scholarly journals BREAKWATER ARMOR DISPLACEMENT THRESHOLDS: A POSSIBLE CORRELATION WITH CUMULATIVE WAVE ENERGY

1984 ◽  
Vol 1 (19) ◽  
pp. 186
Author(s):  
Daniel L. Behnke ◽  
Frederic Raichlen
Keyword(s):  
Wave Energy ◽  
Wave Train ◽  
Wave Length ◽  
Simple Wave ◽  
Wave Theory ◽  
Irregular Waves ◽  
Reconstruction Technique ◽  
Regular Wave ◽  
Regular Waves ◽  
Three Dimensional Model

An extensive program of stability experiments in a highly detailed three-dimensional model has recently been completed to define a reconstruction technique for a damaged breakwater (Lillevang, Raichlen, Cox, and Behnke, 1984). Tests were conducted with both regular waves and irregular waves from various directions incident upon the breakwater. In comparison of the results of the regular wave tests to those of the irregular wave tests, a relation appeared to exist between breakwater damage and the accumulated energy to which the structure had been exposed. The energy delivered per wave is defined, as an approximation, as relating to the product of H2 and L, where H is the significant height of a train of irregular waves and L is the wave length at a selected depth, calculated according to small amplitude wave theory using a wave period corresponding to the peak energy of the spectrum. As applied in regular wave testing, H is the uniform wave height and L is that associated with the period of the simple wave train. The damage in the model due to regular waves and that caused by irregular waves has been related through the use of the cumulative wave energy contained in those waves which have an energy greater than a threshold value for the breakwater.

scholarly journals OVERTOPPING OF RUBBLE-MOUND BREAKWATERS BY IRREGULAR WAVES

1976 ◽  
Vol 1 (15) ◽  
pp. 157
Author(s):  
Yvon Ouellet ◽  
Pierre Eubanks
Keyword(s):  
Wave Train ◽  
The Other ◽  
Irregular Waves ◽  
Regular Wave ◽  
Regular Waves ◽  
Irregular Wave ◽  
Wave Trains ◽  
Rubble Mound ◽  
The Stability ◽  
Rubble Mound Breakwaters

This paper describes the results of an experimental study on the effect of waves on rubble-mound breakwaters, wave transmission subsequent to wave overtopping, the stability of the three sides subjected to wave action and the effect of the breakwaters on waves. Two different rubble-mound breakwaters were tested, i. e. one with a rigid impermeable crest and the other with a flexible permeable crest. Tests were performed with both regular and irregular wave train systems. To obtain the simulated irregular wave trains, four theoretical spectra were chosen: Neumann, Bretschneider, Moskowitz, and Scott. Results obtained from tests with irregular wave trains were compared to those obtained from tests with regular wave trains. It was found that more information was obtained on the behaviour of the structure when it was submitted to the attack of irregular waves than when submitted to regular waves, and that the use of irregular wave trains gave more interesting results.

Alternative Methodologies for Subsea Flexible Strength Analysis

2018 ◽  
Author(s):  
Anskey A. Miranda ◽  
Fred P. Turner ◽  
Nigel Barltrop
Keyword(s):  
Real World ◽  
Wave Train ◽  
Irregular Waves ◽  
Wave Crest ◽  
Strength Analysis ◽  
New Wave ◽  
Regular Wave ◽  
Wave Analysis ◽  
Sea State ◽  
Irregular Wave

This paper presents a study of the analysis methodologies used to predict the most likely response of flexibles in a subsea environment, with the aim of determining an efficient and reliable prediction methodology. The most accurate method involves simulating multiple wave realisations of a real world sea state, i.e. irregular waves, and post-processing the results to determine the most probable maximum (MPM). Due to the computationally intensive nature of this approach, however, regular wave analysis is typically used to determine flexible response. This approach considers the maximum wave within a design storm at a desired period; the choice of periods may leave room for uncertainty in the conservatism of the approach. With proper screening, regular wave analysis can be a valid yet overly conservative approach resulting in over design and additional cost. However, if screened incorrectly, there is a possibility that the choice of periods could give results that are under conservative. In addition to regular wave analysis, the paper presents two alternative methodologies to determine the most likely response, with the focus on reducing the computational resources required. The first alternative is an ‘Irregular Wave Screen’ approach in which the wave train is screened at areas of interest for waves within a user defined threshold of the maximum wave height, in addition to other user defined parameters. Only waves within these parameters are simulated to determine responses. The second alternative is the ‘New Wave’ approach, which models the most probable wave elevation around the maximum wave crest. The calculated new wave is then placed at the desired location to determine responses. The responses of the Regular, Irregular Wave Screen and New Wave methodologies are compared with the Irregular MPM approach to determine their feasibility to predict the response of flexibles in a real world irregular sea state with lower computational requirements.

Experimental Study on Model Predictive Control for a Point Absorber Type Wave Energy Converter With a Linear Generator

2018 ◽  
Author(s):  
Jun Umeda ◽  
Hiroki Goto ◽  
Toshifumi Fujiwara ◽  
Tomoki Taniguchi ◽  
Shunji Inoue
Keyword(s):  
Predictive Control ◽  
Wave Energy ◽  
Spectral Distribution ◽  
Time Horizon ◽  
Production Efficiency ◽  
Power Production ◽  
Irregular Waves ◽  
Regular Waves ◽  
Energy Converter ◽  
Point Absorber

This paper presents the experimental evaluation results of power production efficiency of model predictive control (MPC) on a wave energy converter (WEC) with a linear generator in regular and irregular waves. A bottom-fixed WEC of point absorber type was subjected to the WEC model in this paper. To compare the power production efficiency, the power production efficiency of the approximate complex-conjugate control with considering the copper loss (ACL) was also evaluated. In regular waves, the MPC performance was comparable to the ACL one in the power-production amount reasonably. In irregular waves which have narrow band spectral distribution, a same trend as the trend in regular waves was obtained. On the other hand, in irregular waves which have broadband spectral distribution, the MPC was more effective than the ACL. Moreover, Experiments in regular and irregular waves were carried out in the MPC under the constraint of the small heave displacement. The constraint of the displacement was approximately satisfied by the MPC. This is useful in practical operation. It is also investigated experimentally how time horizon affects the performance of the MPC. When the time horizon is short, the power production amount of the MPC increases.

Latching Control of an OWC Spar-Buoy Wave Energy Converter in Regular Waves

2012 ◽  
Author(s):  
J. C. C. Henriques ◽  
A. F. O. Falcão ◽  
R. P. F. Gomes ◽  
L. M. C. Gato
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Phase Control ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Wave Direction ◽  
Regular Waves ◽  
Energy Converter ◽  
Chamber Volume ◽  
The Time Domain

The present paper concerns an OWC spar-buoy, possibly the simplest concept for a floating oscillating-water-column (OWC) wave energy converter. It is an axisymmetric device (and so insensitive to wave direction) consisting basically of a (relatively long) submerged vertical tail tube open at both ends, fixed to a floater that moves essentially in heave. The length of the tube determines the resonance frequency of the inner water column. The oscillating motion of the internal free surface relative to the buoy, produced by the incident waves, makes the air flow through a turbine that drives an electrical generator. It is well known that the frequency response of point absorbers like the spar buoy is relatively narrow, which implies that their performance in irregular waves is relatively poor. Phase control has been proposed to improve this situation. The present paper presents a theoretical investigation of phase control by latching of an OWC spar-buoy in which the compressibility of air in the chamber plays an important role (the latching is performed by fast closing and opening an air valve in series with the turbine). In particular such compressibility may remove the constraint of latching threshold having to coincide with an instant of zero relative velocity between the two bodies (in the case under consideration, between the floater and the OWC). The modelling is performed in the time domain for a given device geometry, and includes the numerical optimization of the air turbine rotational speed, chamber volume and latching parameters. Results are obtained for regular waves.

scholarly journals MEASUREMENT OF INCIDENT WAVE HEIGHT IN COMPOSITE WAVE TRAINS

1974 ◽  
Vol 1 (14) ◽  
pp. 21
Author(s):  
Ake Sandstrom
Keyword(s):  
Wave Height ◽  
Incident Wave ◽  
Wave Train ◽  
Wave Length ◽  
Wave Theory ◽  
Arithmetic Mean ◽  
Reflected Waves ◽  
Wave Heights ◽  
Wave Trains ◽  
Composite Wave

A method is proposed for measurement of the incident wave height in a composite wave train. The composite wave train is assumed to consist of a superposition of regular incident and reflected waves with the same wave period. An approximate value of the incident wave height is obtained as the arithmetic mean of the wave heights measured "by two gauges separated a quarter of a wave length. The accuracy of the method in relation to the location of the gauges and the wave parameters is investigated using linear and second order wave theory. Results of the calculations are presented in diagrams.

scholarly journals Modeling Link for Ocean Wave Energy of Point Absorbers: A Mathematical Framework

2017 ◽  
Author(s):  
Lorenzo Baños Hernandez
Keyword(s):  
Wave Energy ◽  
Radiation Force ◽  
Ocean Wave ◽  
Irregular Waves ◽  
Mathematical Framework ◽  
Wave Direction ◽  
Regular Waves ◽  
Wave Regime ◽  
Ocean Wave Energy ◽  
Point Absorbers

This compendium presents new mathematical techniques for modeling Point Absorbers. A combined frequency-time domain framework is developed. It is used to simulate the energy generated by the wave farms. With Matlab and Fortran as a base, this leads to obtain physical variables of primary importance, namely position, velocity and power to energy net balance relationships of absorption. Integration of different degrees of freedom with heave as main executable leads in turn to a single buoy motion focus. Acquisition of the needed hydrodynamic coefficients is provided through application of potential field solvers with Boundary Element Methodology background. Initially, this Wave-to-motion model is validated by comparison with previous experimental results for a floating cone cylinder shape (Buldra-FO3). A single, generic, vertical floating cylinder is contemplated then, that responds to the action of the passing regular waves excitation. Later, two equally sized vertical floating cylinders aligned with the incident wave direction are modeled for a variable distance between the bodies. For both unidirectional regular and irregular waves as an input in deep water, we approximate the convolutive radiation force function term through the Prony method. By changing the spatial disposition of the axisymmetric buoys, using for instance triangular or rectangular shaped arrays of three and four bodies respectively, the study delves into motion characteristics for regular waves. The results highlight efficient layouts for maximizing the energy production whilst providing important insights into their performance, revealing displacement amplification- and capture width-ratios, while deriving in possible interpretations of scenarios related to the known park effect. These terms are encompassed by the novelty of a new conceptual Post-Processing methodology in the field, which leads to obtain an optimal distance for the separated bodies with effective energy absorption in a regular wave regime. The main objective is to generate a tendency within the hydrodynamic field of study, which is the Wave to motion perspective. More generally, this computational excursion envisions and depicts potential fields of study, which will surely enhance new connections and link this renewable energy form. Therefore, this research delves first into the historical and technical background on Ocean Wave Energy. Next, it is in the section regarding Materials and Methods, where boundaries and related equations are introduced step by step, together with latter mentioned case scenarios, and their corresponding configuration parameters. A separate section frames then the scope of results, while finally, there is an ensuing discussion and conclusions for evaluation assessment.

On cnoidal waves and bores

1954 ◽  
Vol 224 (1159) ◽  
pp. 448-460 ◽  
Keyword(s):  
Wave Train ◽  
Wave Length ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Stationary Waves ◽  
Steady Flows ◽  
Left Hand ◽  
Total Head ◽  
The Right ◽  
Supercritical Flows

For a train of gravity waves of finite amplitude in a frame of reference in which they are stationary, it is suggested that, in addition to the volume flow per unit span Q and the total head R , one may usefully study a third constant S , the rate of flow of horizontal momentum(corrected for pressure force, and divided by the density). The values of Q , R and S probably determine the wave-train uniquely; this is proved explicitly for long waves in a new presenta­tion of the ‘cnoidal wave’ theory (§3). The combinations of Q , R and S which are possible in the general case are illustrated by a diagram (figure 2) in which the co-ordinates are r = R / R c and s = S / S c ; here suffix c refers to ‘critical’ flow at the volume rate Q . There are two barriers on this diagram beyond which no stationary waves, or other steady flows, are possible; at the left-hand barrier (corresponding to uniform subcritical flows) the amplitude tends to zero; at the right-hand barrier (corresponding to uniform supercritical flows) the wave-length tends to infinity (case of the solitary wave). The diagram needs to be completed by a third barrier corresponding to ‘waves of greatest height’. This starts at the point marked Z and moves to infinity within the unshaded region without ever intersecting the left-hand barrier. The diagram may be used to determine what losses of momentum and energy a given stream can undergo, without departing from the condition of steady flow. Thus, one can determine the maximum wave resistance on a cylindrical obstacle athwart a given subcritical stream, or on a two-dimensional ‘step’ in the bed, in the absence of energy dissipation. Again, one can study the transition to a wave-train behind a bore. Such a wave-train (present in all but very strong bores) is shown to be capable of absorbing almost the whole energy which according to classical theory is liberated at the bore, although some minute residual dissipation of energy still appears to be necessary.

scholarly journals Array modeling and testing of fixed OWC type Wave Energy Converters

2020 ◽  
Vol 3 (3) ◽  
pp. 137-143
Author(s):  
Bret Bosma ◽  
Ted Brekken ◽  
Pedro Lomonaco ◽  
Bryony DuPont ◽  
Chris Sharp ◽  
...  
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Average Power ◽  
Irregular Waves ◽  
Regular Waves ◽  
Wave Energy Converters ◽  
Phase Errors ◽  
Array Optimization ◽  
Tank Test ◽  
Energy Converters

If wave energy technology is to mature to commercial success, array optimization could play a key role in that process. This paper outlines physical and numerical modeling of an array of five oscillating water column wave energy converters. Numerical model simulations are compared with experimental tank test data for a non-optimal and optimal array layout. Results show a max increase of 12% in average power for regular waves, and 7% for irregular waves between the non-optimized and optimized layouts. The numerical model matches well under many conditions; however, improvement is needed to adjust for phase errors. This paper outlines the process of numerical and physical array testing, providing methodology and results helpful for researchers and developers working with wave energy converter arrays.

The Spring-Like Air Compressibility Effect in OWC Wave Energy Converters: Hydro-, Thermo- and Aerodynamic Analyses

2018 ◽  
Author(s):  
António F. O. Falcão ◽  
João C. C. Henriques
Keyword(s):  
Wave Energy ◽  
Process Model ◽  
Wave Theory ◽  
Theoretical Models ◽  
Irregular Waves ◽  
Power Performance ◽  
Floating Structure ◽  
Wells Turbine ◽  
Compressibility Effect ◽  
Linear Water Wave Theory

The oscillating-water-column (OWC) wave energy converter consists of a hollow (fixed or floating) structure, open to the sea below the water surface. Wave action alternately compresses and decompresses the air trapped above the inner water free-surface, which forces air to flow through a turbine coupled to a generator. The spring-like effect of air compressibility in the chamber is related to the density-pressure relationship. It is known to significantly affect the power performance of the full-sized converter, and is normally not accounted for in model testing at reduced scale. Three theoretical models of increasing complexity are analysed and compared: (i) the incompressible air model; (ii) the isentropic process model; (iii) and the (more difficult and rarely adopted) adiabatic non-isentropic process model in which losses due to the imperfectly efficient turbine are accounted for. The air is assumed as a perfect gas. The hydrodynamic modelling of wave energy absorption is based on linear water wave theory. The validity of the various simplifying assumptions, especially in the aero-thermodynamic domain, is examined and discussed. The validity of the three models is illustrated by a case study with numerical results for a fixed-structure OWC equipped with a Wells turbine subject to irregular waves.

scholarly journals TRANSMISSION OF REGULAR WAVES PAST FLOATING PLATES

1974 ◽  
Vol 1 (14) ◽  
pp. 112
Author(s):  
Uygur Sendil ◽  
W.H. Graf
Keyword(s):  
Water Depth ◽  
Wave Length ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Linear Wave ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Wave Flume ◽  
Wave Heights ◽  
Incident Waves

Theoretical solutions for the transmission beyond and reflection of waves from fixed and floating plates are based upon linear wave theory, as put forth by John (1949), and Stoker (1957), according to which the flow is irrotational, the fluid is incompressible and frictionless, and the waves are of small amplitude. The resulting theoretical relations are rather complicated, and furthermore, it is assumed that the water depth is very small in comparison to the wave length. Wave transmissions beyond floating horizontal plates are studied in a laboratory wave flume. Regular (harmonic) waves of different heights and periods are generated. The experiments are carried out over a range of wave heights from 0.21 to 8.17 cm (0.007 to 0.268 ft), and wave periods from 0.60 to 4.00 seconds in water depth of 15.2, 30.5, and 45.7 cm (0.5, 1.0 and 1.5 ft). Floating plates of 61, 91 and 122 cm (2, 3 and 4 ft) long were used. From the analyses of regular waves it was found that: (1) the transmission coefficients, H /H , obtained from the experiments are usually less than those obtained from the theory. This is due to the energy dissipation by the plate, which is not considered in the theory. (2) John's (1949) theory predicts the transmission coefficients, H /H , reasonably well for a floating plywood plate, moored to the bottom and under the action of non-breaking incident waves of finite amplitude. (3) a floating plate is less effective in damping the incident waves than a fixed plate of the same length.

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