A time integration method for analysis of dynamic systems using domain decomposition technique

This paper presents a precise and stable time integration method for dynamic analysis of vibration or multibody systems A total system is divided into several subsystems and then responses are calculated separately, while the coupling effect is treated equivalently as constant force during time steps By using iterative procedure to improve equivalent coupling forces, a precise and stable solution is obtained Some examples such as a seismic response and multibody analyses were carried out to demonstrate its usefulness

     

Dynamic simulation of wire rope with contact

We present a dynamic simulation of a wire rope involving both contacts with a winch drum and hydraulic systems using the finite element method. Rapid winch operation often causes disorderly winding of the wire rope, which is an important quality problem. Dynamic simulation is, therefore, required for design of the hydraulic winch system on construction machinery. The wire rope is modeled using by truss elements considering large displacement motion. The contact between the wire rope and the winch drum is modeled using by variable-length truss elements and bilinear spring elements. An improved Newton method is proposed for nonlinear dynamic analysis. Simulation results show that some lever operations result in rope looseness and intense pressure fluctuation. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Etsujiro Imanishi received his master degree in Mechanical Engineering from Ritsumeikan University, in 1981. He is working for KOBE STEEL, LTD. since 1981. He received his doctor degree in 1992. Dr. Imanishi’s research interests include dynamics of construction machinery, numerical analysis and multibody dynamics.     

Integrity against arbitrary feedback-loop failure in linear multivariable control systems

This paper is concerned with the integrity problem in linear multivariable control systems. System integrity is defined as the property whereby the closed-loop system remains stable against arbitrary feedback-loop failures.^§ Introducing a new class of matrices, called the U-matrix, necessary and sufficient conditions for integrity are established with a stable plant. The results show that integrity is ensured if and only if all principal minors of the return difference matrix or the sensitivity matrix are units, with the controller being stable. Some useful sufficient conditions for integrity are also derived by utilizing interesting properties of the U-matrix. In particular, many previously known results concerning integrity are unified and several are extended. Moreover, the set of all proper controllers ensuring integrity can be characterized with the U-matrix. Based on this characterization, a procedure for synthesizing a controller which ensures integrity, and attains desirable input-output responses with decoupling, is proposed.     

Determining quadratic weighting matrices to locate poles in a specified region

A new procedure of selecting weighting matrices in linear quadratic optimal control problems (LQ-problems) is proposed. In LQ-problems, the quadratic weights are usually decided on trial and error to get good responses. But using the proposed method, the quadratic weights are decided in such a way that all poles of the closed loop system are located in the desired region for good response as well as for stability. As the system constructed by this method has merits of an LQ-problem as well as a pole-assignment problem, this procedure will be useful for designing a linear feedback system.     

An experimental study of the acousto-elastic effect in a rolled plate of steel

The acousto-elastic effect in rolled steel is studied experimentally by transmitting ultrasonic transverse waves and measuring amplitudes of reflected echoes. A Y-cut quartz transducer with a frequency 4.8 MH_z and ultrasonic flaw detection equipment are used for generation and detection of waves, and three tensile specimens with different orientations are prepared from a rolled plate so as to ascertain an important role of its slight orthotropy. At first the variation of amplitude with the transducer direction is examined in the unstressed state, and the slight orthotropy of each specimen is determined quantitatively. Then the variation of amplitude with the tensile stress is examined in the elastic range. The results depend clearly on the orientation of each specimen, and rotation of polarization direction is affirmed in the specimen with an inclination 45° against the rolling direction. Quantitative discussions about the whole experimental results give the conclusion that the acousto elastic effect in this rolled plate obeys the relations which were proposed theoretically by one of the authors.     

Effects of mismatched smith controller on stability in systems with time-delay

Stability of systems with a Smith controller is studied by taking into account the possibility of mismatch between plants and controllers. A necessary and sufficient condition for a system to maintain its stability in the presence of small mismatch is obtained. It follows from the condition that, depending on the growth rate of plant uncertainty towards high frequency, a Smith controller should be designed so that the control system has sufficiently steep high-cut-off frequency response.