In this study,it is aimed to develop a generic model which calculates the trajectory of the ejection seat from the jet aircraft,by taking into account the parameters that will affect the seat movement such as the seat...In this study,it is aimed to develop a generic model which calculates the trajectory of the ejection seat from the jet aircraft,by taking into account the parameters that will affect the seat movement such as the seat’s launch speed,ejection direction,ejection angle,altitude of the aircraft,distance/height from the aircraft rudder and canopy,pilot and ejection seat weight.With the model algorithm proposed,the ejection seat trajectory model was developed on MATLAB.The ejection seat trajectory model is based on point mass trajectory mathematical model.In this study,an analytical study of the problem has been made for modeling the flight trajectory of the ejection seat after it has been ejected.Past studies were used as a basis for validation and simulation.By writing a generic MATLAB code,a user interface was developed and presented to the user as a module.This generic code that has been developed could be used for simulations by users in the future by revising it in accordance with their own job descriptions.展开更多
To achieve the secondary production in multistage fracturing wells of tight oil,milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later.In thi...To achieve the secondary production in multistage fracturing wells of tight oil,milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later.In this paper,first of all,the working mechanism of milling tools for multistage fracturing ball seats was studied and a mechanical analysis model of single abrasive grain was established.Then,an experimental system for milling tools was developed,and the experimental tests of the flat,the blade,and the slope milling tool were conducted in order.Besides,the morphology of chips and the surface morphology of the workpiece after the experiment were analyzed.Also,the working performance of milling tools was evaluated from the perspectives of working safety,working efficiency,and wear resistance of the milling tool.The results show that the torque of the milling tool increases nonlinearly with the increase in the cutting depth of the abrasive grain and increases linearly with the increase in the cutting width.Also,the chips are irregular particles and the size is mainly from 10 to 50μm.So,the chips should be pumped up with a small pump pressure and a large displacement.Besides this,the cutting depths of the abrasive grains are from 216.20 to 635.47μm and the bottom surface of the milling tool should be eccentric to avoid the zero point of cutting speed.Furthermore,the torque of the slope milling tool is 23.8%larger than that of the flat milling tool,which is also 30.4%smaller than that of the blade milling tool.Compared with the flat milling tool,the working efficiency of the blade milling tool improves by 79.9%and the slope milling tool improves by 111.1%.Also,the wear resistance of the blade milling tool decreases by 102.7%,while the slope milling tool declines by 32.6%when compared with the flat milling tool.Therefore,the slope milling tool has the characteristics of moderate torque,stable working conditions,the highest working efficiency,and fine wear resistance,which is preferably used to mill multistage fracturing ball seats.This study provides a theoretical basis and guidance for milling multistage fracturing ball seats on-site and realizing production with a large diameter in later stages of multistage fracturing wells.展开更多
In this study,a human-sensitive frequency band vibration isolator(HFBVI)with quasi-zero stiffness(QZS)characteristics for heavy-duty truck seats is designed to improve the comfort of heavy-duty truck drivers on uneven...In this study,a human-sensitive frequency band vibration isolator(HFBVI)with quasi-zero stiffness(QZS)characteristics for heavy-duty truck seats is designed to improve the comfort of heavy-duty truck drivers on uneven roads.First,the analytical expressions for the force and displacement of the HFBVI are derived with the Lagrange equation and d'Alembert's principle,and are validated through the prototype restoring force testing.Second,the harmonic balance method(HBM)is used to obtain the dynamic responses under harmonic excitation,and further the influence of pre-stretching on the dynamic characteristics and transmissibility is discussed.Finally,the experimental prototype of the HFBVI is fabricated,and vibration experiments are conducted under harmonic excitation to verify the vibration isolation performance(VIP)of the proposed vibration isolator.The experimental results indicate that the HFBVI can effectively suppress the frequency band(4-8 Hz)to which the human body is sensitive to vertical vibration.In addition,under real random road spectrum excitation,the HFBVI can achieve low-frequency vibration isolation close to 2 Hz,providing new prospects for ensuring the health of heavy-duty truck drivers.展开更多
This study explores the aesthetic dimensions of Kwame Nkrumah＇s cultural policies in the creation of Ghana＇s Presidential Seats and the State Sword. The study is an Art Historical research situated within the qualit...This study explores the aesthetic dimensions of Kwame Nkrumah＇s cultural policies in the creation of Ghana＇s Presidential Seats and the State Sword. The study is an Art Historical research situated within the qualitative research paradigm. It had a population of a defmed class of cultural policy makers, art historians, traditional rulers, nationalists, visual artists and Ghanaians resident both in and outside Ghana. The study examined how the creation of Ghana＇s Presidential Seats and the State Sword were influenced by Kwame Nkrumah＇s cultural policies and the cultural significance of the aesthetic interplay of ethnic insignias used in capturing the Ghanaian concept of Political authority. The study revealed that, Nkrumah recognised the cultural art forms and elements of ethnic Ghana as assets for national development. In line with his policy of building the Nation State of Ghana, he used ethnic cultural art forms and elements. At independence, Nkrumah commissioned some visual artist to create some artistic pieces （politico-cultural artefacts） for the Ghanaian political authority with inspiration or based on what pertains in the traditional authority （Chieftaincy） of Ghana. Politico-cultural artefacts as used in this study refer to the artefacts produced based on the cultural concepts of the ethnic states for the use of the political authority of the Republic of Ghana. Among these artistic pieces are the three Presidential Seats, The State Sword, The President＇s Personal Standard Pole and the State Mace.展开更多
A high-temperature and high-pressure valve is the key equipment of a wind tunnel system;it controls the generation of high-temperature and high-pressure gas.To reduce the adverse impact of high-temperature and high-pr...A high-temperature and high-pressure valve is the key equipment of a wind tunnel system;it controls the generation of high-temperature and high-pressure gas.To reduce the adverse impact of high-temperature and high-pressure gas on the strength of the valve body,a cooling structure is set on the valve seat.This can significantly reduce the temperature of the valve body and valve seat.The effects of its structure on the cooling characteristics and stress of the valve seat are studied,and six main parameters that can completely describe the geometry of the cooling structure are proposed.The central composite design method is used to select sample points,and the multi-objective genetic algorithm(MOGA)method is used for optimal structural design.A modification method according to the main parameters for the valve seat is proposed.The results show that the cooling structure weakens the pressure-bearing capability of the valve seat.Among the six main parameters of the valve seat,the distance from the end face of the lower hole to the Z-axis and the distance from the axis of the lower hole to the origin of the coordinates have the most obvious effects on the average stress of the valve seat.An optimum design value is proposed.This work can provide a reference for the design of high-temperature and high-pressure valves.展开更多
This study presents the development of a Magnesium Alloy Seat Frame(MASF),supported by case studies from automotive original equipment manufacturers.The process covers integrated design,simulation,manufacturing,and te...This study presents the development of a Magnesium Alloy Seat Frame(MASF),supported by case studies from automotive original equipment manufacturers.The process covers integrated design,simulation,manufacturing,and testing,aiming to boost industry confidence in Mg alloy applications.A novel structural design is developed that integrates the headrest with the backrest,achieving a balance between lightweight performance and safety.Structural optimization is guided by stress–strain simulations under diverse conditions within a complete forward development process.Casting simulations are conducted to analyze process characteristics,resulting in a verified MASF yield rate exceeding 90%.The final 9.88 kg MASF represents a 24.6%(3.23 kg)weight reduction versus a steel seat.This research contributes to advancements in defect control technology for large die casting magnesium alloy parts and has broad implications for their application in automotive manufacturing.展开更多
Typically,seat or floor acceleration is used to evaluate the ride comfort of a high-speed train.However,the dynamic performance of the human body significantly differs from that of the floor.Therefore,using the car bo...Typically,seat or floor acceleration is used to evaluate the ride comfort of a high-speed train.However,the dynamic performance of the human body significantly differs from that of the floor.Therefore,using the car body floor and seat accelerations to calculate the ride comfort index of a high-speed train may not reflect the true feelings of passengers.In this study,a 3D human-seat-vehicle-track coupling model was established to investigate the ride comfort of highspeed train passengers.The seated human model,which considers the longitudinal,lateral,vertical,pitching,yawing,and rolling motions,comprises the head,upper torso,lower torso,pelvis,thighs,and shanks.The model parameters were determined using multi-axis excitation measurement data based on a genetic algorithm.Subsequently,the applicability of the small-angle assumption and natural modes of the human model is analyzed.Using the coupling system model,the vibration characteristics of the human-seat interaction surface were analyzed.The ride comfort of the high-speed train and human body dynamic performance were analyzed under normal conditions,track geometric irregularities and train meeting conditions.The results showed that the passenger seats in the front and rear rows adjacent to the window had a higher acceleration value than the others.The human backrest and seat pad connection points have higher vibration amplitudes than the car body floor in the human-sensitive frequency range,indicating that using the acceleration values on the floor may underestimate the discomfort of passengers.The ride comfort of high-speed trains diminishes in the presence of track geometric irregularities and when trains pass each other.When the excitation frequency of track geometry irregularities approached the natural frequency of the human-seat-vehicle system,ride comfort in high-speed trains decreased significantly.Moreover,using seat acceleration to evaluate passenger ride comfort overlooks the vibration characteristics of the human body.The transient aerodynamic force generated when the train meets can cause a larger car body roll and lateral motion at 2 Hz,which,in turn,decreases the passenger ride comfort.This study presents a detailed human-seat-vehicle-track coupling system that can reflect a passenger’s dynamic performance under complex operating conditions.展开更多
文摘In this study,it is aimed to develop a generic model which calculates the trajectory of the ejection seat from the jet aircraft,by taking into account the parameters that will affect the seat movement such as the seat’s launch speed,ejection direction,ejection angle,altitude of the aircraft,distance/height from the aircraft rudder and canopy,pilot and ejection seat weight.With the model algorithm proposed,the ejection seat trajectory model was developed on MATLAB.The ejection seat trajectory model is based on point mass trajectory mathematical model.In this study,an analytical study of the problem has been made for modeling the flight trajectory of the ejection seat after it has been ejected.Past studies were used as a basis for validation and simulation.By writing a generic MATLAB code,a user interface was developed and presented to the user as a module.This generic code that has been developed could be used for simulations by users in the future by revising it in accordance with their own job descriptions.
基金supported by the National Science and Technology Major Project under Grant Nos.2016ZX05042004 and 2017ZX05072the Joint Funds of the National Natural Science Foundation of China under Grant No.U1762104+2 种基金the Postgraduate Innovation Project Foundation under Grant No.YCX2019054the Fundamental Research Funds for the Central Universities under Grant No.20CX02306Athe Opening Fund of National Engineering Laboratory of Offshore Geophysical and Exploration Equipment。
文摘To achieve the secondary production in multistage fracturing wells of tight oil,milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later.In this paper,first of all,the working mechanism of milling tools for multistage fracturing ball seats was studied and a mechanical analysis model of single abrasive grain was established.Then,an experimental system for milling tools was developed,and the experimental tests of the flat,the blade,and the slope milling tool were conducted in order.Besides,the morphology of chips and the surface morphology of the workpiece after the experiment were analyzed.Also,the working performance of milling tools was evaluated from the perspectives of working safety,working efficiency,and wear resistance of the milling tool.The results show that the torque of the milling tool increases nonlinearly with the increase in the cutting depth of the abrasive grain and increases linearly with the increase in the cutting width.Also,the chips are irregular particles and the size is mainly from 10 to 50μm.So,the chips should be pumped up with a small pump pressure and a large displacement.Besides this,the cutting depths of the abrasive grains are from 216.20 to 635.47μm and the bottom surface of the milling tool should be eccentric to avoid the zero point of cutting speed.Furthermore,the torque of the slope milling tool is 23.8%larger than that of the flat milling tool,which is also 30.4%smaller than that of the blade milling tool.Compared with the flat milling tool,the working efficiency of the blade milling tool improves by 79.9%and the slope milling tool improves by 111.1%.Also,the wear resistance of the blade milling tool decreases by 102.7%,while the slope milling tool declines by 32.6%when compared with the flat milling tool.Therefore,the slope milling tool has the characteristics of moderate torque,stable working conditions,the highest working efficiency,and fine wear resistance,which is preferably used to mill multistage fracturing ball seats.This study provides a theoretical basis and guidance for milling multistage fracturing ball seats on-site and realizing production with a large diameter in later stages of multistage fracturing wells.
基金supported by the National Natural Science Foundation of China(No.12172226)。
文摘In this study,a human-sensitive frequency band vibration isolator(HFBVI)with quasi-zero stiffness(QZS)characteristics for heavy-duty truck seats is designed to improve the comfort of heavy-duty truck drivers on uneven roads.First,the analytical expressions for the force and displacement of the HFBVI are derived with the Lagrange equation and d'Alembert's principle,and are validated through the prototype restoring force testing.Second,the harmonic balance method(HBM)is used to obtain the dynamic responses under harmonic excitation,and further the influence of pre-stretching on the dynamic characteristics and transmissibility is discussed.Finally,the experimental prototype of the HFBVI is fabricated,and vibration experiments are conducted under harmonic excitation to verify the vibration isolation performance(VIP)of the proposed vibration isolator.The experimental results indicate that the HFBVI can effectively suppress the frequency band(4-8 Hz)to which the human body is sensitive to vertical vibration.In addition,under real random road spectrum excitation,the HFBVI can achieve low-frequency vibration isolation close to 2 Hz,providing new prospects for ensuring the health of heavy-duty truck drivers.
文摘This study explores the aesthetic dimensions of Kwame Nkrumah＇s cultural policies in the creation of Ghana＇s Presidential Seats and the State Sword. The study is an Art Historical research situated within the qualitative research paradigm. It had a population of a defmed class of cultural policy makers, art historians, traditional rulers, nationalists, visual artists and Ghanaians resident both in and outside Ghana. The study examined how the creation of Ghana＇s Presidential Seats and the State Sword were influenced by Kwame Nkrumah＇s cultural policies and the cultural significance of the aesthetic interplay of ethnic insignias used in capturing the Ghanaian concept of Political authority. The study revealed that, Nkrumah recognised the cultural art forms and elements of ethnic Ghana as assets for national development. In line with his policy of building the Nation State of Ghana, he used ethnic cultural art forms and elements. At independence, Nkrumah commissioned some visual artist to create some artistic pieces （politico-cultural artefacts） for the Ghanaian political authority with inspiration or based on what pertains in the traditional authority （Chieftaincy） of Ghana. Politico-cultural artefacts as used in this study refer to the artefacts produced based on the cultural concepts of the ethnic states for the use of the political authority of the Republic of Ghana. Among these artistic pieces are the three Presidential Seats, The State Sword, The President＇s Personal Standard Pole and the State Mace.
基金supported by the National Natural Science Foundation of China(No.52175067)the Zhejiang Key Research&Development Project(No.2021C01021)+1 种基金the Natural Science Foundation of Zhejiang Province(No.LY20E050016)the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation(CPSF)(No.GZC20241478)。
文摘A high-temperature and high-pressure valve is the key equipment of a wind tunnel system;it controls the generation of high-temperature and high-pressure gas.To reduce the adverse impact of high-temperature and high-pressure gas on the strength of the valve body,a cooling structure is set on the valve seat.This can significantly reduce the temperature of the valve body and valve seat.The effects of its structure on the cooling characteristics and stress of the valve seat are studied,and six main parameters that can completely describe the geometry of the cooling structure are proposed.The central composite design method is used to select sample points,and the multi-objective genetic algorithm(MOGA)method is used for optimal structural design.A modification method according to the main parameters for the valve seat is proposed.The results show that the cooling structure weakens the pressure-bearing capability of the valve seat.Among the six main parameters of the valve seat,the distance from the end face of the lower hole to the Z-axis and the distance from the axis of the lower hole to the origin of the coordinates have the most obvious effects on the average stress of the valve seat.An optimum design value is proposed.This work can provide a reference for the design of high-temperature and high-pressure valves.
基金supported in part by the project is supported partly by National Key Research and Development Program of China(no.2022YFB2503504)Chongqing Technology Innovation and Application Development Project(no.CSTB2022TIAD-DEX0011)China Scholarship Council.
文摘This study presents the development of a Magnesium Alloy Seat Frame(MASF),supported by case studies from automotive original equipment manufacturers.The process covers integrated design,simulation,manufacturing,and testing,aiming to boost industry confidence in Mg alloy applications.A novel structural design is developed that integrates the headrest with the backrest,achieving a balance between lightweight performance and safety.Structural optimization is guided by stress–strain simulations under diverse conditions within a complete forward development process.Casting simulations are conducted to analyze process characteristics,resulting in a verified MASF yield rate exceeding 90%.The final 9.88 kg MASF represents a 24.6%(3.23 kg)weight reduction versus a steel seat.This research contributes to advancements in defect control technology for large die casting magnesium alloy parts and has broad implications for their application in automotive manufacturing.
基金Supported by National Natural Science Foundation of China(Grant No.U1934203)Research and Development Project of Science and Technology of China Railway Corporation(Grant No.P2023T002)。
文摘Typically,seat or floor acceleration is used to evaluate the ride comfort of a high-speed train.However,the dynamic performance of the human body significantly differs from that of the floor.Therefore,using the car body floor and seat accelerations to calculate the ride comfort index of a high-speed train may not reflect the true feelings of passengers.In this study,a 3D human-seat-vehicle-track coupling model was established to investigate the ride comfort of highspeed train passengers.The seated human model,which considers the longitudinal,lateral,vertical,pitching,yawing,and rolling motions,comprises the head,upper torso,lower torso,pelvis,thighs,and shanks.The model parameters were determined using multi-axis excitation measurement data based on a genetic algorithm.Subsequently,the applicability of the small-angle assumption and natural modes of the human model is analyzed.Using the coupling system model,the vibration characteristics of the human-seat interaction surface were analyzed.The ride comfort of the high-speed train and human body dynamic performance were analyzed under normal conditions,track geometric irregularities and train meeting conditions.The results showed that the passenger seats in the front and rear rows adjacent to the window had a higher acceleration value than the others.The human backrest and seat pad connection points have higher vibration amplitudes than the car body floor in the human-sensitive frequency range,indicating that using the acceleration values on the floor may underestimate the discomfort of passengers.The ride comfort of high-speed trains diminishes in the presence of track geometric irregularities and when trains pass each other.When the excitation frequency of track geometry irregularities approached the natural frequency of the human-seat-vehicle system,ride comfort in high-speed trains decreased significantly.Moreover,using seat acceleration to evaluate passenger ride comfort overlooks the vibration characteristics of the human body.The transient aerodynamic force generated when the train meets can cause a larger car body roll and lateral motion at 2 Hz,which,in turn,decreases the passenger ride comfort.This study presents a detailed human-seat-vehicle-track coupling system that can reflect a passenger’s dynamic performance under complex operating conditions.
