Buoy Response Amplitude Operators Obtained From Step Response Tests

1976 ◽  
Author(s):  
David Price
Keyword(s):  
Response Amplitude ◽  
Step Response ◽  
Response Amplitude Operators

scholarly journals Switching Control Strategy for Oscillating Water Columns Based on Response Amplitude Operators for Floating Offshore Wind Turbines Stabilization

2021 ◽  
Vol 11 (11) ◽  
pp. 5249
Author(s):  
Payam Aboutalebi ◽  
Fares M’zoughi ◽  
Itziar Martija ◽  
Izaskun Garrido ◽  
Aitor J. Garrido
Keyword(s):  
Switching Control ◽  
Response Amplitude ◽  
Offshore Wind ◽  
Oscillating Water Column ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Water Columns ◽  
Switching Control Strategy ◽  
Response Amplitude Operators ◽  
Oscillating Water Columns

In this article, a new strategy for switching control has been proposed with the aim of reducing oscillations in floating offshore wind turbines. Such oscillations lead to a shortage in the system’s efficiency, lifespan and harvesting capability of wind and wave energies. In order to study the decreasing of undesired oscillations in the system, particularly in pitch and top tower fore-aft movements, a square-shaped platform barge equipped with four symmetric oscillating water columns has been considered. The oscillating water columns’ air flux valves allow to operate the air columns so that to control the barge movements caused by oscillatory motion of the waves. In order to design the control scheme, response amplitude operators have been used to evaluate the performance of the system for a range of wave frequency profiles. These response amplitude operators analysis makes it possible to implement a switching control strategy to adequately regulate the valves opening/closing transition. The obtained results show that the proposed controlled oscillating water column-based barge present a better performance compared to the traditional barge one. In the case study with the period of 10 s, the results indicate the significant oscillation reduction for the controlled oscillating water column-based system compared to the standard barge system by 30.8% in pitch angle and 25% in fore-aft displacement.

The Effect of Pitch Gyradius on Added Resistance of Yacht Hulls

1991 ◽  
Author(s):  
James F. Moran
Keyword(s):  
Water Resistance ◽  
Wave Spectrum ◽  
Response Amplitude ◽  
Added Resistance ◽  
Regular Waves ◽  
Low Frequencies ◽  
Irregular Wave ◽  
Wave Data ◽  
The Difference ◽  
Response Amplitude Operators

The purpose of this investigation was to determine the effect of pitch gyradius on added resistance of yacht hulls. Tank testing of a model yacht in head seas was performed in the Webb Robinson Model Basin. The model was tested in regular waves at two speeds and five variations of gyradius. The model was also evaluated in irregular seas of the Pierson-Moskowitz spectrum at various speeds with two gyradii. Response Amplitude Operators were developed from the regular wave data and comparisons made. The irregular wave data were analyzed for the effect of speed on the difference in added resistance between the maximum and minimum gyradius settings. Several conclusions were arrived at after analyzing the data. The Response Amplitude Operaters shift as the gyradius changes. In regular waves, at low frequencies of encounter, a lower, gyradius resulted in less added frequencies of encounter in regular waves, this trend reverses itself and the higher gyradii result in reduced added resistance. However, at higher frequencies of encounter in regular waves, this trend reverses, reverses itself in reduced added resistance. The peaks of the RAO curves shift to higher frequencies at higher gyradii. It was also concluded that at the higher speed, Froude Number of 0.3, the added resistance was lower relative to the still-water resistance for each gyradius tested. The irregular wave testing revealed the effect of the lower frequencies dominating the irregular wave spectrum. The minimum gyradius, in irregular seas showed less added resistance than the maximum gyradius. In addition, the irregular wave testing verified, the reduction of added resistance, relative to still-water resistance, at increasing speeds for both the minimum and maximum gyradii.

The Double Step Analysis of Rapid Manual Aiming Movements

1988 ◽  
Vol 40 (2) ◽  
pp. 299-322 ◽  
Author(s):  
Nicholas C. Barrett ◽  
Denis J. Glencross
Keyword(s):  
Control System ◽  
Initial Response ◽  
Response Amplitude ◽  
Step Response ◽  
Oculomotor Control ◽  
Second Step ◽  
Double Step ◽  
Home Base ◽  
Transition Functions ◽  
Corrective Response

The present paper examines the control principles underlying rapid manual tracking responses to horizontal double-step stimuli. The paper reports an experiment concerned with responses made to step-stimuli presented in quick succession. The amplitude of the second-step was varied between the initial step-position and the home-base. Double-step response parameters were analysed as a function of the determinant time interval (D) between the second step and the onset of the initial response. The initial response amplitude was observed to vary as a function of D. Amplitude transition functions were constructed representing the transition of the initial response amplitude between the two step positions; their slopes, furthermore, depended on the amplitude of the second target step. No delays in the initial reaction time with the interstimulus interval were observed. Minor delays to the onset of a corrective response were observed. These delays were in part related to a movement time constraint that is independent of any limitations in central processing capacity. The present findings for the manual control system are compared to double-step tracking analyses of the oculomotor control system.

Model Tests of the PACT Base America's Cup Hull in Following Seas

1997 ◽  
Author(s):  
Jesse Falsone
Keyword(s):  
Degrees Of Freedom ◽  
Model Tests ◽  
Response Amplitude ◽  
Scale Model ◽  
Radius Of Gyration ◽  
Added Resistance ◽  
Following Seas ◽  
America’S Cup ◽  
Wave Slope ◽  
Response Amplitude Operators

Model tests were conducted at the Davidson Laboratory to investigate the effect of following seas on the added resistance of the PACT (Partnership for America's Cup Technology) base America's Cup hull. A 1 :8 scale model of an International America's Cup Class yacht was provided by Team Dennis Conner and was refinished with funding from US Sailing to its original lines as the PACT base hull. Using this hull (canoe body with no appendages), model tests were conducted in the following seas condition. Upright, resistance tests were carried out at constant speed in both smooth water and regular waves of varying length and slope. The model was free to heave and pitch while restraining all other degrees of freedom. The data analysis revealed that at wavelengths approximately greater than two model lengths, the added resistance of the model is negative. A negative added resistance implies that the average drag force of the model in a particular following sea is less than the still-water drag of the model at the same speed. At wavelengths below this point, the added resistance of the model is greater than the still-water resistance. Furthermore, the form of the data suggests that at waves longer than were tested in this experiment (wavelengths greater than five model lengths), the added resistance of the model converges to the still­water resistance. The experiment also verifies that the added resistance is proportional to the square of the wave height. The pitch and heave characteristics of the model as expressed in the form of response amplitude operators are independent of wave slope. This is to say that for a particular motion, the response amplitude operators for each wave slope overlap one another. The results of these model tests were to be used as a database for the IMS Pitching Moment Project established in an attempt to quantify the sensitivity of radius of gyration on yacht performance. Also, these results were to be used to validate CFD estimates of added resistance.

Estimation of Response Amplitude Operators for Ships via the Circular-Hyperbolic Decomposition

2001 ◽  
Vol 45 (02) ◽  
pp. 103-110
Author(s):  
B. M. Suleiman ◽  
S. O’F. Fahey ◽  
A. H. Nayfeh ◽  
M. R. Hajj
Keyword(s):  
Transfer Functions ◽  
Frequency Domain Analysis ◽  
Response Amplitude ◽  
Ship Motion ◽  
Frequency Content ◽  
Promising Technique ◽  
Motion Data ◽  
Frequency Components ◽  
Response Amplitude Operators ◽  
Motion Characteristics

The frequency-domain analysis is commonly used to determine ship-motion characteristics, such as transfer functions and Response Amplitude Operators (RAOs). The Discrete Fourier Transform (DFT) has been the most widely used technique to conduct such an analysis. Nevertheless, application of the DFT is not always desirable because of leak-age. This problem cannot be eliminated unless the frequency content of a signal is known and all frequency components are rational multiples of each other. In this paper, we apply a recently developed closed-form decomposition technique, called the circular-hyperbolic decomposition (CHD), to estimate the RAOs of coupled heave and pitch motions using evenly sampled discrete ship-motion data. We show the advantages of the new technique over the DFT when leakage is present. We also introduce enhancements to the CHD in terms of a decimation parameter and a generalization for multiple signals. The results show that it is a promising technique.

Modal Test for Response Amplitude Operator of a Deepwater Semi-Submersible Platform

2014 ◽  
Vol 945-949 ◽  
pp. 725-729 ◽  
Author(s):  
Li Ping Sun ◽  
Shu Long Cai ◽  
Zhuang Kang
Keyword(s):  
Model Test ◽  
Oil And Gas ◽  
Numerical Results ◽  
Response Amplitude ◽  
Dynamic Responses ◽  
Experimental Measurements ◽  
Regular Waves ◽  
Motion Response ◽  
Modal Test ◽  
Response Amplitude Operators

Semi-submersible plays an important role in ocean oil and gas exploitation. This paper carried out a model test for motion response of a deepwater semi-submersible in regular waves with the model oriented in the head, beam and quartering directions. The results were presented as Response Amplitude Operators (RAO) of the platform. Dynamic responses measured in the model test were compared with the numerical results obtained by the software HYDROSTAR. Results show that the numerical results generally tally well with the experimental measurements. This illustrates the accuracy of the numerical results, and proves that the numerical results are reliable to be the reference of judging performance of the platform.

The Water Column Oscillation in a Duct Between Two Half Ship Section Barriers

1986 ◽  
Vol 30 (02) ◽  
pp. 127-133
Author(s):  
B. S. Lee ◽  
A. H. Day
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Response Amplitude ◽  
Peak Response ◽  
Practical Applications ◽  
Energy Devices ◽  
Distinct Peak ◽  
Response Amplitude Operators ◽  
Heave Motion ◽  
Key Parameter

The oscillation of a water column in a duct between two half ship section barriers is relevant to several practical applications, notably wave energy devices and moonpools for the launch/retrieval of subsea units from diving support vessels. The oscillation is solved for the case where the barriers are space fixed, and the method used is then extended to include effects due to the heave motion of the barriers. Results obtained in the form of response amplitude operators indicate that the water column oscillation demonstrates a distinct peak response, and that the key parameter controlling this response is the ratio of duct width to barrier draft.

Response Amplitude Operators of a Wigley Ship Model via Computational Fluid Dynamics

2017 ◽  
Author(s):  
Roger Matsumoto Moreira ◽  
rafael santos ◽  
Sergio Daruis ◽  
Guilherme Rojo ◽  
Raphael David Aquilino Bacchi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Response Amplitude ◽  
Ship Model ◽  
Response Amplitude Operators

scholarly journals Prediction of Ship Motions in Irregular Waves Based on Response Amplitude Operators Evaluated Experimentally in Noise Waves

2021 ◽  
Vol 28 (1) ◽  
pp. 16-27
Author(s):  
Sebastian Bielicki
Keyword(s):  
Wave Amplitude ◽  
Response Amplitude ◽  
Irregular Waves ◽  
Alternative Methods ◽  
Spectral Energy ◽  
Ship Motions ◽  
Sea Waves ◽  
Sea State ◽  
Coloured Noise ◽  
Response Amplitude Operators

Abstract The most common methods for predicting ship roll motions in a specified sea state are direct measurements of motions in a representative irregular wave realisation (time domain) or calculations of motions from response amplitude operators (RAOs) in the frequency domain. The result of the first method is valid only for the tested sea state, whilst the second method is more flexible but less accurate. RAO-based predictions are calculated assuming a linear model of ship motions in waves. RAO functions are usually evaluated by means of tests in regular waves for a limited number of frequencies and a constant wave amplitude. This approach is time-consuming and the discrete form of the RAO functions obtained for a limited number of frequencies may lead to discrepancies in the prediction of seakeeping and often does not allow the actual amplitude of the response in resonant frequency to be determined. Another challenge is the appropriate selection of wave amplitude for tests due to the considerable influence of viscous damping on roll response in irregular sea waves. There are alternative methods for the experimental determination of RAO functions and one of them is presented in this study. The presented approach allows RAO functions to be evaluated in one run by the generation of irregular waves characterised by a white or coloured noise spectrum. This method reduces the experiment duration, with almost continuous RAO characteristics obtained. The flat (white noise) and linear (coloured noise) wave spectral energy characteristics are considered in the experiment and the obtained predictions are compared with the results of accurate measurements in irregular waves.

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