Tomasz Krzyzynski

Application of the Pareto-optimal approach for selecting dynamic characteristics of seat suspension systems

In this paper, a method for selecting the dynamic characteristics of seat suspension systems is presented. The basic principle of such a method consists in the shaping of nonlinear seat suspension dynamic behaviour for the different requirements defined by machine operators. A combined optimisation procedure has allowed to find the Pareto-optimal system configuration with simultaneous minimisation of conflicted optimisation criteria: the suspended body acceleration and suspension travel. As an example of the proposed method, the seat with a viscous-elastic passive suspension is investigated and its vibro-isolation properties are shaped by the air-spring and shock-absorber force characteristics.

Control system synthesis of seat suspensions used for protection of working machine operators

This paper deals with a novel approach to the control system synthesis of semi-active and active seat suspensions. An original control strategy is discussed in order to increase the effectiveness of vibration isolators used for protection of working machines operators. As an example of the proposed control system design, the suspension systems with a magneto-rheological damper and a pneumatic spring are investigated using a laboratory experimental set-up with seated humans.

ON THE DYNAMICS AND CONTROL OF A GUIDEWAY UNDER A MOVING MASS

The paper deals with the dynamics and control of lightweight guideway structures subjected to a moving load. Firstly, a continuous finite beam under a moving mass is considered. The solution is obtained in the form of a Fourier series by generalisation of an approach by Kaczkowski (1963). Critical parameters of the load, i.e. the mass and the velocity, are determined and compared with results calculated by a finite element approach and a modal transformation. Secondly, a control concept is investigated. The aim is to minimise the follower deflection under the moving mass. Using the finite element approach static control schemes, a PID–controller and a controller that uses observer techniques are introduced. Measurements are carried out on an experimental set–up for comparison.

On some regularities in dynamic response of cyclic periodic structures

Abstract The paper deals with cyclic periodic structures modelling bladed disk assemblies of blades with friction elements for vibration damping. These elements placed between adjacent blades reduce the vibration amplitudes by means of dry friction resulting from centrifugal forces acting on the elements and relative displacements of the blades. However, the application of these friction elements results in an additional dynamical coupling which together with mistuning of some system parameters (e.g., blade eigenfrequency or contact parameters) may cause localization of vibration. In the present paper a linear approximation of such a system is investigated. The structure composed of cyclic periodic cells modelled each as a clamped-free beam interacting with each other by means of viscoelastic elements of complex stiffness is applied for dynamic system analysis. In case of free vibrations as well as in case of steady-state dynamic response to a harmonic pressure field, a perfect periodic structure and the structures with periodically mistuned parameters (blade eigenfrequencies and contact parameters) are studied. Some regularities in the dynamic response of the systems with mistuning have been noticed. Despite the fact that only a linear approximation has been used, the results and conclusions can be applied for models which describe the blade interaction in a nonlinear way.

Localization in Nonlinear Mistuned Systems with Cyclic Symmetry

In forced systems with cyclic symmetry localization can occur due toparameter uncertainties. Often, Monte-Carlo simulations are used to findregions, where the system response is sensitive to parameteruncertainties. These simulations require a large computation time.Therefore, an approximate method to calculate the envelopes of thefrequency response functions is developed in this paper. An example of anonlinear system with cyclic symmetry is a bladed disk assembly withfriction dampers. Friction dampers can be installed underneath the bladeplatforms of turbine blades. Due to dry friction and the relative motionbetween blades and dampers, energy is dissipated, which results in areduction of blade vibration amplitudes. By optimizing the mass of thefriction dampers, the best damping effects are obtained, which lead toan increase in the reliability of the turbine. In this paper, thecalculated response of a mistuned bladed disk assembly with frictiondampers is discussed. An approximate method is developed to calculatethe envelopes of the corresponding frequency response function forstatistically varying eigenfrequencies of the blades. Regions wherelocalization can occur with a high probability, are calculated by thismethod.

Shaping the vibro-isolation properties of horizontal seat suspension:

In this paper, an effective procedure of shaping the vibro-isolation properties of seat suspension system is presented. The simulation model is created to determine the dependence of evaluation criteria to the design parameters by means of which the system characteristics are formed. The developed optimisation procedure allows to find Pareto-optimal system configuration for the conflicted vibro-isolating criteria, i.e. the frequency weighted transmissibility factor used to evaluate dynamic seat comfort based on acceleration signals and the suspension travel. In order to optimise both the conflicted vibro-isolation criteria, a minimising of the transmissibility factor (primary criterion) is proposed taking into account the suspension travel that is transferred to a non-linear inequality constraint. The correctness of proposed procedure is evaluated using experimental research of the best solution of horizontal seat suspension. This research is performed using the passive system with optimal visco-elastic characteristics, which are selected especially for the well-defined input vibration. The satisfactory agreement of experimental and numerical results is obtained for the analysed vibration reduction system.

Inertial Sensors and Wavelets Analysis as a Tool for Pathological Gait Identification

The human gait analysis by using wavelets transform of signal obtained from six inertial ProMove mini sensors is proposed in this work. The angular velocity data measured by the gyro sensors were used to estimate the translational acceleration in the gait analysis. As a result, the flexion - extension of joint angles of the knees were calculated for healthy people and with impaired locomotion system. After measurements we propose to use one of wavelet transform (wavelet type) in order to analyze the signals, indicate a characteristic feature and compare them.

Modeling and vibration control of an active horizontal seat suspension with pneumatic muscles

In the following paper, the dynamic modeling of a horizontal seat suspension which uses pneumatic muscles for the purpose of active vibration control is discussed. An original control system structure is proposed in order to improve the vibro-isolation properties of a horizontal seat suspension system. The presented control system design is based on inverse models of the pneumatic muscles and the primary controller that calculates the desired active force. By using the configurable control algorithm developed in this paper, it is possible to achieve a significant reduction in vibrations transmitted into the human body with just a slight increasing of the suspension travel. The active seat shows improved performance over the passive system in the 1–10 Hz frequency range. The results presented in this paper are useful in selecting the horizontal vibration control system for improving the comfort of a drive.

VIBRATION CONTROL WITH SHUNTED PIEZOCERAMICS - THE ENERGY BALANCE

Abstract The paper presents the recent research on power and the energy balance in semi-active vibration control with shunted piezoceramics, where a negative capacitance circuit is involved. The work provides the general description of the piezoceramics as the power source element, which has the ability of converting the mechanical energy of the vibrating structure into the electrical energy, and by delivering it to the external shunt branch dissipates or generates the feedback reaction force damps the system.

Global Sensitivity Analysis of the Vibration Reduction System with Seated Human Body

The paper deals with the global sensitivity analysis for the purpose of shaping the vibroisolation properties of suspension systems under strictly defined operating conditions. The variance-based method is used to evaluate an influence of nonlinear force characteristics on the system dynamics. The proposed sensitivity indices provide the basis for determining the effect of key design parameters on the vibration isolation performance. The vibration transmissibility behaviour of an exemplary seat suspension system is discussed in order to illustrate the developed methodology.