The interaction of high-power laser pulses with undercritical foams produced by different techniques but with the same average density is studied at the PALS laser facility.The spatial-temporal evolution of X-ray emis...The interaction of high-power laser pulses with undercritical foams produced by different techniques but with the same average density is studied at the PALS laser facility.The spatial-temporal evolution of X-ray emission is observed using an X-ray streak camera,electron and ion temperatures are measured by X-ray spectroscopy,and hot-electron production is characterized by monochromatic X-ray imaging.Transmission of a femtosecond laser probe pulse through foams is observed in the near and far fields.In spite of large differences in pore size and foam structure,the velocity of ionization front propagation is quite similar for all the foams studied and is slower than that in a homogeneous material of the same average density.The ion temperature in the plasma behind the ionization front is a few times higher than the electron temperature.Hot-electron production in plastic foams with small pores is strongly suppressed compared with that in solid targets,whereas in foams produced by additive manufacturing,it is significantly increased to the level observed in bare copper foil targets.展开更多
Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of supr...Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.展开更多
This paper proposes an adaptive nonlinear proportional-derivative(ANPD)controller for a two-wheeled self-balancing robot(TWSB)modeled by the Lagrange equation with external forces.The proposed control scheme is design...This paper proposes an adaptive nonlinear proportional-derivative(ANPD)controller for a two-wheeled self-balancing robot(TWSB)modeled by the Lagrange equation with external forces.The proposed control scheme is designed based on the combination of a nonlinear proportional-derivative(NPD)controller and a genetic algorithm,in which the proportional-derivative(PD)parameters are updated online based on the tracking error and the preset error threshold.In addition,the genetic algorithm is employed to adaptively select initial controller parameters,contributing to system stability and improved control accuracy.The proposed controller is basic in design yet simple to implement.The ANPD controller has the advantage of being computationally lightweight and providing high robustness against external forces.The stability of the closed-loop system is rigorously analyzed and verified using Lyapunov theory,providing theoretical assurance of its robustness.Simulations and experimental results show that the TWSB robot with the proposed ANPD controller achieves quick balance and tracks target values with very small errors,demonstrating the effectiveness and performance of the proposed controller.The proposed ANPD controller demonstrates significant improvements in balancing and tracking performance for two-wheeled self-balancing robots,which has great applicability in the field of robot control systems.This represents a promising solution for applications requiring precise and stable motion control under varying external conditions.展开更多
To gain access to networks,various intrusion attack types have been developed and enhanced.The increasing importance of computer networks in daily life is a result of our growing dependence on them.Given this,it is gl...To gain access to networks,various intrusion attack types have been developed and enhanced.The increasing importance of computer networks in daily life is a result of our growing dependence on them.Given this,it is glaringly obvious that algorithmic tools with strong detection performance and dependability are required for a variety of attack types.The objective is to develop a system for intrusion detection based on deep reinforcement learning.On the basis of the Markov decision procedure,the developed system can construct patterns appropriate for classification purposes based on extensive amounts of informative records.Deep Q-Learning(DQL),Soft DQL,Double DQL,and Soft double DQL are examined from two perspectives.An evaluation of the authors’methods using UNSW-NB15 data demonstrates their superiority regarding accuracy,precision,recall,and F1 score.The validity of the model trained on the UNSW-NB15 dataset was also checked using the BoT-IoT and ToN-IoT datasets,yielding competitive results.展开更多
The objective of the paper was to compare values of the muzzle brake efficiency coefficient for a rifle with active or inactive automatics systems.Special laboratory stand designed for investigating the recoil process...The objective of the paper was to compare values of the muzzle brake efficiency coefficient for a rifle with active or inactive automatics systems.Special laboratory stand designed for investigating the recoil process was used.The motion of the rifle was detected by the use of the laser interferometer and the optical camera.The recoil velocity time courses were determined by smoothing and differentiation of experimental position records.The results of the experiments indicated that in the case of an active automatics system two values of the recoil velocity can be used for calculation of the energetic efficiency coefficient:the maximum recoil velocity and the final recoil velocity at the end of the automatics action cycle.The values of the coefficient,calculated using these two values of the recoil velocity,distinctly differ.However,it was shown that their values indicate the same relation between the efficiency of various muzzle brakes.The value of the efficiency coefficient,determined on the basis of the final recoil velocity value,is practically the same as that determined on the basis of the final recoil velocity value for the rifle with an inactive automatics system.展开更多
The paper explores the possibilities of using carbonyl iron in the form of a powder for the manufacture of radar-absorbing paints-reducing the radar signature of the objects that they cover.The attenuation values in t...The paper explores the possibilities of using carbonyl iron in the form of a powder for the manufacture of radar-absorbing paints-reducing the radar signature of the objects that they cover.The attenuation values in the range of 4-18 GHz for various coating thicknesses,ranging from 0.5 to 2.00 mm with 0.5 mm increment,and for different absorber content-75%and 80%,as well as the use of two different binders in the form of epoxy resins with hardeners,were investigated.For the frequency of 18 GHz and a 1.5 mm thick coating with a 75%absorber content,Epidian 112 resin and Saduramid 10/50 hardener used as a binder,and the maximum attenuation level obtained equalled 20.2 d B at 16 GHz.Additionally,the absorber particle size ranging from 3 to 4μm and its higher mass content resulted in achieving the reflection loss above-12 d B in the entire 8-12.5 GHz range for layers between 1-and 1.5 mm thickness.The qualitative assessment of the tested samples in the context of camouflage in the radar range was also performed,using statistical analysis.展开更多
The human body has symmetric bones.This paper uses control engineering concepts to design a suitable controller to synchronize two symmetric bones of the human body to control and treat bone cancer.A Nonsingular Termi...The human body has symmetric bones.This paper uses control engineering concepts to design a suitable controller to synchronize two symmetric bones of the human body to control and treat bone cancer.A Nonsingular Terminal Sliding Mode Control(NTSMC)method will be employed to design the proposed control inputs.The control inputs can be the chemical drugs that can be used to treat bone cancer.The dynamical equations of bone cancer will be used to apply the designed control method and test it.For testing the designed controller,Simulink/MATLAB software will be used.The proposed controller is chattering-free,robust against uncertainties and external disturbances,and finite-time stable in the control engineering view.Bone cancer will be treated for almost one year using the proposed control method.展开更多
This paper provides a detailed analysis of the performance and economics of a 50 MW grid-connected solar power plant in Vietnam over a 4.5-year operational period from January 2020 to June 2024.The study systematicall...This paper provides a detailed analysis of the performance and economics of a 50 MW grid-connected solar power plant in Vietnam over a 4.5-year operational period from January 2020 to June 2024.The study systematically collected and analyzed key solar performance metrics,including the correlation between solar irradiance and temperature,as well as the relationship between irradiance and the plant’s performance ratio(PR).The findings indicate that PR ranged from 0.61%to 0.84%,with solar irradiance varying between 128 and 192 kWh/m^(2)/month.The capacity utilization factor ranged from 12.82%to 19.47%,and the average final yield varied between 3.24 and 4.23 h/d,consistent with other studies.Power losses ranged from 50 to 130 MWh/month,totaling 5978.2 MWh over the period.The cumulative electricity generation reached 383768 MWh.The economic analysis revealed a simple payback period of 7 years with a levelized cost of electricity of 0.05 USD/kWh.The study highlights the importance of implementing effective maintenance strategies to minimize the gap between theoretical and actual performance,thereby ensuring long-term economic viability,particularly in the context of high interest rates in developing countries.展开更多
The trend of increasing the power-to-weight ratios of aircraft turbofan engines and efficiency of steam turbines leads to designs with long and slender blades often operating at transonic flow conditions.Such blades a...The trend of increasing the power-to-weight ratios of aircraft turbofan engines and efficiency of steam turbines leads to designs with long and slender blades often operating at transonic flow conditions.Such blades are prone to undesirable and possibly destructive vibra-tions caused by engine-order excitation or induced by flow itself.To shed more light on this problem and to extend the existing knowledge,this paper presents experimental and numerical study on torsional mode vibration of one blade in a linear blade cascade of flat profiles.In this study,dynamic loading and pressure distributions were investigated at subsonic,supercritical and transonic flow regimes while the blade was kinematically excited by a motor and shaft mechanism at reduced frequencies up to k Z 0.47.Dynamic flow structure development was documented and analyzed based on numerical simulations.Furthermore,dependence of energy transfer over an oscillation cycle on frequency and exit Mach number was investigated.Results revealed significant hysteresis in the flow field configuration particularly at supercrit-ical and transonic cases.Hysteresis is manifested namely by different development of supersonic regions when the oscillating blade passes through the zero deflection during upstroke and downstroke.Resulting aerodynamic moment is non-harmonic and there is an increasing phase lag with respect to the blade deflection when oscillation frequency increases.In majority of investigated regimes,hysteresis resulted in aerodynamic damping of the blade oscillation.展开更多
This paper presents a defect analysis and performance evaluation of photovoltaic(PV)modules using quantitative electroluminescence imaging(EL).The study analyzed three common PV technologies:thin-film,monocrystalline ...This paper presents a defect analysis and performance evaluation of photovoltaic(PV)modules using quantitative electroluminescence imaging(EL).The study analyzed three common PV technologies:thin-film,monocrystalline silicon,and polycrystalline silicon.Experimental results indicate that monocrystalline silicon panels have the lowest degradation rate,ranging from 0.861%to 0.886%,compared to thin-film panels,which range from 1.39%to 1.53%,and polycrystalline panels,which range from 1.32%to 1.62%.The primary defects in thin-film technology include the formation of small shunts that gradually accumulate,causing shading and obstructing current flow,thereby reducing efficiency.For monocrystalline and polycrystalline technologies,defects include oxidation leading to loss of connection,layer wrinkles causing shading,and the accumulation of dust and animal waste.The study also demonstrates the effectiveness of using EL to identify micro-defects with high accuracy.The comprehensive quantitative EL method not only assesses defects with high accuracy but also offers practical insights for improving maintenance strategies and performance in tropical climates.展开更多
During traction and braking of multiple-unit trains,substantial longitudinal dynamic forces might occur in couplers due to the non-optimal distribution of traction and braking forces generated by self-propelled carria...During traction and braking of multiple-unit trains,substantial longitudinal dynamic forces might occur in couplers due to the non-optimal distribution of traction and braking forces generated by self-propelled carriages.These dynamic forces might create shocks affecting the reduction of endurance of the weakest train structural components primarily.Thus,the overall operational safety of the train is also lowered.The purpose of the paper is to develop a new control system to supervise the activities related to the longitudinal dynamics of each train carriage in a multiple-unit train to reduce the longitudinal coupler forces acting during train traction and braking.The hierarchical structure of the control system consists of two levels.The first master level of control works like standard cruise control.However,the reduction of longitudinal coupler forces is achieved by applying a second level of slave control systems with a control configuration of feedback compensation.展开更多
The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition model.As a first step towards simul...The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition model.As a first step towards simulation of blade flutter in turbomachinery,various incidence angle offsets of the middle blade were modeled.All simulations were run for the flow regime characterized by outlet isentropic Mach number M_(is)=0.5and zero incidence.The results of the LES/RANS simulations(pressure and Mach number distributions)were compared to a baseline RANS model,and to experimental data measured in a high-speed wind tunnel.The numerical results show that both methods overpredict flow separation taking place at the leading edge.In this regard,the hybrid LES/RANS method does not provide superior results compared to the traditional RANS simulations.Nevertheless,the LES/RANS results also capture vortex shedding from the blunt trailing edge.The frequency of the trailing edge vortex shedding in CFD simulations matches perfectly the spectral peak recorded during wind tunnel measurements.展开更多
One of the requirements for modem production machine is versatility and easy reconfiguration to produce new products. The production machines use fixed gearing and mechanical cams in history. The cams were used for sp...One of the requirements for modem production machine is versatility and easy reconfiguration to produce new products. The production machines use fixed gearing and mechanical cams in history. The cams were used for specific stokes and cam switches were used for commissioning of technological process. This solution has disadvantages in lower production speed and no flexibility of production. This article summaries practical steps for machine modernization and highlight practical problems in modernization of older production machine. The electronic cam with direct linear drive was used for traversal motion with high peak acceleration. This paper discusses cam stoke curve design, redesign and fitting.展开更多
The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to...The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers.Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms,and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection,clinical diagnosis,and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear.Specifically we study the eardrum,the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing.Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second.Two shape measurement modalities had previously been implemented into our holographic systems:(1)a multi-wavelength method with a wavelength tunable laser;and(2)a multi-angle illumination method with a single wavelength laser.In this paper,we present a third method using a miniaturized fringe projection system with a microelectromechanical system(MEMS)mirror.Further,we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm.We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology(NIST)traceable gauge and sound-activated latex membranes and human eardrums.展开更多
基金supported by the Center of Advanced Applied Sciences(CAAS)Project No.(CZ.02.1.01/0.0/0.0/16019/0000778)from the European Regional Development Fundalso supported in part by the Czech Technical University in Prague Project No.SGS22/184/OHK4/3T/14+1 种基金partial funding via EUROfusion Enabling Research Project No.AWP24-ENR-03-CEA-02“Foams as a pathway to energy from high gain direct drive ignition,”within the framework of the EUROfusion Consortium,funded by the European Union via the Euratom Research and Training Program(Grant Agreement No.101052200-EUROfusion)the Czech Ministry of Education,Youth and Sports(CMEYS)for funding the operation of the PALS facility(Grant No.LM2023068)。
文摘The interaction of high-power laser pulses with undercritical foams produced by different techniques but with the same average density is studied at the PALS laser facility.The spatial-temporal evolution of X-ray emission is observed using an X-ray streak camera,electron and ion temperatures are measured by X-ray spectroscopy,and hot-electron production is characterized by monochromatic X-ray imaging.Transmission of a femtosecond laser probe pulse through foams is observed in the near and far fields.In spite of large differences in pore size and foam structure,the velocity of ionization front propagation is quite similar for all the foams studied and is slower than that in a homogeneous material of the same average density.The ion temperature in the plasma behind the ionization front is a few times higher than the electron temperature.Hot-electron production in plastic foams with small pores is strongly suppressed compared with that in solid targets,whereas in foams produced by additive manufacturing,it is significantly increased to the level observed in bare copper foil targets.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure Activity (Application No. 23068)carried out within the framework of EUROfusion Enabling Research Projects AWP21-ENR-01-CEA02 and AWP24-ENR-IFE-02-CEA-02+3 种基金received funding from Euratom Research and Training Programme 2021–2025 under Grant No. 633053supported by the Ministry of Youth and Sports of the Czech Republic [Project No. LM2023068 (PALS RI)]by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA25030200 and XDA25010100)supported by COST (European Cooperation in Science and Technology) through Action CA21128 PROBONO (PROton BOron Nuclear Fusion: from energy production to medical applicatiOns)
文摘Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.
文摘This paper proposes an adaptive nonlinear proportional-derivative(ANPD)controller for a two-wheeled self-balancing robot(TWSB)modeled by the Lagrange equation with external forces.The proposed control scheme is designed based on the combination of a nonlinear proportional-derivative(NPD)controller and a genetic algorithm,in which the proportional-derivative(PD)parameters are updated online based on the tracking error and the preset error threshold.In addition,the genetic algorithm is employed to adaptively select initial controller parameters,contributing to system stability and improved control accuracy.The proposed controller is basic in design yet simple to implement.The ANPD controller has the advantage of being computationally lightweight and providing high robustness against external forces.The stability of the closed-loop system is rigorously analyzed and verified using Lyapunov theory,providing theoretical assurance of its robustness.Simulations and experimental results show that the TWSB robot with the proposed ANPD controller achieves quick balance and tracks target values with very small errors,demonstrating the effectiveness and performance of the proposed controller.The proposed ANPD controller demonstrates significant improvements in balancing and tracking performance for two-wheeled self-balancing robots,which has great applicability in the field of robot control systems.This represents a promising solution for applications requiring precise and stable motion control under varying external conditions.
文摘To gain access to networks,various intrusion attack types have been developed and enhanced.The increasing importance of computer networks in daily life is a result of our growing dependence on them.Given this,it is glaringly obvious that algorithmic tools with strong detection performance and dependability are required for a variety of attack types.The objective is to develop a system for intrusion detection based on deep reinforcement learning.On the basis of the Markov decision procedure,the developed system can construct patterns appropriate for classification purposes based on extensive amounts of informative records.Deep Q-Learning(DQL),Soft DQL,Double DQL,and Soft double DQL are examined from two perspectives.An evaluation of the authors’methods using UNSW-NB15 data demonstrates their superiority regarding accuracy,precision,recall,and F1 score.The validity of the model trained on the UNSW-NB15 dataset was also checked using the BoT-IoT and ToN-IoT datasets,yielding competitive results.
基金supported by the National Research Centre[grant number DOBR/0046/R/ID1/2012/03]。
文摘The objective of the paper was to compare values of the muzzle brake efficiency coefficient for a rifle with active or inactive automatics systems.Special laboratory stand designed for investigating the recoil process was used.The motion of the rifle was detected by the use of the laser interferometer and the optical camera.The recoil velocity time courses were determined by smoothing and differentiation of experimental position records.The results of the experiments indicated that in the case of an active automatics system two values of the recoil velocity can be used for calculation of the energetic efficiency coefficient:the maximum recoil velocity and the final recoil velocity at the end of the automatics action cycle.The values of the coefficient,calculated using these two values of the recoil velocity,distinctly differ.However,it was shown that their values indicate the same relation between the efficiency of various muzzle brakes.The value of the efficiency coefficient,determined on the basis of the final recoil velocity value,is practically the same as that determined on the basis of the final recoil velocity value for the rifle with an inactive automatics system.
文摘The paper explores the possibilities of using carbonyl iron in the form of a powder for the manufacture of radar-absorbing paints-reducing the radar signature of the objects that they cover.The attenuation values in the range of 4-18 GHz for various coating thicknesses,ranging from 0.5 to 2.00 mm with 0.5 mm increment,and for different absorber content-75%and 80%,as well as the use of two different binders in the form of epoxy resins with hardeners,were investigated.For the frequency of 18 GHz and a 1.5 mm thick coating with a 75%absorber content,Epidian 112 resin and Saduramid 10/50 hardener used as a binder,and the maximum attenuation level obtained equalled 20.2 d B at 16 GHz.Additionally,the absorber particle size ranging from 3 to 4μm and its higher mass content resulted in achieving the reflection loss above-12 d B in the entire 8-12.5 GHz range for layers between 1-and 1.5 mm thickness.The qualitative assessment of the tested samples in the context of camouflage in the radar range was also performed,using statistical analysis.
基金support from Warsaw University of Technology(WUT),grant No:504440200003.
文摘The human body has symmetric bones.This paper uses control engineering concepts to design a suitable controller to synchronize two symmetric bones of the human body to control and treat bone cancer.A Nonsingular Terminal Sliding Mode Control(NTSMC)method will be employed to design the proposed control inputs.The control inputs can be the chemical drugs that can be used to treat bone cancer.The dynamical equations of bone cancer will be used to apply the designed control method and test it.For testing the designed controller,Simulink/MATLAB software will be used.The proposed controller is chattering-free,robust against uncertainties and external disturbances,and finite-time stable in the control engineering view.Bone cancer will be treated for almost one year using the proposed control method.
文摘This paper provides a detailed analysis of the performance and economics of a 50 MW grid-connected solar power plant in Vietnam over a 4.5-year operational period from January 2020 to June 2024.The study systematically collected and analyzed key solar performance metrics,including the correlation between solar irradiance and temperature,as well as the relationship between irradiance and the plant’s performance ratio(PR).The findings indicate that PR ranged from 0.61%to 0.84%,with solar irradiance varying between 128 and 192 kWh/m^(2)/month.The capacity utilization factor ranged from 12.82%to 19.47%,and the average final yield varied between 3.24 and 4.23 h/d,consistent with other studies.Power losses ranged from 50 to 130 MWh/month,totaling 5978.2 MWh over the period.The cumulative electricity generation reached 383768 MWh.The economic analysis revealed a simple payback period of 7 years with a levelized cost of electricity of 0.05 USD/kWh.The study highlights the importance of implementing effective maintenance strategies to minimize the gap between theoretical and actual performance,thereby ensuring long-term economic viability,particularly in the context of high interest rates in developing countries.
基金supported by the Ministry of Educa-tion Youth and Sports of the Czech Republic under the grant LUAUS23231 Origins and mechanisms of flutter and non-synchronous vibration in modern turbomachines oper-ating at wide range of regimes.
文摘The trend of increasing the power-to-weight ratios of aircraft turbofan engines and efficiency of steam turbines leads to designs with long and slender blades often operating at transonic flow conditions.Such blades are prone to undesirable and possibly destructive vibra-tions caused by engine-order excitation or induced by flow itself.To shed more light on this problem and to extend the existing knowledge,this paper presents experimental and numerical study on torsional mode vibration of one blade in a linear blade cascade of flat profiles.In this study,dynamic loading and pressure distributions were investigated at subsonic,supercritical and transonic flow regimes while the blade was kinematically excited by a motor and shaft mechanism at reduced frequencies up to k Z 0.47.Dynamic flow structure development was documented and analyzed based on numerical simulations.Furthermore,dependence of energy transfer over an oscillation cycle on frequency and exit Mach number was investigated.Results revealed significant hysteresis in the flow field configuration particularly at supercrit-ical and transonic cases.Hysteresis is manifested namely by different development of supersonic regions when the oscillating blade passes through the zero deflection during upstroke and downstroke.Resulting aerodynamic moment is non-harmonic and there is an increasing phase lag with respect to the blade deflection when oscillation frequency increases.In majority of investigated regimes,hysteresis resulted in aerodynamic damping of the blade oscillation.
文摘This paper presents a defect analysis and performance evaluation of photovoltaic(PV)modules using quantitative electroluminescence imaging(EL).The study analyzed three common PV technologies:thin-film,monocrystalline silicon,and polycrystalline silicon.Experimental results indicate that monocrystalline silicon panels have the lowest degradation rate,ranging from 0.861%to 0.886%,compared to thin-film panels,which range from 1.39%to 1.53%,and polycrystalline panels,which range from 1.32%to 1.62%.The primary defects in thin-film technology include the formation of small shunts that gradually accumulate,causing shading and obstructing current flow,thereby reducing efficiency.For monocrystalline and polycrystalline technologies,defects include oxidation leading to loss of connection,layer wrinkles causing shading,and the accumulation of dust and animal waste.The study also demonstrates the effectiveness of using EL to identify micro-defects with high accuracy.The comprehensive quantitative EL method not only assesses defects with high accuracy but also offers practical insights for improving maintenance strategies and performance in tropical climates.
文摘During traction and braking of multiple-unit trains,substantial longitudinal dynamic forces might occur in couplers due to the non-optimal distribution of traction and braking forces generated by self-propelled carriages.These dynamic forces might create shocks affecting the reduction of endurance of the weakest train structural components primarily.Thus,the overall operational safety of the train is also lowered.The purpose of the paper is to develop a new control system to supervise the activities related to the longitudinal dynamics of each train carriage in a multiple-unit train to reduce the longitudinal coupler forces acting during train traction and braking.The hierarchical structure of the control system consists of two levels.The first master level of control works like standard cruise control.However,the reduction of longitudinal coupler forces is achieved by applying a second level of slave control systems with a control configuration of feedback compensation.
基金supported by the Czech Science Foundation(GACR)(Grant No.20-11537S)Institutional support RVO:61388998。
文摘The paper reports on 3D numerical simulations of unsteady compressible airflow in a blade cascade consisting of flat profiles using a hybrid LES/RANS approach including a transition model.As a first step towards simulation of blade flutter in turbomachinery,various incidence angle offsets of the middle blade were modeled.All simulations were run for the flow regime characterized by outlet isentropic Mach number M_(is)=0.5and zero incidence.The results of the LES/RANS simulations(pressure and Mach number distributions)were compared to a baseline RANS model,and to experimental data measured in a high-speed wind tunnel.The numerical results show that both methods overpredict flow separation taking place at the leading edge.In this regard,the hybrid LES/RANS method does not provide superior results compared to the traditional RANS simulations.Nevertheless,the LES/RANS results also capture vortex shedding from the blunt trailing edge.The frequency of the trailing edge vortex shedding in CFD simulations matches perfectly the spectral peak recorded during wind tunnel measurements.
文摘One of the requirements for modem production machine is versatility and easy reconfiguration to produce new products. The production machines use fixed gearing and mechanical cams in history. The cams were used for specific stokes and cam switches were used for commissioning of technological process. This solution has disadvantages in lower production speed and no flexibility of production. This article summaries practical steps for machine modernization and highlight practical problems in modernization of older production machine. The electronic cam with direct linear drive was used for traversal motion with high peak acceleration. This paper discusses cam stoke curve design, redesign and fitting.
基金support from the US National Institute on Deafness and Other Communication Disorders(NIDCD R01 DC016079)is gratefully acknowledgedsupport by the Center for Holographic Studies and Laser micro-mechaTronics(CHSLT)at WPI.
文摘The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers.Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms,and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection,clinical diagnosis,and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear.Specifically we study the eardrum,the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing.Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second.Two shape measurement modalities had previously been implemented into our holographic systems:(1)a multi-wavelength method with a wavelength tunable laser;and(2)a multi-angle illumination method with a single wavelength laser.In this paper,we present a third method using a miniaturized fringe projection system with a microelectromechanical system(MEMS)mirror.Further,we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm.We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology(NIST)traceable gauge and sound-activated latex membranes and human eardrums.
