Study on 2nd-Order Wave Loads With Forward Speed Through Aranha’s Formula and Neumann-Kelvin Linearization

2020 ◽  
Author(s):  
Zhitian Xie ◽  
Jeffery Falzarano
Keyword(s):  
Current Velocity ◽  
Near Field ◽  
Field Method ◽  
Wave Loads ◽  
Forward Speed ◽  
Floating Bodies ◽  
Floating Structure ◽  
Sum Frequency ◽  
Wave Drift Damping ◽  
The Mean

Abstract The 2nd-order wave loads consist of difference frequency, sum frequency components and a steady drift component that is also called the mean drift load. The first two components are usually not of interest, because of their small amplitudes compared with the 1st-order wave loads. The remaining mean drift load should be taken into consideration due to its steady effect on floating bodies. In the previous research, the full derivation and expression of the 2nd-order wave loads applied to a floating structure was presented. Moreover, numerically estimated quadratic transfer function was also illustrated with both off-diagonal elements and diagonal elements called the mean drift coefficients. Most research topics in this scenario consider the wave only case. In this paper, the mean drift wave loads applied to a floating structure with forward speed or current velocity has been numerically estimated through Aranha’s formula, a far field method and Neumann-Kelvin linearization, a near field method. Therefore, the effect of the floating structure’s forward speed or current velocity on the 2nd-order mean drift loads that is also called the wave drift damping has been discussed through these two methods. This work will provide a meaningful reference and numerical basis for the ongoing projects of the floating structure’s seakeeping and maneuvering problems.

scholarly journals Wave forces on three-dimensional floating bodies with small forward speed

1991 ◽  
Vol 227 ◽  
pp. 135-160 ◽  
Author(s):  
Jan Nossen ◽  
John Grue ◽  
Enok Palm
Keyword(s):  
Velocity Potential ◽  
The Body ◽  
Wave Forces ◽  
Forward Speed ◽  
Floating Bodies ◽  
Wave Drift ◽  
Exciting Forces ◽  
Wave Exciting Forces ◽  
Wave Drift Damping ◽  
The Mean

A boundary-integral method is developed for computing first-order and mean second-order wave forces on floating bodies with small forward speed in three dimensions. The method is based on applying Green's theorem and linearizing the Green function and velocity potential in the forward speed. The velocity potential on the wetted body surface is then given as the solution of two sets of integral equations with unknowns only on the body. The equations contain no water-line integral, and the free-surface integral decays rapidly. The Timman-Newman symmetry relations for the added mass and damping coefficients are extended to the case when the double-body flow around the body is included in the free-surface condition. The linear wave exciting forces are found both by pressure integration and by a generalized far-field form of the Haskind relations. The mean drift force is found by far-field analysis. All the derivations are made for an arbitrary wave heading. A boundary-element program utilizing the new method has been developed. Numerical results and convergence tests are presented for several body geometries. It is found that the wave exciting forces and the mean drift forces are most influenced by a small forward speed. Values of the wave drift damping coefficient are computed. It is found that interference phenomena may lead to negative wave drift damping for bodies of complicated shape.

First and Second Order Wave-Current Interactions for Floating Bodies

2012 ◽  
Author(s):  
Charles Monroy ◽  
Yann Giorgiutti ◽  
Xiao-Bo Chen
Keyword(s):  
Field Method ◽  
Boundary Integral ◽  
Second Order ◽  
Boundary Integral Method ◽  
Diffraction Radiation ◽  
Floating Bodies ◽  
Order Problem ◽  
First Order ◽  
Wave Drift Damping ◽  
Order Quantities

The influence of current in sea-keeping problems is felt not only for first order quantities such as wave run-ups in front of the structure, but also mainly for second order quantities. In particular, the wave drift damping (which is expressed as the derivative of drift force with respect to the current) is of special interest for mooring systems. The interaction effects of a double-body steady flow on wave diffraction-radiation is studied through a decomposition of the time-harmonic potential into linear and interaction components. A boundary integral method is used to solve the first order problem. Ultimately, a far-field method is proposed to get access to second order drift forces.

Drift of an articulated cylinder in regular waves

1984 ◽  
Vol 394 (1807) ◽  
pp. 363-385 ◽  
Keyword(s):  
Near Field ◽  
Second Order ◽  
Regular Waves ◽  
Floating Bodies ◽  
Wave Heights ◽  
Tilt Mode ◽  
The Mean ◽  
Wave Induced ◽  
Theoretical Results ◽  
Drift Forces

Potential flow theory is used to investigate the wave induced harmonic response and the mean drift of an articulated column in regular waves. The mean drift horizontal force is evaluated by means of the Stokes expansion to second order in wave steepness. Analyses based on both near field and far field formulations are shown to give identical expressions, provided that the second-order forces at the intersection between column and seabed are included in the near field approach. The latter have not been considered in previous studies concerned with drift forces on floating bodies. It is shown that the drift forces on a column, although of second order, can excite piech responses of first order: this is because articulated columns are designed to have a low natural frequency in the tilt mode, relative to wave frequencies. Comparison of the theoretical results with experimental data, from a model tested in regular waves, suggests reasonable agreement for the drift forces over a range of frequencies and two wave heights.

A Study on the Added Resistance Performance of Catamarans in Waves

2018 ◽  
Author(s):  
Emanuela Ageno ◽  
Luca Bonfiglio ◽  
Dario Bruzzone ◽  
Giuliano Vernengo ◽  
Diego Villa
Keyword(s):  
Near Field ◽  
Field Method ◽  
Longitudinal Component ◽  
Added Resistance ◽  
Systematic Analysis ◽  
First Order ◽  
Heading Angle ◽  
The Mean ◽  
State Force ◽  
Resistance Performance

The added resistance of a catamaran advancing in waves is investigated in the framework of a non-viscous potential theory. A linear Boundary Element Method (BEM) is used for the first order seakeeping prediction and the mean longitudinal component of the second-order steady-state force is computed by using a near-field method. Both methods are briefly presented and preliminary validations on both a mono-hull and a catamaran are shown. A systematic analysis of the added resistance of the so-called DUT catamaran is presented highlighting the effects of the advancing speed and those of the ship-wave heading angle.

The Lateral Drifting Forces and Moments on Two Ships in Proximity in Waves

1990 ◽  
Vol 112 (3) ◽  
pp. 223-229
Author(s):  
M.-C. Fang ◽  
C. H. Kim
Keyword(s):  
Near Field ◽  
Field Method ◽  
Theoretical Explanation ◽  
Nonlinear Phenomena ◽  
Random Waves ◽  
Following Seas ◽  
Strip Theory ◽  
Present Technique ◽  
The Mean ◽  
Physical Phenomena

An analytical procedure for evaluating the lateral drifting forces and moments between two ships in oblique waves by near-field method is presented in this paper. The velocity potential, including the hydrodynamic interactions are evaluated by a two-dimensional sink-source technique. Then the strip theory is applied to calculate the sectional force and the drifting forces and moments of the whole ships can be obtained by Simpson rules. Four components of the mean drifting force are obtained in which the relative wave term is dominant, whereas the Bernoulli quadratic component is secondary. The negative drifting force is observed at some frequency for the ship which is in the weather side of the wave. The lateral drifting force even occurs while the ships are in the head or following seas, which is consistent with the real physical phenomena at sea. The present technique offers the theoretical explanation for nonlinear phenomena between two ships in waves and will be helpful for the further practical study in random waves.

Two-Dimensional Analysis on the Lateral Drifting Force Between Two Floating Structures

1986 ◽  
Vol 30 (03) ◽  
pp. 194-200
Author(s):  
M. C. Fang ◽  
C. H. Kim
Keyword(s):  
Near Field ◽  
Field Method ◽  
Hydrodynamic Interactions ◽  
Quadratic Term ◽  
Two Dimensional ◽  
Floating Structures ◽  
Frequency Responses ◽  
Wave Elevation ◽  
The Mean ◽  
Two Bodies

An analytical procedure for evaluating the lateral drifting forces between two structures by the near-field method is presented. The velocity potentials, including the hydrodynamic interactions, are evaluated by a two-dimensional sink-source technique. This method yields the mean drifting force consisting of four components of which the relative wave elevation term is dominant, whereas the Bernoulli quadratic term is secondary. The phenomena of negative drifting force have been found in the study, which are consistent with the standing wave or negative added mass. The near-field method clearly reveals the effects of the behavior of the response motions such as heave and roll resonances, although it seems to be complicated at first and difficult to use. It is also found that the hydrodynamic interactions between two bodies cannot be neglected. The near-field solutions are required for the further analysis of the quadratic frequency responses function in order to obtain the nonlinear (second order) interaction effects in the presence of dual waves.

A Study on the Wave Drift Forces Calculation on Two Floating Bodies Based on the Boundary Element Method: Attempt for Improvement of the Constant Panel Method

2016 ◽  
Author(s):  
Qiao Li ◽  
Takashi Tsubogo ◽  
Yoshiho Ikeda ◽  
Yasunori Nihei
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Velocity Potential ◽  
Near Field ◽  
Field Method ◽  
Panel Method ◽  
Floating Bodies ◽  
Wave Drift ◽  
Wave Drift Forces ◽  
Drift Forces

The boundary element method (BEM) which can solve the boundary integral equations is used to calculate the velocity potential on the floating bodies. The equation is discretized by the higher order BEM or the constant panel method. The constant panel method is relatively easy to compute the velocity potential. However the near field method cannot evaluate the wave drift forces and moment accurately, when the velocity potential is computed by the constant panel method. In the article, a new numerical technic of the constant panel method is proposed. Then it is easy to take advantage of the near field method to calculate the wave drift forces and moment, especially considering two floating system. In addition, the results of the fluid forces calculated by new method are compared to the other methods results. At last the hydrodynamic interaction between two floating bodies is assessed in the calculation of the wave exciting forces and the wave drift forces.

Design and development of manually operated gladiolus planter

2018 ◽  
Vol 5 (01) ◽  
Author(s):  
TAPAN K. KHURA ◽  
H. L. KUSHWAHA ◽  
SATISH D LANDE ◽  
PKSAHOO . ◽  
INDRA L . KUSHWAHA
Keyword(s):  
Coefficient Of Variation ◽  
Field Capacity ◽  
Power Source ◽  
Forward Speed ◽  
Cereal Crop ◽  
Maximum Coefficient ◽  
Coefficient Of Uniformity ◽  
The Mean ◽  
The Cost ◽  
Immense Potential

Floriculture is an age-old farming activity in India having immense potential for generating selfemployment and income to farmers. However, the cost of cultivation of flower is high as compared to cereal crop. Level of mechanization for different field operations is one but foremost reason for the higher cost of cultivation. As most of the Indian farmers are marginal and small, a need for manually operated gladiolus planter was felt. The geometric properties of gladiolus corm were determined for designing the seed metering system and seed hopper of the planter. The planter was evaluated in the field when pulled by two persons as a power source and guided by a person. The coefficient of variation and highest deviation from the mean spacing was observed as 12.93% and 2.65cm respectively. The maximum coefficient of uniformity of 90.59% was observed for a nominal corm spacing of 15cm at 0.56 kmh-1 forward speed. An average MISS percentage was observed as 2.65 and 2.25 for nominal corm spacing of 15 and 20 cm. The multiple index was zero for two levels corm spacing and forward speed of operation. The QFI was found in the range of 97.2 and 97.9 percent. The average field capacity of the planter was observed as 0.02 hah-1.The average draft requirement of the planter was found as 821 ± 50.3 N.

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

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