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Results
A Study On the Rotating Flow In an Annulus
Kim, Young-Ju (Korea Institute of Geoscience and Mineral Resources(KIGAM), Daejeon, Korea) | Yoon, Chi-Ho (Korea Institute of Geoscience and Mineral Resources(KIGAM), Daejeon, Korea) | Park, Yong-Chan (Korea Institute of Geoscience and Mineral Resources(KIGAM), Daejeon, Korea) | Park, Jongmyung (Korea Institute of Geoscience and Mineral Resources(KIGAM), Daejeon, Korea) | Kang, Joong Seok (Korea Institute of Geoscience and Mineral Resources(KIGAM), Daejeon, Korea) | Kwon, Seok-Ki (Korea Institute of Geoscience and Mineral Resources(KIGAM), Daejeon, Korea) | Woo, Nam Sub (School of Mechanical Engineering, Sungkyunkwan University Suwon, Korea) | Hwang, Young Kyu (School of Mechanical Engineering, Sungkyunkwan University Suwon, Korea)
ABSTRACT Lift forces acting on a fluidized particle play a central role in many importance applications, such as the removal of drill cuttings in horizontal drill holes, sand transport in fractured reservoirs, sediment transport and cleaning of particles from surfaces. An experimental and numerical investigation is conducted to study a solid-liquid mixture upward-transporting hydraulically by Newtonian fluid and non- Newtonian fluid such as sodium carboxymethyl cellulose(CMC) solution by weight in a slim hole concentric annuli with rotation of the inner cylinder. Annular fluid velocities varied from 0.2 m/s to 2.0 m/s under the actual drilling operational condition. Macroscopic behavior of solid particles, averaged flow rate, and particle rising velocity are observed. For both waater and CMC solutions, the higher the concentration of the solid particles are, the larger the pressure gradients become. Also, CMC solutions have been observed to provide better capability to mobilize and transport particles. The mean diameter of particles was 0.1 cm and a material density of 2.55 g/cm3 were used in the experiment. INTRODUCTION Among the various industrial unit operations involved with multiphase systems, agitation of solid-liquid systems is quite commonly encountered such as catalytic reactions, drilling operation of oil well, etc. Although there are many industrial applications of solid-liquid flows in technology, the available knowledge about particle flows is not complete due to the difficulties encountered in analyzing these complex systems. Rotating flows in annular passages are important, since they have many engineering applications in bearings, rotating-tube heat exchangers and, especially, annulus flows of mud in case of slim hole drilling of oil well. When an oil well is drilled, it is necessary to transport the cuttings up to the ground. To this end, fluid is pumped through the center of drill pipe and back up to the ground through the annular gap between the drill pipe and the drilled hole.
An Experimental Study of Closely Spaced Point Absorber Arrays
Stallard, Tim (School of Mechanical, Aerospace and Civil Engineering, University of Manchester. Manchester, UK.) | Stansby, Peter K. (School of Mechanical, Aerospace and Civil Engineering, University of Manchester. Manchester, UK.) | Williamson, Alan J. (School of Mechanical, Aerospace and Civil Engineering, University of Manchester. Manchester, UK.)
ABSTRACT Experimental measurements of the response of a group of closely spaced heaving devices are reported. Details of the experimental technique are presented and the effect of both array size and configuration on the power output and response of individual floats is reported and compared to an isolated float. Power output measurements relate to a non-linear drivetrain representative of the Manchester Bobber wave energy device in which each float and counterweight is supported from a pulley which drives a flywheel and generator. Net power amplification relative to an equal number of isolated floats is observed at several wave frequencies, generally when the wave period is greater than natural period. Response measurements are also presented with negligible mechanical friction (i.e. free-response) to provide dataset for easy comparison of response to general numerical simulation. As theory suggests, the measurements indicate that response and net power capture is amplified at particular ratios of device spacing to wavelength. INTRODUCTION Many wave energy devices generate electricity by restraining the motion of a rigid body subject to wave excitation. One emerging class of wave energy device consists of a number of generating units installed in close proximity and supported from a common structure. The Manchester Bobber, the WaveStar the Fred Olsen FO (Buldra) and Trident Energy are examples of this type of device. Indicative dimensions of these systems are a float radius a = 5 m at spacing s = 4a (i.e. separation of the order of one diameter). In wave periods between 6 and 12 s, these dimensions correspond to normalized radius in the range 0.55 > ka > 0.15 and normalized spacing in the range 2.25 > ks > 0.55. At the close separations considered the response of each device is influenced by the diffracted and radiated wave fields due to the other devices.
- Research Report > New Finding (0.64)
- Research Report > Experimental Study (0.50)
Hydrodynamic Forces On Multiple Hanging-off Circular Cylinders In Uniform Flows
Prastianto, Rudi Walujo (Department of Marine System Engineering, Osaka Prefecture University Sakai, Osaka, Japan) | Otsuka, Koji (Department of Marine System Engineering, Osaka Prefecture University Sakai, Osaka, Japan) | Ikeda, Yoshiho (Department of Marine System Engineering, Osaka Prefecture University Sakai, Osaka, Japan)
ABSTRACT This study is addressed to evaluate the hydrodynamic forces experienced by multiple flexible cylinders arrays which are free to oscillate due to water crossflows. This paper presents a part of experimental results of two different configurations of three flexible circular cylinders which were towed in still water. The cylinders were submerged partially into the still water from a towing carriage as hanging-off vertical cantilevers. Each cylinder has length-to-diameter ratio of 34.4 with low mass ratio (= 1.24). The Reynolds number varied from 1.08 × 10 up to 3.78 × 10. A longitudinal gap between upstream and downstream cylinder (LUD) was varied by 5D, 7D, 9D, and 10D, respectively. The measurement of the hydrodynamics forces in two, in-line (drag force) and transverse (lift force) directions were performed simultaneously. Frequency of the drag force was found approximately twice the corresponding lift force frequency at the related reduced velocity (Ur) for all cases, except at low Ur, and linearly increased as a function of the Ur. The variables Ur and LUD revealed have significant influence on the characteristics of CD and CL for each test configuration. For upstream cylinders in both two configurations, there are basically three distinct regions dealing with the CD and CL characteristics as function of Ur, while for downstream cylinders the CD and CL decreased as Ur and LUD increased. At the medium Ur, the configuration with two cylinders at the downstream position (Case B) produced higher total drag and lift coefficients on the downstream cylinders than another one. INTRODUCTION The dynamics response of an array of circular flexible cylinders subjected to cross-flow is very complex. Some factors dictated the response, such as Reynolds number, cylinders arrangement, and incoming flow condition. General characteristics of cylinders response in the cross-flow are not well understood in the various parameter ranges.
- North America (0.68)
- Asia > Japan > Kansai (0.29)
Transformations of Wave Passing Around Cylinders
Lin, Ming-Chung (Department of Engineering Science and Ocean Engineering, National Taiwan University Taipei, TAIWAN, China) | Hsu, Chao-Min (Department of Engineering Science and Ocean Engineering, National Taiwan University Taipei, TAIWAN, China) | Ting, Chao-Lung (Department of Engineering Science and Ocean Engineering, National Taiwan University Taipei, TAIWAN, China)
ABSTRACT This study investigates wave transformation when a wave passes over circular cylinders. The numerical model is based on the Boussinesq equation developed by Nwogu (1993), expressed by velocity with arbitrary water depth. The numerical model utilizes the Fourth-Order Adams-Bashforth-Moulton Predictor-Corrector Scheme and is combined with a source function and absorbing boundary condition to enhance calculations stability and reduce the required processing time. The absorbing boundary condition is a sponge layer combined with a radiation boundary condition. Several numerical experiments are made to simulate wave transformations over circular cylinders. The interactions among incident wave, reflected wave and scattered waves due to cylinder are obvious in wave height distributions. INTRODUCTION Recently, Boussinesq equation has become the most popular equation in the prediction of wave transformations. Boussinesq (1872) derived the original Boussinesq equations. Thereafter, numerous researchers improved and extended their applicability. Peregrine (1967) considered various water depth conditions to derive a shallow-water wave equation from small amplitude wave theory. He used a depth-averaged velocity as the dependent variable to derive the Boussinesq equation at a constant water depth. Witting (1984) included the free surface velocity as the dependent variable in a nonlinear depth-integrated momentum equation. Expanding velocity terms as Taylor series yields a onedimensional Boussinesq equation; however, the weakness of the equation is its limited applicability to constant-depth situations and the difficulty of applying it to two-dimensional cases. Conventional Boussinesq equations are limited to relatively shallow water. Hence, many studies have focused on extending them to deeper water. McCowan (1985, 1987) calculated nonlinear wave propagations in shallow water using the Boussinesq equation. The error between the derived phase velocity and the linear phase velocity was under 5%, and the relative depth of the water was extended to 0.2. improved the Boussinesq equation to enable it to be applied to relatively deeper water.
Fatigue Life Calculations of Risers By Taking Into Account the Higher Harmonic Force Components
Modarres-Sadeghi, Yahya (Department of Mechanical Engineering, Massachusetts Institute of Technology Cambridge, MA, USA) | Triantafyllou, Michael S. (Department of Mechanical Engineering, Massachusetts Institute of Technology Cambridge, MA, USA) | Hover, Franz S. (Department of Mechanical Engineering, Massachusetts Institute of Technology Cambridge, MA, USA)
ABSTRACT We apply systematic diagnostics obtained form laboratory experiments at MIT to the strain and acceleration signals of model scale experiments on a riser, in order to assess the predictability of the response, and also extract the contribution of the higher-harmonic force components. A large third-harmonic contribution is observed for the majority of the cases, suggesting the importance of considering the influence of higher harmonic force components, when analyzing the fatigue life of a riser subjected to uniform or linearly sheared current. The region of excitation for various sheared flow cases remains almost constant, independent of the maximum sheared flow, suggesting about half of the riser is excited. The excited part covers the region where counterclockwise figure-eight motions are observed. Sample fatigue life calculations show a decrease of orders of magnitude when the high frequency forcing is taken into account for a model scale experiment. INTRODUCTION Vortex Induced Vibrations (VIV) of long flexible cylinders (risers) has been recently studied extensively mainly due the growing interest in deep water oil exploration among other industrial applications. VIV of short rigid cylinders, on the other hand, is a relatively older problem and is much more well-understood than that of long flexible cylinders. Papers by Sarpkaya (2004) and Williamson and Govarhan (2004) on rigid cylinders and by Vandiver (1993) on flexible cylinders give comprehensive reviews on VIV problems. The majority of works on VIV of flexible cylinders (similar to those on rigid cylinders until very recently) have been focused on cross-flow oscillations, with neglecting the relatively small in-line oscillations. Recently it has been shown (see, e.g., Dahl et al., 2007) that for rigid cylinders, if the IL oscillations are allowed, a non-negligible 3 (or even 5) harmonic force component is observed, which can influence the physical behavior ofthe rigid cylinder.
Study of the Smoothing Effect On the Power Production In an Array of SEAREV Wave Energy Converters.
Tissandier, J. (Laboratoire de Mécanique des Fluides/EHGO (UMR CNRS 6598) Ecole Centrale de Nantes, Nantes, France) | Babarit, A. (Laboratoire de Mécanique des Fluides/EHGO (UMR CNRS 6598) Ecole Centrale de Nantes, Nantes, France) | Clément, A.H. (Laboratoire de Mécanique des Fluides/EHGO (UMR CNRS 6598) Ecole Centrale de Nantes, Nantes, France)
ABSTRACT This paper deals with the smoothing effect on power production in an array of SEAREV wave energy converters (WEC) due to the summation of each single converter's production. A numerical model of the SEAREV WEC developed in previous works is used in this study to perform numerical simulations of motions of each WEC in the array in order to compute the full energy production. Comparisons are made between the electricity produced by each single device and the array. It shows the benefit of this smoothing effect on the global energy production. In mono-directionnal random waves, results show only a few devices are needed in order to reduce strongly the standard deviation of the instantaneous power with the mean power. Several device layouts are also considered, for different sets of random directional waves. It is shown that the smoothing effect does not depend on the sea state conditions nor on the layout of the array but only on the number of systems in the array. INTRODUCTION In case of wave activated bodies, wave energy converters such as the Pelamis () or the AWS (), ocean waves are used to make masses move. The mechanical energy of the waves is hence converted into masses mechanical energy. Then, the mechanical energy of these masses is converted into electricity by means of a Power Take Off (PTO). As waves are a random oscillating phenomenon, the motion of the masses is not a steady motion, but an oscillation. Being a quadratic function of first order responses, the power production is also oscillating, and the resulting instantaneous power varies from zero to peak values which can be several times the mean value of the power production. From the grid's point of view, such behaviour of the input electricity flow is not acceptable and solutions for smoothing the power production have to be found.
- Europe (0.29)
- North America (0.28)
Experimental Study On Flow Induced Vibration of a Cylinder With Two Degrees of Freedom Near a Rigid Wall
Yang, Bing (Institute of Mechanics, Chinese Academy of Sciences, Beijing, China) | Gao, Fuping (Institute of Mechanics, Chinese Academy of Sciences, Beijing, China) | Wu, Yingxiang (Institute of Mechanics, Chinese Academy of Sciences, Beijing, China)
ABSTRACT The flow-induced vibration of a cylinder with two degrees of freedom near a rigid wall under the action of steady flow is investigated experimentally. The vibration amplitude and frequency of the cylinder and the vortex shedding frequency at the wake flow region of the cylinder are measured. The influence of gap-to-diameter ratio upon the amplitude response is analyzed. The experimental results indicate that when the reduced velocity (Vr) is in the range of 1.2 < Vr < 2.6, only streamwise vibration with small amplitude occurs, whose frequency is quite close to its natural frequency in the still water. When the reduced velocity Vr > 3.4, both the streamwise and transverse vibrations of the cylinder occur. In this range, the amplitudes of transverse vibration are much larger than those of streamwise vibrations, and the amplitudes of the streamwise vibration also get larger than those at the range of 1.2 < Vr < 2.6. At the range of Vr > 3.4, the frequency of streamwise vibration undergoes a jump at certain values of Vr, at which the streamwise vibrating frequency is twice as much as the transverse one. However, when the streamwise vibration does not experience a jump, its frequency is the same as that of the transverse vibration. The maximum values of second streamwise and transverse vibration amplitudes increase with increasing gap-to-diameter ratios. INTRODUCTION The flow-induced vibrations of a cylinder are a fluid-structure interaction problem, which have a wide practical background. For example, the bridges and chimneys under wind actions in civil engineering, the risers and pipelines in offshore engineering, the heat exchangers tubes in chemical engineering, are prone to flow-induced vibrations, which have attracted wide interests from numerous researchers, e.g., Sarpkaya (1979), Griffin & Ramberg (1982), Bearman (1984), Parkinson (1989), Sumer & Fredsoe (1997), Williamson & Govardhan (2004). Most of previous researches have mainly focused.
- Asia (0.29)
- North America > Canada (0.28)
- Research Report > New Finding (0.50)
- Research Report > Experimental Study (0.41)
ABSTRACT Measurements are made of vortex-induced vibration of an elastically supported circular cylinder in water with reduced velocity (U/fnD) from 2 to 12, damping factors from 0.2% to 20% of critical damping, mass ratios (m/ρD2) from 2.8 to 17, and transverse, inline, and combined inline and transverse motions with up to 1.49 diameters amplitude. Effects of mass ratio, damping, and strakes are investigated. INTRODUCTION It is well known that vortices are periodically shed by a cylinder in a cross flow. Vortex shedding induces vibration of elastic cylinders and cylinder motion affects the shedding process. Ten reviews of vortexinduced forces and vortex-induced vibration are Gabbai and Benaroya (2005), Williamson and Govardhan (2004), Norberg (2003), Sarpkaya (1979, 2004), Khalak and Williamson (1999), Griffin and Hall (1991), Blevins (1990), Bearman (1984), King (1977), and Leinhard (1966). Recent experimental papers include Jeon and Gharib (2004), Flemming and Williamson (2005), Dahl, Hover, and Triantafyllou (2006), Laneville (2006), Klamo (2006), Dipankar, Sengupta and Talla, (2007), Carberry and Sheridan (2007), Prasanth and Mittal (2008). A test program of vortex-induced vibration of elastically supported circular cylinders was made with reduced velocity (U/fnD) from 2 to 12, damping factors from 0.2 to 20%, mass ratios from 2.8 to 17 and transverse, inline, and combined inline and transverse motion. DESCRIPTION OF TESTS Tests were conducted on an aluminum cylinder with 2.5 inch (6.35 cm) outside diameter in the stratified flow channel at the Scripps Institution of Oceanography. Its surface was sanded with 220 grit sand paper to give a average roughness of approximately 30 micro inch (Ra) roughness, k/D = 10 x10−5. The cylinder pierces the water surface and extends 44.3 inch (1.125 m) into the flow, ending 2 mm (0.08 inch) above the channel bottom.
ABSTRACT Vortex-induced vibrations (VIV) and galloping effects are studied for the case of two cylinders in tandem arrangement. Both cylinders are allowed to move in X and Y directions and rigidity is kept the same for both directions. The cross-flow around moving cylinders is computed using a specifically designed numerical method which has been thoroughly validated through systematic comparisons between numerical and available experimental results. The motion of cylinders is computed with a 4th order explicit Runge-Kutta method. The coupling between flow and structural computations is semi-implicit in the sense that the potential part of the flow is implicitly taken into account by the structural solver. This confers the required stability to the coupling procedure. After validation results, we present configurations for center-to-center distances L/D=2 and 4 and reduced velocities ranging from 3 to 10 at laminar Reynolds number of 200. INTRODUCTION Flow-Induced Vibrations of structures are a phenomenon well known to civil engineers since it may generate structural fatigue or threaten the integrity of the overall structure in extreme situations. For arrays of offshore risers, both VIV and fluidelastic instabilities, such as wake galloping, have been observed. If VIV for single circular cylinders are well documented, VIV, interference and galloping phenomena studies for arrays of cylinders remain sparse since Zdravkovitch (1985). Since then we may notice, for example, the investigation of Assi et al. (2006) concerning flow-induced vibration interference for a Cylinder free to move in the Y direction while the front cylinder is kept fixed. To our knowledge, there exists no numerical study of flow-induced vibration cylinder arrays. In this paper we study VIV, interference and galloping phenomena occurring when two circular cylinders in tandem arrangement are placed in a uniform cross-flow. These configurations are evaluated numerically.
Fluid Forces And Structure-Induced Damping of Obliquely-Oscillating Offshore Structures
Marzouk, Osama A. (Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University Blacksburg, Virginia, USA) | Nayfeh, Ali H. (Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University Blacksburg, Virginia, USA)
ABSTRACT We use high-order CFD methods and statistical analysis techniques to study the flow over a cylinder, approximating circular cross-section offshore structures, oscillating in a direction inclined to the horizontal direction. We vary the orientation angle from 0 to 180 degrees, where the 90-degree case corresponds to oscillation perpendicular to the incoming stream. We study (in the time-domain and through the angle-response curves) variations of the induced force properties, their symmetry or skew symmetry about the case of a 90-degree orientation angle, and the structure-induced damping of the flow. We identify the range of orientation angles where the entrainment phenomenon takes place and study the influence of the motion amplitude on this phenomenon. We propose a technique to derive reference (scaling) quantities for the oblique fluid force. Unlike the lift and drag, such reference quantities cannot be obtained from the stationary-structure case because such an oblique force is not defined then. INTRODUCTION Fixed platforms, tension-leg platforms, spars, offshore wind turbines, and chimneys share a rigid circular cross-section element. Several studies have investigated the flow over stationary and moving cylinders and cables, and the fluid-structure interaction (FSI) associated with the latter two cases. Different cross-sections have been considered, including circular, elliptic, and square ones. In addition, for two-dimensional moving-structure cases, different motion orientations have been also considered. These include 1 DOF perpendicular to the incoming flow stream (Carberry et al., 2001; Marzouk and Nayfeh, 2008), 1 DOF parallel to the incoming flow (Kim and Williams, 2006; Guilmineau and Queutey, 2004), and both 2 DOFs (Jauvtis and Williamson, 2003). There have been studies that even explored angular oscillations of the structure instead of the translational one (Baek and Lee, 2001). We here examine the influence of tilting an oscillating cylinder from the vertical direction (the incoming stream sets the horizontal direction).