Improvement of Rankine Panel Method for Seakeeping Prediction of a Ship in Low Frequency Region

2016 ◽  
Author(s):  
Eiji Yasuda ◽  
Hidetsugu Iwashita ◽  
Masashi Kashiwagi
Keyword(s):  
Low Frequency ◽  
Radiation Condition ◽  
Panel Method ◽  
Ship Motions ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Computational Region ◽  
Rankine Panel Method ◽  
Free Surface Boundary Condition ◽  
Wave Induced

Rankine panel methods have been studied for solving 3D seakeeping problems of a ship with forward speed and oscillatory motions. Nevertheless, there is a drawback in the numerical method for satisfying the radiation condition of outgoing waves at low frequencies, because the waves generated ahead of a ship reflect from the outward computational boundary and smear the flow around the ship. The so-called panel shift technique has been adopted in the frequency-domain Rankine panel method, which is effective when the generated waves propagate downstream of a ship. In this paper, in addition to this conventional panel shift method, Rayleigh’s artificial friction is introduced in the free-surface boundary condition to suppress longer wave components in a computational region apart from the ship. With this practical new method, it is shown that there is no prominent wave reflection from the side and/or upstream computational boundaries even in the range of low frequencies. As a consequence, the unsteady pressure, hydrodynamic forces, wave-induced ship motions, added resistance are computed with reasonable accuracy even in following waves and in good agreement with measured results in the experiment using a bulk carrier model which is also conducted for the present study.

Water Wave Singularities in a Prolate Spheroidal Coordinate System

1972 ◽  
Vol 16 (01) ◽  
pp. 41-46
Author(s):  
J. N. Newman
Keyword(s):  
Radiation Condition ◽  
Point Sources ◽  
The Body ◽  
Surface Boundary ◽  
Spheroidal Harmonics ◽  
Free Surface Boundary Condition ◽  
Special Cases ◽  
Analogous Manner ◽  
Surface Boundary Condition ◽  
Unbounded Fluid

Singular velocity potentials are derived which satisfy the linear free-surface boundary condition and appropriate initial condition or radiation condition, but which are singular in the same form as a spheroidal harmonic. Thus these singularities can be utilized to satisfy boundary conditions on submerged spheroids without integrating conventional point sources or dipoles over the body surface or axis, in an analogous manner to the use of spheroidal harmonics in an unbounded fluid. In addition to the general unsteady case, equations are derived for the special cases of steady forward motion and of sinusoidal time-dependence, either at zero or constant forward velocity of the spheroid. Wave-free singularities are derived for the case of zero forward speed, and applications to problems in wave resistance and in seakeeping are discussed briefly.

A Rankine Panel Method for Added Resistance of Ships in Waves

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Heinrich Söding ◽  
Vladimir Shigunov ◽  
Thomas E. Schellin ◽  
Ould el Moctar
Keyword(s):  
Degrees Of Freedom ◽  
Periodic Wave ◽  
Panel Method ◽  
Navier Stokes ◽  
Ship Motions ◽  
Added Resistance ◽  
Rankine Panel Method ◽  
Head Waves ◽  
Wigley Hull ◽  
The Time Domain

A new Rankine panel method and an extended Reynolds-Averaged Navier–Stokes (RANS) solver were employed to predict added resistance in head waves at different Froude numbers of a Wigley hull, a large tanker, and a modern containership. The frequency domain panel method, using Rankine sources as basic flow potentials, accounts for the interaction of the linear periodic wave-induced flow with the nonlinear steady flow caused by the ship's forward speed in calm water, including nonlinear free surface conditions and dynamic squat. Added resistance in waves is obtained by the pressure integration method. The time domain RANS solver, based on a finite volume method, is extended to solve the nonlinear equations of the rigid body six-degrees-of-freedom ship motions. The favorable comparison of the panel and RANS predictions demonstrated that the Rankine method is suitable to efficiently obtain reliable predictions of added resistance of ships in waves. Comparable model test predictions correlated less favorably, although the overall agreement was felt to be acceptable, considering the difficulties associated with the procedures to obtain accurate measurements.

Properties of Finite-Difference Operators for the Steady-Wave Problem

1993 ◽  
Vol 37 (01) ◽  
pp. 1-7
Author(s):  
John S. Letcher
Keyword(s):  
Free Surface ◽  
Finite Difference ◽  
Radiation Condition ◽  
Free Surface Flows ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Difference Operators ◽  
Surface Boundary ◽  
Free Surface Boundary Condition ◽  
Surface Boundary Condition

A feature of most implementations of Dawson's boundary-integral method for steady free-surface flows is the use of upstream finite-difference operators for the streamwise derivative occurring in the linearized free-surface boundary condition. An algebraic analysis of a family of candidate operators reveals their essential damping and dispersion error characteristics, which correlate well with their observed performance in two-dimensional example flows. Some new operators are found which perform somewhat better than Dawson's, but the general outlook for accurate results using difference operators is nevertheless bleak. It is shown that the calculation necessarily diverges as panel size is reduced, and a breakdown at higher speeds is also inevitable. More promise appears to lie in satisfying the radiation condition by several alternative ways, which are briefly discussed.

A Rankine Panel Method for Added Resistance of Ships in Waves

2012 ◽  
Author(s):  
Heinrich Söding ◽  
Vladimir Shigunov ◽  
Thomas E. Schellin ◽  
Ould el Moctar
Keyword(s):  
Degrees Of Freedom ◽  
Periodic Wave ◽  
Panel Method ◽  
Ship Motions ◽  
Added Resistance ◽  
Rankine Panel Method ◽  
Head Waves ◽  
Calm Water ◽  
Wigley Hull ◽  
The Time Domain

A new Rankine panel method and an extended RANS solver were employed to predict added resistance in head waves at different Froude numbers of a Wigley hull, a large tanker, and a modern containership. The frequency domain panel method, using Rankine sources as basic flow potentials, accounts for the interaction of the linear periodic wave-induced flow with the nonlinear steady flow caused by the ship’s forward speed in calm water, including nonlinear free surface conditions and dynamic squat. Added resistance in waves is obtained by pressure integration method. The time domain RANS solver, based on a finite volume method, is extended to solve the nonlinear equations of the rigid body six-degrees-of-freedom ship motions. The favorable comparison of panel and RANS predictions demonstrated that the Rankine method is suitable to efficiently obtain reliable predictions of added resistance of ships in waves. Comparable model test predictions correlated less favorably although overall agreement was felt to be acceptable, considering the difficulties associated with procedures to obtain accurate measurements.

The effect of non-linearity at the free surface on flow past a submerged cylinder

1965 ◽  
Vol 22 (2) ◽  
pp. 401-414 ◽  
Author(s):  
E. O. Tuck
Keyword(s):  
Free Surface ◽  
Surface Condition ◽  
Second Order ◽  
Order Effects ◽  
Surface Boundary ◽  
First Order ◽  
Flow Past ◽  
Free Surface Boundary Condition ◽  
Non Linear ◽  
Wave Induced

Plane potential flow past a circular cylinder beneath a free surface under gravity is investigated in order to determine the importance or otherwise of non-linear effects from the free-surface boundary condition. It is shown that non-linear second-order corrections to the first-order linearized expressions for the wave-induced forces on the cylinder are considerably larger than second-order effects which are present even with a linear free-surface condition. Further evidence for the importance of non-linearity is presented in the form of streamline plots of the first-order solution showing strange behaviour at wave crests.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

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