Showing papers on "Vortex-induced vibration published in 1994"
01 Jan 1994
TL;DR: In this article, the in-line motion amplitude reached a maximum of almost one diameter, which was slightly smaller than for the subcritical case, and the dominant transverse motion amplitude was observed in the case where transverse flexibility only was allowed.
Abstract: Vortex induced motion of risers in a steady, uniform flow has been investigated experimentally in subcritical flow in a water flume and under critical flow conditions in a high speed cavitation tunnel. Both experimental arrangements provided flexibility in the in-line direction as well as transverse to the flow. Considerable in-line motions were seen in combination with the dominant transverse motions, and the latter were different from those observed in the case where transverse flexibility only was allowed. The tests at critical Reynolds number showed some 80% increase in the average drag coefficient, compared to the results for a fixed cylinder. This is a much more modest increase than for the subcritical flows where an increase of 2--300% was found. The transverse motion amplitude reached a maximum of almost one diameter, which was slightly smaller than for the subcritical case.
19 citations
01 Jan 1994
TL;DR: In this article, a means of alleviating vortex shedding-induced vibration of a deep-ocean mining pipe and measuring flow-induced torsional moment of the pipe was carried out, and the two most effective configurations were a pipe, straked with electromechanical power cables arranged in helical form with a pitch angle of 580 and a pipe with a perforated shroud.
Abstract: Tests were carried out to find a means of alleviating vortex- shedding-induced vibration of a deep-ocean mining pipe and to measure flow-induced torsional moment of the pipe. Test measurements included mean and root-squared values of lift, drag, torsional moment, and frequency and relative intensity of the shed vortices. Vortex-shedding characteristics were further investigated through flow visualization techniques. Five pipe configurations were tested at Reynolds number, Re = 5x104 ~ 2.5x105, for their effectiveness in reducing vortex-shedding intensity. The two most effective configurations were a pipe, straked with electro-mechanical power cables arranged in helical form with a pitch angle of 580, and a pipe with a perforated shroud. These two configurations generated the least vortex-shedding intensity, had minimum unsteady lift, and the smallest increment in drag compared to a bare pipe. Tests of a straight-down power-cable configuration (cable parallel to pipe axis) showed significant drag and lift increase, plus larger flow-induced torsional moment and, a mean nonzero lift.
12 citations
10 citations
Journal Article•
TL;DR: In this paper, a two-dimensional incompressible viscous flow around a fixed or elastically supported circular cylinder with a splitter plate of attached rigid, hinged or elastic types was simulated by a finite difference method.
Abstract: A two-dimensional incompressible viscous flow around a fixed or elastically supported circular cylinder with a splitter plate of attached rigid, hinged or elastic types, has been simulated by a finite difference method, to study the effect of splitter plate on drag and vortex shedding frequency of the cylinder The computation is carried out a Re = 1000, and the results show good agreement with available experimental data The relationship between the unsteady flow patterns and hydrodynamic force coefficients is also discussed
6 citations
TL;DR: In this article, a vortex-induced vibration of an elstically supported cylinder is simulated in two-dimensional by using a flowinduced vibration analysis program which has been developed in order to evaluate flow induced vibration in various components such as the heat exchanger.
Abstract: A vortex-induced vibration of an elstically supported cylinder is simulated in two-dimension by using a flow-induced vibration analysis program which has been developed in order to evaluate flow induced vibration in various components such as the heat exchanger From the comparison of calculated results and the experimental data, the following conclusions could be obtained (1) Although the vibration amplitudes were overestimated, the synchronization phenomenon between cylinder vibration and Karman vortex shedding could be simulated successfully (2) The 'lock in' phenomenon, in which a vortex shedding frequency coincides with a cylinder natural frequency in a certain reduced velocity range, could be simulated successfully (3) The 'lock in' phenomenon occurs when an ordinary vortex shedding pattern is broken by cylinder motion, and synchronization between vortex shedding and cylinder vibration occurs After synchronization occurs, the vortex shedding pattern becomes the same as in forced vibration
2 citations
TL;DR: In this paper, the effect of the vibration of trees on the flow in river was investigated experimentally, and the locking-in phenomenon was also recognized in the flow induced vibration of pine tree.
Abstract: In order to study the effect of vibration of trees on the flow in river, the characteristics of flow-induced vibration of a circular cylinder and a twig of pine tree elastically mounted in open channel were investigated experimentally. The amplificationof drag force and lift force acting on a cylinder in flow-inducecd vibration and that of a twig of pine tree were evaluated quantitatively. The locking-in phenomenon was also recognized in the flow induced vibration of pine tree.
2 citations
TL;DR: A numerical model and a solution method to analyze the labyrinth seal flow induced vibration by Oscillating Fluid Mechanics Method (OFMM) are presented in this article, including the basic equations and solution procedure to determine the oscillating velocity, pressure and the dynamic characteristic coefficients of Labyrinth seal such as the stiffness coefficients and damping coefficients.
Abstract: A numerical model and a solution method to analyze the labyrinth seal flow induced vibration by Oscillating Fluid Mechanics Method (OFMM) are presented in this paper, including the basic equations and solution procedure to determine the oscillating velocity, pressure and the dynamic characteristic coefficients of Labyrinth seal such as the stiffness coefficients and damping coefficients. The results show that this method has the advantages of both less time consuming and high accuracy. In addition, it can be applied to the field diagnosis of the vibration of the axis of turbomachinery system.
2 citations
TL;DR: In this paper, a fully coupled analysis of fluid-structure interaction has been realized in a turbulent flow field using the following calculational steps: a) solving turbulent flow by a direct simulation method where the ALE (arbitrary Lagrangian-Eulerian)-type approximation is adopted to take account of structural displacements; b) estimating fluid force on structures by integrating fluid pressure and shear stress; c) calculating dynamic response of structures and determining the amount of displacement.
Abstract: A new approach to simulate flow-induced vibration is introduced A fully coupled analysis of fluid-structure interaction has been realized in a turbulent flow field using the following calculational steps : a) solving turbulent flow by a direct simulation method where the ALE (arbitrary Lagrangian-Eulerian)-type approximation is adopted to take account of structural displacements ; b) estimating fluid force on structures by integrating fluid pressure and shear stress ; c) calculating dynamic response of structures and determining the amount of displacement ; d) re-generating curvilinear grids for new geometry using the boundary-fitted coordinate transformation method Vortex-induced vibration of a circular cylinder in a cross flow were successfully simulated and the synchronization phenomena between Karman-vortices and cylinder vibrations were clearly observed
2 citations
01 Jan 1994
TL;DR: In this article, the analytical models necessary for the design and optimization of practical wave absorbing mechanical devices used at the termination of cables are presented, where the reflection of travelling waves in the cable creates the standing wave model shape.
Abstract: Large amplitude flow-induced vibration of cables and risers is often associated with a phenomenon known as lockin, in which the vortex shedding process is synchronized with single frequency resonant vibration of the structure. Such vibration is characterized by a standing wave pattern in the mode shape of the resonant natural mode. The lockin phenomenon is dependent on the presence of this standing wave pattern. This paper provides the analytical models necessary for the design and optimization of practical wave absorbing mechanical devices used at the termination of cables. It is the reflection of travelling waves in the cable which creates the standing wave model shape. If the waves are absorbed at the termination, the resonance vanishes, no standing waves are found, and lockin is prevented. Less vibration, lower drag coefficients, and longer fatigue life are the result.
1 citations
TL;DR: In this paper, a simplified analytical solution for viscous damping has been formulated, considering the results obtained by an existing numerical method, for relatively narrow annular configurations: (i) when a rigid cylinder executes translational oscillation in the plane of symmetry, and (ii) a flexible cylinder vibrates in its first mode as a clamped-clamped beam subject to axial flow.
Abstract: The simplified analytical solutions for viscous damping have been formulated, considering the results obtained by an existing numerical method, for relatively narrow annular configurations: (i) when a rigid cylinder executes translational oscillation in the plane of symmetry, and (ii) a flexible cylinder vibrates in its first mode as a clamped-clamped beam subject to axial flow. For narrow annular passages, the viscous damping has significant effects on fluid-dynamic forces. In such a case, an inviscid fluid model is acceptable for estimating added mass. This theory is developed for both relatively high and low oscillatory Reynolds numbers. In terms of computational efficiency, it is useful to obtain the viscous damping forces using this approximate method. Also this method has important benefit for the future study of stability analysis of system; since, the viscous damping forces obtained by the present method can be expressed in terms of the oscillatory Reynolds number explicitly. To validate this theory, the results are compared with the ones obtained by the full viscous theories in the previous works. These results were found to be in reasonably good agreement with the results of the full theories.
1 citations
01 Oct 1994
TL;DR: Vortex breakdown is a deceptively simple looking, complex and poorly understood phenomenon as mentioned in this paper, it is an abrupt and drastic change of structure which sometimes occurs in swirling flows and is commonly found to occur on leading edge vortices over delta wings and on trailing vortice in aircraft wakes.
Abstract: Vortex breakdown is a deceptively simple looking, complex and poorly understood phenomenon. According to Benjamin (1962), vortex breakdown or bursting is an abrupt and drastic change of structure which sometimes occurs in swirling flows. This phenomenon is commonly found to occur on leading edge vortices over delta wings and on trailing vortices in aircraft wakes. While it is necessary to prevent vortex breakdown over a delta wing, since it results in loss of lift, it is desirable to allow vortices to burst in aircraft wakes since it reduces hazard to follower aircraft. Vortex breakdown is also useful in chemically reacting flows where it is employed as a flame holder. But, more than anything, this phenomenon is studied because it is one of the basic problems in fluid dynamics. What follows is the authors own limited perspective of the problem. The reader will find that he/she is not introduced to the problem directly. Instead, a whole lot of material is devoted to the development of the equations of vortex dynamics with special emphasis on the motion of a vortex filament. The intention here is to motivate the reader about the merits of describing fluid flows using vortex elements as building blocks rather than velocity and pressure. Model equations of vortex breakdown are derived next using these equations. Other theoretical descriptions of the phenomenon are also stated, Benjamin's theory being of prime importance.
TL;DR: In this paper, with the help fixed point principle, the existence condition of the periodic solution as well as the region of parameters of the vortex-induced vibration was found. But the authors did not consider the problem of vortex induced vibration.
Abstract: The vortex-induced vibration is a well-known problem in mechanics. In this paper, with the help fixed point principle, we study this problem and find the existence condition of the periodic solution as well as the region of parameters.
TL;DR: In this paper, the velocity field in a two-dimensional hexagonal lattice gas for flow around a cylinder at Reynolds numbers of 100 and 185 was studied and agreement with data is at best semi-quantitative.
Abstract: We study the velocity field in a two-dimensional hexagonal lattice gas for flow around a cylinder at Reynolds numbers of 100 and 185. We discuss drag, lift and Strouhal number. Agreement with data is at best semi-quantitative.
01 Dec 1994
TL;DR: In this paper, the authors developed and applied efficient adaptive numerical algorithms for the study of active vortex generators via direct numerical simulations, using innovative computational schemes to investigate flows past complex configurations undergoing arbitrary motions.
Abstract: The objective of the present research is the development and application of efficient adaptive numerical algorithms for the study, via direct numerical simulations, of active vortex generators. We are using innovative computational schemes to investigate flows past complex configurations undergoing arbitrary motions. Some of the questions we try to answer are: Can and how may we control the dynamics of the wake? What is the importance of body shape and motion in the active control of the flow? What is the effect of three-dimensionality in laboratory experiments? We are interested not only in coupling our results to ongoing, related experimental work, but furthermore to develop an extensive database relating the above mechanisms to the vortical wake structures with the long-range objective of developing feedback control mechanisms. This technology is very important to aircraft, ship, automotive, and other industries that require predictive capability for fluid mechanical problems. The results would have an impact in high angle of attack aerodynamics and help design ways to improve the efficiency of ships and submarines (maneuverability, vortex induced vibration, and noise).