Maneuvering in Waves Based on Potential Theory

2014 ◽  
Author(s):  
Jochen Schoop-Zipfel ◽  
Moustafa Abdel-Maksoud
Keyword(s):  
Potential Theory ◽  
State Of The Art ◽  
Equations Of Motion ◽  
Test Results ◽  
Wave Excitation ◽  
Slender Body Theory ◽  
Strip Theory ◽  
Maneuvering In Waves ◽  
Semi Empirical ◽  
Body Theory

The forces acting on a maneuvering ship are determined with the in-house potential code panMARE. For slender ships with salient hull features, the forces and moments can be captured by properly treating the shed vorticity. For blunt ships it is not possible to directly determine the strength of the vorticity and the position where it leaves the hull. Therefore, it is easier and not less accurate to account for separation forces via semi-empirical formulae. These corrections are based on slender body theory or extensive RANS computations. The mass forces can be determined directly by potential theory. Forces and moments due to rudder and propeller are calculated using state-of-the-art procedures. Arbitrary maneuvers can be simulated by using the equations of motion. With the applied corrections a satisfactory agreement with model test results can be obtained. Wave excitation forces can be introduced to incorporate the influence of sea states. These forces are determined with strip theory. While the forces agree well with measured data, a deviation can be observed in the motions.

A Linear Theory of Springing

1980 ◽  
Vol 24 (02) ◽  
pp. 74-84
Author(s):  
Svein O. Skjørdal ◽  
Odd M. Faltinsen
Keyword(s):  
Pressure Distribution ◽  
Linear Theory ◽  
Short Wavelength ◽  
Numerical Results ◽  
Experimental Results ◽  
Function Approach ◽  
Wave Excitation ◽  
Slender Body Theory ◽  
Forced Motion ◽  
Body Theory

A linear slender-body theory of springing is derived. The wave excitation loads are calculated by a generalization of the short-wavelength theory of Faltinsen. A Green's function approach is used to find the pressure distribution. Numerical results are compared with experimental results of Wereldsma and Moeyes. The "forced-motion loads" are obtained by a generalization of the Ogilvie and Tuck approach for forced heave and pitch motions. Discrepancies with other methods are discussed. Numerical results of springing are presented.

Three-Dimensional Effects in Ship Relative-Motion Problems

1989 ◽  
Vol 33 (04) ◽  
pp. 261-268 ◽  
Author(s):  
Robert F. Beck ◽  
Arne E. Loken
Keyword(s):  
Relative Motion ◽  
Theoretical Calculations ◽  
Three Dimensional ◽  
Ship Motions ◽  
Slender Body Theory ◽  
Strip Theory ◽  
Diffracted Waves ◽  
Motion Problems ◽  
Incident Waves ◽  
Body Theory

The total relative motion between a ship and the sea surface, including the effects of the ship motions, the incident waves, the diffracted waves, and the radiated waves, is discussed. The radiated and diffracted wave components are calculated using the theory of Salvesen, Tuck, and Faltinsen (1970) with the zero-speed potentials determined by fully three-dimensional calculations. Comparisons with experiments and other theoretical calculations for a simple mathematical hull form are given. The proposed theory shows significant improvement over slender-body theory for the diffraction component and is equal to or better than strip theory for the radiation component.

The distortion of a flexible inextensible thread in a shearing flow

1976 ◽  
Vol 74 (2) ◽  
pp. 317-333 ◽  
Author(s):  
E. J. Hinch
Keyword(s):  
Shear Flow ◽  
Simple Shear ◽  
Stokes Flow ◽  
Equations Of Motion ◽  
Simple Shear Flow ◽  
Qualitative Behaviour ◽  
Slender Body Theory ◽  
Shearing Flow ◽  
Numerical Studies ◽  
Body Theory

Using the slender-body theory for Stokes flow, the equations of motion are developed for a small flexible inextensible thread. The nearly straight thread is examined analytically, and is shown to straighten rapidly. In a simple shear flow the distortions decay less rapidly, but rapidly enough not to rotate the thread through the plane of flow. Numerical studies of simple shear with more substantially distorted threads show the same qualitative behaviour. Additionally some differences are revealed in the nonlinear regime between the buckling and stretching processes which occur in the compressive and tensile quadrants of the flow.

Experiences in Field Testing a Variety of Aeration Equipment in Sweden and in the U.S.A. by Offgas Analysis

1989 ◽  
Vol 21 (10-11) ◽  
pp. 1421-1429
Author(s):  
D. T. Redmon ◽  
W. C. Boyle ◽  
B. G. Hellstrom
Keyword(s):  
Oxygen Transfer ◽  
State Of The Art ◽  
Field Testing ◽  
Analysis Procedure ◽  
Test Results ◽  
Transfer Testing ◽  
Parallel Tests

The background and theory of the offgas analysis procedure used in oxygen transfer testing of diffused aeration tanks is reviewed. Correlation of this method with other applicable procedures in parallel tests is reported. State-of-the-art equipment and accessories are described. Advantages of the procedure are identified, as are precautionary considerations regarding its use. Applications considered appropriate for its employment are delineated. Experience and test results in both Sweden and the U.S.A. on a variety of aeration devices are disclosed.

Note on the swimming of slender fish

1960 ◽  
Vol 9 (2) ◽  
pp. 305-317 ◽  
Author(s):  
M. J. Lighthill
Keyword(s):  
Swimming Speed ◽  
Critical Value ◽  
Slender Body ◽  
Vortex Wake ◽  
Frictional Drag ◽  
Slender Body Theory ◽  
Propulsive Efficiency ◽  
Deformable Bodies ◽  
Work Done ◽  
Body Theory

The paper seeks to determine what transverse oscillatory movements a slender fish can make which will give it a high Froude propulsive efficiency, $\frac{\hbox{(forward velocity)} \times \hbox{(thrust available to overcome frictional drag)}} {\hbox {(work done to produce both thrust and vortex wake)}}.$ The recommended procedure is for the fish to pass a wave down its body at a speed of around $\frac {5} {4}$ of the desired swimming speed, the amplitude increasing from zero over the front portion to a maximum at the tail, whose span should exceed a certain critical value, and the waveform including both a positive and a negative phase so that angular recoil is minimized. The Appendix gives a review of slender-body theory for deformable bodies.

Slender-body theory for slow viscous flow

1976 ◽  
Vol 75 (4) ◽  
pp. 705-714 ◽  
Author(s):  
Joseph B. Keller ◽  
Sol I. Rubinow
Keyword(s):  
Integral Equation ◽  
Incompressible Fluid ◽  
Viscous Incompressible Fluid ◽  
Unit Length ◽  
The Body ◽  
Slender Body ◽  
Slow Flow ◽  
Slender Body Theory ◽  
Slow Viscous Flow ◽  
Body Theory

Slow flow of a viscous incompressible fluid past a slender body of circular crosssection is treated by the method of matched asymptotic expansions. The main result is an integral equation for the force per unit length exerted on the body by the fluid. The novelty is that the body is permitted to twist and dilate in addition to undergoing the translating, bending and stretching, which have been considered by others. The method of derivation is relatively simple, and the resulting integral equation does not involve the limiting processes which occur in the previous work.

Phoretic self-propulsion of helical active particles

2021 ◽  
Vol 927 ◽  
Author(s):  
Ruben Poehnl ◽  
William Uspal
Keyword(s):  
Particle Surface ◽  
Design Parameters ◽  
Strong Impact ◽  
Directed Motion ◽  
Concentration Gradients ◽  
Slender Body Theory ◽  
Active Particles ◽  
Straight Line ◽  
Judicious Choice ◽  
Body Theory

Chemically active colloids self-propel by catalysing the decomposition of molecular ‘fuel’ available in the surrounding solution. If the various molecular species involved in the reaction have distinct interactions with the colloid surface, and if the colloid has some intrinsic asymmetry in its surface chemistry or geometry, there will be phoretic flows in an interfacial layer surrounding the particle, leading to directed motion. Most studies of chemically active colloids have focused on spherical, axisymmetric ‘Janus’ particles, which (in the bulk, and in absence of fluctuations) simply move in a straight line. For particles with a complex (non-spherical and non-axisymmetric) geometry, the dynamics can be much richer. Here, we consider chemically active helices. Via numerical calculations and slender body theory, we study how the translational and rotational velocities of the particle depend on geometry and the distribution of catalytic activity over the particle surface. We confirm the recent finding of Katsamba et al. (J. Fluid Mech., vol. 898, 2020, p. A24) that both tangential and circumferential concentration gradients contribute to the particle velocity. The relative importance of these contributions has a strong impact on the motion of the particle. We show that, by a judicious choice of the particle design parameters, one can suppress components of angular velocity that are perpendicular to the screw axis, or even select for purely ‘sideways’ translation of the helix.

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