The slip-sweep technique is one of the high-efficiency, high-fidelity, and environmental vibroseis seismic prospecting techniques which consists of a vibrator group sweeping without waiting for the previous group＇s s...The slip-sweep technique is one of the high-efficiency, high-fidelity, and environmental vibroseis seismic prospecting techniques which consists of a vibrator group sweeping without waiting for the previous group＇s sweep to terminate. The cycle time can be reduced drastically and hence the production efficiency can be increased significantly but harmonic distortion of one sweep will leak into the record of the other sweep. In this paper, we propose an anti-correlation method for removing harmonic distortion in vibroseis data. This method is based on decomposition of the ground force signal into fundamental and harmonic components. Then the corresponding anti-correlation operator can be computed to estimate the energy of each harmonic after correlating the vibroseis data with the corresponding harmonic component. Finally, the vibroseis harmonic noise to be removed can be obtained by subtracting the extracted harmonic noise from the traces of the previous group＇s sweep. The advantage of the proposed method is that it can process both uncorrelated and correlated vibroseis seismic data. Moreover, the algorithm is simple, stable, and computationally fast. Especially, the significant contribution of this method is a considerable reduction in the harmonic without any alteration of the desired signals. The method was tested on both synthetic and field data sets to validate the good harmonic noise suppression results.展开更多
Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the...Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the 2-D conservation laws.Comparisons between the numerical results and the experimental measurements show excellent agreements.The computed results are in good agreement with the numerical solutions obtained by using third order accurate RKDG finite element method.The results show larger gradient at discontinuous points compared with those obtained by second order accurate TVD schemes.It indicates that the presented method is efficient and reliable for solving the axisymmetric jet with external freestream flows,and shows that the method captures shocks well without numerical noise.展开更多
One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expr...One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expressions of the limits of mean velocity and diffusion constant of this model as the number of internal mechanochemical sates tend to infinity are obtained.These results will be helpful to understand the limit of the one dimensional hopping model.At the same time, the work can be used to get more useful results in continuous form from the corresponding ones obtained by discrete models.展开更多
Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application...Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.展开更多
In order to solve the difficulty of detailed recognition of subdivisions of structural coal types,a differentiation model that combines BP neural network with an ultrasonic reflection method is proposed.Structural coa...In order to solve the difficulty of detailed recognition of subdivisions of structural coal types,a differentiation model that combines BP neural network with an ultrasonic reflection method is proposed.Structural coal types are recognized based on a suitable consideration of ultrasonic speed,an ultrasonic attenuation coefficient,characteristics of ultrasonic transmission and other parameters relating to structural coal types.We have focused on a computational model of ultrasonic speed,attenuation coefficient in coal and differentiation algorithm of structural coal types based on a BP neural network.Experiments demonstrate that the model can distinguish structural coal types effectively.It is important for the improved ultrasonic differentiation model to predict coal and gas outbursts.展开更多
Experiments involving a sonar platform with a sound absorption wedge were carried out for the purpose of obtaining the low frequency acoustic characteristics. Acoustic characteristics of a sonar platform model with a ...Experiments involving a sonar platform with a sound absorption wedge were carried out for the purpose of obtaining the low frequency acoustic characteristics. Acoustic characteristics of a sonar platform model with a sound absorption wedge were measured, and the effects of different wedge laid areas on platform acoustic characteristic were tested. Vibration acceleration and self-noise caused by model vibration were measured in four conditions: 0%, 36%, 60%, and 100% of wedge laid area when the sonar platform was under a single frequency excitation force. An experiment was performed to validate a corresponding numerical calculation. The numerical vibration characteristics of platform area were calculated by the finite element method, and self-noise caused by the vibration in it was predicted by an experiential formula. The conclusions prove that the numerical calculation method can partially replace the experimental process for obtaining vibration and sound characteristics.展开更多
As one of the important components of computational flight mechanics and control,numerical algorithms of trajectory optimization for flight vehicles are currently studied by many researchers in aerospace engineering t...As one of the important components of computational flight mechanics and control,numerical algorithms of trajectory optimization for flight vehicles are currently studied by many researchers in aerospace engineering to completely solve these difficult problems,but few papers on the survey of this research field have been published recently.Based on the investigation of more than one hundred literatures,considering the application perspectives of computational flight mechanics and recent developments of trajectory optimization,the numerical algorithms of trajectory optimizations for aerospace vehicles are summarized and systematically analyzed.This paper summarized the basic principle,characteristics and application for all kinds of current trajectory optimization algorithms;and introduced some new methods and theories appearing in recent years.Finally,collaborative trajectory optimization for many flight vehicles,and hypersonic vehicle trajectory optimization were mainly reviewed in this paper.In the conclusion of this paper,the future research properties are presented regarding to numerical algorithms of trajectory optimization and control for flight vehicles as follows:collaboration and antagonization for many flight vehicles and multiple targets,global,real-time online,high accuracy of 7-D trajectory,considering all kinds of unknown random disturbances in trajectory optimization,and so on.展开更多
In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The...In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The shock-shock interaction theory in conjunction with a three dimensional correction and checked with computational fluid dynamics (CFD) is used to analyze the lift and drag forces as function of the geometrical parameters and inflow Mach number. Through this study, though limited to only inviscid flow, we conclude that it is possible to obtain a high lift to drag ratio by suitably arranging the shock interaction generator.展开更多
Numerical experiments are carried out using the standard hypersonic ballistic-type model(HB-2) to investigate the effect of forward-facing cavity on the aerodynamic heating. A general concept is proposed which utilize...Numerical experiments are carried out using the standard hypersonic ballistic-type model(HB-2) to investigate the effect of forward-facing cavity on the aerodynamic heating. A general concept is proposed which utilizes the flow disturbances generated passively in the nosed subsonic region to weaken the detached shock wave. Several aspects are mainly studied, including shock shape and standoff distance, surface heat flux and pressure, flowfield feature and cooling mechanism. The numerical results indicate that shock strength and standoff distance increase with an increase in the L/D ratio of the cavity. Interestingly, a bulge structure of the detached shock associated with a deep cavity is observed for the first time. Local surface heat flux and pressure around the concave nose are much lower respectively than those at the stagnation point of the baseline model. In addition, both surface heat and pressure reductions are proportional to the L/D ratio. A negative heating phenomenon may occur in the vicinity of a sharp lip or on the base wall of a deep cavity. If the L/D ratio exceeds 0.7, the detached shock appears as a self-sustained oscillation which can be referred to as the cooling mechanism.展开更多
基金supported by the Sinopec Service Company and China National Petroleum Corporation
文摘The slip-sweep technique is one of the high-efficiency, high-fidelity, and environmental vibroseis seismic prospecting techniques which consists of a vibrator group sweeping without waiting for the previous group＇s sweep to terminate. The cycle time can be reduced drastically and hence the production efficiency can be increased significantly but harmonic distortion of one sweep will leak into the record of the other sweep. In this paper, we propose an anti-correlation method for removing harmonic distortion in vibroseis data. This method is based on decomposition of the ground force signal into fundamental and harmonic components. Then the corresponding anti-correlation operator can be computed to estimate the energy of each harmonic after correlating the vibroseis data with the corresponding harmonic component. Finally, the vibroseis harmonic noise to be removed can be obtained by subtracting the extracted harmonic noise from the traces of the previous group＇s sweep. The advantage of the proposed method is that it can process both uncorrelated and correlated vibroseis seismic data. Moreover, the algorithm is simple, stable, and computationally fast. Especially, the significant contribution of this method is a considerable reduction in the harmonic without any alteration of the desired signals. The method was tested on both synthetic and field data sets to validate the good harmonic noise suppression results.
基金Supported by the National Natural Defense Basic Scientific Research Program of China(A262006-1288)the Key Disciplines Program of Shanghai Municipal Commission of Education(J50501)~~
文摘Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the 2-D conservation laws.Comparisons between the numerical results and the experimental measurements show excellent agreements.The computed results are in good agreement with the numerical solutions obtained by using third order accurate RKDG finite element method.The results show larger gradient at discontinuous points compared with those obtained by second order accurate TVD schemes.It indicates that the presented method is efficient and reliable for solving the axisymmetric jet with external freestream flows,and shows that the method captures shocks well without numerical noise.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10701029） and the Shanghai Key Laboratory for Contemporary Applied Mathematics （No.SGST09DZ2272900）.
文摘One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expressions of the limits of mean velocity and diffusion constant of this model as the number of internal mechanochemical sates tend to infinity are obtained.These results will be helpful to understand the limit of the one dimensional hopping model.At the same time, the work can be used to get more useful results in continuous form from the corresponding ones obtained by discrete models.
基金Project(51606220)supported by the National Natural Science Foundation of ChinaProject(1194028)supported by the Beijing Natural Science Foundation,China。
文摘Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.
基金Projects 50674093 supported by the National Natural Science Foundation of China20050290010 by the Doctoral Foundation of the Chinese Education Ministry
文摘In order to solve the difficulty of detailed recognition of subdivisions of structural coal types,a differentiation model that combines BP neural network with an ultrasonic reflection method is proposed.Structural coal types are recognized based on a suitable consideration of ultrasonic speed,an ultrasonic attenuation coefficient,characteristics of ultrasonic transmission and other parameters relating to structural coal types.We have focused on a computational model of ultrasonic speed,attenuation coefficient in coal and differentiation algorithm of structural coal types based on a BP neural network.Experiments demonstrate that the model can distinguish structural coal types effectively.It is important for the improved ultrasonic differentiation model to predict coal and gas outbursts.
基金Supported by Harbin Talents of Science and Technology Innovation Special Fund(2011RFQXG021)
文摘Experiments involving a sonar platform with a sound absorption wedge were carried out for the purpose of obtaining the low frequency acoustic characteristics. Acoustic characteristics of a sonar platform model with a sound absorption wedge were measured, and the effects of different wedge laid areas on platform acoustic characteristic were tested. Vibration acceleration and self-noise caused by model vibration were measured in four conditions: 0%, 36%, 60%, and 100% of wedge laid area when the sonar platform was under a single frequency excitation force. An experiment was performed to validate a corresponding numerical calculation. The numerical vibration characteristics of platform area were calculated by the finite element method, and self-noise caused by the vibration in it was predicted by an experiential formula. The conclusions prove that the numerical calculation method can partially replace the experimental process for obtaining vibration and sound characteristics.
基金supported by the Fundatmental Research Funds for the Central Universities of China (Grant No. CXZZ11_0215)
文摘As one of the important components of computational flight mechanics and control,numerical algorithms of trajectory optimization for flight vehicles are currently studied by many researchers in aerospace engineering to completely solve these difficult problems,but few papers on the survey of this research field have been published recently.Based on the investigation of more than one hundred literatures,considering the application perspectives of computational flight mechanics and recent developments of trajectory optimization,the numerical algorithms of trajectory optimizations for aerospace vehicles are summarized and systematically analyzed.This paper summarized the basic principle,characteristics and application for all kinds of current trajectory optimization algorithms;and introduced some new methods and theories appearing in recent years.Finally,collaborative trajectory optimization for many flight vehicles,and hypersonic vehicle trajectory optimization were mainly reviewed in this paper.In the conclusion of this paper,the future research properties are presented regarding to numerical algorithms of trajectory optimization and control for flight vehicles as follows:collaboration and antagonization for many flight vehicles and multiple targets,global,real-time online,high accuracy of 7-D trajectory,considering all kinds of unknown random disturbances in trajectory optimization,and so on.
文摘In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The shock-shock interaction theory in conjunction with a three dimensional correction and checked with computational fluid dynamics (CFD) is used to analyze the lift and drag forces as function of the geometrical parameters and inflow Mach number. Through this study, though limited to only inviscid flow, we conclude that it is possible to obtain a high lift to drag ratio by suitably arranging the shock interaction generator.
基金supported by the National Natural Science Foundation of China(Grant No.11532014)
文摘Numerical experiments are carried out using the standard hypersonic ballistic-type model(HB-2) to investigate the effect of forward-facing cavity on the aerodynamic heating. A general concept is proposed which utilizes the flow disturbances generated passively in the nosed subsonic region to weaken the detached shock wave. Several aspects are mainly studied, including shock shape and standoff distance, surface heat flux and pressure, flowfield feature and cooling mechanism. The numerical results indicate that shock strength and standoff distance increase with an increase in the L/D ratio of the cavity. Interestingly, a bulge structure of the detached shock associated with a deep cavity is observed for the first time. Local surface heat flux and pressure around the concave nose are much lower respectively than those at the stagnation point of the baseline model. In addition, both surface heat and pressure reductions are proportional to the L/D ratio. A negative heating phenomenon may occur in the vicinity of a sharp lip or on the base wall of a deep cavity. If the L/D ratio exceeds 0.7, the detached shock appears as a self-sustained oscillation which can be referred to as the cooling mechanism.
