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An efficient approximate expression for unsteady pipe flow with high- viscosity fluid

Description: An approximate first-order expression for modeling frequency-dependent friction of unsteady pipe flow with high-viscosity fluid has been deveoped with the method of nonlinear square integral optimum in the frequency domain. This simple expression of first-order lag elements is more accurate and efficient than others in both the frequency and domain domains and can be applied to calculations of both frequency and transient response of unsteady pipe flow for oil hydraulic systems.
Date: June 1996
Creator: Cai, Y.
Partner: UNT Libraries Government Documents Department

Vibration and stability of a group of tubes in crossflow

Description: This paper presents an unsteady flow theory for flow-induced vibration and instability of tube arrays in crossflow. It includes measurements of motion-dependent fluid forces, mathematical model, and experiments on nonlinear response of tube arrays. The unsteady flow theory can be used to provide answers to complex vibration problems in steam generators.
Date: December 31, 1995
Creator: Chen, S.S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

A review of dynamic characteristics of magnetically levitated vehicle systems

Description: The dynamic response of magnetically levitated (maglev) ground transportation systems has important consequences for safety and ride quality, guideway design, and system costs. Ride quality is determined by vehicle response and by environmental factors such as humidity and noise. The dynamic response of the vehicles is the key element in determining ride quality, while vehicle stability is an important safety-related element. To design a guideway that provides acceptable ride quality in the stable region, vehicle dynamics must be understood. Furthermore, the trade-off between guideway smoothness and levitation and control systems must be considered if maglev systems are to be economically feasible. The link between the guideway and the other maglev components is vehicle dynamics. For a commercial maglev system, vehicle dynamics must be analyzed and tested in detail. This report, which reviews various aspects of the dynamic characteristics, experiments and analysis, and design guidelines for maglev systems, discusses vehicle stability, motion dependent magnetic force components, guideway characteristics, vehicle/ guideway interaction, ride quality, suspension control laws, aerodynamic loads and other excitations, and research needs.
Date: November 1, 1995
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics of a stack/cable system subjected to vortex-induced vibration

Description: A model of a stack/wire system, wind-induced vibration of the stack based on an unsteady-flow theory, and nonlinear dynamics of the stack`s heavy elastic suspended cables was developed in this study. The response characteristics of the stack and cables are presented for different conditions. The dominant excitation mechanisms are lock-in resonance of the stack by vortex shedding and parametric resonance of suspended cables by stack motion at their support ends.
Date: December 31, 1995
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Chaotic dynamics of loosely supported tubes in crossflow

Description: By means of the unsteady-flow theory and a bilinear mathematical model, a theoretical study was conducted of the chaotic dynamics associated with the fluidelastic instability of loosely supported tubes. Calculations were performed for the RMS of tube displacement, bifurcation diagram, phase portrait, power spectral density, and Poincare map. Analytical results show the existence of chaotic, quasiperiodic, and periodic regions when flow velocity exceeds a threshold value. 38 refs., 15 figs., 2 tabs.
Date: July 1, 1991
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Chaotic vibrations of nonlinearly supported tubes in crossflow

Description: By means of the unsteady-flow theory and a bilinear mathematical model, a theoretical study is presented for chaotic vibrations associated with the fluidelastic instability of nonlinearly supported tubes in a crossflow. Effective tools, including phase portraits, power spectral density, Poincare maps, Lyapunov exponent, fractal dimension, and bifurcation diagrams, are utilized to distinguish periodic and chaotic motions when the tubes vibrate in the instability region. The results show periodic and chaotic motions in the region corresponding to fluid-damping-controlled instability. Nonlinear supports, with symmetric or asymmetric gaps, significantly affect the distribution of periodic, quasiperiodic, and chaotic motions of a tube exposed to various flow velocities in the instability region of the tube-support-plate-inactive mode.
Date: February 1, 1992
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics of a stack/cable system

Description: In this study, we developed a coupled model of wind-induced vibration of a stack, based on an unsteady-flow theory and nonlinear dynamics of the stack`s heavy elastic suspended cables. Numerical analysis was performed to identify excitation mechanisms. The stack was found to be excited by vortex shedding. Once lock-in resonance occurred, the cables were excited by the transverse motion of the stack. Large-amplitude oscillations of the cables were due to parametric resonance. Appropriate techniques have been proposed to alleviate the vibration problem.
Date: July 1, 1995
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Theory of Microwave Instability and Coherent Synchrotron Radiation in Electron Storage Rings

Description: Bursting of coherent synchrotron radiation has been observed and in fact used to generate THz radiation in many electron storage rings. In order to understand and control the bursting, we return to the study of the microwave instability. In this paper, we will report on the theoretical understanding, including recent developments, of the microwave instability in electron storage rings. The historical progress of the theories will be surveyed, starting from the dispersion relation of coasting beams, to the work of Sacherer on a bunched beam, and ending with the Oide and Yokoya method of discretization. This theoretical survey will be supplemented with key experimental results over the years. Finally, we will describe the recent theoretical development of utilizing the Laguerre polynomials in the presence of potential-well distortion. This self-consistent method will be applied to study the microwave instability driven the impedances due to the coherent synchrotron radiation. Over the past quarter century, there has been steady progress toward smaller transverse emittances in electron storage rings used for synchrotron light sources, from tens of nm decades ago to the nm range recently. In contrast, there is not much progress made in the longitudinal plane. For an electron bunch in a typical ring, its relative energy spread {sigma}{sub {delta}} remains about 10{sup -3} and its length {sigma}{sub z} is still in between 5 mm to 10 mm. Now the longitudinal emittance ({sigma}{sub {delta}}{sigma}{sub z}) becomes a factor of thousand larger than those in the transverse dimensions. In this paper, we will address questions of: How short a bunch can be? What is the fundamental limit? If there is a limit, is there any mitigation method? Since the synchrotron radiation is so fundamental in electron storage rings, let us start with the coherent synchrotron radiation (CSR).
Date: December 9, 2011
Creator: Cai, Y.
Partner: UNT Libraries Government Documents Department

A Multi-Bunch, Three-Dimensional, Strong-Strong Beam-Beam Simulation Code for Parallel Computers

Description: For simulating the strong-strong beam-beam effect, using Particle-In-Cell codes has become one of the methods of choice. While the two-dimensional problem is readily treatable using PC-class machines, the three-dimensional problem, i.e., a problem encompassing hourglass and phase-averaging effects, requires the use of parallel processors. In this paper, we introduce a strong-strong code NIMZOVICH, which was specifically designed for parallel processors and which is optimally used for many bunches and parasitic crossings. We describe the parallelization scheme and give some benchmarking results.
Date: May 11, 2005
Creator: Cai, Y. & Kabel, A. C.
Partner: UNT Libraries Government Documents Department

Dynamical Effects Due to Fringe Field of the Magnets in Circular Accelerators

Description: The leading Lie generators, including the chromatic effects, due to hard-edge fringe field of single multipole and solenoid are derived from the vector potentials within a Hamiltonian system. These nonlinear generators are applied to the interaction region of PEP-II to analyze the linear errors due to the feed-down from the off-centered quadrupoles and solenoid. The nonlinear effects of tune shifts at large amplitude, the synchro-betatron sidebands near half integer and their impacts on the dynamic aperture are studied in the paper.
Date: May 16, 2005
Creator: Cai, Y. & Nosochkov, Yu
Partner: UNT Libraries Government Documents Department

Beam-Beam Study on the Upgrade of Beijing Electron Positron Collider

Description: It is an important issue to study the beam-beam interaction in the design and performance of such a high luminosity collider as BEPCII, the upgrade of Beijing Electron Positron Collider. The weak-strong simulation is generally used during the design of a collider. For performance a large scale tune scan, the weak-strong simulation studies on beam-beam interaction were done, and the geometry effects were taken into account. The strong-strong simulation studies were done for investigating the luminosity goal and the dependence of the luminosity on the beam parameters.
Date: February 10, 2006
Creator: Wang, S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

Accelerator modeling system for the future

Description: Many computer programs and a variety of models exist for the design of accelerator lattices and the correction of errors. Many physicists contributed to this work by developing codes to suit a variety of machines. At present, we are integrating some of these codes into a unified framework to design and control any type of machine. We will refer to this system of interactive accelerator design, control, and analysis codes as the All-In-One Modeling system (AIM). This paper will explore the utilities of AIM for future accelerator modeling and control. As an example, we will describe a procedure to produce both a linear and a nonlinear model for SPEAR.
Date: December 1, 1994
Creator: Lee, M.; Cai, Y. & Tran, P.
Partner: UNT Libraries Government Documents Department

Wind induced vibration of a stack

Description: A stack supported by guy wires at four levels is subjected to large-amplitude oscillations when the wind speed is over 15 m/s. The excitation mechanisms are identified based on scoping calculations, analytical prediction using a finite element code, and observation of the stack/wire response. The stack is determined to be excited by vortex shedding. Once lock-in resonance occurs, the guy wires are excited by the transverse motion of the stack. Large-amplitude oscillations of the guy wires are due to parametric resonance. Several methods are recommended to alleviate vibrational problem for short-term and long-term solutions. A new stack which is modified based on the results of this study is not subjected to any unacceptable oscillations.
Date: December 1, 1992
Creator: Chen, S. S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

Wind induced vibration of a stack

Description: A stack supported by guy wires at four levels is subjected to large-amplitude oscillations when the wind speed is over 15 m/s. The excitation mechanisms are identified based on scoping calculations, analytical prediction using a finite element code, and observation of the stack/wire response. The stack is determined to be excited by vortex shedding. Once lock-in resonance occurs, the guy wires are excited by the transverse motion of the stack. Large-amplitude oscillations of the guy wires are due to parametric resonance. Several methods are recommended to alleviate vibrational problem for short-term and long-term solutions. A new stack which is modified based on the results of this study is not subjected to any unacceptable oscillations.
Date: January 1, 1992
Creator: Chen, S.S. & Cai, Y.
Partner: UNT Libraries Government Documents Department

Chaotic vibrations of tubes with nonlinear supports in crossflow

Description: By means of the unsteady flow theory and a bilinear mathematical model, a theoretical study is presented for chaotic vibrations associated with the fluidelastic instability of nonlinearly supported tubes in a crossflow. A series of effective tools, including phase portraits, power spectral density, Poincar'e maps, Lyapunov exponent, fractal dimension, and bifurcation diagrams, are utilized to distinguish periodic and chaotic motions when the tubes vibrate in the instability region. Results show periodic and chaotic motions in the region corresponding to the fluid damping controlled instability. Nonlinear supports, with symmetric or asymmetric gaps, significantly affect the distributions of periodic, quasiperiodic and chaotic motions of the tube with various flow velocity in the instability region of the TSP(tube-support-plate)-inactive mode.
Date: January 1, 1992
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Chaotic vibrations of tubes with nonlinear supports in crossflow

Description: By means of the unsteady flow theory and a bilinear mathematical model, a theoretical study is presented for chaotic vibrations associated with the fluidelastic instability of nonlinearly supported tubes in a crossflow. A series of effective tools, including phase portraits, power spectral density, Poincar`e maps, Lyapunov exponent, fractal dimension, and bifurcation diagrams, are utilized to distinguish periodic and chaotic motions when the tubes vibrate in the instability region. Results show periodic and chaotic motions in the region corresponding to the fluid damping controlled instability. Nonlinear supports, with symmetric or asymmetric gaps, significantly affect the distributions of periodic, quasiperiodic and chaotic motions of the tube with various flow velocity in the instability region of the TSP(tube-support-plate)-inactive mode.
Date: December 1, 1992
Creator: Cai, Y. & Chen, S. S.
Partner: UNT Libraries Government Documents Department

Chaotic vibrations of nonlinearly supported tubes in crossflow

Description: By means of the unsteady-flow theory and a bilinear mathematical model, a theoretical study is presented for chaotic vibrations associated with the fluidelastic instability of nonlinearly supported tubes in a crossflow. Effective tools, including phase portraits, power spectral density, Poincare maps, Lyapunov exponent, fractal dimension, and bifurcation diagrams, are utilized to distinguish periodic and chaotic motions when the tubes vibrate in the instability region. The results show periodic and chaotic motions in the region corresponding to fluid-damping-controlled instability. Nonlinear supports, with symmetric or asymmetric gaps, significantly affect the distribution of periodic, quasiperiodic, and chaotic motions of a tube exposed to various flow velocities in the instability region of the tube-support-plate-inactive mode.
Date: February 1, 1992
Creator: Cai, Y. & Chen, S. S.
Partner: UNT Libraries Government Documents Department

Fluid-damping-controlled instability of tubes in crossflow

Description: A mathematical model for fluid damping controlled instability of tubes presented in this paper is based on the unsteady flow theory. Motion dependent fluid forces are measured in a water channel. From the measured fluid forces, fluid stiffness and fluid damping coefficients, are calculated as a function of reduced flow velocity, oscillation amplitude, and Reynolds number. Once these coefficients are known, the mathematical model can be applied to predict structural instability due to fluid damping. Many cases are considered: single tube, twin tubes, tube row, triangular array, and square arrays. The results show the instability regions based on the fluid damping coefficients and provide the answers to a series of questions on fluid elastic instability of tube arrays in crossflow.
Date: November 1, 1997
Creator: Chen, S. S.; Cai, Y. & Srikantiah, G. S.
Partner: UNT Libraries Government Documents Department

Swamp plots for dynamic aperture studies of PEP-II lattices

Description: With a newly developed algorithm using resonance basis Lie generators and their evaluation with action-angle Poisson bracket maps (nPB tracking) the authors have been able to perform fast tracking for dynamic aperture studies of PEP-II lattices as well as incorporate lattice nonlinearities in beam-beam studies. They have been able to better understand the relationship between dynamic apertures and the tune shift and resonance coefficients in the generators of the one-turn maps. To obtain swamp plots (dynamic aperture vs. working point) of the PEP-II lattices, they first compute a one-turn resonance basis map for a nominal working point and then perform nPB tracking by switching the working point while holding fixed all other terms in the map. Results have been spot-checked by comparing with element-by-element tracking.
Date: June 1, 1995
Creator: Yan, Y.T.; Irwin, J.; Cai, Y.; Chen, T. & Ritson, D.
Partner: UNT Libraries Government Documents Department

Detector solenoid compensation in the PEP-II B-Factory

Description: The PEP-II experimental detector includes a strong 1.5 T solenoid field in the interaction region (IR). With the fringe fields, the solenoid extends over a range of 6 m. Additional complications are that (1) it is displaced longitudinally from the interaction point (IP) by about 40 cm, (2) neither beam is parallel to the solenoid axis, and (3) the solenoid overlaps a dipole and a quadrupole on either side of the IP. In each half IR the correction system includes a set of skew quadrupoles, dipole correctors and normal quadrupoles to independently compensate the coupling, orbit perturbation, dispersion and focusing effect produced by the solenoid. The correction schemes for the Low Energy Ring (LER) and for the High Energy Ring (HER) are described, and the impact on the dynamic aperture is evaluated.
Date: June 1, 1995
Creator: Nosochkov, Y.; Cai, Y.; Irwin, J.; Sullivan, M. & Forest, E.
Partner: UNT Libraries Government Documents Department

A review of dynamic stability of repulsive-force maglev suspension systems

Description: Vehicle dynamics and the need to satisfy ride quality requirements have long been recognized as crucial to the commercial success of passenger-carrying transportation systems. Design concepts for maglev systems are no exception. Early maglev investigators and designers were well aware of the importance of ride quality and took care to ensure that their designs would meet acceptable ride quality standards. In contrast, the dynamic stability of electrodynamic suspension (EDS) systems, which has obvious implications for system safety and cost as well as for ride quality, has not received nearly as much attention. Because of the well-known under-damped nature of EDS suspension systems and the observation of instabilities in laboratory-scale model systems, it is prudent to develop a better understanding of vehicle stability characteristics. The work reported in this was undertaken with the intention of summarizing information that has been accumulated worldwide and that is relevant to dynamic stability of repulsive-force maglev suspension systems, assimilating that information, and gaining an understanding of the factors that influence that stability. Included in the paper is a discussion and comparison of results acquired from some representative tests of large-scale vehicles on linear test tracks, together with analytical and laboratory-scale investigations of stability and dynamics of EDS systems. This paper will also summarize the R and D activities at Argonne National Laboratory (ANL) since 1991 to study the nature of the forces that are operative in an EDS system and the dynamic stability of such systems.
Date: July 1, 1998
Creator: Cai, Y. & Rote, D.M.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics of a stack/cable system subjected to vortex-induced vibration

Description: A model of a stack/wire system, wind-induced vibration of the stack based on an unsteady-flow theory, and nonlinear dynamics of the stack`s heavy elastic suspended cables was developed in this study. The response characteristics of the stack and cables are presented for different conditions. The dominant excitation mechanisms are lock-in resonance of the stack by vortex shedding and parametric resonance of suspended cables by stack motion at their support ends.
Date: August 1, 1997
Creator: Cai, Y. & Chen, S.S.
Partner: UNT Libraries Government Documents Department

Vibration and stability of two tubes in crossflow

Description: Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel, and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in crossflow can be predicted.
Date: August 1, 1997
Creator: Zhu, S.; Chen, S.S. & Cai, Y.
Partner: UNT Libraries Government Documents Department