Proceedings of DINAME 2017

In high-speed rotational machinery such as pumps or compressors, contactless seals are commonly used to separate different fluids or gases and pressure levels. However, the presence of a leakage flow through the seal gap exerts forces on a rotor. These can culminate in stiffening, restoring, and damping effects as well as in unstable, self-excited vibrational behavior. The Jeffcott rotor model and rotordynamic seal coefficients are put under investigation to prevent instability in the rotating machinery and to determine the rotor-seal systems dynamic behavior. This paper focuses on an experimental methodology, examined on a flexible rotor-seal test rig using an active magnetic bearing for excitation. Coefficient identification problems due to unknown random force (noise) in the experiment are shown and a solution is described in detail and validated on the test rig. The presented methodology leads to a calculation of rotordynamic seal coefficients during safe operating conditions. They are ultimately used to describe the system’s behavior and to predict the onset speed of instability.

A specific class of rotary machines is the high rotation turbochargers, to automotive application, wherein the shaft is continually subjected to axial forces of different magnitudes due to gas flows in the turbine and the compressor. These forces are supported by axial lubricated thrust bearings. The thrust bearings are modeled through equivalent stiffness and damping coefficients and the objective of the work is to get good estimates of these coefficients, comparing simulated results with experimental results. The stiffness coefficient is first obtained by small perturbation around the equilibrium position and used in a finite element model of the system at specific rotational speeds, and this value is compared to experimental results. Then, the damping coefficient is estimated, by running an optimization problem on this parameter, to approximate the simulated dynamic response of the system to experimental results of the turbocharger excited by an impact hammer, where both the displacement and force were measured.

There are several SHM techniques proposed in the literature for crack detection in rotating machines. Among them, the ones based on vibration measurements are recognized as useful tools in the industrial context. Although widely used, when applied under non-ideal conditions, such techniques can only detect cracks that eventually have already spread significantly along the cross section of the shaft. Therefore, currently, the researchers’ attention is turning to more sophisticated methods capable of identifying incipient cracks, which represent a type of damage that are hardly observable in classical vibration analysis. In a previous contribution, a crack identification methodology based on a nonlinear approach was proposed. The technique uses external applied diagnostic forces at certain frequencies attaining combinational resonances, together with a pseudo-random optimization code, known as Differential Evolution, in order to characterize the signatures of the crack in the spectral responses of flexible rotor. In the present paper, the favorable conditions to apply the proposed methodology are investigated. The analysis procedure is confined to the operating parameters of the system, being characterized by the rotation speed of the rotor and the amplitude and frequency of the diagnostic forces. The harmonic balance approach is used to determine the vibration responses of the cracked rotor system and the open crack behavior is simulated according to the FLEX model. For illustration purposes, a rotor composed by a horizontal flexible shaft, two rigid discs, and two self-aligning ball bearings is used to compose a FE model of the system.

Auxiliary Mass Dampers (AMD) are often used to reduce excessive vibration amplitude in mechanical systems. It is also known that their performances are susceptible to changes in the frequency or in the nature of the excitation force. Therefore, to improve the robustness of the AMD it is necessary to design new systems which are adaptable to the excitation, i.e., tunable devices that could be used over large frequency range. In this work a friction damper, which is the association of an elastic element and a scratcher, is used to tune the AMD by changing the normal force in the scratcher at the same time that it dissipates the mechanical energy of the principal mass. This AMD is named Tunable Auxiliary Mass Damper (TAMD). Three normal force control strategies, and two combinations of them, are studied: (i) The normal force is assumed constant; (ii) The normal force is obtained from the solution of the equation of motion assuming null displacement for the principal mass; (iii) The normal force is obtained based on the vibratory system’s movement, warranting that the direction of the friction force promotes the movement of the principal mass toward its static equilibrium position. The effectiveness of the proposed TAMD is numerically evaluated based on mass and frequency ratios variations for each strategy. Therefore, a multi-degree-of-freedom (MDOF) system analysis is made in order to verify the TAMD’s robustness and efficiency.

In the last few decades, a growing need for new materials for several applications led to the development and increase of studies in new theories such as viscoelasticity. Many efforts have been done to understand and characterize the mechanical behavior of these materials. The purpose of this work is to determine the viscoelastic Poisson’s ratio in the frequency domain, $$\nu ^*(\omega )$$ν∗(ω), for a viscoelastic material in order to characterize its three-dimensional behavior. To do so, the work is based on the elastic-viscoelastic correspondence principle (EVCP) and the time-temperature superposition principle (TTSP). Measurements of the complex shear modulus, $$G^*(\omega )$$G∗(ω), and the complex modulus, $$E^*(\omega )$$E∗(ω), were performed using a dynamic mechanical analyzer (DMA). To consider eventual uncertainties, each specific mechanical test was carried out using three test-specimens.

This study discusses an approach to analyze curvature effects on the vibrational powerflow of slender beams. A finite element method (FEM) model was used to calculate transmitted and reflected power via the “propagating wave approach”. Previously, the same investigation was addressed with focus on the analytical formulation of curved beams, and an FEM model was programmed using simple two-node straight (Euler-Bernoulli) beam elements. However, the model could simulate in-plane vibrations only, with restrictions to high frequencies (lower than two wavelengths inside the curvatures length). Hence, a new model was proposed, and the curvature parametrization was updated. A novel method to parametrize the curvature in 3D is discussed using quaternions. Results from the updated FEM model and analytical approach were compared for validation. Moreover, the algorithm performed almost exactly like the analytical model, even at high frequencies, which made it suitable to simulate power flow based on the wave approach. The algorithm allows any type of curve configuration to be tested. Curvature effects for in- and out-of-plane vibrations are shown as well. Finally, this work introduces a basis for designing and optimizing slender pipe structures from the perspective of vibration control.

This work describes the nonlinear identification applied to an aeroelastic pitch-plunge system using polynomial NARMAX model and a stability analysis. The apparatus is available and consists of a wing typical section with pitch and plunge degrees of freedom. The identification procedure aims to obtain the parameters for the mathematical model including the torsional stiffness as a quadratic polynomial function. The candidate structure to the polynomial model is obtained from discretization of a continuous-time state-space model and the predictions are obtained via the identification procedure using simulated data. The simulation is performed considering the aerodynamics with free stream velocity increased within an established velocity range which includes the flutter phenomenon. In future work, a data acquisition from the experimental apparatus will be performed. The NARMAX model indicates a polynomial function of fourth order for the nonlinearity and a stability analysis, discussed in this work, mapping the nonlinear regions.

This paper evaluates the effects and effectiveness of a dynamic vibration absorber (DVA) designed for mitigation of unstable oscillations of helicopters when it is on the ground, i.e.: ground resonance phenomenon. For this purpose, firstly, a parametric analysis shows the stability charts obtained for helicopters without and with DVA as function of the fuselage and rotor damping levels. Also, the present paper is interested on determining the influence of designed DVA devices on the stability robustness of the aircraft once uncertainties are considered in the blade’s hinge stiffness. In this sense, $$\mu $$μ-analysis is used to predict the smallest stiffness perturbation that leads the helicopter to instability. Indeed, it is not possible to assure the same properties of mechanical components which may alters the effectiveness of the designed DVA. Therefore, the assessment of stability robustness is verified and compared between both aircrafts (without and with DVA). The results showed for both helicopters, if proper combination of fuselage and rotor damping is considered, stability robustness is verified. Also, the inclusion of DVA device on helicopters does not affect the aircraft stability robustness.

Dynamic modeling of cables in three-dimensional space is a problem with great difficulty and complexity. This article discusses a new dynamic modeling formalism, including applications in the underwater environment. It is assumed that the cable is formed by rigid links connected by elastic fictitious joints, allowing elevation, azimuth and torsion movements. Algorithms have been developed to automatically generate the dynamic model for any number of links selected for the discrete approximation of the flexible structure. Three practical situations are tested: cable out of the water with free terminal load; underwater considering dynamics with or without ocean current; with terminal load fixed to the seabed. Constraint forces obtained through proportional and derivative control were applied to the terminal load to fix it to the seabed. The algorithms were determined from the Euler-Lagrange formalism, and in all situations the simulations showed physically consistent results.

A hierarchical structure is a structure that can be described by different characteristic lengths, and is such that its layout in the smaller scale (microscale) affects its behavior in the bigger scale (macroscale). Each hierarchical level is treated as a continuous medium composed of one or more materials. The simultaneous design of multiphase composite structures aims at finding the optimal distribution of materials such that one or more structural parameters are maximized (or minimized). In this work, the Bi-directional Evolutionary Structural Optimization method, BESO hereinafter, is applied to the maximization of the fundamental frequency of a structure subjected to a constraint on the total volume of materials used. Numerical experiments are made in order to validate the implementation and confirm the efficacy of the method in optimizing the topology of the structure.

Applied system identification is an important issue in science and engineering. Experimental modal analysis is used to describe the dynamical behavior of structures, in general, for a given set of input and output data. This article deals with multidimensional modal parameters identification valid for output-only data—operational modal analysis (OMA). This approach is interesting when the input is not known or difficult to be measured. A linear, time-invariant and finite dimensional mechanical system is considered, which is described mathematically by an autoregressive-moving-average-vector (ARMAV) model, excited by unknown operating forces assumed to be a white Gaussian process—a persistent excitation. The focus of the study is, both, theoretical and practical aspects, of the use of the ARMAV model in OMA. Specifically, it discusses the need of using an output-vector as reference for output-only parameters identification scheme. The model order is identified by inspection of the most significant singular values of a block Hankel matrix derived directly from the formulation of the model. The AR parameters matrices of the ARMAV model, contained in a companion matrix, are determined via least-squares technique. Natural frequencies, damping factors and modal shapes are identified by means of eigenvalues and eigenvectors of that companion matrix. Examples using computational simulated data are presented.

In the last years, many techniques and procedures have been employed to optimize traditional composite laminates, which can be classified as constant-stiffness composite laminates (CSCL), since the local stiffness is independent on the position over the laminate. On the other hand, recent advances in manufacturing processes now enable to explore non conventional designs. In particular, the development of automatic fiber placement allows the realization of variable stiffness composite laminates (VSCL), in which the local stiffness varies over the laminated as intended by the designer. In practice, VSCL can be achieved by making the fibers follow curvilinear trajectories over the plies (tow steering), or varying the matrix/fiber fraction over the laminate. Some authors have explored the benefits of VSCL to improve the performance of composite laminates in terms of stress distributions, static deformations, buckling, dynamic behavior and aeroelastic stability. In this context, this work proposes a strategy to optimize tow steered rectangular plates by controlling the angles that define the fiber trajectories. These latter are described by Lagrange polynomials of different orders, and two different sets of boundary conditions are considered. A structural model based on the Ritz method, combined with the classical lamination theory to model the composite laminate are used. The plate is considered thin, being modeled based on Kirchhoffs hypotheses. The equations of motion are obtained from Lagrange equations. The proposed model is validated by comparing natural frequencies and mode shapes with the counterparts obtained by using Nastran finite element software. The model is also validated by using experimental results obtained from a tow steered plate manufactured by the automatic fiber placement. A convergence analysis is carried-out to determine the number of functions in the Ritz basis necessary to ensure convergence of the semi-analytical model. A differential evolution (DE) algorithm is used to maximize the first natural frequency by finding the optimal fiber placement, defined by controlling the interpolation points of Lagrange polynomials of different orders. The results show the possibility of increasing the value of the fundamental frequency for various orders of the interpolation polynomials. However, as this order increases, the fiber paths become more complex, which brings about challenges to manufacturing process. For all simulated conditions, one notices the benefits of VSCL in terms of the vibration behavior, which leads to conclude that tow steering can indeed be used to cope with practical design goals such as to avoid resonances in a specific range of excitation frequency, or to increase the aeroelastic stability margin.

There is ample evidence that TMDs attenuate the vibration response of buildings subject to low-frequency wind loads. The same is not true for broad-banded earthquake loading. This paper investigates the effectiveness of TMDs in attenuation of vibration in buildings submitted to earthquake ground motion. A positional finite element model is developed, and employed to evaluate linear and geometrically nonlinear dynamical responses of building structures with TMDs under earthquakes. It was noted that TMDs tuned to higher frequencies work better at minimizing displacements and oscillation frequency, in contrast to what is popularly believed, that devices tuned to the building’s fundamental frequencies present ideal performance. The linear regimen showed to be sufficient to estimates the displacements of the building and the imposition of earthquake loads as equivalent lateral forces was not representative and does not describe accurately the behavior of the structure. The incorporation of TMDs showed to be very effective in reducing vibrations when the structure is subjected to earthquake loads. However, benefits are only achieved when TMDs are properly designed, and when structural responses are correctly evaluated.

Model Based System Testing (MBST) can be defined as the discipline combining physical testing and simulation models with the aim to study, identify, validate and improve the behavior of multiphysical and mechatronic systems. One of its benefits is related to the use of simulation models to improve or accelerate the testing process, using well known procedures, such as optimal sensor and excitation placement, but also more recent methodologies, such as virtual testing or human-in-the-loop interactions. In this context, these MBST methodologies can be used for Electrical power steering (EPS) system testing, to allow for better characterization of the overall system and subsystems, and to better identify and model nonlinearities. This paper presents a testing and simulation combined approach used to optimally define test conditions, such as sensor placement, test boundary conditions, excitation inputs and how they affect parameter identification.

A flexible vertical cylinder model, fixed at both ends, is tested experimentally immersed in water and then in air. Galerkin’s decomposition is applied to obtain a Reduced Order Model (ROM) from a continuum one. Two closed-form trial modal shapes are chosen for the modal decomposition process. Then, modal added mass is assessed using classical Fourier and Hilbert transform (HT) signal analyses, comparing the model eigenvalues with the frequency evaluated from the experimental signals. The choice of modal shape is shown to alter significantly added mass experimental assessment. Similarity to classic results with rigid cylinders is achieved by taking a sufficiently proper modal representation. Moreover, the first mode added mass coefficient attains the same value of that previously determined for a cantilevered flexible circular cylinder, by Pesce and Fujarra in (Pesce and Fujarra, Int J Offshore Polar Eng 10:26–33, 2000) [1].

This work presents the analytical form determination of the dynamic model of a parallel planar mechanism with three degrees of freedom through the characterization of the power flow between its components. From the geometrical relations associated to the displacement of their degrees of freedom, the kinematic relations associated to their speeds are determined. Considering the power flow between the degrees of freedom, and also between these and the actuating elements (linear electric actuators) the equilibrium relations of the forces and torques are obtained. Accounting for inertial effects of system components, the stiffness and damping effects, the equations of motion or the state equations are analytically determined. Besides, the relation between the inverse kinematics and the direct dynamics is presented. The proposed methodology is generalized and applicable in any type of mechanism (open or closed, planar or spatial). Thus, this methodology (power flow) is more efficient to achieve the dynamic analytical (closed) models of parallel mechanisms. Simulations are performed to validate this approach, using the real data (geometry, inertia, damping, actuators forces, etc.) from a planar mechanism designed and built especially for the purpose to compare the simulated and experimental results. The analytical equations lead to a more efficient simulation process and real-time control of these systems.

A parallel two degrees of freedom manipulator designed for a variable orientation of a body in space is analyzed. The manipulator consists of one universal joint with one axis fixed to the base and the other axis fixed to a moving platform. A similar device is used in spacecraft to orient the rocket nozzle. In this work, two parallel linear hydraulic actuators move the platform. A novel proportional digital hydraulic valve is used to control the actuators. Each fork of the universal joint has an angular position sensor mounted to measure the relative motion of the cross and an inertial measurement unit (IMU) is fixed to the moving platform. Load cells and pressure transducers are mounted on the actuators to measure force and chambers pressure. Numerical simulations are presented using a desired trajectory as input for a proportional controller (P-controller). An experimental apparatus is used to validate the numerical results.

This paper has as object of study a simplified model for the the automobile suspension system, which can become a regenerative system by coupling a RLC electric circuit to the mechanical system. The main objectives of this paper are to study and optimize a simplified electromechanical suspension model that, when in passive mode, harvests energy, while maintaining the handling stability and passenger comfort, and when in active mode, uses energy to improve comfort for passengers and handling stability with least effort. A multi-objective optimization procedure was carried out and Pareto frontier was obtained for the objective functions when considering the passive mode. When considering active control, changes were proposed to the optimal control in order to reduce control effort for feedforward strategy, while for feedback strategies, the stability gain range was obtained by Routh-Hurwitz criterion. The proposed control sets have particular advantages regarding isolation, energy harvested and control effort.

The objective of this study is to present a neural observer that estimates changing injection behavior due to wear and aging effects within the nozzle of a common rail diesel injector. Using a dynamic identification system in combination with a modified learning rule, the neural observer is applicable to a wide range of problem sets. A multilayer perceptron (MLP) network with three layers and few neurons in the hidden layer ensures fast computing and high efficiency; network learning is based on quasi-Newton optimization and an additional line search algorithm. Modeling the bottom part of the injector introduces a simulation model, which is validated with experimental data from a solenoid common rail diesel injector. Estimation results conform well with the altered plant and therefore demonstrate the significant benefit of using the proposed neural network observer concept.

Robot Manipulators have been employed in many types of industries, such as pharmaceutical, chemical, automotive, aerospace, etc. A manipulator is a mechanism used to move an object along a given trajectory. Topologically, the mechanism can be constituted by parallel or serial chains. The serial kinematic chain is constituted by links connected sequentially by joints. The aim of this work is to obtain a qualitative comparison among three approaches typically applied to the modelling of multibody mechanical systems. The chosen system is a 5-DOF serial robot manipulator and the three approaches are based on the use of Lagrange’s, Maggi’s and Kane’s equations. The purpose of the modelling is to obtain the equations of motion for this serial robotic manipulator. Some numerical simulations are performed to illustrate how the obtained models can be used to predict the dynamic behavior of the chosen system.

Small hydraulic excavators are versatile machines used in a wide range of operations such as digging, removal of debris, transportation of cargo and earthmoving. Operating a hydraulic excavator in certain environments is a difficult and dangerous task, especially in hazardous environments subject to natural disturbances or inadequate health conditions for human work. Because of these conditions, the automation of excavators or its components has been the subject of many studies in recent years. In this paper, to enable the development of a control system for the manipulator of a mini excavator, a complete mathematical model of the manipulator dynamics is developed. The work includes the validation of the model of the manipulator by means of simulation of a computational model and by comparison with the results obtained by a commercial software of dynamic analysis. Results are discussed and evaluated and suggestions for future work are enclosed.

This paper presents the implementation of an optimization method to find, without knowledge of the environment characteristics, the best interaction controller parameters to revamp the coupled dynamics. The objective is to improve various industrial robot applications that involves mechanical contact. An enhanced contact is accomplished by lowering the following metrics: rise time, total variation and steady state error. Hence, the impedance controller was the interaction control technique chosen to be optimized. Contact is established between a Kuka KR16 robot TCP and an aluminum platform, where the force data was acquired by a 6-axis force-torque sensor located in the robot’s end-effector. Using a hardware-in-the-loop optimization approach, the force feedback is processed by a NSGA-II algorithm. Each individual of the GA represents a specific impedance controller and as the generations passes, these values get more suitable for lowering the metrics. Results show convergence in 5 generations.

A hovercraft is an amphibious vehicle lifted by a propeller that causes the effect of an air cushion between the vehicle and the surface. This way, a hovercraft becomes a fast and versatile vehicle to be used in different kinds of tasks such as rescues, environmental monitoring and coast guard patrolling. This paper presents the control problem formulation in order to track a reference trajectory of a hovercraft dynamical model. For this purpose the SDRE (State Dependent Riccati Equation) control method is applied to the model of this dynamical system. The nonlinear control problem is formulated in order to minimize the cost functional. Numerical simulations are performed using Matlab®, so that, the equations of the system and the reference are integrated to generate data about the position, orientation and velocities of the hovercraft. The results confirm that the control method succeeded in controlling the hovercraft in all proposed cases.

Systems actuated trough a flexible shaft poses a big challenge to control strategies as the actuator is not connected directly to the end effector, causing propagation effects as well as an energy accumulation and dissipation in the shaft. This paper focuses on the top driven drilling system used in the oil and gas industry. In these systems, all kind of vibrations are found: longitudinal deformations (bit bouncing), flexional (rubbing), and torsional (stick-slip). This paper is about the torsional deformation of the highly flexible string modeled as a 20 DOF Lumped parameters system. A method for reducing stick-slip vibrations is presented and its results analyzed. The investigation includes the development of a reduced scale test rig adequate for torsional vibrations under damping. Results from the mathematical model and experimental tests are then compared.

This work deals with the control of multiple mobile robots in trajectory, while maintaining a formation, through the use of State-Dependent Riccati Equation control method. Three robots with differential drive are used in a scheme in which one is considered the leader and the other two are considered followers. By changing formation parameters, this work seeks to achieve two different formations, V-shaped and Echelon formation, very common in the military field. Simulations are performed using LabVIEW, demonstrating the successful application of the control method in mobile robot tracking problems while maintaining formations.

The goal of this work is to present applications of recent results in the Lurie problem, also known as the absolute stability problem, to Hopfield neural networks, aiming its stability analysis. We show how to obtain the mathematical model of a neural network, in terms of differential equations, and present simulations for some examples. We give special attention to networks with multiple inputs and outputs, and point future directions of research to be followed.

In this article the nonlinear dynamics of a parametric pendulum considering a reciprocating excitation is addressed. The interest in the study of this kind of forcing lies in its wide use in machines and industrial equipment including a crank-rod mechanism. The work aims at the further development of pendulum devices for energy harvesting. In this context, the study is focused on pendulum rotations, which are highly energetic. Although reciprocating excitation is similar to the classic sinusoidal excitation, a different and more complex rotational behavior is observed and more rotating attractors are found as new rotation zones arise in the space of forcing parameters. It is shown that the existence of these additional rotating attractors, which depend on crank-rod ratio and the amount of damping, increases the possibilities of energy extraction.

Autonomous vehicles—defined as vehicles with carrying capacity of persons or property without the use of a human driver—are an interesting and recent problem, with increasing studies in the last 20 years. Regarding this type of vehicles, a less explored option is the motorcycle: apart from the difficulties inherent in making a vehicle move independently, autonomous motorcycles have to be able to remain stable at any speed and trajectory. This work’s main object of study is a small-scale electric motorcycle; represented by a linear model through a multibody approach: its four rigid bodies—wheels, chassis, handlebar and fork—have separately a characteristic behavior and together they influence the dynamics of each other. This approach results in lower order models, easier to simulate and to apply classical or modern control strategies. The two-wheeled vehicle is considered an inverted pendulum with a mobile base and other simplifications are proposed, as constant displacement speed or small steering and yaw angles. Since this vehicle is naturally unstable, to ensure a follow-up course without overturning it is necessary to apply an adjusted control signal; once the autonomous system studied will not have the presence of a mechanical counterbalance, there remains only the steering as a control strategy. Thus, this work analyzes the dynamic characteristics of the zero track vehicles and verifies the validity of different stability and path tracking control strategies of a motorcycle using as input only the steering of the handlebar.

In this work, a 6 degree-of-freedom analytical model that describes the rolling dynamics of an articulated heavy-duty vehicle composed by a tractor and a trailer was developed and numerically simulated. The behaviour of a typical medium-duty truck-trailer set was evaluated in two common traffic manoeuvres, namely, performing a constant steering wheel angle curve and a change of direction, both at constant velocity (36 km/h). In the latter case, in order to simulate a sudden change, steering amplitude ranging from zero to 30° was imposed to the front wheels through a step function during 2 s. Results of the first trial revealed that the tractor roll angle presents a peak of 2.6° and achieves a steady value of 0.8° respectively at 4 and 20 s after the beginning of the manoeuvre. Roll angle amplitudes of the trailer, spanning from −0.015 to 0.023° (a negative value means the vehicle is leaning inwards at the curve), revealed an oscillatory characteristic, before reaching a stable value of 0.0025° in about 15 s. In the second trial, roll angles of both tractor and trailer reach maximum values higher than those of the previous test (respectively 11.5 and −0.5°); in addition, the oscillatory movement of the trailer was enhanced, since positive and negative roll angles alternated five times until both units return to a steady (zero roll angle) condition after about 20 s from the beginning of the manoeuvre. Those results are compatible with the expected behaviour of actual vehicles, thus suggesting that the proposed model can be tailored to include other truck-trailer configurations and manoeuvres.

In this work, an integrated vehicle control system (IC) is tested in run-off-road scenarios. The integrated approach was employed in order to coordinate vehicle control systems, i.e. the Anti-Lock Brake System (ABS), Four-wheel Steering (4WS) and the Electronic Stability Program (ESP). To perform a run-off-road maneuver, a fuzzy virtual test driver was designed. By receiving the lateral position of an obstacle and the vehicle’s relative yaw angle, the virtual test driver is capable of following a reference trajectory. Furthermore, to test the performance of the standalone controllers, i.e. ABS, ESP and 4WS, individual maneuvers are performed using a multibody vehicle model. The vehicle without any coordination between the control systems is used as reference. For the simulation results, it is concluded that the IC improves the vehicle stability and maneuverability in comparison with the non-integrated approach.

This paper addresses the yaw stability analysis of articulated vehicles using the phase trajectory method. The goal of this work is to ascertain the dynamic conditions that the articulated vehicle can assume without the occurrence of instability events such as jackknife and rollover. The study focuses on the vehicle configuration composed by one tractor unit and a driven unit such as, for instance, a tractor semi-trailer combination. The system consists of a nonlinear tire model and a nonlinear articulated bicycle model with four degrees of freedom. The analysis presented in this paper illustrates the convergence regions of equilibrium points obtained through numerical integration of the equations of motion of the model for different initial conditions in the phase plane. In addition, the changes in the obtained regions are presented as a function of the tractor speed and the position of the articulation point between the two units.

Both experimental and computational studies have contributed to the understanding of the loads during wheelchair propulsion and the factors leading to the incidence of musculoskeletal disorders. However, few studies have addressed the influence of inertial forces on wheelchair propulsion, which are potentially large as upper limb segments undergo large accelerations along the different phases of the propulsion cycle. This study determines and investigates the influence of inertial forces during manual wheelchair propulsion for a subject at two different locomotion velocities. The isolated influence of inertial as well as gravitational forces is determined using a planar model of the upper extremity and an inverse-dynamics approach. The results show that the inertial forces are preponderant even at lower speeds. These findings evidence that quasi-static models are inappropriate to investigate wheelchair propulsion and show the importance of accurate estimation of anthropometric parameters such as segment masses and moments of inertia, which directly affect inertial force estimations in inverse dynamics-based studies of wheelchair propulsion. The results can also help guide investigations on efficient propulsion techniques, as they show that the radial component of the pushrim forces are, to a large extent, determined by inertial effects rather than by an inefficient propulsion technique.

A novel and numerical methodology to analyse the train/track dynamic interaction and its influence on the overall track settlement mechanism is presented. This will be achieved by creating an iterative loop that makes possible to assess the condition of the track based on the vehicle forces. The main contribution of this work rests on performing a track degradation analysis considering a regular stretch of railway track. In the first phase, a train/track interaction analysis is developed and assessed by evaluating the contact forces between the wheel and the rail. In a second phase, the forces at each particular support, beneath the rail, are extracted and transformed, by applying a degradation law at the ballast layer, into vertical displacements that in turn are applied as longitudinal level irregularities in the rail. The process is completed by including the updated geometry that enables the further calculations, in a loop mode, considering as many cycles as required.

The forced response of flexural waves propagating in a 1D phononic crystal (PC) beam and its band structure are investigated theoretically and experimentally. PC beam unit cell is composed by steel and polyethylene. The study is performed by using six methods, finite element (FE), spectral element (SE), wave finite element (WFE), wave spectral element (WSE), conventional plane wave expansion (CPWE) and improved plane wave expansion (IPWE). Simulated examples of a 1D PC beam considering unit cells of different sizes are analyzed. Forced response results are presented in the form of displacement, transmittance and receptance, and the elastic band structure is investigated using its real and imaginary (attenuation) parts. Numerical and analytical results of all approaches are in a good agreement, except by WFE and FE numerical results in high frequencies. The effect of the amounts of polyethylene on the attenuation constant is studied. Depending on the application, choosing polyethylene quantity correctly is not simple, because it is related to the unit cell size and in which frequency the band gap is opened up. An experiment with a 1D PC beam is proposed and numerical and analytical results can localize the band gap position and width close to the experimental results. A small Bragg-type band gap with low attenuation is observed between 405 and 720 Hz. The 1D PC beam with unit cells of steel and polyethylene presents potential application for vibration control.

Due to their particular wave propagation characteristics, phononic crystals (PC’s) and acoustic metamaterials have numerous potential applications in passive vibration and noise control. In this context, some geometric phase concepts originally developed in electronics have inspired research in phononics. As a result of the non-trivial topology of the band structure, these concepts allow exploring particular behaviors such as edge and interface modes. For acoustic systems, it has been recently shown that interface modes appear at the boundary separating two PC’s having different Zak phases. In this paper, one-dimensional spectral elements are used to investigate interface modes in one-dimensional acoustic (tube) and elastic (rod) systems. The band structure and the forced response are computed using the spectral element method. It is shown that the interface mode appears within the second band gap when a geometrical parameter of one of the connected PC’s is varied so that this bandgap closes and reopens, characterizing a change in the Zak phase. The forced response at the interface mode frequency shows that the sound (acoustic) or vibration (elastic) is spatially concentrated (localisation phenomenon) at the interface. Different PC combinations and different excitation locations are investigated. This behavior may have useful engineering applications, such as in sound and vibration energy harvesting.

To accurately determine the position of a leak in a buried plastic water pipe using acoustic correlation, a good estimate of the speed of noise propagation (wave speed) is required. The factors that affect this wave speed, and attenuation of the wave as it propagates along the pipe, include the pipe flexibility and the soil properties. These effects are discussed in this paper, and are illustrated by way of simulations for two different pipe sizes and two different soil types. It is shown that the soil type in Brazil can have a profound effect on the wave speed and hence the accuracy of leak location. Some practical problems in estimating the wave speed from in-situ measurements are also outlined. Although this is relatively simple to measure in principle, in practice it is extremely difficult to do, for a variety of reasons. Some of these are discussed and the reason why this measurement is particularly problematic with plastic water distribution pipes is illustrated.

Noise control in acoustic tube systems is a classical problem. The use of periodic geometries and resonators is also classic in acoustic filter design. The phononic approach to the problem is much more recent. Looking at this classic problem with a novel approach may lead to innovative solutions. This work investigates the band gaps created in acoustic pipe systems using axisymmetric finite element models, wave finite element models and experiments. Periodic geometry variations are investigated. The Floquet-Bloch theorem is used on a transfer matrix of the periodic cell rearranged from a dynamic stiffness matrix to obtain the dispersion diagrams that reveal the band gaps caused by Bragg scattering. Numerical predictions of the forced response obtained with the full finite element axisymmetric model of a duct system with five cells are compared with a wave finite element model and with experimental results.

In this paper simplified models for hydraulic transmission lines and hoses, for both time and frequency domain simulation, are presented. Flexible hoses have, in addition to a higher capacitance, also an considerable damping effect, that can reduce noise and vibrations, and in this paper, efficient approximate models for flexible hoses are presented. In hydraulic transmission lines with laminar flow the losses can be divided into two parts. One term that is distributed friction, and one term that is frequency dependent. It is shown that in general, the effect from the hose wall dominate the frequency response characteristics over the frequency dependent friction. A very simple frequency dependent model of the damping term of the hose can then be combined with an equally simple model of the distributed friction to represent a simple but accurate model of a flexible hose for system simulation in the time domain.

Natural gas has a great importance in actual economy, and its transport is done usually through pipeline networks. The operation of a gas pipeline uses numerical models for calculation of intermediate properties, prediction of future behavior and estimation of the integrated flow capacity. These models are based on physical assumptions, closure laws and field measurements of boundary conditions such as pressure, flow, temperature and composition of the natural gas. This paper presents a development proposed for state and parameter estimation based on the implementation of an extended Kalman filter, in order to determine appropriate values for the flow parameters and use of complementary measurements in the boundary conditions. These results are compared to the ones obtained by using the Equal Error Fraction Method. It was found reduced pressure and flow systematic errors when the Kalman filter was used to estimate parameters.