1st Asian Wave and Tidal Conference Series Dynamic Tidal Power for Korea Kees Hulsbergen1,#, Dimitri de Boer2, Rob Steijn3 and Gijs van Banning3 1 Hulsbergen Hydraulic innovation & Design H2iD, Johanneshof 44, 6953 CR, Dieren, The Netherlands 2 UNIDO- ITPO-China, Team Leader EU Programs, Tayuan Diplomatic Office Building 2-141, No. 14 Liangmahenanlu, Chaoyang District, 100600 Beijing , China 3 ARCADIS, POB 137, 8000AC, Zwolle, The Netherlands # Corresponding Author / E-mail: [email protected], TEL: +31-313-844515 KEYWORDS : tidal power, new concept, mature technology, no basin, environmentally neutral, twin mode, base load, 100 GW for China, 50 GW for Korea Abstract. This paper describes the fluid mechanical background of Dynamic Tidal Power (DTP), reports highlights of recent developments in China, and looks ahead to its potential for Korea. DTP is a revolutionary concept (patented) to tap huge amounts of tidal energy of semi-enclosed seas like North Sea, East China Sea and West Korean Sea. DTP uses a new source, ‘hidden’ in tides, through applying Newton’s Second Law but now ‘in reverse direction’, liberating Force from accelerating water masses. This Force emerges as hydraulic head of several m created by long ‘artificial peninsulas’: dams built out from the shore right into the sea. Constructing dams using prefab caissons is mature technology based on centuries of Dutch self-protection, while power take-off is based on bi-directional turbines. The rate of flow is huge thanks to a long row (about 30 km) of 5 MW turbines mounted in caissons. Best dam perforation rate is 10 to 15% to create an optimum combination of head and rate of flow, generating 5-15 GW per dam. Typical qualities of DTP include absence of a closed basin, preservation of tidal flats and nature values, easy access to turbines and power cables, stable base load through twin dams 200 km apart feeding into a common grid, and ‘natural’ multiple functions such as ‘dry offshore wind’, deep sea ports, reclamation works, and inter-island connection. Estimated DTP potential for China is 100 GW, for Korea 50 GW. NOMENCLATURE Δpaverage = time-maximum differential pressure a = acceleration of flow or plate = dv/dt averaged over the whole plate length D = length representing size of submerged object Δpcentre total = total net differential pressure F = force working over the plate’s centre Fmax = maximum total force over whole plate Δpmax = time-maximum differential pressure g = acceleration of gravity over the plate’s centre (maximum pressure head) h = depth of immersion ρ = mass density of water KC = Keulegan-Carpenter number Vmax*T/D ω = angular frequency 2π/T m = mass p = water pressure 1. Introduction p = pressure on the central right hand centre right side of the plate Dynamic Tidal Power (DTP) is a patented way to extract large R = radius of added mass cylinder enveloping amounts of energy from tides in a cost-effective and environmentally plate length; halve plate length; dam length careful manner. While DTP’s power source differs from the well- t = time known concepts of Tidal Barrage and Tidal Stream, its technical T = period of oscillation or of (tidal) wave implementation is mature and reliable: prefab concrete caissons v = velocity of flow or plate containing turbines. DTP however does not apply a closed basin like V = maximum velocity of flow or plate max Tidal Barrage, but instead catches tidal energy ‘on the fly’, using a Δh = maximum differential head over a dam max very long (>10 km) perforated dam built out from the shore, applying at coast attachment point Newton’s Second Law ‘in reverse mode’ as its energy source. 1 1st Asian Wave and Tidal Conference Series Tidal power attracts new world-wide interest. Tidal Barrage plans maximum of 0.85 m. This head (= force leaning against the peninsula) in England and Korea however recently came under public criticism could drive turbines producing electric power, just like a conventional Tidal Barrage would, but without a closed basin. mainly by concerns about effects on intertidal flats and associated environmental and social impacts. Developments in Tidal Stream on the other hand show a steep upward curve perhaps because it is environmentally less intrusive and comes in small units. However, the associated costs per kWh are regarded still too high. Meanwhile, urgency grows to implement national energy security measures and meet international goals set for curbing GHG growth. In this context Dynamic Tidal Power forms a new option to deliver huge amounts of renewable energy, while its technology is surprisingly mature. 2 Nature, for example Fig. 3 Tides W (red) and E (blue) of Portland Bill peninsula The 2012 Olympic sailing contests took place at England’s south Many peninsulas worldwide show similar phenomena, e.g. Dalian in coast off Weymouth, in a bay sheltered by Portland Bill, a peninsula China. DTP however calls for longer artificial peninsulas creating higher heads, less hydraulic loss, more power, and lower costs per about 10 km long amidst quite strong oscillating tidal streams (Vmax up to 1.6 m/s at springs) in the English Channel, see Fig. 1. kWh compared with natural peninsulas. DTP specially provides the option to create artificial peninsulas along otherwise straight coastlines, thereby possibly connecting strings of offshore islands. Offshore wind turbines may be placed on such DTP ‘peninsula’, enabling exploitation of significantly less costly ‘dry offshore wind power’. Looking back at Fig. 3 one might think that the head actually is a locally generated ‘added wave system’, provoked by Portland Bill while interacting with the strong tidal streams. This is indeed what happens, as will be shown below. Key to appreciate this interpretation 100 km is recognizing the dominant role of oscillating streams, and in Fig.1Weymouth and Portland Bill, south England particular of the acceleration (dv/dt), inherently present amidst these rhythmically unsteady tidal water masses, though not directly visible A numerical tidal model was used to examine an interesting to the casual observer. phenomenon, which illustrates the concept of Dynamic Tidal Power [1]. At two locations just W (red) and E (blue) of the peninsula’s neck 3 Newton (Fig. 2) water levels were computed for spring tide on 18 Sep 2012, Newton combined acceleration (a), mass (m) and force (F) into his famous trinity [2]. One consequence of the finite dimensions of any mass volume is the creation of tides, generated by interplanetary dynamics (gravitation, the spinning Earth, and the Moon and Earth revolving around their common centre of gravity), making huge nd masses of ocean water accelerate according to Newton’s 2 Law: Force = mass * acceleration. Once set in motion, these water masses keep obeying F = m * a, propagating as long tidal waves navigating the oceans until they finally arrive at continental edges (where seabed and coastal configuration have a predominant effect on the tides’ local Fig. 2 Locations West (red) and East (blue) of Portland’s Neck characteristics), while the deforming tides are still loaded with energy. To release a part of this energy from its bond with water masses in resulting in the graphs shown in Fig. 3. These tides, at locations just acceleration, DTP applies Newton’s Second Law, but this time ‘in 20 km apart as measured around Portland Bill, show distinctly reverse direction’, since mass and acceleration are already present: different amplitudes and shapes. The resulting time-dependent mass * acceleration Force. This is where the (artificial) peninsula differential water level, i.e. the hydraulic head across Portland Neck, is shown in Fig. 3 by a black dashed line in absolute value, with a comes in, taking the leading part in liberating this Force, as in Fig. 3. 2 1st Asian Wave and Tidal Conference Series 4 Birth of DTP velocity) or inertia (coupled to acceleration) [9]. KC is a dimensionless parameter defined as Vmax*T/D, where Vmax is the Back in 1996 two researchers from Delft Hydraulics tested a 50 km maximum ambient flow velocity, T is the oscillation period, and D is long solid dam in a well validated numerical tidal model of the North the relevant object diameter. For large KC numbers the flow behaves Sea. The local tide is modest with a mean tidal range of 1.5 m and quasi steady so that drag force is dominant, whereas for small KC maximum coast-parallel stream velocities of 0.7 m/s at springs. This numbers inertia force prevails. For the dam/peninsula case KC turns ‘modeled dam’ was attached to the straight Dutch coast, extending out to be very small, about unity (Vmax is 0.7 m/s, T = 12.4 hours = perpendicularly to the shoreline, the tip standing in 35 m deep water. 45,000 s, and D = 50,000 m), meaning that drag force is irrelevant Much to the surprise of many, a time-dependent hydraulic head of compared to inertia. In other words: in such very long peninsula more than 2 m appeared across almost the entire dam length. Nobody situations acceleration (dv/dt) plays an absolutely dominant role. This had seen this before. We stared at an artificial peninsula with its own is crucial to Kolkman’s further approach of the conundrum. locally generated tides, not knowing how to explain its creation. For a description of the way this problem was tackled we also refer to [3, 4]. It may be noted that Kolkman applied the KC tool here in a daring way, not afraid to stretch the range of its application to the 5 Fluid mechanics of DTP: the Kolkman-effect extreme. While KC analysis is well established for pile diameters of 10 m, ship lengths of 300 m and wave periods of 10 seconds, This Section highlights the peculiar effects of accelerating and Kolkman applied KC to a 50,000 m long dam and to wave periods of decelerating flow and associated ‘added mass’, forming the driving 45,000 seconds.