*2.1.2.1. Float pitching convertors*

Developed in Lancaster University and off-shore WEC, *PS Frog Mk 5* is the best example of Floating Pitching Convertors [26]. As it is illustrated in fig. 15, PS Frog Mk 5 is composed of a large buoyant paddle with an internal ballasted handle below it. It oscillates in pitching mode and is float on sea level. When wave acts on paddle the ballast provides necessary re‐ action for pitch motion, consequently the wave power is absorbed by partially resisting the sliding of a PTO mass, which moves in guides above sea level. The sliding mass (PTO) con‐ verts the wave motion into differential mechanical motion within device then the mechani‐ cal motion is transferred via hydraulic circuit to an electrical generator.

The main advantages of PS Frog Mk 5 is its self-orienting capability with which the device spontaneously adjusts to face incident waves. Meanwhile, by moving ballast in the hall or by controlling sliding mass, it is viable to control PS Frog Mk 5 in resonance frequency in which device has the maximum capture width.

**Figure 16. Left side:** Scheme of Pelamis and principle of working [27]. **Right side:** Full scale prototype (By Ocean Pow‐

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The PTO section of Pelamis is divided to two main parts which are called primary and sec‐ ondary transmissions. The primary transmission, which stores wave power in hydraulic ac‐ cumulator, consists of the hydraulic cylinders and their controllers. The secondary transmission, consisting of hydraulic motors coupled to electric generators, converts the en‐ ergy stored in the hydraulic accumulators into electricity transmitted to shore. The separa‐ tion provided by high pressure accumulator and controlling of electronically controlled valves, which controls input and output fluid of accumulators, makes it feasible efficient

Full scale prototype Pelamis WEC, 120 m long and 3.5 m diameter, has been constructed and

Yet, there are different devices that fall in this category [29, 30] one of which is Oyster [31], Aquamarine Power Ltd developed near-shore WEC. The Oyster is a bottom hinged rigid flap which completely penetrates the water column from above the surface to the sea bed. When wave attach the Oyster, WEC starts to oscillate in pitch mode, rotational motion around hinging axis, and this motion moves a double acting high pressure sea water pump. A set of non-return valves rectify the flow from the double acting pump consequently the flow is regulated by a gas accumulator. The flow (water) is transferred to the shore through pipeline. In the onshore hydraulic plant, hydraulic pressure is converted into electric power via a Pelton wheel. Finally the water passes back to device in a close lop via a second low pressure return pipeline. The schematic of Oyster is presented in fig. 17. Another WEC that work in the same principle is WaveRoller WEC. In spite of Oyster, the rigid flaps of WaveR‐

has been successfully connected to local electrical power network.

oller are short and it harvests wave power only near seabed [30].

er Delivery Ltd).

power absorption from ocean waves.

*2.1.2.3. Submerged pitching convertors*

**Figure 15. Left side:** 2D illustration of PS Frog Mk 5 [16]. **Right side:** Perspective view of PS Frog Mk 5 [26].

#### *2.1.2.2. Two body pitching convertors*

Pelamis is a multi-body, floating, off-shore WEC. This device consists of several slender semi-submerged cylinders linked by hinged joins [27, 28]. When wave acts on Pelamis, adja‐ cent cylinders start to fluctuating by angular motion in the joins in which wave power is ab‐ sorbed in Pitch and Yaw mods. The scheme of Pelamis is presented in Fig. 16. In this figure, the left side represents the working concept of Pelamis and the right side shows a full scale Pelamis. In Pelamis the motion of cylinders is used to move hydraulic cylinders which pump fluid to high pressure fluid accumulators for short term energy storage. Furthermore, the smooth supply of high pressure fluid in accumulators drives hydraulic motors which are coupled with grid-connected electric generators. About device mooring, because of the selfreferencing no rigid connection to the sea-bed is required and a slack mooring is sufficient to hold the device on station.

**Figure 16. Left side:** Scheme of Pelamis and principle of working [27]. **Right side:** Full scale prototype (By Ocean Pow‐ er Delivery Ltd).

The PTO section of Pelamis is divided to two main parts which are called primary and sec‐ ondary transmissions. The primary transmission, which stores wave power in hydraulic ac‐ cumulator, consists of the hydraulic cylinders and their controllers. The secondary transmission, consisting of hydraulic motors coupled to electric generators, converts the en‐ ergy stored in the hydraulic accumulators into electricity transmitted to shore. The separa‐ tion provided by high pressure accumulator and controlling of electronically controlled valves, which controls input and output fluid of accumulators, makes it feasible efficient power absorption from ocean waves.

Full scale prototype Pelamis WEC, 120 m long and 3.5 m diameter, has been constructed and has been successfully connected to local electrical power network.

### *2.1.2.3. Submerged pitching convertors*

*2.1.2.1. Float pitching convertors*

286 New Developments in Renewable Energy

Developed in Lancaster University and off-shore WEC, *PS Frog Mk 5* is the best example of Floating Pitching Convertors [26]. As it is illustrated in fig. 15, PS Frog Mk 5 is composed of a large buoyant paddle with an internal ballasted handle below it. It oscillates in pitching mode and is float on sea level. When wave acts on paddle the ballast provides necessary re‐ action for pitch motion, consequently the wave power is absorbed by partially resisting the sliding of a PTO mass, which moves in guides above sea level. The sliding mass (PTO) con‐ verts the wave motion into differential mechanical motion within device then the mechani‐

The main advantages of PS Frog Mk 5 is its self-orienting capability with which the device spontaneously adjusts to face incident waves. Meanwhile, by moving ballast in the hall or by controlling sliding mass, it is viable to control PS Frog Mk 5 in resonance frequency in

**Figure 15. Left side:** 2D illustration of PS Frog Mk 5 [16]. **Right side:** Perspective view of PS Frog Mk 5 [26].

Pelamis is a multi-body, floating, off-shore WEC. This device consists of several slender semi-submerged cylinders linked by hinged joins [27, 28]. When wave acts on Pelamis, adja‐ cent cylinders start to fluctuating by angular motion in the joins in which wave power is ab‐ sorbed in Pitch and Yaw mods. The scheme of Pelamis is presented in Fig. 16. In this figure, the left side represents the working concept of Pelamis and the right side shows a full scale Pelamis. In Pelamis the motion of cylinders is used to move hydraulic cylinders which pump fluid to high pressure fluid accumulators for short term energy storage. Furthermore, the smooth supply of high pressure fluid in accumulators drives hydraulic motors which are coupled with grid-connected electric generators. About device mooring, because of the selfreferencing no rigid connection to the sea-bed is required and a slack mooring is sufficient to

cal motion is transferred via hydraulic circuit to an electrical generator.

which device has the maximum capture width.

*2.1.2.2. Two body pitching convertors*

hold the device on station.

Yet, there are different devices that fall in this category [29, 30] one of which is Oyster [31], Aquamarine Power Ltd developed near-shore WEC. The Oyster is a bottom hinged rigid flap which completely penetrates the water column from above the surface to the sea bed. When wave attach the Oyster, WEC starts to oscillate in pitch mode, rotational motion around hinging axis, and this motion moves a double acting high pressure sea water pump. A set of non-return valves rectify the flow from the double acting pump consequently the flow is regulated by a gas accumulator. The flow (water) is transferred to the shore through pipeline. In the onshore hydraulic plant, hydraulic pressure is converted into electric power via a Pelton wheel. Finally the water passes back to device in a close lop via a second low pressure return pipeline. The schematic of Oyster is presented in fig. 17. Another WEC that work in the same principle is WaveRoller WEC. In spite of Oyster, the rigid flaps of WaveR‐ oller are short and it harvests wave power only near seabed [30].

electric machine is switched to motor operation and drives the system, lifting the first pad‐

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Another surge WEC is designed by these authors [34, 35]. It consists of a rigid plate which is installed in near-shore vertical to the sea bed. The plate has been connected to a linear gener‐ ator. When waves attack the plate it fluctuate in horizontal direction, parallel to the wave propagation direction (See Fig. 19). Various power electronic instruments has been imple‐ mented to deliver ocean wave power to electric network. The device is still under develop‐

Interface-WECs are device that have no oscillation in interacting ocean wave. In fact these devices are designed to deliver wave energy via an interface (Air or Water) to the PTO. In

Oscillating water column (OWC) WEC is an Air-interface WEC in which wave power is con‐ verted to the electrical power without direct oscillation of WEC body by water particle. OWC is consists of a floating or bottom fixed structure whose upper part encloses a column of air and whose immersed part is open to the wave action [36]. The scheme of OWC is pre‐

dle out of the path of the waves and lowering the next paddle into the wave path.

**Figure 19.** Schematic of Surge WEC.

**2.2. Interface-WECs**

*2.2.1. Air-interface*

sented in Fig. 20.

ment in Altin Tara Electric Ltd. in Iran.

comparison to Oscillation-WECs they require less maintain.

**Figure 17. Left Side:** Schematic of pitching flap WEC. **Right Side:** The Oyster WEC by Aquamarine Power Ltd [32].

**Figure 18.** The power matrix of bottom hinged pitching flap [22].

The power capture performance of submerged pitching convertor is presented in Fig. 18.

#### *2.1.3. Surging oscillators*

However, waves' force in near-shores is concentrated in surge direction [8], surge wave en‐ ergy convertors are less developed WECs in comparison to other types.

Developed in Western Ontario University namely "Surfing Wave Energy Convertor" is one of the surge WECs [33]. The Surfing Wave Energy Convertor is comprised of several pad‐ dles connected to a common drive train, which mechanically links them to an electric ma‐ chine. The operating cycle begins with a paddle suspended in the path of the incoming wave. As the waves impact the paddle it is driven horizontally in the direction of wave trav‐ el in a 'Surfing' like motion. The horizontal motion of the paddle in-turn drives the electric machine, generating power. Once the paddle reaches the downstream end of the system, the electric machine is switched to motor operation and drives the system, lifting the first pad‐ dle out of the path of the waves and lowering the next paddle into the wave path.

**Figure 17. Left Side:** Schematic of pitching flap WEC. **Right Side:** The Oyster WEC by Aquamarine Power Ltd [32].

The power capture performance of submerged pitching convertor is presented in Fig. 18.

However, waves' force in near-shores is concentrated in surge direction [8], surge wave en‐

Developed in Western Ontario University namely "Surfing Wave Energy Convertor" is one of the surge WECs [33]. The Surfing Wave Energy Convertor is comprised of several pad‐ dles connected to a common drive train, which mechanically links them to an electric ma‐ chine. The operating cycle begins with a paddle suspended in the path of the incoming wave. As the waves impact the paddle it is driven horizontally in the direction of wave trav‐ el in a 'Surfing' like motion. The horizontal motion of the paddle in-turn drives the electric machine, generating power. Once the paddle reaches the downstream end of the system, the

ergy convertors are less developed WECs in comparison to other types.

**Figure 18.** The power matrix of bottom hinged pitching flap [22].

*2.1.3. Surging oscillators*

288 New Developments in Renewable Energy

Another surge WEC is designed by these authors [34, 35]. It consists of a rigid plate which is installed in near-shore vertical to the sea bed. The plate has been connected to a linear gener‐ ator. When waves attack the plate it fluctuate in horizontal direction, parallel to the wave propagation direction (See Fig. 19). Various power electronic instruments has been imple‐ mented to deliver ocean wave power to electric network. The device is still under develop‐ ment in Altin Tara Electric Ltd. in Iran.

### **2.2. Interface-WECs**

Interface-WECs are device that have no oscillation in interacting ocean wave. In fact these devices are designed to deliver wave energy via an interface (Air or Water) to the PTO. In comparison to Oscillation-WECs they require less maintain.
