燃气透平冷却空气量及变工况估值计算的研究

根据大型发电燃气轮机的结构和性能资料,对西门子V94.3燃气轮机冷却空气量的计算方法进行了研究。从燃气透平叶片冷却方式和机理入手,得到燃机冷却空气量的计算模型。该方法简单易于理解,计算精度满足实际工程分析需要。

EDLC charging performance for microgrid applications

In order to review storage performance of the electric double layer capacitor （EDLC） in microgrid applications, charging time and storage efficiency issues are mainly studied aiming at three different charging modes, including the constant voltage charging mode （CVCM）, the constant current charging mode （CCCM） and the constant power charging mode （CPCM）, based on the practical EDLC product. Numerical calculation methods are presented for different charging modes, and the charging efficiency is also reviewed with strict mathematical deductions, which is validated to be accurate enough and applicable through a simple case with the PV/EDLC system illustration. Finally, trade-off problems between charging time and energy loss are also studied. Research results show that the CPCM is more suitable for microgrid networks compared with the traditional constant-voltage and constant-current charging modes. The hybrid charging method is recommended to save energy and keep high efficiency relatively at the same time. However, how to manage the combination percentage of different charging modes in a reasonable way should be dealt with according to the practical requirements.

2016年第二季度富美实农化销售额下滑12%

2016年第二季度富美实农业解决方案业务销售额为5.52亿美元,同比下滑11.8%,利润同比下降1了.1%,为1.01亿美元.若以合并科麦农报表后的预估值计算,则营收同比下滑19%,

On the Existence of Positive Solutions of Singular Second Order Boundary Value Problems

This paper deals with the existence of positive solutions of the equation u'+f(t, u)=0 with linear boundary conditions. We show the existence of at least one positive solution if / is neither superlinear nor sublinear on u by a simple application of a fixed point Theorem in cones.

Fatigue Life Assessment of Top Tensioned Risers Under Vortex-Induced Vibrations

The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of the riser under VIVs are calculated and the mean stresses,the number of stress cycles and amplitudes are determined by the rainflow counting method.The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser.The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled.Finally the influences of the riser's parameters such as flexural rigidity,top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.

DOA ESTIMATION FOR WIDEBAND SOURCES BASED ON UCA

A new Direction Of Arrival （DOA） estimation algorithm for wideband sources based on Uniform Circular Array （UCA） is presented via analyzing widcband performance of the general ESPRIT. The algorithm effectively improves the wideband performance of ESPRIT based on the interpolation principium and UCA-ESPRIT. The simulated results by computer demonstrate its efficiency.

Numerical assessment on improving multistage centrifugal impeller performance by changing inlet skew angle at impeller inlet

Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the impeller inlet.Four variations of lean angles,that is,8°,10°,15° and 20°,were made at first stage impeller.Reynolds Average Navier Stokes equation was used in simulation together with a shear?stress transport(SST) k-w turbulence model and mixing-plane approach,respectively.Three dimensional fluid flows were simplified using periodic model to reduce the computational cost and time required.A good performance was expected that the secondary flow can be effectively reduced in the flow passage of the impeller without excessive increase in manufacturing cost caused by the secondary flow.The results show that secondary flow affects the main flow intricately to form vortices or having non-uniform velocity in the flow passage,which in turn results in substantial fluid energy loss not only in the impeller but also in the guide vane downstream of impeller.The numerical solutions were performed and allowed the optimum design and operating conditions to be obtained.

Motion estimation based feature selection for visual SLAM

Feature selection is always an important issue in the visual SLAM （simultaneous location and mapping） literature. Considering that the location estimation can be improved by tracking features with larger value of visible time, a new feature selection method based on motion estimation is proposed. First, a k-step iteration algorithm is presented for visible time estimation using an affme motion model; then a delayed feature detection method is introduced for efficiently detecting features with the maximum visible time. As a means of validation for the proposed method, both simulation and real data experiments are carded out. Results show that the proposed method can improve both the estimation performance and the computational performance compared with the existing random feature selection method.

EVA based model to estimate the Chinese listed company’s intrinsic value

This article is based on traditionally intrinsic value assessment model. We employed the assumption on the differences in future increase rates of companies, taking into account of the expected Economic Value Added (EVA) discount and the capital investment, to establish a high increase model, a two-stage EVA discount model and a three-stage EVA discount model for the intrinsic value assessment. Those models eliminate the great fluctuation of free cash flow in calculating the capital expenditure by setting aside the cash flow of the company’s investment in the year and considering only the capital cost. This method needs only to assess the EVA flow in different year in probing the intrinsic value of a company, thus give more consistent conclusion than conventional methods.

A Review and Reflection of Value Account of Forest Resources

The framework of forest valuation accounting has been formed through the development stages of timber value calculation, forest ecosystem valuation and entire value accounting of forest resources, including the forest values of resources in kind, environmental resources and social benefits in China. These theory and methods still face deviation of theories and methods from vague position of discipline, larger accounting results from ignoring differences between forest ecological functions and ecosystem services, and unrealistic and other problems from non-standard index system and accounting methods due to the development history and other reasons. Five suggestions are proposed to make explicit the object and purpose of the forest resource value accounting, establish universal, scientific, measurable and concise index system for value evaluation, calculate forest resources value in consideration of forest type and position, distinguish accurately the functions from benefits of the forest resources, and suit value calculation result to the practice of social economy.

On expansion of estimated stability region:Theory,methodology,and application to power systems

The expansion of the estimated stability region plays an important role in the stability analysis of nonlinear systems.However,current literatures have not provided a complete mathematical description for this problem.This paper reveals that essentially the enlargement or the compression of the estimated stability region results directly from the diffeomorphism map,which is induced by the flow contained in the stability region.By proving that any integration algorithm with an order higher than one can approximately trace the flow of the system,a generalized methodology is proposed to construct various algorithms to realize the enlargement or the compression of the estimated stability region.With this methodology,two new algorithms based on symbolic calculation are suggested to reduce the computational burden.Furthermore,this methodology is applied to construct a scalable numerical algorithm to calculate the critical clearing time(CCT) of the power system for given faults.Tests on the IEEE 10-machine 39-bus system show that the computational results coincide well with the step-by-step simulation with high accuracy.

A survey on artificial boundary method Dedicated to Professor Shi Zhong-Ci on the Occasion of his 80th Birthday

The artificial boundary method is one of the most popular and effective numerical methods tor solving partial differential equations on unbounded domains, with more than thirty years development. The artificiM boundary method has reached maturity in recent years. It has been applied to various problems in scientific and engineering computations, and the theoretical issues such as the convergence and error estimates of the artificial boundary method have been solved gradually. This paper reviews the development and discusses different forms of the artificial boundary method.