In this study,Inconel 738 alloy was diffusion bonded to a ferritic stainless steel.The effect of bonding temperature on the microstructural development across the joint region was investigated.Following the diffusion ...In this study,Inconel 738 alloy was diffusion bonded to a ferritic stainless steel.The effect of bonding temperature on the microstructural development across the joint region was investigated.Following the diffusion bonding,conventional characterization techniques such as scanning electron microscopy(SEM),energy dispersive X-ray(EDX) and microhardness were used to examine the interfacial microstructure.It was seen that bonding temperature was effective on the diffusion of Ni from Inconel 738 to ferritic stainless steel that affected the microstructure of the interface.Austenite phase was formed at the interface as a result of Ni diffusion from the Inconel 738 to the interface.展开更多
Some properties of hyperchaos are exploited by studying both uncou-pled and coupled CML. In addition to usual properties of chaotic strange attractors,there are other interesting properties, such as: the number of uns...Some properties of hyperchaos are exploited by studying both uncou-pled and coupled CML. In addition to usual properties of chaotic strange attractors,there are other interesting properties, such as: the number of unstable periodic pointsembedded in the strange attractor increases dramatically increasing and a large num-ber of low-dimensional chaotic invariant sets are contained in the strange attractor.These properties may be useful for regarding the edge of chaos as the origin of com-plexity of dynamical systems.展开更多
To increase the competition of the solar energy collection system, the size of the solar panel module during the manufacturing process is being increased continuously. As the size of the solar panel increases, the siz...To increase the competition of the solar energy collection system, the size of the solar panel module during the manufacturing process is being increased continuously. As the size of the solar panel increases, the size of the robot to handle the panel increased also. The change in scale of the robot inevitably results in the amplification of the adverse effect of the flexure. The main source of the flexure in the large scale solar cell panel handling system is the long and thin fork fingers of the hand and the solar cell panel. In addition, the belt-driven actuator system used by most of the large scale panel handling robot is another significant source of the vibration. In this paper, the flexible multi body dynamic model of a large scale solar cell panel handling robot, which is being designed and constructed with the help of Kyung Hee University, is developed. The belt-driven system in the robot is also modeled as flexible system and included in the robot to represent the actual vibrationcharacteristics of the actuator system.展开更多
Nanoparticles are generally characterized by their size,morphology and surface charge using such advanced microscopic techniques as SEM(scanning electron microscopy),TEM(transmission electron microscopy)and XRD(X-ray ...Nanoparticles are generally characterized by their size,morphology and surface charge using such advanced microscopic techniques as SEM(scanning electron microscopy),TEM(transmission electron microscopy)and XRD(X-ray diffraction).The average particle diameter,size distribution and charge affect the physical stability and the entire distribution of the nanoparticles.In this paper,the PKF(palm kernel fibre)nanofluid was prepared and characterized using TEM,SEM and XRD.The TEM results showed a mixture of different particle sizes with the lowest size measuring a diameter of 100 nm.The SEM showed particles of different shapes and distributions with some possible level of agglomerations.The stability of the nanofluid was evaluated using sedimentation by retention time and the spectrophotometric method.In the retention time method,the volume of the supernatant of the nanofluid sample was carefully measured using a 25 mL beaker and a pipette,and the solution was left for a period of time(two weeks),and then the supernatant was measured again.A constant volume supernatant was obtained though with little sedimentation,and that indicated a stable solution.UV-Vis(ultra aviolet-visible spectrophotometer)spectrum of the nanoparticles prepared with 0.01,0.02 and 0.03wt%concentrations were measured.The absorbance was measured with a start wavelength 230 nm and an end wavelength of 900 nm.The peak absorbance for each of the volume fractions was observed at 290,299 and 298 nm wavelengths by scanning.A quantum leap in wavelength above the listed range was an indication of instability at some point in the fluid.A good particle size correlation between the SEM,XRD and TEM measurements was observed.展开更多
For helping find out the cause of the extrusion wound of gear and the abnormal abrasion wear in the process of gear shaping, this disquisition studies the varying law of the cut-thickness of chips in gear shaping and ...For helping find out the cause of the extrusion wound of gear and the abnormal abrasion wear in the process of gear shaping, this disquisition studies the varying law of the cut-thickness of chips in gear shaping and deduces a set of formulas for it.展开更多
This paper presents an elasto-viscoplastic consistent tangent oper-ator (CTO) based boundary element formulation, and application for calculation ofpath-domain independent J integrals (extension of the classical J int...This paper presents an elasto-viscoplastic consistent tangent oper-ator (CTO) based boundary element formulation, and application for calculation ofpath-domain independent J integrals (extension of the classical J integrals) in non-linear crack analysis. When viscoplastic deformation happens, the effective stressesaround the crack tip in the nonlinear region is allowed to exceed the loading sur-face, and the pure plastic theory is not suitable for this situation. The concept ofconsistency employed in the solution of increment viscoplastic problem, plays a cru-cial role in preserving the quadratic rate asymptotic convergence of iterative schemesbased on Newton’s method. Therefore, this paper investigates the viscoplastic crackproblem, and presents an implicit viscoplastic algorithm using the CTO concept in aboundary element framework for path-domain independent J integrals. Applicationsare presented with two numerical examples for viscoplastic crack problems and Jintegrals.展开更多
DDGS high speed camera is an improved version of the multisparksystem.In this system the time delay and the frame interval can be set arbitrarilyfrom 5μs to 10000μs,and the intervals may be equal or not.The modified...DDGS high speed camera is an improved version of the multisparksystem.In this system the time delay and the frame interval can be set arbitrarilyfrom 5μs to 10000μs,and the intervals may be equal or not.The modified sparkgaps can provide point flashes that are small enough in size and strong enough in lightfor both dynamic caustics and dynamic photo-elasticity.In addition,this system canbe changed easily to observe the flow by schlieren method.Thus,this optical systemis suitable to investigate many dynamic problems in the fields of solid and fluidmechanics.展开更多
This article is devoted to the study of the propagations of the non-linear water waves on the shear flows. Assuming μ = kh is small and ε/μ~2 ～ 0 (1),and the base flow is uniformly sheared, the modified Boussinesq...This article is devoted to the study of the propagations of the non-linear water waves on the shear flows. Assuming μ = kh is small and ε/μ~2 ～ 0 (1),and the base flow is uniformly sheared, the modified Boussinesq equation is obtained.We calculate propagations of the single sohtary wave with vorticity Γ = 0, 】0 and【0. The influences of the vorticity are manifested. At the end examples of theinteractions of two solitary waves, moving in opposite and the same directions, aregiven. Besides the phase shift, there also occur second wavelets after head-on collision.展开更多
The distribution function and orientation tensor of fiber suspensions in wedge shaped flow field were computed . The results indicate that with time increasing, the fiber orient themselves to flow direction gradually....The distribution function and orientation tensor of fiber suspensions in wedge shaped flow field were computed . The results indicate that with time increasing, the fiber orient themselves to flow direction gradually. At the locations with same pole radii, the angle between fiber orientation and centerline, which occurs with the most probability, decreases with the pole angle increasing . At the locations with same pole angle, the angle between fiber orientation and centerline increases with the pole radii decreasing. The second order tensors get steady more quickly at the points where the velocity g radients are larger. At the locations with same pole angle, the steady values of orientation tensors are identical. At the locations with same pole radii is, streamline becomes flatter as the pole angle decreases.展开更多
This paper presents a high-accuratcy method for solving 2-D incompressible viscous N-S equations in tensor forms. A domain decomposition method was used to divide the computational domain into several regular blocks w...This paper presents a high-accuratcy method for solving 2-D incompressible viscous N-S equations in tensor forms. A domain decomposition method was used to divide the computational domain into several regular blocks with the overlapping grid in order to transfer data between sub-domains and to remove numerical singularity caused by domain decomposition. Using the method and algorithm presented above, the flow passing an ellipse was computed and the formation and evolution of the vortex shedding was successfully simulated.展开更多
Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction ...Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.展开更多
The bejavior of a bubble near a rigid structure was considered by using the local surface fitting method and the "jet prediction" method. The convergence difficulty caused by the abnormality of the elements ...The bejavior of a bubble near a rigid structure was considered by using the local surface fitting method and the "jet prediction" method. The convergence difficulty caused by the abnormality of the elements was overcome. The flow was numerically simulated by using the boundary-integral method on the assumption that the water was inviscid and incompressible, and the bubble gas obeyed the isoentropic rule. The evolution of the bubble was investigated by means of the mixed Euler-Lagrange method, and the Runge-Kutta method. The important behavior of the bubble, such as migration and jetting, was analyzed in several examples. And the solution of one period of the explosion bubble was obtained.展开更多
Scattering characteristics of liquid droplets spun off from a rotating disk edge are experimentally investigated. In the present research, aluminum disks are utilized and ethanol is employed for liquid. Scattering phe...Scattering characteristics of liquid droplets spun off from a rotating disk edge are experimentally investigated. In the present research, aluminum disks are utilized and ethanol is employed for liquid. Scattering phenomena of the droplets are captured by the high-speed digital camera. Frequency distribution of the droplet diameter is evaluated from these images and distributions of horizontal flying velocity and angle of the droplets were measured by PTV. Liquid filaments are stretched outward from the stagnant liquid layer by centrifugal force and skew complicatedly by aerodynamic force. Some peaks appear in the distribution of the scattered droplet diameter and they are origi- nated from large terminal droplets and small droplets generated from filamentwise breakup. Most of the scattered droplets fly slightly inside in the tangential direction of the disk edge. The droplets spun off from the thin disk scatter widely compared with that from the thick one.展开更多
The eigenfunctions in a stability problem of boundary-layer flow over a viscoelastic compliant wall were studied. Two categories of modes, TSI and CIFI, exist in the eigenvalue solutions. The eigenfunctions of flow-ba...The eigenfunctions in a stability problem of boundary-layer flow over a viscoelastic compliant wall were studied. Two categories of modes, TSI and CIFI, exist in the eigenvalue solutions. The eigenfunctions of flow-based TSI were investigated together with those in the flow over rigid wall, whereas the eigenfunctions of wall-based CIFI were compared with the wall functions in an individual wall without fluid constraint. The physical characteristics of the eigenmodes were discussed based on their eigenfunctions.展开更多
The mixing layer of fiber suspensions was simulated numerically with the spectral method and the fibers in the flow were traced individually with calculation. The corresponding experiments were made. The results show ...The mixing layer of fiber suspensions was simulated numerically with the spectral method and the fibers in the flow were traced individually with calculation. The corresponding experiments were made. The results show that the Stokes number of particles is the key parameter to determine the spatial distribution of fibers and the coherent structures control the orientation of fibers. Direct simulations of the motion of cylindrical particles were carried out via lattice Boltzmann method. It is found that the aspect ratio of particles has significant effects on the translation and rotation of the cylindrical particles. A new lattice Boltzmann method which is convenient to deal with the curved boundary is proposed.展开更多
The three-dimensional (3D) pairing process of coherent structures in a plane mixing layer was simulated numerically with the pseudo-spectral method. The behaviors of spanwise cup-shaped vortices, streamwise rib-shaped...The three-dimensional (3D) pairing process of coherent structures in a plane mixing layer was simulated numerically with the pseudo-spectral method. The behaviors of spanwise cup-shaped vortices, streamwise rib-shaped vortices and quadrupoles were obtained in terms of their iso-surfaces. The results show that three-dimensional structures are strongly influenced by the initial ampiitude of the 3D disturbance, and that in most cases the local pairing finishes in a roughly two-dimensional manner. In pairing region, the streamwise vortices are chaotic after pairing due to the breakdown of the engulfed ribs and especially the subsequent breakdown of the quadrupoles. The surviving ribs extend to the top (or bottom) of the paired vortices under the stretch of them. In addition, it is revealed that three dimensional vortices pairing can enhance the mixing of fluid. Finally, some patterns of numerical flow visualization are presented by computing the passive scalar.展开更多
文摘In this study,Inconel 738 alloy was diffusion bonded to a ferritic stainless steel.The effect of bonding temperature on the microstructural development across the joint region was investigated.Following the diffusion bonding,conventional characterization techniques such as scanning electron microscopy(SEM),energy dispersive X-ray(EDX) and microhardness were used to examine the interfacial microstructure.It was seen that bonding temperature was effective on the diffusion of Ni from Inconel 738 to ferritic stainless steel that affected the microstructure of the interface.Austenite phase was formed at the interface as a result of Ni diffusion from the Inconel 738 to the interface.
基金The project supported by the National Natural Science Foundation of China
文摘Some properties of hyperchaos are exploited by studying both uncou-pled and coupled CML. In addition to usual properties of chaotic strange attractors,there are other interesting properties, such as: the number of unstable periodic pointsembedded in the strange attractor increases dramatically increasing and a large num-ber of low-dimensional chaotic invariant sets are contained in the strange attractor.These properties may be useful for regarding the edge of chaos as the origin of com-plexity of dynamical systems.
基金supported by the Korean Ministry of Knowledge and Economics(10035218)
文摘To increase the competition of the solar energy collection system, the size of the solar panel module during the manufacturing process is being increased continuously. As the size of the solar panel increases, the size of the robot to handle the panel increased also. The change in scale of the robot inevitably results in the amplification of the adverse effect of the flexure. The main source of the flexure in the large scale solar cell panel handling system is the long and thin fork fingers of the hand and the solar cell panel. In addition, the belt-driven actuator system used by most of the large scale panel handling robot is another significant source of the vibration. In this paper, the flexible multi body dynamic model of a large scale solar cell panel handling robot, which is being designed and constructed with the help of Kyung Hee University, is developed. The belt-driven system in the robot is also modeled as flexible system and included in the robot to represent the actual vibrationcharacteristics of the actuator system.
文摘Nanoparticles are generally characterized by their size,morphology and surface charge using such advanced microscopic techniques as SEM(scanning electron microscopy),TEM(transmission electron microscopy)and XRD(X-ray diffraction).The average particle diameter,size distribution and charge affect the physical stability and the entire distribution of the nanoparticles.In this paper,the PKF(palm kernel fibre)nanofluid was prepared and characterized using TEM,SEM and XRD.The TEM results showed a mixture of different particle sizes with the lowest size measuring a diameter of 100 nm.The SEM showed particles of different shapes and distributions with some possible level of agglomerations.The stability of the nanofluid was evaluated using sedimentation by retention time and the spectrophotometric method.In the retention time method,the volume of the supernatant of the nanofluid sample was carefully measured using a 25 mL beaker and a pipette,and the solution was left for a period of time(two weeks),and then the supernatant was measured again.A constant volume supernatant was obtained though with little sedimentation,and that indicated a stable solution.UV-Vis(ultra aviolet-visible spectrophotometer)spectrum of the nanoparticles prepared with 0.01,0.02 and 0.03wt%concentrations were measured.The absorbance was measured with a start wavelength 230 nm and an end wavelength of 900 nm.The peak absorbance for each of the volume fractions was observed at 290,299 and 298 nm wavelengths by scanning.A quantum leap in wavelength above the listed range was an indication of instability at some point in the fluid.A good particle size correlation between the SEM,XRD and TEM measurements was observed.
文摘For helping find out the cause of the extrusion wound of gear and the abnormal abrasion wear in the process of gear shaping, this disquisition studies the varying law of the cut-thickness of chips in gear shaping and deduces a set of formulas for it.
基金The project supported by National Natural Science Foundation of China(9713008)Zhejiang Natural Science Foundation Special Funds No. RC.9601
文摘This paper presents an elasto-viscoplastic consistent tangent oper-ator (CTO) based boundary element formulation, and application for calculation ofpath-domain independent J integrals (extension of the classical J integrals) in non-linear crack analysis. When viscoplastic deformation happens, the effective stressesaround the crack tip in the nonlinear region is allowed to exceed the loading sur-face, and the pure plastic theory is not suitable for this situation. The concept ofconsistency employed in the solution of increment viscoplastic problem, plays a cru-cial role in preserving the quadratic rate asymptotic convergence of iterative schemesbased on Newton’s method. Therefore, this paper investigates the viscoplastic crackproblem, and presents an implicit viscoplastic algorithm using the CTO concept in aboundary element framework for path-domain independent J integrals. Applicationsare presented with two numerical examples for viscoplastic crack problems and Jintegrals.
文摘DDGS high speed camera is an improved version of the multisparksystem.In this system the time delay and the frame interval can be set arbitrarilyfrom 5μs to 10000μs,and the intervals may be equal or not.The modified sparkgaps can provide point flashes that are small enough in size and strong enough in lightfor both dynamic caustics and dynamic photo-elasticity.In addition,this system canbe changed easily to observe the flow by schlieren method.Thus,this optical systemis suitable to investigate many dynamic problems in the fields of solid and fluidmechanics.
基金The project supported by the National Natural Science Foundation of China
文摘This article is devoted to the study of the propagations of the non-linear water waves on the shear flows. Assuming μ = kh is small and ε/μ~2 ～ 0 (1),and the base flow is uniformly sheared, the modified Boussinesq equation is obtained.We calculate propagations of the single sohtary wave with vorticity Γ = 0, 】0 and【0. The influences of the vorticity are manifested. At the end examples of theinteractions of two solitary waves, moving in opposite and the same directions, aregiven. Besides the phase shift, there also occur second wavelets after head-on collision.
基金Project supported by the National Natural Science Foundation for Outstanding Youth of China. (Grant No: 19925210)
文摘The distribution function and orientation tensor of fiber suspensions in wedge shaped flow field were computed . The results indicate that with time increasing, the fiber orient themselves to flow direction gradually. At the locations with same pole radii, the angle between fiber orientation and centerline, which occurs with the most probability, decreases with the pole angle increasing . At the locations with same pole angle, the angle between fiber orientation and centerline increases with the pole radii decreasing. The second order tensors get steady more quickly at the points where the velocity g radients are larger. At the locations with same pole angle, the steady values of orientation tensors are identical. At the locations with same pole radii is, streamline becomes flatter as the pole angle decreases.
文摘This paper presents a high-accuratcy method for solving 2-D incompressible viscous N-S equations in tensor forms. A domain decomposition method was used to divide the computational domain into several regular blocks with the overlapping grid in order to transfer data between sub-domains and to remove numerical singularity caused by domain decomposition. Using the method and algorithm presented above, the flow passing an ellipse was computed and the formation and evolution of the vortex shedding was successfully simulated.
文摘Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.
文摘The bejavior of a bubble near a rigid structure was considered by using the local surface fitting method and the "jet prediction" method. The convergence difficulty caused by the abnormality of the elements was overcome. The flow was numerically simulated by using the boundary-integral method on the assumption that the water was inviscid and incompressible, and the bubble gas obeyed the isoentropic rule. The evolution of the bubble was investigated by means of the mixed Euler-Lagrange method, and the Runge-Kutta method. The important behavior of the bubble, such as migration and jetting, was analyzed in several examples. And the solution of one period of the explosion bubble was obtained.
文摘Scattering characteristics of liquid droplets spun off from a rotating disk edge are experimentally investigated. In the present research, aluminum disks are utilized and ethanol is employed for liquid. Scattering phenomena of the droplets are captured by the high-speed digital camera. Frequency distribution of the droplet diameter is evaluated from these images and distributions of horizontal flying velocity and angle of the droplets were measured by PTV. Liquid filaments are stretched outward from the stagnant liquid layer by centrifugal force and skew complicatedly by aerodynamic force. Some peaks appear in the distribution of the scattered droplet diameter and they are origi- nated from large terminal droplets and small droplets generated from filamentwise breakup. Most of the scattered droplets fly slightly inside in the tangential direction of the disk edge. The droplets spun off from the thin disk scatter widely compared with that from the thick one.
文摘The eigenfunctions in a stability problem of boundary-layer flow over a viscoelastic compliant wall were studied. Two categories of modes, TSI and CIFI, exist in the eigenvalue solutions. The eigenfunctions of flow-based TSI were investigated together with those in the flow over rigid wall, whereas the eigenfunctions of wall-based CIFI were compared with the wall functions in an individual wall without fluid constraint. The physical characteristics of the eigenmodes were discussed based on their eigenfunctions.
文摘The mixing layer of fiber suspensions was simulated numerically with the spectral method and the fibers in the flow were traced individually with calculation. The corresponding experiments were made. The results show that the Stokes number of particles is the key parameter to determine the spatial distribution of fibers and the coherent structures control the orientation of fibers. Direct simulations of the motion of cylindrical particles were carried out via lattice Boltzmann method. It is found that the aspect ratio of particles has significant effects on the translation and rotation of the cylindrical particles. A new lattice Boltzmann method which is convenient to deal with the curved boundary is proposed.
文摘The three-dimensional (3D) pairing process of coherent structures in a plane mixing layer was simulated numerically with the pseudo-spectral method. The behaviors of spanwise cup-shaped vortices, streamwise rib-shaped vortices and quadrupoles were obtained in terms of their iso-surfaces. The results show that three-dimensional structures are strongly influenced by the initial ampiitude of the 3D disturbance, and that in most cases the local pairing finishes in a roughly two-dimensional manner. In pairing region, the streamwise vortices are chaotic after pairing due to the breakdown of the engulfed ribs and especially the subsequent breakdown of the quadrupoles. The surviving ribs extend to the top (or bottom) of the paired vortices under the stretch of them. In addition, it is revealed that three dimensional vortices pairing can enhance the mixing of fluid. Finally, some patterns of numerical flow visualization are presented by computing the passive scalar.
