This paper addresses the source seeking problems for an autonomous underwater vehicle（AUV） with the estimated gradients. The AUV is embedded with multiple sensors, which are only able to detect the signal strengths ...This paper addresses the source seeking problems for an autonomous underwater vehicle（AUV） with the estimated gradients. The AUV is embedded with multiple sensors, which are only able to detect the signal strengths of the source with unknown distribution. To resolve this challenge,a sensor configuration is explicitly designed as a semicircle to estimate gradients of the signal field.Then, a controller is obtained via the estimated gradients to drive the AUV to approach the source.Moreover, an upper bound for the localization error is provided in terms of the radius of the semicircle and the signal distribution. Finally, the authors include a simulation example by applying the strategy to a Remote Environmental Monitoring Unit S（REMUS） for seeking the deepest point of a region of seabed in the South China Sea.展开更多
Effective operation strategies in the solid oxide fuel cell(SOFC)can adjust the spatial distribution of temperature gradient favoring the long-term stability.To investigate the effects of different operating condition...Effective operation strategies in the solid oxide fuel cell(SOFC)can adjust the spatial distribution of temperature gradient favoring the long-term stability.To investigate the effects of different operating conditions on the thermal behavior inside SOFC,a three-dimensional model is developed in this study.The model is verified by comparing it with the experimental data.The heat generation rate and its variation under different operating conditions are analyzed.The combined effects of operating voltage and gas temperature are considered to be the key factor influencing the temperature gradient.Compared to the original case,the temperature of SOFC decreases by 21.4 K when the fuel velocity reaches 5 m/s.But the maximum temperature gradient increases by21.2%.Meanwhile,higher fuel velocities can eliminate about 32%of the area with higher temperature gradient.And when the oxidant velocity reaches 7.5 m/s,the peak temperature gradient effectively decreases by 16.59%.Simultaneous adjustment of the oxidant and fuel velocities can effectively reduce the peak temperature gradient and increase the safety zone.The effects of operation conditions on the temperature gradient of the cell are clarified in this study,which can be a reference for further research on the reliability of SOFCs.展开更多
Forward modelling of gravity and magnetic data was done simultaneously to show the correlation between gravity and magnetic anomalies on a measured heat flux region. The results were used to characterize the heat sour...Forward modelling of gravity and magnetic data was done simultaneously to show the correlation between gravity and magnetic anomalies on a measured heat flux region. The results were used to characterize the heat source structures in Eburru area. Modelling was done using Oasis montaj geosoft software which is an iteration process where the gravity and magnetic anomalies were calculated and compared to the observed residual anomaly until there was a fit. The start model was constructed based on depths from Euler deconvolution and models constrained using stratigraphy data from the existing wells in the study area. <span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Forward modelling of gravity and magnetic data revealed intrusions within the Earth’s subsurface with depth to the top of the sources ranging from </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">739 m</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> to </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">5811 m</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. The density of the sources ranges between </span></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;">3.0 g/cm</span><sup><span style="font-family:Verdana;">3</span></sup></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> and </span></span></span></span><span><span><span><span styl展开更多
This study presents the RF design of a linear accelerator(linac)operated in single-bunch mode.The accelerator is powered by a compressed RF pulse produced from a SLED-I type RF pulse compressor.The compressed RF pulse...This study presents the RF design of a linear accelerator(linac)operated in single-bunch mode.The accelerator is powered by a compressed RF pulse produced from a SLED-I type RF pulse compressor.The compressed RF pulse has an unflattened shape with a gradient distribution which varies over the structure cells.An analytical study to optimize the accelerating structure together with the RF pulse compressor is performed.The optimization aims to maximize the efficiency by minimizing the required RF power from the generator for a given average accelerating gradient.The study shows that,owing to the compressed RF pulse shape,the constant-impedance structure has a similar efficiency to the optimal structure using varying iris apertures.The constant-impedance structure is easily fabricated and is favorable for the design of a linac with a pulse compressor.We utilize these findings to optimize the RF design of a X-band linac using the constant-impedance accelerating structure for the Tsinghua Thomson X-ray source facility.展开更多
Detection and localization of acoustic events in an environment are important to protect the military and civilian installations. While there are finite paths of wave propagation in simple or low reverberant environme...Detection and localization of acoustic events in an environment are important to protect the military and civilian installations. While there are finite paths of wave propagation in simple or low reverberant environments, in complex environments (e.g. a complex urban environment) obstacles such as terrain or buildings introduce multipath propagations, reflections and diffractions which make source localization challenging. Therefore, numeric results of simulated models (simplified and Fort Benning urban models) of 3D complex environments can highly help in real applications. Some of the conventional beamformer algorithms have been used in order to localize point sound source. Analyzing results shows that MRCB beamformer has better performance than others in this issue and its accuracy superiority is more than 3 m in simplified urban model and 5 m in Fort Benning urban model with respect to the SOC. Moreover, due to possible uncertainties between the numerical model and the actual environment such as squall effect, temperature gradient etc., sensitivity of the beamformers to temperature gradient is investigated which shows higher robustness of SOC beamformer than the MRCB beamformer. According to the results, due to gradient temperature uncertainty the accuracy degradation of the SOC is about 1m while in MRCB it alters from 0.5 m to 20 m approximately at all SNRs. COMSOL Multiphysics has been used to numerically simulate the environment of wave propagation.展开更多
基金supported by the National Key Research and Development Program of China under Grant No.2016YFC0300801the National Natural Science Foundation of China under Grants Nos.41576101 and 41427806
文摘This paper addresses the source seeking problems for an autonomous underwater vehicle（AUV） with the estimated gradients. The AUV is embedded with multiple sensors, which are only able to detect the signal strengths of the source with unknown distribution. To resolve this challenge,a sensor configuration is explicitly designed as a semicircle to estimate gradients of the signal field.Then, a controller is obtained via the estimated gradients to drive the AUV to approach the source.Moreover, an upper bound for the localization error is provided in terms of the radius of the semicircle and the signal distribution. Finally, the authors include a simulation example by applying the strategy to a Remote Environmental Monitoring Unit S（REMUS） for seeking the deepest point of a region of seabed in the South China Sea.
基金the supports provided by the Science and Technology Research Program of Henan Province,China(No.222102320230)the National Natural Science Foundation of China(No.51776190)。
文摘Effective operation strategies in the solid oxide fuel cell(SOFC)can adjust the spatial distribution of temperature gradient favoring the long-term stability.To investigate the effects of different operating conditions on the thermal behavior inside SOFC,a three-dimensional model is developed in this study.The model is verified by comparing it with the experimental data.The heat generation rate and its variation under different operating conditions are analyzed.The combined effects of operating voltage and gas temperature are considered to be the key factor influencing the temperature gradient.Compared to the original case,the temperature of SOFC decreases by 21.4 K when the fuel velocity reaches 5 m/s.But the maximum temperature gradient increases by21.2%.Meanwhile,higher fuel velocities can eliminate about 32%of the area with higher temperature gradient.And when the oxidant velocity reaches 7.5 m/s,the peak temperature gradient effectively decreases by 16.59%.Simultaneous adjustment of the oxidant and fuel velocities can effectively reduce the peak temperature gradient and increase the safety zone.The effects of operation conditions on the temperature gradient of the cell are clarified in this study,which can be a reference for further research on the reliability of SOFCs.
文摘Forward modelling of gravity and magnetic data was done simultaneously to show the correlation between gravity and magnetic anomalies on a measured heat flux region. The results were used to characterize the heat source structures in Eburru area. Modelling was done using Oasis montaj geosoft software which is an iteration process where the gravity and magnetic anomalies were calculated and compared to the observed residual anomaly until there was a fit. The start model was constructed based on depths from Euler deconvolution and models constrained using stratigraphy data from the existing wells in the study area. <span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">Forward modelling of gravity and magnetic data revealed intrusions within the Earth’s subsurface with depth to the top of the sources ranging from </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">739 m</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> to </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">5811 m</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. The density of the sources ranges between </span></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;">3.0 g/cm</span><sup><span style="font-family:Verdana;">3</span></sup></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> and </span></span></span></span><span><span><span><span styl
文摘This study presents the RF design of a linear accelerator(linac)operated in single-bunch mode.The accelerator is powered by a compressed RF pulse produced from a SLED-I type RF pulse compressor.The compressed RF pulse has an unflattened shape with a gradient distribution which varies over the structure cells.An analytical study to optimize the accelerating structure together with the RF pulse compressor is performed.The optimization aims to maximize the efficiency by minimizing the required RF power from the generator for a given average accelerating gradient.The study shows that,owing to the compressed RF pulse shape,the constant-impedance structure has a similar efficiency to the optimal structure using varying iris apertures.The constant-impedance structure is easily fabricated and is favorable for the design of a linac with a pulse compressor.We utilize these findings to optimize the RF design of a X-band linac using the constant-impedance accelerating structure for the Tsinghua Thomson X-ray source facility.
文摘Detection and localization of acoustic events in an environment are important to protect the military and civilian installations. While there are finite paths of wave propagation in simple or low reverberant environments, in complex environments (e.g. a complex urban environment) obstacles such as terrain or buildings introduce multipath propagations, reflections and diffractions which make source localization challenging. Therefore, numeric results of simulated models (simplified and Fort Benning urban models) of 3D complex environments can highly help in real applications. Some of the conventional beamformer algorithms have been used in order to localize point sound source. Analyzing results shows that MRCB beamformer has better performance than others in this issue and its accuracy superiority is more than 3 m in simplified urban model and 5 m in Fort Benning urban model with respect to the SOC. Moreover, due to possible uncertainties between the numerical model and the actual environment such as squall effect, temperature gradient etc., sensitivity of the beamformers to temperature gradient is investigated which shows higher robustness of SOC beamformer than the MRCB beamformer. According to the results, due to gradient temperature uncertainty the accuracy degradation of the SOC is about 1m while in MRCB it alters from 0.5 m to 20 m approximately at all SNRs. COMSOL Multiphysics has been used to numerically simulate the environment of wave propagation.
