This paper analyzes the applications of four air terminal device（ATD）models（i.e.,the basic model,the box model,the N-point momentum model,the jet main region specification model）in computational fluid dynamics（CF...This paper analyzes the applications of four air terminal device（ATD）models（i.e.,the basic model,the box model,the N-point momentum model,the jet main region specification model）in computational fluid dynamics（CFD）simulation and their performance in case study.A full-scale experiment is performed in an environment chamber,and the measured air velocity and temperature fields are compared with the simulation results by using four ATD models.The velocity and temperature fields are measured by an omni-directional thermo-anemometer system.It demonstrates that the basic model and the box model are not applicable to complicated air terminal devices.At the occupant area,the relative errors between simulated and measured air velocities are less than 20% based on the N-point momentum model and the jet main region specification model.Around the ATD zone,the relative error between the numerical and measured air velocity based on the jet main region specification model is less than 15%.The jet main region specification model is proved to be an applicable approach and a more accurate way to study the airflow pattern around the ATD with complicated geometry.展开更多
A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper,which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic ch...A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper,which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magneticfield of the disc-type MR fluid damper is analysed by the finite element method ; the controllability of the disctype MR fluid damper on the dynamic behaviour of a rotor system ; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an over-hung disc. It is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil ; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery.展开更多
Underwater gliders are recent innovative types of autonomous underwater vehicles （AUVs） used in ocean exploration and observation. They adjust their buoyancy to dive and to return to the ocean surface. During the ch...Underwater gliders are recent innovative types of autonomous underwater vehicles （AUVs） used in ocean exploration and observation. They adjust their buoyancy to dive and to return to the ocean surface. During the change of altitude, they use the hydrodynamic forces developed by their wings to move forward. Their flights are controlled by changing the position of their centers of gravity and their buoyancy to adjust their trim and heel angles. For better flight control, the understanding of the hydrodynamic behavior and the flight mechanics of the underwater glider is necessary. A 6-DOF motion simulator is coupled with an unsteady potential flow model for this purpose. In some specific cases, the numerical study demonstrates that an inappropriate stabilizer dimension can cause counter-steering behavior. The simulator can be used to improve the automatic flight control. It can also be used for the hydrodynamic design optimization of the devices.展开更多
Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-mo...Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-moving state AUV navigating in head sea at high speed were studied. The mathematical model on longitudinal motion of the high-speed AUV in head sea was established with considering the hydrodynamic lift based on strip theory, which was solved to get the heave and pitch of the AUV by Gaussian elimination method. Based on this, computational fluid dynamics （CFD） method was used to establish the mathematical model of the unsteady viscous flow around the AUV with considering free surface effort by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and volume of fluid （VOF） model. The three-dimensional numerical wave in the computational field was realized through defining the unsteady inlet boundary condition. The motion forms of the AUV navigating in head sea at high speed were carried out by the program source code of user-defined function （UDF） based on dynamic mesh. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque, velocity, pressure and wave profile were got, which reflect well the real ambient flow field of the AUV navigating in head sea at high speed. The computational wave profile agrees well with the experimental phenomenon of a wave-piercing surface vehicle. The force law of the AUV under the impacts of waves was analyzed qualitatively and quantitatively, which provides an effective theoretical guidance and technical support for the dynamics research and shape design of the AUV in real complex environnaent.展开更多
Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, an...Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, analyzing and suppressing the MR-damper hysteresis effects, therefore, impose a great challenge. A quarter-vehicle MR-suspension model is formulated in conjunction with proposed hysteretic and mean MR-damper models, and the passive and semi-actively controlled MR-suspension systems are focused to investigate the influence of MR-damper force hysteresis. The semi-actively controlled MR-suspension employs the “on-off” control law in response to direction of the damper velocity, so as to generate the asymmetric damping force property form the symmetric MR-damper design. The results show that the MR-damping hysteresis yields serious transients and oscillations in responses for the semi-actively controlled MR-suspension than the passive MR-suspension due to the current-switching discontinuity, and would thus deteriorate the suspension performance. The undesired strong transients and oscillations in responses can be effectively suppressed by employing the proposed smooth technique without phase shift for modulating the command current discontinuity.展开更多
文摘This paper analyzes the applications of four air terminal device（ATD）models（i.e.,the basic model,the box model,the N-point momentum model,the jet main region specification model）in computational fluid dynamics（CFD）simulation and their performance in case study.A full-scale experiment is performed in an environment chamber,and the measured air velocity and temperature fields are compared with the simulation results by using four ATD models.The velocity and temperature fields are measured by an omni-directional thermo-anemometer system.It demonstrates that the basic model and the box model are not applicable to complicated air terminal devices.At the occupant area,the relative errors between simulated and measured air velocities are less than 20% based on the N-point momentum model and the jet main region specification model.Around the ATD zone,the relative error between the numerical and measured air velocity based on the jet main region specification model is less than 15%.The jet main region specification model is proved to be an applicable approach and a more accurate way to study the airflow pattern around the ATD with complicated geometry.
文摘A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper,which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magneticfield of the disc-type MR fluid damper is analysed by the finite element method ; the controllability of the disctype MR fluid damper on the dynamic behaviour of a rotor system ; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an over-hung disc. It is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil ; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery.
文摘Underwater gliders are recent innovative types of autonomous underwater vehicles （AUVs） used in ocean exploration and observation. They adjust their buoyancy to dive and to return to the ocean surface. During the change of altitude, they use the hydrodynamic forces developed by their wings to move forward. Their flights are controlled by changing the position of their centers of gravity and their buoyancy to adjust their trim and heel angles. For better flight control, the understanding of the hydrodynamic behavior and the flight mechanics of the underwater glider is necessary. A 6-DOF motion simulator is coupled with an unsteady potential flow model for this purpose. In some specific cases, the numerical study demonstrates that an inappropriate stabilizer dimension can cause counter-steering behavior. The simulator can be used to improve the automatic flight control. It can also be used for the hydrodynamic design optimization of the devices.
基金Project(2006AA09Z235)supported by the National High Technology Research and Development Program of ChinaProject(CX2009B003)supported by Hunan Provincial Innovation Foundation For Postgraduate,China
文摘Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-moving state AUV navigating in head sea at high speed were studied. The mathematical model on longitudinal motion of the high-speed AUV in head sea was established with considering the hydrodynamic lift based on strip theory, which was solved to get the heave and pitch of the AUV by Gaussian elimination method. Based on this, computational fluid dynamics （CFD） method was used to establish the mathematical model of the unsteady viscous flow around the AUV with considering free surface effort by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and volume of fluid （VOF） model. The three-dimensional numerical wave in the computational field was realized through defining the unsteady inlet boundary condition. The motion forms of the AUV navigating in head sea at high speed were carried out by the program source code of user-defined function （UDF） based on dynamic mesh. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque, velocity, pressure and wave profile were got, which reflect well the real ambient flow field of the AUV navigating in head sea at high speed. The computational wave profile agrees well with the experimental phenomenon of a wave-piercing surface vehicle. The force law of the AUV under the impacts of waves was analyzed qualitatively and quantitatively, which provides an effective theoretical guidance and technical support for the dynamics research and shape design of the AUV in real complex environnaent.
文摘Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, analyzing and suppressing the MR-damper hysteresis effects, therefore, impose a great challenge. A quarter-vehicle MR-suspension model is formulated in conjunction with proposed hysteretic and mean MR-damper models, and the passive and semi-actively controlled MR-suspension systems are focused to investigate the influence of MR-damper force hysteresis. The semi-actively controlled MR-suspension employs the “on-off” control law in response to direction of the damper velocity, so as to generate the asymmetric damping force property form the symmetric MR-damper design. The results show that the MR-damping hysteresis yields serious transients and oscillations in responses for the semi-actively controlled MR-suspension than the passive MR-suspension due to the current-switching discontinuity, and would thus deteriorate the suspension performance. The undesired strong transients and oscillations in responses can be effectively suppressed by employing the proposed smooth technique without phase shift for modulating the command current discontinuity.
