### 1. Introduction

### 2. Design of Current Generator in DOEB

### 2.1 Numerical Analysis for Design of Current Channel (Waterway) in DOEB

*P*is the viscous resistance,

_{v}*P*is the inertial resistance, and

_{i}*V̄*is the mean velocity through a perforated wall with a given degree of solidity. The current study neglected the viscous term and calculated the inertial resistance by using a pressure loss formula as follows: where

*ρ*is the fluid density,

*K*is the loss coefficient,

_{o}*R*is the Reynolds number based on the diameter of wire screen, and

_{ed}*β*is the solidity.

*f*(

*R*) is a function of the pressure drop and has a converged value of 0.5 at

_{ed}*R*> 100. More details of the numerical methodology can be found in a previous study (Park et al., 2014).

_{ed}^{st}channel layer, and its length spanned 5.9 m from the exit of the channels. However, the effects of the re-circulation flow are not expected to be significant since the location of the model test zone is 50 m from the current channel exit.

*x*= 50 m in the y direction. As shown in Fig. 5(a), re-circulation flow regions were formed in the upstream and downstream parts of the basin. The current speed slowed as the flow went downstream of the basin, but sufficiently constant current distribution was obtained over the measurement zone.

*x*= 50 m satisfies the extreme current speed target of 0.5 m/s. On the other hand, the uniformities of the velocity profiles below the free surface were slightly low. This can be overcome by using higher solidity, but it causes an increase in the head loss of the current pumps. In model tests, it is necessary to investigate the effects of the non-uniformity of the current below the free surface according to the draft of offshore structure models.

*x*= 50 m and

*y*= 17.5 m. The water depth influenced by the three upper current channel layers that were directly considered in the grid was about z = −5.8 m. Below this depth, the current profile was generated by a constant velocity inlet condition with an inclined angle imposed at the inflow section of each of the three lower current channel layers. Within the design capacity of the pump, the current generation system reproduced the design extreme current profile well and showed good agreement. Table 2 shows the calculated results of the head loss of the current channel at the design flow rate. The maximum head loss value was used for the pump capacity and impeller design.

### 2.2 Design of Current Generation System

^{3}/s and required head loss of 1.33 m) and to absorb the motor power. Two types of impellers were designed to ensure suitability for different loads due to the head loss across the flow layer. The first impeller type was designed for the second and third layers, and the second impeller type was designed for the first, fourth, and fifth layers.

### 2.3 FAT (Factory Test) of Current Generation System

### 2.4 Installation and Testing of Current Generation System

### 3. Analysis of the Current Characteristics in DOEB

### 3.1 Characteristics of Flow Rate of the RPM Current in the Current Generation System

### 3.2 Spatial Area Characteristics of Current in DOEB

*T*) was examined based on the equation obtained by Bas Buchner (Buchner and Wilde, 2008). where σ is the standard deviation of the velocity fluctuations, and

*V*is the mean velocity.