Research of multi-restriction energy management of solid rocket
In order to implement depleted shutdown and improve guidance precision in launching process of a solid rocket, the trajectory energy management approaches should be studied. First, the rocket inserting trajectory problem is described. The real velocity and the required velocity calculating model are given. Second, under the multi-restriction conditions, the spline energy management model is given. Third, required velocity is parameterized by a B-spline function. Take required velocity function to initial conditions, terminal conditions and process conditions, the energy management problem can be solved by an optimum approach. The optimum trajectory can be followed up with trajectory tracking control approach, and make the velocity vector track the required velocity vector. The simulation results show that the terminal and process restrictions are met.
An ascent guidance algorithm for the energy management of solid rockets.
Efficient energy management for the solid rocket is very important to exhaust excess energy and to meet the various terminal constraints. Based on the online planning of the velocity capability curve, a Double-arcs Energy Management (DAEM) guidance algorithm is proposed in this paper. In the DAEM, the velocity capability curve is designed with two tangential arcs. By using the elegant geometric characteristic of the arcs, the closed-loop guidance problem is transformed as a problem of solving a system of nonlinear equations about the parameters (radius and center position) of the two arcs, and the nonlinear equations can be solved in real time. The main advantages of this algorithm are that the height increment constraint, which is difficult to be satisfied in traditional energy management methods, can be satisfied theoretically, and the convergence of the solution of the DAEM is quadratic. The effectiveness and advantages of the proposed DAEM algorithm are demonstrated by simulations and comparisons with other energy management algorithms.
Complications of motility peg placement for porous hydroxyapatite orbital implants
Aim: To evaluate the complications associated with pegging of porous hydroxyapatite orbital implants. Methods: Complications associated with pegging were retrospectively reviewed from the charts of 100 of 133 patients with hydroxyapatite implantation from 1993 to 2000. Results: 48 (48%) of the 100 hydroxyapatite implanted patients who had undergone pegging were found to have problems with their pegs, including discharge (45.8%), peg falling out (20.8%), pyogenic granulomas (16.7%), popping peg (14.6%), hydroxyapatite visible around peg hole (8.3%), part of peg shaft visible (6.2%), peg drilled off centre (6.2%), peg drilled at an angle (4.2%), and excess movement of peg (4.2%). The standard peg fell out statistically more often than the peg and sleeve system (Yates's corrected χ2, p=0.038). There was a trend towards complications of the peg with use of a standard peg (versus sleeved peg) (p=0.226). Conclusions: There are several potential complications of pegging. Most complications are minor and can be managed successfully.