| Study of Flexible multi-body dynamics (FMD) has been developed nearly 40 years. Theory of the FMD modeling still doesn't reach perfect condition and involves in difficult of farther breakthrough. Comparing with the modeling theory, studies of computational strategies and experiment technologies are more weakness. There are a lot of problems which wait for further more discussion.Based on modeling a condensed formulation of FMD problem, this paper makes a deep study of its analysis problem and presents subcycling algorthms, which are suitable for the FMD problem, based on the central difference method and the Newmark algorithm respectively. This will actively promote development of the FMD computational theory. Research of the FMD computational methods includes several contents as following.1?Applying the FEM method to discrete an arbitrary spatial flexible body, describing position of a point in the body by means of a float frame and measuring deformation of the body in a generalized mode coordinate style, a self-contained FMS formulation was established based on the second Lagrange equation. Separating the generalized variables to a group of independent variables and a group of dependent variables, a condensed FMS equation was established. Based on this result, Special problems, which exist in solution process of a FMS equation, are deeply analyzed. In order to deal with stiffness of the FMS differential equation, we proposed to modify the algorithms, which are frequently used in FMD problems, based on subcycling principles. Thereby, solution efficiency of the FMD problem can be enhanced and stiffness of the differential equation can be effectively managed at the same time.2?Based on the central difference method, separating unknown variables of the condensed FMS equation in larger cycling domain and smaller cycling domain and using different step sizes to integrate these variables, common update formula and sub-step update formula are carried out and a central-difference-based sub-cycling algorithm, which is suitable for FMD problems, was established. An integral approximation operator method is used for analyzing stability of the sub-cycling algorithm. It is proved that the algorithm can hold stable property only if the step sizes in each domain do not exceed their critical limits. Due to sub-step cycles of the central-difference-based sub-cycling algorithm are explicit processes, there is still error accumulation phenomenon in the algorithm. However, numerical examples indicate that the central-difference-based sub-cycling algorithm can enhance the computational efficiency greatly without intensely dropping of the precision.3?Also, based on the Newmark algorithm, modifying the sub-cycling by means of similar manner mentioned above, a Newmark-based sub-cycling, which is suitable for FMD problems, was presented. By means of checking energy balance status and changing the step sizes during the integral process, favourable stability of the sub-cycling can be preserved and reasonable numerical results can be obtained. Compared with the central-difference-based sub-cycling algorithm, the implicit iterative processes are performed whether in the common-update or in the sub-step-update. Accordingly, error accumulation phenomenon is eliminated during the numerical integrate process. Numerical examples indicate that the Newmark-based sub-cycling is more efficient and more precise than the central-difference-based sub-cycling algorithm.FMD theory has been largely applied in simulation of deploying process of artificial satellite mounted antennas. However, this application has not been expanded to design of mobile-mounted deployable antenna. This paper established FEM model, multi rigid body model and FMS model of a mobile-mounted deployable antenna. Comparing computational results from the FMS model with that from the FEM model and that from the multi rigid body model, we got some relative conclusions. These conclusions have a little reference values for further developing engineering application domain of the FMD theory.1?FEM model and FMS model of a large mobile-mounted deployable antenna were respectively established. FEM analysis and FMD analysis are separately performed for the two models. Comparison of the results illustrate that some differences exist between the FEM analysis and the FMD analysis during motion process of the antenna frame. The FEM analysis only got hold of deformation condition of the frame resulting from its deadweight and external loads during a large range motion. Time-domain deformation curve is continued, slippy and without fluctuate phenomenon. On the contrary, the FMD analysis reflected evidently that a small range oscillating deformation was produced due to motion inertia of the frame. And this oscillation also affected motion trajectory of the frame by contraries. This interaction exhibited coupling between large range motion and small range deformation of the frame. And this result is more according with actual condition of the frame during motion process.2?Deploying process of the antenna frame were analyzed by means of the multi rigid-bodies model and the FMS model respectively. A notable difference was displayed between the two results. Driving forces of frame deploying oil-cylinders, which were resulted from anti-dynamic analysis technique, revealed evident relativity between loads and locations. Rotation angle and deformation result from the FMS model are also according with actual phenomenon enough. On the contrary, Rotation angle and deformation result from the multi rigid-bodies model induced a bound exceeded phenomenon, which is unnatural. This result indicates that the multi rigid-bodies model is shortage for dynamic analysis of a large deployable flexible antenna. At the same time, to validate applicable property of the sub-cycling on a complicated FMS model, the Newmark integral and the Newmark-based sub-cycling were used to calculate dynamic response of the antenna, respectively. It shows that the subcycling algorithms can be used in a broad application area.3?Inverse uprighting process and circumrotating process of the antenna frame were analyzed by means of the multi rigid-bodies model and the FMS model respectively. Results showed that whether wind loads are taken into account, a startup oscillation phenomenon usually existed during the motion process due to large inertia and flexibility of the frame. During circumrotating service status, deformation oscillation displayed distinctive periodicity due to periodic variety of the wind loads. This periodic deformation conditions will induce a dropping precision of electromagnetism of the antenna system. This result informed us that the inertia and the external variational loads need to be sufficiently regarded for design of a large frame antenna. To satisfy enough reliability and precision of an antenna, structure of the frame need to be strengthened appropriately. |
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