Critical speed

About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.

Parameters’ changing influence with different lateral stiffnesses on nonlinear analysis of hunting behavior of a bogie

Abstract: Conventionally a railway vehicle has stable motion in low speeds, when it reaches to high speeds stability changes to unstable form. The main purpose of this article is to show the authors' view of analytical investigation of bifurcation, nonlinear lateral stability and hunting behavior of rail vehicles in a tangent track. The paper includes nonlinear primary yaw dampers, and flange contact and also bogie existence. This study contains Bogoliubov method for the analysis. Linear and nonlinear critical speeds are obtained, and changing parameters' effect in differing the speeds with altered lateral stiffness in primary suspension system has been studied. General works about hunting phenomenon show that nonlinear critical speed is less than linear one.

Dimensionless modeling and nonlinear analysis of a coupled pitch–plunge–leadlag airfoil-based piezoaeroelastic energy harvesting system

Abstract: In this paper, an airfoil-based piezoaeroelastic energy harvesting system is proposed with an additional supporting device to harvest the mechanical energy from the leadlag motion. A dimensionless dynamic model is built considering the large-effective-angle-of-attack vibrations causing (1) the nonlinear coupling between the pitch–plunge–leadlag motions, (2) the inertia nonlinearity, and (3) the aerodynamic nonlinearity modeled by the ONERA dynamic stall model. Cubic hardening stiffness is introduced in the pitch degree of freedom for persistent vibrations with acceptable amplitude beyond the flutter boundary. The nonlinear aeroelastic response and the average power output are numerically studied. Limit cycle oscillations are observed and, as the flow velocity exceeds a secondary critical speed, the system experiences complex vibrations. The power output from the leadlag motion is smaller than that from the plunge motion, whereas the gap is narrowed with increasing flow velocity. Case studies are performed toward the effects of several dimensionless system parameters, including the nonlinear torsional stiffness, airfoil mass eccentricity, airfoil radius of gyration, mass of the supporting devices, and load resistances in the external circuits. The optimal parameter values for the power outputs from the plunge and leadlag motions are, respectively, obtained. Beyond the secondary critical speed, it is shown that the variations of the power outputs with those parameters become irregular with fluctuations and multiple local maximums. The bifurcation analysis shows the mutual transitions between the limit cycle oscillations, multi-periodic vibrations, and possible chaos. The influences of these complex vibrations on the power outputs are discussed.

Display control device and display control method

Abstract: PROBLEM TO BE SOLVED: To provide a display control device that allows a flexible and high-speed scroll operation while minimizing the load of reading huge amount of data, with a sense of distance SOLUTION: The display control device is provided with: an acquisition means 34 for acquiring data configuring predetermined information; a detection means 34 for detecting the scroll speed; a generation means 34 for calculating a moving speed when a frame is displayed, for each frame, based on the scroll speed, and for generating moving speed information based on the result; a determination means 34 for, based on the generated moving speed information and a predetermined visual recognition critical speed, determining whether the moving speed of the frame exceeds a visual recognition critical speed; and a display control means 34 for, when the moving speed of the frame does not exceed the visual recognition critical speed, controlling the acquisition means 34 to acquire the data configuring the predetermined information of the item, and for controlling the display to display the predetermined information when the frame is displayed on the display, and for, when the moving speed of the frame exceeds the visual recognition critical speed, controlling the display to display the predetermined image when the frame of the item is displayed on the display COPYRIGHT: (C)2011,JPO&INPIT

Magnetic Bearing Application by Time Delay Control

Abstract: In this paper a magnetic bearing system is designed for the suppression of rotor vibration. Magnetic bearing is able to support the shaft without mechanical contacts, and it is also able to control the rotational vibration. Magnetic bearing is composed of position sensors, a digital controller, actuating amplifiers, and electromagnets. In order to control the vibration of a magnetic bearing system effectively, Time Delay Control (TDC) is utilized. It proposes the design skill of an optimal controller when the system has the uncertainty, i.e. it has a difficulty in extracting the exact mathematical expressions, as well as it has external disturbances. The observer with the position information is utilized as a feedback signal for regulating the rotor whirling motion. Simulation is performed first to check the validation of the proposed controller in suppressing the rotor whirling. Experiments are followed to guarantee its usefulness in the rotor rig with a magnetic actuator. The vibrating suppression is co...