Application of Absolute Nodal Coordinate Formulation in Calculation of Space Elevator System

The space elevator system is a space tether system used to solve low-cost space transportation. Its high efficiency, large load, reusability and other characteristics have broad application prospects in the aerospace field. Most of the existing mechanical models are based on “chain-bar” and a lumped mass tether model, which cannot effectively reflect the flexible behaviour of the rope of space elevator system. To establish an accurate mechanical model, the gradient deficient beam elements of the absolute nodal coordinate formulation (ANCF) are used to build the mechanical model of the space elevator system. The universal gravitation and centrifugal force in the model are derived. The calculation results of the ANCF model are compared with the results of the finite element method (FEM) and lumped mass (LM) models. The results show that the calculation results of the ANCF method are not very different from the results of the FEM and LM models in the case of axial loading. In the case of lateral loading, the calculation results of the ANCF method are basically the same as the results of the FEM and LM models, but can better reflect the local flexible deformation of the space elevator rope, and have a better calculation stability than FEM. Under the same calculation accuracy, the ANCF method can use fewer elements, and the speed of convergence is faster than the FEM and LM models.

Adaptive Control of Space Robot Despinning Tumbling Target Using Flexible Brushes

A flexible brush mechanism is designed and mounted at the end of a seven-degree-of-freedom robotic arm to despin a tumbling target. The dynamics model of the flexible brush is established using the absolute nodal coordinate method (ANCF), and its contact collision with the solar wing of the tumbling target is analysed. The H ∞ optimal control is proposed for a seven-degree-of-freedom robotic arm during despinning of a tumbling target while ensuring the global robustness and stability. Simulations verify that the despinning strategy can successfully eliminate the rotation speed and is feasible and effective.

A new thin beam element with cross-section distortion of the absolute nodal coordinate formulation

A novel modelling approach to beams with thin cross-sections is proposed in the absolute nodal coordinate formulation (ANCF), where the Lagrange interpolating and curve fitting techniques of numerical analysis are utilized for construction of the thin beam cross-section contour. Although the slope vector with respect to the coordinate line on cross-section contour is not considered in nodal coordinates, the cross-section distortion could be adequately captured through selecting an appropriate degree of polynomial. The main advantages of the present ANCF thin beam element are that the computational costs are more inexpensive than the ANCF shell element due to less generalized coordinates, there is very small amount of input data because slope vectors of the cross-section are eliminated, and the cross-sectional stress distribution may always be continuous on account of the fact that the cross-section is not discretized into a set of finite elements. Moreover, the formulations of elastic forces and Jacobian of thin laminated composite beam are also derived based on the continuum mechanics. Finally, several examples including both static and dynamic problems are performed to verify the new element and meanwhile demonstrate its general characteristics.

Numerical Investigation of Dynamics of the Flexible Riser by Applying Absolute Nodal Coordinate Formulation

In this paper, the dynamics of the flexible riser are investigated based on the absolute nodal coordinate formulation (ANCF). The stiffness, generalized elastic force, external load, and mass matrixes of the element are deduced based on the principle of energy conversion and assembled with the finite element method. The motion equation of the flexible riser is established. The influence of the environmental load conditions on the flexible riser model is studied in the MATLAB environment. Moreover, the accuracy and reliability of the programs are verified for a beam model with theoretical solutions. Finally, the static and dynamic characteristics of the flexible riser are analyzed, systematically adopting the ANCF method, which in turn proves the effectiveness and feasibility of the ANCF. Therefore, the proposed method is a powerful scheme for investigating the dynamics of flexible structures with large deformation in ocean engineering.

Absolute Nodal Coordinate Formulations for Aeroelastic Analysis of Next-Generation Aircraft Wings

Future aircraft have a high aspect ratio wing (HARW). The low induced drag of the wing can reduce fuel consumption, which enables eco-friendly flight. HARW cannot be designed by using conventional linear aeroelastic analysis methods because it undergoes very flexible motion. Although absolute nodal coordinate formulations (ANCF) have been widely used for analyzing various flexible structures, their application to HAWR is limited because the derivation of the ANCF elastic force for wing cross section is difficult. In this paper, we first describe three ANCF-based beam models that address the difficulty. The three models have different characteristics. Second, an aeroelastic coupling between the beam models and a medium-fidelity aerodynamic model based on unsteady vortex lattice method (UVLM) is briefly explained. Especially, the advantage of ANCF in the aeroelastic coupling is emphasized. Finally, we newly compare the three ANCF-based models in structural and aeroelastic analyses. From the viewpoint of the convergence performance and calculation time, we found the best ANCF-based beam model among the three models in static structural and aeroelastic analyses, while the three models have comparable performances in dynamic structural and aeroelastic analyses. These findings contribute to the development of aeroelastic analysis framework based on ANCF and the design of next-generation aircraft wings.