Narrow Results

Wettability, porosity and mechanical properties of ultrasonic-aided laser reflow soldering lead-free solder Sn-3.0Ag-0.5Cu (SAC305) on Cu pad have been investigated at ultrasonic vibration (USV) of different power. The parameters of laser reflow soldering are determined by the wetting experiment, and the effects of different ultrasonic powers on the performance of the solder joint are studied. Results showed that USV can improve wettability without keyholes on top of the solder joint, and the contact angle between the solder joint and the substrate decreases first and then increases as the ultrasonic power increases. The cavitation effect caused by USV effectively reduces the porosity of the solder joints. When the ultrasonic power is 225 W, the porosity of the solder joint is reduced from the initial 13.2% to 5.2%. Through X-ray Diffraction (XRD) analysis of the solder joint matrix, all solder joints have diffraction peaks of $\beta$-Sn, Cu₆Sn₅ and Ag₃Sn, and the solder joints show higher diffraction peak intensity with USV treated. Furthermore, the solder joints prepared by ultrasonic-aided laser reflow soldering show better shear strength compared with laser reflow soldering.

Decentralized control allows each unmanned surface vehicle (USV) in a flock to be autonomous to some extent. In this paper, the flocking algorithm put forth by Olfati-Saber was improved and applied in the multi-leader scenario based on its original flocking movement. Repulsion was also taken into account in the formation. Subsequently, the concept of neighborhood in finite-range communications was borrowed to control the communication distance of each USV. In this way, USVs could satisfy the restriction of a given communication distance, and avoid collision in motion. USVs might have collaborative tracking of a virtual leader and obtain the distributed cooperative control strategy. Based on the simulation results, the improved flocking control algorithm allowed every USV to accurately track the speed of the virtual leader they followed, respectively. The test results also demonstrated the effectiveness of the algorithm in safe flock navigation, and proved that the proposed control algorithm must be an effective way to ensure the safe flocking of multiple USVs.

Multi-sensors system is important in the research of unmanned surface vehicle for the environmental perception. The ASAROME project * (Autonomous SAiling Robot for Oceanographic MEasurements) is focused on an autonomous sailboat to make measurements and observations with a multi-sensor system in the marine environment for long term.

This paper is based on a green energy USV model which is designed and built by ourselves. In this paper, we conducted a series of roll decay tests on the USV model under different loads and tilt angles. According to the characteristics of USV hull we established the corresponding mathematical model. We analyzed the experimental data through an identification program with optimization. In the process of the swing we got some curves including roll angle and roll angular velocity, at the same time we found the changes of the hydrodynamic derivatives. Eventually, the processed data was analyzed and the related hydrodynamic coefficients were acquired. The research for unmanned vehicle motion and its method in this paper would improve the basic technical support for USV airworthiness, and put forward the improvement method of reference of sea worthiness.

Optimization is an important part of the design on Unmanned Surface Vehicle (USV). In this paper, considering the rapidity, maneuverability, seakeeping and rollover resistance performance of the USV, the design variables of the optimization system of the USV have been determined a mathematical model for comprehensive optimization of USV has been established. Integrated optimization design of multi-target and multi-constrain is achieved by computer programs. However, the influence degree of each design variable are different on the final optimization results, in order to determine the degree of influence of each design variables, find out the key variables for a further optimization analysis and sensitivity studies of the design variables to optimization will be crucial. For solving this problem, a C++ program has been written by genetic algorithm and five discrete variables have been selected which are used to study the sensitivity of optimization. The results showed that different design variables have different effects on the optimization. The length of the ship and the speed of propeller have the greatest effect on the total objective function. The speed of propeller has a greater impact on both rapidity and seakeeping. The length of ship L, the molded breadth of ship B, the draft of ship T and design speed Vs have a greater sensitivity to maneuverability. Also, molded breadth B has the greatest effect on the rollover resistance.