Critical speed

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

Automotive composite driveshafts: investigation of the design variables effects

Abstract: Laminated composites, with their advantage of higher specific stiffness, gained substantiality in the field of torque carrying structures through many applications. Composite drive shafts offer the potential of lighter and longer life drive train with higher critical speed. In this study, finite element analysis performed to investigate the effects of fibers winding angle and layers stacking sequence on the critical speed, critical buckling torque and fatigue resistance. A configuration of a hybrid of one layer of carbon-epoxy (0o) and three layers of glass-epoxy (±45o, 90o) was used. The results show that, in changing carbon fibers winding angle from 0o to 90o, the loss in natural frequency is 44.5% and shifting from the best to the worst stacking sequence the DS loses 46.07% of its buckling strength, which gain the major concern over shear strength in DS design. The layers of ±45o angles are to be located far at inner side and that of cross-ply configuration located at top face with the 90o layer exposed to outside to increase the fatigue resistance, that the stacking sequence has an effect on fatigue properties.

Hydroelastic response of an ice sheet with a lead to a moving load

Abstract: The hydroelastic symmetric response of a floating ice sheet caused by a pressure moving either in the ice lead or on the infinite ice sheet with a crack (a lead of zero width) is investigated. The ice sheet is modeled as a viscoelastic thin plate. The water is of constant depth. The flow under the ice is potential and linear. A boundary integral method (BIM) for the flow under the ice is combined with the finite difference method for the ice plate with free-free edge conditions to solve the coupled problem of linear hydroelasticity. Numerical results for deflections and stress distributions are shown to agree well with the available results by others. The proposed approach can be applied to problems with different edge conditions and different positions of the load with respect to the lead. The ice responses are studied with respect to the speed of the load. The speed can be subcritical, critical, and supercritical with respect to the critical speed for a floating infinite elastic plate. The speeds of the load, which provide maximum deflection, maximum stress, and maximum wave-making resistance, are determined. All these speeds are different and greater than the critical speed for an infinite elastic plate. The effect of the ice thickness, lead width, and load properties on these speeds is discussed.

Optimum Weight Design of a Rotor Bearing System With Dynamic Behavior Constraints

Abstract: The constraints include restrictions on stresses, unbalance response, and/or critical speeds. The system dynamic behaviors are analyzed by the finite element method. The exterior penalty function method is used as the optimization technique to minimize the system weight. The system design variables are the cross-sectional areas of the shaft and the stiffnesses of the bearings. The example of a single spool rotor bearing system is employed to demonstrate the merits of the design algorithm

Rotor dynamics analysis and experiment study of the flywheel spin test system

Abstract: The strength study of the flywheel is important to the flywheel energy storage. The motor and bearing are the key challenges for the high-speed flywheel spin test device in vacuum. By using a small stiffness pivot-jewel bearing and a spring squeeze film damper as the lower support of the flywheel, a simple spin system was designed at a low cost and is suitable for longtime operation. The auxiliary sup- port at the top was not removed until the flywheel passed the first critical speed. The flywheel that kept its rigid state in sub-critical state was tested at the high speed without the top support. The dynamic model of the flywheel-bearing-damper was built by means of the La- grangian equation to calculate critical speeds, mode shapes and modal damping ratios at different speeds. The lower damper's effects on the modal damping ratios and forced vibration were discussed. The vibrations of the flywheel-bearing-damper system were measured at the different damping coefficients in the experiment. When the lower damper was adjusted to be overdamped, the flywheel ran up to 50000 r/min steadily, and the experimental result was in agreement with the theoretical assumption. The sub-critical rotor dynamics de- sign and pivot-jewel bearing proved to be good solutions to the spin test for the composite flywheel.