Real-time simulation of multibody systems with applications for working mobile vehicles

This dissertation describes an approach for developing a real-time simulation for working mobile vehicles based on multibody modeling. The use of multibody modeling allows comprehensive description of the constrained motion of the mechanical systems involved and permits real-time solving of the equations of motion. By carefully selecting the multibody formulation method to be used, it is possible to increase the accuracy of the multibody model while at the same time solving equations of motion in real-time. In this study, a multibody procedure based on semi-recursive and augmented Lagrangian methods for real-time dynamic simulation application is studied in detail. In the semirecursive approach, a velocity transformation matrix is introduced to describe the dependent coordinates into relative (joint) coordinates, which reduces the size of the generalized coordinates. The augmented Lagrangian method is based on usage of global coordinates and, in that method, constraints are accounted using an iterative process. A multibody system can be modelled as either rigid or flexible bodies. When using flexible bodies, the system can be described using a floating frame of reference formulation. In this method, the deformation mode needed can be obtained from the finite element model. As the finite element model typically involves large number of degrees of freedom, reduced number of deformation modes can be obtained by employing model order reduction method such as Guyan reduction, Craig-Bampton method and Krylov subspace as shown in this study The constrained motion of the working mobile vehicles is actuated by the force from the hydraulic actuator. In this study, the hydraulic system is modeled using lumped fluid theory, in which the hydraulic circuit is divided into volumes. In this approach, the pressure wave propagation in the hoses and pipes is neglected. The contact modeling is divided into two stages: contact detection and contact response. Contact detection determines when and where the contact occurs, and contact response provides the force acting at the collision point. The friction between tire and ground is modelled using the LuGre friction model, which describes the frictional force between two surfaces. Typically, the equations of motion are solved in the full matrices format, where the sparsity of the matrices is not considered. Increasing the number of bodies and constraint equations leads to the system matrices becoming large and sparse in structure. To increase the computational efficiency, a technique for solution of sparse matrices is proposed in this dissertation and its implementation demonstrated. To assess the computing efficiency, augmented Lagrangian and semi-recursive methods are implemented employing a sparse matrix technique. From the numerical example, the results show that the proposed approach is applicable and produced appropriate results within the real-time period.

Financial working capital - management and measurement

Unexpected changes in cash flow have started to occur more frequently after the financial crisis. The capital structures of companies have also changed, and financial flexibility as well as flexible asset management have therefore become more important. This thesis aims at presenting financial working capital management, a part of flexible asset management, as a possibility to gain financial flexibility and survive the changes. This thesis operates in the interface of corporate finance, strategic management and management accounting, and it has two main objectives: to examine financial working capital management and to develop measures of financial working capital. The research in this thesis has been conducted using archival research and design science. Qualitative comparative analysis and model building are used to formulate tools and strategies for financial working capital management. The tools are tested with simulations, case studies and statistical analysis. The empirical data is collected from companies listed in the Helsinki Stock Exchange. The results of this thesis indicate that there are several possible financial working capital management strategies. FOCAL matrix is created in the thesis to assist in the selection of a strategy. The results also imply that profitability can be improved by reducing financial working capital, which creates a need to change the financial working capital management strategy. Financial flow cycle, and its modification, is developed in this thesis to measure financial working capital. Financial working capital as a concept is presented in this thesis with an orientation towards the management view. New dimensions have also been produced to financial management and working capital management, while providing a holistic approach to financial flexibility. Financial working capital management strategies are presented to managers and practical tools are provided for decision-making.