV response amplitude, response frequency, fluid force, pressure distribution and vortex structure of the tandem cylinders with different spacing ratios under different reduced velocities were compared. The results indicate that there is a great difference between the lift forces on the downstream and upstream cylinders. The lift coefficient of the downstream cylinder undergoing the wake-induced vibrations (WIV) is larger than that of the upstream cylinder, and the dominant frequency curves of the lift coefficients of the upstream and downstream cylinders separate. It can be found that the length and intensity of the wake are quite different under different reduced velocities and spacing ratios, and the reattachment positions between the wake and the downstream cylinder are different, which leads to a great change in the flow around the downstream cylinder and have a great effect on the wake-induced lift force on the downstream cylinder. Considering these factors, an empirical model for the wake-induced lift force on a cylinder with low mass ratio was proposed and verified. 相似文献
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《船舶与海洋工程学报》2021,(1)
Temporal evolutions of scour at submerged circular cylinders were investigated. Flow visualization was carried out around the cylinders over plane, under developed and equilibrium scour holes. Video analysis technique was used to formulate the equations for determining the diameter of the horseshoe vortex around the submerged cylinders, which is also verified from the vector diagrams drawn using the velocity measurements. The scour process similar to live bed scour was noticed around the downstream cylinder. The diameter of the horseshoe vortex is found to depend on the diameter of respective cylinder, submergence ratio,spacing between the cylinders and skew angle. This formulation along with the dislodgement and transportation of a single sediment particle is further incorporated in the proposed model for determining the time variation of scour around the submerged cylinders. It is evident from the results that the upstream cylinder shelters the downstream cylinder and thereby reduces the scour at the downstream cylinder. Proposed model is further extended to incorporate the effect of non-uniformity of the sediment particles on the time variation of scour depth. The results indicate significant reduction of scour depth of around 6% and 35% for upstream and downstream cylinders respectively due to the formation of the armor layer. The model is also compared with the local scour component of field data around cylindrical bridge piers to establish the differences in the scour process around a partially submerged cylinder and fully submerged tandem and skewed cylinders. 相似文献
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Multiple side-by-side cylinders are widely employed in many engineering applications. Consequently, flow-induced vibrations (FIV), which have a significant influence on structural reliability, have drawn considerable concern from many investigators. Due to the complicated wake interactions behind the cylinders, the hydrodynamic characteristics of multiple side-by-side cylinders subject to FIV are obviously different from those of a single cylinder. Hydrodynamic force coefficients play an important role in evaluating structural reliability and predicting fatigue damage. However, few relevant investigations have been performed on hydrodynamic force coefficients of multiple side-by-side flexible cylinders, which require further research. In this paper, the hydrodynamic force coefficients of three and four side-by-side flexible cylinders with a spacing ratio of 6.0 are obtained by an inverse analysis method based on the oscillation displacements. In the resonance regions, the hydrodynamic force coefficients of multiple cylinders exhibit variation trends similar to those of a single cylinder, especially at higher reduced velocities. In the mode switch regions, relatively large deviations exist between the coefficients of multiple cylinders and single cylinder. The inner cylinder in the three-cylinder system shows prominently distinctive behaviour compared with the outer two cylinders. For the four-cylinder system in a side-by-side arrangement, the outer two cylinders show relatively slight differences between each other compared with the inner two cylinders. 相似文献
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《船舶与海洋工程学报》2015,(2)
The free surface flow generated by twin-cylinders in forced motion submerged beneath the free surface is studied based on the boundary element method. Two relative locations, namely, horizontal and vertical, are examined for the twin cylinders. In both cases, the twin cylinders are starting from rest and ultimately moving with the same constant speed through an accelerating process. Assuming that the fluid is inviscid and incompressible and the flow to be irrotational, the integral Laplace equation can be discretized based on the boundary element method. Fully-nonlinear boundary conditions are satisfied on the unknown free surface and the moving body surface. The free surface is traced by a Lagrangian technique. Regriding and remeshing are applied, which is crucial to quality of the numerical results. Single circular cylinder and elliptical cylinder are calculated by linear method and fully nonlinear method for accuracy checking and then fully nonlinear method is conducted on the twin cylinder cases, respectively. The generated wave elevation and the resultant force are analysed to discuss the influence of the gap between the two cylinders as well as the water depth. It is found that no matter the kind of distribution, when the moving cylinders are close to each other, they suffer hydrodynamic force with large absolute value in the direction of motion. The trend of force varying with the increase of gap can be clearly seen from numerical analysis. The vertically distributed twin cylinders seem to attract with each other while the horizontally distributed twin cylinders are opposite when they are close to each other. 相似文献
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A quadratic eigenvalue problem (QEP) was posed in order to study the dynamics of flexible cylinders in cross-flow, simulating slender offshore structures such as risers, catenaries or tendons. The Euler–Bernoulli equation was used to model the structure assuming a fluid loading model, and yielding a quadratic eigenvalue problem that included a form of damping dependent not only on the structural damping itself, but also on the free stream velocity and the fluid force coefficients. We solved the QEP using the finite element method. We also derived a simplified analytical solution in this work for comparison with the QEP, however this solution does not consider changes in tension along the length of the cylinder as the QEP does. In our study, the QEP solutions were first validated against the simplified analytical solution, and also against a well-known experimental dataset obtained in 2003, in which a flexible circular cylinder model was used to model the dynamics of a riser undergoing multi-mode vortex-induced vibrations. 相似文献
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Sandwich pipe (SP) combining high-strength performance and thermal insulation has been considered an effective solution for oil and gas transportation in ultra-deepwater. Strain hardening cementitious composite (SHCC) is well known for its capacity to withstand both tensile load and external hydrostatic pressure. The sandwich pipe considered in the research is constituted of concentric steel pipes with SHCC annular layer. In the present research work, the SHCC was manufactured, and full scale sandwich pipes were assembled. Intact and damaged specimens were submitted to controlled external pressure in a hyperbaric chamber to obtain the collapse and propagation pressures, respectively. Modeling and simulation of the buckle propagation of the SPs were correlated with the experimental results. The results show that sandwich pipe with SHCC core has an excellent structural strength under high external pressure in both intact and damaged conditions. Moreover, the results also show that the interaction between the annular and the inner/outer pipes provides a significant contribution to the buckling resistance under propagation pressure. 相似文献
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基于势流理论和波浪辐射/绕射理论,利用水动力分析软件(AQWA)研究两圆柱体在波浪作用下的运动响应特性,给出不同入射角与不同频率规则波作用下,小圆柱体单独运动时的六自由度响应幅值算子(RAOs)及运动响应,并与两个并排圆柱体六自由度响应幅值算子(RAOs)及运动响应作比较。结果表明:大圆柱体的干扰将使小圆柱体的纵摇、横摇、横荡、垂荡运动加剧,对小圆柱体漂移力也有较大影响,但对小圆柱体的纵荡与首摇运动影响不大。计算结果与传统方法计算值相近,证明此软件合理,可为两船在波浪中的干扰模拟计算提供参考。 相似文献
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Slender subsea structures like pipelines, jumpers and umbilicals when exposed to currents may experience vortex-induced vibrations (VIV), which can shorten their fatigue life and increase the risk of structural failure. In the present study, flow around different configurations of a piggyback pipeline close to a flat seabed has been investigated using the two-dimensional (2D) Unsteady Reynolds-Averaged Navier Stokes (URANS) equations with the k − ω Shear Stress Transport (SST) turbulence model. The Reynolds number (based on the free stream velocity and large cylinder diameter) is equal 3.6 × 106 corresponding to upper-transition regime. The drag forces acting on the cylinders and base pressure coefficient value are well predicted by the present simulations, while the other hydrodynamic quantities (root-mean-square lift coefficient, Strouhal number) are predicted reasonably well as compared to published experimental data. The piggyback pipeline in the present study is modeled as two circular cylinders with a diameter ratio d/D = 0.2 (D denoting diameter of the large cylinder, d is diameter of the small cylinder). These two cylinders are clamped together at a distance G/D = 0.2. The two rigidly coupled cylinders are elastically supported and free to vibrate in two degrees of freedom. The effects on the vibration amplitudes and hydrodynamic forces are analyzed. The flow structures around the cylinders are investigated to explain the variations in observed structural responses. Depending on the angular position (α) of the small cylinder, the lock-in regime is narrower (α = 0°) or significantly wider (α = 180°) when compared to that of a single cylinder. 相似文献
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Takeshi Kinoshita Weiguang Bao Shunji Sunahara 《Journal of Marine Science and Technology》1997,2(3):135-147
The problem of the interaction of multiple cylinders oscillating in waves and slow current is considered. The interaction
is represented by waves emitted from adjacent cylinders towards the cylinder under consideration. Wave drift forces and moment
in the horizontal plane are calculated by the far-field method based on the conservation of momentum or angular momentum.
A semianalytical formula for the calculation of the wave drift damping is then deduced. The conservation of the integrals
in these formulae is proved. Special treatments to improve the accuracy of results are discussed. Comparisons between calculated
results and experimental measurements are made, showing satisfactory agreement. Effects of various combinations of current
direction and incident wave angle on the wave drift damping and damping moment are also examined. 相似文献
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This paper describes the application of finite element (FE) analysis to the prediction of the non-linear elasto-plastic collapse of ring-stiffened cylinders under hydrostatic loading. A range of legacy experimental test models have been analysed using FE idealisations generated using measured as-built shape data including out-of-circularity (OOC), frame alignment and tilt and other scantlings. The FE models also explicitly included the residual stresses caused by cold bending. Short and long ring-stiffened cylinders, which were designed to isolate interframe and overall collapse modes, respectively, were considered as were some intermediate length cylinders where the possibility of interactive collapse was also present. In general, the collapse pressures were predicted to within 6%. However, for some of the interframe collapse models, it was necessary to use the minimum measured plate thickness to achieve this. This was largely attributable to the limited measured plate thickness data. 相似文献
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为解决规则圆柱桩群阻力计算问题,以指导涉及规则圆柱桩群的物理模型试验和数值模拟计算等工作,在归纳总结已有研究成果的基础上,通过先进的数显式测力设备和较为准确的悬浮测力法,对有限深度均匀水流中多圆柱横向等间距不同方式的排列桩群进行了阻力测试研究,得出了有限深度均匀水流中圆柱横向阻力影响特性规律,并归纳总结出了圆柱横向阻力影响系数的经验公式。通过大量的测试试验数据证实了这些研究规律的准确性、有效性及实用性,对工程实践具有参考价值。 相似文献
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为加强港口工程钢筋连接的全面质量管理,以京唐港某码头工程为依托,提出港口工程管理的内部质量和外部质量概念。根据西格玛管理的理念和现场钢筋连接的调查考证,将钢筋连接质量缺陷数字化,提出影响钢筋连接质量的关键因素。 相似文献