Pracownicy

Streszczenie:
This work derives and simulates a two-dimensional extension of the nonlinear Gao beam, by adding the cross-sectional shear variable, similarly to the extension of the usual Bernoulli-Euler beam into the Timoshenko beam. The model allows for oscillatory motion about a buckled state, as well as adds vertical shear of the cross sections, thus reflecting better nonlinear thick beams. The static model is derived from the principle of virtual elastic energy, and is in the form of a highly nonlinear coupled system for the beams transverse vibrations and the motion of the cross sections. The model allows for general distributive transversal and longitudinal loads and a compressive horizontal load acting on its edges.

The model is simulated numerically, using the dynamic version for better insight into the steady solutions. The terms that distinguish our numerical solutions from the solutions of the Gao beam, described in the literature, are highlighted. The numerical scheme and its characteristic finite element matrices allow us to obtain simulation results that demonstrate the type of vibrations of our extended and modified beam, and also the differences between these solutions and those of the Gao beam model.

Słowa kluczowe:
Gao beam, nonlinear vibration

Streszczenie:
An experimental and modelling study of the properties of a prototype layered beam with a core made of a non-Newtonian sand mixture is presented. The non-typical dilatant sand was covered with an elastic envelope that restricted its movement, which allowed us to pressurise the grains by evacuating the air from within the cover. By applying controlled underpressure, the compressed sand grains become jammed, which resulted in an increased stiffness and damping. This gives the possibility to attenuate vibrations of a cantilever in an adaptive manner. The experiment was performed for free vibrations and prescribed sinusoidal base motion, to demonstrate the possibility of tuning material parameters in a vast range. The experimental amplitude, frequency and damping capacity of the kinetic sand are discussed. An analytical model is proposed to verify how many parameters are necessary to describe the material behaviour. Based on the experimental results, a parameter identification of a custom rheological model is performed and practical simplifications reducing complexity of the problem are elaborated. The performed parameter identification is indispensable for the further development of potential control strategies for effective vibration abatement of dynamic systems using such types of alternative smart materials.

Słowa kluczowe:
Granular material,Damping,Dilatant sand,Identification,Control

Streszczenie:
This paper presents an efficient parallel computing strategy to solve large-scale structural vibration problems. The proposed approach utilises a novel direct method that operates using simplex-shaped space-time finite elements and allows for the direct decoupling of variables during the assembly of global matrices. The method uses consistent stiffness, inertia and damping matrices and deals with non-symmetric matrices. One significant advantage of this approach is that the computational cost remains unaffected by the bandwidth of the matrix in the traditional sense because only non-zero coefficients are retained. The speed of computations demonstrates a noticeable increase as the number of nodes and the problem's dimensionality grow. To demonstrate the effectiveness of the parallel space-time approach, a comparison with a sequentially executed code was conducted. The results indicate that the proposed method enables calculations at least 20 times faster than those achieved using the classical finite element method. Furthermore, the parallelisation algorithm was successfully implemented to solve a dynamics problem involving a large-scale, three-dimensional railway structure subjected to a moving load. Remarkably, the problem was solved in a reasonable amount of time using a relatively low-cost personal computer.

Słowa kluczowe:
Space-time, Finite element, Direct decoupling, Vibration, Moving load, Parallel algorithm

Streszczenie:
The elastic material properties which change momentarily and locally under the high deformation rate due to the movement of a wavefront are presented. The work contains mathematical formulation, semianalytical results, numerical formulations, and simulation results demonstrating the effectiveness of modifying the rheological properties of the elastic material upon shock load or contact with a rigid obstacle. While the semianalytical solutions can be obtained in a narrow time interval, numerical solutions allow us to track the process of wavefront reflections from edges. The effectiveness of reducing the physical quantities significant for impact in the presented examples reaches 30–70% of forces or accelerations, depending on the adopted criteria.

Streszczenie:
In this paper, we address the numerical aspects and implementation of a nonlinear viscoplastic model of the mechanical behaviour of brain tissue to simulate the dynamic responses related to impact loads which may cause traumatic injury. Among the various viscoelastic models available, we deliberately considered modifying the Norton–Hoff model in order to introduce non-typical viscoplastic softening behaviour that imitates a brain’s response just several milliseconds after a rapid impact. We describe the discretisation and three dimensional implementation of the model, with the aim of obtaining accurate numerical results in a reasonable computational time. Due to the large scale and complexity of the problem, a parallel computation technique, using a space–time finite element method, was used to facilitate the computation boost. It is proven that, after calibrating, the introduced viscoplastic-softening model is better suited for modelling brain tissue behaviour for the specific case of rapid impact loading rather than the commonly used viscoelastic models

Słowa kluczowe:
brain biomechanics, brain injury, mechanical properties of brain tissue, viscoplastic materials, numerical modelling, finite element method (FEM), dynamic response, acceleration, space–time FEM

Streszczenie:
A container partially filled with loose plastic granules was attached to the shovel of the snowboard to suppress large-amplitude lateral vibrations by dissipating energy through non-conservative multi-granule interactions. A custom laboratory stand allowed to evaluate the performance using a full-scale snowboard deck. The response of the system with a prototype granular dissipator was measured for free lateral vibrations of the initially deflected board and under prescribed sinusoidal base motion. The damping characteristics for different fill ratios of the container were obtained using a direct method of nonparametric identification. The applied Hilbert–Huang transform-based vibration analysis method gave more insight into the board’s damping performance than the logarithmic decrement analysis. The results show that using the granular dissipator with a predestined number of granules increases the damping capacity at large amplitudes but is less effective at small amplitudes. At best, the damping factor was 70% higher when the granular dissipator was used than when the board was damped only intrinsically.

Słowa kluczowe:
Vibration, Damping, Granular material, Dissipation, Hilbert transform, Bending

Streszczenie:
Due to the continuous deformations and irregularities of the surface of snow, alpine skis exhibit dynamic excitation, leading to drastic vibrations and decreased manoeuvrability. Therefore, attenuating these unwanted vibrations, while ensuring that the ski experience is not compromised, is an important challenge. The possibility of using granular material in a damping device is studied in this paper. A container that was partially filled with loose granules was fixed at the tip of an alpine ski to suppress vibrations by dissipating energy through collisions. The performance was verified experimentally by studying the transient response of a ski mounted in a horizontal cantilever orientation. Moreover, on-snow tests were performed. Different numbers of plastic granules were used as a dissipating material. To identify the nonlinear damping characteristics of the system, a Hilbert transform was used. In the laboratory test, the displacement amplitude decay was up to 16 percentage points higher when a granular dissipator was attached to the ski than without the damper. During field testing, acceleration amplitudes were 9% lower compared to the ski without the dissipator. This solution could possibly be adapted to other boardsports on a wide variety of terrain, including ground, water and snow.

Słowa kluczowe:
vibration damping, alpine ski, granular material, Hilbert transform, bending beam

Streszczenie:
We consider a theoretical analysis and experimental test of a sandwich beam, with a core layer made of controllable material that can change its properties over time. We show that this dynamically excited beam can be sequentially controlled to obtain higher amplitude attenuation and resistance to the amplitude growth in resonant ranges than when the smart beam parameters are constant over time. Numerical simulations were performed to study the possibility of shifting beam vibration frequency towards ranges distant from resonance. An experimental study on a layered beam consisting of two steel bars with a pneumatically controlled core made of pressurized granular material was considered. A simplified control was performed to detune the beam from the resonance frequencies and reduce the vibrations by 30% in simulations and 10% in experiment.

Słowa kluczowe:
smart material, granular structures, structural control, semi-active control, layered beam

Streszczenie:
This paper models, analyzes and simulates the vibrations of a nonlinear Gao beam that is subjected to a moving mass or a massless point-force. Such problems arise naturally in transportation systems such as trains or trams. The dynamics of the system as the mass or the force move on the beam are investigated numerically in the cases when the vibrations are about a buckled state, and in the cases when the mass is positive or vanishes. The simulations are compared to those of the Euler–Bernoulli linear beam and the differences are highlighted. It is seen that the linear beam may be used only when the loads are small, while the Gao beam allows for moderate loads. The simulations are based on a time-marching finite elements algorithm for the model that has been developed and implemented. The results of representative and interesting computer simulations are depicted. The existence of weak solutions of the model is established using a variational formulation of the problem and results about variational set-inclusions.

Słowa kluczowe:
dynamic vibrations, buckling of a Gao beam, moving point-load

Streszczenie:
A model for the dynamics of a Gao elastic or viscoelastic nonlinear beam that is subject to a horizontally moving vertical point-force is modeled and computationally studied. In particular, the behavior and vibrations of the beam as the mass is moving on it is investigated. Such problems arise naturally in transportation systems with rails. A time-marching finite element numerical algorithm for the problem is developed and implemented. Results of representative simulations are depicted and compared to the behavior of a linear Euler beam with a moving mass.

Słowa kluczowe:
Gao beam, moving inertial point load, Finite Element simulations, beam vibration

Streszczenie:
In this paper, a semi-active method to control the vibrations of twin beams connected at their tips by a smart damping element is investigated. The damping element can be made of a magnetorheological elastomer or a smart material of another type, for instance, vacuum packed particles. What is crucial is the ability to modify the storage and loss moduli of the damping block by means of devices attached directly to the vibrating structure. First, a simple dynamical model of the system is proposed. The continuous model is discretized using the Galerkin procedure. Then, a practical state-feedback control law is developed. The control strategy aims at achieving the best instantaneous energy dissipation of the system. Numerical simulations confirm its effectiveness in reducing free vibrations. The proposed control strategy appears to be robust in the sense that its application does not require any knowledge of the initial conditions imposed on the structure, and its performance is better than passive solutions, especially for the system induced in the first mode.

Słowa kluczowe:
Vibration control, Double-beam structure, Sandwich beam, Magnetorheological elastomer, Semi-active damping, Stabilization

Streszczenie:
Reducing displacements of a plate vibrating under a pair of masses traveling in opposite directions can be improved by adding a smart subsoil instead of a classical damping layer. We propose a material that acts according to the instantaneous state of the plate, i.e., its displacements and velocity. Such an intelligent damping layer reduces vertical displacements even by 40%–60%, depending on the type of load and the assumed objective function. Existing materials enable the application of the proposed layer in a semi-active mode. The passive mode can be applied with materials exhibiting direction-dependent viscosity.

Słowa kluczowe:
plate vibration, moving load, intelligent damping layer, semi-active damping

Streszczenie:
A Mindlin plate subjected to a pair of inertial loads traveling at a constant high speed in opposite directions along arbitrary trajectory, straight or curved, is presented. The masses represent vehicles passing a bridge or track plates. A numerical solution is obtained using the space-time finite element method, since it allows a clear and simple derivation of the characteristic matrices of the time-stepping procedure. The transition from one spatial finite element to another must be energetically consistent. In the case of the moving inertial load the classical time-integration schemes are methodologically difficult, since we consider the Dirac delta term with a moving argument. The proposed numerical approach provides the correct definition of force equilibrium in the time interval. The given approach closes the problem of the numerical analysis of vibration of a structure subjected to inertial loads moving arbitrarily with acceleration. The results obtained for a massless and an inertial load traveling over a Mindlin plate at various speeds are compared with benchmark results obtained for a Kirchhoff plate. The pair of inertial forces traveling in opposite directions causes displacements and stresses more than twice as large as their corresponding quantities observed for the passage of a single mass.

Słowa kluczowe:
Mindlin plate, mass moving at varying speed, arbitrary trajectory, inertial load, space–time finite element method

Streszczenie:
The paper deals with a control method for semi-active damping of a double beam system with a smart granular structure placed in a thin silicone envelope. The damping properties of the system are controlled pneumatically, by subjecting the granular material to underpressure at particular moments. A mathematical model of the layered beam with a granular damping structure is represented by the two degrees of freedom, modified Kelvin–Voigt model of two masses, a spring with controllable stiffness, and a viscous damper with a variable damping coefficient. The optimal control problem is posed, using the concept of switching of the parameters to increase the efficiency of suppressing the displacement׳s amplitude. The resulting control strategy was verified experimentally for free vibrations of a cantilever system. The research proved that the appropriate, periodic switching of the properties of the considered structure enables reducing the vibration more effectively than if the material is treated passively.

Słowa kluczowe:
Granular materials, Smart materials, Adaptive control, Vibration damping

Streszczenie:
In this paper, a control method to stabilize the vibration of adjacent structures is presented. The control is realized by changes of the stiffness parameters of the structure׳s couplers. A pulse excitation applied to the coupled adjacent beams is imposed as the kinematic excitation. For such a representation, the designed control law provides the best rate of energy dissipation. By means of a stability analysis, the performance in different structural settings is studied. The efficiency of the proposed strategy is examined via numerical simulations. In terms of the assumed energy metric, the controlled structure outperforms its passively damped equivalent by over 50 percent. The functionality of the proposed control strategy should attract the attention of practising engineers who seek solutions to upgrade existing damping systems.

Słowa kluczowe:
vibration, damping, smart materials, control, semi-active

Streszczenie:
A novel type of pneumatic device filled with granular material is proposed in the implementation of a switched control strategy to stabilize the vibration of slender structures. The analytically obtained control law for the airtight, elastic, granular coupler is implemented in a test structure with a relay-type control logic. In the experiment, the deformable granular coupler semi-actively damps an initially deflected pair of adjacent, aluminum beams. Two cases of initial excitation are considered, showing an improvement of up to 33 percent in vibration abatement efficiency compared to the passive case. Although this semi-active device is conceptually simple, its ease of operation and low cost should attract the attention of engineers who seek solutions that can be used to build new structures and upgrade existing ones.

Streszczenie:
A control method to stabilize vibration of a double cantilever system with a set of smart damping blocks is designed and numerically evaluated. The externally controlled magnetorheological sheared elastomer damping block is considered, but other smart materials can be used as well. The robust bang-bang control law for stabilization the bilinear system is elaborated. The key feature of the closed loop controller is the efficiency for different types of initial excitement. By employing the finite element model, the performance of the controller is validated for strong wind blow load and concentrated impact excitement of the particular point of one of the beams. For each of the excitations, the closed loop control outperforms the optimal passive damping case by over 27% for the considered energy metric.

Streszczenie:
The paper deals with the semi-active control of vibrations of structural elements. Elastomer composites with ferromagnetic particles that act as magnetorheological fluids are used. The damping coefficient and the shear modulus of the elastomer increases when it is exposed to an electro-magnetic field. The control of this process in time allows us to reduce vibrations more effectively than if the elastomer is permanently exposed to a magnetic field.

First the analytical solution for the vibrations of a sandwich beam filled with an elastomer is given. Then the control problem is defined and applied to the analytical formula. The numerical solution of the minimization problem results in a periodic, perfectly rectangular control function if free vibrations are considered. Such a temporarily acting magnetic field is more efficient than a constantly acting one. The surplus reaches 20–50% or more, depending on the filling ratio of the elastomer. The resulting control was verified experimentally in the vibrations of a cantilever sandwich beam.

The proposed semi-active control can be directly applied to engineering vibrating structural elements, for example helicopter rotors, aircraft wings, pads under machines, and vehicles.

Słowa kluczowe:
Semi-active control, Beam vibration, Magnetorheological elastomer, Sandwich beam, Damping

Streszczenie:
This paper presents the strategy of semi-active damping of vibrations of a beam span subjected to a moving load. Intermediate supports as controlled dampers significantly decrease transverse displacements in comparison with a system with permanently active dampers. The gain can reach 40% in the case of high speed loads. In a real structure with a load moving at 3 m/s, considered in this paper, the improvement is about 10%. The control is determined by a minimization procedure. Numerical simulations are confirmed experimentally on a stand with a length of 4 m. Controlled dampers can be replaced with an intelligent material. The potential applications are in transport or robotics.

Słowa kluczowe:
Moving inertial load, Intelligent adaptive control, Semi-active damping, Beam vibration

Streszczenie:
An experimental study of the properties of a layered beam partially treated with a damping element based on a granular material is presented. The beam structure comprises two aluminium face strips connected at the tip by a hermetic, elastic envelope, filled with bulk granules. Changing the underpressure value inside the airtight envelope allows variation of the mechanical properties of such a complex system, like stiffness or damping coefficients. Four types of granules, different in size, shape, and material, were examined to find the most promising one. A detailed discussion of the experimental amplitude, frequency, and damping capacity of the cantilever is given. The Zener, Kelvin–Voigt, and classic Maxwell models were employed for modelling and parameter identification. The range of applicability and limitations of the proposed solution has been given, as well as the benefits from the application.

Słowa kluczowe:
Granular materials, smart materials, vibrations

Streszczenie:
We demonstrate that the dynamic simulation of a vehicle moving on a track requires the correct mass distribution in the wheel–rail system. A wheel travelling on a rail should be modelled as a pair of masses coupled as a double mass oscillator. One of the masses is attached to the rail and carries the moving inertial load, while the second one is treated classically, being connected to the rail only through an elastic spring. This model is called the ‘mass splitting model’. The classical approach overestimates the accelerations by a factor of 10. The presented method produces displacements and velocities which agree well with the results of a precise finite element method and with measurements. Some real-life problems of a vehicle moving on a track at high speed are solved numerically by own computer program and the results are compared with measurements and with the solutions obtained using other codes.

Słowa kluczowe:
moving mass, numerical mass modelling, wheel–rail interaction

Streszczenie:
The present paper solves numerically the problem of vibrations of infinite structures under a moving load. A velocity formulation of the space–time finite element method was applied. In the case of simplex shaped space–time finite elements, the ‘steady state’ dynamic behaviour of the system was obtained. A properly performed discretization allowed of propagating information in a given direction at a limited velocity. The solutions were obtained under the assumption that the deformation is quasi-stationary, i.e., stationary in the coordinate system that moves with the load. The unbounded Timoshenko beam subjected to a distributed moving load was used as a test example. The dynamical system is placed on an elastic foundation. The matrices describing an infinite dynamical system subjected to a moving load are derived and the stability of the numerical scheme is analysed. The numerical results are compared with the analytical solutions in the literature and the classical numerical method.

Słowa kluczowe:
Vibrations, Moving load, Steady-state, Space–time element method, Simplex shaped elements, Infinite systems

Streszczenie:
In the present paper, an adaptive control of structural vibrations is presented. Based on earlier research, we claim that the periodical switching on of magneto-rheological controlled dampers results in the reduction of the amplitudes of vibrations more than does their permanent actuation. This statement, when applied to a moving load problem, was mathematically proved in earlier papers. In the present paper we determine the efficiency of such a control applied to a rotating shaft. The earlier mathematical analysis allows us to propose a control strategy. A finite element simulation together with the solution of the control problem shows that the dampers should act only during a short period of the highest displacements of the structure. The same conclusion is found in experimental tests. Although high frequency control with MR dampers is less efficient than in the theoretical investigations, we have found an amplitude reduction in the range of 10–20%.

Słowa kluczowe:
Adaptive control, Semi-active control, Vibration control, Shaft vibrations, Torsional vibrations, Magneto-rheological dampers

Streszczenie:
The paper deals with the vibrations of structures subjected to a moving inertial load. Classical description of the moving mass particle based on the Hermitian shape functions fails in the case of wave equations of motion. Especially for hyperbolic equations solutions diverge. The velocity approach to the space–time finite element method has been used. Continuous Galerkin method for solving differential equations of motion was applied. Comprehensive moving mass matrices and elemental matrices for the case of a string, the Euler beam, and the Timoshenko beam have been derived. The numerical results are compared with the literature semi-analytical solutions. These numerical algorithms can be applied in transport engineering, manufacturing, and robotics.

Streszczenie:
This paper deals with vibrations of structures subjected to moving inertial loads. In literature structures are usually subjected to massless forces. In numerical applications, however, the direct influence of the inertia of a moving object is usually neglected since the characteristic matrices, although simple, can not be easily derived. The paper presents a direct, non-iterative treatment of the motion of a mass along the finite element edge. The general characteristic matrices of finite elements that carry an inertial particle are given an d can be applied directly to almost all types of structures. Numerical tests and a comparison with examples from the literature and especially with analytical results, prove the efficiency and accuracy of our analysis.

Słowa kluczowe:
Vibrations, Moving Mass, Moving Inertial Load, Time Integration

Streszczenie:
The paper deals with the problem of stabilization of vibrations of the load carrying structure via adaptive damping performed with a smart material. The properties of such a material must ensure reduction of vibrations, especially accelerations and displacements of selected stationary or follower points in a higher range than in the case of the material with homogeneous bilateral characteristics. Analytical calculations and numerical simulations proved the efficiency of the approach. Results obtained with the testing system equipped with magnetorheological controlled dampers will allow us to prove experimentally assumed control strategies and rheological properties of the filling material.

Słowa kluczowe:
control, moving inertial load, vibrations, smart materials

Streszczenie:
The paper deals with the problem of vibrations of a Timoshenko beam loaded by a travelling mass particle. Such problems occur in a vehicle/track interaction or a power collector in railways. Increasing speed involves wave phenomena with significant increase of amplitudes. The travelling speed approaches critical values. The moving point mass attached to a structure in some cases ca n exceed the mass of the structure, i.e. a string or a beam, locally engaged in vibrations. In the literature, the travelling inertial load is often replaced by massless forces or oscillators. Classical solution of the motion equation may involve discussion concerning the contribution of the Dirac delta term, multiplied by the acceleration of the beam in a moving point in the differential equation. Although the solution scheme i s classical and successfully applied to numerous problems, in the paper the Lagrange equation of the second kind applied to the problem allows us to obtain the final solution with new features, not reported in the literature. In the case of a string or the Timoshenko beam, the inertial particle trajectory exhibits discontinuity and this phenomenon can be demonstrated or proved mathematically in a particular case. In practice, large jumps of the travelling inertial load is observed.

Słowa kluczowe:
moving mass, travelling inertial load, Timoshenko beam, Lagrange equation

Streszczenie:
Prawidłowe funkcjonowanie sieci kolejowej wymaga poznania stanu wyeksploatowanego toru oraz podtorza. Diagnozowanie sieci kolejowej wymaga m. in. Budowy poprawnego modelu numerycznego, symulującego możliwie wiernie badany układ, zachowując przy tym rozsądny czas obliczeń. W pracy przedstawiono wyniki eksperymentów zrealizowanych na doświadczalnym stanowisku polowym. W pomiarach wykorzystano czujniki piezoelektryczne wykonane w formie płytek o prostokątnym kształcie. Otrzymane wyniki porównano z rezultatami obliczeń numerycznych wykonanych metodą elementów czasoprzestrzennych. Wykazano skuteczność symulacji komputerowych w opisie dynamiki rzeczywistych torów kolejowych.

Streszczenie:
The paper deals with the problem of modelling of the moving mass particle in numerical computation by using the finite element method in one dimensional wave problems in which both the displacement and angle of the pure bending are described by linear shape functions. The analysis is based on the Timoshenko beam theory. We consider the simply supported beam, in a range of small deflections with zero initial conditions.

Słowa kluczowe:
numerical method, moving mass, moving inertial load, vibrations

Streszczenie:
W pracy przedstawiono algorytmy numeryczne metody elementów skończonych, dotyczące analizy drgań konstrukcji pod ruchomym obciążeniem bezwładnościowym. Niektóre problemy dynamiki konstrukcji trudno jest rozwiązać metodą elementów skończonych, stosowaną do zmiennych przestrzennych i metodą Newmarka, stosowaną do zmiennej czasu. Osobliwe cechy analitycznych rozwiązań równań różniczkowych, opisujących drgania wywołane ruchomym punktem masowym, muszą znaleźć swoje odzwierciedlenie również w ich rozwiązaniach numerycznych. Duże gradienty przebiegu rozwiązań, skoki wartości lub nieciągłości rozwiązań trudno jest uzyskać numerycznymi metodami dyskretnymi. Metody te same wymagają przybliżeń i wnoszą błędy, których oszacowanie jest trudne. W pracy omawiamy rozwiązania numeryczne, pozwalające uzyskać wyniki dokładne w pełnym zakresie prędkości przejazdu obciążenia bezwładnościowego.

Streszczenie:
Classical time integration schemes fail in vibration analysis of complex problems with moving concentrated parameters. Moving mass problems and moving support problems belong to this group. Commercial systems of dynamic simulations do not support such an analysis. Moreover, the classical finite element method with the Newmark-type time integration method does not allow us to obtain convergent results at all. The reason lies in the impossibility of full mathematical consideration of the time integration stage and the analysis of inertial terms of a travelling mass. Both of them, unfortunately, are decoupled. In this paper we propose an efficient and exact numerical approach to the problem by using the space–time finite element method. We derive characteristic matrices of the discrete element of the string and the Bernoulli–Euler beam that carry the concentrated mass. We present four types of virtual functions in time and we apply two of them to the practical analysis. Displacements in time obtained numerically are compared with semi-analytical results. Almost perfect coincidence proves the efficiency of the approach.

Słowa kluczowe:
Space–time finite element method, Vibrations, Virtual function, Moving mass

Streszczenie:
Inertial loading of structures by mass travelling with near-critical velocity has been intensively debated. In the literature a moving mass is replaced by an equivalent force or an oscillator that is in permanent contact with the structure. A direct mass matrix modification method frequently implemented in the finite element approach gives reasonable results only in the range of relatively low velocities and for low mass value if compared with the mass of a structure. However, existing solutions are incorrect and are not implemented in commercial computer codes. In this paper we present the space–time finite element approach to the problem. The interaction of the moving mass/supporting structure is described in a local coordinate system of the space-time finite element domain. Resulting characteristic matrices include inertia, Coriolis and centrifugal forces. Simple modification of matrices in the discrete equations of motion allows us to gain accuracy in a wide range of velocity, up to the over-critical speed. Numerical examples of string and beam vibrations prove the simplicity and efficiency of the method.

Słowa kluczowe:
moving mass, inertial load, space–time finite element method, vibrations

Streszczenie:
This paper deals with the paradoxical properties of the solution of string vibration under a moving mass. The solutions published to date are not simple enough and cannot be applied to investigations in the entire range of mass speeds, including the overcritical range. We propose a formulation of the problem that allows us to reduce the problem to a second-order matrix differential equation. Its solution is characteristic of all features of the critical, subcritical, and overcritical motion. Results exhibit discontinuity of the mass trajectory at the end support point, which has not been previously reported in the literature. The closed solution in the case of a massless string is analyzed and the discontinuity is proved. Numerical results obtained for an inertial string demonstrate similar features. Small vibrations are analyzed, which is why the effect discussed in the paper is of purely mathematical interest. However, the phenomenon results in complexity in discrete solutions.

Słowa kluczowe:
Moving mass, Vibrations of string, Inertial load

Streszczenie:
Inertial loading of strings, beams and plates by mass travelling with near-critical velocity has been a long debate. Typically, a moving mass is replaced by an equivalent force or an oscillator (with ‘rigid’ spring) that is in permanent contact with the structure. Such an approach leads to iterative solutions or imposition of artificial constraints. In both cases, rigid constraints result in serious computational problems. A direct mass matrix modification method frequently implemented in the finite element approach gave reasonable results only in the range of relatively low velocities. In this paper we present the space–time approach to the problem. The interaction of the moving mass/supporting structure is described in a local coordinate system of the space–time finite element domain. The resulting characteristic matrices include inertia, Coriolis and centrifugal forces. A simple modification of matrices in the discrete equations of motion allows us to gain accurate analysis of a wide range of velocities, up to the velocity of the wave speed. Numerical examples prove the simplicity and efficiency of the method. The presented approach can be easily implemented in the classic finite element algorithms

Streszczenie:
The paper deals with the original analytical-numerical approach to the Bernoulli—Euler beam with additional tensile effect under a moving inertial load. The authors applied the 2nd kind Lagrange equation to derive a motion differential equation of the problem. The moving mass can travel through the string-beam with a whole range constant speed, also overcritical. The analytical solution requires a numerical calculation in the last stage and is called a semi—analytical one.

Słowa kluczowe:
moving mass, inertial load, string, beam

Streszczenie:
In the present work the dynamics of the system of a mass moving on the beam is investigated in detail numerically in the case of vibrations about a buckled state. The differential equation that describes the motion is strongly nonlinear. Simulations are based on the space-time finite element method. It enabled us easily determine the influence of the moving inertial particle. At the computational stage it becomes a real problem when the mass particle traverses joints of neighbouring elements. The results of representative and interesting computer simulations are enclosed.

Streszczenie:
A semi-active control of structural vibrations is presented as an efficient method of damping. We consider structures subjected to a load applied in stationary points or to a moving load. We claim that the periodically switched magnetorheological actuators, controlled dampers, or elastic envelopes filled with granular materials subjected to controlled underpressure, give a more efficient vibration reduction than a permanently activated ones. In our work we show the efficiency of such a control strategy applied to a beams under moving inertial load, cantilevers and rotating shaft. The mathematical analysis allowed as to propose the particular control strategy. The finite element simulation, together with the solution for the control problem, proved that the damping devices should act only for a short period of each cycle of vibration. The control function depends on the type of the structure, excitation and the type of vibrations. The efficiency of the concept was proved in the experimental tests. The considered structures exhibit the reduction of amplitudes at the range 10-40% in the periodically controlled case, in comparison to the constant damping.

Słowa kluczowe:
Mechanical vibrations, semi-active control, smart materials

Streszczenie:
The paper deals with the problem of stabilization of vibrations of the load carrying structure via adaptive damping performed with a smart material. The properties of such a material must ensure reduction of vibrations, especially accelerations and displacements of selected stationary or follower points in a higher range than in the case of the material with homogeneous bilateral characteristics. Analytical calculations and numerical simulations proved the efficiency of the approach. Results obtained with the testing system equipped with magnetorheological controlled dampers will allow us to prove experimentally assumed control strategies and rheological properties of the filling material.

Słowa kluczowe:
control, moving inertial load, vibrations, smart materials

Streszczenie:
The paper deals with vibrations of structures under a moving inertial load. The space- time finite element approach has been used for a general description of the moving mass particle. Problems occur when we perform computer simulations. In the case of wave problem numerical description of the moving inertial loads requires great mathematical care. Otherwise we get a wrong solution. There is no commercial computing packages that would enable us direct simulation of moving loads, both gravitational and inertial.

Słowa kluczowe:
space-time finite element method, moving mass, vibrations

Streszczenie:
In the paper the spring-mass system describing the moving lo ad, determined with the Hertz theory, was replaced with the spring-mass system with an inertial part being in contact with the beam, rail, or a track. Computational problems can b e reduced significantly. Results are qualitatively and quantitatively improved, especially at higher range of the speed, related to critical values.

Słowa kluczowe:
wheel/rail contact, train-track system, moving loads

Streszczenie:
The paper deals with vibrations of structures under a moving inertial load. The space- time finite element approach has been used for a general description of the moving mass particle. Problems occur when we perform computer simulations. In the case of wave problem numerical description of the moving inertial loads requires great mathematical care. Otherwise we get a wrong solution. There is no commercial computing packages that would enable us direct simulation of moving loads, both gravitational and inertial.

Słowa kluczowe:
space-time finite element method, moving mass, vibrations

Streszczenie:
The work presents a novel distributed vibration control method of twin cantilever beams system coupled by a set of magnetorheological elastomers. The control is realized by a change of magnetic field influencing elastomers’ mechanical properties. The objective is to stabilize the system with the optimal rates of decrease of the energy. The control is based on an easy for practical implementation distributed state-feedback structure. It employs a set of communication channels to exchange the state information between the neighboring controllers. The performance of the designed method is validated by means of the numerical experiments. In terms of the assumed metrics, the proposed distributed method significantly outperforms the passive case and is competitive to standard centralized control.

Streszczenie:
In the work, a novel control method to stabilize vibrations of high structures is presented. The control is realized by changes of the stiffness parameters of the structural couplers. A seismic pulse excitation applied to the structure is submitted as a kinematic excitation. For such a representation the designed control law provides the best rate of the energy dissipation. Performance in different structural settings is studied by means of the stability analysis. Then, the efficiency of the proposed strategy is examined via numerical simulations. In terms of the assumed energy metric, the controlled structure outperforms its passively damped equivalent by over 50 percent.

Słowa kluczowe:
Structural control, semi-active control, smart materials, smart buildings, stabilization