Cantilevered Cylinder Research Articles

Wind pressures measurement on end-cell-induced vibration of a cantilevered circular cylinder

In the case of a circular tower with high aspect ratio, “end-cell-induced vibration (ECIV)” occurs at a wind speed a few times higher than the occurrence wind speed of the vortex-induced vibration (J. Fluids Struct. 13 (1999) 499–518). In order to elucidate the characteristics of aerodynamic forces due to “tip-associated vortices (TAV)” which are considered as the cause of ECIV, wind pressure acting on a rigid circular tower are measured. Proper orthogonal decomposition applied to the pressure data clarifies the structure of the fluctuating pressures due to TAV and the results of wavelet analyses indicate “non-alternate generation” of them.

322 管内流に直交する片持ち円柱の流力弾性振動特性

322 管内流に直交する片持ち円柱の流力弾性振動特性

Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel

Flow-induced in-line oscillation of a circular cylinder has been experimentally studied by free-oscillation tests in a water tunnel. Response amplitudes of a circular cylinder have been measured for determining the values of the reduced mass-damping parameter of less than 1.0. In the free-oscillation tests, the cylinder models were spring-mounted so as to oscillate as a two-dimensional rigid cylinder in the water tunnel. Two types of excitation phenomena appear at approximately half of the resonance flow velocity. The response amplitudes are sensitive to the reduced mass-damping parameter during the in-line oscillation of the first excitation region with a symmetric vortex street, and the alternate vortices are periodically shed, locking-in with the vibration of the cylinder in the second excitation region. A hysteresis phenomenon is observed to appear in the in-line oscillation of the latter region. A cantilevered circular cylinder with a finite length aspect ratio of 10 was tested for fluid-elastic characteristics of the cylinder, and these characteristics are found to be quite different from those of the two-dimensional cylinder, having only one wide velocity region of excitation. The results of this study are providing important supporting data for the recent publication “Guideline for Evaluation of Flow-Induced Vibration of a Cylindrical Structure in a Pipe,” by the Japan Society of Mechanical Engineers, Standard JSME S012-1998.

Large deflection analysis of pneumatic envelopes using a penalty parameter modified material model

The computational challenge associated with pneumatic envelopes, such as balloons and parachutes, is due to the complication of their underconstrained and no-compression nature. Underconstrained behavior leads to large displacements without concomitant strain energy; no-compression behavior leads to a degenerate, wrinkled state. In this paper, we discuss issues surrounding modeling such structures. We provide a method to analyze pneumatic envelopes through a penalty parameter-modified constitutive relation embedded in a non-linear finite element code. Such an approach is also adaptable to the user-provided material function port available with many commercial finite element codes. Validation examples given are the inflated cantilever cylinder subjected to transverse tip load, inflated cantilever cylinder subjected to twist moment, and the inflation of a round parachute.

Flow-Induced Vibration of Bluff Bodies. Experiments on Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel. 2nd Report, Influence of the Aspect Ratio of a Cantilevered Circular Cylinder.

The flow-induced in-line oscillation of a cantilevered circular cylinder was experimentally studied through free-oscillation tests in a water tunnel. The response displacement amplitude at a circular cylinder tip was measured at reduced velocity from 1.0 to 4.0. A cantilevered cylinder was supported by a plate spring mounted on the water tunnel wall. The cylinder aspect ratio was varied from 5 to 21 to investigate the effect of aspect ratio on the response displacement. It is found that cylinders with aspect ratios of 5 and 10 have one excitation region, while cylinders with aspect ratios of 14 and 21 have two excitation regions. The aspect ratio, therefore, affects the amplitude of the excitation regions. The influence of end-effect was also investigated using cylinders with an end plate attached to the free end. Since the cylinders with an end plate show two excitation regions, even at an aspect ratio of 5, the flow around the free end of a cantilevered cylinder causes the end-effect. The mechanism of vibration was investigated using a cylinder with a splitter plate in wake to prevent alternate vortices. The amplitude is greater than those of a normal cylinder without a splitter plate, especially at Vr=2.3 to 3.0, where a cylinder with an end plate shows the second excitation region. In other words, the alternate vortices suppress the amplitude in this range. The maximum amplitude of each excitation region decreases in proportion to Cn and the amplitude of the first excitation is more sensitive to Cn.

Flow-Induced Vibration of Bluff Bodies. Vortex-Induced Vibration of a Cantilever Circular Cylinder in Super-Critical Reynolds Number Flow and Its Suppression by Structure Damping.

Experimental validation of the design criteria for preventing the failure of a thermometer well by vortex-induced vibration is presented, clarifying the effects of Reynolds number and structure damping. An existing avoidance criterion for the vortex-induced vibration in the flow direction, which is given in terms of the reduced velocity Vr as Vr<1.0, has been developed based on the experimental data mainly in the sub-critical range. The applicability of this criterion in the super-critical range is examined in this paper based on the results of experiments performed in the Reynolds number region from 7.8×104 up to 1.1×106 at Vr=1.0. On the other hand, an existing suppression criterion of vortex-induced vibration in the flow direction is given in terms of the reduced damping Cn as Cn>1.2 (or 2.5) under the condition of Vr<3.3 in design guidelines. This criterion, however, has been proposed based on very limited available data The appropriateness of the suppression criterion is also examined in this paper based on the results of experiments in realistic thermometer well conditions, i.e. cantilever cylinders with varied structure damping in a pipe water flow. As a result, it becomes clear that Vr<1.0 is applicable in the super-critical range up to 1.1×106 and that the criteria of Vr<3.3 and Cn>1.2 are reasonably applicable to a cantilever cylinder in a pipe water flow.

Flow-Induced Vibration of Bluff Bodies. Experiments on Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel. 1st-Report, The Difference of the Response Characteristics When a Cylinder is Elastically Supported at Both Ends and Cantilevered.

Flow-induced in-line oscillation of a circular cylinder has been experimentally studied by free-oscillation tests in a water tunnel. Response amplitudes of a circular cylinder have been measured for determining the values of the reduced mass-damping parameter of less than 1.0. In the free-oscillation tests, the cylinder models were spring-mounted so as to oscillate as a two-dimensional rigid cylinder in the water tunnel. Two types of excitation phenomena appear at approximately half of the resonance flow velocity. The response amplitudes are sensitive to the reduced mass-damping parameter during the in-line oscillation of the first excitation region with a symmetric vortex street, and the alternate vortices are periodically shed, locking-in with the vibration of the cy]inder in the second excitation region. A hysteresis phenomenon is observed to appear in the in-line oscillation of the latter region. A cantilevered circular cylinder with a finite length aspect ratio of 10 was tested for fluid-elastic characteristics of the cylinder, and these characteristics are found to be quite different from those of the two-dimensional cylinder, having only one wide velocity region of excitation. The results of this study are providing important supporting data for the recent publication Guideline for Evaluation of Flow Induced Vibration of a Cylindrical Structure in a Pipe by the Japan Society of Mechanical Engineers, Standard JSME S()12 1998.

Free vibration of cantilevered cylinders: effects of cross-sections and cavities

This study investigates the influence of a cavity on the natural frequencies and mode shapes of a homogeneous, isotropic, elastic solid cylinder. Cavities of different shapes and sizes are often found in engineering applications to provide access, reduce weight and to cut cost in production. As a result, detailed quantitative solutions to this class of problem will be of great interest to engineering practitioners. In this study, a highly efficient and accurate numerical algorithm is proposed to examine the vibrations of elastic solid cylinders with a deep cavity. The technique uses the exact theory of three-dimensional elasticity in conjunction with the Ritz form of minimum energy principle to derive the governing eigenvalue equation. Within the context of three-dimensional elasticity, displacement functions composed of a set of twodimensional lateral surface functions and one-dimensional longitudinal functions are defined for each displacement component. The orthogonality inherent in these functions has resulted in well form eigen value matrices which can be manipulated and solved with ease. The technique yields upper-bound natural frequencies and three-dimensional deformed mode shapes for a wide range of elastic hollow cylinders with an arbitrary cross section. Most of the results presented herein are believed to be new to the existing literature.

Aerodynamic forces on circular cylinders of finite height

Aerodynamic forces on a cantilevered circular cylinder have been studied in a wind tunnel using rough-walled models. The primary purpose of this study is to construct models of the aerodynamic coefficients for full-scale application. Measurements were made of the mean and fluctuating wind pressures in three kinds of flows, i.e., a smooth flow, a grid-produced turbulent flow and a turbulent boundary layer. The data gathered from a number of experiments concerned with this subject are also reviewed. The results indicate that the aerodynamic coefficients in the transcritical regime are primarily functions of the aspect ratio and the surface roughness of the cylinder. For the drag coefficient and the circumferential pressure distribution, quantitative descriptions of their behavior as functions of these two factors are suggested. Furthermore, it was found that the fluctuating wind pressures can adequately be predicted by a quasi-steady theory for actual structures in turbulent atmospheric winds.

Fluid-Induced Loading of Cantilevered Circular Cylinders in a Low-Turbulence Uniform Flow. Part 3: Fluctuating Loads with Aspect Ratios 4 to 25

Part 3 of this study presents details of an investigation into the fluctuating pressures and loads induced on smooth, cantilevered circular cylinders immersed in a low-turbulence, uniform flow. Experiments were carried out in a wind tunnel at a Reynolds number of 4·4 × 104 for aspect ratios in the range 4 to 25. R.m.s. pressures on the surface of the cylinder and r.m.s. lift and drag were measured, and the frequency content of the fluctuation was analysed. The results are consistent with the mean loading pattern presented in Part 1, particularly with regard to the existence of a significant aspect ratio of 13, and complete the data set for aspect ratios in the range 4 to 30.

Fluid-Induced Loading of Cantilevered Circular Cylinders in a Low-Turbulence Uniform Flow. Part 1: Mean Loading with Aspect Ratios in the Range 4 to 30

Part 1 presents details of an investigation into the mean loading of smooth, cantilevered circular cylinders immersed in a low-turbulence uniform flow. Experiments were performed in a wind tunnel at a Reynolds number of 4·4 × 10 4 for aspect ratios in the range 4 to 30. Mean surface pressures and vortex-shedding frequencies were measured, from which the local mean pressure drag and Strouhal number were calculated at various spanwise locations. The results reveal the extent of the disturbance induced by the flow around the free-end of a cantilever and the existence of a significant aspect ratio of 13.

Fluid-Induced Loading of Cantilevered Circular Cylinders in a Low-Turbulence Uniform Flow. Part 2: Fluctuationg Loads on a Cantilever of Aspect Ratio 30

Part 2 presents details of an investigation into the fluctuating loads induced on a smooth, cantilevered circular cylinder with an aspect ratio of 30 immersed in a low-turbulence uniform flow. Experiments were carried out in a wind tunnel at a Reynolds number of 4·4 × 10 4 and involved the measurement of fluctuating pressures and forces. Oil-flow visualization was performed to determine the flow pattern at the surface of the cylinder. The results reveal the nature of the disturbance induced by the flow around the free-end of a cantilever and the full extent of the spanwise variation of fluctuating pressures and forces.

Three‐Dimensional Stresses in Short Cantilevered Cylinders

A three‐dimensional stress analysis for a short cantilevered cylinder subjected to a partial shear load on one end is presented based on the theory of elasticity. A solution to three‐dimensional elasticity problems proposed by the writer is used for the analysis. Boundary conditions on the fixed end are rigorously prescribed by three components of displacement. Basic and additional solutions are determined to satisfy boundary conditions. Numerical results for stresses and displacements in the short cantilevered cylinder, with a length‐to‐radius ratio of 2.0, are illustrated and are compared to those obtained by Saint‐Venant's method. A criterion of applicability of Saint‐Venant's method to this problem is proposed. The values of three components of stress at the loaded end become infinite at the boundary of the loaded area. The values of four components of stress at the fixed end show a tendency for stress concentration at the circumference of the end.

Some effects of free-stream turbulence on the flow past a cantilevered circular cylinder

Flow around a cantilevered circular cylinder has been studied experimentally in the subcritical and critical Reynolds-number ranges. Particular attention was paid to the free-stream turbulence effects on the steady aerodynamic characteristics of the cylinder. Measurements were made of the surface pressure distribution, flow separation line and vortex shedding frequency in grid-generated turbulent flows. The aerodynamic characteristics of a cylinder were only minutely affected by the free-stream turbulence in the subcritical flow. The critical Reynolds number was expressed as a function of the Taylor number Tx defined in terms of the longitudinal integral scale of the free-stream turbulence. The mean drag coefficient and the position of the flow separation point were fairly well-correlated with the parameter Re 1.34 Tx , with Re being the Reynolds number. Furthermore, it was found that some steady aerodynamic coefficients of the cylinder were closely correlated among themselves.

Some Effects of Free-Stream Turbulence on the Flow Past a Cantilevered Circular Cylinder

Flow around a cantilevered circular cylinder has been studied experimentally in the subcritical and critical Reynolds-number ranges. Particular attention was paid to the free-stream turbulence effects on the steady aerodynamic characteristics of the cylinder. Measurements were made of the surface pressure distribution, flow separation line and vortex shedding frequency in gridgenerated turbulent flows. The aerodynamic characteristics of a cylinder were only minutely affected by the free-stream turbulence in the subcritical flaw. The critical Reynolds number was expressed as a function of the Taylor number Tx defined in terms of the longitudinal integral scale of the free-stream turbulence. The mean drag coefficient and the position of the flow separation point were fairly well-correlated with the parameter Re1.34.Tx, with Re being the Reynolds number. Furthermore, it was found that some steady aerodynamic coefficients of the cylinder were closely correlated among themselves.

Analysis of cylindrical shells under patch loading

AbstractThe object of this study is to predict the peak values of the stress resultants and couples in a relatively thick cylindrical shell under a concentrated local loading in order to guide the design of a large‐scale reinforced concrete test specimen. Four finite element programs, SHORE‐III, two versions of RONALD, and ANSYS, were employed here. The SHORE‐III and RONALD analyses considered a complete cantilevered cylinder, while the ANSYS model treated a cylindrical panel free along the curved edge and constrained in various ways along the longitudinal edge. Comprehensive comparative results are provided for the linear elastic loading case, which indicate the magnitude and attenuation of concentrated loading effects on cylindrical shells and panels.

Vortex-excited vibrations of yawed cantilevered circular cylinders with different scruton numbers

In a wind tunnel test the vortex-excited vibrations of a cantilevered circular cylinder yawed relative to the flow direction were investigated. The Scruton number, Sc, of the model cylinder was varied between 2.27 ⩽ Sc ⩽ 25.3 and the yaw angle ϕ between −50° ⩽ ϕ ⩽ 50°. The Reynolds number referred to the normal flow component, ν n , was in the range of 10 4, the flow had a uniform turbulence intensity of 7.1%, and the cylinder had a smooth surface. The tests showed that the vortex-excited oscillation is stable in the investigated yaw angle range for Scruton numbers below 20. In case of Sc = 25.3 the vibration amplitude decreases for yaw angles above 20°. In the last case thlative amplitude y 0/d is below 0.02. The critical wind speed increases with ( cos ϕ) −1 , so the cosine rule is accurately followed.

A study of response and response spectra of offshore structures to regular waves

The response of a simplified offshore structure to waves is examined, the structure being idealizedas a mass mounted on a light circular cantilever cylinder of uniform cross-section. Waves are simple sinusoidal and wave forces are computed according to the Morison equation. The solution to the nonlinear equation of motion is obtained by assuming that the velocities of the structure are smaller than those of the fluid induced by waves and is given in a simple form so that the parameters affecting the response can be clearly seen. Based on the solution various methods of constructing response spectra for offshore structure to wave excitation are examined.

Stability of flexible slender cylinders in pulsatile axial flow

A theoretical analysis is presented of the dynamical behaviour of flexible cylinders in axial flow, the velocity of which is perturbed harmonically in time. It is found that parametric instabilities are possible for certain ranges of frequencies and amplitudes of the perturbations. These instabilities occur over specific ranges of flow velocities, and in the case of cantilevered cylinders are associated with only some of the modes of the system.

On a theory for the vortex-excited oscillations of flexible cylindrical structures

The periodic shedding of vortices that accompanies the cross-flow past a bluff cylindrical body can excite the body into resonant transverse oscillations when the vortex shedding frequency and a body natural frequency are sufficiently close to one another. In this paper, a mathematical model that enables one to predict the vortex-excited resonant response of bluff elastic cylinders is developed. Based on some previous work by the authors, a modified van der Pol equation is employed as the governing equation for the fluctuating lift on the cylinder and is coupled to the equation of motion of the cylinder. With previously developed relations between the empirical parameters in the model and the physical mass and damping parameters that appear in the equation of motion of the elastic cylinder, the model is used to predict the resonant response of taut strings and circular cylindrical beams with differing end conditions. These predictions are compared with available experimental results for taut strings, pivoted rods and flexible, cantilevered cylinders. Quite good agreement is obtained.