bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Particle Characteristics on Trajectories and Blade Impact Patterns
Authors: Hamed A.
Published: November 2009

This work presents the results of a detailed study of the effect of particle characteristics on the particle dynamics and on the resulting pattern of blade impacts in a two stage axial flow gas turbine operating with particle laden flows. The particle dynamics computations combine the particle-blade impact characteristics, as determined from a three dimensional trajectory analysis with the particle rebound characteristics, which are obtained from experimental data. The results show the pattern of blade impacts in all stationary and rotating blade rows for fly ash and for sand particles. The results demonstrate that drastically different patterns of particle blade impacts are associated with the different particles.
A Reynolds-Stress Model for Near-Wall and Low-Reynolds-Number Regions
Authors: Shima Nobuyuki
Published: November 2009

The Reynolds stress model for high Reynolds numbers proposed by Launder et al. is extended to near-wall and low-Reynolds-number regions. In the development of the model, particular attention is given to the high anisotropy of turbulent stresses in the immediate vicinity of a wall and to the behavior of the exact stress equation at the wall. A transport model for the turbulence energy dissipation rate is also developed by taking into account its compatibility with the stress model at the wall. The model and the low-Reynolds-number model of Hanjali’c and Launder are applied to fully-developed pipe flow. Comparison of the numerical results with Laufer’s data shows that the present model gives significantly improved predictions. In particular, the present model is shown to reproduce the sharp peak in the distribution of the streamwise turbulence intensity in the immediate vicinity of the wall.
Fluids Engineering Education: Current Status and Future Directions
Authors: Dalton C. , Lamb J. P.
Published: November 2009

This paper presents a summary of panel presentations at the 1986 ASME Winter Annual Meeting. A total of eleven panelists from university, industry, and governmental organizations participated in the program. The authors have also included a number of editorial and interpretative comments to enhance the breadth of coverage.
Noise and Vibration Related to the Patterns of Supersonic Annular Flow in a Pressure Reducing Gas Valve
Authors: Nakano Masami , Outa Eisuke , Tajima Kiyohiro
Published: November 2009

Cause of intense aerodynamic noise and vibration from a contoured type valve is revealed in close relation to the supersonic flow patterns. Simple conical plugs are used in the experiments, and the valve pressure ratio is up to twenty. Four typical patterns of the flow are observed by schlieren photography. In one of these patterns, the jet flow along the plug separates from the wall to form an annular jet impinging on the inner wall of the valve chest. Such flow oscillates significantly in resonance with the acoustic modes of the chest cavity. The radiated noise and the dynamic force acting on the valve stem reach intense levels, dominated by some discrete components of the corresponding frequencies. The mechanisms to generate or to suppress the flow oscillation, leading to the intense noise and vibration, are discussed.
Solution Procedure for Unsteady Two-Dimensional Boundary Layers
Authors: Kwon O. Key , Pletcher R. H. , Delaney R. A.
Published: November 2009

An accurate and reliable solution procedure is presented for solving the two-dimensional, compressible, unsteady boundary layer equations. The procedure solves the governing equations in a coupled manner using a fully implicit finite-difference numerical algorithm. Several unsteady compressible and incompressible laminar flows are considered. Example results for two unsteady incompressible turbulent flows are also included. An algebraic mixing length closure model is used for the turbulent flow calculations. The computed results compare favorably with experimental data and available analytical/numerical solutions.
The Dynamics of Small Annular Jets
Authors: Meseguer Jose´
Published: November 2009

The experiments on small annular water jets performed by Hoffman et al. (1980) are analyzed by using a mathematical model similar to that developed by these authors. Such mathematical model has been modified to account for the difference in pressure between the region inside the annular jet and the atmosphere, the results obtained being in complete agreement with the experimental ones.
Development of the Reattached Flow Behind Surface-Mounted Two-Dimensional Prisms
Authors: Antoniou J. , Bergeles G.
Published: November 2009

Velocity and turbulence measurements are presented for the region after reattachment behind a two dimensional surface-mounted prism of varying length. The prism is mounted on the floor of an open circuit blow down wind tunnel and flow parameters for the developing boundary layer are deduced from the measurements; longitudinal integral time and length scales are estimated through autocorrelations. Reattchment on top of the prism, due to its increased length, affects the characteristics of the developing boundary layer; in this case the shear layer originating from the up-stream edge of the prism splits twice at reattachment points on top and behind the prism and the integral length scales of the turbulent eddies are found to be smaller due to the splitting.
Thermally Induced Flow in a Rotating Annulus Filled With a Compressible Fluid
Authors: Ortega M. A. , Sielawa J. T.
Published: November 2009

The thermally induced flow field, in a rapidly rotating container consisting of a pair of coaxial cylinders bounded on the top and bottom by horizontal end plates, is considered. The top plate is heated and the bottom plate is cooled, both by small amounts, so that the thermal Rossby number is small, and the cylinders are supposed to be conductive. The induced velocity and temperature fields are determined by subdivision of the flow field; the equation for the central part, the inner core, is solved numerically as well as analytically.
Effect of Free-Stream Turbulence on Characteristics of Fluctuating Forces Acting on Two Square Prisms in Tandem Arrangement
Authors: Sakamoto H. , Haniu H.
Published: November 2009

The effect of the addition of the turbulence intensity to the free stream on the characteristics of the bistable flow which takes place around two square prisms in tandem arrangement was studied experimentally at a Reynolds number of 3.32 × 104. A method of obtaining the fluid forces acting on two prisms in the bistable flow regimes where two flow patterns appear intermittently was introduced, and then the characteristics of the fluid forces, the Strouhal number, and the switching frequency of the switch phenomenon with the variation of the freestream turbulence intensity were investigated. Furthermore, the behavior of the fluid forces and the vortex shedding for other spacings between the two prisms were presented for the variation of the turbulence intensity.
Deposition and Resuspension of Gas-Borne Particles in Recirculating Turbulent Flows
Authors: Reeks M. W. , Hall D.
Published: November 2009

This paper proposes an integro-differential equation to describe the decay of particle gas-borne concentration in recirculating turbulent flows which are fully mixed. Its application to the decay of gas-borne concentration for particles injected into the primary circuit of an Advanced Gas Cooled Reactor is considered. The novel aspect of this work is the way the resuspension following initial deposition is modeled.
Development of Rotational Speed Control Systems for a Savonius-Type Wind Turbine
Authors: Ogawa T. , Yoshida H. , Yokota Y.
Published: November 2009

An attempt is made here to increase the output of a Savonius rotor by using a flow deflecting plate. When the deflecting plate is located at the optimum position, the rotor power increases nearly 30 percent over that when no deflecting plate is present. The rotor torque was found to become almost zero, when the plate is placed just in front of the rotor. In addition, two systems to control the rotational speed of a Savonius rotor are developed. These permit the rotor to be stopped in strong wind. Operating characteristics of the two control systems are investigated.
Numerical Computation of Turbulent Flow in a Square-Sectioned 180 Deg Bend
Authors: Choi Y. D. , Iacovides H. , Launder B. E.
Published: November 2009

Fine-grid computations are reported of turbulent flow through a square sectioned U-bend corresponding to that for which Chang et al. (1983a) have provided detailed experimental data. A sequence of modeling refinements is introduced: the replacement of wall functions by a fine mesh across the sublayer; the abandonment of the PSL approximation (in which pressure variations across the near-wall sublayer are neglected); and the introduction of an algebraic second-moment (ASM) closure in place of the usual k–ε eddy-viscosity model. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation. Direct comparisons with the measured rms turbulent velocity give further support to the view that the ASM scheme achieves a generally satisfactory description of the Reynolds stress field. Even with the most refined model some discrepancies between the experiment and computed development are apparent. It is suggested that their removal may require the use of a turbulent transport model in the semi-viscous sublayer in place of the van Driest (1956) mixing-length treatment used at present.
Studies on Two-Dimensional Curved Nonbuoyant Jets in Cross Flow
Authors: Haniu H. , Ramaprian B. R.
Published: November 2009

An experimental study of two-dimensional, curved, heated (but essentially non-buoyant) jets is reported. The experiments were conducted in a hydraulic flume in which a curved jet was produced by injecting a plane jet of slightly heated water vertically upwards in to a small cross flow. The data presented include mean and turbulent flow properties obtained from the measurement of instantaneous velocity and temperature, using two-component Laser Doppler Anemometry (LDA) and microresistance thermometry. The measurements extended over the near-to-intermediate field, namely, y/D < 60, where y is the distance along the flume and D is the width of the jet at the exit. The study has demonstrated the stabilizing effects of streamline curvature in the inner (lower) portion and the destabilizing effects of curvature and the coflowing ambient in the outer (upper) portion of the curved jet in cross flow. The quantitative effects on the mean and turbulent properties are presented and discussed in this paper.
Effect of 90 Degree Flap on the Aerodynamics of a Two-Element Airfoil
Authors: Katz J. , Largman R.
Published: November 2009

The aerodynamic performance of a two-element airfoil with a 90 deg. trailing edge flap was experimentally investigated. The 5 percent-chord long flap, significantly increased the lift of the baseline airfoil, throughout a wide range of angles of attack. The maximum lift coefficient of the flapped wing increased too, whereas the lift/drag ratio decreased.
A New Model for Leakage Prediction in Shrouded-Impeller Turbopumps
Authors: Baskharone E. A. , Hensel S. J.
Published: November 2009

The swirling secondary flow in the shroud-to-housing passage of a turbopump stage is analyzed. The flow model is based on the weighted-residual finite-element method to solve the axisymmetric flow field in this passage. A unique feature of the present analysis is the inclusion of two primary flow segments in the definition of the solution domain. This allows full interaction between the primary and secondary flow streams and alleviates what would otherwise be an iterative procedure to calculate the leakage flow rate. Full ellipticity of the flow field throughout the entire domain is maintained for accurate modeling of separation and recirculation zones. Applicability of the computational model to generally shaped secondary flow passages is illustrated through a sample pump that is similar to the boost-impeller stage in the oxidizer turbopump of the U.S. Space Shuttle Main Engine. The secondary flow field in this case is investigated over a range of Reynolds number.
Flow About a Circular Cylinder in and Near a Turbulent Plane Mixing Layer
Authors: Kiya M. , Tamura H.
Published: November 2009

This paper deals with an experimental study of the fluid forces, surface pressure, and vortex-shedding frequency of a circular cylinder placed in and near a turbulent plane mixing layer with zero velocity ratio. These characteristics are given as functions of the cylinder diameter d divided by the local mixing-layer width δ and the nondimensional transverse coordinate of the center of the cylinder in a Reynolds number range 5500–46000. For the cylinder d/δ = 2.2–2.3 the r.m.s. lift attained a maximum 40 percent higher than that in the uniform flow when a part of the cylinder surface was near an intermittently turbulent edge on the high-velocity side of the mixing layer; the time-mean resultant force attained a sharp maximum as high as 80 percent of that in the uniform flow when the axis of the cylinder was located at the center of the mixing layer. The former maximum was interpreted in terms of a vortex-body interaction while the latter maximum was found to be associated with a large delay of the boundary-layer separation on the low-velocity side of the cylinder.
Experimental Study of the Aerodynamic Interaction Between an Enclosed-Wheel Racing-Car and Its Rear Wing
Authors: Katz J. , Largman R.
Published: November 2009

A quarter-scale model of an enclosed wheel racing car was tested using the elevated ground plane wind tunnel technique. To increase the aerodynamic down force, two longitudinal underbody channels were built into the vehicle’s lower surface, and a rear wing was added. The effect of these underbody channels, and of wing angle of attack and position, on the vehicle’s drag and down force was experimentally investigated. Results of the experiments indicate that the flow under the car is affected by the presence of the wheels, and the vehicle without a rear wing generates only a negligible downforce. However, the addition of a rear wing enhanced the flow under the vehicle body, resulting in an increased aerodynamic downforce.
Measurements of the Flow and Turbulence Characteristics of Round Jets in Crossflow
Authors: Sherif S. A. , Pletcher R. H.
Published: November 2009

Measurements of the velocity and turbulence characteristics of a round turbulent jet in crossflow are reported. The experiments were conducted in a water channel, 8.53 m long, 0.61 m wide, and 1.067 m deep, of the recirculation type. Water was injected vertically upward from a circular pipe located near the channel bottom to simulate the turbulent jet. Normal and 45 deg-slanted fiber-film probes along with appropriate anemomenters and bridges were operated in the constant temperature mode to measure mean velocities, turbulence intensities, Reynolds stresses, structural parameters, correlation coefficients, and the turbulent kinetic energy. The measurements were carried out in the jet and its wake both in and outside the jet plane of symmetry. Details of the jet-wake cross section (including the vortex region) were revealed at a number of downstream locations using constant velocity and turbulence intensity contours.
Application of Computer Modeling in the Design of a Multiphase Flow Metering System
Authors: Sharma M. P. , Crowe C. T.
Published: November 2009

Two numerical models (CONVAS and PSI-Cell) for analyzing steady non-equilibrium gas-particle flow through a venturi and an orifice plate are discussed. These models are validated by comparing the predictions with experimental data. Utilizing these models, parametric curves for venturis and orifice plates have been generated. Using these curves a methodology has been outlined for designing a two-phase mass flowmeter.
Comparison of a Cavitation Susceptibility Meter and Holography for Nuclei Detection in Liquids
Authors: d’Agostino L. , Pham T. , Green S.
Published: November 2009

This work compares the results obtained from a Cavitation Susceptibility Meter (CSM) and from direct holographic observations for the detection of cavitation nuclei in tap water samples. The CSM uses a cavitating venturi tube to measure the concentration of active cavitation nuclei as a function of the pressure at the venturi throat, while the holographic system measures the nuclei concentration size distribution. Microbubbles are used as the dominant type of cavitation nuclei. The data from the two nuclei detection methods are then compared and interpreted in view of the expected dynamic behavior of microbubbles in the CSM venturi throat. Both results show that the concentration of active cavitation nuclei initially increases exponentially with the applied tension, reaches a maximum and remains nearly constant thereafter when few additional nuclei are left to cavitate. In its current configuration the CSM tends to underestimate the concentration of active cavitation nuclei and to overestimate the value of the nuclei critical pressure as a consequence of sensitivity limitations and interference effects between the cavities.
A Multi-Sensor Hot-Wire Probe to Measure Vorticity and Velocity in Turbulent Flows
Authors: Vukoslavc˘evic´ P. , Balint J.-L. , Wallace J. M.
Published: November 2009

The design and construction of a miniature hot-wire probe capable of simultaneously measuring all components of the velocity and vorticity vectors in turbulent flows are presented. A brief description of the probe resolution and calibration as well as the procedure to solve the cooling equations are given. Preliminary testing in the irrotational region of the flow shows that the spurious vorticity obtained from the probe due to system measurement error does not exceed 8 percent of the RMS vorticity fluctuation levels measured over the region y+ = 15 − 45 in a turbulent boundary layer.
Experimental Research of the Effects of Sweep on Unsteady Hydrofoil Loadings in Cavitation
Authors: Ihara A. , Watanabe H. , Shizukuishi S.
Published: November 2009

An experiment was conducted to investigate the effects of sweep angle on hydrofoil loadings in cavitation. Tests were carried out in a water tunnel on constant-chord full-span hydrofoils at four angles of attack for sweep angle 0, 15, 30, and 45 deg, respectively. The results obtained were that the strong, periodic oscillations which appeared under some conditions of partial cavitation decreased their amplitudes with an increase in sweep angle. Moreover, the lift-drag ratio showed the higher value for the highly swept hydrofoil and remained higher down to some lower cavitation numbers than those for the slightly swept model.
The Synergistic Effect of Cavitation Erosion and Corrosion for Copper and Cupro-Nickel in Seawater
Authors: Wood R. J. K. , Fry S. A.
Published: November 2009

Experiments are described in which attempts have been made to investigate the fundamental mechanisms of the synergistic effect of cavitation erosion and corrosion. The design of an all-plastic cavitation tunnel is described which allows specimens to be held under potentiostatic control in a flowing seawater system. Experiments were conducted in a 10 × 20 mm working section with a 60° symmetrical wedge cavitation source at an upstream flow velocity of 14.7 m/s. An extensive test programme has been completed comprising three separate tests: Pure Erosion, Pure Corrosion and Combined Erosion and Corrosion, each conducted at two different cavitation intensities. These tests have concentrated on investigating the erosion/corrosion performance of copper in seawater. Preliminary results using cupro-nickel are also reported. It was found that a clearer indication of the synergistic effect was obtained from depth of penetration measurements than from mass loss measurements. The synergistic effect was found to be most marked when cavitation erosion occurs in the presence of mild corrosion. For the worse case studied, 50 percent of the depth of penetration was caused by synergistic mechanisms.
A Portable Slurry Wear Test for the Field
Authors: Madsen B. W.
Published: November 2009

A new portable slurry wear test apparatus developed by the Bureau of Mines, U.S. Department of the Interior, makes it possible to gather materials wear and corrosion data at a mineral processing site. The portable wear cell is identical in design to a laboratory cell reported previously. It allows simultaneous evaluation of 16 specimens in a continuous flow of fresh slurry. Data obtained from selected metals and polymers showed high-chromium white cast irons to perform particularly well in tests with an aqueous lead-zinc sulfide ore slurry. However, ultra-high-molecular-weight polyethylene that exhibited superior wear resistance in comparable laboratory tests with an aqueous slurry of silica sand did not perform as well in field tests. Such results show how misleading it can be to use laboratory data to predict relative rates of wear in industrial slurries, even under nominally identical flow conditions. Field testing is therefore needed. In situ electrochemical corrosion measurements on a low-alloy steel showed that the field and laboratory slurries were similarly corrosive.
Flow Speed Measurement and Rheometry by Pulsed Neutron Activation
Authors: Porges K. G. A. , Cox S. A. , Herzenberg C. , Kampschoer C.
Published: November 2009

Pulsed Neutron Activation (PNA) is a means of noninvasive flow velocity measurement based on tagging the flowing medium with a short-lived radioactivity. Previous work with salt or dye-tagging showed poor accuracy in turbulent and failed in laminar flow when conventional data processing was used. However, use of a data acquisition and processing scheme that is based on tag dispersion modelling can produce absolute values over a wide range of flow speeds and regimes with high accuracy. For non-Newtonian/laminar flow, rheological information can also be obtained. The inherently non-intrusive nature of PNA tagging makes this scheme available for slurry measurements. The performance of PNA in slurry flow at up to 60 percent solid content was compared to full-flow diversion and weighing. Errors ranged from less than 0.2 percent at high Reynolds’ numbers to about 2 percent for paste flow. Rheological parameters (yield shear stress or flow behavior index) could be determined with an accuracy that compared to that of a spindle viscometer with grab-samples. The PNA scheme thus offers a unique means of studying slurry flow in a dedicated laboratory facility, or of providing calibration for other flowmeters in an industrial plant through temporary installation by a team of expert consultants.
Determination of Surface Pressure Distributions for Axisymmetric Bluff Bodies
Authors: Nelson D. A. , Evers L. W. , O’Donnell D. M. , Morgan E. J.
Published: November 2009

The conditions governing liquid droplet breakup are particularly important to the process of fuel atomization for spark-ignition engines. A proper mathematical description of the problem requires knowledge of the pressure distributions about the droplet surface. This work presents the results of measurements of pressure distributions about the surfaces of certain bluff, axi-symmetric bodies in airflows at ReD = 3 × 104 and ReD = 105. The results of measurements from a sphere, disk, and two ellipsoids are used to develop a general method for estimating surface pressures. These estimates are compared with the results of pressure measurements about the surfaces of a concave and a nonellipsoidal convex body and with results obtained from a numerical study by other authors.
Hot-Wire Measurements Inside a Centrifugal Fan Impeller
Authors: Kjo¨rk A. , Lo¨fdahl L.
Published: November 2009

Measurements of the three mean velocity components and five of the Reynolds stresses have been carried out in the blade passage of a centrifugal fan impeller. The impeller was of ordinary design, with nine backward curved blades, and all measurements were carried out at the design flow rate. The mean velocity measurements show that the flow can be characterized as an attached flow with almost linearly distributed velocity profiles. However, in a region near the suction side close to the shroud a low velocity region is created. From the turbulence measurements it can be concluded that relatively low values of the turbulent stresses are predominating in the center region of the channel. Closer to the walls higher values of the normal as well as shear stresses are noted.
Secondary Flows in a Transonic Cascade: Comparison Between Experimental and Numerical Results
Authors: Bassi F. , Osnaghi C. , Perdichizzi A. , Savini M.
Published: November 2009

The paper presents a comparison between numerical results and experimental data about the secondary flow development in a linear transonic turbine cascade. Computations are carried out by using a three-dimensional inviscid Euler code, based on a Runge-Kutta explicit finite volume method. The experimental inlet total pressure distribution is imposed as inlet boundary condition to simulate the incoming endwall boundary layer. The comparison is made in four planes downstream of the cascade where detailed experimental data obtained in a transonic wind tunnel are available. For each of these planes secondary velocities and streamwise vorticity contour plots are presented and discussed. Moreover pitchwise mass averaged flow angle distributions showing overturning and underturning regions are shown. The comparison shows that an Euler code can predict the essential features of secondary flow phenomena like passage vortex location and intensity but a certain disagreement is found in the overturning and underturning angles evaluation. Numerical results also allow for the investigation of the development of secondary flows inside the blade channel. The investigation is carried out for three different Mach numbers: M2is = 0.5, 1.02, 1.38, in order to show the influence of compressibility on the flow vortex structure.
Radial, Turbulent Flow of a Fluid Between Two Coaxial Disks
Authors: Ervin J. S. , Suryanarayana N. V. , Ng Hon Chai
Published: November 2009

An experimental study to determine the flow characteristics of an incompressible fluid in turbulent, radially outward flow between two coaxial, stationary disks was conducted employing a split film anemometer probe. Instantaneous velocity components in the radial and axial directions were measured; from these measurements, average velocity profiles, turbulence intensities, Reynolds stresses, energy spectra and probability density functions for the fluctuating components were computed. It is observed that the law of the wall may not be applicable everywhere. A criterion established earlier for reverse transition to laminar flow may be valid with a value of the constant smaller than suggested. A few other aspects of the flow are also discussed.
Three-Dimensional Particle Tracking Velocimetry Based on Automated Digital Image Processing
Authors: Nishino Koichi , Kasagi Nobuhide , Hirata Masaru
Published: November 2009

A three-dimensional particle tracking velocimeter for measuring an instantaneous distribution of all the three velocity components in a liquid flow is developed using an automated digital image processing technique. The measurement system consists of three TV cameras, a digital image processor, a laser disk recorder and a 16-bit microcomputer. Motions of neutrally buoyant tracer particles introduced into the flow field are observed by the cameras, and the three-dimensional displacement of each particle is calculated from consecutive TV frames recorded on the laser disk. Instantaneous velocity profiles in an unsteady laminar Couette flow between two concentric cylinders are measured. The results are in good agreement with predictions within the measurement uncertainties evaluated systematically. Furthermore, the measurement of a decaying turbulence in a stirred water tank demonstrates that the present technique is applicable to turbulent flows.
Aerodynamic Torque Characteristics of Butterfly Valves in Compressible Flow
Authors: Morris M. J. , Dutton J. C.
Published: November 2009

The results of an experimental investigation of the aerodynamic torque characteristics of butterfly valves under compressible flow conditions are reported. Both three-dimensional prototype valves and two-dimensional planar models have been studied at choked and unchoked operating points. Other parameters investigated include the operating pressure ratio across the valve, the valve disk angle, and the disk shape. The results demonstrate the importance of flow separation and reattachment phenomena on the valve aerodynamic torque characteristics, the importance of disk shape at intermediate angles, and the sensitivity of the torque to the valve disk geometry near the leading and trailing edges where extreme pressure gradients can occur.
Bistable Flow Patterns in a Free Surface Water Channel
Authors: Adams E. W. , Stamou A. I.
Published: November 2009

A series of experiments is reported on a free surface water tunnel with a slot inlet centered at mid-depth in which the flow exhibited equally probable bistable flow patterns. The two flow fields are strongly asymmetric even when the geometry is symmetric and consists of a long stall on one side of the inlet and a short stall on the opposite side. Flow visualization and laser-Doppler velocimetry were performed to examine the flow structure of both stable states in detail. Results showed that the mean flow and turbulence structure of the two bistable states are largely mirror images of each other within the separation zone. The effect of the wall on the flow is minor, only very close to the wall/free surface did the difference in wall constraints cause the two flow patterns to diverge. After reattachment both flows relax to free-surface channel flow. It is shown that the bistable flow pattern results from the interaction of the free shear layers and that only strong disturbances in the free shear layers can cause the flow in one stable state to switch to the other stable state. Bistable flow exists for geometries with asymmetry up to 10 percent for the expansion ratio studied.
Supplementary Boundary-Layer Approximations for Turbulent Flow
Authors: Thomas L. C. , Hasani S. M. F.
Published: November 2009

Approximations for total stress τ and mean velocity u are developed in this paper for transpired turbulent boundary layer flows. These supplementary boundary-layer approximations are tested for a wide range of near equilibrium flows and are incorporated into an inner law method for evaluating the mean wall shear stress τ0. The testing of the proposed approximations for τ and u indicates good agreement with well-documented data for moderate rates of blowing and suction and pressure gradient. These evaluations also reveal limitations in the familiar logarithmic law that has traditionally been used in the determination of wall shear stress for non-transpired boundary-layer flows. The calculations for τ0 obtained by the inner law method developed in this paper are found to be consistent with results obtained by the modern Reynolds stress method for a broad range of near equilibrium conditions. However, the use of the proposed inner law method in evaluating the mean wall shear stress for early classic near equilibrium flow brings to question the reliability of the results for τ0 reported for adverse pressure gradient flows in the 1968 Stanford Conference Proceedings.
Shear-Driven Flow in a Porous Cavity
Authors: Hamdan M. H. , Barron R. M.
Published: November 2009

The shear-driven cavity flow is studied when the cavity is assumed to contain a porous material. A finite difference solution is obtained for the flow in a rectangular cavity for various cavity aspect ratios and permeability values. The effect of these parameters on the flow, and in particular on the development of corner eddies is illustrated.
Boundary Layer Measurements at an Internal Free Surface in a Partially Filled Horizontal and Rapidly-Rotating Container
Authors: Singler T. J.
Published: November 2009

Steady flow in a partially filled horizontal circular cylinder rotating rapidly about its symmetry axis is investigated experimentally. Radial boundary layer profiles of the azimuthal velocity in the neighborhood of the internal free surface are reported for a range of inverse Froude numbers and for two types of free surfaces. Results indicate good agreement with an existing theory.
Characteristics of Tip Vortex Cavitation Noise
Authors: Higuchi H. , Arndt R. E. A. , Rogers M. F.
Published: November 2009

Tip vortex cavitation noise was experimentally investigated utilizing hydrofoils with an elliptic planform. The noise was monitored by an array of hydrophones. A variety of cavitating conditions were studied, including inception, fully developed vortex cavitation, and surface cavitation. An analysis of noise source distribution indicated that sound at cavitation inception is radiated from either just downstream of the vortex roll-up region or right at the tip of the hydrofoil where the vortex cavity intially develops.
Strategies for Fatigue Design of Deepwater Platforms
Authors: Marshall P. W.
Published: November 2009

After reviewing strategies used for designing the 1000-ft Cognac platform, this paper will describe recent developments, which have been applied to preliminary designs of fixed platforms in up to 1600 ft of water, and to compliant towers in 2000 ft. The first is a strategy in which the waterline geometry and tower dimensions are coordinated so as to minimize wave forces at the natural frequency. This was first suggested by John Nath in 1967, and has come to be known as the “Nath hole” strategy [1]. The second is rationalization of allowable hot spot stress in terms of the Weibull shape parameter, “squiggly.” For structures which have been optimized as described in the foregoing, the trend of fatigue versus natural period can be much less severe than described by the author at the BOSS-82 conference [2].
Tradeoffs in Optimization of Deepsea Electro-Optical Cables
Authors: Wilkins G.
Published: November 2009

The efficient use of optical fibers for telemetry in a deepsea tether cable requires that interactions of such telemetry with the total system be examined and carefully optimized. For example, telemetry bandwidth and system power will no longer be closely coupled as they are in a coaxial cable. In the electro-optical (E-O) cable, power cannot ride free on the back of the large dielectric and copper cross sections needed for conventional coaxial telemetry. Instead, power transfer can (and should) be treated independently at the system level—in simple terms of its own penalties and benefits to the total system. The term “optimum” means much more than increased bandwidth; although that can grow by at least an order of magnitude. It also means increased cable strength, reduced cable diameter, more efficient power transfer and longer cable flexure life. To achieve these, it may be necessary to assign multiple roles to critical cable components. For example, the electrical conductor(s) may also be tasked to supply a fraction of the cable’s strength, or to serve as protective enclosures around the optical fiber(s). In this paper design tradeoffs are evaluated for three types of E-O cables—with 1, 2 and 3 electrical conductors.
Viscous Forces Acting on Irregularly Oscillating Circular Cylinders and Flat Plates
Authors: Ikeda Y. , Osa K. , Tanaka N.
Published: November 2009

In the present paper hydrodynamic forces acting on oscillating circular cylinders as well as flat plates perpendicular to the motion in regular and irregular modes due to vortex shedding are experimentally investigated in order to clarify the memory effect or history effect on the hydrodynamic forces. The experimental results for sinusoidal motion show that the drag and added mass coefficients in steady-state condition are significantly different from those of the first swing from the start because of the existence of old vortices generated in the previous cycles around the cylinder. It is found from the experiments in irregular modes that the drag and added mass coefficients significantly vary every swing. It is confirmed that these coefficients during a swing depend on the relative amplitude or the Keulegan-Carpenter number of the previous swings as well as that of the swing under consideration.
Elasto-Plastic Response of Pipes Under External Pressure and Bending
Authors: Tay C. J. , Toh S. L.
Published: November 2009

The collapse of thin cylindrical pipes subject to combined bending moment and external pressure has been studied. Nonlinear finite deflection thin shell theory is employed in the elastic solution. The analysis is extended to include the plastic behavior with the assumption of linear work-hardening material. Results are presented for various geometric material and load configurations.
Whole-Field Measurement of Ice Displacement and Strain Rates
Authors: Conley E. , Cloud G.
Published: November 2009

The flow of glacier ice is mapped using high-resolution photography and noncoherent light speckle interferometry. Time-lapse, double-exposures of a straining surface yield Young’s fringes when the resulting image is interrogated by a narrow beam of coherent light. Such fringe patterns, when corrected for camera motion, are indicative of the surface displacement occurring between exposures. Results of glacier field experiments are consistent with those garnered by conventional methods at the Nisqually Glacier, Washington. The interferometric method seems amenable to other geophysical applications, such as mapping sea ice flow, using terrestrial or space-based camera platforms.
Nowcasting Sea Ice Movement Through the Bering Strait
Authors: Kozo T. L. , Stringer W. J. , Torgerson L. J.
Published: November 2009

Geostrophic wind velocities were calculated using atmospheric pressure data from Bering Strait stations at Uelen (Siberia), Bukhta Provideniya (Siberia) and Nome (Alaska). These velocities were matched to Strait sea ice displacements derived from satellite imagery (1974–1984), resulting in an all-weather ice movement and now-casting model. Also, five ice displacement modes were identified. The first mode is Chukchi to Bering Sea movement when northeasterly winds exceed 11.5 m/s. The second and third modes are Bering to Chukchi Sea movement. Mode two is driven by a pre-existing north-flowing ocean current during weak opposing winds. Mode three is due to winds and currents acting in concert. The first immobilization mode (maximum duration one week) is an apparent balance between northerly wind stress, water stress from the south, and internal ice stresses. The second immobilization mode is due to large, double, solid ice arches jamming the Strait up to four weeks.
Plunging Wave Forces on Surface-Piercing Structures
Authors: Chan E.-S. , Melville W. K.
Published: November 2009

An experimental study of deepwater plunging wave loads on vertical walls and cylinders is reported. Simultaneous measurements of the forces and pressures are obtained. The characteristics of the impact loads are presented and the scaling of pressures from model results to prototype scales is discussed. Overall, the characteristics of forces and pressures vary systematically with the structure’s location relative to the wave-breaking location. Impacts on cylinders are similar to those on a flat plate; however, the presence of the wall has a larger influence on the dynamics of impact compared to that of the cylinder.
Random Extreme Wave Analysis of Deepwater Structures
Authors: Chen C. Y. , Armbrust S. , Llorente C.
Published: November 2009

This paper reviews various wave analysis procedures for designing deepwater structures under an extreme seastate. The random wave analysis procedures suitable for fixed stiff platforms and compliant towers are discussed. The random wave analysis procedures are then applied to a 1350-ft water depth fixed platform. The reduction in design force levels due to random waves is indicated by comparing with the conventional regular wave analysis approach. The second harmonic effects due to waves can be easily identified through the dynamic response spectrum which has two peaks occurring at the peak frequency of the input wave spectrum and the natural frequency of the structure. The study also shows that the expected extreme value estimated based on the upcrossing approach agrees well with the snapshot peak response derived from a wave record containing an extreme wave height.
The Effect of Sub-Surface Irregularities on the Strength of
Multi-Year Ice
Authors: Hallam S. D. , Jones N. , Howard M. W.
Published: November 2009

Presented in this paper is a simple two-dimensional model to examine the effects of sub-surface irregularities on the strength of multi-year ice. The irregularities cause bending moments which can lead to surface tensile stresses. When these tensile stresses are sufficiently high for crack nucleation to occur, a very brittle fracture of the entire ice sheet will ensue. The fracture is brittle because, for the large grain sizes in the natural ice cover, the stress required for crack nucleation is greater than that necessary to propagate a crack. The theory has been examined with experimental laboratory tests on columnar ice. The importance and significance of the results are that old thick multi-year ice in winter conditions may be substantially weaker than expected, and thus it is the limited strength of the multi-year ice that may dominate design ice forces on arctic structures rather than a limited driving force.
Softening of the Clayey Seabed Foundation due to Earthquakes
Authors: Mori N. , Ishikawa Y. , Hirayama A. , Tamaoki K. , Kobayashi H.
Published: November 2009

Offshore structures are subjected to repeated loads from earthquakes and waves which may cause softening of the clayey seabed foundation. Carrying out a series of model tests on a shaking table, the following results are obtained. Settlement and inclination of a model of the base-part of the structure occur when the excess pore water pressure beneath the model rises to about 5 percent of the initial confining pressure. The earthquake response analysis even taking the nonlinearity of the soil into account cannot predict the results of the model test when the pore water pressure does generate and accumulate. Model tests show that the values of the pore water pressure are about twice as large as those predicted by calculation. From these results, rough evaluation of earthquake stability of the clayey seabed under offshore structures are obtained.
A Simplified Treatise on the Effect of Wear in Cables
Authors: Velinsky S. A. , Schmidt J. D.
Published: November 2009

Cables and wire ropes are known to both elongate and reduce diametrically during their lifetime. The relationship between cable elongation and cable life has been observed for many years and includes three distinct stages. The first, the constructional stretch stage, occurs early in the cable’s use and is mostly the result of the core compressing and the cable elements fitting closely together. The second stage of the cable’s life is referred to as the normal life stretch stage and is a much more gradual occurrence in which wear is the most dominant mechanism. The third stage includes a rapid elongation and indicates impending failure. The current study offers a simplified explanation on the effect of wear in cables. This work utilizes the recently developed theory for wire ropes and cables in which the cable is considered to be a collection of thin helical wires and the equations of equilibrium for bending and twisting of thin rods are applied. A simple cable cross section is considered and the effects of wear on cable stiffness, diameter reduction and individual wire strains are evaluated. It is determined that cable stiffness can actually increase for small amounts of wire wear due to the disparity between the changes in the geometric and elastic stiffness components with wear.
Analysis of Brief Tension Loss in TLP Tethers
Authors: Brekke J. N. , Gardner T. N.
Published: November 2009

The avoidance of “slack” tethers is one of the factors which may establish the required tether pretension in a tension leg platform (TLP) design. Selection of an appropriate safety factor on loss of tension depends on how severe the consequences may be. It is sometimes argued that if tethers go slack, the result may be excessive platform pitch or roll motions, tether buckling, or “snap” or “snatch” loading of the tether. The results reported here show that a four-legged TLP would not be susceptible to larger angular motions until two adjacent legs lose tension simultaneously. Even then, this analysis shows that a brief period of tether tension loss (during the passage of a large wave trough) does not lead to excessive platform motion. Similarly, momentary tension loss does not cause large bending stress in the tether or significant tension amplification as the tether undergoes retensioning. This paper presents TLP platform and tether response analysis results for a representative deepwater Gulf of Mexico TLP with large-diameter, self-buoyant tethers. The time-domain, dynamic computer analysis included nonlinear effects and platform/tether coupling.
Helical Wire Stresses in Bent Cables
Authors: Knapp R. H.
Published: November 2009

An approximate theory is developed to determine the compound stress state existing in helical wires of a cable bent through a planar circular arc. Approximations arise through the treatment of the frictional interface between layers of wires. Furthermore, all materials are assumed to be linearly elastic. The model does, however, recognize geometric nonlinearities in terms of the strain-displacement relations for wire elongation and curvature. The theory presented reveals the nature of axial, bending and torsional shearing stresses produced in round helical wires. Comparisons with experimental data show reasonable agreement.
Nonlinear Wave Forces Acting on Submerged Horizontal Cylinders
Authors: Inoue R. , Kyozuka Y.
Published: November 2009

This paper is to present experimental results of the first and second-order wave forces acting on three kinds of horizontally submerged cylinders. Wave height, wave frequency and the models’ submergence were varied in the experiments. These results are compared with the numerical calculations based on the regular perturbation theory. Through this study, it was found that the calculations of both the first and second-order wave forces coincide with the experiments when the cylinders are submerged at a sufficient depth. However, in the case that the cylinders are close to the free surface and/or wave amplitudes are relatively large, the experimental results become small compared with the calculations because of nonlinear effects, such as wave breaking observed in the experiments.
Three-Dimensional Analysis of Ice Sheet Indentation: Lower-Bound Solutions
Authors: Karr D. G.
Published: November 2009

The methods of plastic limit analysis are used to determine the indentation pressures of a flat rigid punch on a columnar ice sheet. The ice sheet is idealized as a semi-infinite layer of elastic-perfectly plastic material. Representative strength parameters of columnar sea ice are used to define anisotropic yield criteria for the ice sheet. The anisotropic yield criteria reflect the variations in mechanical properties caused by the horizontal orientation of the c-axis of sea ice in the columnar zone. Numerical results are obtained by applying the lower-bound theorem of plastic limit analysis. A three-dimensional stress field is optimized for a given ice condition for various indentor sizes. The effects of varying the aspect ratio (defined as the ratio of indentor width to ice thickness) are then addressed. A comparison of results for intermediate aspect ratios to results for extremely high (plane stress) and extremely low (plane strain) aspect ratios is presented. It is found that the transition from plane stress to plane strain is governed by the tensile strength of the ice medium.