A complete model of switch-mode plasma cutting power supply and its simulation are developed. The full bridge isolated pulse width modulation (PWM) buck converter in continuous conduction mode (CCM) for high watt plas...A complete model of switch-mode plasma cutting power supply and its simulation are developed. The full bridge isolated pulse width modulation (PWM) buck converter in continuous conduction mode (CCM) for high watt plasma power supply is approached. Reduced ripple current and improved power factor are achieved in the plasma power supply. With a PID control strategy, circuit responses become more stable and faster with low overshoot during load and current changing. The converter achieved high efficiency under 3 to 15kW load conditions.展开更多
A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with ...A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with parasitic elements extracted to reveal their impacts on the EMI noises. Circuit simulations have been used to analyze and minimize the EMI noises. Conducted EMI noise measurement and filter design of this power supply have been achieved which successfully satisfy the FCC class B limits in the frequency range from 150 kHz to 30 MHz. The analyses and experimental results show that the designed filter guarantees that the required attenuation will be achieved.展开更多
The generation expansion planning is one of complex mixed-integer optimization problems, which involves a large number of continuous or discrete decision variables and constraints. In this paper, an interior point wit...The generation expansion planning is one of complex mixed-integer optimization problems, which involves a large number of continuous or discrete decision variables and constraints. In this paper, an interior point with cutting plane （IP/CP） method is proposed to solve the mixed-integer optimization problem of the electrical power generation expansion planning. The IP/CP method could improve the overall efficiency of the solution and reduce the computational time. Proposed method is combined with the Bender＇s decomposition technique in order to decompose the generation expansion problem into a master investment problem and a slave operational problem. The numerical example is presented to compare with the effectiveness of the proposed algorithm.展开更多
This study deals with Nd：YAG laser cutting nonmetallic materials, which is one of the most important and popular industrial applications of laser. The main theme is to evaluate the effects of Nd：YAG laser beam power...This study deals with Nd：YAG laser cutting nonmetallic materials, which is one of the most important and popular industrial applications of laser. The main theme is to evaluate the effects of Nd：YAG laser beam power besides work piece scanning speed. For approximate cutting depth, a theoretical study is conducted in terms of material property and cutting speed. Results show a nonlinear relation between the cutting depth and input energy. There is no significant effect of speed on cutting depth with the speed being larger than 30 mm/s. An extra energy is utilized in the deep cutting. It is inferred that as the laser power increases, cutting depth increases. The experimental outcomes are in good agreement with theoretical results. This analysis will provide a guideline for laser-based industry to select a suitable laser for cutting, scribing, trimming, engraving, and marking nonmetallic materials.展开更多
The dynamic performances of an ultra-precision fly cutting machine tool(UFCMT)has a dramatic impact on the quality of ultra-precision machining.In this study,the dynamic model of an UFCMT was established based on the ...The dynamic performances of an ultra-precision fly cutting machine tool(UFCMT)has a dramatic impact on the quality of ultra-precision machining.In this study,the dynamic model of an UFCMT was established based on the transfer matrix method for multibody systems.In particular,the large-span scale flow field mesh model was created;and the variation in linear and angular stiffness of journal and thrust bearings with respect to film thickness was investigated by adopting the dynamic mesh technique.The dynamic model was proven to be valid by comparing the dynamic characteristics of the machine tool obtained by numerical simulation with the experimental results.In addition,the power spectrum density estimation method was adopted to simulate the statistical ambient vibration excitation by processing the ambient vibration signal measured over a long period of time.Applying it to the dynamic model,the dynamic response of the tool tip under ambient vibration was investigated.The results elucidated that the tool tip response was significantly affected by ambient vibration,and the isolation foundation had a good effect on vibration isolation.展开更多
Reliability evaluation is important in high speed railway external power supply design, based on probability reasoning bayesian network applied in high-speed railway external power supply reliability evaluation, estab...Reliability evaluation is important in high speed railway external power supply design, based on probability reasoning bayesian network applied in high-speed railway external power supply reliability evaluation, establish the minimum cut and the minimum path of bayesian network model, quantitative calculation external power supply system in each element posterior probability, and the example analysis verified the feasibility and correctness of the above method. Using bayesian network bidirection reasoning technology, quantitative calculation the posterior probability of each element in external power supply system, realized the identification of weak link in external power supply. The research methods and the results of the study can be used in the scheme optimization design of high speed railway external power supply.展开更多
Metal laser cutting belongs to mature laser material processing technologies in industry applications. However, without understanding of the mechanism underlying the overall process, the improvement of the cutting qua...Metal laser cutting belongs to mature laser material processing technologies in industry applications. However, without understanding of the mechanism underlying the overall process, the improvement of the cutting quality is restricted. In this paper, an instantaneous melt removal model is presented to describe the process of material removal and striation formation. In the temperature field calculation, melted metal layer is removed when it grows to an assumed thickness. The effects of cutting parameters including cutting speed, gas pressure and laser power on the shape of striation are discussed. A novel method of getting striation free cutting surface is presented. Finally, laser cutting experiments of mild steel is conducted to validate the model. The striation variation trend can be well predicted by the model presented here and the disagreement may be caused by the coupling effect of cutting speed and critical thickness value.展开更多
Background: The ability to climb stairs (ascending and descending stair without using a handrail) and rise from a chair (rising from chairs without using an elbow rest) are among the most important measures of physica...Background: The ability to climb stairs (ascending and descending stair without using a handrail) and rise from a chair (rising from chairs without using an elbow rest) are among the most important measures of physical function for ADL evaluation for the independent living, and assessed by the questioners on many epidemiological studies in elderly. But little is known about the relationship between the self-reported performance level of the tasks and lower leg strength and power in very elderly people. The purpose of this study was to ascertain the relationship between the self-reported performance level of two tasks and the lower leg function in community-dwelling 80-year-old population. Methods: Out of 994 persons who were 80 years old living in Morioka City, Iwate Prefecture, Japan, 607 individuals (236 men and 371 women) underwent a physical fitness test that included measurements of leg extensor power and knee extensor strength. The ability to climb up stair and to rise from a chair was assessed by self- reported questionnaire which was ranked in three levels. The area under the receiver-operating characteristic (ROC) curve (AUC) was used to evaluate the measurements. Results: The cut-off points for the leg extensor power of subjects who could completely perform the stair-climbing and chair-rising functions were determined to be approximately 8.6 watt/kg body mass for men and 5.6 watt/kg body mass for women. In addition, the cut-off points for the knee extensor strength of subjects who could completely perform the stair-climbing and chair-rising functions were determined to be approximately 0.97 kg/kg body mass for men and 0.84 kg/kg body mass for women. Conclusions: From a practical viewpoint, the present study suggested that the cut-off points of leg extensor power and knee extensor strength can be used as targets in simple self-reported questionnaires to help in screening for mobility in 80-year-old展开更多
An exact and fast analytic method based on power series is established to predict the modal field distributions, Petermann-2 spot size, the normalized propagation constant corresponding to fundamental and first higher...An exact and fast analytic method based on power series is established to predict the modal field distributions, Petermann-2 spot size, the normalized propagation constant corresponding to fundamental and first higher order mode in graded index fibers with any arbitrary power law profile. The variation of normalized cut-off frequencies of some LPlm modes in graded index fibers with different profile exponents are also shown here and an empirical relation between them is determined.展开更多
文摘A complete model of switch-mode plasma cutting power supply and its simulation are developed. The full bridge isolated pulse width modulation (PWM) buck converter in continuous conduction mode (CCM) for high watt plasma power supply is approached. Reduced ripple current and improved power factor are achieved in the plasma power supply. With a PID control strategy, circuit responses become more stable and faster with low overshoot during load and current changing. The converter achieved high efficiency under 3 to 15kW load conditions.
基金National Natural Science Foundation of China (No. 50477009)
文摘A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with parasitic elements extracted to reveal their impacts on the EMI noises. Circuit simulations have been used to analyze and minimize the EMI noises. Conducted EMI noise measurement and filter design of this power supply have been achieved which successfully satisfy the FCC class B limits in the frequency range from 150 kHz to 30 MHz. The analyses and experimental results show that the designed filter guarantees that the required attenuation will be achieved.
文摘The generation expansion planning is one of complex mixed-integer optimization problems, which involves a large number of continuous or discrete decision variables and constraints. In this paper, an interior point with cutting plane （IP/CP） method is proposed to solve the mixed-integer optimization problem of the electrical power generation expansion planning. The IP/CP method could improve the overall efficiency of the solution and reduce the computational time. Proposed method is combined with the Bender＇s decomposition technique in order to decompose the generation expansion problem into a master investment problem and a slave operational problem. The numerical example is presented to compare with the effectiveness of the proposed algorithm.
基金supported by the Science Foundation of the Ministry of Science and Technology Malaysiathe Islamic Development Bank Jeddahsupport of the Universiti Teknologi Malaysia for this research work
文摘This study deals with Nd：YAG laser cutting nonmetallic materials, which is one of the most important and popular industrial applications of laser. The main theme is to evaluate the effects of Nd：YAG laser beam power besides work piece scanning speed. For approximate cutting depth, a theoretical study is conducted in terms of material property and cutting speed. Results show a nonlinear relation between the cutting depth and input energy. There is no significant effect of speed on cutting depth with the speed being larger than 30 mm/s. An extra energy is utilized in the deep cutting. It is inferred that as the laser power increases, cutting depth increases. The experimental outcomes are in good agreement with theoretical results. This analysis will provide a guideline for laser-based industry to select a suitable laser for cutting, scribing, trimming, engraving, and marking nonmetallic materials.
文摘The dynamic performances of an ultra-precision fly cutting machine tool(UFCMT)has a dramatic impact on the quality of ultra-precision machining.In this study,the dynamic model of an UFCMT was established based on the transfer matrix method for multibody systems.In particular,the large-span scale flow field mesh model was created;and the variation in linear and angular stiffness of journal and thrust bearings with respect to film thickness was investigated by adopting the dynamic mesh technique.The dynamic model was proven to be valid by comparing the dynamic characteristics of the machine tool obtained by numerical simulation with the experimental results.In addition,the power spectrum density estimation method was adopted to simulate the statistical ambient vibration excitation by processing the ambient vibration signal measured over a long period of time.Applying it to the dynamic model,the dynamic response of the tool tip under ambient vibration was investigated.The results elucidated that the tool tip response was significantly affected by ambient vibration,and the isolation foundation had a good effect on vibration isolation.
文摘Reliability evaluation is important in high speed railway external power supply design, based on probability reasoning bayesian network applied in high-speed railway external power supply reliability evaluation, establish the minimum cut and the minimum path of bayesian network model, quantitative calculation external power supply system in each element posterior probability, and the example analysis verified the feasibility and correctness of the above method. Using bayesian network bidirection reasoning technology, quantitative calculation the posterior probability of each element in external power supply system, realized the identification of weak link in external power supply. The research methods and the results of the study can be used in the scheme optimization design of high speed railway external power supply.
文摘Metal laser cutting belongs to mature laser material processing technologies in industry applications. However, without understanding of the mechanism underlying the overall process, the improvement of the cutting quality is restricted. In this paper, an instantaneous melt removal model is presented to describe the process of material removal and striation formation. In the temperature field calculation, melted metal layer is removed when it grows to an assumed thickness. The effects of cutting parameters including cutting speed, gas pressure and laser power on the shape of striation are discussed. A novel method of getting striation free cutting surface is presented. Finally, laser cutting experiments of mild steel is conducted to validate the model. The striation variation trend can be well predicted by the model presented here and the disagreement may be caused by the coupling effect of cutting speed and critical thickness value.
文摘Background: The ability to climb stairs (ascending and descending stair without using a handrail) and rise from a chair (rising from chairs without using an elbow rest) are among the most important measures of physical function for ADL evaluation for the independent living, and assessed by the questioners on many epidemiological studies in elderly. But little is known about the relationship between the self-reported performance level of the tasks and lower leg strength and power in very elderly people. The purpose of this study was to ascertain the relationship between the self-reported performance level of two tasks and the lower leg function in community-dwelling 80-year-old population. Methods: Out of 994 persons who were 80 years old living in Morioka City, Iwate Prefecture, Japan, 607 individuals (236 men and 371 women) underwent a physical fitness test that included measurements of leg extensor power and knee extensor strength. The ability to climb up stair and to rise from a chair was assessed by self- reported questionnaire which was ranked in three levels. The area under the receiver-operating characteristic (ROC) curve (AUC) was used to evaluate the measurements. Results: The cut-off points for the leg extensor power of subjects who could completely perform the stair-climbing and chair-rising functions were determined to be approximately 8.6 watt/kg body mass for men and 5.6 watt/kg body mass for women. In addition, the cut-off points for the knee extensor strength of subjects who could completely perform the stair-climbing and chair-rising functions were determined to be approximately 0.97 kg/kg body mass for men and 0.84 kg/kg body mass for women. Conclusions: From a practical viewpoint, the present study suggested that the cut-off points of leg extensor power and knee extensor strength can be used as targets in simple self-reported questionnaires to help in screening for mobility in 80-year-old
文摘An exact and fast analytic method based on power series is established to predict the modal field distributions, Petermann-2 spot size, the normalized propagation constant corresponding to fundamental and first higher order mode in graded index fibers with any arbitrary power law profile. The variation of normalized cut-off frequencies of some LPlm modes in graded index fibers with different profile exponents are also shown here and an empirical relation between them is determined.
