No abstract

Service composition is a technology capable of combing a collection of existing services where many smaller services are coordinated together to form a larger one. Functionally similar services can often show different quality-of-service (QoS) properties. For a specific service composition request, how to choose from a bag of suitable services that fulfill the required functions under given quality-ofservice constraints is widely believed to be a great challenge. The traditional approach usually tackles this problem by assuming fixed, bounded, or statistic QoS and views the decision-making of service composition as a static process. Instead, we address this problem by considering time-varying and fluctuating QoS and presenting a predictive-trend-aware service composition method by using a time series prediction model and genetic algorithms. We conduct extensive case studies based on multiple randomly-generated service templates with varying process configurations and show that our method outperforms existing ones. INDEX TERMS Time series, Quality-of-Service (QoS), service composition, genetic algorithm (GA).

Traditional wind turbine control algorithms attempt to maximize power capture at low speeds and maintain rated power at high wind speeds. Active power control refers to a mode of operation where the turbine tracks a desired power reference command. Active power control enables wind farms to perform frequency regulation and to provide ancillary services in the energy markets. This paper presents a multiple input, multiple output strategy for active power control. An H∞ controller is designed at several operating points to coordinate the blade pitch angle and generator torque. The objective is to track a given power reference command while also minimizing the structural loads. The controller is gain-scheduled based on the wind speed and the power output in order to compensate for the nonlinear turbine dynamics. This allows the turbine to be operated smoothly anywhere within the power / wind speed envelope. The performance of this gain-scheduled design is evaluated using high fidelity simulations.

Quantitative risk assessment (QRA) has been widely used in the oil and gas pipeline industry. QRA mainly includes four steps, namely, hazard identification, probability calculation, consequence assessment, and risk quantification. Consequence assessment is an integral part of QRA, which aims to quantify the negative impacts when pipeline failure events take place. However, the current consequence assessment methods mainly pay attention to the determination of the influence area around accidents and to simple assimilations of the losses, ignoring the components of these losses. This leads to the deterioration of the quality of the QRA. In this article, a methodology for overall consequence assessment in the oil and gas pipeline industry is proposed. The methodology mainly involves three stages, namely, identification of the accident scenario, the determination of influence area, and the calculation of possible losses. The most important innovation spot is integrating four aspects of release accident loss into a quantitative model, to calculate a quantitative result of the loss value of a release accident. Therefore, this study can overcome the limitations of current QRA methodologies and improve the quality of QRA for oil and gas pipelines.

Coal dust is a primary threat to underground coal miners. The most common approach to control coal dust is hydraulic methods, such as water spray and coal seam water injection. To improve the dust suppressant efficiency of hydraulic methods, a novel chemical composite dust suppressant, called NCZ, was prepared in this study using calcium chloride (CaCl2), magnesium chloride (MgCl2), and nonionic surfactants using a thermal synthesis method. The water-retaining properties of NCZ powder and its solutions were characterized using the water absorption rate (WAR) and evaporation rate (ER), respectively, and the wetting abilities of the NCZ solutions on coal dust were tested using the initial contact angle (ICA) and sink rate (SR). The results indicate that the NCZ solutions have anti-evaporation effects, and the ER of the solution with a 20.0 wt% NCZ is reduced by 11.7% compared with that of clean water. Furthermore, NCZ solutions have remarkable enhancement effects on the wettability of coal dust. The ICA and SR of clean water and the NCZ solution at 20.0 wt% are 141.9° and 0 mg/s, and 29.3° and 1.46 mg/s, respectively. Finally, quantitative relationships between the solution surface tension and the ICA and IR were established using the least squares method. This study provides a new product for dust suppression in underground mines, which is significant for the optimum applied concentration of dust suppressant in mining operations.