Dynamics Modeling and Simulation for Moving-mass Reentry Vehicle
With respect to hypersonic re-entry vehicle, by applying the Newton-Euler's method, the six-degrees of freedom(6-DOF) dynamical equations of moving mass for a re-entry vehicle are derived and the control mechanism is analyzed according to the dynamical equations. Under the environment of Matlab, the 6-DOF trajectory simulation is presented based on the dynamical equations considering the earth's rotation and non-spherosomes factors, the cross-range and down-range of the impact point cause by lateral movement of the moving masses are computed by simulation and the results validate the feasibility of moving mass control.
A design on moving-mass actuated reentry vehicle with predictive guidance law
A new predictive guidance law for moving-mass actuated reentry vehicle is presented in this paper. The proposed approach is based on the fact that lateral force is formed in a plane which is perpendicular to the reentry vehicle velocity. Particularly, the nominal impact point is defined as the impact point generated by zero lift trajectory. The virtual displacement is defined as the tiny change of the nominal impact point, which is caused by any instantaneous lateral force at the beginning of the trajectory. The optimal direction of the lateral force is obtained by the solution of optimal virtual displacement, in which the optimal virtual displacement should point to the target. The linear quadratic gauss (LQG) method and the analytical solution of the reentry trajectory are used in this guidance method. Simulation results demonstrate the effectiveness of the proposed method.
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.