The Wind-Induced Vibration Response for Tower Crane Based on Virtual Excitation Method
The Dynamics characteristic of Tower Crane is complicated under the wind excitation which complicates the wind-induced vibration response analysis. The random wind-induced response analysis of tower crane is presented based on finite element method and Virtual Excitation Method. The pulsating wind loads are changed into multiple-point correlation stationary excitation. This papers uses Davenport's wind speed spectrum which does not change with height, and considers multiple-point correlation of wind-induction. The Tower Crane is employed as a numerical example, the response spectra and Mean Square Root (RMS) of the tower crane is obtained by wind-induced vibration. The results indicate that the vibration of the tower crane has a large response in low frequency and the One-third Octave acceleration RMS is lower, the influences of the wind-induced vibration on comfort are analyzed.
Wind-induced tower crane vibration and safety evaluation
The maximum wind load direction of tower crane is considered to be perpendicular to its jib. The interference effects of its different segments and across-wind loads are ignored in traditional crane safety evaluation. This study proposes a general scheme for the safety evaluation of tower cranes under fluctuating wind loads. The wind coefficients of a full-scale model of a tower crane were calculated by computational fluid dynamics, and then the time history of wind loads, simulated through the autoregressive method, were applied to the finite element model of a tower crane. The results reveal that the maximum along-wind load direction deflected 30°–60°, and the mean ratio of the absolute value of the across-wind coefficient to the along-wind coefficient of the tower crane was 8.56%, which indicated that the across-wind loads should be taken into account in wind-resistant design. Comparing the wind-induced responses of four typical wind directions, the maximum displacement, the bending stress and the axial stress of the tower crane occurred in the positive direction. Furthermore, the maximum acceleration of the cat-head was 0.028 m/s2, which met the comfort requirements of the operator. Although the tower crane met the strength and static stiffness requirements of design rules, the maximum bending stress at the junctions between the jib and the slewing platform, the counterweight and the counter-jib, exceeded the allowable stress, and the first modal of the tower crane was excited. These results warrant considering the effect of fluctuating wind loads in the safety evaluation of a tower crane.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.