Dynamic stability study of an isolated wind-diesel hybrid power system with wind power generation using IG,PMIG and PMSG: A comparison

This paper presents a comparative study of reactive power control for isolated wind-diesel hybrid power system in three different cases with wind power generation by induction generator (IG), permanent-magnet induction generator (PMIG) and permanent-magnet synchronous generator. The synchronous generator (SG) is used with diesel engine set. A mathematical model of the system based on small signal analysis, is developed considering reactive power flow balance equations. The variable reactive power needed by the system is provided by a static synchronous compensator (STATCOM) when wind power generation is done by IG and PMIG. When permanent-magnet synchronous generator (PMSG) is used for wind power generation, the variable reactive power demand is fulfilled by a voltage source converter (VSC) which is on the load side. A new mathematical approximation model for VSC connected with PMSG is proposed such that the voltage source converter fulfills the increased reactive power requirement of load and also increases its active power equal to the increased input wind power. Proportional and integral (PI) gains of the STATCOM and VSC controllers are optimized using integral square error criterion (ISE). The dynamic responses of the system for small (1%) step increase in load reactive power with and without 1% step increase in input wind power are shown. The paper also shows the dynamic responses of the system for random step change in load reactive power plus random step change in input wind power. The MATLAB/SIMULINK environment is used for simulation.     

Three-dimensional laminar flow and heat transfer in a parallel array of microchannels etched on a substrate

Heat transfer and laminar fluid flow in an array of parallel microchannels etched on a silicon substrate with water as the circulating fluid was studied numerically. The fluid region consisted of a microchannel with a hydraulic diameter of 85.6 μm and aspect ratios ranging from 0.10 to 1.0. A constant heat flux of 90 W/cm² was applied to the y = H face of the computational domain, which simulates thermal energy generation from an integrated circuit. Generalized transport equations were discretized and solved in three dimensions for velocities, pressure, and temperature. The SIMPLE algorithm [S.V. Patankar, Numerical Heat Transfer and Fluid Flow, Hemisphere, New York, 1980] was used to link pressure and velocity fields, and a thermally repeated boundary condition was applied in the lateral direction to model the repeating nature of the geometry. The numerical results for apparent friction coefficient and convective thermal resistance at the channel inlet and exit closely matched the experimental data in the literature for the case of 0.32 aspect ratio. Apparent friction coefficients were found to increase linearly with Reynolds number. Inlet and outlet thermal resistance values monotonically decreased with increasing Reynolds number and increased with aspect ratio.     

Variability and phasing of tidal current energy around the United Kingdom

Tidal energy has the potential to play a key role in meeting renewable energy targets set out by the United Kingdom (UK) government and devolved administrations. Attention has been drawn to this resource as a number of locations with high tidal current velocity have recently been leased by the Crown Estate for commercial development. Although tides are periodic and predictable, there are times when the current velocity is too low for any power generation. However, it has been proposed that a portfolio of diverse sites located around the UK will deliver a firm aggregate output due to the relative phasing of the tidal signal around the coast. This paper analyses whether firm tidal power is feasible with ‘first generation’ tidal current generators suitable for relatively shallow water, high velocity sites. This is achieved through development of realistic scenarios of tidal current energy industry development. These scenarios incorporate constraints relating to assessment of the economically harvestable resource, tidal technology potential and the practical limits to energy extraction dictated by environmental response and spatial availability of resource. The final scenario is capable of generating 17 TWh/year with an effective installed capacity of 7.8 GW, at an average capacity factor of 29.9% from 7 major locations. However, it is concluded that there is insufficient diversity between sites suitable for first generation tidal current energy schemes for a portfolio approach to deliver firm power generation.     

Analysis and numerical simulation of phytoplankton–nutrient systems with nutrient loss

The dynamics of a mathematical model of a layer of single phytoplankton species growing over a pool of nutrients, proposed by [A.H. Taylor, J.R.W. Harris, J. Aiken, The interaction of physical and biological process in a model of the vertical distribution of phytoplankton under stratification, Mar. Int. Ecohyrd., J.C. Nihoul (Ed.) 42 (1986) 313–330] is analyzed. Both cases of presence and absence of a phytoplankton in the water below the layer of interest are considered. Positive and elementary stable nonstandard (PESN) methods, having the same qualitative features as the corresponding continuous models, are formulated and analyzed. Biological implications and a set of numerical simulations supporting the mathematical and numerical analysis are also presented.     

Analysis of impact energy factors in ductile materials using single particle impact tests on gas gun

Wear is surface damage that involves progressive material loss due to relative motion between the contacting surfaces. Removal of material by action of impacting particles is known as erosion. Single particle impact tests were conducted using small particles (95–100 μm) and impact velocity 90 ms⁻¹. A new technique has been developed to measure the impact crater using Laser Scanning Confocal Microscope (LSCM). Depth of craters was calculated based on the impact parameters and the material properties and compared with measured values. The variations are discussed with the high strain-rate deformation and energy loss in the material through strain energy and heating.     

Black Sea wave energy atlas from 13 years hindcasted wave data

The present study aims to evaluate the wave energy potential of the Black Sea. Wave properties were calculated using 3rd generation Spectral Wave Model for years 1996–2009 by using wind data from European Center for Medium-Range Weather Forecasts (ECMWF). The wave model was calibrated using the wave measurements conducted at five different stations. Wave power atlas displaying time – averaged wave power for entire Black Sea was generated. Also wave power roses and wave power distribution tables in means of periods and heights for different regions were presented. Wave energy found to be decreasing along the coast from west to east. It was found that the most energetic region is the South Western part of the sea. The eastern part of the Black Sea is the least energetic in means of wave power. It was concluded that the most promising location is the Thracian shores of Turkey, especially west side of Istanbul. Beside this, other promising locations in the Black Sea Basin were also evaluated. Annual wave energies (kWh/m) for different regions were presented in this study.     

限矩型液力偶合器内部两相流动数值模拟

限矩型液力偶合器内部存在着复杂的气液两相流动,为掌握限矩型液力偶合器内部流场分布及转矩特性变化,分别采用VOF(Volume of fluid)与Mixture两相流模型对偶合器内部流场进行模拟计算,并对其转矩特性进行监测。通过VOF模型获得的偶合器内部气液两相分布情况和通过Mixture模型得到的其内部压力速度分布图能够较好地反映偶合器内部流场变化情况。仿真结果表明：VOF模型能够较好地模拟出偶合器因流态转变而造成的转矩跌落情况,Mixture模型不能模拟出该效果,但在高、低转速比工况下模拟的转矩值仍具有一定参考意义。     

The effect of Zr on the microstructure and tensile properties of hot-extruded Al–Mg2Si composite

This work was carried out to investigate the effect of different amounts of Zr on the microstructure and tensile properties of homogenized and hot extruded Al-15% Mg₂Si composite using optical microscopy and scanning electron microscopy (SEM). The results showed that Zr addition has no significant effect on the morphology of both primary and eutectic Mg₂Si phase in as-cast condition. But, applying homogenizing and extrusion processes changed the morphology of Mg₂Si phases from irregular to a more spherical shape. Further results demonstrated that the average size of primary Mg₂Si decreases with the addition of Zr up to 0.1% from 56 μm to 24 μm in hot-extruded condition. As the mount of Zr increased up to 0.1 wt.%, ultimate tensile strength (UTS) and elongation values were also increased from 160 MPa and 3.2% to 292 MPa and 9.5%, respectively. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in hot-extruded Zr-modified specimens. This can be attributed to the changes in size and morphology of Mg₂Si intermetallic and porosity content.     

PIV measurement on internal instantaneous flows of a centrifugal pump

In this paper,the internal flow field in a centrifugal pump working at the design flow rate operating condition has been measured using the particle image velocimetry(PIV)technique with the fluorescent particles and the index-matched fluid technology.The index-marching fluid with the same refractive index as the transparent material has been prepared and applied in the present test of pump with geometrical complex walls.The comparison between velocity distributions of PIV results both with and without fluor...