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The combined effects of different overload ratios(OLRs)and nitriding process on fatigue crack growth(FCG)were analyzed.Steel compact tension specimens made of AISI 4140 steel were subjected to the plasma nitrification process using agas mixture of 50% N2 and 50% H2 at 500℃for 2h.Structural properties of the samples were studied by scanning electron microscopy,optical microscopy,microhardness testing and digital imaging.Plasma nitriding slowed down FCG,but the crack growth retardation caused by the overload was reduced when the OLR was 2.0and 2.5.Nitriding did not take effect when the OLR was 1.5and 3.0. 相似文献
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Electric and magnetic fields generated by lightning cause a serious hazard to various systems.Now wind turbine installations with higher power capacity are increasing.Higher power capacity requires higher height and so there is more probability of lightning strike.Blades are the most probable components to be struck by lightning.The most common lightning protection system for the blades consists of several metallic receptors on the blade surface.Those are connected to the ground by metallic down-conductors placed inside the blade shell.This paper studies effects of the receptor configurations on protecting the blade against lightning strike.For this purpose,an analysis procedure based on finite element method(FEM)in COMSOL Multiphysics software environment is used.The voltage distribution around the blade is simulated for various configurations of receptors.The best configuration is presented.Simulations are performed on the blade model of a special wind turbine,which isVESTAS V47". 相似文献
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Francisco GONZ?LEZ-LONGATT Pawel REGULSKI Happy NOVANDA Vladimir TERZIJA 《电力系统自动化》2012,36(8):191-197
Future power system faces several challenges,one of them is the high penetration level of intermittent wind power generation,providing small or even no inertial response and being not contributing to the frequency stability.The effect of shaft stiffness on inertial response of fixed speed wind turbines is presented.Four different drive-train models based on the multi-body system are developed.The small-signal analysis demonstrates no significant differences between models in terms of electro-mechanical eigen-values for increasing shaft stiffness.The natural resonance frequency of drive-train torsion modes shows slightly different values between damped and undamped models,but no significant differences are found in the number-mass models.Time-domain simulations show the changes in the active power contribution of a wind farm based on a fixed speed wind turbine during the system frequency disturbance.The changes in the kinetic energy during the dynamic process are calculated and their contribution to the inertia constant is small and effective.The largest contribution of the kinetic energy is provided at the beginning of the system frequency disturbance to reduce the rate of the frequency change,it is positive for the frequency stability. 相似文献
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针对频谱共享环境,研究了采用OFDM调制方式的多用户认知无线电系统中,综合考虑自身发射功率约束与主用户干扰功率约束的资源分配问题.基于最大化认知用户和速率的优化目标,给出了连续比特条件下最优的多水位注水功率分配表达式;针对更实际的整数比特要求情况,通过基于相对增益因子RG的子信道选择机制与每个认知用户内多约束的贪婪比特与功率分配策略,来最大限度地提高频谱利用率.仿真结果表明:联合的子信道、功率与比特分配算法在不同的参数设置下均达到了良好的性能,在不影响主用户通信的前提下有效地提高了认知系统的频谱利用率. 相似文献
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在已有协同ALOHA (CALOHA)协议的基础上,提出了一种基于分布式协同节点选择的新型协同ALOHA( NCALOHA)协议,该协议比CALOHA协议更为简单实用.建立了一种吞吐量理论分析模型,并经过仿真证实基于该模型所得到的时隙ALOHA(SALO-HA)协议的吞吐量与已有的结论完全一致,且仿真结果显示NCALO... 相似文献
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一种无线Mesh网络中基于协同通信的多包接收方法 总被引:1,自引:0,他引:1
协同通信容许移动节点共享彼此的天线以构建虚拟多入多出系统,可有效获得空间分集增益。为利用虚拟多入多出信道的分集增益,该文提出了一种在无线Mesh网络上行链路中采用协同策略的多包接收方法。该方法中提出由发生冲突的Mesh终端及其协同节点构建虚拟多入多出信道,且多天线Mesh路由器通过串行干扰消除算法来快速分离冲突包。理论分析和仿真结果表明该方法可充分利用空间资源,相比NDMA和TDMA可有效提高系统的有效吞吐量并降低时延。 相似文献