Vertical Relative Motion Between Two Adjacent Platforms in Oblique Waves

1985 ◽  
Vol 107 (4) ◽  
pp. 455-460 ◽  
Author(s):  
C. H. Kim ◽  
M. C. Fang
Keyword(s):  
Relative Motion ◽  
Hydrodynamic Interaction ◽  
Two Dimensional ◽  
Oblique Waves ◽  
Strip Method ◽  
Strip Theory ◽  
Close Proximity ◽  
Relative Motions

The paper presents a strip theory and its correlation with experiment and analysis on the relative motions of two ships. The ships are in close proximity and in parallel position in oblique waves. The two-dimensional procedure takes account of the hydrodynamic interaction between two cylindrical bodies. It was found that the strip method is a useful technique to predict the hydrodynamically coupled motions of two ships.

Transient Analysis of Hydrodynamic Interaction Effects on an Autonomous Underwater Vehicle in Proximity of a Moving Submarine

2015 ◽  
Vol 157 (A4) ◽  
pp. 205-218
Keyword(s):  
Relative Motion ◽  
Transient Analysis ◽  
Hydrodynamic Interaction ◽  
Autonomous Underwater Vehicle ◽  
Underwater Vehicle ◽  
Cfd Simulations ◽  
Close Proximity ◽  
Computational Fluid Dynamics Cfd ◽  
Submarine Hull ◽  
Hull Forms

"When an Autonomous Underwater Vehicle (AUV) is operating close to a moving submarine, the hydrodynamic interaction between the two vehicles can prevent the AUV from maintaining its desired trajectory. This can lead to mission failure and, in extreme cases, collision with the submarine. This paper outlines the transient interaction influence on the hydrodynamic coefficients of an AUV operating in close proximity and in relative motion to a larger moving submarine. The effects of relative motion on the interaction behaviour were investigated via two manoeuvres, i.e. the AUV overtaking and being overtaken by the submarine at different relative forward velocities and lateral distances. The results presented are from a series of Computational Fluid Dynamics (CFD) simulations on axisymmetric AUV and submarine hull forms, with validation of the CFD model carried out through scaled captive model experiments. The results showed that an AUV becomes less susceptible to the interaction influence when overtaking at speeds higher than the submarine. The implications of the interaction influence on the AUV’s ability to safely manoeuvre around the submarine are also discussed."

The Motions of Adjacent Floating Structures in Oblique Waves

1984 ◽  
Vol 106 (2) ◽  
pp. 199-205 ◽  
Author(s):  
N. Kodan
Keyword(s):  
Hydrodynamic Interaction ◽  
Diffraction Theory ◽  
Added Mass ◽  
Exciting Force ◽  
Irregular Waves ◽  
Two Dimensional ◽  
Oblique Waves ◽  
Floating Structures ◽  
The Relationship ◽  
Good Agreement

This paper describes the theory on the effects of hydrodynamic interaction between two parallel slender structures in oblique waves. The method is based on the two-dimensional diffraction theory including the interaction effect. According to Ohkusu’s theory, the sectional interaction effects on the added mass, damping coefficient and wave exciting force are evaluated by analyzing incoming waves generated by the oscillatory motion of corresponding sections. Numerical results of the wave exciting force and moment and motions for the case of a combination of a ship and a rectangular barge are presented and compared with the results from model experiments. The comparison shows good agreement. Finally, some attention is given to the relationship between the arrangement of the two structures and responses in irregular waves.

Hydrodynamically Coupled Motions of Two Ships Advancing in Oblique Waves

1986 ◽  
Vol 30 (03) ◽  
pp. 159-171
Author(s):  
M. C. Fang ◽  
C. H. Kim
Keyword(s):  
Integral Equation ◽  
Interaction Effect ◽  
Hydrodynamic Interaction ◽  
Integral Equation Method ◽  
Analytical Investigation ◽  
Rolling Motion ◽  
Two Dimensional ◽  
Oblique Waves ◽  
Slender Bodies ◽  
Wave Induced

An analytical investigation is carried out on the wave-induced motions on two closely spaced, hydrodynamically interacting slender bodies advancing in oblique waves. The two-dimensional procedure, including the hydrodynamic interaction and an integral equation method, is utilized. Numerical results are presented for the coupled motions of two ships. Comparisons are made with the behavior of a monohull and the interaction effect is found to be very important. Different headings and speeds are investigated. It has been found that the rolling motion is reduced while the ships are advancing—a helpful circumstance for cargo transfer between two ships. This study shows that the strip method is a useful technique to predict the hydrodynamically coupled motions between two ships advancing in oblique seas.

TRANSIENT ANALYSIS OF HYDRODYNAMIC INTERACTION EFFECTS ON AN AUTONOMOUS UNDERWATER VEHICLE IN PROXIMITY OF A MOVING SUBMARINE

2021 ◽  
Vol 157 (A4) ◽  
Author(s):  
Z Q Leong ◽  
D Ranmuthugala ◽  
I Penesis ◽  
H D Nguyen
Keyword(s):  
Relative Motion ◽  
Transient Analysis ◽  
Hydrodynamic Interaction ◽  
Autonomous Underwater Vehicle ◽  
Underwater Vehicle ◽  
Cfd Simulations ◽  
Close Proximity ◽  
Computational Fluid Dynamics Cfd ◽  
Submarine Hull ◽  
Hull Forms

When an Autonomous Underwater Vehicle (AUV) is operating close to a moving submarine, the hydrodynamic interaction between the two vehicles can prevent the AUV from maintaining its desired trajectory. This can lead to mission failure and, in extreme cases, collision with the submarine. This paper outlines the transient interaction influence on the hydrodynamic coefficients of an AUV operating in close proximity and in relative motion to a larger moving submarine. The effects of relative motion on the interaction behaviour were investigated via two manoeuvres, i.e. the AUV overtaking and being overtaken by the submarine at different relative forward velocities and lateral distances. The results presented are from a series of Computational Fluid Dynamics (CFD) simulations on axisymmetric AUV and submarine hull forms, with validation of the CFD model carried out through scaled captive model experiments. The results showed that an AUV becomes less susceptible to the interaction influence when overtaking at speeds higher than the submarine. The implications of the interaction influence on the AUV’s ability to safely manoeuvre around the submarine are also discussed.

The Aerodynamics of Three-Dimensional Vaned Diffusers in Industrial Centrifugal Compressors

2005 ◽  
Author(s):  
Ahmed Abdelwahab
Keyword(s):  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Three Dimensional ◽  
Pressure Recovery ◽  
Navier Stokes ◽  
Spanwise Direction ◽  
Two Dimensional ◽  
Blade Loading ◽  
Recovery Capacity ◽  
Close Proximity

Vaned diffusers have been used successfully as efficient and compact dynamic pressure recovery devices in industrial centrifugal compressor stages. Typically such diffusers consist of a cascade of two-dimensional blades distributed circumferentially at close proximity to the impeller exit. In this paper three low-solidity diffuser blade geometries are numerically investigated. The first geometry employs variable stagger stacking of similar blade sections along the blade span. The second employs linearly inclined stacking to generate blade lean along the diffuser span. The third geometry employs the conventional two-dimensional low-solidity diffuser geometry with no variable stagger or lean. The variable stagger blade arrangement has the potential of better aligning the diffuser leading edges with the highly non-uniform flow leaving the impeller. Both variable stagger and linearly leaned diffuser blade arrangements, however, have the effect of redistributing the blade loading and flow streamlines in the spanwise direction leading to improved efficiency and pressure recovery capacity of the diffuser. In this paper a description of the proposed diffuser geometries is presented. The results of Three-dimensional Navier-Stokes numerical simulations of the three centrifugal compressor arrangements are discussed. Comparisons between the performance of the two and three-dimensional diffuser blade geometries are presented. The comparisons indeed show that the variable stagger and leaned diffusers present an improvement in the diffuser operating range and pressure recovery capacity over the conventional two-dimensional diffuser geometry.

scholarly journals The influence of vortices upon the resitance experienced by solids moving through a liquid

1928 ◽  
Vol 119 (781) ◽  
pp. 146-156 ◽  
Keyword(s):  
Perfect Fluid ◽  
Relative Motion ◽  
Constant Velocity ◽  
Fluid Motion ◽  
Resultant Force ◽  
The Other ◽  
Two Dimensional ◽  
Perfect Fluids ◽  
Potential Problems ◽  
The Moment

(1) It is not so long ago that it was generally believed that the "classical" hydrodynamics, as dealing with perfect fluids, was, by reason of the very limitations implied in the term "perfect," incapable of explaining many of the observed facts of fluid motion. The paradox of d'Alembert, that a solid moving through a liquid with constant velocity experienced no resultant force, was in direct contradiction with the observed facts, and, among other things, made the lift on an aeroplane wing as difficult to explain as the drag. The work of Lanchester and Prandtl, however, showed that lift could be explained if there was "circulation" round the aerofoil. Of course, in a truly perfect fluid, this circulation could not be produced—it does need viscosity to originate it—but once produced, the lift follows from the theory appropriate to perfect fluids. It has thus been found possible to explain and calculate lift by means of the classical theory, viscosity only playing a significant part in the close neighbourhood ("grenzchicht") of the solid. It is proposed to show, in the present paper, how the presence of vortices in the fluid may cause a force to act on the solid, with a component in the line of motion, and so, at least partially, explain drag. It has long been realised that a body moving through a fluid sets up a train of eddies. The formation of these needs a supply of energy, ultimately dissipated by viscosity, which qualitatively explains the resistance experienced by the solid. It will be shown that the effect of these eddies is not confined to the moment of their birth, but that, so long as they exist, the resultant of the pressure on the solid does not vanish. This idea is not absolutely new; it appears in a recent paper by W. Müller. Müller uses some results due to M. Lagally, who calculates the resultant force on an immersed solid for a general fluid motion. The result, as far as it concerns vortices, contains their velocities relative to the solid. Despite this, the term — ½ ρq 2 only was used in the pressure equation, although the other term, ρ ∂Φ / ∂t , must exist on account of the motion. (There is, by Lagally's formulæ, no force without relative motion.) The analysis in the present paper was undertaken partly to supply this omission and partly to check the result of some work upon two-dimensional potential problems in general that it is hoped to publish shortly.

On the Heaving Motion of Cylinders of Shallow Draft

1961 ◽  
Vol 5 (04) ◽  
pp. 34-43
Author(s):  
R. C. MacCamy
Keyword(s):  
Integral Equations ◽  
Circular Disk ◽  
Finite Width ◽  
Two Dimensional ◽  
Virtual Mass ◽  
Method Of Integral Equations ◽  
First Approximation ◽  
Strip Theory ◽  
Considerable Simplification ◽  
Special Case

A perturbation procedure is developed for the two-dimensional motion produced by a long ship in heave when the draft is assumed small. The procedure reduces the shallow draft problem to a series of problems for a "raft" of zero draft. A considerable simplification in the method of integral equations is found to occur. For the first approximation, that is, a raft of finite width, the integral equations are solved numerically to determine pressure, virtual mass and damping. The problem of heave of a circular disk of zero draft is treated by the same methods so that an evaluation of strip theory in this special case is possible.

Prediction of Blade Flutter in a Tuned Rotor

1985 ◽  
Author(s):  
Jianmin Xu ◽  
Zhaohong Song
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Rotating Blades ◽  
Multiple Degrees Of Freedom ◽  
Strip Theory ◽  
Blade Flutter ◽  
Good Agreement

This paper is about blade flutter in a tuned rotor. With the aid of the combination of three dimensional structural finite element method, two dimensional aerodynamical finite difference method and strip theory, the quasi-steady models in which two degrees of freedom for a single wing were considered have been extended to multiple degrees of freedom for the whole blade in a tuned rotor. The eigenvalues solved from the blade motion equation have been used to judge whether the system is stable or not. The calculating procedure has been formed and using it the first stage rotating blades of a compressor where flutter had occurred, have been predicted. The numerical flutter boundaries have good agreement with the experimental ones.

Hydrodynamic Interaction Forces on Ship Hulls Equipped With Propulsors

2012 ◽  
Author(s):  
Serge Sutulo ◽  
C. Guedes Soares
Keyword(s):  
Pressure Distribution ◽  
Hydrodynamic Interaction ◽  
Potential Interaction ◽  
Interaction Forces ◽  
Ship Hulls ◽  
Actuator Disk ◽  
Close Proximity ◽  
Body Potential ◽  
Yaw Moment ◽  
Accelerating Motion

Typically, study of hydrodynamic interaction between vessels navigating in close proximity to each other is limited to hydrodynamics of bare hulls. Meanwhile, ship propulsors, especially heavily loaded, which may happen in accelerating motion, can alter substantially the flow and distribution of pressure on the hulls which can be viewed as generalization of the thrust deduction phenomenon. The 3D doubled body potential interaction code based on the source panel method developed earlier by the authors has been enhanced to include the effect of a propeller on each of the interacting ships under the assumption that the propeller jets (slipstreams) are not involved into the interaction. Each propeller is simulated by a disk of sinks further approximated with a polygon composed of identical triangular panels with identical constant sink density linked to the thrust of the propulsor according to the actuator disk theory. Comparative computations were carried out for two identical tanker vessels in the close-proximity overtaking manoeuvre at various values of the loading coefficient of each propeller. The loading coefficient is not supposed to be necessarily defined by the steady propulsion point. Numerical results demonstrate that a heavily loaded propeller substantially modifies the pressure distribution on both hulls resulting in alteration of the hydrodynamic interaction loads, especially of the surge force and yaw moment.

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