Influence of counterbalance valve parameters on stability of the crane lifting system
In this paper, a model of the large crane lifting system has been developed in the AMESim environment. The comparison between the simulation results and the experimental data shows good agreement in both time and frequency domains, indicating the correctness of the model. Furthermore, the causes of pressure pulsations of the lifting system are described by means of dynamic simulation and experimental research. The analysis result indicates that the pressure pulsation of the lifting system is closely related to dynamic characteristic of the counterbalance valve, and stability of the system can be improved by means of the flow area of counterbalance valve with linear small gradient.
Motion analysis of a suspended mass attached to a crane
Abstract This paper presents a qualitative study of the pendulum motion of the load suspended from the jib of a crane. The objective is to investigate the effect of various jib motions on the trajectory of the suspended load. The system equations are formulated such that the mass of the load has no effect on the trajectory. Two types of jib slewing motion are studied independently: rotation of the jib about r-axis, rotation of the cab about the y -axis, and translation of the crane along the x -axis. Solving for the y -axis rotation and using state space plots show that the load motion is a two-dimensional motion which can be classified into three types: (1) limit cycles; (2) rotating plots; and (3) rotating non-symmetrical plots. In the absence of control and damping, the most favourable response is a limit cycle with small amplitudes in two angular directions. For a given cable length, this can be achieved by the use of a smooth velocity profile like a half-sine instead of a trapezoidal type. In the z -axis rotation, the load trajectory is generally the same for the two types of jib input profiles at high slewing speed. At a slower input speed, however, the half-sine gives smaller swing angle of the load. For the x -axis crane translation over a short distance, the pendulum motion of the load can be reduced substantially if the cable length is adjusted to suit the input. For a triangular input with acceleration time t a = 0.5 τ , where τ is the time of the travel, the cable length ( L ) must be such that the resulting period of swing ( T ) is equal to t a . For a trapezoidal input L must be such that T = ( τ - t a ).
Using Fuzzy-Delphi technique to determine the concession period in BOT projects
BOT projects are affected by several risks and uncertainties. One of the most important issues in this type of contract is to determine the length of concession period considering these uncertainties. The previous studies have developed several models to determine the concession period. However, the uncertainties are not taking into account in most of the previous works. Moreover, none of the previous researches has the capability to aggregate the opinions of different experts being involved in a project regarding the values of the uncertain input parameters. In this research, a Fuzzy-Delphi technique is implemented to determine the length of concession period considering uncertainties. Using the proposed Fuzzy-Delphi technique, the values of different uncertain factors affecting a BOT project is determined considering opinions of a group of experts. The NPV value is calculated considering the resulted aggregated values of uncertain input parameters. Finally, the concession period is determined using fuzzy approach. A case study is conducted to evaluate the performance of the proposed methodology. It is shown that the concession period is determined more effectively using the proposed approach.