An underwater wireless sensor network (UWSN) has multiple functions in ocean survey. A kind of UWSN has been proposed by Zhejiang University. In this paper the CFD method is utilized to verify the ability of a node to adjust its posture in deploying and recovering process. The minimum depth and the minimum time for a node to adjust itself to vertical were obtained in different initial inclined angles and different ocean current velocities. The different initial inclined angles were chosen as 45 degree, 60 degree and 90 degree. The different ocean current velocities were chosen as 0.5m/s and 1m/s according to the actual sea conditions around the Zhoushan Island. The minimum rising height and the minimum time for the retrievable cabin to turn 180 degree were obtained in still water. The purpose of the retrievable cabin to turn 180 degree is to keep antenna upright on the ocean surface. Because the antenna was installed on the bottom of the retrievable cabin. These results show that the design of the UWSN node is reliable as to the scheme of the node to deployment and recovery.
I. INTRODUCTION
The underwater wireless sensor network (UWSN) has been utilized in various scenarios including oceanic ecosystem preservation, petroleum exploration, fresh water quality monitoring, and others [1]. The underwater wireless sensor network consists of several UWSN nodes with many functions including data collecting, data memorizing, and acoustical communication. For each UWSN node, it has to be deployed before working underwater and recovered after completing its mission. University of Pennsylvania designed a kind of UWSN node and verified its feasibility by experiment [2]. But there are no guarantees for this node to be deployed stably on the seabed and no scheme to retrieve. University of Buffalo proposed a sort of UWSN node which is linked with a floating ball [3]. This node takes advantage of itself structure and mass distribution to make the deployment process easy and stable. The retrieve process is triggered by an electromagnetic detacher. However, there is no assessment for the deployment and retrieve process. The commercial product SM-75 [4] of Teledyne Benthos company used some weight to fix a node of UWSN on seabed and the node has positive buoyancy. After its mission has been finished, the node would detach from the weight and come up to ocean surface. This product has been used by Taiwan University to perform scientific research under hundreds meters of water. In actual use, SM-75 has a high performance [5]. However, this design has some drawbacks on fixing a node. When ocean current velocity becomes large, the distance between the node and weight which is used to fix the node would change with time. Then Doppler Effect would appear and the stability of underwater acoustic communication would be affected. In China, Northwestern Polytechnical University designed a kind of UWSN. It has a compact structure and lower energy consumption [6].
IV. RESULTS AND DISCUSSIONS
CFD simulations have been implemented to verify the ability that a node adjusts its posture in deploying and recovering process. The following figures show these results.
For the deployment process, the minimum depth about 20m and the minimum time about 7 seconds for a node to adjust itself to vertical are obtained despite of the different initial inclined angles. The ocean current has little influence on the deployment process. Figure 3 and Figure 4 show the time of the node to adjust itself to vertical in different initial inclined angles which are 45 degree, 60 degree and 90 degree. We can conclude that the current and the initial inclined angles almost have no influence on the time that the node would adjust itself to vertical. It means that the node needs about 7 seconds to adjust itself to vertical despite of the ocean current and initial inclined angles. Then, from Figure 5 to Figure 7, we can conclude that current has an influence on the process of adjustment.
