As most closed-loop multibody systems do not have independent generalized coordinates, their dynamic equations are differential/algebraic equations (DAEs). In order to accurately solve DAEs, a usual method is using generalized α-class numerical methods to convert DAEs into difference equations by differential discretization and solve them by the Newton iteration method. However, the complexity of this method is O(n 2 ) or more in each iteration, since it requires calculating the complex Jacobian matrix. Therefore, how to improve computational efficiency is an urgent problem. In this paper, we modify this method to make it more efficient. The first change is in the phase of building dynamic equations. We use the spatial vector note and the recursive method to establish dynamic equations (DAEs) of closed-loop multibody systems, which makes the Jacobian matrix have a special sparse structure. The second change is in the phase of solving difference equations. On the basis of the topology information of the system, we simplify this Jacobian matrix by proper matrix processing and solve the difference equations recursively. After these changes, the algorithm complexity can reach O(n) in each iteration. The algorithm proposed in this paper is not only accurate, which can control well the position/velocity constraint errors, but also efficient. It is suitable for chain systems, tree systems, and closed-loop systems.
KEYWORDSclosed-loop multibody systems, constrained multibody systems, differential/algebraic equation (DAE), efficient multibody algorithm, generalized α method, recursive multibody algorithm Int J Numer Methods Eng. 2019;118:181-208.wileyonlinelibrary.com/journal/nme One approach to solving DAEs is converting DAEs into index 1 or index 2 form equations. These equations are similar to ODEs and can be solved by ODE integration schemes, such as the Runge-Kutta method, 2,3 the Adams method, or the backward difference formulas method. 4 This approach is simple and could be very efficient. For example, the articulated-body algorithm (ABA) proposed by Featherstone 5,6 and the spatial operator algebra (SOA) proposed by Rodriguez et al 7-10 can reach O(n) complexity. With the application of the computer parallel technology, Featherstone 11,12 presented the divide-and-conquer algorithm (DCA), which promotes efficiency to the O(log(n)) complexity. Some other efficient algorithms can be found in the literature. [13][14][15][16][17][18] By converting the DAEs into ODEs, the above algorithms may be efficient in dealing with the closed-loop system, but it will cause serious position and velocity constraint violation problems and inaccurate results. 19 Although there are some methods to correct the constraint violation problems, such as the Baumgarte method, 19,20 the Moore-Penrose generalized inverse method, 21 and the geometrical projection method, 22 these methods may have some defects. For example, the Baumgarte method can only deal with small constraint violation problems, 23 and the Moore-Penrose generalized inverse me...