A fine pointing system for the large space telescope

The large space telescope (LST) developed by NASA requires ultrahigh pointing stability within 0.0005 arc sec rms. A fine guidance system is proposed to body-point the entire spacecraft within this limit. The spacecraft is modeled as a rigid body having reaction wheel actuators and subject to gravitational and magnetic disturbance torques. The fine guidance sensor is cluttered with electronic noise. The disturbance accommodation standard deviation optimal controller (DASOC) is designed to be optimal with respect to the transient and the steady state response to noise, whereas the steady state response to deterministic external torques is exactly zero. Compared with conventional controllers, the fine guidance system with the DASOC offers as much as a factor of 30 improvement in pointing stability, resulting in an optimal performance of nearly 0.0001 arc sec rms. Thus, the required pointing stability can easily be obtained, and a large margin remains for the compensation of possibile deteriorations

Symbolic vector/dyadic multibody formalism for tree-topology systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76159/1/AIAA-20780-671.pd

Control and optimization of semi-passively actuated multibody systems

The controlled multibody systems are under the consideration. At the lecture special emphasis is put on the study of underactuated and overactuated systems having different type of actuators (external powered drives, unpowered spring-damper like drives, etc.). Several questions are addressed about the role of inherent dynamics, and how much multibody system should be governed by external powered drives and how much by the systems inherent dynamics. The lecture consists of the following parts: introduction to the subject in question; mathematical statement of the optimal control problems that are suitable for modelling of controlled motion and optimization of semi-passively controlled multibody systems with different degrees of actuation; description of the methodology and the numerical algorithms for solution of control and optimization problems for semi-passively actuated multibody systems. The solutions of several optimal control problems for different kind of semi-passively actuated multibody systems are presented. Namely, the energy-optimal control of planar semi-passively controlled three-link manipulator robot, the energy-optimal control of closed-loop chain semi-passively actuated SCARA-like robot; optimization of the hydraulic and pneumatic drives of the multibody system modelled the human locomotor apparatus with above-knee prostheses, and others. Future perspectives in area of control and optimization problems of the semi-passively actuated multibody systems are discussed

A study on wear evaluation of railway wheels based on multibody dynamics and wear computation

The wear evolution of railway wheels is a very important issue in railway engineering. In the past, the reprofiling intervals of railway vehicle steel wheels have been scheduled according to designers' experience. Today, more reliable and accurate tools in predicting wheel wear evolution and wheelset lifetime can be used in order to achieve economical and safety benefits. In this work, a computational tool that is able to predict the evolution of the wheel profiles for a given railway system, as a function of the distance run, is presented. The strategy adopted consists of using a commercial multibody software to study the railway dynamic problem and a purpose-built code for managing its pre- and post-processing data in order to compute the wear. The tool is applied here to realistic operation scenarios in order to assess the effect of some service conditions on the wheel wear progression

Automated approach for optimizing dynamic systems

The optimal design of nonlinear dynamic systems can be formulated as a multicriteria optimization problem. On the basis of a multibody system model integral type objective functions are defined evaluating the dynamic behavior of the system under consideration. Multicriteria optimization methods reduce the problem to nonlinear programming problems which can be solved with standard algorithms like the SQP method. The gradients required for such an efficient optimization procedure are computed by solving, additional differential equations resulting from an adjoint variable approach. The whole design process can be highly automated by using computer algebra packages

Symbolic computer language for multibody systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76245/1/AIAA-20770-590.pd