Numerical simulations for a wave driven hydro pneumatic electric plant.

Marin, Dorian ; Samoilescu, Gheorghe ; Nicolaie, Sergiu 等

1. INTRODUCTION

The simulation was done using a finite element for the conversion pillar. It used a structured exterior layer as a simulation domain, having the following dimensions: 16 m in length, 6 m in width. The matrix of the exterior layer consists of 41800 cells and 42498 nodes. The settings of the problem are exposed in Figure 1.

[FIGURE 1 OMITTED]

For the simulation, a VOF model and the dynamic exterior layer were used. The simulation time was 12 seconds, with difference interval varying from [10.sup.-6] to [10.sup.-4] seconds. Figure 2 shows the results for one difference interval.

The direction of the speed vectors from the Speed vectors Field has a downward orientation towards the intake. In the difference interval, a growth of pressure from one step to another can be observed. For the conversion of the wave action into mechanical energy a power unit alike hydro pneumatic station is necessary on the intake (Olaru, 2005). This system gathers the waves in a partially sunk artificial chamber, having a wall opening above the sea level. The opening leads to an air driven turbine. The wave crest enters the chamber, rapidly rising the water level, pressurizing the air as to exhaust it through the opening and spin the turbine's blades (Tanasescu, 1986).

The study conducts towards two different directions:

--the dynamic study of the wave impact on the base structure of the station;

--the dynamic response of the base structure of the hydro-pneumatic station. The best design of the base structure of the station is going to be chosen comparing the results produced by the two models. A dynamic study of the base structure of the station response to the mechanical stress will be performed.

[FIGURE 2 OMITTED]

For the numeric simulation, the following hypotheses were formulated:

--the wave force exceeds the stream power;

--the direct variation of pressure in depth will not be taken into consideration;

--only dynamic forces will be used;

--a flow surface of app. 3-6 sqm. will be considered.

2. MATHEMATICAL FORMULATION OF THE PROBLEM

As to obtain the dynamic force a numeric simulation of the flow, using a dynamic type external layer was performed. The wave energy is the sum of the Kinetic and the Potential Energy of the waves. The Potential Energy results from the following formula:

PE = m x g x y(x,t)/2, [J] (1)

where:

--m = w x [rho] x y, [kg],: wave mass;

--[rho]: water density, [kg/m3];

--w: wave width, [m], considered equal to the width of the chamber;

--y = y(x,t) = a x sin(kx - [omega]t), [m]: wave equation, considering sinusoidal waves;

--a = h/2, [m]: wave amplitude;

--h: wave height;

--k = -2[pi]/[lambda]: wave number;

--[lambda], [m]: wave length;

--[omega] = 2[pi]/T, [rad/sec]: wave frequency;

--T: wave period. (Volcanic & Matusevschi, 1985) The Potential Energy may also be written as:

PE = w x [rho] x g x [y.sup.2]/2 = w x [rho] x g x [a.sup.2]/2 x [sin.sup.2] (kx - [omega]t) (2)

Considering k = 2[pi]/[lambda] and [omega] = 2[pi]/T, we reach to

PE = 1/4 x w x [rho] x g x [a.sup.2] x [lambda] (3)

The pressure inside the chamber of the station obtained at the second difference interval is shown in Figure 3.

[FIGURE 3 OMITTED]

As to reveal the response of the base structure of the station to the wave action, a study in Cosmoworks will be performed. A dynamic test was applied to the base structure of the station, considering a difference interval of 0.314 s and a total length in time of 6s. The simulated material was AISI 1020 steel. The results are shown below:

Comparing Figures 4 and 5, we may conclude that in B configuration there a higher tension in the material, so the A configuration will be preferred.

[FIGURE 4 OMITTED]

The drifts are twice bigger in B configuration, so a configuration is preferred (Figures 6 and 7).

3. CONCLUSIONS

The present paper describes the best fitted model design for the Black Sea shore. Due to the comparison of the simulations in the study, a configuration could be considered as the optimum base structure design.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

4. REFERENCES

Olaru Gh. (2005), Masina motrica pentru utilizarea energiei valurilor (Car wave power for energy use). Brevet Ro 79184

Olaru Gh. & Lazar P.D. (2005), Rotor pentru turbine unisons (Turbine rotor unisens). Dosar OSIM A/00752-01.09

Tanasescu F.T. (1986), Conversia energiei--Tehnici neconvenpionale (Energy Conversion--unconventional techniques). Ed. Tehnica, 1986, p 30-50

Volcanic V.V. & Matusevschi G.B. (1985), Energhia Morschih vetrovih volni printip eio preobrazovania. In: Ghidrotehniceskoe stroitelstvo, 4. 1985, p. 52-74

*** Wave Energy Summit 2008, http://www.waveenergytoday.com/wave08; Accessed on: 2009-03-10

*** Wavegen a world leader in marine renewable energy, httm://www.wavegen.co.uk; Accessed on: 2009-03-10

*** Wave Power--energy from the wind on the sea. http://www.darvill.clara.net/altenerg/wave.htm Accessed on: 2009-03-10