Hydrodynamic instability growth at the deuterium-tritium(DT)fuel-ablator interface plays a critical role in determining the performance of inertial confinement fusion implosions.During the late stages of implosion,ins...Hydrodynamic instability growth at the deuterium-tritium(DT)fuel-ablator interface plays a critical role in determining the performance of inertial confinement fusion implosions.During the late stages of implosion,insufficient doping of the ablator material can result in highenergy X-ray preheat,which may trigger the development of a classical-like Rayleigh-Taylor instability(RTI)at the fuel-ablator interface.In implosion experiments at the Shenguang 100 kJ-level laser facility,the primary source of perturbation is the roughness of the inner DT ice interface.In this study,we propose an analytical model to describe the feed-out process of the initial roughness of the inner DT ice interface.The perturbation amplitude derived from this model serves as the initial seed for the late-time RTI during the acceleration phase.Our findings confirm the presence of classical-like RTI at the fuel-ablator interface.Numerical simulations conducted using a radiation hydrodynamic code validate the proposed analytical model and demonstrate the existence of a peak mode number in both the feed-out process and the classical-like RTI.It provides an alternative bridge between the current target fabrication limitations and the unexpected implosion performance.展开更多
In the direct drive inertial confinement fusion(ICF)scheme,a rippled interface between the ablator and the deuterium–tritium ice fuel can feed out and form perturbation seeds for the ablative Rayleigh–Taylor instabi...In the direct drive inertial confinement fusion(ICF)scheme,a rippled interface between the ablator and the deuterium–tritium ice fuel can feed out and form perturbation seeds for the ablative Rayleigh–Taylor instability,with undesirable effects.However,the evolution of this instability remains insufficiently studied,and the effects of high-Z dopant on this instability remain unclear.In this paper,we develop a theoretical model to calculate the feedout seeds and describe this instability.Our theory suggests that the feedout seeds are determined by the ablation pressure and the adiabatic index,while the subsequent growth depends mainly on the ablation velocity.Two-dimensional radiation hydrodynamic simulations confirm our theory.It is shown that targets with high-Z dopant in the outer ablator exhibit more severe feedout seeds,because of their higher ionization compared with undoped targets.The X-ray pre-ablation in high-Z doped targets significantly suppresses subsequent growth,leading to suppression of short-wavelength perturbations.However,for long-wavelength perturbations,this suppression is weakened,resulting in increased instability in high-Z doped targets.The results are helpful for understanding the innerinterface-initiated instability and the influence of high-Z dopant on it,providing valuable insights for target design and instability control in ICF.展开更多
The evolution of an initially flat sandy bed is studied in a laboratory wave flume under enoidal waves and acoustic Doppler velocimeter （ADV） was utilized in the detailed velocity measurements at different positions...The evolution of an initially flat sandy bed is studied in a laboratory wave flume under enoidal waves and acoustic Doppler velocimeter （ADV） was utilized in the detailed velocity measurements at different positions. The ripple formation and evolution have been analyzed by CCD images and the asymmetric rippled bed is induced by the nonlinear wave flow. The flow structure and a complete process of vortex formation, evolvement and disappearance were observed on the asymmetric rippled bed under cnoidal waves. With the increasing nonlinearity of waves, which is an important factor in the sand ripple formation, the vortex intensity becomes stronger and shows different characteristics on both sides of the ripple crest. The vorticity and wave velocity reach their maximum values at different phase angles. The vortex value reaches the maximum value at a small phase angle with the increasing Ursell number. The near bed flow patterns are mainly determined by the ripple forms and the averaged longitudinal velocity over a wave period above the ripple trough and crest are positive, which indicates the possibility of significant onshore sediment transport and a corresponding ripple drift. The phase averaged vertical velocity has noticeable positive values near the bottom of the ripple crest and trough. Sediments may be lifted from the ripple surface, picked up in suspension by the local velocity, and deposited over the crest and on the lee of the ripples.展开更多
This paper is mainly concerned with the turbulence in oscillatory bottom boundary layers over flat or rippled seaheds. Owing to the strong shear and anisotmpy of oscillatory flow, an anisotropic turbulence mathematica...This paper is mainly concerned with the turbulence in oscillatory bottom boundary layers over flat or rippled seaheds. Owing to the strong shear and anisotmpy of oscillatory flow, an anisotropic turbulence mathematical model is set up using the finite difference method, and the computational results of the model are verified by comparisons with wellknown experiments. Turbulent energy, dissipation and Reynolds stress can all be computed with this mathematical model, and the development processes of a large coherent vortex structure over a rippled bed, such as main flow separation, coherent vortex formation and curling, coherent vortex ejection and breaking up, are successfully simulated.展开更多
We propose to investigate the THz field generation using nonlinear mixing mechanism of laser beat wave with inclined rippled density plasmas.Two laser pulses with frequencies(ω_(1),ω_(2)) and wave vectors(k_(1),k_(2...We propose to investigate the THz field generation using nonlinear mixing mechanism of laser beat wave with inclined rippled density plasmas.Two laser pulses with frequencies(ω_(1),ω_(2)) and wave vectors(k_(1),k_(2)) co-propagate and resultant laser beat wave forms at beat frequency(ω_(1)-ω_(2)).Laser beat wave imparts a nonlinear force on the ambient electrons and pushes them outward with nonlinear velocity v_(NL).Coupling of induced density perturbation and nonlinear velocity v_(NL)generates nonlinear currents at laser beat frequency that further generates electromagnetic field E_((ω_(1)-ω_(2))) in terahertz(THz)range.In the present scheme,density ripples are introduced at an angle with respect to laser propagation and flat Gaussian index(f) is introduced in laser field profile that transform curved top of Gaussian field envelope into flat top field envelope.The combined effect of flat laser pulses with inclined density ripples in plasmas shows 10-fold enhancement in THz field amplitude when flat-Gaussian index(f) varies from 1 to 4.Also,the THz field intensifies when density ripples inclination increases upto a certain angle and then decreases.展开更多
The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth initially, disturbances arising from the bed or other external sources will cause the laminar ...The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth initially, disturbances arising from the bed or other external sources will cause the laminar flow in an open channel to become unstable as soon as the flow develops, thereby leading to the formation of sand ripples on the bed. In return, the formation of the sand ripples will modfy the instability path of the laminar flow passing over them. The wavy character of the bed will induce further instability of the flow, which is essentially different from that on a smooth bed: the neutral curve will move forward and the critical Reynolds number will decrease. The flow is unstable in response to a wider range of the disturbance wave number, or the laminar flow instability can happen more easily. The propagation speed of the sand ripples also affects the flow instability, since the stability of open channel flow over a movable bed is fundamentally different from that on a rigid bed. These instability effects are discussed in detail in this paper.展开更多
Permanent-magnet(PM)machines are the important driving components of various mechanical equipment and industrial applications,such as robot joints,aerospace equipment,electric vehicles,actuators,wind generators and el...Permanent-magnet(PM)machines are the important driving components of various mechanical equipment and industrial applications,such as robot joints,aerospace equipment,electric vehicles,actuators,wind generators and electric traction systems.The PM machines are usually expected to have high torque/power density,low torque ripple,reduced rotor mass,a large constant power speed range or strong anti-magnetization capability to match different requirements of industrial applications.The structural topology of the electric machines,including stator/rotor arrangements and magnet patterns of rotor,is one major concern to improve their electromagnetic performance.However,systematic reviews of structural topology are seldom found in literature.Therefore,the objective of this paper is to summarize the stator/rotor arrangements and magnet patterns of the permanent-magnet brushless machines,in depth.Specifically,the stator/rotor arrangements of the PM machines including radial-flux,axialflux and emerging hybrid axial-radial flux configurations are presented,and pros and cons of these topologies are discussed regarding their electromagnetic performance.The magnet patterns including various surface-mounted and interior magnet patterns,such as parallel magnetization pole pattern,Halbach arrays,spoke-type designs and their variants are summarized,and the characteristics of those magnet patterns in terms of flux-focusing effect,magnetic self-shielding effect,torque ripple,reluctance torque,magnet utilization ratio,and anti-demagnetization capability are compared.This paper can provide guidance and suggestion for the structure selection and design of PM brushless machines for high-performance industrial applications.展开更多
Switched Reluctance Motors(SRMs),outfitted with rugged construction,good speed range,high torque density,and rare earth-free nature that outweigh induction motors(IM)and permanent magnet synchronous motor(PMSM),afford...Switched Reluctance Motors(SRMs),outfitted with rugged construction,good speed range,high torque density,and rare earth-free nature that outweigh induction motors(IM)and permanent magnet synchronous motor(PMSM),afford a broad range of applications in the domain of electric vehicles(EVs).Standard copper magnetic wire and low-carbon steel laminations are used to construct SRMs,which give them high efficiency in the range of 85-95%.Despite SRM's desirable features over traditional motor-speed drives,high torque ripples and radial distortions constrain their deployment in EVs.Precise rotor position is imperative for effective management of the speed and torque of SRMs.This paper provides an illustrative compendium on review of the torque-speed control and ripple mitigation techniques using design enhancements and control methods for SRM drives for EV applications.The various schemes were evaluated on their performance metricsoperational speed range,control complexity,practical realization,need for pre-stored parameters(look-up tables of current,inductance and torque profiles)and motor controller memory requirements.The findings provide valuable insights into balancing the gains and trade-offs associated with EV applications.Furthermore,they pinpoint opportunities for enhancement by analyzing the cost and technical aspects of different SRM controllers.展开更多
Caregivers play an essential but often unacknowledged role in healthcare,particularly in chronic illness and post-transplantation scenarios.We highlight the profound emotional,physical,and logistical challenges caregi...Caregivers play an essential but often unacknowledged role in healthcare,particularly in chronic illness and post-transplantation scenarios.We highlight the profound emotional,physical,and logistical challenges caregivers face,as illuminated by recent studies,including the work of Virches et al about liver transplantation.Pre-transplant caregiving is marked by heightened stress,depression,and emotional strain,as caregivers navigate the unpredictability of conditions like cirrhosis.While liver transplantation significantly alleviates caregiver burden by stabilizing patient health,caregiving evolves rather than ends,requiring ongoing vigilance for post-transplant care,medication adherence,and lifestyle adjustments.We examine the disproportionate impact of caregiving on the family,due to entrenched cultural and gender norms and highlight how these disparities reinforce systemic neglect.Caregiving,often viewed as a familial duty,carries financial,mental,and physical health costs,perpetuating inequities and marginalization.We argue that caregivers are integral to healthcare outcomes and must be included in systemic frameworks to improve patient care.We also advocate for a paradigm shift from patient-centered to family-centered care,emphasizing caregiver inclusion as a core healthcare priority.Policy recommendations related to financial support,respite care,education,and mental health services should be tailored for caregivers.By addressing caregiver needs,healthcare systems can improve patient outcomes,reduce costs,and foster equity.This editorial underscores that caregivers are not ancillary but central to healthcare’s success.Recognizing and supporting them is both an ethical responsibility and a practical necessity for sustainable healthcare.展开更多
Purpose–This study aims to propose a novel identification method to accurately estimate linear and nonlinear dynamics in permanent magnet synchronous linear motor(PMSLM)based on the time-domain analysis of relay feed...Purpose–This study aims to propose a novel identification method to accurately estimate linear and nonlinear dynamics in permanent magnet synchronous linear motor(PMSLM)based on the time-domain analysis of relay feedback.Design/methodology/approach–A mathematical model of the PMSLM-based servo-mechanical system was first established,incorporating the aforementioned nonlinearities.The model’s velocity response was derived by analyzing its behavior as a first-order system under arbitrary input.To induce oscillatory dynamics,an ideal relay with artificially introduced dead-time components was then integrated into the servo-mechanism.Depending on the oscillations and the time-domain analysis,nonlinear formulas were deduced according to the velocity response of the servo-mechanism.Afterwards,the unknown model parameters can be solved on account of the cost function which utilizes the discrepancy between nominal position characteristics and temporary position characteristics,both of which are extracted from the oscillations.The proposed recognition method was validated through a twostage process:(1)numerical simulation and calculation,followed by(2)real-time experimental verification on a direct-drive servo platform.Subsequently,leveraging the identification results,a novel control strategy was developed and its tracking performance was benchmarked against conventional control schemes.Findings–Simulation results demonstrate that the proposed method achieves estimation accuracy within 8%.Building on this,a novel control strategy is developed by incorporating both friction pulsation and force pulsation identification results into the feedforward compensator.Comparative experiments reveal that this strategy significantly enhances tracking and positioning performance over traditional control schemes.In a word,this new identification method can be used in different process control and servo control systems.Moreover,parameter auto-tuning,feed forward compensation or disturbance observer can be investigated based on the obtained information to improve the system stability and control accuracy.Originality/value–It is of great significance for the performance improvement of rail transit motor control equipment,such as electro-mechanical braking systems.By enhancing the efficiency of motor control,the performance of the product will be more outstanding.展开更多
The solar interfacial evaporation has a broad application prospect in the fields of steam generation and seawater desalination to deal with the global shortage of fresh-water resources.Bamboo is a great material for s...The solar interfacial evaporation has a broad application prospect in the fields of steam generation and seawater desalination to deal with the global shortage of fresh-water resources.Bamboo is a great material for solar interface evaporators because of its low thermal conductivity and inherent micro-channel porous structure.In this paper,a novel bamboo-based solar interface evaporator with a bionic ripple wave surface structure has been proposed.The subsequent evaporation experiments have been conducted to investigate the salt resistance,stability and water absorption of the bionic ripple bamboo based solar interface evaporator.The results have exhibited that the bamboo's water absorption has been enhanced after carbonization modification.Besides,it should be pointed out that this bamboo-based evaporator’s evaporation rate has dropped during the prolonged simulated seawater evaporation experiment,yet it remained fairly consistent at approximately 1.626 kg·m^(-2)·h^(-1).The appearance for this experimental phenomenon is the decrease of the floatability of the evaporator constricted by the stored water body absorbed by the evaporator and the deposition of NaCl crystals at the photothermal interface.Besides,compared with the plate-structure evaporator,the salt deposition in the evaporator equipped with the bionic ripple wave surface structure is greatly improved.In regard to its advantages in low cost,environmental friendliness,good salt tolerance and high evaporation rate,the bamboo-based solar interface evaporator with a bionic ripple wave surface structure can provide a potential solution to the global problem of fresh-water shortage.展开更多
EMC anechoic chamber is used for radiation emission and radiation immunity test,and the wireless performance of products needs to be tested in OTA anechoic chamber.With more and more electronic and electrical equipmen...EMC anechoic chamber is used for radiation emission and radiation immunity test,and the wireless performance of products needs to be tested in OTA anechoic chamber.With more and more electronic and electrical equipment with wireless communication function,the rapid construction of a compatible OTA test system in the existing EMC anechoic chamber can save the cost and space of enterprises and third-party laboratories that already have EMC anechoic chamber.In this paper,the OTA test system is built in the existing EMC anechoic room,the ripple calibration test is carried out according to the OTA standard,the TRP and TIS tests are carried out on two test samples with different wireless communication standards,and the test samples are taken to the OTA anechoic room for a comparison test.The comparison between the ripple calibration data and the OTA test data showed that the EMC anechoic chamber could perform OTA test without affecting the original test ability.The data results provide a basis for the implementation of EMC anechoic chamber compatibility upgrade OTA test,and provide reference for further optimization of the compatible test system,reduction of test differences,and the design of anechoic chamber integrating two test functions.展开更多
The flow ripple caused by an axial piston pump may lead to pipe vibrations and lower hydraulic component reliability,which are of particular concern in hydraulic systems.The valve plate of the pump is considered the p...The flow ripple caused by an axial piston pump may lead to pipe vibrations and lower hydraulic component reliability,which are of particular concern in hydraulic systems.The valve plate of the pump is considered the part most related to flow ripple,and its structural design is an important topic.In this study,an analytical model for the axial piston pump flow ripple was established and verified using a numerical analysis with computational fluid dynamics(CFD)calculations.Moreover,a parametric analysis of the valve plate was performed to investigate the critical parameters and their ranges.A fast optimization method,the rotation vector optimization method(RVOM),was proposed for the valve plate design and compared with the currently used optimization methods to prove its efficiency.As a constant-pressure pump works in different states of swashplate angle,outlet pressure,and pump speed,an optimization principle for the entire working status was proposed to achieve the overall reduction performance.A test rig for an aircraft hydraulic pump was established,and validation experiments were conducted.It was determined that the optimized pump could achieve reduction at multiple working statuses,and the largest pressure pulsation reduction ratios for the typical speed and speed sweep tests reached 64.7%and 71.7%,respectively.The model and method proposed in this study are proven to be effective and accurate.展开更多
Linear flux-switching permanent magnet motors(LFSPMs) have been proposed for long stator applications such as rail transit. However, the conventional linear permanent magnet synchronous motor(LPMSM) suffers from thrus...Linear flux-switching permanent magnet motors(LFSPMs) have been proposed for long stator applications such as rail transit. However, the conventional linear permanent magnet synchronous motor(LPMSM) suffers from thrust ripple, which degrades the motor performance. The thrust ripple in LFSPMs is mainly caused by detent force and asymmetric electromagnetic parameters, excluding external disturbances. Moreover, the 12/13 slot-pole LFSPM exhibits unique inductance characteristics, which lead to different effects on thrust ripple. First, the detent force in the LFSPM is analyzed through finite element method(FEM). In addition, new finite element(FE) models are proposed for further analysis of the cogging force in LFSPMs. Second, the unique inductance characteristics of the 12/13 slot-pole LFSPM are investigated, and then the thrust ripple caused by asymmetric electromagnetic parameters is calculated by the virtual displacement method. Third, the mathematical model considering the thrust ripple is established for the LFSPM, which provides a foundation for subsequent research on thrust ripple suppression control strategies. Finally, the thrust ripple analysis is validated by comparing FEM results, modeling simulations, and experimental data.展开更多
With the development of More Electric Aircraft(MEA),the Permanent Magnet Synchronous Motor(PMSM)is widely used in the MEA field.The PMSM control system of MEA needs to consider the system reliability,and the inverter ...With the development of More Electric Aircraft(MEA),the Permanent Magnet Synchronous Motor(PMSM)is widely used in the MEA field.The PMSM control system of MEA needs to consider the system reliability,and the inverter switching frequency of the inverter is one of the impacting factors.At the same time,the control accuracy of the system also needs to be considered,and the torque ripple and flux ripple are usually considered to be its important indexes.This paper proposes a three-stage series Model Predictive Torque and Flux Control system(three-stage series MPTFC)based on fast optimal voltage vector selection to reduce switching frequency and suppress torque ripple and flux ripple.Firstly,the analytical model of the PMSM is established and the multi-stage series control method is used to reduce the switching frequency.Secondly,selectable voltage vectors are extended from 8 to 26 and a fast selection method for optimal voltage vector sectors is designed based on the hysteresis comparator,which can suppress the torque ripple and flux ripple to improve the control accuracy.Thirdly,a three-stage series control is obtained by expanding the two-stage series control using the P-Q torque decomposition theory.Finally,a model predictive torque and flux control experimental platform is built,and the feasibility and effectiveness of this method are verified through comparison experiments.展开更多
A robust adaptive control approach is presented to improve the performance of the control scheme proposed in the authors＇ previous work, aiming at producing a low ripple hybrid stepping motor servo drive for precisio...A robust adaptive control approach is presented to improve the performance of the control scheme proposed in the authors＇ previous work, aiming at producing a low ripple hybrid stepping motor servo drive for precision profile tracking at a low speed. In order to construct a completely integrated control design philosophy to reduce torque ripple and at the same time to enhance tracking performance, the properties of nonlinear uncertainties in the system dynamics are uncovered, and then incorporated into the design of the controller. The system uncertainties concerned with ripple dynamics and other external disturbances are composed of two categories. The first category of uncertainties with linear parameterization arising from the detention effect is dealt with by the wellknown adaptive control method. A robust adaptive method is used to deal with the second category of uncertainties resulting from the non-sinusoidal flux distribution. The μ-modification scheme is used to cease parameter adaptation by the robust adaptive control law, thus ensuring that the trajectory tracking error asymptotically converges to a pre-specified boundary. Experiments are performed with a typical hybrid stepping motor to test its profile tracking accuracy. Results confirm the proposed control scheme.展开更多
基金funded by the National Key R&D Program of China(Grant No.2023YFA1608400)the National Natural Science Foundation of China(Grant No.12302281).
文摘Hydrodynamic instability growth at the deuterium-tritium(DT)fuel-ablator interface plays a critical role in determining the performance of inertial confinement fusion implosions.During the late stages of implosion,insufficient doping of the ablator material can result in highenergy X-ray preheat,which may trigger the development of a classical-like Rayleigh-Taylor instability(RTI)at the fuel-ablator interface.In implosion experiments at the Shenguang 100 kJ-level laser facility,the primary source of perturbation is the roughness of the inner DT ice interface.In this study,we propose an analytical model to describe the feed-out process of the initial roughness of the inner DT ice interface.The perturbation amplitude derived from this model serves as the initial seed for the late-time RTI during the acceleration phase.Our findings confirm the presence of classical-like RTI at the fuel-ablator interface.Numerical simulations conducted using a radiation hydrodynamic code validate the proposed analytical model and demonstrate the existence of a peak mode number in both the feed-out process and the classical-like RTI.It provides an alternative bridge between the current target fabrication limitations and the unexpected implosion performance.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Science(Grant Nos.XDA25050200 and XDA25010100)the National Natural Science Foundation of China(Grant Nos.12175309,12475252,and 12275356)+2 种基金the Defense Industrial Technology Development Program(Grant No.JCKYS2023212807)the Natural Science Foundation of Hunan Province,China(Grant No.2025JJ20007)the Postgraduate Scientific Research Innovation Project of Hunan Province,China(Grant No.CX20230005).
文摘In the direct drive inertial confinement fusion(ICF)scheme,a rippled interface between the ablator and the deuterium–tritium ice fuel can feed out and form perturbation seeds for the ablative Rayleigh–Taylor instability,with undesirable effects.However,the evolution of this instability remains insufficiently studied,and the effects of high-Z dopant on this instability remain unclear.In this paper,we develop a theoretical model to calculate the feedout seeds and describe this instability.Our theory suggests that the feedout seeds are determined by the ablation pressure and the adiabatic index,while the subsequent growth depends mainly on the ablation velocity.Two-dimensional radiation hydrodynamic simulations confirm our theory.It is shown that targets with high-Z dopant in the outer ablator exhibit more severe feedout seeds,because of their higher ionization compared with undoped targets.The X-ray pre-ablation in high-Z doped targets significantly suppresses subsequent growth,leading to suppression of short-wavelength perturbations.However,for long-wavelength perturbations,this suppression is weakened,resulting in increased instability in high-Z doped targets.The results are helpful for understanding the innerinterface-initiated instability and the influence of high-Z dopant on it,providing valuable insights for target design and instability control in ICF.
基金The study was financially supported by the National Natural Science Foundation of China under contract Nos 50479015 and 10202003also supported by Program for New Century Talents Excellent Talents in University(NCET-05-0710).
文摘The evolution of an initially flat sandy bed is studied in a laboratory wave flume under enoidal waves and acoustic Doppler velocimeter （ADV） was utilized in the detailed velocity measurements at different positions. The ripple formation and evolution have been analyzed by CCD images and the asymmetric rippled bed is induced by the nonlinear wave flow. The flow structure and a complete process of vortex formation, evolvement and disappearance were observed on the asymmetric rippled bed under cnoidal waves. With the increasing nonlinearity of waves, which is an important factor in the sand ripple formation, the vortex intensity becomes stronger and shows different characteristics on both sides of the ripple crest. The vorticity and wave velocity reach their maximum values at different phase angles. The vortex value reaches the maximum value at a small phase angle with the increasing Ursell number. The near bed flow patterns are mainly determined by the ripple forms and the averaged longitudinal velocity over a wave period above the ripple trough and crest are positive, which indicates the possibility of significant onshore sediment transport and a corresponding ripple drift. The phase averaged vertical velocity has noticeable positive values near the bottom of the ripple crest and trough. Sediments may be lifted from the ripple surface, picked up in suspension by the local velocity, and deposited over the crest and on the lee of the ripples.
基金This research work was supported by the National Natural Science Foundation of China (NSFC)the ResearchGrants Council of the Hong Kong Special Administrative Region,through Projects 40376028 ,50279030 ,HKU7081/02E,and HKU7199/03E.
文摘This paper is mainly concerned with the turbulence in oscillatory bottom boundary layers over flat or rippled seaheds. Owing to the strong shear and anisotmpy of oscillatory flow, an anisotropic turbulence mathematical model is set up using the finite difference method, and the computational results of the model are verified by comparisons with wellknown experiments. Turbulent energy, dissipation and Reynolds stress can all be computed with this mathematical model, and the development processes of a large coherent vortex structure over a rippled bed, such as main flow separation, coherent vortex formation and curling, coherent vortex ejection and breaking up, are successfully simulated.
文摘We propose to investigate the THz field generation using nonlinear mixing mechanism of laser beat wave with inclined rippled density plasmas.Two laser pulses with frequencies(ω_(1),ω_(2)) and wave vectors(k_(1),k_(2)) co-propagate and resultant laser beat wave forms at beat frequency(ω_(1)-ω_(2)).Laser beat wave imparts a nonlinear force on the ambient electrons and pushes them outward with nonlinear velocity v_(NL).Coupling of induced density perturbation and nonlinear velocity v_(NL)generates nonlinear currents at laser beat frequency that further generates electromagnetic field E_((ω_(1)-ω_(2))) in terahertz(THz)range.In the present scheme,density ripples are introduced at an angle with respect to laser propagation and flat Gaussian index(f) is introduced in laser field profile that transform curved top of Gaussian field envelope into flat top field envelope.The combined effect of flat laser pulses with inclined density ripples in plasmas shows 10-fold enhancement in THz field amplitude when flat-Gaussian index(f) varies from 1 to 4.Also,the THz field intensifies when density ripples inclination increases upto a certain angle and then decreases.
基金supported by the National Natural Science Foundation of China(Grant Nos.50279030,40376028).
文摘The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth initially, disturbances arising from the bed or other external sources will cause the laminar flow in an open channel to become unstable as soon as the flow develops, thereby leading to the formation of sand ripples on the bed. In return, the formation of the sand ripples will modfy the instability path of the laminar flow passing over them. The wavy character of the bed will induce further instability of the flow, which is essentially different from that on a smooth bed: the neutral curve will move forward and the critical Reynolds number will decrease. The flow is unstable in response to a wider range of the disturbance wave number, or the laminar flow instability can happen more easily. The propagation speed of the sand ripples also affects the flow instability, since the stability of open channel flow over a movable bed is fundamentally different from that on a rigid bed. These instability effects are discussed in detail in this paper.
基金Supported by National Natural Science Foundation of China(NSFC)(Grant No.52130505)Zhejiang Provincial Natural Science Foundation of China(Grant No.LD24E050005)+1 种基金Ningbo Key Scientific and Technological Project of China(Grant No.2022Z040)Academic Excellence Foundation of BUAA for PhD Students.
文摘Permanent-magnet(PM)machines are the important driving components of various mechanical equipment and industrial applications,such as robot joints,aerospace equipment,electric vehicles,actuators,wind generators and electric traction systems.The PM machines are usually expected to have high torque/power density,low torque ripple,reduced rotor mass,a large constant power speed range or strong anti-magnetization capability to match different requirements of industrial applications.The structural topology of the electric machines,including stator/rotor arrangements and magnet patterns of rotor,is one major concern to improve their electromagnetic performance.However,systematic reviews of structural topology are seldom found in literature.Therefore,the objective of this paper is to summarize the stator/rotor arrangements and magnet patterns of the permanent-magnet brushless machines,in depth.Specifically,the stator/rotor arrangements of the PM machines including radial-flux,axialflux and emerging hybrid axial-radial flux configurations are presented,and pros and cons of these topologies are discussed regarding their electromagnetic performance.The magnet patterns including various surface-mounted and interior magnet patterns,such as parallel magnetization pole pattern,Halbach arrays,spoke-type designs and their variants are summarized,and the characteristics of those magnet patterns in terms of flux-focusing effect,magnetic self-shielding effect,torque ripple,reluctance torque,magnet utilization ratio,and anti-demagnetization capability are compared.This paper can provide guidance and suggestion for the structure selection and design of PM brushless machines for high-performance industrial applications.
基金supported in part by the Universitat Politècnica de València under grant PAID-10-21supported through AMRITA Seed Grant(Proposal ID:ASG2022188)。
文摘Switched Reluctance Motors(SRMs),outfitted with rugged construction,good speed range,high torque density,and rare earth-free nature that outweigh induction motors(IM)and permanent magnet synchronous motor(PMSM),afford a broad range of applications in the domain of electric vehicles(EVs).Standard copper magnetic wire and low-carbon steel laminations are used to construct SRMs,which give them high efficiency in the range of 85-95%.Despite SRM's desirable features over traditional motor-speed drives,high torque ripples and radial distortions constrain their deployment in EVs.Precise rotor position is imperative for effective management of the speed and torque of SRMs.This paper provides an illustrative compendium on review of the torque-speed control and ripple mitigation techniques using design enhancements and control methods for SRM drives for EV applications.The various schemes were evaluated on their performance metricsoperational speed range,control complexity,practical realization,need for pre-stored parameters(look-up tables of current,inductance and torque profiles)and motor controller memory requirements.The findings provide valuable insights into balancing the gains and trade-offs associated with EV applications.Furthermore,they pinpoint opportunities for enhancement by analyzing the cost and technical aspects of different SRM controllers.
文摘Caregivers play an essential but often unacknowledged role in healthcare,particularly in chronic illness and post-transplantation scenarios.We highlight the profound emotional,physical,and logistical challenges caregivers face,as illuminated by recent studies,including the work of Virches et al about liver transplantation.Pre-transplant caregiving is marked by heightened stress,depression,and emotional strain,as caregivers navigate the unpredictability of conditions like cirrhosis.While liver transplantation significantly alleviates caregiver burden by stabilizing patient health,caregiving evolves rather than ends,requiring ongoing vigilance for post-transplant care,medication adherence,and lifestyle adjustments.We examine the disproportionate impact of caregiving on the family,due to entrenched cultural and gender norms and highlight how these disparities reinforce systemic neglect.Caregiving,often viewed as a familial duty,carries financial,mental,and physical health costs,perpetuating inequities and marginalization.We argue that caregivers are integral to healthcare outcomes and must be included in systemic frameworks to improve patient care.We also advocate for a paradigm shift from patient-centered to family-centered care,emphasizing caregiver inclusion as a core healthcare priority.Policy recommendations related to financial support,respite care,education,and mental health services should be tailored for caregivers.By addressing caregiver needs,healthcare systems can improve patient outcomes,reduce costs,and foster equity.This editorial underscores that caregivers are not ancillary but central to healthcare’s success.Recognizing and supporting them is both an ethical responsibility and a practical necessity for sustainable healthcare.
文摘Purpose–This study aims to propose a novel identification method to accurately estimate linear and nonlinear dynamics in permanent magnet synchronous linear motor(PMSLM)based on the time-domain analysis of relay feedback.Design/methodology/approach–A mathematical model of the PMSLM-based servo-mechanical system was first established,incorporating the aforementioned nonlinearities.The model’s velocity response was derived by analyzing its behavior as a first-order system under arbitrary input.To induce oscillatory dynamics,an ideal relay with artificially introduced dead-time components was then integrated into the servo-mechanism.Depending on the oscillations and the time-domain analysis,nonlinear formulas were deduced according to the velocity response of the servo-mechanism.Afterwards,the unknown model parameters can be solved on account of the cost function which utilizes the discrepancy between nominal position characteristics and temporary position characteristics,both of which are extracted from the oscillations.The proposed recognition method was validated through a twostage process:(1)numerical simulation and calculation,followed by(2)real-time experimental verification on a direct-drive servo platform.Subsequently,leveraging the identification results,a novel control strategy was developed and its tracking performance was benchmarked against conventional control schemes.Findings–Simulation results demonstrate that the proposed method achieves estimation accuracy within 8%.Building on this,a novel control strategy is developed by incorporating both friction pulsation and force pulsation identification results into the feedforward compensator.Comparative experiments reveal that this strategy significantly enhances tracking and positioning performance over traditional control schemes.In a word,this new identification method can be used in different process control and servo control systems.Moreover,parameter auto-tuning,feed forward compensation or disturbance observer can be investigated based on the obtained information to improve the system stability and control accuracy.Originality/value–It is of great significance for the performance improvement of rail transit motor control equipment,such as electro-mechanical braking systems.By enhancing the efficiency of motor control,the performance of the product will be more outstanding.
基金financially supported by the National Natural Science Foundation of China(12,405,179)the Natural Science Foundation of Hunan Province(2023JJ40744)+1 种基金the Natural Science Foundation of Hunan Province(2025JJ50227)the High Performance Computing Center of Central South University(2025JJ50226).
文摘The solar interfacial evaporation has a broad application prospect in the fields of steam generation and seawater desalination to deal with the global shortage of fresh-water resources.Bamboo is a great material for solar interface evaporators because of its low thermal conductivity and inherent micro-channel porous structure.In this paper,a novel bamboo-based solar interface evaporator with a bionic ripple wave surface structure has been proposed.The subsequent evaporation experiments have been conducted to investigate the salt resistance,stability and water absorption of the bionic ripple bamboo based solar interface evaporator.The results have exhibited that the bamboo's water absorption has been enhanced after carbonization modification.Besides,it should be pointed out that this bamboo-based evaporator’s evaporation rate has dropped during the prolonged simulated seawater evaporation experiment,yet it remained fairly consistent at approximately 1.626 kg·m^(-2)·h^(-1).The appearance for this experimental phenomenon is the decrease of the floatability of the evaporator constricted by the stored water body absorbed by the evaporator and the deposition of NaCl crystals at the photothermal interface.Besides,compared with the plate-structure evaporator,the salt deposition in the evaporator equipped with the bionic ripple wave surface structure is greatly improved.In regard to its advantages in low cost,environmental friendliness,good salt tolerance and high evaporation rate,the bamboo-based solar interface evaporator with a bionic ripple wave surface structure can provide a potential solution to the global problem of fresh-water shortage.
基金Yancheng Science and Technology Bureau(YCBK2023027)。
文摘EMC anechoic chamber is used for radiation emission and radiation immunity test,and the wireless performance of products needs to be tested in OTA anechoic chamber.With more and more electronic and electrical equipment with wireless communication function,the rapid construction of a compatible OTA test system in the existing EMC anechoic chamber can save the cost and space of enterprises and third-party laboratories that already have EMC anechoic chamber.In this paper,the OTA test system is built in the existing EMC anechoic room,the ripple calibration test is carried out according to the OTA standard,the TRP and TIS tests are carried out on two test samples with different wireless communication standards,and the test samples are taken to the OTA anechoic room for a comparison test.The comparison between the ripple calibration data and the OTA test data showed that the EMC anechoic chamber could perform OTA test without affecting the original test ability.The data results provide a basis for the implementation of EMC anechoic chamber compatibility upgrade OTA test,and provide reference for further optimization of the compatible test system,reduction of test differences,and the design of anechoic chamber integrating two test functions.
基金Supported by National Natural Science Foundation of China(Grant No.51975025)National Key Research and Development Program of China(Grant No.2019YFB2004500)。
文摘The flow ripple caused by an axial piston pump may lead to pipe vibrations and lower hydraulic component reliability,which are of particular concern in hydraulic systems.The valve plate of the pump is considered the part most related to flow ripple,and its structural design is an important topic.In this study,an analytical model for the axial piston pump flow ripple was established and verified using a numerical analysis with computational fluid dynamics(CFD)calculations.Moreover,a parametric analysis of the valve plate was performed to investigate the critical parameters and their ranges.A fast optimization method,the rotation vector optimization method(RVOM),was proposed for the valve plate design and compared with the currently used optimization methods to prove its efficiency.As a constant-pressure pump works in different states of swashplate angle,outlet pressure,and pump speed,an optimization principle for the entire working status was proposed to achieve the overall reduction performance.A test rig for an aircraft hydraulic pump was established,and validation experiments were conducted.It was determined that the optimized pump could achieve reduction at multiple working statuses,and the largest pressure pulsation reduction ratios for the typical speed and speed sweep tests reached 64.7%and 71.7%,respectively.The model and method proposed in this study are proven to be effective and accurate.
基金partly supported by the CAS Project for Young Scientists in Basic Research under Grant YSBR-045the National Natural Science Foundation of China under Grant 52307071。
文摘Linear flux-switching permanent magnet motors(LFSPMs) have been proposed for long stator applications such as rail transit. However, the conventional linear permanent magnet synchronous motor(LPMSM) suffers from thrust ripple, which degrades the motor performance. The thrust ripple in LFSPMs is mainly caused by detent force and asymmetric electromagnetic parameters, excluding external disturbances. Moreover, the 12/13 slot-pole LFSPM exhibits unique inductance characteristics, which lead to different effects on thrust ripple. First, the detent force in the LFSPM is analyzed through finite element method(FEM). In addition, new finite element(FE) models are proposed for further analysis of the cogging force in LFSPMs. Second, the unique inductance characteristics of the 12/13 slot-pole LFSPM are investigated, and then the thrust ripple caused by asymmetric electromagnetic parameters is calculated by the virtual displacement method. Third, the mathematical model considering the thrust ripple is established for the LFSPM, which provides a foundation for subsequent research on thrust ripple suppression control strategies. Finally, the thrust ripple analysis is validated by comparing FEM results, modeling simulations, and experimental data.
基金co-supported by the National Natural Science Foundation of China(No.52477063)the National Key Research and Development Program of China(No.2023YFF0719100)。
文摘With the development of More Electric Aircraft(MEA),the Permanent Magnet Synchronous Motor(PMSM)is widely used in the MEA field.The PMSM control system of MEA needs to consider the system reliability,and the inverter switching frequency of the inverter is one of the impacting factors.At the same time,the control accuracy of the system also needs to be considered,and the torque ripple and flux ripple are usually considered to be its important indexes.This paper proposes a three-stage series Model Predictive Torque and Flux Control system(three-stage series MPTFC)based on fast optimal voltage vector selection to reduce switching frequency and suppress torque ripple and flux ripple.Firstly,the analytical model of the PMSM is established and the multi-stage series control method is used to reduce the switching frequency.Secondly,selectable voltage vectors are extended from 8 to 26 and a fast selection method for optimal voltage vector sectors is designed based on the hysteresis comparator,which can suppress the torque ripple and flux ripple to improve the control accuracy.Thirdly,a three-stage series control is obtained by expanding the two-stage series control using the P-Q torque decomposition theory.Finally,a model predictive torque and flux control experimental platform is built,and the feasibility and effectiveness of this method are verified through comparison experiments.
文摘A robust adaptive control approach is presented to improve the performance of the control scheme proposed in the authors＇ previous work, aiming at producing a low ripple hybrid stepping motor servo drive for precision profile tracking at a low speed. In order to construct a completely integrated control design philosophy to reduce torque ripple and at the same time to enhance tracking performance, the properties of nonlinear uncertainties in the system dynamics are uncovered, and then incorporated into the design of the controller. The system uncertainties concerned with ripple dynamics and other external disturbances are composed of two categories. The first category of uncertainties with linear parameterization arising from the detention effect is dealt with by the wellknown adaptive control method. A robust adaptive method is used to deal with the second category of uncertainties resulting from the non-sinusoidal flux distribution. The μ-modification scheme is used to cease parameter adaptation by the robust adaptive control law, thus ensuring that the trajectory tracking error asymptotically converges to a pre-specified boundary. Experiments are performed with a typical hybrid stepping motor to test its profile tracking accuracy. Results confirm the proposed control scheme.
