In order to enhance the safety of the catapult launch of the carrier-based aircraft,the catapult launch multibody dynamic model is established aiming at the problem of off center catapult launch.The whole catapult pro...In order to enhance the safety of the catapult launch of the carrier-based aircraft,the catapult launch multibody dynamic model is established aiming at the problem of off center catapult launch.The whole catapult process including four stages which are buffering,tensioning,releasing and taxiing is taken into consideration and the body dynamics of the off-center catapult during each stage is analyzed.The catapult launch dynamic differences between the conditions only considering taxiing and that considering four stages are compared,and the effects of the different initial off center distances considering four stages on the attitude,landing gear load and acceleration of the carrier based aircraft during catapult launch are discussed.The results show that only considering taxiing may underestimate the dynamics of the carrier-based aircraft substantially.When taking four stages into consideration,the initial off-center distance has small influence on the aircraft dynamic characteristics during buffering and tensioning but has larger influence on that during releasing and taxiing.The increase of the off-center distance will cause the enhancement of the aircraft rolling and yawing,which may lead to the load difference between the left and right landing gears and the increase of the aircraft lateral acceleration.The establishment and simulation of the catapult launch multi body dynamic model founded on buffering,tensioning,releasing and taxiing provide reference for the carrier-based aircraft design and analysis of the catapult launch dynamics.展开更多
CBCT scanners have been widely used in angiography,radiotherapy guidance,mammography and oral maxillofacial imaging.To cut detector size,reduce manufacturing costs and radiation dose while keeping a reasonable FOV,the...CBCT scanners have been widely used in angiography,radiotherapy guidance,mammography and oral maxillofacial imaging.To cut detector size,reduce manufacturing costs and radiation dose while keeping a reasonable FOV,the flat panel detector can be placed off-center horizontally.This scanning configuration extends the FOV effectively.However,each projection is transversely truncated,bringing errors and artifacts in reconstruction.In this paper,a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK algorithm.Numerical simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method.A novel CBCT system for maxillofacial imaging is used for clinical test,which is equipped with an off-center small size flat panel detector.Results show that reconstruction accuracy is acceptable for clinical use,and the image quality appears sufficient for specific diagnostic requirements.It provides a novel solution for clinical CBCT system,in order to reduce radiation dose and manufacturing cost.展开更多
Recently,off-centering behavior has been discovered in a series of thermoelectric materials.This behavior indicates that the constituent atoms of the lattice displace from their coordination centers,leading to the loc...Recently,off-centering behavior has been discovered in a series of thermoelectric materials.This behavior indicates that the constituent atoms of the lattice displace from their coordination centers,leading to the locally distorted state and local symmetry breaking,while the material still retains its original crystallographic symmetry.This effect has been proved to be the root cause of ultralow thermal conductivity in off-centering materials,and is considered as an effective tool to regulate the thermal conductivity and improve the thermoelectric performance.Herein,we present a collection of recently discovered off-centering compounds,discuss their electronic origins and local coordination structures,and illuminate the underlying mechanism of the off-centering effect on phonon transport and thermal conductivity.This paper presents a comprehensive view of our current understanding to the off-centering effect,and provides a new idea for designing high performance thermoelectrics.展开更多
The situation of an off-center casing under non-uniform ground stress can occur in the process of drilling a salt-gypsum formation,and the related casing stress calculation has not yet been solved analytically. In add...The situation of an off-center casing under non-uniform ground stress can occur in the process of drilling a salt-gypsum formation,and the related casing stress calculation has not yet been solved analytically. In addition,the experimental equipment in many cases cannot meet the actual conditions and the experimental cost is very high. These comprehensive factors cause the existing casing design to not meet the actual conditions and cause casing deformation,affecting the drilling operation in Tarim oil field. The finite element method is the only effective method to solve this problem at present,but the re-modelling process is time-consuming because of the changes in the parameters,such as the cement properties,casing centrality,and the casing size. In this article,an artificial intelligence method based on support vector machine(SVM) to predict the maximum stress of an offcenter casing under non-uniform ground stress has been proposed. After a program based on a radial basis function(RBF)-support vector regression(SVR)(ε-SVR) model was established and validated,we constructed a data sample with a capacity of 120 by using the finite element method,which could meet the demand of the nine-factor ε-SVR model to predict the maximum stress of the casing. The results showed that the artificial intelligence prediction method proposed in this manuscript had satisfactory prediction accuracy and could be effectively used to predict the maximum stress of an off-center casing under complex downhole conditions.展开更多
In this investigation,a semi-numerical method based on Bernstein polynomials for solving off-centered stagnation flow towards a rotating disc is introduced.This method expands the desired solutions in terms of a set o...In this investigation,a semi-numerical method based on Bernstein polynomials for solving off-centered stagnation flow towards a rotating disc is introduced.This method expands the desired solutions in terms of a set of Bernstein polynomials over a closed interval and then makes use of the tau method to determine the expansion coefficients to construct approximate solutions.This method can satisfy boundary conditions at infinity.The properties of Bernstein polynomials are presented and are utilized to reduce the solution of governing nonlinear equations and their associated boundary conditions to the solution of algebraic equations.Graphical results are presented to investigate the influence of the rotation ratioαon the radial velocity,azimuthal velocity and the induced velocities.A comparative study with the previous results of viscous fluid flow in the literature is made.展开更多
文摘In order to enhance the safety of the catapult launch of the carrier-based aircraft,the catapult launch multibody dynamic model is established aiming at the problem of off center catapult launch.The whole catapult process including four stages which are buffering,tensioning,releasing and taxiing is taken into consideration and the body dynamics of the off-center catapult during each stage is analyzed.The catapult launch dynamic differences between the conditions only considering taxiing and that considering four stages are compared,and the effects of the different initial off center distances considering four stages on the attitude,landing gear load and acceleration of the carrier based aircraft during catapult launch are discussed.The results show that only considering taxiing may underestimate the dynamics of the carrier-based aircraft substantially.When taking four stages into consideration,the initial off-center distance has small influence on the aircraft dynamic characteristics during buffering and tensioning but has larger influence on that during releasing and taxiing.The increase of the off-center distance will cause the enhancement of the aircraft rolling and yawing,which may lead to the load difference between the left and right landing gears and the increase of the aircraft lateral acceleration.The establishment and simulation of the catapult launch multi body dynamic model founded on buffering,tensioning,releasing and taxiing provide reference for the carrier-based aircraft design and analysis of the catapult launch dynamics.
基金Supported by National Key Technology R&D Program of the Ministry of Science and Technology(No.2012BAI07B05)
文摘CBCT scanners have been widely used in angiography,radiotherapy guidance,mammography and oral maxillofacial imaging.To cut detector size,reduce manufacturing costs and radiation dose while keeping a reasonable FOV,the flat panel detector can be placed off-center horizontally.This scanning configuration extends the FOV effectively.However,each projection is transversely truncated,bringing errors and artifacts in reconstruction.In this paper,a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK algorithm.Numerical simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method.A novel CBCT system for maxillofacial imaging is used for clinical test,which is equipped with an off-center small size flat panel detector.Results show that reconstruction accuracy is acceptable for clinical use,and the image quality appears sufficient for specific diagnostic requirements.It provides a novel solution for clinical CBCT system,in order to reduce radiation dose and manufacturing cost.
基金supported by National Natural Science Foundation of China(52250090,52371208,51571007,51772012)the Beijing Natural Science Foundation(JQ18004),111 Project(B17002)L D Z appreciates the National Science Fund for Distinguished Young Scholars(51925101).
文摘Recently,off-centering behavior has been discovered in a series of thermoelectric materials.This behavior indicates that the constituent atoms of the lattice displace from their coordination centers,leading to the locally distorted state and local symmetry breaking,while the material still retains its original crystallographic symmetry.This effect has been proved to be the root cause of ultralow thermal conductivity in off-centering materials,and is considered as an effective tool to regulate the thermal conductivity and improve the thermoelectric performance.Herein,we present a collection of recently discovered off-centering compounds,discuss their electronic origins and local coordination structures,and illuminate the underlying mechanism of the off-centering effect on phonon transport and thermal conductivity.This paper presents a comprehensive view of our current understanding to the off-centering effect,and provides a new idea for designing high performance thermoelectrics.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.U1663205,51704191 and 51804194)the Shanghai Leading Academic Discipline Project(Grant No.S30106)+1 种基金the Shanghai Municipal Education Commission(Peak Discipline Construction Program)the Shanghai Sailing Program(Grant No.17YF1428000)。
文摘The situation of an off-center casing under non-uniform ground stress can occur in the process of drilling a salt-gypsum formation,and the related casing stress calculation has not yet been solved analytically. In addition,the experimental equipment in many cases cannot meet the actual conditions and the experimental cost is very high. These comprehensive factors cause the existing casing design to not meet the actual conditions and cause casing deformation,affecting the drilling operation in Tarim oil field. The finite element method is the only effective method to solve this problem at present,but the re-modelling process is time-consuming because of the changes in the parameters,such as the cement properties,casing centrality,and the casing size. In this article,an artificial intelligence method based on support vector machine(SVM) to predict the maximum stress of an offcenter casing under non-uniform ground stress has been proposed. After a program based on a radial basis function(RBF)-support vector regression(SVR)(ε-SVR) model was established and validated,we constructed a data sample with a capacity of 120 by using the finite element method,which could meet the demand of the nine-factor ε-SVR model to predict the maximum stress of the casing. The results showed that the artificial intelligence prediction method proposed in this manuscript had satisfactory prediction accuracy and could be effectively used to predict the maximum stress of an off-center casing under complex downhole conditions.
文摘In this investigation,a semi-numerical method based on Bernstein polynomials for solving off-centered stagnation flow towards a rotating disc is introduced.This method expands the desired solutions in terms of a set of Bernstein polynomials over a closed interval and then makes use of the tau method to determine the expansion coefficients to construct approximate solutions.This method can satisfy boundary conditions at infinity.The properties of Bernstein polynomials are presented and are utilized to reduce the solution of governing nonlinear equations and their associated boundary conditions to the solution of algebraic equations.Graphical results are presented to investigate the influence of the rotation ratioαon the radial velocity,azimuthal velocity and the induced velocities.A comparative study with the previous results of viscous fluid flow in the literature is made.
