Critical Fluid Velocity Research Articles

Vibration and stability of ring-stiffened thin-walled cylindrical shells conveying fluid

Based on the Flügge shell theory, equations of motion of ring-stiffened thin-walled cylindrical shells conveying fluid are developed with the aid of the Hamilton's principle. Analysis is carried out on the vibration and stability of the ring-stiffened shells conveying fluid, and the effects of fluid velocity, the Young modulus, the size, and the number of the ring stiffeners on the natural frequency and the instability characteristics are examined. It is found that stiffeners can reduce the number of circumferential waves for the fundamental mode, and increase the shell's natural frequency, and thus the critical fluid velocity. For the number of longitudinal half waves being equal to one, the natural frequency and the corresponding critical fluid velocity are the largest for the internal-ring stiffened shell and are the smallest for the symmetrical-ring stiffened shell. The natural frequencies and the corresponding critical fluid velocity predicted by the established model increase with the increase in the Young modulus, the size, or the number of the stiffeners.

Dynamic instability analysis of single walled Carbone Nano Tubes conveying fluid under generalized boundary conditions

The dynamic instabilities of Carbon NanoTubes (CNTs) conveying fluid are modeled and numerically simulated based on the nonlocal elasticity theory. The small scale parameter and the fluid-tube interaction effects on the dynamic behaviors of the CNT-fluid system as well as the instabilities induced by the fluid-velocity are investigated. The critical fluid-velocity and frequency-amplitude relationships as well as the flutter and divergence instability types and the associated time responses can be obtained based on the presented methodological approach.

On the stability of a microbeam conveying fluid considering modified couple stress theory

In this paper, the size-dependent vibrational behavior of a microbeam conveying fluid was investigated using the Modified Couple Stress Theory. For cantilever and clamped-clamped microbeams, the small amplitude vibration equation of the micro-beams was solved using a Galerkin based reduced order model and the effects of material length-scale parameter on its natural frequencies were evaluated. It was found that for the both cantilever and clamped-clamped conditions, the critical fluid velocities predicted by the modified couple stress theory are higher than those predicted by the classical beam theory. In addition, the differences between the eigen-frequencies and the critical fluid velocities predicted by the modified couple stress theory and classical beam theory depends on the ratio of the material length-scale parameter to the beam height. In addition an unexpected result in the difference between the first eigen-frequency of the cantilever micro-beam obtained by the classical and the modified couple stress theory has been achieved.

Dynamic modeling of mass-flowing linear medium with large amplitude displacement and rotation

In this paper, a dynamic model of a linear medium with mass flow, such as traveling strings, cables, belts, beams or pipes conveying fluids, is proposed, in the framework of Arbitrary-Lagrange–Euler (ALE) description. The material coordinate is introduced to characterize the mass-flow of the medium, and the Absolute Nodal Coordinate Formulation (ANCF) is employed to capture geometric nonlinearity of the linear media under large displacement and rotation. The governing equations are derived in terms of d'Alembert's principle. When using an ALE description, complex mass-flowing boundary conditions can be easily enforced. Numerical examples are presented to validate the proposed method by comparison with analytical results of simplified models. The computed critical fluid velocity for the stability of a cantilevered pipe conveying fluid is correlated with the available theory in literature. The large amplitude limit-cycle oscillations of flexible pipes conveying fluid are presented, and the effect of the velocity of the fluid on the static equilibrium of the pipe under gravity is investigated.

중간 지지된 유체 유동 외팔형 원통셸의 임계유속

The critical fluid velocity of cantilevered cylindrical shells subjected to internal fluid flow is investigated in this study. The fluid-structure interaction is considered in the analysis. The cantilevered cylindrical shell is supported intermediately at an arbitrary axial position. The intermediate support is simulated by two types of artificial springs: translational and rotational spring. It is assumed that the artificial springs are placed continuously and uniformly on the middle surface of an intermediate support along the circumferential direction. The steady flow of fluid is described by the classical potential flow theory. The motion of shell is represented by the first order shear deformation theory (FSDT) to account for rotary inertia and transverse shear strains. The effect of internal fluid can be considered by imposing a relation between the fluid pressure and the radial displacement of the structure at the interface. Numerical examples are presented and compared with existing results.

Critical Fluid Velocities for Removing Cuttings Bed Inside Horizontal and Deviated Wells

This study aims to estimate the critical fluid flow velocity for preventing the development of a stationary bed using empirical correlations valid for horizontal and highly inclined wellbores that can be easily used at the field. For this purpose, experiments have been conducted at METU-PETE Cuttings Transport Flow Loop for various conditions. Observations showed that a stationary bed is developed when the fuid velocity is less than 6.0 ft/s, and a critical fluid velocity of 8.0 ft/s is required to establish a no-bed condition. Results showed that the critical velocity and the thickness of the stationary bed, if developed, could be estimated with a reasonable accuracy.

Stability and Chaotic Vibrations of a Fluid-Conveying Pipe with Additional Combined Constraints

AbstractThe stability and possible chaotic vibrations of a fluid-conveying pipe with additional combined constraints are investigated. The pipe, restrained by motion constraints somewhere along the length of the pipe, is modeled by a beam clamped at the left end and supported by a special device (a rotational elastic constraint plus a Q-apparatus) at the right end. The motion constraints are modeled by both cubic and trilinear models. Based on the Differential Quadrature Method (DQM), the nonlinear dynamical equations of motion for the system are formulated, and then solved via a numerical iterative technique. Calculations of bifurcation diagrams, phase portraits, time responses and Poincare maps of the oscillations establish the existence of chaotic vibrations. The route to chaos is shown to be via period-doubling bifurcations. It is found that the effect of spring constant of the rotational elastic constraint on the dynamics is significant. Moreover, the critical fluid velocity at the Hopf bifurcation point for the cubic model is higher than that for the trilinear model.

Pipe-Rotation Effect on Hole Cleaning for Water-Based Drilling Fluids in Horizontal and Deviated Wells

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 114965, "Effect of Pipe Rotation on Hole Cleaning for Water- Based Drilling Fluids in Horizontal and Deviated Wells," by M.E. Ozbayoglu, Middle East Technical University; A. Saasen, StatoilHydro; M. Sorgun, Middle East Technical University; and K. Svanes, StatoilHydro, prepared for the 2008 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Jakarta, 25-27 August. The paper has not been peer reviewed. A major concern while drilling horizontal and directional wells is proper hole cleaning. For a stationary bed of drilling cuttings in the annulus, generally, an increase in the fluid velocity will erode the bed significantly. However, depending on the drilling conditions, very-high fluid velocities are needed for bed removal, which may not be possible because of hydraulic and physical limitations. In such cases, pipe rotation may enhance cuttings transport mechanically, and effective hole cleaning may be achieved even at fluid velocities lower than the critical annular fluid velocities required to prevent stationary-bed development. The effect of pipe rotation on hole cleaning was investigated. Introduction Increasing the fluid viscosity or flow rates for vertical wells can improve the cuttings-transport performance. However, as hole inclination progresses from vertical to horizontal, additional challenges arise, such as cuttings-bed development. At inclinations between 40 and 60°, hole cleaning is most difficult because of back sliding of the cuttings inside the wellbore. Such cases require higher flow rates. Also, for inclined wellbores, fluids with high viscosities do not clean the hole as observed in vertical cases. Also, during drilling operations, the drillstring usually is rotating, which increases the complexity of the drilling-fluid behavior and cuttings transport inside the wellbore. Although many studies on the relationship between the pipe rotation and cuttings-transport performance are available in the literature, there is a lack of understanding about the contribution of pipe rotation to hole cleaning. This study provides detailed information on the effects of pipe rotation on hole cleaning. The basis of the information was experimental work conducted by varying major drilling parameters. Theory Many drilling variables influence hole cleaning. For realistic modeling, all variables that affect cuttings transport should be taken into consideration. From the point of view of hole cleaning, pipe rotation will affect not only the cuttings-distribution scheme inside the wellbore but also the fluid properties and pipe alignment, especially in eccentric cases. Use of all data will increase the difficulty of predicting the contribution that pipe rotation makes in cuttings transport and hydraulics. For example, in an eccentric annulus, frictional pressure loss will decrease as the pipe eccentricity increases, if all other parameters are kept constant. However, when the pipe is rotated, frictional pressure loss increases, most probably because of the orbital motion. It is more difficult to predict the behavior of pressure loss with the presence of cuttings in the system. However, the volume of stationary bed decreases with increased pipe rotation, which leads to an increased fluid-flow area. Thus, frictional pressure losses might decrease as pipe rotation is increased.

Experimental investigation of dynamic stability of a cantilever pipe aspirating fluid

The dynamic stability of a submerged cantilever pipe conveying fluid from the free end to the fixed one is considered as one of the unresolved issues in the area of fluid–structure interaction. There is a contradiction between theoretical predictions and experiments. Reported experiments did not show any instability, while theory predicts instability beyond a critical fluid velocity. Recently, several papers appeared, improving the theoretical modelling of pipe dynamics. All theories predict instability, either oscillatory or static, referred to here as flutter and divergence, respectively. A new test set-up was designed to investigate the hypothesis that previous experimental set-ups could not allow observations of pipe instability or the pipe aspirating water is unconditionally stable. In this new test set-up, the fluid velocity could exceed the theoretically predicted critical velocities. A cantilever pipe of about 5 m length was partly submerged in water. The free open end of the pipe was in the water, whereas the fixed end was above the waterline. The experiments clearly showed that the cantilever pipe aspirating water is unstable beyond a critical velocity of water convection through the pipe. Below this velocity the pipe is stable, whereas above it the pipe shows a complex motion that consists of two alternating phases. The first phase is a nearly periodic orbital motion with maximum amplitude of a few pipe diameters, whereas the second one is a noise-like vibration with very small amplitudes. Increasing the internal fluid velocity results in a larger amplitude of the orbital motion, but does not change the pipe motion qualitatively.

Dynamic analysis of conical shells conveying fluid

A formulation, based on the semi-analytical finite element method, is proposed for elastic conical shells conveying fluids. The structural equations are based on the shell element proposed by Ramasamy and Ganesan [Finite element analysis of fluid-filled isotropic cylindrical shells with constrained viscoelastic damping, Computers & Structures 70 (1998) 363–376] while the fluid model is based on velocity potential formulation used by Jayaraj et al. [A semi-analytical coupled finite element formulation for composite shells conveying fluids, Journal of Sound and Vibration 258(2) (2002) 287–307]. Dynamic pressure acting on the walls is derived from Bernoulli's equation. By imposing the requirement that the normal component of velocity of the solid and fluid are equal leads to fluid–structure coupling. The computer code developed has been validated using results available in the literature for cylindrical shells conveying fluid. The study has been carried out for conical shells of different cone angles and for boundary condition like clamped–clamped, simply supported and clamped free. In general, instability occurs at a critical fluid velocity corresponding to the shell circumferential mode with the lowest natural frequency. Critical fluid velocities are lower than that of equivalent cylindrical shells. This result holds good for all boundary conditions.

유체유동 회전 외팔 파이프의 안정성 해석

In this paper the vibration system is composed of a rotating cantilever pipe conveying fluid. The equation of motion is derived by using the Lagrange's equation. Generally, the system of pipe conveying fluid becomes unstable by flutter. Therefore, the influence of the rotating angular velocity, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method are studied. The influence of mass ratio, the velocity of fluid, the angular velocity of a cantilever pipe and the coupling of these factors on the stability of a cantilever pipe are analytically clarified. The critical fluid velocity (<TEX>$u_{cr}$</TEX>) is proportional to the angular velocity of the cantilever pipe. In this paper Flutter(instability) is always occurred in the second mode of the system.

Hydromechanical signaling between the ciliate Mesodinium pulex and motile protist prey

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 44:197-206 (2006) - doi:10.3354/ame044197 Hydromechanical signaling between the ciliate Mesodinium pulex and motile protist prey H. H. Jakobsen1,2,*, L. M. Everett1, S. L. Strom1 1Western Washington University, Shannon Point Marine Center, 1900 Shannon Point Road, Anacortes, Washington 98221, USA 2Present address: Danish Institute for Fisheries Research, Dept. of Marine Ecology and Aquaculture, Kavalergården 6, 2920 Charlottenlund, Denmark *Email: hhj@dfu.min.dk ABSTRACT: The raptorial ciliate Mesodinium pulex (Claparéde & Lachmann, 1858) was fed 3 different prey species: Rhodomonas salina, Heterocapsa rotundata and Gymnodinium simplex. Each prey displayed different motility patterns, including dramatic and effective escape responses. M. pulex only fed while motionless and responded only to motile prey by either an attack or an escape. Both the attack and escape responses are associated with a strong directional component in M. pulex. M. pulex responded to motile prey when the critical fluid velocity exceeded ~15 to 42 µm s–1, depending on prey species. These values are similar to hydromechanical signal thresholds found in marine metazoans. Prey-induced escape responses in M. pulex are associated with fast-swimming prey such as G. simplex. Deformation rates calculated in these specialized cases exceed the reported critical deformation rate for escape in ciliated protists, suggesting that fast-swimming prey mimic an approaching predator. Microscopic observations indicate that the band of equatorial cirri encircling M. pulex is the principal detector of motile prey. We propose that M. pulex exhibits a specialized fluid velocity-sensitive mechanoreceptor analogous to the fluid motion mechanoreceptors found in metazoans. M. pulex fails to ingest the cryptophytic prey R. salina. Our observations suggest that this is due to mismatch between the capturing organelles of the ciliate and surface properties of the prey. Dinoflagellate prey are more effectively ingested, but a high percentage escaped from M. pulex. Pre-capture escape responses may be triggered by ciliate-generated hydromechanical signals and facilitated by the strong swimming ability of the flagellates. Hydromechanical signaling can affect the outcome of predator–prey interactions and may select for distinctive morphological and behavioral features in planktonic protists. KEY WORDS: Sensory ecology · Hydrodynamical signals · Escape behavior · Predator avoidance · Protist–protists interactions · Microzooplankton Full text in pdf format Supplementary Videos PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 44, No. 2. Online publication date: September 12, 2006 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2006 Inter-Research.

Manipulation and filtration of low index particles with holographic Laguerre-Gaussian optical trap arrays

Multiple low index particles (micrometer-sized ultrasound contrast agent), have been optically trapped using a 4 x 4 Laguerre- Gaussian trap array. The trapping efficiency of the Laguerre-Gaussian arrangement was measured using a Stokes' flow approach whereby the critical relative fluid velocity required to remove particles from the optical trap was measured. The dependence of trapping efficiency on beam power was also explored and the optimum beam parameters were identified. Finally, the utility of the array as a selective filter was demonstrated by tweezing multiple low-index particles from a population exhibiting an inherent distribution in size. This procedure represents a unique remote non-contact process that may have significant applicability throughout the fields of biophysics and biotechnology.

A semi-analytical coupled finite element formulation for shells conveying fluids

A new formulation, based on the semi-analytical finite element method, is proposed for elastic shells conveying fluids. The structural equations are based on the shell element proposed by Ramasamy and Ganesan [Comput Struct 70 (1998) 363] while the fluid model is based on velocity potential. Dynamic pressure acting on the walls is derived from Bernoulli's equation. Imposing the requirement that the normal components of velocity of the solid and fluid be equal, introduces fluid–structure coupling. The proposed technique has been validated using results available in the literature. This study shows that instability occurs at a critical fluid velocity corresponding to the shell circumferential mode with the lowest natural frequency and this phenomenon is also independent of the type of structural boundary conditions imposed.

The influence of rotary inertia of concentrated masses on the natural vibrations of a clamped–supported pipe conveying fluid

Effects of rotary inertia of concentrated masses on the natural vibrations of a fluid-conveying pipe have been studied by theoretical modeling and numerical calculations. For the analysis, a clamped–supported pipe is assumed and Galerkin’s method is used for transformation of the governing equation to the eigenvalue problem. The natural frequencies and mode shapes for the system have been calculated by using the newly developed computer code. In addition, the threshold values of flow velocity for the onset of unstable motions have been investigated. The main conclusions for the present study are (1) rotary inertia gives much change on the higher natural frequencies and mode shapes, (2) the number and location of nodes can be changed by rotary inertia, (3) by introducing rotary inertia, the second natural frequency approaches the first as the location of the concentrated mass approaches the midspan of the pipe, and (4) the critical fluid velocities are unchanged by introduction of rotary inertia and the first three dimensionless values are u≈4.49, 7.73, and 10.91, respectively.

Development of a New Cuttings-Transport Model for High-Angle Wellbores Including Horizontal Wells

Summary This paper presents a new design model that will enable the drilling engineer to select the proper hydraulics for problem-free drilling in high-angle holes (from 55 to 90° from vertical). Empirical correlations have been developed after carrying out an extensive experimental study of cuttings transport in a 5-in. full-scale flowloop. The model predicts the required critical transport fluid velocity (CTFV), the average cuttings travel velocity (CTV), and the annular cuttings concentration under most given sets of drilling operating conditions.

Characteristics of Debris Flow Caused by Denser Fluid

Sediment discharge and concentration are experimentally investigated for debris flows caused by denser fluid and by plain water, respectively. Denser fluid is represented by the mixture flow of sand and water. The former debris flow is found to carry more gravels than the latter. Gravel discharge and concentration increase with the decrease in the sand grain diameter. This can be explained by critical fluid velocity for gravel movement in the mixture flow. For the estimate of the critical velocity the drag force is also investigated. The value of the drag force in the mixture flow of very fine sand is close to that in plain water. Therefore, such mixture flow is found to behave like a single fluid.

Fluid-conveying damped Rayleigh-Timoshenko beams in transverse vibration analyzed by use of an exact finite element part I: Theory

Free and forced nonsynchronous harmonic linear vibrations of piecewise uniform straight beam structures supported by a Winkler-type ambient medium and conveying a piecewise constant-speed plug flow of material along the deflected beam axis are studied by means of finite elements. Hysteretic and viscous damping in the beam material and ambient medium are considered. Large static axial loads may act on the beam and fluid calling for use of a second-order theory. In a companion paper, exact complex-valued nonsymmetric transcendentally frequency-dependent member stiffness matrices have been established for uniform Rayleigh-Timoshenko beams, uniform Euler-Bernoulli beams (with infinite shear stiffness), and also for uniform strings (with zero bending stiffness). In the present paper, the corresponding approximate member stiffness matrices based on standard polynomial shape functions are given. Fluid-conveying rigid bodies are treated. Six numerical examples are presented for beam structures. Comparisons between results found by use of exact and approximate finite elements are performed. Forced and free harmonic vibrations are studied including the calculation of critical fluid velocities and mechanical power flows.

MECHANISM OF CRYSTALLIZATION IN AGITATED SOLUTIONS

A new concept of molecular cluster dynamics in turbulent flows is used to develop a physical model and mechanism of homogeneous and heterogeneous nucleation in solutions. The proposed physical model considers the motion of molecular clusters in centrifugal fields of free eddies induced in turbulent flows. The clusters are moved to an eddy boundary region where they are concentrated and aggregated to form critical nuclei. It is shown theoretically that a critical fluid velocity exists, below which nuclei are not formed, and that its value depends upon the degree of solution supersaturation. The nucleation theory takes into account the hydrodynamic parameters of the process and permits calculation of the number of nuclei formed. Satisfactory agreement was obtained between calculated values and published experimental data.

海洋における垂直流体輸送用パイプの横振動 Ｉ

In order to get the information on the dynamic strength of a vertical pipe for transporting mineral resources under the sea floor to a platform on the sea surface, the lateral vibration of the pipe due to external forces, such as waves, currents, impacts of icebergs, etc., must be analysed. As the first step for this purpose, the natural frequency of lateral vibration of the pipe has been analysed theoretically and experimentally, especially taking the effect of the flowing fluid in the pipe into consideration. The results obtained are summarized as follows: (1) The natural frequency of lateral vibration of the pipe decreases gradually as the velocity of inner fluid increases. There is the critical fluid velocity at which the natural frequency of the pipe becomes zero and its lateral vibration corresponding to the frequency vanishes. The value of the critical fluid velocity is smaller in cases of larger length and own weight of the pipe, larger compressive load applied axially at the top of the pipe, larger specific gravity of the inner fluid and smaller dimension of the cross-section of the pipe. (2) The natural frequency of the pipe also decreases as the length and own weight of the pipe increase, and as the above-mentioned compressive load increases. Furthermore, the frequency becomes zero when the own weight and compressive load reach the buckling load of the pipe. (3) In the practical range, the natural frequency of the pipe is little affected by the damping force due to the surrounding water. (4) As the ratio of the mass of the surrounding water to that of the pipe with inner fluid increases, the natural frequency of the pipe decreases, but the ratio does not affect the critical fluid velocity. (5) The same relationship between the natural frequency and the other quantities as mentioned above can be seen in cases of pipes with various kinds of supports. However, the frequency itself depends upon the condition for supporting the pipe at its ends. The frequency pertaining to the fixed-fixed supports of the pipe is almost twice as large as that pertaining to the pinned-pinned supports of the pipe. Besides, the frequency pertaining to the pipe which is fixed at the sea floor and pinned at the sea surface is about one and half times greater than that pertaining to the pinned-pinned supports of the pipe.