Michal Hajžman

APPROACHES TO THE CREATION OF MULTIBODY MODELS OF THE VVER 1000 NUCLEAR REACTOR CONTROL ASSEMBLY

Multibody systems modelling and analysis are efficient tools utilizable in general tasks of nonlinear dynamics. One of the branches suitable for the application of multibody approaches is the modelling of nonlinear motion and dynamical analysis in nuclear engineering. The motion of important parts of nuclear reactors called control assemblies has to be analyzed. The purpose of these control systems is to control the power of a nuclear reactor and possibly to stop the reaction in case of an emergency state. With respect to different types of nuclear reactors, different control systems composed of various mechanical parts and transmissions can be distinguished. Generally, they can be simplified to the typical problem of a long thin rod moving through guide tubes and driven by a motor. Then the modelling approach depends on the chosen mode of operation, which can be operation (regulation) under normal conditions or a certain emergency state. The paper is focused on the control assembly of the VVER 1000 nuclear reactor. The VVER 1000 reactor is a pressurized water-cooled and water-moderated reactor consisting of a reactor pressure vessel with an interior structure and a reactor upper block with 61 control assembly drives. Under the vessel head with nozzles of the control assembly drives there is a block of protective tubes, which is above the core with 163 fuel assemblies. A moveable part of the control assembly, i.e. a rod control cluster assembly (this part is the necessary condition for stopping the nuclear reaction), is composed of a suspension bar, a spider and 18 long thin absorber rods. Two modular spatial multibody models of the LKP-M/3 control assembly of the VVER 1000 nuclear reactor were created in the alaska simulation tool and they differ in their kinematic scheme and in the number of contact positions. Both models are meant for the simulations of the control assembly moving parts drop. The first one is intended for the simulations of the rod control cluster assembly drop during the seismic event, where the total time of the drop is the significant measured and computed quantity, and the second one for investigating limit curves of deformations of fuel assembly guide tubes, at which the absorber rods still reach the lower part of the core.

Various Strategies of Elastic Forces Evaluation in the Absolute Nodal Coordinate Formulation

This paper deals with the description of the absolute nodal coordinate formulation (ANCF) which is suitable for the flexible bodies modelling considering large deformation. As it is shown for beam ANCF elements, this formulation leads to the nonlinear expression of elastic forces, which could be the main disadvantage of the ANCF. The evaluation of these forces can be done by numerical integration in each computational step or by analytical derivation with the help of a software for symbolic operations. The computational performance of various elastic forces evaluation strategies is investigated using a benchmark problem of falling flexible pendulum.

Complex Modelling and Dynamical Analysis of Parallel Cable Mechanisms

This paper deals with the modelling of flexible cables, which are parts of multibody systems. The common approaches suitable for the cable modelling are summarized. Force representation of a cable, a point-mass model and an absolute nodal coordinate formulation are discussed. The experimental results from the weight-fibre-pulley-drive mechanical system are used to compare possibilities of common modelling approaches. Then the widely used MSC.Adams software is employed for modelling the Quadrosphere mechanism, which contains flexible fibers. The results of dynamical analysis are presented.

Nonlinear Dynamics of the Car Driving System with a Sequential Manual Transmission

Sequential manual transmissions are the most common sources of various contacts and impacts especially in rally cars. Dynamics of such systems can be very interesting and can influence the overall dynamic performance of a whole car. Therefore, it is necessary to have proper tools for dynamical modelling of gearboxes. This paper deals with the modelling and dynamic analysis of a driving system of a real car with a sequential manual transmission. A complex computational model of the sequential gearbox was created and after verification it allows to study nonlinear behaviour of the whole driving system. Parametric studies can be performed in order to investigate various qualitative effects of chosen design elements, etc.

Influence of the mass of the weight on the dynamic response of the asymmetric laboratory fibre-driven mechanical system

Experimental measurements focused on the investigation of a fibre behaviour are performed on an assembled weigh-fibre-pulley-drive mechanical system. The fibre is driven with one drive and it is led over a pulley. On its other end there is a prism-shaped steel weight, which moves in a prismatic linkage on an inclined plane. An extra mass can be added to the weight. Drive exciting signals can be of a rectangular, a trapezoidal and a quasi-sinusoidal shape and there is a possibility of variation of a signal rate. Time histories of the weight position and of the force acting in the fibre are measured. The same system is numerically investigated by means of a multibody model. The influence of the mass of the weight on the coincidence of results of experimental measurements and simulations is evaluated. The simulations aim is to create a phenomenological model of a fibre, which will be utilizable in fibre modeling in the case of more complicated mechanical or mechatronic systems.

Basic Optimization Methodology for the Design of Friction Damping in Blade Shrouds

This paper is focused on the optimization of friction element parameters in blade shrouds for various types of excitation. In order to create and validate a proper modelling methodology an experimental stand and a numerical simulation of blades interaction by means of a friction element placed in the shrouds were prepared. Mathematical models are based on the finite element method combined with rigid bodies. The interaction of the friction element and blades is described by normal contact and tangential friction forces derived for particular geometrical parameters of the studied mechanical system. The models can be analyzed both in frequency domain (by the harmonic balance method) or in time domain (by the numerical integration). The results of the optimization of friction element parameters with respect to the bending vibration suppression are documented in the paper. Another contact modelling approach intended for more complex contact surfaces is based on the decomposition of a contact surface into a set of elementary areas and on the expression of contact and friction forces between these areas. All methodologies are implemented in the MATLAB system and the results for the chosen test cases are compared with the results obtained by a measurement or by the ANSYS software.© 2013 ASME

Multipoint Contact Approach to the Analysis of Interacting Flexible Bodies Vibration

The efficient method usable for the vibrational analysis of interacting flexible bodies is presented in this paper. It is motivated by the research of blades interaction in the framework of turbine bladed disks. The approach is based on the decomposition of a contact surface into a set of elementary areas and on the expression of contact and friction forces between these areas. The methodology is implemented in the MATLAB system and obtained results for the chosen test case are compared with the results obtained by the ANSYS software.

SENSITIVITY ANALYSIS OF THE INFLUENCE OF A TIRE CONTACT SURFACE SHAPE IN TROLLEYBUS VERTICAL DYNAMICS

Vertical dynamic properties of the SKODA 21 Tr low-floor trolleybus were investigated on an artificial test track when driving with a real vehicle and when simulating driving with a multibody model on a virtual test track. Driving on the artificial test track was aimed at determining the vertical dynamic properties of the real trolleybus, and on such basis, the computer trolleybus models were verified. Time histories and extreme values of the relative deflections of air springs are monitored. The influence of the tire radial characteristics is determined on the basis of measurements on contact surfaces of different shapes that are evaluated.