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1.
In this paper, vortex-induced vibrations of a cylinder are simulated by use of ANSYS CFX simulation code. The cylinder is treated as a rigid body and transverse displacements are obtained by use of a one degree of freedom spring damper system. 2-D as well as 3-D analysis is performed using air as the fluid. Reynolds number is varied from 40 to 16000 approx., covering the laminar and turbulent regimes of flow. The experimental results of （Khalak and Williamson, 1997） and other researchers are used for validation purposes. The results obtained are comparable. 相似文献
2.
Large-eddy simulation of turbulent flow past a circular cylinder at sub- to super-critical Reynolds numbers is performed using a high-fidelity orthogonal curvilinear grid solver. Verification studies investigate the effects of grid resolution, aspect ratio and convection scheme. Monotonic convergence is achieved in grid convergence studies. Validation studies use all available experimental benchmark data. Although the grids are relatively large and fine enough for sufficiently resolved turbulence near the cylinder, the grid uncertainties are large indicating the need for even finer grids. Large aspect ratio is required for sub-critical Reynolds number cases, whereas small aspect ratio is sufficient for critical and super-critical Reynolds number cases. All the experimental trends were predicted with reasonable accuracy, in consideration the large facility bias, age of most of the data, and differences between experimental and computational setup in particular free stream turbulence and roughness. The largest errors were for under prediction of turbulence separation. 相似文献
3.
Perforated plates, relevant for several marine applications, are experimentally and numerically investigated. The numerical investigations are performed using a presently developed Navier–Stokes solver. Several comparison and sensitivity studies are presented, in order to validate and verify the solver. Forced heave experiments are performed on two perforated plates with perforation ratios 19% and 28%. Amplitude-dependent added mass and damping coefficients are presented. Good agreement is obtained between the solver and the present experiments. Consistent with existing data, the results show that the hydrodynamic coefficients of perforated plates are highly amplitude dependent. The damping force is found to dominate over added mass force. The damping force dominance increases with increasing perforation ratio. It is highlighted that plate-end flow separation has an important effect on the damping coefficient. The developed numerical solver is two-dimensional, but is found to yield reasonable estimates of hydrodynamic force coefficients when compared with a previous three-dimensional experimental investigation. This could indicate that three-dimensional effects are not dominant for the hydrodynamic forces of perforated plates, and that a two-dimensional viscous flow solver could have relevance as a tool for estimating hydrodynamic forces on three-dimensional perforated structures. 相似文献
4.
Benchmark computations of wave run-up on single cylinder and four cylinders by naoe-FOAM-SJTU solver
The benchmark simulations of wave run-up on a fixed single truncated circular cylinder and four circular cylinders are presented in this paper. Our in-house CFD solver naoe-FOAM-SJTU is adopted which is an unsteady two-phase CFD code based on the open source package OpenFOAM. The Navier-Stokes equations are employed as the governing equations, and the volume of fluid (VOF) method is applied for capturing the free surface. Monochromatic incident waves with the specified wave period and wave height are simulated and wave run-up heights around the cylinder are computed and recorded with numerical virtual wave probes. The relationship between the wave run-up heights and the incident wave parameters are analyzed. The numerical results indicate that the presented naoe-FOAM-SJTU solver can provide accurate predictions for the wave run-up on one fixed cylinder and four cylinders, which has been proved by the comparison of simulated results with experimental data. 相似文献
5.
The response of an oscillating circular cylinder at the wake of an upstream fixed circular cylinder was classified by different researchers as galloping, wake induced galloping or wake induced vibration. Furthermore it is already known that a sharp edge square cylinder would undergo galloping if it is subjected to uniform flow. In this study the influence of the wake of a fixed circular cylinder on the response of a downstream square cylinder at different spacing ratios (S/D = 4, 8, 11) is experimentally investigated. The subject appears not to have received previous attention. The lateral displacements, lift forces and the pressure data from gauges mounted in the wake of the oscillating cylinder are recorded and analyzed. The single degree of freedom vibrating system has a low mass-damping parameter and the Reynolds number ranges from 7.7 × 102 to 3.7 × 104.In contrast to that for two circular cylinders in tandem arrangement, the freely mounted downstream square cylinder displays a VIV type of response at all spacing ratios tested. There is no sign of galloping or wake induced galloping with the square cylinder. With increase at the spacing ratio the cross-flow oscillations decrease. It is shown that the vortices arriving from the upstream fixed circular cylinder play a major role on the shedding mechanism behind the downstream square cylinder and cause the square cylinder to shed vortices with frequencies above Strouhal frequency of the fixed square cylinder (St = 0.13). The VIV type of oscillations in the downstream square cylinder is most probably caused by the vortices newly generated behind the square cylinder. 相似文献
6.
This paper describes a plane regular wave interaction with a combined cylinder which consists of a solid inner column and a coaxial perforated outer cylinder.The outer perforated surface is a thin porous cylinder with an annular gap between it and the inner cylinder.The non-linear boundary condition at the perforated wall is a prime focus in the study;energy dissipation at the perforated wall occurs through the resistance to the fluid across the perforated wall.Explicit analytical formulae are presented to calculate the wave run-up on the outer and inner surfaces of the perforated cylinder and the surface of the inner column.The theoretical results of the wave run-up are compared with previous experimental data.Numerical results have also been obtained:when the ratio of the annular gap between the two cylinders to incident wavelength(b-a)/L≤0.1,the wave run-up on the inner surface of the perforated cylinder and the surface of inner column can partially or completely exceed the incident wave height. 相似文献
7.
The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements. 相似文献
8.
In this paper, the hydrodynamic coefficients of a horizontal semi-immersed cylinder in steady current and oscillatory flow combining with constant current are obtained via forced oscillation experiments in a towing tank. Three non-dimensional parameters (Re, KC and Fr) are introduced to investigate their effects on the hydrodynamic coefficients. The experimental results show that overtopping is evident and dominates when the Reynolds number exceeds 5×105 in the experiment. Under steady current condition, overtopping increases the drag coefficient significantly at high Reynolds numbers. Under oscillatory flow with constant current condition, the added mass coefficient can even reach a maximum value about 3.5 due to overtopping while the influence of overtopping on the drag coefficient is minor. 相似文献
9.
The flow around a cylinder, surface mounted or partly buried has been examined at Reynolds number of 1.3×104 and 2.6×104 by using the flow visualization method in the case of steady current. The lengths of the upstream and downstream separation regions were determined and the characteristics of the flow area were discussed for the cylinder having different burial depth to the diameter ratio (G/D). For comparsion, some numerical results obtained from the application of the FLUENT, computational fluid dynamics (CFD) software package have also been presented. Both experimental and numerical results indicated that the lengths of the separation regions near the upstream and downstream of the cylinder decreased with the increasing burial ratio (G/D=0, 0.20, 0.50). The results have significant implications both for the illustration of the potential for using CFD software and highlighting the need for data of two dimensional flow around the buried cylinder. 相似文献
10.
Both analytical (small time expansion) and numerical (finite-difference) approaches have been used to solve the earthquake-induced nonlinear hydrodynamic pressure acting on a rigid high rise offshore cylinder. For the high rise offshore cylinder, the most part of the flow field is independent of z and a three dimensional hydrodynamic analysis can be reduced to a two dimensional analysis. At onset, the dimensionless ground displacement ?2 = 0 for the two dimensional analysis, the normalized hydrodynamic pressures across cylinder face is a constant and is independent of the radius of the cylinder. The normalized horizontal force coefficient Cfx is independent of intensity of ground acceleration and is approximately linear and proportional to ?2 and its onset value is equal to π. For a linear analysis i.e. neglecting nonlinear convective acceleration, the normalized hydrodynamic pressure coefficient is also independent of the radius of cylinder. The analytical method was good for ground motion in a single direction, the results of simultaneous action of two components of ground acceleration can be obtained by the superposition of the results due to separate excitation. But the superposition method is only valid in the linear analysis. For highly nonlinear problem, the present finite difference approach is recommended. 相似文献
11.
Experimental Study on Vortex-Induced Vibrations of Submarine Pipeline near Seabed Boundary in Ocean Currents 总被引：2，自引：3，他引：2
1 .IntroductionThe submarine pipeline is a commonfacility widely usedfor offshore oil and gastransport . Whena pipeline is installed on a seabed and not buried,unsupportedspans may exist insomelocations ,es-peciallyinthe uneven zones of the seabed.The spa… 相似文献
12.
A horizontal, circular cylinder fitted with one bilge keel is forced to rotate harmonically around its axis. The bilge keel load and hull pressure distribution are investigated. A fully submerged condition (infinite fluid), and three partly-submerged conditions are considered. A two-dimensional numerical study is performed, and the results are validated against recently published experimental data by van’t Veer et al. [30]. In addition, comparisons for mass and drag coefficients are also made with experimental data for plate in infinite fluid (Keulegan and Carpenter [8]), and wall-mounted plate (Sarpkaya and O’Keefe [9]) in oscillatory flow.A Navier–Stokes solver based on the Finite Volume Method is adopted for solving laminar flow of incompressible water. The free-surface condition is linearized by neglecting the nonlinear free-surface terms and the influence of viscous stresses in the free surface zone, while the body-boundary condition is exact. This simplified modeling of the problem required the mesh to be fine only around the bilge keels, leading to a total number of cells around N ≃ 1 ×104, which reduced computational cost significantly.The influence of draft and amplitude of oscillations on the bilge keel force and hull pressure distribution are considered. The bilge keel force is presented in terms of non-dimensional drag and mass coefficients including higher harmonic components. The numerical results are also compared with the industry standard empirical method for calculation of roll damping proposed by Ikeda et al. [4]. In general, a good agreement between the results of the present numerical method and the experimental data is obtained and the differences with those predicted by the empirical method are addressed. 相似文献
13.
This paper reports on laboratory experiments conducted for the loop manoeuvre of underwater towed models of a cable-array system. The purpose of the experiment is to record the cable-array configuration in the vertical and azimuthal planes, and measure the tow-point tension while the tow-ship model is performing a full 360° loop manoeuvre at different radii and speeds, in the calm waters of the wave-basin test facility. The test setup utilises an underwater video camera, TV, VCR and a ring-type strain-gauge load cell. The X, Y, Z coordinates of the cable-array system are obtained by measuring frozen displays of the experimental configuration. The coordinate and tension results obtained from experiments are compared with computed values. 相似文献
14.
《中国海洋工程》2020,(3)
The interaction between structure and wave is a typical phenomenon in naval architecture and ocean engineering. In this paper, numerical simulation is carried out to study the interaction between a two-dimensional submerged, fixed,horizontal rigid plate and solitary wave with our in-house meshless particle CFD solver MLParticle-SJTU. First, the in-house CFD solver is verified by experimental results conducted at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. During the verification, the plate is submerged under water and the solitary wave with a given amplitude is generated by a piston-type wave maker. Free surface elevation of the wave and the pressure impacting on the plate is recorded and compared with experimental data respectively. The predicted pressure and surface elevation agree well with the experimental results. Then in order to further investigate factors affecting wave-structure interaction, wave height, submerged depth and plate length are analyzed. 相似文献
15.
The hydrodynamic pressures induced by regular waves around the circumference of a pipeline normal to the wave direction and near a rigid bed of slope 1:10 have been investigated in a wave flume. The pressures were integrated to obtain the force time history, from which the peak horizontal and vertical forces are evaluated. The maximum and root mean square horizontal and transverse force coefficients are correlated with the Keulegan–Carpenter (KC) number. The effect of the distance between the sloping bed and the pipeline on the force coefficients is discussed. The force coefficients are found to decrease with an increase in KC number and with the decrease in the relative clearance of the pipeline from the boundary. In addition, the reflection characteristics of the sloping bed in the presence of the pipeline as a function of surf similarity parameter and their comparison with the results from existing literature are also reported. The details of the model setup, experimental procedure, results and discussion are presented in this paper. 相似文献
16.
Prediction of streamwise flow-induced vibration of a circular cylinder in the first instability range 总被引：1，自引：0，他引：1
The streamwise flow-induced vibration of a circular cylinder with symmetric vortex shedding in the first instability range is investigated, and a wake oscillator model for the dynamic response prediction is proposed. An approach is applied to calibrate the empirical parameters in the present model; the numerical and experimental results are compared to validate the proposed model. It can be found that the present prediction model is accurate and sufficiently simple to be easily applied in practice. 相似文献
17.
The members of many offshore structures and pipelines are circular cylinders which are often near to or penetrating the fluid boundaries, i.e. the sea bed, other solid boundary or free surface. It seems appropriate therefore to collect together some known analytical results concerning the cylinder added masses in such cases, the free surface (z = 0) condition being simplified. Comparison with simple experiments indicates that for horizontal motions, φ/z = 0z = 0 is appropriate while for vertical motions φ = 0 on z = 0 is appropriate. The effects caused by the variation in the added mass with cylinder submergence in both modes are important for a wide range of practical situations. For high speed entry (slamming) of the cylinder the effect of free surface rise is significant. 相似文献
18.
In this paper, equations calculating lift force of a rigid circular cylinder at lock-in in uniform flow are deduced in detail. Besides, equations calculating the lift force on a long flexible circular cylinder at lock-in are deduced based on mode analysis of a multi-degree freedom system. The simplified forms of these equations are also given. Furthemore, an approximate method to predict the forces and response of rigid circular cylinders and long flexible circular cylinders at lock-in is introduced in the case of low mass-damping ratio. A method to eliminate one deficiency of these equations is introduced. Comparison with experimental results shows the effectiveness of this approximate method. 相似文献
19.
In this paper the fully nonlinear potential model based on a finite element method is used to investigate the nonlinear wave motion around a moving circular cylinder. The results for the cylinder in transient motion are compared with the experimental data and a much better agreement than the linear theory is found. Further simulation for a circular cylinder in sinusoidal motion is made. It is found that when the ratio of the cylinder diameter D to the wavelength L is relatively small at a fixed motion amplitude the nonlinear components of the runup on the cylinder surface at the second- and third-harmonic frequencies become more important and this is confirmed by the experimental data. Results for the hydrodynamic force are also provided for a cylinder oscillating in a channel. It is noticed that when the frequency of the cylinder motion in a channel is between the first and the second natural frequencies of the symmetric mode, the time history has components not only at the frequency of the cylinder motion but also at the first natural frequency. The latter remains significant over the period that the simulation is made. This has important implications to model testing. If measurement is to be made at such a frequency it may take long time for the motion to become periodic at the frequency of the cylinder motion. 相似文献
20.
The seakeeping characteristics of various boom geometries in irregular waves and currents are investigated. The response of a floating boom section on the open sea is a function of a number of parameters, such as boom geometry, distribution of mass, buoyancy/weight ratio, and wave and current characteristics. To understand the relationship between these design parameters more clearly, a series of regular and irregular wave tests were conducted with six different 1:4 scale models for three current velocities and six different wave conditions. To simplify the problem, only rigid boom sections consisting of a buoyancy cylinder and vertical skirt were used. In parallel with this experimental program, a numerical model for the responses of two-dimensional floating boom sections in small-amplitude waves is also developed. The numerical results are compared with our large-scale experimental results. The boom effectiveness on the open sea is evaluated based on the concept of “effective draft” and “effective freeboard” assuming that drainage and oversplashing failures are the prime mechanisms of containment failure. Using the present results, a guideline for the optimum design/selection of future booms is developed. 相似文献