Plasma membrane vesicles of chrysanthemum ( Dendranthema morifolium (Ramat.) Tzvel.) callus was purified by sucrose gradient centrifugation to investigate the influence of sound stimulation on the lipid physical st...Plasma membrane vesicles of chrysanthemum ( Dendranthema morifolium (Ramat.) Tzvel.) callus was purified by sucrose gradient centrifugation to investigate the influence of sound stimulation on the lipid physical states and metabolism of plasma membrane. The results showed that sound stimulation decreased the content of phosphodiesters and the fluorescent intensity of DPH, but increased the light scattering value of the membrane, the fluorescent intensity of MC540 and the content of phosphomonoesters, indicating that the vesicles got looser, the charge density and hydrophobicity of membrane surface decreased under sound stimulation of some strength and frequency. However, the membrane fluidity increased under the condition. Meanwhile, the anabolism of membrane lipid increased and the catabolism decreased. It can be seen that the physical state and metabolism of membrane lipid is sensitive to sound stimulation.展开更多
Two-dimensional and three-dimensional shock control contour bumps are designed for a supercritical wing section with the aim of transonic wave drag reduction. The supercritical airfoil （NASA SC （02）-0714） is selec...Two-dimensional and three-dimensional shock control contour bumps are designed for a supercritical wing section with the aim of transonic wave drag reduction. The supercritical airfoil （NASA SC （02）-0714） is selected considering the fact that most modern jet transport aircrafts that operate in the transonic flow regime （cruise at transonic speeds） employ supercritical airfoil sections. Here it is to be noted that a decrease in the transonic wave drag without loss in lift would result in an increased lift to drag ratio, which is a key range parameter that can potentially increase both the range and endurance of the aircraft. The major geometric bump parameters such as length, height and span are altered for both the two-dimensional and three-dimensional bumps in order to obtain the optimum location and shape of the bump. Once an optimum standalone three-dimensional bump is acquired, an array of bumps is manually placed spanwise of an unswept supercritical wing and analyzed under fully turbulent flow conditions. Different configurations are tested with varying three-dimensional bump spacing in order to determine the contribution of bump spacing on overall performance. The results show a 14% drag reduction and a consequent 16% lift to drag ratio rise at the design Mach number for the optimum arrangement of bumps along the wing span.展开更多
Supercritical CO2 (SC-CO2) extraction technology and ultrasonic technology were used to extract two active sex hormones, estradiol and progesterone, and insulin-like growth factor-1 (IGF-1) from antler velvet. The eff...Supercritical CO2 (SC-CO2) extraction technology and ultrasonic technology were used to extract two active sex hormones, estradiol and progesterone, and insulin-like growth factor-1 (IGF-1) from antler velvet. The effects of SC-CO2 extraction condition on the extraction yield and content of sex hormones, the ultrasonic extrac-tion condition on the content of IGF-1 and the SC-CO2 extraction condition on the activity remaining of IGF-1 were studied. The optimal conditions were obtained. The experimental results showed that, in presence of 75% ethanol as the co-solvent, the mean yield and content of estradiol and progesterone were 87.67 pg·g-1 and 1224.10 pg·g-1, 12.38 ng·g-1 and 354.06 ng·g-1, respectively, with extraction pressure of 30 MPa, temperature of 35°C, extraction time of 30 min and CO2 consumption of 15 L·g-1 at the flow rate of 2.0 L·min-1. The highest content of IGF-1 was 7425.75 ng·g-1 antler velvet residue, when the pH10 ammonia-ammonium chloride buffer solution was used as the solvent, the ratio of solvent to sample was 20/1 (volume/mass), the extraction temperature was 0-35°C, and the ex-traction time was 4×15 min. Under these conditions, 93.68% activity remaining of IGF-1 in the residue was ob-tained, while little IGF-1 activity exists in traditional residue. The experimental results indicate that the technology of SC-CO2 with co-solvent is of advantage for getting high content sexual hormones and keeping high activity of IGF-1 in the residue, which can not be achieved by traditional extraction methods.展开更多
In this paper,wavefield storage optimization strategies are discussed with respect to reverse-time migration(RTM)imaging in reflection-acoustic logging,considering the problem of massive wavefield data storage in RTM ...In this paper,wavefield storage optimization strategies are discussed with respect to reverse-time migration(RTM)imaging in reflection-acoustic logging,considering the problem of massive wavefield data storage in RTM itself.In doing so,two optimization methods are proposed and implemented to avoid wavefield storage.Firstly,the RTM based on the excitation-amplitude imaging condition uses the excitation time to judge the imaging time,and accordingly,we only need to store a small part of wavefield,such as the wavefield data of dozens of time points,the instances prove that they can even be imaged by only two time points.The traditional RTM usually needs to store the wavefield data of thousands of time points,compared with which the data storage can be reduced by tens or even thousands of times.Secondly,the RTM based on the random boundary uses the idea that the wavefield scatters rather than reflects in a random medium to reconstruct the wavefield source and thereby directly avoid storing the forward wavefield data.Numerical examples show that compared with other migration algorithms and the traditional RTM,both methods can effectively reduce wavefield data storage as well as improve data-processing efficiency while ensuring imaging accuracy,thereby providing the means for high-efficiency and highprecision imaging of fractures and caves by boreholes.展开更多
The standard model of sonoluminescence suggests that the Coulomb barrier to deuterium fusion may be overcome by high bubble gas temperatures caused by compression heating if the bubble diameter remains spherical durin...The standard model of sonoluminescence suggests that the Coulomb barrier to deuterium fusion may be overcome by high bubble gas temperatures caused by compression heating if the bubble diameter remains spherical during bubble collapse.However, in the more likely collapse geometry of a pancake shape, the temperature rise in the bubbles is negligible. But the collapsing pancake bubble is found to significantly increase the frequency of the infrared energy available in the vibrational state of the water molecules at ambient temperature. For a collapse to liquid density, ultraviolet radiation at about 10eV is found. Although the ultraviolet radiation is of a low intensity, higher intensities may be possible if the bubble collapse is enhanced by visible and infrared lasers. Neither hot nor cold fusion is predicted in bubble collapse,but the ultraviolet energy at about 10eV developed in the bubble is sufficient to provide the basis for a new field of chemistry called ultrasound induced and laser enhanced cold fusion chemistry.展开更多
Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected...Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected by the boundaries between layers of different materials or same material but in different states （solid or liquid or gas）. This paper investigates the effects of ultrasound （US） on the surface of the solidified weld which has been subjected to ultrasonic vibrations of 20 kHz frequency during laser welding. Vibrations due to ultrasound normally exert a very high force which is usually hundred or thousand times the gravity. The transverse waves will also cause movement of molten material in the weld. As the surface of the weld beads were of interest and not the mechanical properties and the microstructure, investigation of bead on plate welds were found to be sufficient. High carbon steel plate was held at one end by the ultrasonic horn through which ultrasound was injected. A bead on plate weld using a CO2 laser （1 kW） was then performed along the center of the plate using three different welding speeds namely, 400, 1200 and 2000 mm per minute. The ultrasonic powers selected were 3 W and 6 W respectively for each welding speed as higher acoustical power was causing ejection of molten metal from the pool during welding. 3D surface measurements and analysis were then made on a section of length 20 mm using a Talysurf machine. The results show that the surface of the weld was affected to different extent depending on the positions being considered in the weld. Some regions were similar to the reference weld whereas some specific regions were heavily disrupted with deep valleys followed by high peak/s. This shows that US vibration of weld pools, even at very small acoustical power, is a more complex problem than other similar processes such as casting because of the very small volume of molten metal involved.展开更多
In this paper, we study a fluctuating potential barrier system with correlated spatial noises. Study shows that for this system, there is the resonant activation over the fluctuating potential barrier, and that the co...In this paper, we study a fluctuating potential barrier system with correlated spatial noises. Study shows that for this system, there is the resonant activation over the fluctuating potential barrier, and that the correlation between the different spatial noises can enhance (or weaken) the resonant activation.展开更多
We consider the escape of the particles multi-state noise. It is shown that, the noise can make over fluctuating potential barrier for a system only driven by a the particles escape over the fluctuating potential barr...We consider the escape of the particles multi-state noise. It is shown that, the noise can make over fluctuating potential barrier for a system only driven by a the particles escape over the fluctuating potential barrier in some circumstances; but in other circumstances, it can not. If the noise can make the particle escape over the fluctuating potential barrier, the mean first passage time （MFPT） can display the phenomenon of multi-resonant-activation. For this phenomenon, there are two kinds of resonant activation to appear. One is resonant activation for the MFPTs as the function of the flipping rates of the fluctuating potential barrier; the other is that for the MFPTs as the functions of the transition rates of the multi-state noise.展开更多
The effect of magnetohydrodynamic(MHD)plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low mag...The effect of magnetohydrodynamic(MHD)plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low magnetic Reynolds number approximation.A Mach 5 oblique shock/turbulent boundary layer interaction was adopted as the basic configuration in this numerical study in order to assess the effects of flow control using different combinations of magnetic field and plasma.Results show that just the thermal effect of plasma under experimental actuator parameters has no significant impact on the flow field and can therefore be neglected.On the basis of the relative position of control area and separation point,MHD control can be divided into four types and so effects and mechanisms might be different.Amongst these,D-type control leads to the largest reduction in separation length using magnetically-accelerated plasma inside an isobaric dead-air region.A novel parameter for predicting the shock wave/turbulent boundary layer interaction control based on Lorentz force acceleration is then proposed and the controllability of MHD plasma actuators under different MHD interaction parameters is studied.The results of this study will be insightful for the further design of MHD control in hypersonic vehicle inlets.展开更多
Strong, normal shock wave, terminating a local supersonic area on an airfoil, not only limits aerodynamic performance but also becomes a source of a high-speed impulsive helicopter noise. The application of a passive ...Strong, normal shock wave, terminating a local supersonic area on an airfoil, not only limits aerodynamic performance but also becomes a source of a high-speed impulsive helicopter noise. The application of a passive control system （a cavity covered by a perforated plate） on a rotor blade should reduce the noise created by a moving shock. This article covers the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes an extended validation against the experimental data for relatively simple geometries of transonic nozzles. It is a first step towards a full simulation of a helicopter rotor equipped with a noise reducing passive control device in hover and in forward flight conditions.展开更多
The supersonic ejector-diffuser system with a second throat was simulated using CFD. An explicit finite volumescheme was aPPlied to solve tWo-dimensional Navier-Stokes equations with standard k - E tulbulence model. T...The supersonic ejector-diffuser system with a second throat was simulated using CFD. An explicit finite volumescheme was aPPlied to solve tWo-dimensional Navier-Stokes equations with standard k - E tulbulence model. Thevacuum Performance of the supersonic ejector-diffuser system was investigated by changing the ejector throat arearatio and the operating Pressure ratio. Two convergent-divergent nozzles with design Mach nUmber of 2. 11 and 3.41were selected to give the supersonic operahon of the ejector-diffoser system. The presence of a second throat stronglyaffected the shock wave sir’UctUI’e inside the "dxing tube as well as the spreading of the under-expanded jetdischarging from the Primary nozzle. There were optimum values of the operating pressure ratio and ejector throatarea ratio for the vacuum performance of the system to maximize.展开更多
In the present study, the flow visualizations were performed around the NACA 0012 models which differ in aspect ratios. We discussed the effects of the aspect ratio in the test models. Additionally the unsteady, two-d...In the present study, the flow visualizations were performed around the NACA 0012 models which differ in aspect ratios. We discussed the effects of the aspect ratio in the test models. Additionally the unsteady, two-dimensional, compressible Euler equations were solved for the NACA 0012 airfoil. Experiments were performed utilizing the conventional gas driven shock tube as the intermittent transonic wind tunnel. The aspect ratios of the models are about 0.86 and 1.5, respectively. The Mach numbers M 2 are about 0.84. The Reynolds numbers of the present experimental conditions were constant that Re based on chord length is about 4.0×10 5 . The results are as follows: in different aspect ratios, the difference of the shock wave location is confirmed though the Mach number and Reynolds number are same. It indicates the different correction Mach number by the effects of the side wall boundary layer though the nominal Mach number measured the same value. Also, on the difference of shock wave location for the effects of the aspect ratio, the tend of CFD shows the qualitative agreement with the result of an experiment.展开更多
In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium an...In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium and perfect gas flows, respectively. Experiments were performed at the Key Laboratory of High Temperature Gas Dynamics(LHD), Institute of Mechanics, Chinese Academy of Sciences. Corresponding numerical simulations were also conducted in effort to better understand the phenomena accompanying in these experiments. By assessing the consistency and accuracy of all the data gathered during this study, a detailed comparison of sharp cone heat transfer under a totally different kind of freestream conditions was build and analyzed. One specific parameter, defined as the product of the Stanton number and the square root of the Reynold number, was found to be more characteristic for the aerodynamic heating phenomena encountered in hypersonic flight. Adequate use of said parameter practically eliminates the variability caused by the deferent flow conditions, regardless of whether the flow is in dissociation or the boundary condition is catalytic. Essentially, the parameter identified in this study reduces the amount of ground experimental data necessary and eases data extrapolation to flight.展开更多
We studied the feedback maximization of reliability of multi-degree-of-freedom （MDOF） quasi integrable-Hamiltonian systems under combined harmonic and white noise excitations. First, the partially averaged Ito equat...We studied the feedback maximization of reliability of multi-degree-of-freedom （MDOF） quasi integrable-Hamiltonian systems under combined harmonic and white noise excitations. First, the partially averaged Ito equations are derived by using the stochastic averaging method for quasi integrable-Hamiltonian systems under combined harmonic and white noise excitations. Then, the dynamical programming equation and its boundary and final time conditions for the control problems of maximizing the reliability is established from the partially averaged equations by using the dynamical programming principle. The nonlinear stochastic optimal control for maximizing the reliability is determined from the dynamical programming equation and control constrains. The reliability function of optimally controlled systems is obtained by solving the final dynamical programming equation. Finally, the application of the proposed procedure and effectiveness of the control strategy are illustrated by using an example.展开更多
The radiation of noise from a parallelly rib-stiffened skin plate of aircraft cabin fuselage in the presence of external mean flow is theoretically investigated.An aero-acoustic-elastic model is developed and used to ...The radiation of noise from a parallelly rib-stiffened skin plate of aircraft cabin fuselage in the presence of external mean flow is theoretically investigated.An aero-acoustic-elastic model is developed and used to calculate the radiated sound pressure level(SPL) versus frequency curves with reference to sound radiation of a bare plate immersed in a steady fluid.The flexural and rotational motions of the rib stiffeners are described by applying the Euler-Bernoulli beam theory and torsional wave equation,respectively.Therefore,the coupling forces and moments between the ribs and the face-panel,caused separately by flexural and rotational motion of the ribs,are both taken into account.Given the periodicity of the structure,the Fourier transform technique is employed to solve panel vibration equations and acoustic equations.Systematic parametric investigation demonstrates that the presence of mean flow as well as rib spacings play significant roles in the sound radiation behavior of parallelly rib-stiffened plates.The proposed model provides a convenient and efficient tool for the factual engineering design of this kind of periodic structures with acoustic requirements.展开更多
文摘Plasma membrane vesicles of chrysanthemum ( Dendranthema morifolium (Ramat.) Tzvel.) callus was purified by sucrose gradient centrifugation to investigate the influence of sound stimulation on the lipid physical states and metabolism of plasma membrane. The results showed that sound stimulation decreased the content of phosphodiesters and the fluorescent intensity of DPH, but increased the light scattering value of the membrane, the fluorescent intensity of MC540 and the content of phosphomonoesters, indicating that the vesicles got looser, the charge density and hydrophobicity of membrane surface decreased under sound stimulation of some strength and frequency. However, the membrane fluidity increased under the condition. Meanwhile, the anabolism of membrane lipid increased and the catabolism decreased. It can be seen that the physical state and metabolism of membrane lipid is sensitive to sound stimulation.
文摘Two-dimensional and three-dimensional shock control contour bumps are designed for a supercritical wing section with the aim of transonic wave drag reduction. The supercritical airfoil （NASA SC （02）-0714） is selected considering the fact that most modern jet transport aircrafts that operate in the transonic flow regime （cruise at transonic speeds） employ supercritical airfoil sections. Here it is to be noted that a decrease in the transonic wave drag without loss in lift would result in an increased lift to drag ratio, which is a key range parameter that can potentially increase both the range and endurance of the aircraft. The major geometric bump parameters such as length, height and span are altered for both the two-dimensional and three-dimensional bumps in order to obtain the optimum location and shape of the bump. Once an optimum standalone three-dimensional bump is acquired, an array of bumps is manually placed spanwise of an unswept supercritical wing and analyzed under fully turbulent flow conditions. Different configurations are tested with varying three-dimensional bump spacing in order to determine the contribution of bump spacing on overall performance. The results show a 14% drag reduction and a consequent 16% lift to drag ratio rise at the design Mach number for the optimum arrangement of bumps along the wing span.
基金Supported by the Natural Science Foundation of Tianjin (06YFJMJC10500)
文摘Supercritical CO2 (SC-CO2) extraction technology and ultrasonic technology were used to extract two active sex hormones, estradiol and progesterone, and insulin-like growth factor-1 (IGF-1) from antler velvet. The effects of SC-CO2 extraction condition on the extraction yield and content of sex hormones, the ultrasonic extrac-tion condition on the content of IGF-1 and the SC-CO2 extraction condition on the activity remaining of IGF-1 were studied. The optimal conditions were obtained. The experimental results showed that, in presence of 75% ethanol as the co-solvent, the mean yield and content of estradiol and progesterone were 87.67 pg·g-1 and 1224.10 pg·g-1, 12.38 ng·g-1 and 354.06 ng·g-1, respectively, with extraction pressure of 30 MPa, temperature of 35°C, extraction time of 30 min and CO2 consumption of 15 L·g-1 at the flow rate of 2.0 L·min-1. The highest content of IGF-1 was 7425.75 ng·g-1 antler velvet residue, when the pH10 ammonia-ammonium chloride buffer solution was used as the solvent, the ratio of solvent to sample was 20/1 (volume/mass), the extraction temperature was 0-35°C, and the ex-traction time was 4×15 min. Under these conditions, 93.68% activity remaining of IGF-1 in the residue was ob-tained, while little IGF-1 activity exists in traditional residue. The experimental results indicate that the technology of SC-CO2 with co-solvent is of advantage for getting high content sexual hormones and keeping high activity of IGF-1 in the residue, which can not be achieved by traditional extraction methods.
基金supported by CNPC scientific research and technology development projects(No.2016A-3605)
文摘In this paper,wavefield storage optimization strategies are discussed with respect to reverse-time migration(RTM)imaging in reflection-acoustic logging,considering the problem of massive wavefield data storage in RTM itself.In doing so,two optimization methods are proposed and implemented to avoid wavefield storage.Firstly,the RTM based on the excitation-amplitude imaging condition uses the excitation time to judge the imaging time,and accordingly,we only need to store a small part of wavefield,such as the wavefield data of dozens of time points,the instances prove that they can even be imaged by only two time points.The traditional RTM usually needs to store the wavefield data of thousands of time points,compared with which the data storage can be reduced by tens or even thousands of times.Secondly,the RTM based on the random boundary uses the idea that the wavefield scatters rather than reflects in a random medium to reconstruct the wavefield source and thereby directly avoid storing the forward wavefield data.Numerical examples show that compared with other migration algorithms and the traditional RTM,both methods can effectively reduce wavefield data storage as well as improve data-processing efficiency while ensuring imaging accuracy,thereby providing the means for high-efficiency and highprecision imaging of fractures and caves by boreholes.
文摘The standard model of sonoluminescence suggests that the Coulomb barrier to deuterium fusion may be overcome by high bubble gas temperatures caused by compression heating if the bubble diameter remains spherical during bubble collapse.However, in the more likely collapse geometry of a pancake shape, the temperature rise in the bubbles is negligible. But the collapsing pancake bubble is found to significantly increase the frequency of the infrared energy available in the vibrational state of the water molecules at ambient temperature. For a collapse to liquid density, ultraviolet radiation at about 10eV is found. Although the ultraviolet radiation is of a low intensity, higher intensities may be possible if the bubble collapse is enhanced by visible and infrared lasers. Neither hot nor cold fusion is predicted in bubble collapse,but the ultraviolet energy at about 10eV developed in the bubble is sufficient to provide the basis for a new field of chemistry called ultrasound induced and laser enhanced cold fusion chemistry.
文摘Power ultrasound is finding widespread applications in assisting conventional processes yielding products of better quality at lower processing power and temperature. Transmission of ultrasound is known to be affected by the boundaries between layers of different materials or same material but in different states （solid or liquid or gas）. This paper investigates the effects of ultrasound （US） on the surface of the solidified weld which has been subjected to ultrasonic vibrations of 20 kHz frequency during laser welding. Vibrations due to ultrasound normally exert a very high force which is usually hundred or thousand times the gravity. The transverse waves will also cause movement of molten material in the weld. As the surface of the weld beads were of interest and not the mechanical properties and the microstructure, investigation of bead on plate welds were found to be sufficient. High carbon steel plate was held at one end by the ultrasonic horn through which ultrasound was injected. A bead on plate weld using a CO2 laser （1 kW） was then performed along the center of the plate using three different welding speeds namely, 400, 1200 and 2000 mm per minute. The ultrasonic powers selected were 3 W and 6 W respectively for each welding speed as higher acoustical power was causing ejection of molten metal from the pool during welding. 3D surface measurements and analysis were then made on a section of length 20 mm using a Talysurf machine. The results show that the surface of the weld was affected to different extent depending on the positions being considered in the weld. Some regions were similar to the reference weld whereas some specific regions were heavily disrupted with deep valleys followed by high peak/s. This shows that US vibration of weld pools, even at very small acoustical power, is a more complex problem than other similar processes such as casting because of the very small volume of molten metal involved.
文摘In this paper, we study a fluctuating potential barrier system with correlated spatial noises. Study shows that for this system, there is the resonant activation over the fluctuating potential barrier, and that the correlation between the different spatial noises can enhance (or weaken) the resonant activation.
基金Supported by National Natural Science Foundation of China under Grant No. 10975079by K.C. Wong Magna Fund of Ningbo University in Chinaby the Ningbo Natural Sciences Foundation in China
文摘We consider the escape of the particles multi-state noise. It is shown that, the noise can make over fluctuating potential barrier for a system only driven by a the particles escape over the fluctuating potential barrier in some circumstances; but in other circumstances, it can not. If the noise can make the particle escape over the fluctuating potential barrier, the mean first passage time （MFPT） can display the phenomenon of multi-resonant-activation. For this phenomenon, there are two kinds of resonant activation to appear. One is resonant activation for the MFPTs as the function of the flipping rates of the fluctuating potential barrier; the other is that for the MFPTs as the functions of the transition rates of the multi-state noise.
基金Project supported by the National Key R&D Program of China(Nos.2019YFA0405300 and 2019YFA0405203)the Chinese Scholarship Council(CSC)(No.201903170195)。
文摘The effect of magnetohydrodynamic(MHD)plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low magnetic Reynolds number approximation.A Mach 5 oblique shock/turbulent boundary layer interaction was adopted as the basic configuration in this numerical study in order to assess the effects of flow control using different combinations of magnetic field and plasma.Results show that just the thermal effect of plasma under experimental actuator parameters has no significant impact on the flow field and can therefore be neglected.On the basis of the relative position of control area and separation point,MHD control can be divided into four types and so effects and mechanisms might be different.Amongst these,D-type control leads to the largest reduction in separation length using magnetically-accelerated plasma inside an isobaric dead-air region.A novel parameter for predicting the shock wave/turbulent boundary layer interaction control based on Lorentz force acceleration is then proposed and the controllability of MHD plasma actuators under different MHD interaction parameters is studied.The results of this study will be insightful for the further design of MHD control in hypersonic vehicle inlets.
文摘Strong, normal shock wave, terminating a local supersonic area on an airfoil, not only limits aerodynamic performance but also becomes a source of a high-speed impulsive helicopter noise. The application of a passive control system （a cavity covered by a perforated plate） on a rotor blade should reduce the noise created by a moving shock. This article covers the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes an extended validation against the experimental data for relatively simple geometries of transonic nozzles. It is a first step towards a full simulation of a helicopter rotor equipped with a noise reducing passive control device in hover and in forward flight conditions.
文摘The supersonic ejector-diffuser system with a second throat was simulated using CFD. An explicit finite volumescheme was aPPlied to solve tWo-dimensional Navier-Stokes equations with standard k - E tulbulence model. Thevacuum Performance of the supersonic ejector-diffuser system was investigated by changing the ejector throat arearatio and the operating Pressure ratio. Two convergent-divergent nozzles with design Mach nUmber of 2. 11 and 3.41were selected to give the supersonic operahon of the ejector-diffoser system. The presence of a second throat stronglyaffected the shock wave sir’UctUI’e inside the "dxing tube as well as the spreading of the under-expanded jetdischarging from the Primary nozzle. There were optimum values of the operating pressure ratio and ejector throatarea ratio for the vacuum performance of the system to maximize.
文摘In the present study, the flow visualizations were performed around the NACA 0012 models which differ in aspect ratios. We discussed the effects of the aspect ratio in the test models. Additionally the unsteady, two-dimensional, compressible Euler equations were solved for the NACA 0012 airfoil. Experiments were performed utilizing the conventional gas driven shock tube as the intermittent transonic wind tunnel. The aspect ratios of the models are about 0.86 and 1.5, respectively. The Mach numbers M 2 are about 0.84. The Reynolds numbers of the present experimental conditions were constant that Re based on chord length is about 4.0×10 5 . The results are as follows: in different aspect ratios, the difference of the shock wave location is confirmed though the Mach number and Reynolds number are same. It indicates the different correction Mach number by the effects of the side wall boundary layer though the nominal Mach number measured the same value. Also, on the difference of shock wave location for the effects of the aspect ratio, the tend of CFD shows the qualitative agreement with the result of an experiment.
基金the National Natural Science Foundation of China(Grant Nos.1140227511472280 and 11532014)
文摘In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium and perfect gas flows, respectively. Experiments were performed at the Key Laboratory of High Temperature Gas Dynamics(LHD), Institute of Mechanics, Chinese Academy of Sciences. Corresponding numerical simulations were also conducted in effort to better understand the phenomena accompanying in these experiments. By assessing the consistency and accuracy of all the data gathered during this study, a detailed comparison of sharp cone heat transfer under a totally different kind of freestream conditions was build and analyzed. One specific parameter, defined as the product of the Stanton number and the square root of the Reynold number, was found to be more characteristic for the aerodynamic heating phenomena encountered in hypersonic flight. Adequate use of said parameter practically eliminates the variability caused by the deferent flow conditions, regardless of whether the flow is in dissociation or the boundary condition is catalytic. Essentially, the parameter identified in this study reduces the amount of ground experimental data necessary and eases data extrapolation to flight.
基金Project supported by the National Natural Science Foundation of China (No. 10772159)the Research Fund for the Doctoral Program of Higher Education of China (No. 20060335125)the Zhejiang Provincial Nature Science Foundation of China (No. Y7080070)
文摘We studied the feedback maximization of reliability of multi-degree-of-freedom （MDOF） quasi integrable-Hamiltonian systems under combined harmonic and white noise excitations. First, the partially averaged Ito equations are derived by using the stochastic averaging method for quasi integrable-Hamiltonian systems under combined harmonic and white noise excitations. Then, the dynamical programming equation and its boundary and final time conditions for the control problems of maximizing the reliability is established from the partially averaged equations by using the dynamical programming principle. The nonlinear stochastic optimal control for maximizing the reliability is determined from the dynamical programming equation and control constrains. The reliability function of optimally controlled systems is obtained by solving the final dynamical programming equation. Finally, the application of the proposed procedure and effectiveness of the control strategy are illustrated by using an example.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2011CB610300)the National Natural Science Foundation of China (Grant Nos. 11102148,11072188,11021202 and 10825210)the Fundamental Research Funds for the Central Universities
文摘The radiation of noise from a parallelly rib-stiffened skin plate of aircraft cabin fuselage in the presence of external mean flow is theoretically investigated.An aero-acoustic-elastic model is developed and used to calculate the radiated sound pressure level(SPL) versus frequency curves with reference to sound radiation of a bare plate immersed in a steady fluid.The flexural and rotational motions of the rib stiffeners are described by applying the Euler-Bernoulli beam theory and torsional wave equation,respectively.Therefore,the coupling forces and moments between the ribs and the face-panel,caused separately by flexural and rotational motion of the ribs,are both taken into account.Given the periodicity of the structure,the Fourier transform technique is employed to solve panel vibration equations and acoustic equations.Systematic parametric investigation demonstrates that the presence of mean flow as well as rib spacings play significant roles in the sound radiation behavior of parallelly rib-stiffened plates.The proposed model provides a convenient and efficient tool for the factual engineering design of this kind of periodic structures with acoustic requirements.
