Excitation regulator has played an important role to ensure that generator run safely and stably. However, in some remote areas, the rural small generator excitation control system is very backward, and it has hindere...Excitation regulator has played an important role to ensure that generator run safely and stably. However, in some remote areas, the rural small generator excitation control system is very backward, and it has hindered the development of Chinese agriculture and the pace of new countryside construction. This paper introduced a kind of structure and basic principle of DSP-based automatic excitation regulator, which was applied to rural small generator. We chose TMS320LF2407A chip as the core of regulator control system; the regulator adjusted PWM based on PID control strategy to control the exciting current. The theoretical analysis showed that the regulator had the characteristics of simplicity and reliability, well dynamic and static characteristics, and it could also adjust its own state quickly. The result was applicable to small rural hydropower station.展开更多
Earthquake is a kind of sudden and destructive random excitation in nature.It is significant to determine the probability distribution characteristics of the corresponding dynamic indicators to ensure the safety and t...Earthquake is a kind of sudden and destructive random excitation in nature.It is significant to determine the probability distribution characteristics of the corresponding dynamic indicators to ensure the safety and the stability of structures when the intensive seismic excitation,the intensity of which is larger than 7,acts in train-bridge system.Firstly,the motion equations of a two-dimensional train-bridge system under the vertical random excitation of track irregularity and the vertical seismic acceleration are established,where the train subsystem is composed of 8 mutually independent vehicle elements with 48 degrees of freedom,while the single-span simple supported bridge subsystem is composed of 102D beam elements with 20 degrees of freedom on beam and 2 large mass degrees of freedom at the support.Secondly,Monte Carlo method and pseudo excitation method are adopted to analyze the statistical parameters of the system.The power spectrum density of random excitation is used to define a series of non-stationary pseudo excitation in pseudo excitation method and the trigonometric series of random vibration history samples in Monte Carlo method,respectively solved by precise integral method and Newmark-βmethod through the inter-system iterative procedure.Finally,the results are compared with the case under the weak seismic excitation,and show that the samples of vertical acceleration response of bridge and the offload factor of train obeys the normal distribution.In a high probability,the intensive earthquakes pose a greater threat to the safety and stability of bridges and trains than the weak ones.展开更多
To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the gird...To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.展开更多
Laptop personal computers(LPCs) and their components are vulnerable devices in harsh mechanical environments. One of the most sensitive components of LPCs is hard disk drive(HDD) which needs to be protected against da...Laptop personal computers(LPCs) and their components are vulnerable devices in harsh mechanical environments. One of the most sensitive components of LPCs is hard disk drive(HDD) which needs to be protected against damages attributable to shock and vibration in order to have better magnetic read/write performance. In the present work, a LPC and its HDD are modeled as two degrees of freedom system and the nonlinear optimization method is employed to perform a passive control through minimizing peak of HDD absolute acceleration caused by a base shock excitation. The presented shock excitation is considered as half-sine pulse of acceleration. In addition, eleven inequality constraints are defined based on geometrical limitations and allowable intervals of lumped modal parameters. The target of the optimization is to reach optimum modal parameters of rubber mounts and rubber feet as design variables and subsequently propose new characteristics of rubber mounts and rubber feet to be manufactured for the HDD protection against shock excitation. The genetic algorithm and the modified constrained steepest descent algorithm are employed in order to solve the nonlinear optimization problem for three widely-used commercial cases of HDD. Finally, the results of both optimization methods are compared to make sure about their accuracy.展开更多
The digital excitation regulator is very popular in the small electric plant. This kind of regulator can im- prove the working condition of generator and its working efficiency. It is on the base of the 80C51 Micro-co...The digital excitation regulator is very popular in the small electric plant. This kind of regulator can im- prove the working condition of generator and its working efficiency. It is on the base of the 80C51 Micro-con- troller. The regulator can automatically finish some functions through the combination of software and hard- ware. Through the experiment we can know it is more intellectual than the traditional analog excitation regu- lator.展开更多
To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography （TFCCE） was propose...To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography （TFCCE） was proposed. TFCCE adopts the chirp signal excitation scheme and strikes a balance in the selection of sub-signal bandwidth, the bandwidth overlap and the number of sub-strain image based on theoretical derivation, so as to further improve the quality of elastic image. Experiments have proved that, compared with the other optimizing methods, the elastographyic signal-to-noise ratio（Re-SN） and contrast-to-noise ratio（Re-CN） are improved significantly with different echo signal-to-noise ratios （ReSN） and attenuation coefficients. When ReSN is 50 dB, compared with short pulse, Rc-SN and Re-CN obtained by TFCCE increase by 53% and 143%, respectively. Moreover, in a deeper investigation （85-95 mm）, the image has lower strain noise and clear details. When the attenuation coefficient is in the range of 0-1 dB/（cm.MHz）, Re-SN and Re-CN obtained by TFCCE can be kept in moderate ranges of 5〈Re-SN〈6.8 and 11.4〈Re-CN〈15.2, respectively. In particular, for higher tissue attenuation, the basic image quality cannot be ensured with short pulse excitation, while mediocre quality strain figure can be obtained by TFCCE. Therefore, the TFCCE technology can effectively improve the elastography quality and can be applied to ultrasonic clinical trials.展开更多
The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insu...The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insulated switchgear (GIS) contains not only transverse electromagnetic (TEM) wave, but also high-order transverse electric (TE) and high-order transverse magnetic (TM) waves, we analyzed the proportions between the TEM wave and the high order waves, as well as the influence of the PD position on this proportion, using the finite different time domain (FDTD) method. According to the unique characteristics of the waves, they are separated only ap- proximately. It is found that the high-order mode is the main component, more than 70%, of the electric field around the enclosure of GIS, and that with the increasing distance between PD source and inner conductors, the low frequency ( below about 800 MHz) component of EW decreases, but the high frequency component (above 1 GHz) increases, meanwhile the proportion of high-order components in EW could reach 77% from 70%. It concluded that the closer the PD source to the enclosure is, the easier high order EW may be excited.展开更多
To improve the microcrystalline silicon thin film deposition in quality and to increase its microcrystalline silicon content,we numerically investigated the characteristics of homogeneous discharges in hydrogen dilute...To improve the microcrystalline silicon thin film deposition in quality and to increase its microcrystalline silicon content,we numerically investigated the characteristics of homogeneous discharges in hydrogen diluted silane and argon mixed gases at atmospheric pressure using a two-dimensional fluid model.The model takes into account the primary processes of excitation and ionization,sixteen reactions of radicals with radicals in silane/hydrogen/argon discharges,so this model can adequately describe the discharge plasma.The effects of very high frequency(VHF)excitation on the electron density in such discharges are analyzed.The simulation results show that the electron density does not linearly vary with the excitation frequency within from 90150 MHz.he maximum value occurs at an appropriate excitation frequency i.e.the transition frequency.Increasof the excitation frequency would effectively increase the electron density before the transition frequency,but decreases the density afterwards.is.Moreover,the densities of involved particle species,including H2+,H,Ar*,Ar+,SiH3+,SiH3,SiH3,SiH2are closely interrelated.展开更多
文摘Excitation regulator has played an important role to ensure that generator run safely and stably. However, in some remote areas, the rural small generator excitation control system is very backward, and it has hindered the development of Chinese agriculture and the pace of new countryside construction. This paper introduced a kind of structure and basic principle of DSP-based automatic excitation regulator, which was applied to rural small generator. We chose TMS320LF2407A chip as the core of regulator control system; the regulator adjusted PWM based on PID control strategy to control the exciting current. The theoretical analysis showed that the regulator had the characteristics of simplicity and reliability, well dynamic and static characteristics, and it could also adjust its own state quickly. The result was applicable to small rural hydropower station.
基金Project(52178101) supported by the National Natural Science Foundation of China。
文摘Earthquake is a kind of sudden and destructive random excitation in nature.It is significant to determine the probability distribution characteristics of the corresponding dynamic indicators to ensure the safety and the stability of structures when the intensive seismic excitation,the intensity of which is larger than 7,acts in train-bridge system.Firstly,the motion equations of a two-dimensional train-bridge system under the vertical random excitation of track irregularity and the vertical seismic acceleration are established,where the train subsystem is composed of 8 mutually independent vehicle elements with 48 degrees of freedom,while the single-span simple supported bridge subsystem is composed of 102D beam elements with 20 degrees of freedom on beam and 2 large mass degrees of freedom at the support.Secondly,Monte Carlo method and pseudo excitation method are adopted to analyze the statistical parameters of the system.The power spectrum density of random excitation is used to define a series of non-stationary pseudo excitation in pseudo excitation method and the trigonometric series of random vibration history samples in Monte Carlo method,respectively solved by precise integral method and Newmark-βmethod through the inter-system iterative procedure.Finally,the results are compared with the case under the weak seismic excitation,and show that the samples of vertical acceleration response of bridge and the offload factor of train obeys the normal distribution.In a high probability,the intensive earthquakes pose a greater threat to the safety and stability of bridges and trains than the weak ones.
基金Project(50608008) supported by the National Natural Science Foundation of Chinaproject(20050536002) supported by the Specialized Research Fund for the Doctoral Program of Higher Education
文摘To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.
文摘Laptop personal computers(LPCs) and their components are vulnerable devices in harsh mechanical environments. One of the most sensitive components of LPCs is hard disk drive(HDD) which needs to be protected against damages attributable to shock and vibration in order to have better magnetic read/write performance. In the present work, a LPC and its HDD are modeled as two degrees of freedom system and the nonlinear optimization method is employed to perform a passive control through minimizing peak of HDD absolute acceleration caused by a base shock excitation. The presented shock excitation is considered as half-sine pulse of acceleration. In addition, eleven inequality constraints are defined based on geometrical limitations and allowable intervals of lumped modal parameters. The target of the optimization is to reach optimum modal parameters of rubber mounts and rubber feet as design variables and subsequently propose new characteristics of rubber mounts and rubber feet to be manufactured for the HDD protection against shock excitation. The genetic algorithm and the modified constrained steepest descent algorithm are employed in order to solve the nonlinear optimization problem for three widely-used commercial cases of HDD. Finally, the results of both optimization methods are compared to make sure about their accuracy.
文摘The digital excitation regulator is very popular in the small electric plant. This kind of regulator can im- prove the working condition of generator and its working efficiency. It is on the base of the 80C51 Micro-con- troller. The regulator can automatically finish some functions through the combination of software and hard- ware. Through the experiment we can know it is more intellectual than the traditional analog excitation regu- lator.
基金Project(2013GZX0147-3) supported by the Natural Science Foundation of Sichuan Province,China
文摘To improve the quality of ultrasonic elastography, by taking the advantage of code excitation and frequency compounding, a transmitting-side multi-frequency with coded excitation for elastography （TFCCE） was proposed. TFCCE adopts the chirp signal excitation scheme and strikes a balance in the selection of sub-signal bandwidth, the bandwidth overlap and the number of sub-strain image based on theoretical derivation, so as to further improve the quality of elastic image. Experiments have proved that, compared with the other optimizing methods, the elastographyic signal-to-noise ratio（Re-SN） and contrast-to-noise ratio（Re-CN） are improved significantly with different echo signal-to-noise ratios （ReSN） and attenuation coefficients. When ReSN is 50 dB, compared with short pulse, Rc-SN and Re-CN obtained by TFCCE increase by 53% and 143%, respectively. Moreover, in a deeper investigation （85-95 mm）, the image has lower strain noise and clear details. When the attenuation coefficient is in the range of 0-1 dB/（cm.MHz）, Re-SN and Re-CN obtained by TFCCE can be kept in moderate ranges of 5〈Re-SN〈6.8 and 11.4〈Re-CN〈15.2, respectively. In particular, for higher tissue attenuation, the basic image quality cannot be ensured with short pulse excitation, while mediocre quality strain figure can be obtained by TFCCE. Therefore, the TFCCE technology can effectively improve the elastography quality and can be applied to ultrasonic clinical trials.
基金Project supported by National High-tech Research and Development Program of China (863 Program) (2011AA05A121)
文摘The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insulated switchgear (GIS) contains not only transverse electromagnetic (TEM) wave, but also high-order transverse electric (TE) and high-order transverse magnetic (TM) waves, we analyzed the proportions between the TEM wave and the high order waves, as well as the influence of the PD position on this proportion, using the finite different time domain (FDTD) method. According to the unique characteristics of the waves, they are separated only ap- proximately. It is found that the high-order mode is the main component, more than 70%, of the electric field around the enclosure of GIS, and that with the increasing distance between PD source and inner conductors, the low frequency ( below about 800 MHz) component of EW decreases, but the high frequency component (above 1 GHz) increases, meanwhile the proportion of high-order components in EW could reach 77% from 70%. It concluded that the closer the PD source to the enclosure is, the easier high order EW may be excited.
基金Project supported by Liaoning Provincial Natural Science Foundation of China （201202037）.
文摘To improve the microcrystalline silicon thin film deposition in quality and to increase its microcrystalline silicon content,we numerically investigated the characteristics of homogeneous discharges in hydrogen diluted silane and argon mixed gases at atmospheric pressure using a two-dimensional fluid model.The model takes into account the primary processes of excitation and ionization,sixteen reactions of radicals with radicals in silane/hydrogen/argon discharges,so this model can adequately describe the discharge plasma.The effects of very high frequency(VHF)excitation on the electron density in such discharges are analyzed.The simulation results show that the electron density does not linearly vary with the excitation frequency within from 90150 MHz.he maximum value occurs at an appropriate excitation frequency i.e.the transition frequency.Increasof the excitation frequency would effectively increase the electron density before the transition frequency,but decreases the density afterwards.is.Moreover,the densities of involved particle species,including H2+,H,Ar*,Ar+,SiH3+,SiH3,SiH3,SiH2are closely interrelated.
