This article proposes a control strategy that combines optimized loudspeaker arrays using constrained matching pursuit and zero pressure constrained points. The proposed control strategy is used to optimize the loudspeaker placement of an active control system that aims to control the scattered sound field of a rigid sphere. Compared to the strategy employing uniformly placed loudspeaker arrays, the proposed control strategy has a better reduction performance in the square target area and less amplification in other areas. This advantage becomes greater with increases in the power constraint on the secondary loudspeaker and the frequency of the primary field.

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TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThis paper presents a new method and flowchart of risk assessment for the oil and gas upstream industry to identify and evaluate the risks in the oil and gas investment activities. It integrates several commonly used risk identification techniques, including fault tree analysis, brainstorming, and Delphi and event tree analysis methods. This paper divides the risk factors into three categories: social environment, natural environment and resources, technology and management, there are several risk factors in each category; therefore, a risk assessment system of the three hierarchies is built up. In the third hierarchy, a risk grade standard is established according to expected economic loss, which is determined by the risk probability and the consequence of the risk factors. A new method of the risk assessment was presented, Fuzzy Analytical Hierarchy Process (Fuzzy-AHP). The integrated risk grade of oil and gas exploration and development project can be obtained. In this method, the influence weight and the consequence of risk factors are comprehensively considered. It gives a significant reference for decision-makers of the oil and gas upstream industry. At present, this method has been recommended to the exploration and development risk assessment projects in the oilfields, China.

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Abstract:In this paper, the effect of oil injection flow rate on the performance of a variable speed twin-screw compressor was investigated experimentally. Comprehensive experiments were conducted at different compressor rotational speeds and oil injection flow rates. As the rotational speed increased from 1000 to 3000 rpm, the compressor volumetric and adiabatic efficiencies increased while the specific power consumption decreased. However, the oil injection flow rate showed different influences on the compressor performance. As the oil injection flow rate increased from 27 to 50 L/min, the adiabatic and volumetric efficiencies increased while the compressor discharge temperature and specific power decreased. Further increases in the oil injection flow rate had little effect on compressor performance at flow rates above 50 L/min. The analysis indicated that the oil injection flow rate was limited by the discharge temperature at low compressor rotational speeds and was a trade-off among two efficiencies and specific power consumption at high rotational speeds.