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To establish the dynamic model of machine tool structure is an important means to assess the performance of the machine tool structure during the cutting process. It is necessary to study the dynamics of the machine tools in different configurations for the sake of analyzing the dynamic behavior of the machine tools in the entire workspace. In this paper, a robust approach is presented to build an efficient and reliable dynamic model to evaluate the position-dependent dynamics of the twin ball screw (TBS) feed system. First, the TBS feed system is divided into several components, and a finite element (FE) model is built for each component. Second, the Craig-Bampton method is proposed to reduce the order of the substructures. Third, a multipoint constraints (MPCs) method was introduced to model the mechanical joint substructures of the TBS system, and the spring-damper element (SDE) is employed to connect the condensation nodes. Finally, a series experimental tests and full-order FE analysis are conducted on the self-designed TBS worktable in the four positions to validate the effectiveness of the proposed dynamic model. The results show that the proposed approach evaluates accurately the position-dependent behavior of the TBS system. [ABSTRACT FROM AUTHOR]

The problem of modeling for the linear structure with nonlinear boundary conditions in a more efficient manner is considered by proposing a novel condensation modeling method. The key idea of the proposed method is to reduce the overall number of degrees-of-freedom (DOFs) for the nonlinear jointed structure being analyzed, which can be implemented in the following two steps. Firstly, linear DOFs of the structure are truncated via finite element model reduction by using the free-interface mode synthesis method, as numerical integration of governing equations of structures with large numbers of DOFs is always time-consuming. Secondly, nonlinear DOFs at the boundary interface are reduced via coordinate condensation, so as to further minimize the model size of the structure being analyzed and make the subsequent analysis computationally efficient and memory economical. The performance of the proposed condensation modeling method is validated via case studies focused on an experimental structure with adjustable boundary conditions. Comparative results demonstrate that the computational efficiency can be extremely improved while the accuracy is simultaneously guaranteed by using the proposed method to model the linear structure with nonlinear boundary conditions. [ABSTRACT FROM AUTHOR]

The dynamic properties of machine tools are frequently calculated by means of finiteelement (FE) models. Usually, in a first step, the structural components, such as machine bed, slides, columns, spindle housing, spindle, and work piece, are meshed. In a second step, these components are positioned relatively to each other and are connected by joints. Usually, the joints comprise a three-dimensional spring-damper element (SDE) and constraints that connect the SDE to adjacent structural components. Commercial FE programs do rarely offer insight into the underlying constraint equations. Rather, the constraints are realized by selecting the faces or nodes to connect and the type of constraint over a graphical user interface. Moreover, when insight into the underlying equations is offered, it is normally difficult to implement user-defined constraint equations. So far, literature lacks a coherent and in-depth description of constraints that are used for assembly of machine tool FE components. This drawback is addressed here. Different common constraints are revisited while particular focus is put on simulating moving machine axes. Common multipoint constraints (MFC) are supplemented by a shape function based node weighting. Thus, two new MFC are introduced, which improve model quality for ball screw joints (named node-to-beam (NB)-constraint) and lineal- guides (named RBE4-constraint). A three-axis milling machine serves as an application example for the different constraints. Simulation results are compared to experimentally derived results. Both, frequency response functions (FRF) and time-domain forced responses are considered. Showing reasonable correlation, the comparison of simulation and experiment indicates the validity of the constraints that have been introduced. [ABSTRACT FROM AUTHOR]

The paper presents an efficient and reliable implementation of numerical methods for constrained generalized eigenvalue problems, specialized for the modal analysis of linear elastic structures in a finite-element setting. The implementation, which takes into account the sparsity of the stiffness and mass matrices and the features of master-slave constraints, is based on open-source packages embedded in the finite-element code NOSA-ITACA. Numerical tests on historical building are performed, with the aims of calculating their vibration frequencies and mode shape vectors, comparing them to the results of a general purpose commercial code and assessing the accuracy of the tool developed. [ABSTRACT FROM AUTHOR]

The influence of interface reduction on the dynamics of flexible multibody systems has not been well investigated and the conventional multipoint constraints still suffer when applied to multibody systems. Here, we propose a novel approach to derive rigid and interpolation multipoint constraints exploiting the role of the reference conditions, used in the Floating Frame of Reference Formulation to cancel rigid body modes from the elastic field. Since the connection of the reference conditions to the multipoint constraints seems to be limited to the free-surface case, the proposed formulation combines the interface reduction problem to create a novel Component Mode Synthesis method able to work with any reference condition. Two case studies are presented to show the differences between models with different combinations of reference conditions and multipoint constraints. • Interface reduction including all types of reference conditions. • Same framework for rigid and interpolation multipoint constraints. • Interpolation multipoint constraints defined without dependent nodes. • New method to derive classic component modes including reference conditions and interfaces. • Planar and spatial applications. [ABSTRACT FROM AUTHOR]

Abstract: Two approaches are presented for extending the FETI-DP domain-decomposition-based iterative method to the solution of problems with Linear Multipoint Constraints (LMPCs). Both cases of arbitrary LMPCs and LMPCs generated by the mortar method for enforcing a weak continuity of the solution across non-matching finite element interfaces are considered. In the first approach, the LMPCs are addressed during the preconditioning step but enforced only at convergence. In the second approach, the LMPCs are enforced at each iteration through the solution of an auxiliary coarse problem. Both extended FETI-DP solvers are benchmarked on a parallel processor for a wide range of constrained structural mechanics problems. The obtained results reveal that both solvers are numerically scalable and complement each other from the memory and CPU performance viewpoints. [Copyright &y& Elsevier]

A number of key aspects of the three-dimensional finite element (FE) modelling of spline couplings for fretting and fatigue assessment are discussed. The primary issue addressed is the development of an efficient and accurate modelling technique for non-symmetric shaft loading of the couplings, which is an important mode of loading for fretting fatigue assessment. An improved method is presented for implementing an axial modification of the contact geometry, commonly referred to as barrelling, which is also important for fretting fatigue assessment of splines. [ABSTRACT FROM AUTHOR]