A Prediction of Dynamic Stresses for Long, Large-Diameter Horizontal Pipes at or Near the Ocean Free Surface

1995 ◽  
Vol 117 (4) ◽  
pp. 239-244 ◽  
Author(s):  
G. C. Nihous
Keyword(s):  
Free Surface ◽  
Large Diameter ◽  
Vertical Plane ◽  
Slender Body Theory ◽  
Modal Expansion ◽  
Horizontal Pipes ◽  
Straight Beam ◽  
Bending Stresses ◽  
Wave Angle ◽  
Body Theory

A straight-beam approximation is applied to a long, stiff pipeline located at or near the ocean free surface. The analytical model determines vertical and horizontal transverse motions in a linear frequency-domain framework. Longitudinal dependence is expressed through a modal expansion, with the hydrodynamic loads calculated through slender-body theory. This method is validated by comparing predicted bending stresses for a 9.1-m-(30-ft-) dia pipe with corresponding model basin data. Maximum stresses occur when the wave angle allows a simultaneous matching of frequencies and projected wavelengths. Results also show peak stresses near the aft end of the pipe. Finally, it is confirmed that in deep water, bending stresses in the horizontal plane are in general smaller than those in the vertical plane.

scholarly journals Numerical estimation of aircrafts' unsteady lateral-directional stability derivatives

2006 ◽  
Vol 33 (4) ◽  
pp. 311-337
Author(s):  
N.L. Maricic
Keyword(s):  
Cross Sections ◽  
Vertical Plane ◽  
Lattice Method ◽  
Slender Body Theory ◽  
Directional Stability ◽  
Load Distributions ◽  
Stability Derivatives ◽  
Lifting Surfaces ◽  
Body Theory ◽  
Control Surfaces

A technique for predicting steady and oscillatory aerodynamic loads on general configuration has been developed. The prediction is based on the Doublet-Lattice Method, Slender Body Theory and Method of Images. The chord and span wise loading on lifting surfaces and longitudinal bodies (in horizontal and vertical plane) load distributions are determined. The configuration may be composed of an assemblage of lifting surfaces (with control surfaces) and bodies (with circular cross sections and a longitudinal variation of radius). Loadings predicted by this method are used to calculate (estimate) steady and unsteady (dynamic) lateral-directional stability derivatives. The short outline of the used methods is given in [1], [2], [3], [4] and [5]. Applying the described methodology software DERIV is developed. The obtained results from DERIV are compared to NASTRAN examples HA21B and HA21D from [4]. In the first example (HA21B), the jet transport wing (BAH wing) is steady rolling and lateral stability derivatives are determined. In the second example (HA21D), lateral-directional stability derivatives are calculated for forward- swept-wing (FSW) airplane in antisymmetric quasi-steady maneuvers. Acceptable agreement is achieved comparing the results from [4] and DERIV.

scholarly journals Analysis of Dynamic Stability of Planing Craft on the Vertical Plane

2014 ◽  
Vol 8 (15) ◽  
pp. 35 ◽  
Author(s):  
Roberto Algarín ◽  
Oscar Tascón
Keyword(s):  
Dynamic Model ◽  
Dynamic Stability ◽  
Vertical Plane ◽  
Slender Body ◽  
Critical Conditions ◽  
Wagner Model ◽  
Slender Body Theory ◽  
Planing Craft ◽  
Body Theory

A dynamic model for the motion of planing craft on the vertical plane was developed; the motions ofsurge, heave, and pitch are coupled. Critical conditions that produce the inception of instability are evaluated. The Wagner model (1932) for 2D impact is extended for section with knuckles. Planing hullswere analyzed through the application of slender body theory. The results are compared with Tveitnes(2001), Peterson (1997), Savitsky (1964), Troesch (1992) and Celano (1998).

The flow near the bow of a steadily turning ship

1975 ◽  
Vol 71 (2) ◽  
pp. 283-291 ◽  
Author(s):  
Miguel Hiroo Hirata
Keyword(s):  
Free Surface ◽  
Surface Condition ◽  
Rate Of Change ◽  
Slender Body ◽  
Free Surface Elevation ◽  
Transform Method ◽  
Slender Body Theory ◽  
High Froude Number ◽  
Number Flow ◽  
Body Theory

The flow near the bow of a steadily turning ship is analysed using a modified slender-body theory. The rate of change of flow quantities in the longitudinal (x) direction is assumed to be greater than that implied by ‘conventional’ slender-body theory. As a consequence some features of high Froude number flow are apparent which cannot be predicted by the ‘conventional’ theory. The modified slender-body theory proposed requires the solution of a two-dimensional Laplace equation (in y and z) but its free-surface condition still involves an x derivative. A Fourier-transform method is used to solve this problem. A simple bow configuration of constant draft is analysed and numerical results for the free-surface elevation are presented.

Impulsive Motion of a Wide Torus Submerged Below a Free Surface

1997 ◽  
Vol 41 (03) ◽  
pp. 195-209
Author(s):  
Peder A. Tyvand
Keyword(s):  
Free Surface ◽  
Degrees Of Freedom ◽  
Small Time ◽  
Nonlinear Interactions ◽  
Leading Order ◽  
Slender Body Theory ◽  
Six Degrees Of Freedom ◽  
Time Expansion ◽  
Body Theory ◽  
Submergence Depth

The impulsively starting motion of a torus submerged horizontally below a free surface is studied analytically, using a small-time expansion. The torus is assumed wide, i.e., the torus radius is much larger than its initial submergence depth. A quasi-two-dimensional theory is applied. Its accuracy is checked by comparing the first-order surface elevation with slender-body theory. The hydrodynamic force and torque are investigated in the first three orders of the small-time expansion. The ratio between the cross-section radius and submergence depth is arbitrary (between 0 and 1). The general motion of the torus consists of all six degrees of freedom. Special emphasis is put on the five different leading-order nonlinear interactions that may occur between these modes: surge/heave, surge/roll, sway/roll, heave/roll, and roll/yaw. These leading-order nonlinear interactions give rise to zeroth-order forces and torques. The leading-order gravitational effects are investigated.

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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