期刊文献+
共找到1,976篇文章
< 1 2 99 >
每页显示 20 50 100
EFFECT OF UPSTREAM ROTOR ON AERODYNAMIC FORCE OF DOWNSTREAM STATOR BLADES
1
作者 王志强 胡骏 +1 位作者 王英锋 赵勇 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI 2006年第2期94-101,共8页
To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure di... To study the amplitude and the frequency of the aerodynamic force on stator blades, micro-sensors are embedded on the surface of stator blades of a low-speed single-stage axial compressor rig. The unsteady pressure distribution on stator blades is measured under the conditions of different axial spacing between the rotor and the stator, different rotating speeds and an extensive range of the mass flow. Amplitudes and frequencies of aerodynamic forces are analyzed by the Fourier transform. Experimental results show that under the effect of the rotor wake, the dominant frequencies of pressure fluctuations on stator blades are the rotor blade passing frequency (BPF) and its harmonics. The higher harmonics of the rotor BPF in the fore part of the suction side are more prominent than that in the other parts of the stator blade. Otherwise, fluctuations of the pressure and the aerodynamic force on stator blades vary with the mass flow, the rotating speed and the axial spacing between the rotor and the stator. 展开更多
关键词 blade-row interaction aerodynamic force COMPRESSOR spectral feature
下载PDF
Effects of unsteady deformation of flapping wing on its aerodynamic forces 被引量:3
2
作者 杜刚 孙茂 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 2008年第6期731-743,共13页
Effects of unsteady deformation of a'flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid. Aerodynamic forces on the flappi... Effects of unsteady deformation of a'flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations on a dynamically deforming grid. Aerodynamic forces on the flapping wing are not much affected by considerable twist, but affected by camber deformation. The effect of combined camber and twist deformation is similar to that of camber deformation. With a deformation of 6% camber and 20% twist (typical values observed for wings of many insects), lift is increased by 10% - 20% and lift-to-drag ratio by around 10% compared with the case of a rigid fiat-plate wing. As a result, the deformation can increase the maximum lift coefficient of an insect, and reduce its power requirement for flight. For example, for a hovering bumblebee with dynamically deforming wings (6% camber and 20% twist), aerodynamic power required is reduced by about 16% compared with the case of rigid wings. 展开更多
关键词 INSECT wing deformation unsteady aerodynamic force computational fluid dynamics
下载PDF
Numerical simulation and optimization of aerodynamic uplift force of a high-speed pantograph 被引量:7
3
作者 Zhiyuan Dai Tian Li +2 位作者 Ning Zhou Jiye Zhang Weihua Zhang 《Railway Engineering Science》 2022年第1期117-128,共12页
Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent,and their magnitudes do not satisfy the corresponding standard,... Aiming at the problem that aerodynamic uplift forces of the pantograph running in the knuckle-downstream and knuckle-upstream conditions are inconsistent,and their magnitudes do not satisfy the corresponding standard, the aerodynamic uplift forces of pantographs with baffles are numerically investigated, and an optimization method to determine the baffle angle is proposed. First, the error between the aerodynamic resistances of the pantograph obtained by numerical simulation and wind tunnel test is less than 5%, which indicates the accuracy of the numerical simulation method. Second, the original pantograph and pantographs equipped with three different baffles are numerically simulated to obtain the aerodynamic forces and moments of the pantograph components.Three different angles for the baffles are-17°, 0° and 17°.Then the multibody simulation is used to calculate the aerodynamic uplift force of the pantograph, and the optimal range for the baffle angle is determined. Results show that the lift force of the baffle increases with the increment of the angle in the knuckle-downstream condition, whereas the lift force of the baffle decreases with the increment of the angle in the knuckle-upstream condition. According to the results of the aerodynamic uplift force, the optimal angle of the baffle is determined to be 4.75° when the running speed is 350 km/h, and pantograph–catenary contact forces are 128.89 N and 129.15 N under the knuckledownstream and knuckle-upstream operating conditions,respectively, which are almost equal and both meet the requirements of the standard EN50367:2012. 展开更多
关键词 High-speed pantograph aerodynamic uplift force BAFFLE Numerical simulation Multibody simulation
下载PDF
A generalized model for estimation of aerodynamic forces and moments for irregularly shaped bodies 被引量:1
4
作者 Elvedin Kljuno Alan Catovic 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2019年第3期369-389,共21页
A novel method for estimation of an aerodynamic force and moment acting on an irregularly shaped body (such as HE projectile fragments) during its flight through the atmosphere is presented. The model assumes that fra... A novel method for estimation of an aerodynamic force and moment acting on an irregularly shaped body (such as HE projectile fragments) during its flight through the atmosphere is presented. The model assumes that fragments can be approximated with a tri-axial ellipsoid that has continuous surface given as a mathematical function. The model was validated with CFD data for a tri-axial ellipsoid and verified using CFD data on aerodynamic forces and moments acting on an irregularly shaped fragment. The contribution of this method is that it represents a significant step toward a modeling that does not require a cumbersome CFD simulation results for estimation of fragment dynamic and kinematic parameters. Due to this advantage, the model can predict the fragment motion consuming a negligible time when compared to the corresponding time consumed by CFD simulations. Parametric representation (generalization) of the fragment geometrical data and the conditions provides the way to analyze various correlations and how parameters influence the dynamics of the fragment flight. 展开更多
关键词 aerodynamic force aerodynamic MOMENT FRAGMENTS
下载PDF
Time-varying nonlinear dynamics of a deploying piezoelectric laminated composite plate under aerodynamic force 被引量:1
5
作者 S.F.Lu W.Zhang X.J.Song 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2018年第2期303-314,共12页
Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, un... Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, under the combined action of aerodynamic load and piezoelectric excitation, is introduced. Two-degree of freedom(DOF)nonlinear dynamic models for the time-varying coefficients describing the transverse vibration of the deploying laminate under the combined actions of a first-order aerodynamic force and piezoelectric excitation were obtained by selecting a suitable time-dependent modal function satisfying the displacement boundary conditions and applying second-order discretization using the Galerkin method. Using a numerical method, the time history curves of the deploying laminate were obtained, and its nonlinear dynamic characteristics,including extension speed and different piezoelectric excitations, were studied. The results suggest that the piezoelectric excitation has a clear effect on the change of the nonlinear dynamic characteristics of such piezoelectric laminated composite plates. The nonlinear vibration of the deploying cantilevered laminate can be effectively suppressed by choosing a suitable voltage and polarity. 展开更多
关键词 Deploying piezoelectric laminated composite plate Time-varying nonlinear dynamics Third-order shear deformation plate theory Time-dependent modal function aerodynamic force
下载PDF
A note on the Galilean invariance of aerodynamic force theories in unsteady incompressible flows 被引量:1
6
作者 An-Kang Gao Jiezhi Wu 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2019年第6期1150-1154,共5页
As a basic principle in classical mechanics,the Galilean invariance states that the force is the same in all inertial frames of reference.But this principle has not been properly addressed by most unsteady aerodynamic... As a basic principle in classical mechanics,the Galilean invariance states that the force is the same in all inertial frames of reference.But this principle has not been properly addressed by most unsteady aerodynamic force theories,if the partial force contributed by a local flow structure is to be evaluated.In this note,we discuss the Galilean-invariance conditions of the partial force for several typical theories and numerically test what would happen if these conditions do not hold. 展开更多
关键词 Galilean invariance aerodynamic force theory Unsteady flow Flow diagnoses
下载PDF
SIMULATION STUDY OF AERODYNAMIC FORCE FOR HIGH-SPEED MAGNETICALLY-LEVITATED TRAINS
7
作者 LI Renxian LIU Yingqing ZHAI Wanming 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2006年第2期226-232,共7页
Based on Reynolds average Navier-Storkes equations of viscous incompressible fluid and k-ε two equations turbulent model, the aerodynamic forces of high-speed magnetically-levitated (maglev) trains in transverse an... Based on Reynolds average Navier-Storkes equations of viscous incompressible fluid and k-ε two equations turbulent model, the aerodynamic forces of high-speed magnetically-levitated (maglev) trains in transverse and longitudinal wind are investigated by finite volume method. Near 80 calculation cases for 2D transverse wind fields and 20 cases for 3D longitudinal wind fields are analyzed. The aerodynamic side force, yawing, drag, lift and pitching moment for different types of maglev trains and a wheel/rail train are compared under the different wind speeds. The types of maglev train models for 2D transverse wind analysis included electromagnetic suspension (EMS) type train, electrodynamic suspension (EDS) type train, EMS type train with shelter wind wall in one side or two sides of guideway and the walls, which are in different height or/and different distances from train body. The situation of maglev train running on viaduct is also analyzed. For 3D longitudinal wind field analysis, the model with different sizes of air clearances beneath maglev train is examined for the different speeds. Calculation result shows that: ① Different transverse effects are shown in different types of maglev trains. ② The shelter wind wall can fairly decrease the transverse effect on the maglev trains. ③ When the shelter wall height is 2 m, there is minimum side force on the train. When the shelter wall height is 2.5 m, there is minimum yawing moment on the train. ④ When the distance between inside surfaces of the walls and center of guideway is 4.0 m, there is minimum transverse influence on the train. ⑤ The size of air clearance beneath train body has a small influence on aerodynamic drag of the train, but has a fairly large effect on aerodynamic lift and pitching moment of the train. ⑥ The calculating lift and pitching moment for maglev train models are minus values. 展开更多
关键词 aerodynamic force Magnetically-levitated (maglev) train Stability Numerical analysis
下载PDF
Characteristics of aerodynamic force and flow structure behind single box girder under isolated slit control
8
作者 CHEN Guan-bin CHENWen-li 《Journal of Central South University》 SCIE EI CAS CSCD 2022年第8期2542-2557,共16页
An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge w... An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge was used as a physical model at a geometric scale of 1:125.Wind tunnel experiments were conducted at an incoming airflow speed of 10 m/s,and the Reynolds number was calculated as 2.3×104 using the test model height and wind speed.The surface pressure distribution was measured,and the aerodynamic force acting on the test model with and without the isolated slit was calculated by integrating the pressure result.It was found that the control using an isolated slit can dramatically decrease the fluctuating surface pressure distribution and aerodynamic force.An analysis on the power spectral density of the lift force revealed that the isolated slit accelerated vortex shedding.Moreover,high-speed particle image velocimetry was used to investigate the wake flow structure behind the test model.A vortex separated from the upper surface was pushed to a lower location and the wake flow structure was modified by the isolated slit.A proper orthogonal decomposition(POD)of the flow field showed that the first two POD modes in the controlled case contributed less energy than those in the uncontrolled case,indicating that more energy was transferred to higher modes,and small-scale vortices had more energy.A secondary instability structure was found in the wake flow for a nondimensional jet momentum coefficient J of 0.0667. 展开更多
关键词 single box girder isolated slit aerodynamic force proper orthogonal decomposition(POD)mode
下载PDF
Evaluation of Aerodynamic Force and Stress Properties of Propeller of Model Airplane Using by Finite Element Analysis
9
作者 Satoshi Fukui Masayuki Nishida 《Journal of Civil Engineering and Architecture》 2019年第4期259-264,共6页
The purpose of this study is to evaluate propeller safety using three-dimensional finite element method analysis software.We concluded that the propeller is safe for flying.Propeller is indispensable for generating th... The purpose of this study is to evaluate propeller safety using three-dimensional finite element method analysis software.We concluded that the propeller is safe for flying.Propeller is indispensable for generating the impellent force.Therefore,safety evaluation of propeller is necessary.The object of the analysis is a propeller for model airplane.The propeller material is carbon fiber reinforced plastics and there is a carbon cross in the one side surface of the propeller.Other parts are formed with resin.The forces acting on a propeller include centrifugal force,air resistance,and vibration by mass imbalance.We analyzed centrifugal force and air resistance in this study.We made analysis model of propeller by ANSYS.Results show,that the maximum principal stress due to centrifugal force was 23.0 MPa.In addition,the maximum principal stress due to aerodynamic force was 2.3 MPa,and the maximum principal stress due to both forces was 24.0 MPa. 展开更多
关键词 method CENTRIFUGAL force aerodynamic forceS
下载PDF
Description and Estimation of Unsteady Aerodynamic Forces for Application to Elastic Aircraft
10
作者 Cui Pingyuan Wu Yaohua Huang Wenhu (School of Astronautics) 《哈尔滨工业大学学报》 EI CAS CSCD 北大核心 1990年第3期77-83,共7页
In this paper, Duhamel's integral of the indicial function is used to describe unsteady aerodynamic forces. An identification method to estimate the aerodynamic forces is proposed for elastic aircraft by the maxim... In this paper, Duhamel's integral of the indicial function is used to describe unsteady aerodynamic forces. An identification method to estimate the aerodynamic forces is proposed for elastic aircraft by the maximum likelihood algorithm with estimated sensi tivities. A numerical example is given and the calculated results show the effectiveness of this method. 展开更多
关键词 弹性航空器 非稳态气动力 描述 估计 数值模型
下载PDF
Impact Force Localization and Reconstruction via ADMM-based Sparse Regularization Method
11
作者 Yanan Wang Lin Chen +3 位作者 Junjiang Liu Baijie Qiao Weifeng He Xuefeng Chen 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2024年第3期170-188,共19页
In practice,simultaneous impact localization and time history reconstruction can hardly be achieved,due to the illposed and under-determined problems induced by the constrained and harsh measuring conditions.Although ... In practice,simultaneous impact localization and time history reconstruction can hardly be achieved,due to the illposed and under-determined problems induced by the constrained and harsh measuring conditions.Although l_(1) regularization can be used to obtain sparse solutions,it tends to underestimate solution amplitudes as a biased estimator.To address this issue,a novel impact force identification method with l_(p) regularization is proposed in this paper,using the alternating direction method of multipliers(ADMM).By decomposing the complex primal problem into sub-problems solvable in parallel via proximal operators,ADMM can address the challenge effectively.To mitigate the sensitivity to regularization parameters,an adaptive regularization parameter is derived based on the K-sparsity strategy.Then,an ADMM-based sparse regularization method is developed,which is capable of handling l_(p) regularization with arbitrary p values using adaptively-updated parameters.The effectiveness and performance of the proposed method are validated on an aircraft skin-like composite structure.Additionally,an investigation into the optimal p value for achieving high-accuracy solutions via l_(p) regularization is conducted.It turns out that l_(0.6)regularization consistently yields sparser and more accurate solutions for impact force identification compared to the classic l_(1) regularization method.The impact force identification method proposed in this paper can simultaneously reconstruct impact time history with high accuracy and accurately localize the impact using an under-determined sensor configuration. 展开更多
关键词 Impact force identification Non-convex sparse regularization Alternating direction method of multipliers Proximal operators
下载PDF
An evaluation of force-based design vs.direct displacement-based design of jointed precast post-tensioned wall systems 被引量:12
12
作者 M. Ataur Rahman Sri Sritharan 《Earthquake Engineering and Engineering Vibration》 SCIE EI CSCD 2006年第2期285-296,共12页
The unique features of jointed post-tensioned wall systems, which include minimum structural damage and re-centering capability when subjected to earthquake lateral loads, are the result of using unbonded post-tension... The unique features of jointed post-tensioned wall systems, which include minimum structural damage and re-centering capability when subjected to earthquake lateral loads, are the result of using unbonded post-tensioning to attach the walls to the foundation, along with employing energy dissipating shear connectors between the walls. Using acceptance criteria defined in terms of inter-story drift, residual drift, and floor acceleration, this study presents a multiplelevel performance-based seismic evaluation of two five-story unbonded post-tensioned jointed precast wall systems. The design and analysis of these two wall systems, established as the direct displacement-based and force-based solutions for a prototype building used in the PREcast Seismic Structural Systems (PRESSS) program, were performed at 60% scale so that the analysis model could be validated using the PRESSS test data. Both buildings satisfied the performance criteria at four levels of earthquake motions although the design base shear of the direct displacement-based jointed wall system was 50% of that demanded by the force-based design method. The study also investigated the feasibility of controlling the maximum transient inter-story drift in a jointed wall system by increasing the number of energy dissipating shear connectors between the walls but without significantly affecting its re-centering capability. 展开更多
关键词 CONCRETE PRECAST unbonded post-tensioning WALL building code performance-based evaluation force-baseddesign direct-displacement based design
下载PDF
Direct numerical simulation on relevance of fluctuating velocities and drag reduction in turbulent channel flow with spanwise space-dependent electromagnetic force
13
作者 Dai-Wen Jiang Hui Zhang +1 位作者 Bao-Chun Fan An-Hua Wang 《Chinese Physics B》 SCIE EI CAS CSCD 2019年第5期166-174,共9页
Based on the Fourier–Chebyshev spectral method, the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with direct numerical simulation(DNS... Based on the Fourier–Chebyshev spectral method, the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with direct numerical simulation(DNS) methods for different Reynolds numbers. A formula is derived to express the relation between fluctuating velocities and the friction drag coefficient. With the application of electromagnetic force, the in-depth relations among the fluctuating velocities near the wall, Reynolds stress, and the effect of drag reduction for different Reynolds numbers are discussed. The results indicate that the maximum drag reductions can be obtained with an optimal combination of parameters for each case of different Reynolds numbers. The fluctuating velocities along the streamwise and normal directions are suppressed significantly,while the fluctuating velocity along the spanwise direction is enhanced dramatically due to the spanwise electromagnetic force. However, the values of Reynolds stress depend on the fluctuating velocities along the streamwise and normal directions rather than that along the spanwise direction. Therefore, the significant effect of drag reduction is obtained. Moreover,the maximum drag reduction is weakened due to the decay of control effect for fluctuating velocities as the Reynolds number increases. 展开更多
关键词 FLOW control TURBULENT channel FLOW electromagnetic force direct numerical simulation
下载PDF
Volume, Side-Area, and Force Direction of Berkovich and Cubecorner Indenters, Novel Important Insights 被引量:1
14
作者 Gerd Kaupp 《Advances in Materials Physics and Chemistry》 2021年第11期212-241,共30页
The iteration-free physical description of pyramidal indentations with closed mathematical equations is comprehensively described and extended for creating new insights in this important field of research and app... The iteration-free physical description of pyramidal indentations with closed mathematical equations is comprehensively described and extended for creating new insights in this important field of research and applications. All calculations are easily repeatable and should be programmed by instrument builders for even easier general use. Formulas for the volumes and side-areas of Berkovich and cubecorner as a function of depth are deduced and provided, as are the resulting forces and force directions. All of these allow for the detailed comparison of the different indenters on the mathematical reality. The pyramidal values differ remarkably from the ones of so-called “equivalent cones”. The worldwide use of such pseudo-cones is in severe error. The earlier claimed and used 3 times higher displaced volume with cube corner than with Berkovich is disproved. Both displace the same amount at the same applied force. The unprecedented mathematical results are experimentally confirmed for the physical indentation hardness and for the sharp-onset phase-transi</span></span><span style="white-space:normal;"><span style="font-family:"">- </span></span><span style="white-space:normal;"><span style="font-family:"">tions with calculated transition energy. The comparison of both indenters pro</span></span><span style="white-space:normal;"><span style="font-family:"">vides novel basic insights. Isotropic materials exhibit the same phase transition onset force, but the transition energy is larger with the cube corner, due to higher force and flatter force direction. This qualifies the cube</span></span><span style="white-space:normal;"><span style="font-family:""> </span></span><span style="white-space:normal;"><span style="font-family:"">corner for fracture toughness studies. Pile-up is not from the claimed “friction with the indenter”. Anisotropic materials with cleavage planes and channels undergo sliding along these</span></span><span style="white-space:normal;"><span style="font-family:""> under pressure</span></span><span style="white-space:normal;"><span style="font-family:"">, both to the surface and internally. Their volumes add to the depression volume. These volumes are essential for the exemplified pile-up management. Phase-transitions produce polymorph interfaces that are nucleation sites for cracks. Technical materials must be developed with onset forces higher than the highest thinkable stresses (at airliners, bridges</span></span><span style="white-space:normal;"><span style="font-family:"">,</span></span><span style="white-space:normal;"><span style="font-family:""> etc</span></span><span style="white-space:normal;"><span style="font-family:"">.</span></span><span style="white-space:normal;"><span style="font-family:"">). This requires urgent revision of ISO 14577-ASTM stan</span></span><span style="white-space:normal;"><span style="font-family:"">dards. 展开更多
关键词 Closed Mathematical Formulas force direction Indenter Volumes and Side-Areas Iteration-less Calculations Equal Base-Area Cones PILE-UP Phase-Transition-Onset and -Energy
下载PDF
Applying Force-Directed Placer to Wafer Scale Placement
15
作者 Ren WenjieDept of Computer Science, Changsha Inst. of Technology, Changsha, 410073, ChinaShen XubangShaanxi Microelectronics Research Institute, P.O. Box 19, Lintong 710600, P.R. China 《Journal of Systems Engineering and Electronics》 SCIE EI CSCD 1992年第4期53-60,共8页
A placement algorithm for discretionary wiring WSI system, WFDP, is proposed in this paper. WFDP employes force-directed placement algorithm. First the relative locations of macro circuit component are determined. In ... A placement algorithm for discretionary wiring WSI system, WFDP, is proposed in this paper. WFDP employes force-directed placement algorithm. First the relative locations of macro circuit component are determined. In the phase of determining the real location of the circuit component, it avoids the problem of determining the real location of arbitrary component by employing divide-conquer strategy and removing the hierarchical division. Its computation is much more simpler than other homologous algorithm. A simple model used to estimate the quality of placement is also proposed. Although the WFDP is aimed at WSI, it can also be used in the placement of other redundancy-oriented device or system such as RVLSI, etc. 展开更多
关键词 WSI PLACEMENT force-directed placement WFDP Quality measure
下载PDF
Wing/body kinematics measurement and force and moment analyses of the takeoff flight of fruitflies 被引量:7
16
作者 Mao-Wei Chen Mao Sun 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2014年第4期495-506,共12页
In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using Based on the meas... In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using Based on the measured data, high-speed video techniques. inertia force acting on the insect was computed and aerodynamic force and moment of the wings were calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. The following has been shown. In its voluntary takeoff, a fruitfly jumps during the first wingbeat and becomes airborne at the end of the first wingbeat. When it is in the air, the fly has a relatively large "initial" pitch-up rotational velocity (more than 5 000~/s) resulting from the jumping, but in about 5 wingbeats, the pitch-up rotation is stopped and the fly goes into a quasi-hovering flight. The fly mainly uses the force of jumping legs to lift itself into the air (the force from the flapping wings during the jumping is only about 5%-10% of the leg force). The main role played by the flapping wings in the takeoff is to produce a pitch-down moment to nullify the large "initial" pitch-up rotational velocity (otherwise, the fly would have kept pitching-up and quickly fallen down). 展开更多
关键词 Fruitfly· Takeoff flight ·Body and wing kine-matics aerodynamic and leg forces
下载PDF
Mechanism of controlling turbulent channel flow with the effect of spanwise Lorentz force distribution 被引量:2
17
作者 韩洋 张辉 +3 位作者 范宝春 李健 江代文 赵子杰 《Chinese Physics B》 SCIE EI CAS CSCD 2017年第8期250-258,共9页
A direct numerical simulation(DNS) is performed to investigate the control effect and mechanism of turbulent channel flow with the distribution of spanwise Lorentz force. A sinusoidal distribution of constant spanwi... A direct numerical simulation(DNS) is performed to investigate the control effect and mechanism of turbulent channel flow with the distribution of spanwise Lorentz force. A sinusoidal distribution of constant spanwise Lorentz force is selected, of which the control effects, such as flow characters, mean Reynolds stress, and drag reductions, at different parameters of amplitude A and wave number k_x are discussed. The results indicate that the control effects vary with the parameter A and k_x. With the increase of A, the drag reduction rate D_r first increases and then decreases rapidly at low k_x,and slowly at high k_x. The low drag reduction(or even drag increase) is due to a weak suppression or even the enhancements of the random velocity fluctuation and mean Reynolds stress. The efficient drag reduction is due to the quasi-streamwise vortex structure induced by Lorentz force, which contributes to suppressing the random velocity fluctuation and mean Reynolds stress, and the negative vorticity improves the distribution of streamwise velocity. Therefore, the optimal control effect with a drag reduction of up to 58% can be obtained. 展开更多
关键词 flow control turbulent channel flow Lorentz force direct numerical simulation
下载PDF
An Experimental Study of Irregular Wave Forces on Multiple Quasi-ellipse Caissons 被引量:2
18
作者 XiaozhongRen Peng Zhang +1 位作者 Yuxiang Ma Yufan Meng 《Journal of Marine Science and Application》 2014年第3期265-273,共9页
An experimental investigation of irregular wave forces on quasi-ellipse caisson structures is presented. Irregular waves were generated based on the Jonswap spectrum with two significant wave heights, and the spectrum... An experimental investigation of irregular wave forces on quasi-ellipse caisson structures is presented. Irregular waves were generated based on the Jonswap spectrum with two significant wave heights, and the spectrum peak periods range from 1.19 s to 1.81 s. Incident wave directions relative to the centre line of the multiple caissons are from 0&#176; to 22.5&#176;. The spacing between caissons ranges from 2 to 3 times that of the width of the caisson. The effects of these parameters on the wave forces of both the perforated and non-perforated caissons were compared and analyzed. It was found that the perforated caisson can reduce wave forces, especially in the transverse direction. Furthermore, the relative interval and incident wave direction have significant effects on the wave forces in the case of multiple caissons. 展开更多
关键词 relative wave length relative interval incident wave direction relative wave height quasi-ellipse caisson perforated quasi-ellipse caisson irregular wave forces
下载PDF
Four-quadrant Force Control with Minimal Ripple for Linear Switched Reluctance Machines 被引量:5
19
作者 Xuanrui Huang Zechuan Lin Xi Xiao 《CES Transactions on Electrical Machines and Systems》 CSCD 2020年第1期27-34,共8页
Linear switch reluctance machine(LSRM)has been tried to act as an alternative generator for direct drive linear wave energy converter(WEC).Many researchers have proposed new topologies of LSRM to improve the power den... Linear switch reluctance machine(LSRM)has been tried to act as an alternative generator for direct drive linear wave energy converter(WEC).Many researchers have proposed new topologies of LSRM to improve the power density,efficiency and reliability.However,the control methods for LSRM applied in direct drive WEC have been paid little attention,especially control methods considering the wave energy generator operating characteristics.In this paper,according to the generator control requirements of the direct drive WEC,force control algorithm for LSRM operating in four quadrants without a speed closed loop is put forward.The force ripple of LSRM is suppressed using force sharing function method.The four-quadrant control is easy to realize requiring only phase currents information.Simulation results validate the proposed method and indicate that LSRM is able to be used as the generator for direct drive WEC. 展开更多
关键词 Linear switched reluctance machine direct drive wave energy converter force ripple suppression four-quadrant operation.
下载PDF
Induction of Forces at Distance Performed by Piezoelectric Materials 被引量:1
20
作者 Elio B. Porcelli Victo S. Filho 《Journal of Power and Energy Engineering》 2018年第1期33-50,共18页
We describe the phenomenon of generation of an external field of forces from piezoelectric materials subjected to the application of electric fields or mechanical stress. We show that piezoelectric materials are capab... We describe the phenomenon of generation of an external field of forces from piezoelectric materials subjected to the application of electric fields or mechanical stress. We show that piezoelectric materials are capable of producing nonlocal forces of induction in external objects and we conclude that the nature of the forces generated is not originated from traditional interactions. Further we specifically assert that the generation of forces by the piezoelectric materials is ruled by the hypothesis of preexisting condition of generalized quantum entanglement between the molecular structure of the material bulk and the surrounding environment. In addition, the widely spread coupling of the molecules with the environment can be manifested from the so-called direct effect or the converse effect in piezoelectric materials and this coupling is not intermediated by acoustic waves or electromagnetic fields. We show that the novel effect has a theoretical explanation consistent with the generalized quantum entanglement framework and the direction of the induced forces depends on either the direction of the mechanical force or the electric field applied in these materials. 展开更多
关键词 Piezoelectric Materials Generalized Quantum ENTANGLEMENT INDUCTION of forceS at DISTANCE REVERSE MODE direct MODE
下载PDF
上一页 1 2 99 下一页 到第
使用帮助 返回顶部