The active control theory and methods of initial disturbances for rockets and missiles are investigated. The rocket or missile/launcher is simplified as a flexible beam excited by a moving varying velocity rigid body ...The active control theory and methods of initial disturbances for rockets and missiles are investigated. The rocket or missile/launcher is simplified as a flexible beam excited by a moving varying velocity rigid body which has two points in contact with the beam. The control force is applied at the supporting point on the beam. Active control strategies based on optimal control theory are proposed and computer simulation is carried out. Simulation results are consistent with the theoretical results, and show that the active control strategies proposed can accomplish the purpose to control the initial disturbances actively. The results show that active control of initial disturbances for rockets and missiles is feasible for application.展开更多
In the range of the rockets/launcher system itself, the dynamic equations for rocket and directional tube during semi-constraint period have been constructed by using Newton-Ether method. Considering the interaction o...In the range of the rockets/launcher system itself, the dynamic equations for rocket and directional tube during semi-constraint period have been constructed by using Newton-Ether method. Considering the interaction of rockets and directional tubes when clearances exist, the method of estimating initial disturbances for the rocket by using vibration data of the directional tube has been given. The estimated results have been compared with the simulation results computed by the dynamic simulating software ADAMS. Results computed by the two methods are basically consistent and the computing errors do not increase with the variation of the clearance. The validity of the proposed method has been proved.展开更多
5 October 2013, Houston--The Houston Rockets and ZTE USA, the fastest-growing smartphone provider in the United States, announced that ZTE will be the official smartphone of the Houston Rockets for the 2013-14 NBA sea...5 October 2013, Houston--The Houston Rockets and ZTE USA, the fastest-growing smartphone provider in the United States, announced that ZTE will be the official smartphone of the Houston Rockets for the 2013-14 NBA season. This is the first partnership of its kind for ZTE globally and the first big consumer marketing push in the United States since the company entered the country 15 years ago.展开更多
A LM-2D/Yuanzheng 3 launch vehicle successfully launched 6 Yunhai 2 satellites and one test microsatellite named'Chongqing'into their preset orbits,concluding China’s final orbital launch of2018.The launch to...A LM-2D/Yuanzheng 3 launch vehicle successfully launched 6 Yunhai 2 satellites and one test microsatellite named'Chongqing'into their preset orbits,concluding China’s final orbital launch of2018.The launch took place at 16:00 Beijing time on December 29,2018 from the Jiuquan Satellite Launch Center.展开更多
This paper develops a modular modeling and efficient formulation of launch dynamics with marching fire(LDMF)using a mixed formulation of the transfer matrix method for multibody systems(MSTMM)and Newton-Euler formulat...This paper develops a modular modeling and efficient formulation of launch dynamics with marching fire(LDMF)using a mixed formulation of the transfer matrix method for multibody systems(MSTMM)and Newton-Euler formulation.Taking a ground-borne multiple launch rocket systems(MLRS),the focus is on the launching subsystem comprising the rocket,flexible tube,and tube tail.The launching subsystem is treated as a coupled rigid-flexible multibody system,where the rocket and tube tail are treated as rigid bodies while the flexible tube as a beam with large motion.Firstly,the tube and tube tail can be elegantly handled by the MSTMM,a computationally efficient order-N formulation.Then,the equation of motion of the in-bore rocket with relative kinematics w.r.t.the tube using the Newton-Euler method is derived.Finally,the rocket,tube,and tube tail dynamics are coupled,yielding the equation of motion of the launching subsystem that can be regarded as a building block and further integrated with other subsystems.The deduced dynamics equation of the launching subsystem is not limited to ground-borne MLRS but also fits for tanks,self-propelled artilleries,and other air-borne and naval-borne weapons undergoing large motion.Numerical simulation results of LDMF are given and partially verified by the experiment.展开更多
Rong Yi,chief designer of the Long March-2F rocket that has launched China’s all manned space flight missions,talks about China’s progress in manned carrier rocket development and launch vehicle technology.AT 10:44 ...Rong Yi,chief designer of the Long March-2F rocket that has launched China’s all manned space flight missions,talks about China’s progress in manned carrier rocket development and launch vehicle technology.AT 10:44 am on June 5,the gaze of TV audiences globally riveted on the Long March-2F Y14 carrier rocket launch at northwest China’s Jiuquan Satellite Launch Center.About 577 seconds later,the Shenzhou-14 crewed spaceship separated from the rocket and entered its designated orbit.展开更多
We present Dark Matter candidates from non SUSY processes, in a way emphasizing how a Dark Matter (DM) candidate of roughly 100 - 400 GeV could be formed. As has been said about the Photon rocket and Axions rockets, t...We present Dark Matter candidates from non SUSY processes, in a way emphasizing how a Dark Matter (DM) candidate of roughly 100 - 400 GeV could be formed. As has been said about the Photon rocket and Axions rockets, the presence of a magnetic field supposedly would switch DM particle candidates to photons, in such a way as to in the end configure a photon rocket style device from DM in a thrust chamber. The presence of Dark Matter (DM) would in itself merely indicate that the emerging photon thrust would be comparatively greater than it would be for more conventional photon rockets. This amplifies and improves upon a so called axion rocket ram jet for interstellar travel. We assume that much the same sort of methodology for a would-be axion ramjet could be employed for DM, with perhaps greater thrust/power conversion efficiencies.展开更多
Gravity-1 solid-propellant carrier rocket utilizes a three-vertical testing and launch mode, and adopts a sea-based launch method. As the demand for satellite launches continues to grow, the scarcity of launch site re...Gravity-1 solid-propellant carrier rocket utilizes a three-vertical testing and launch mode, and adopts a sea-based launch method. As the demand for satellite launches continues to grow, the scarcity of launch site resources,and the consideration of cost savings, the need for rapid testing and launch of carrier rockets has become increasingly strong. The capability of rapid testing and launch has even become one important aspect of evaluating a rocket. This paper focuses on the characteristics of the Gravity-1 solid-propellant strap-on medium-sized carrier rocket and designs and implements a highly reliable, convenient, and intelligent low-cost rapid testing and launch solution. The main aspects include the design of a highly reliable dual-redundant ground architecture and the application of ground-based shelf products.展开更多
Long March 12 Makes Debut Flight from New Commercial Spaceport China successfully launched a new carrier rocket into space from the Hainan commercial spacecraft launch site in the southern island province of Hainan on...Long March 12 Makes Debut Flight from New Commercial Spaceport China successfully launched a new carrier rocket into space from the Hainan commercial spacecraft launch site in the southern island province of Hainan on November 30,2024.The Long March-12 carrier rocket sent two experimental satellites into their planned orbits.The launch mission was a complete success,according to Hainan provincial authorities.The mission was the maiden flight of the Long March-12 carrier rocket,and the first launch mission undertaken by the Hainan commercial spacecraft launch site.展开更多
For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geome...For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ω turbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.展开更多
The hybrid propulsion performed with paraffin waxes exhibits most attractive capabilities compared to solid or liquid engines,e.g.,throttleability and re-ignition,alongside higher regression rates compared to the conv...The hybrid propulsion performed with paraffin waxes exhibits most attractive capabilities compared to solid or liquid engines,e.g.,throttleability and re-ignition,alongside higher regression rates compared to the conventional hydroxyl terminated polybutadiene(HTPB)hybrid fuel.This is because the paraffin wax forms a thin and hydro-dynamically unstable liquid layer,and then enhances the regression rate with the entrainment of droplets from the liquid-gas interface.Nevertheless,some critical open points on the manufacturing of the paraffin fuel grains still persist,because the paraffin wax exhibits high shrinkage during the solidification phase,leading to the formation of cavities,cracks and internal rips,which may be detrimental to the mechanical properties and the structural integrity of the fuel grain.In this context,this paper deals with a wide calorimetric,thermo-mechanical and physical characterization of the paraffin wax selected to manufacture the hybrid rocket engines(HRE)fuel grain,in order to gain a thorough knowledge of the material necessary to avoid the formation of critical defects.Several manufacturing methods were investigated,and it was found that only laboratory scale processes,based on the use of a heated circular mould-piston apparatus,are able to avoid the formation of critical defects,with the application of both high temperature and pressure.展开更多
Besides safety and low-cost,the start/shutdown/restarting and throttling ability are the other two significant advantages of hy-brid rocket motors(HRMs) compared with liquid and solid ones.In this study,a two-stage va...Besides safety and low-cost,the start/shutdown/restarting and throttling ability are the other two significant advantages of hy-brid rocket motors(HRMs) compared with liquid and solid ones.In this study,a two-stage variable thrust and non-toxic 98%HP/HTPB hybrid rocket motor(VTHRM) is designed and applied in a sounding rocket,and the design parameters of the motor are analyzed and optimized.A computational program is developed to design the motor system structure,to predict the interior ballistics and the ballistic trajectory.A star grain and a wheel grain are compared.The design of experiment(DOE),variance analysis and the main effect analysis are employed to investigate the influence of the main design parameters on mo-tor performance.The multidiscipline feasible(MDF) approach is applied to establish the optimization procedure after analyz-ing the system design structure matrix.A modified differential evolution algorithm is employed to maximize the load mass.The results indicate that the wheel grain could obtain a larger load mass and a lower length to diameter ratio,and that throttling markedly meliorates the motor and rocket performance.The conclusions drawn from the analysis and optimization could pro-vide instructive guide and theoretical basis for engineering designs.展开更多
Bayesian estimation is applied to the analysis of backflow vortex instabilities in typical three-and four bladed liquid propellant rocket(LPR)engine inducers.The flow in the impeller eye is modeled as a set of equally...Bayesian estimation is applied to the analysis of backflow vortex instabilities in typical three-and four bladed liquid propellant rocket(LPR)engine inducers.The flow in the impeller eye is modeled as a set of equally intense and evenly spaced 2D axial vortices,located at the same radial distance from the axis and rotating at a fraction of the impeller speed.The circle theorem and the Bernoulli’s equation are used to predict the flow pressure in terms of the vortex number,intensity,rotational speed,and radial position.The theoretical spectra so obtained are frequency broadened to mimic the dispersion of the experimental data and parametrically fitted to the measured pressure spectra by maximum likelihood estimation with equal and independent Gaussian errors.The method is applied to three inducers,tested in water at room temperature and different loads and cavitation conditions.It successfully characterizes backflow instabilities using the signals of a single pressure transducer flush-mounted on the casing of the impeller eye,effectively by-passing the aliasing and data acquisition/reduction complexities of traditional multiple-sensor cross correlation methods.The identification returns the estimates of the model parameters and their standard errors,providing the information necessary for assessing the accuracy and statistical significance of the results.The flowrate is found to be the major factor affecting the backflow vortex instability,which,on the other hand,is rather insensitive to the occurrence of cavitation.The results are consistent with the data reported in the literature,as well as with those generated by the auxiliary models specifically developed for initializing the maximum likelihood searches and supporting the identification procedure.展开更多
BACKGROUND Long-term abdominal drains(LTAD)are a cost-effective palliative measure to manage malignant ascites in the community,but their use in patients with end-stage chronic liver disease and refractory ascites is ...BACKGROUND Long-term abdominal drains(LTAD)are a cost-effective palliative measure to manage malignant ascites in the community,but their use in patients with end-stage chronic liver disease and refractory ascites is not routine practice.The safety and cost-effectiveness of LTAD are currently being studied in this setting,with preliminary positive results.We hypothesised that palliative LTAD are as effective and safe as repeat palliative large volume paracentesis(LVP)in patients with cirrhosis and refractory ascites and may offer advantages in patients’quality of life.AIM To compare the effectiveness and safety of palliative LTAD and LVP in refractory ascites secondary to end-stage chronic liver disease.METHODS A retrospective,observational cohort study comparing the effectiveness and safety outcomes of palliative LTAD and regular palliative LVP as a treatment for refractory ascites in consecutive patients with end-stage chronic liver disease followed-up at our United Kingdom tertiary centre between 2018 and 2022 was conducted.Fisher’s exact tests and the Mann-Whitney U test were used to compare qualitative and quantitative variables,respectively.Kaplan-Meier survival estimates were generated to stratify time-related outcomes according to the type of drain.RESULTS Thirty patients had a total of 35 indwelling abdominal drains and nineteen patients underwent regular LVP.The baseline characteristics were similar between the groups.Prophylactic antibiotics were more frequently prescribed in patients with LTAD(P=0.012),while the incidence of peritonitis did not differ between the two groups(P=0.46).The incidence of acute kidney injury(P=0.014)and ascites/drain-related hospital admissions(P=0.004)were significantly higher in the LVP group.The overall survival was similar in the two groups(log-rank P=0.26),but the endpoint-free survival was significantly shorter in the LVP group(P=0.003,P<0.001,P=0.018 for first ascites/drain-related admission,acute kidney injury and drain-related complications,respectively).CONCLUSION The use of LTAD in the management of refractory ascites in palliated end-stage liver disease is effective,safe,and may reduce hospital admissions and utilisation of healthcare resources compared to LVP.展开更多
How to effectively evaluate the firing precision of weapon equipment at low cost is one of the core contents of improving the test level of weapon system.A new method to evaluate the firing precision of the MLRS consi...How to effectively evaluate the firing precision of weapon equipment at low cost is one of the core contents of improving the test level of weapon system.A new method to evaluate the firing precision of the MLRS considering the credibility of simulation system based on Bayesian theory is proposed in this paper.First of all,a comprehensive index system for the credibility of the simulation system of the firing precision of the MLRS is constructed combined with the group analytic hierarchy process.A modified method for determining the comprehensive weight of the index is established to improve the rationality of the index weight coefficients.The Bayesian posterior estimation formula of firing precision considering prior information is derived in the form of mixed prior distribution,and the rationality of prior information used in estimation model is discussed quantitatively.With the simulation tests,the different evaluation methods are compared to validate the effectiveness of the proposed method.Finally,the experimental results show that the effectiveness of estimation method for firing precision is improved by more than 25%.展开更多
The high turbulence of unstable combustion in the working process of liquid rocket engine will cause periodic pressure pulsation.Therefore,a pressure pulsation device that is easy to reuse,broadband,suited for poisono...The high turbulence of unstable combustion in the working process of liquid rocket engine will cause periodic pressure pulsation.Therefore,a pressure pulsation device that is easy to reuse,broadband,suited for poisonous media,and high pressure is designed and produced.Numerical and experimental studies show that the pulsator produces stable pressure waveforms at different flow rates,pressures,and frequencies,while the pressure waveform amplitude at the excitation frequency is larger.The pressure waveform amplitude increases exponentially with the flow rate and with smaller gaps and linear pressure increasing.The pressure waveform amplitude varies greatly at different frequencies along the pipeline.As the frequency increases,the pressure waveform amplitude of the excitation increases first and then decreases.The pressure waveform amplitude at low frequencies changes little along the pipeline.The pressure waveform amplitude at medium frequencies readily couples to the pipeline flow field and increases its value.The pressure waveform amplitude at high frequencies attenuates along the pipeline,where attenuation increases with frequency.The ability of the pulsator to provide stable excitation and high pressure is verified through normal and high pressure testsindifferentpipelinesystems.展开更多
On December 29,2023,the first launch service tower was completed at the Hainan International Commercial Aerospace Launch Center,marking a key step forward in building the launch capacity of China’s first commercial a...On December 29,2023,the first launch service tower was completed at the Hainan International Commercial Aerospace Launch Center,marking a key step forward in building the launch capacity of China’s first commercial aerospace launch site.On December 10,a Hyperbola-2 methane-liquid oxygen reusable verification rocket was launched successfully,marking the first recovery of reusable carrier rockets in China.展开更多
Our study identifies a subtle deviation from Newton’s third law in the derivation of the ideal rocket equation, also known as the Tsiolkovsky Rocket Equation (TRE). TRE can be derived using a 1D elastic collision mod...Our study identifies a subtle deviation from Newton’s third law in the derivation of the ideal rocket equation, also known as the Tsiolkovsky Rocket Equation (TRE). TRE can be derived using a 1D elastic collision model of the momentum exchange between the differential propellant mass element (dm) and the rocket final mass (m1), in which dm initially travels forward to collide with m1 and rebounds to exit through the exhaust nozzle with a velocity that is known as the effective exhaust velocity ve. We observe that such a model does not explain how dm was able to acquire its initial forward velocity without the support of a reactive mass traveling in the opposite direction. We show instead that the initial kinetic energy of dm is generated from dm itself by a process of self-combustion and expansion. In our ideal rocket with a single particle dm confined inside a hollow tube with one closed end, we show that the process of self-combustion and expansion of dm will result in a pair of differential particles each with a mass dm/2, and each traveling away from one another along the tube axis, from the center of combustion. These two identical particles represent the active and reactive sub-components of dm, co-generated in compliance with Newton’s third law of equal action and reaction. Building on this model, we derive a linear momentum ODE of the system, the solution of which yields what we call the Revised Tsiolkovsky Rocket Equation (RTRE). We show that RTRE has a mathematical form that is similar to TRE, with the exception of the effective exhaust velocity (ve) term. The ve term in TRE is replaced in RTRE by the average of two distinct exhaust velocities that we refer to as fast-jet, vx<sub>1</sub>, and slow-jet, vx<sub>2</sub>. These two velocities correspond, respectively, to the velocities of the detonation pressure wave that is vectored directly towards the exhaust nozzle, and the retonation wave that is initially vectored in the direction of rocket propagation, but subsequently becomes reflected from the thrust surface of the combustion chamber to exit through the exhaust nozzle with a time lag behind the detonation wave. The detonation-retonation phenomenon is supported by experimental evidence in the published literature. Finally, we use a convolution model to simulate the composite exhaust pressure wave, highlighting the frequency spectrum of the pressure perturbations that are generated by the mutual interference between the fast-jet and slow-jet components. Our analysis offers insights into the origin of combustion oscillations in rocket engines, with possible extensions beyond rocket engineering into other fields of combustion engineering.展开更多
At 11:21 on May 7,2024,the Long March 6C carrier rocket was successfully launched from China’s Taiyuan Satellite Launch Center,sending 4 satellites including Neptune 01 into their planned orbits.The launch mission wa...At 11:21 on May 7,2024,the Long March 6C carrier rocket was successfully launched from China’s Taiyuan Satellite Launch Center,sending 4 satellites including Neptune 01 into their planned orbits.The launch mission was a complete success.This mission marks the maiden flight of the Long March 6C carrier rocket,signifying the addition of a new member to the Long March rocket family.It further improves China’s new generation of Long March series launch vehicles and accelerates the upgrading of China’s in-service carrier rockets.The Long March 6C carrier rocket and Neptune 01 were developed by the Shanghai Academy of Spaceflight Technology.展开更多
文摘The active control theory and methods of initial disturbances for rockets and missiles are investigated. The rocket or missile/launcher is simplified as a flexible beam excited by a moving varying velocity rigid body which has two points in contact with the beam. The control force is applied at the supporting point on the beam. Active control strategies based on optimal control theory are proposed and computer simulation is carried out. Simulation results are consistent with the theoretical results, and show that the active control strategies proposed can accomplish the purpose to control the initial disturbances actively. The results show that active control of initial disturbances for rockets and missiles is feasible for application.
文摘In the range of the rockets/launcher system itself, the dynamic equations for rocket and directional tube during semi-constraint period have been constructed by using Newton-Ether method. Considering the interaction of rockets and directional tubes when clearances exist, the method of estimating initial disturbances for the rocket by using vibration data of the directional tube has been given. The estimated results have been compared with the simulation results computed by the dynamic simulating software ADAMS. Results computed by the two methods are basically consistent and the computing errors do not increase with the variation of the clearance. The validity of the proposed method has been proved.
文摘5 October 2013, Houston--The Houston Rockets and ZTE USA, the fastest-growing smartphone provider in the United States, announced that ZTE will be the official smartphone of the Houston Rockets for the 2013-14 NBA season. This is the first partnership of its kind for ZTE globally and the first big consumer marketing push in the United States since the company entered the country 15 years ago.
文摘A LM-2D/Yuanzheng 3 launch vehicle successfully launched 6 Yunhai 2 satellites and one test microsatellite named'Chongqing'into their preset orbits,concluding China’s final orbital launch of2018.The launch took place at 16:00 Beijing time on December 29,2018 from the Jiuquan Satellite Launch Center.
基金The research is financially supported by the National Natural Science Foundation of China(No.11972193).
文摘This paper develops a modular modeling and efficient formulation of launch dynamics with marching fire(LDMF)using a mixed formulation of the transfer matrix method for multibody systems(MSTMM)and Newton-Euler formulation.Taking a ground-borne multiple launch rocket systems(MLRS),the focus is on the launching subsystem comprising the rocket,flexible tube,and tube tail.The launching subsystem is treated as a coupled rigid-flexible multibody system,where the rocket and tube tail are treated as rigid bodies while the flexible tube as a beam with large motion.Firstly,the tube and tube tail can be elegantly handled by the MSTMM,a computationally efficient order-N formulation.Then,the equation of motion of the in-bore rocket with relative kinematics w.r.t.the tube using the Newton-Euler method is derived.Finally,the rocket,tube,and tube tail dynamics are coupled,yielding the equation of motion of the launching subsystem that can be regarded as a building block and further integrated with other subsystems.The deduced dynamics equation of the launching subsystem is not limited to ground-borne MLRS but also fits for tanks,self-propelled artilleries,and other air-borne and naval-borne weapons undergoing large motion.Numerical simulation results of LDMF are given and partially verified by the experiment.
文摘Rong Yi,chief designer of the Long March-2F rocket that has launched China’s all manned space flight missions,talks about China’s progress in manned carrier rocket development and launch vehicle technology.AT 10:44 am on June 5,the gaze of TV audiences globally riveted on the Long March-2F Y14 carrier rocket launch at northwest China’s Jiuquan Satellite Launch Center.About 577 seconds later,the Shenzhou-14 crewed spaceship separated from the rocket and entered its designated orbit.
文摘We present Dark Matter candidates from non SUSY processes, in a way emphasizing how a Dark Matter (DM) candidate of roughly 100 - 400 GeV could be formed. As has been said about the Photon rocket and Axions rockets, the presence of a magnetic field supposedly would switch DM particle candidates to photons, in such a way as to in the end configure a photon rocket style device from DM in a thrust chamber. The presence of Dark Matter (DM) would in itself merely indicate that the emerging photon thrust would be comparatively greater than it would be for more conventional photon rockets. This amplifies and improves upon a so called axion rocket ram jet for interstellar travel. We assume that much the same sort of methodology for a would-be axion ramjet could be employed for DM, with perhaps greater thrust/power conversion efficiencies.
文摘Gravity-1 solid-propellant carrier rocket utilizes a three-vertical testing and launch mode, and adopts a sea-based launch method. As the demand for satellite launches continues to grow, the scarcity of launch site resources,and the consideration of cost savings, the need for rapid testing and launch of carrier rockets has become increasingly strong. The capability of rapid testing and launch has even become one important aspect of evaluating a rocket. This paper focuses on the characteristics of the Gravity-1 solid-propellant strap-on medium-sized carrier rocket and designs and implements a highly reliable, convenient, and intelligent low-cost rapid testing and launch solution. The main aspects include the design of a highly reliable dual-redundant ground architecture and the application of ground-based shelf products.
文摘Long March 12 Makes Debut Flight from New Commercial Spaceport China successfully launched a new carrier rocket into space from the Hainan commercial spacecraft launch site in the southern island province of Hainan on November 30,2024.The Long March-12 carrier rocket sent two experimental satellites into their planned orbits.The launch mission was a complete success,according to Hainan provincial authorities.The mission was the maiden flight of the Long March-12 carrier rocket,and the first launch mission undertaken by the Hainan commercial spacecraft launch site.
文摘For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ω turbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.
文摘The hybrid propulsion performed with paraffin waxes exhibits most attractive capabilities compared to solid or liquid engines,e.g.,throttleability and re-ignition,alongside higher regression rates compared to the conventional hydroxyl terminated polybutadiene(HTPB)hybrid fuel.This is because the paraffin wax forms a thin and hydro-dynamically unstable liquid layer,and then enhances the regression rate with the entrainment of droplets from the liquid-gas interface.Nevertheless,some critical open points on the manufacturing of the paraffin fuel grains still persist,because the paraffin wax exhibits high shrinkage during the solidification phase,leading to the formation of cavities,cracks and internal rips,which may be detrimental to the mechanical properties and the structural integrity of the fuel grain.In this context,this paper deals with a wide calorimetric,thermo-mechanical and physical characterization of the paraffin wax selected to manufacture the hybrid rocket engines(HRE)fuel grain,in order to gain a thorough knowledge of the material necessary to avoid the formation of critical defects.Several manufacturing methods were investigated,and it was found that only laboratory scale processes,based on the use of a heated circular mould-piston apparatus,are able to avoid the formation of critical defects,with the application of both high temperature and pressure.
文摘Besides safety and low-cost,the start/shutdown/restarting and throttling ability are the other two significant advantages of hy-brid rocket motors(HRMs) compared with liquid and solid ones.In this study,a two-stage variable thrust and non-toxic 98%HP/HTPB hybrid rocket motor(VTHRM) is designed and applied in a sounding rocket,and the design parameters of the motor are analyzed and optimized.A computational program is developed to design the motor system structure,to predict the interior ballistics and the ballistic trajectory.A star grain and a wheel grain are compared.The design of experiment(DOE),variance analysis and the main effect analysis are employed to investigate the influence of the main design parameters on mo-tor performance.The multidiscipline feasible(MDF) approach is applied to establish the optimization procedure after analyz-ing the system design structure matrix.A modified differential evolution algorithm is employed to maximize the load mass.The results indicate that the wheel grain could obtain a larger load mass and a lower length to diameter ratio,and that throttling markedly meliorates the motor and rocket performance.The conclusions drawn from the analysis and optimization could pro-vide instructive guide and theoretical basis for engineering designs.
文摘Bayesian estimation is applied to the analysis of backflow vortex instabilities in typical three-and four bladed liquid propellant rocket(LPR)engine inducers.The flow in the impeller eye is modeled as a set of equally intense and evenly spaced 2D axial vortices,located at the same radial distance from the axis and rotating at a fraction of the impeller speed.The circle theorem and the Bernoulli’s equation are used to predict the flow pressure in terms of the vortex number,intensity,rotational speed,and radial position.The theoretical spectra so obtained are frequency broadened to mimic the dispersion of the experimental data and parametrically fitted to the measured pressure spectra by maximum likelihood estimation with equal and independent Gaussian errors.The method is applied to three inducers,tested in water at room temperature and different loads and cavitation conditions.It successfully characterizes backflow instabilities using the signals of a single pressure transducer flush-mounted on the casing of the impeller eye,effectively by-passing the aliasing and data acquisition/reduction complexities of traditional multiple-sensor cross correlation methods.The identification returns the estimates of the model parameters and their standard errors,providing the information necessary for assessing the accuracy and statistical significance of the results.The flowrate is found to be the major factor affecting the backflow vortex instability,which,on the other hand,is rather insensitive to the occurrence of cavitation.The results are consistent with the data reported in the literature,as well as with those generated by the auxiliary models specifically developed for initializing the maximum likelihood searches and supporting the identification procedure.
文摘BACKGROUND Long-term abdominal drains(LTAD)are a cost-effective palliative measure to manage malignant ascites in the community,but their use in patients with end-stage chronic liver disease and refractory ascites is not routine practice.The safety and cost-effectiveness of LTAD are currently being studied in this setting,with preliminary positive results.We hypothesised that palliative LTAD are as effective and safe as repeat palliative large volume paracentesis(LVP)in patients with cirrhosis and refractory ascites and may offer advantages in patients’quality of life.AIM To compare the effectiveness and safety of palliative LTAD and LVP in refractory ascites secondary to end-stage chronic liver disease.METHODS A retrospective,observational cohort study comparing the effectiveness and safety outcomes of palliative LTAD and regular palliative LVP as a treatment for refractory ascites in consecutive patients with end-stage chronic liver disease followed-up at our United Kingdom tertiary centre between 2018 and 2022 was conducted.Fisher’s exact tests and the Mann-Whitney U test were used to compare qualitative and quantitative variables,respectively.Kaplan-Meier survival estimates were generated to stratify time-related outcomes according to the type of drain.RESULTS Thirty patients had a total of 35 indwelling abdominal drains and nineteen patients underwent regular LVP.The baseline characteristics were similar between the groups.Prophylactic antibiotics were more frequently prescribed in patients with LTAD(P=0.012),while the incidence of peritonitis did not differ between the two groups(P=0.46).The incidence of acute kidney injury(P=0.014)and ascites/drain-related hospital admissions(P=0.004)were significantly higher in the LVP group.The overall survival was similar in the two groups(log-rank P=0.26),but the endpoint-free survival was significantly shorter in the LVP group(P=0.003,P<0.001,P=0.018 for first ascites/drain-related admission,acute kidney injury and drain-related complications,respectively).CONCLUSION The use of LTAD in the management of refractory ascites in palliated end-stage liver disease is effective,safe,and may reduce hospital admissions and utilisation of healthcare resources compared to LVP.
基金National Natural Science Foundation of China(Grant Nos.11972193 and 92266201)。
文摘How to effectively evaluate the firing precision of weapon equipment at low cost is one of the core contents of improving the test level of weapon system.A new method to evaluate the firing precision of the MLRS considering the credibility of simulation system based on Bayesian theory is proposed in this paper.First of all,a comprehensive index system for the credibility of the simulation system of the firing precision of the MLRS is constructed combined with the group analytic hierarchy process.A modified method for determining the comprehensive weight of the index is established to improve the rationality of the index weight coefficients.The Bayesian posterior estimation formula of firing precision considering prior information is derived in the form of mixed prior distribution,and the rationality of prior information used in estimation model is discussed quantitatively.With the simulation tests,the different evaluation methods are compared to validate the effectiveness of the proposed method.Finally,the experimental results show that the effectiveness of estimation method for firing precision is improved by more than 25%.
基金National Science and Technology Major Projects(2017-V-0012-0064)。
文摘The high turbulence of unstable combustion in the working process of liquid rocket engine will cause periodic pressure pulsation.Therefore,a pressure pulsation device that is easy to reuse,broadband,suited for poisonous media,and high pressure is designed and produced.Numerical and experimental studies show that the pulsator produces stable pressure waveforms at different flow rates,pressures,and frequencies,while the pressure waveform amplitude at the excitation frequency is larger.The pressure waveform amplitude increases exponentially with the flow rate and with smaller gaps and linear pressure increasing.The pressure waveform amplitude varies greatly at different frequencies along the pipeline.As the frequency increases,the pressure waveform amplitude of the excitation increases first and then decreases.The pressure waveform amplitude at low frequencies changes little along the pipeline.The pressure waveform amplitude at medium frequencies readily couples to the pipeline flow field and increases its value.The pressure waveform amplitude at high frequencies attenuates along the pipeline,where attenuation increases with frequency.The ability of the pulsator to provide stable excitation and high pressure is verified through normal and high pressure testsindifferentpipelinesystems.
文摘On December 29,2023,the first launch service tower was completed at the Hainan International Commercial Aerospace Launch Center,marking a key step forward in building the launch capacity of China’s first commercial aerospace launch site.On December 10,a Hyperbola-2 methane-liquid oxygen reusable verification rocket was launched successfully,marking the first recovery of reusable carrier rockets in China.
文摘Our study identifies a subtle deviation from Newton’s third law in the derivation of the ideal rocket equation, also known as the Tsiolkovsky Rocket Equation (TRE). TRE can be derived using a 1D elastic collision model of the momentum exchange between the differential propellant mass element (dm) and the rocket final mass (m1), in which dm initially travels forward to collide with m1 and rebounds to exit through the exhaust nozzle with a velocity that is known as the effective exhaust velocity ve. We observe that such a model does not explain how dm was able to acquire its initial forward velocity without the support of a reactive mass traveling in the opposite direction. We show instead that the initial kinetic energy of dm is generated from dm itself by a process of self-combustion and expansion. In our ideal rocket with a single particle dm confined inside a hollow tube with one closed end, we show that the process of self-combustion and expansion of dm will result in a pair of differential particles each with a mass dm/2, and each traveling away from one another along the tube axis, from the center of combustion. These two identical particles represent the active and reactive sub-components of dm, co-generated in compliance with Newton’s third law of equal action and reaction. Building on this model, we derive a linear momentum ODE of the system, the solution of which yields what we call the Revised Tsiolkovsky Rocket Equation (RTRE). We show that RTRE has a mathematical form that is similar to TRE, with the exception of the effective exhaust velocity (ve) term. The ve term in TRE is replaced in RTRE by the average of two distinct exhaust velocities that we refer to as fast-jet, vx<sub>1</sub>, and slow-jet, vx<sub>2</sub>. These two velocities correspond, respectively, to the velocities of the detonation pressure wave that is vectored directly towards the exhaust nozzle, and the retonation wave that is initially vectored in the direction of rocket propagation, but subsequently becomes reflected from the thrust surface of the combustion chamber to exit through the exhaust nozzle with a time lag behind the detonation wave. The detonation-retonation phenomenon is supported by experimental evidence in the published literature. Finally, we use a convolution model to simulate the composite exhaust pressure wave, highlighting the frequency spectrum of the pressure perturbations that are generated by the mutual interference between the fast-jet and slow-jet components. Our analysis offers insights into the origin of combustion oscillations in rocket engines, with possible extensions beyond rocket engineering into other fields of combustion engineering.
文摘At 11:21 on May 7,2024,the Long March 6C carrier rocket was successfully launched from China’s Taiyuan Satellite Launch Center,sending 4 satellites including Neptune 01 into their planned orbits.The launch mission was a complete success.This mission marks the maiden flight of the Long March 6C carrier rocket,signifying the addition of a new member to the Long March rocket family.It further improves China’s new generation of Long March series launch vehicles and accelerates the upgrading of China’s in-service carrier rockets.The Long March 6C carrier rocket and Neptune 01 were developed by the Shanghai Academy of Spaceflight Technology.
