The discrete iterative map model of peak current-mode controlled buck converter with constant current load（CCL）,containing the output voltage feedback and ramp compensation, is established in this paper. Based on th...The discrete iterative map model of peak current-mode controlled buck converter with constant current load（CCL）,containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability.展开更多
A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linear...A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.展开更多
The boost converter feeding a constant power load (CPL) is a non-minimum phase system that is prone to the destabilizing effects of the negative incremental resistance of the CPL and presents a major challenge in the ...The boost converter feeding a constant power load (CPL) is a non-minimum phase system that is prone to the destabilizing effects of the negative incremental resistance of the CPL and presents a major challenge in the design of stabilizing controllers. A PWM-based current-sensorless robust sliding mode controller is developed that requires only the measurement of the output voltage. An extended state observer is developed to estimate a lumped uncertainty signal that comprises the uncertain load power and the input voltage, the converter parasitics, the component uncertainties and the estimation of the derivative of the output voltage needed in the implementation of the controller. A linear sliding surface is used to derive the controller, which is simple in its design and yet exhibits excellent features in terms of robustness to external disturbances, parameter uncertainties, and parasitics despite the absence of the inductor’s current feedback. The robustness of the controller is validated by computer simulations.展开更多
Submerged floating tunnel(SFTs)are typically subjected to complex external environmental and internal loads such as wave currents and traffic load.In this study,this problem is investigated through a finite element me...Submerged floating tunnel(SFTs)are typically subjected to complex external environmental and internal loads such as wave currents and traffic load.In this study,this problem is investigated through a finite element method able to account for fluid-structure interaction.The obtained results show that increasing the number of vehicles per unit length enhances the transverse vibrational displacements of the SFT cross sections.Under ultimate traffic load condition,one-way and two-way syntropic distributions can promote the dynamic responses of SFTs whereas two-way reverse distributions have the opposite effect.展开更多
Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three i...Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.展开更多
A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of dr...A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z- pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power展开更多
In this paper, the distribution characteristics of the breaking wave current and suspended load transport in the surf zone are discussed in main. Based on the measured data of the waves, the form of breaking wave, the...In this paper, the distribution characteristics of the breaking wave current and suspended load transport in the surf zone are discussed in main. Based on the measured data of the waves, the form of breaking wave, the breaking wave current and the sediment concentration of suspended load in the offshore surf zone near Nouakchott, the Islamic Republic of Mauritania, the author has analized the law governing the distribution of longshore current and sediment concentration of suspended load by means of statistical method, and presented a calculation method for the longshore sediment transport in offshore surf zone.展开更多
This paper considers the influence of changes of the transmission lines of permissible load current depending on conductor and ambient temperatures, climate conditions. The theoretical background of the allowable cond...This paper considers the influence of changes of the transmission lines of permissible load current depending on conductor and ambient temperatures, climate conditions. The theoretical background of the allowable conductor temperature as well as load current determination principles are proposed. On one hand, the principles are based on mechanical limitations; on the other hand, they are based on thermal limitations. The simulation tasks were based on specific data information of three existing overhead lines of Latvian power system as well as the planned 330 kV overhead line. Moreover, the special thermovision device was used for precious determination of conductor temperature of the existing transmission lines. The simulation results of the obtained data are reviewed in the paper.展开更多
According to the service environment of subway structure,experiment is carried out to simulate influence of different loading levels to reinforcement corrosion of R.C element affected by stray current and chlorine sal...According to the service environment of subway structure,experiment is carried out to simulate influence of different loading levels to reinforcement corrosion of R.C element affected by stray current and chlorine salt solution. The current density of the corrosion is measured with the linear polarization resistance method,together with the qualitative analysis and quantitative calculation. Experiment shows that rebar corrosion current density increase accordingly with the increase of loading level. The quantitative relations and the time of rust corrosion of reinforcement are obtained.展开更多
以带运动抑制结构的圆筒型浮式生产储卸油装置(Cylindrical Floating Production Storage and Offloading,CFPSO)为研究对象,在低速风洞中对CFPSO流载荷进行测量。为获得均匀流并减少边界层的影响,采用距离地面一定高度的小地板。热线...以带运动抑制结构的圆筒型浮式生产储卸油装置(Cylindrical Floating Production Storage and Offloading,CFPSO)为研究对象,在低速风洞中对CFPSO流载荷进行测量。为获得均匀流并减少边界层的影响,采用距离地面一定高度的小地板。热线测量结果表明,采用小地板能够获得更均匀的流剖面。通过风洞试验对4种不同型式的运动抑制结构流载荷进行测量,进一步采用数值模拟方法对不同型式运动抑制结构的尾流场进行分析。结果表明:运动抑制结构通过对尾涡的限制,减少能量损耗,实现减阻效果。研究结果可为运动抑制结构的设计提供一定的参考。展开更多
岩石受压激发电流(pressure-stimulated rock current,PSRC)变化是岩体破裂观测与地壳灾变感知研究的重要内容,但缺乏岩石含水状态与加载模式对PSRC变化特征的影响探究与机理辨析.本文以粒度相对均匀的闪长岩为实验对象,特别制备了方柱...岩石受压激发电流(pressure-stimulated rock current,PSRC)变化是岩体破裂观测与地壳灾变感知研究的重要内容,但缺乏岩石含水状态与加载模式对PSRC变化特征的影响探究与机理辨析.本文以粒度相对均匀的闪长岩为实验对象,特别制备了方柱-锥体闪长岩试件,采用高精度静电计与声发射探测仪,同步观测单、双轴局部加载破裂过程中充分干燥、自然干燥和充分饱水试件的受压端与非受压端之间PSRC及声发射变化,并分析其特征差异,辨析其内在机理.研究揭示:(1)全部试件受力中后期均呈现PSRC显著增长,包括毛刺型、持续增大型和瞬时台阶型,其增幅受含水状态和加载模式综合影响;(2)岩石临失稳前,PSRC均呈现剧烈脉冲式振荡特征,其中单、双轴模式下充分饱水试件的峰值PSRC分别是充分干燥试件的1.3倍和7.1倍,而自然干燥试件的峰值PSRC受加载模式影响不大;(3)自然干燥试件中的微量孔隙水对正空穴电荷传递有损耗作用,而充分饱水试件的流体电动势效应对PSRC变化影响显著,闪长岩所含石英矿物对PSRC的贡献可以忽略.本文揭示的岩石临失稳前PSRC剧变现象、峰值差异及内在机理,对于发展岩体灾变监测预警新技术和构造地震孕震区遥感识别新方法有重要意义.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61371033)the Fok Ying-Tung Education Foundation for Young Teachers in the Higher Education Institutions of China(Grant No.142027)+1 种基金the Sichuan Provincial Youth Science and Technology Fund,China(Grant Nos.2014JQ0015and 2013JQ0033)the Fundamental Research Funds for the Central Universities,China(Grant No.SWJTU11CX029)
文摘The discrete iterative map model of peak current-mode controlled buck converter with constant current load（CCL）,containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability.
文摘A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.
文摘The boost converter feeding a constant power load (CPL) is a non-minimum phase system that is prone to the destabilizing effects of the negative incremental resistance of the CPL and presents a major challenge in the design of stabilizing controllers. A PWM-based current-sensorless robust sliding mode controller is developed that requires only the measurement of the output voltage. An extended state observer is developed to estimate a lumped uncertainty signal that comprises the uncertain load power and the input voltage, the converter parasitics, the component uncertainties and the estimation of the derivative of the output voltage needed in the implementation of the controller. A linear sliding surface is used to derive the controller, which is simple in its design and yet exhibits excellent features in terms of robustness to external disturbances, parameter uncertainties, and parasitics despite the absence of the inductor’s current feedback. The robustness of the controller is validated by computer simulations.
基金supported by Chongqing Natural Science Foundation(Grant No.cstc2020jcyj-msxmX0923).
文摘Submerged floating tunnel(SFTs)are typically subjected to complex external environmental and internal loads such as wave currents and traffic load.In this study,this problem is investigated through a finite element method able to account for fluid-structure interaction.The obtained results show that increasing the number of vehicles per unit length enhances the transverse vibrational displacements of the SFT cross sections.Under ultimate traffic load condition,one-way and two-way syntropic distributions can promote the dynamic responses of SFTs whereas two-way reverse distributions have the opposite effect.
基金the National Natural Science Foundation of China under contract No..59579014.
文摘Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.
基金Project supported by the National Natural Science Foundation of China （Grant No 10035020）.
文摘A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z- pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power
文摘In this paper, the distribution characteristics of the breaking wave current and suspended load transport in the surf zone are discussed in main. Based on the measured data of the waves, the form of breaking wave, the breaking wave current and the sediment concentration of suspended load in the offshore surf zone near Nouakchott, the Islamic Republic of Mauritania, the author has analized the law governing the distribution of longshore current and sediment concentration of suspended load by means of statistical method, and presented a calculation method for the longshore sediment transport in offshore surf zone.
文摘This paper considers the influence of changes of the transmission lines of permissible load current depending on conductor and ambient temperatures, climate conditions. The theoretical background of the allowable conductor temperature as well as load current determination principles are proposed. On one hand, the principles are based on mechanical limitations; on the other hand, they are based on thermal limitations. The simulation tasks were based on specific data information of three existing overhead lines of Latvian power system as well as the planned 330 kV overhead line. Moreover, the special thermovision device was used for precious determination of conductor temperature of the existing transmission lines. The simulation results of the obtained data are reviewed in the paper.
基金National Natural Science Foundation of China (Granted No.50808005)National"11-5"Science and Technology Supporting Program(Granted No.2006BAJ27B04)Major Program of Beijing Municipal Natural Science Foundation(Granted No.8100001)
文摘According to the service environment of subway structure,experiment is carried out to simulate influence of different loading levels to reinforcement corrosion of R.C element affected by stray current and chlorine salt solution. The current density of the corrosion is measured with the linear polarization resistance method,together with the qualitative analysis and quantitative calculation. Experiment shows that rebar corrosion current density increase accordingly with the increase of loading level. The quantitative relations and the time of rust corrosion of reinforcement are obtained.
文摘以带运动抑制结构的圆筒型浮式生产储卸油装置(Cylindrical Floating Production Storage and Offloading,CFPSO)为研究对象,在低速风洞中对CFPSO流载荷进行测量。为获得均匀流并减少边界层的影响,采用距离地面一定高度的小地板。热线测量结果表明,采用小地板能够获得更均匀的流剖面。通过风洞试验对4种不同型式的运动抑制结构流载荷进行测量,进一步采用数值模拟方法对不同型式运动抑制结构的尾流场进行分析。结果表明:运动抑制结构通过对尾涡的限制,减少能量损耗,实现减阻效果。研究结果可为运动抑制结构的设计提供一定的参考。
文摘岩石受压激发电流(pressure-stimulated rock current,PSRC)变化是岩体破裂观测与地壳灾变感知研究的重要内容,但缺乏岩石含水状态与加载模式对PSRC变化特征的影响探究与机理辨析.本文以粒度相对均匀的闪长岩为实验对象,特别制备了方柱-锥体闪长岩试件,采用高精度静电计与声发射探测仪,同步观测单、双轴局部加载破裂过程中充分干燥、自然干燥和充分饱水试件的受压端与非受压端之间PSRC及声发射变化,并分析其特征差异,辨析其内在机理.研究揭示:(1)全部试件受力中后期均呈现PSRC显著增长,包括毛刺型、持续增大型和瞬时台阶型,其增幅受含水状态和加载模式综合影响;(2)岩石临失稳前,PSRC均呈现剧烈脉冲式振荡特征,其中单、双轴模式下充分饱水试件的峰值PSRC分别是充分干燥试件的1.3倍和7.1倍,而自然干燥试件的峰值PSRC受加载模式影响不大;(3)自然干燥试件中的微量孔隙水对正空穴电荷传递有损耗作用,而充分饱水试件的流体电动势效应对PSRC变化影响显著,闪长岩所含石英矿物对PSRC的贡献可以忽略.本文揭示的岩石临失稳前PSRC剧变现象、峰值差异及内在机理,对于发展岩体灾变监测预警新技术和构造地震孕震区遥感识别新方法有重要意义.
