Jianxing Leng

Wavefront Aberration Characterization and Correction for Laser Beam Propagating Over Saline Water and Sands

Abstract Wireless laser communication is a promising method for communication in marine environment. However, as laser beam propagates through atmosphere, both wavefront and intensity of the laser beam can be influenced by the atmospheric turbulence. In this paper, wavefront aberration in the laser beam is characterized and corrected by an adaptive optics system while the laser propagates over saline water in a lab environment. Experiments have also been carried out when the laser beam propagates over sands for a comparison. With the correction by the closed-loop adaptive optics system, the variance of spots displacement in the Shack-Hartmann wavefront sensor has been reduced by 28% for saline water and 10% for sands.

Study of an Underwater retrievable cabin manufactured by hand layup process

Underwater surveillance network (UWSN) has been widely used in various scenarios, which is constructed by several single nodes composed of two parts: triangle bracing frame and retrievable spherical cabin fixed on top of it. This paper mainly presents the study of the cabin made of glass reinforced plastic material (GRP) manufactured by hand layup process. Then the strength and stability of the cabin was analyzed using finite element analysis software named ABAQUS. In addition, many influences were researched affecting the strength of the GRP product in hand layup processing. Especially, effects of resin content (resin weight fraction) were studied. Finally, the results of hyperbaric chamber experiment show that the designed retrievable cabin manufactured by hand layup process can properly work under ocean water of 200 meter.

Research on hydrodynamic performance of modular offshore wave energy platform

This paper presents a new type of modular wave energy generation platform model which is based on wave energy conversion system and offshore platform. In this paper, a hydrodynamic analysis commercial software was used to analyze motion responses to different wave conditions at the joints of each two unit modules of this platform in irregular waves. This wave energy generation device mainly has two kinds of working states: generating state and platform-working state, though this article only considered the former state. Results of simulation analysis were used to establish a quantitative model between the relative angular velocity and power generation efficiency of unit. The results demonstrate that the amplitude of angular velocity becomes larger while the wavelength and wave height increases. It is also demonstrated that there will be a resonance phenomenon when the wavelength is close to the feature size of the floating body. Furthermore, the power generation efficiency presents the characteristics of periodicity and attenuation gradually over time.

Color restoration method for underwater objects based on multispectral images

Perceiving color in water medium is always challenging due to the dense non-uniform attenuation and scattering of light across the visible spectrum. This paper presents a color restoration method for underwater objects based on multispectral images. To begin with, underwater multispectral images are obtained and restored with the influence of attenuation and scattering being eliminated by an in-suit restoration algorithm, and later on color images are restored from the multispectral images. Assessment of the restored color images and images taken by color camera in air medium authenticates the accuracy of the restoration method.

Research on the hydraulic power take-off unit of a hybrid wave energy converter

As an economical and easy deployment wave energy converter (WEC), oscillating bodies WEC is gained more and more attention, and it has great significance of research, especially on supplying power for buoy observation and underwater sensor network. Hybrid wave energy converter, it also named combined mode wave energy converter, can capture the kinetic energy of multiple degrees of freedom of an oscillating body. This paper presents a design of hybrid wave energy converter equipped with a hydraulic power take-off (PTO) unit, and builds the mathematical model of the hydraulic PTO circuit. According to the result of the numerical simulation of the hydraulic circuit, a steady system pressure and an essentially constant motor speed can be obtained with the help of accumulators. More cylinders than one are applied in the hydraulic circuit, and the relative spatial positions of the cylinders will affect the stability of the system pressure. Additionally, the stability of hydraulic system pressure is influenced also by the size of the accumulator and the number of the cylinders.

Numerical simulation on the deploying and recovering process for a node of underwater wireless sensor network

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.

The design and application of a new vertical-axis ship propeller

The new vertical-axis propeller is a kind of propulsion device, which can adjust revolving speed continuously to adapt to changeable working conditions under the constant velocity of diesel engine. Whats more, its own auxiliary transmission mechanism can realize some extra functions, such as clutch and hybrid power. Based on the propellers special steering principle and structure, this paper introduces the design of the propeller and its good application in hybrid power system.

Measurement of wavefront aberration in laser beam propagating over water

Atmospheric turbulence is a main limiting factor to the application of wireless laser communication in marine environment, which causes intensity variation and wavefront aberration in the laser beam. Characterizing the wavefront aberration of the laser beam is an important step for mitigating the effect of turbulence. In this paper, we focus on measurement and analysis of wavefront aberration in laser beam propagating over a lake with a transmitter-receiver distance of about 70 meters. Information of wavefront of the laser beam is obtained with a Shack-Hartman wavefront sensor. Both the spatial and temporal characteristics of the wavefront aberration in the laser beam have been investigated and characterized.