Discrete Damper Research Articles

Hysteresis Evaluation of Discrete Damper with Adaptive Shear Links for Extensively Damaged Reinforced Concrete Frame

Hysteresis Evaluation of Discrete Damper with Adaptive Shear Links for Extensively Damaged Reinforced Concrete Frame

Seismic Overturning Fragility Analysis for Rigid Blocks Subjected to Floor Motions

This paper investigates the seismic rocking-overturning fragility of freestanding rigid blocks subjected to one-sine acceleration pulses from a probabilistic perspective. An equivalent single-degree-of-freedom (SDOF) model with a bespoke discrete damper is used to simulate the responses of four blocks with varying geometries under excitation with various characteristics. The simulation results are used to perform an overturning fragility analysis and evaluate the performance of various intensity measures (IMs). An IM strip, referred to as a hybrid strip, can be observed in the analysis, within which both safe rocking and overturning occur. For IM values outside of the hybrid strip, there exists a clear distinction between these two states. In this study, we introduce the hybrid ratio, a parameter that can estimate the size of the hybrid strip of different IMs. The hybrid ratio is defined as the combination of two ratios of hybrid strip width and the two IM strip widths corresponding to safe rocking and overturning, respectively. The effect of the different analysis strip widths is also examined in the overturning fragility analysis. The results suggest that the IM determined by excitation magnitude, frequency, and block geometry parameters demonstrates its superiority compared with some well-known IMs by having the smallest hybrid ratio and coefficient of variation, as well as good robustness of the overturning fragility curves against the change of the analysis strip width.

An Intensity Measure for the Rocking Fragility Analysis of Rigid Blocks Subjected to Floor Motions

A novel intensity measure (IM), dimensionless floor displacement, is presented for evaluating the seismic fragility of freestanding rigid blocks subjected to one-sine acceleration pulses in this paper. The rocking responses of rigid blocks are simulated using an equivalent single-degree-of-freedom (SDOF) model with a bespoke discrete damper to account for energy dissipation. The performance of various IMs is compared using simulation results for four different block models under different excitation conditions. In comparison to some well-known IMs, the proposed IM, determined by excitation magnitude and frequency as well as block geometry parameters, displays a considerably stronger correlation with the peak rotation of the rocking block. The comparative results show that effective IMs should consider not only the excitation characteristics but also the block geometric parameters. Finally, the fragility curve generated by the proposed IM performs best by significantly reducing the dispersion.

Analysis of vibration high-frequency dynamic characteristics of wheelless rail vehicle system based on fuzzy logic control

Track irregularity is the main source of vibration excitation of vehicle-track weighing system, which has an important impact on the safety, stability and comfort of train operation, and it is also the main factor limiting the speed of train operation. Higher requirements are put forward for track smoothness with the rapid development of China’s railways. Therefore, it has a great theoretical and practical significance to study the relationship between track irregularity and random vibration of vehicle-track cooker-in system and the evaluation method of track smoothness. In this paper, a model construction method is proposed based on machine learning fuzzy logic control and neural network algorithm to analyze the high frequency dynamic characteristics of ballastless track wheel-rail vehicle system. Firstly, a numerical analysis model of high frequency dynamic characteristics of ballastless track wheel-rail vehicle system is established by using linear discrete elastic-yellow damper element connection model; Secondly, the Rough Set Block Neural Network is introduced to optimize the dynamic characteristic analysis model, and the intelligent model of model optimization analysis is established. Finally, the validity of the proposed algorithm is verified by simulation experiments of practical examples.

Effects of Discrete Damping on the Dynamic Behaviour of Rotating Shaft through Extended Lagrangian Formulation

Abstract The main focus of the paper is touted as effects of discrete damping on the dynamic analysis of rotating shaft. The whole analysis is being carried out through extended Lagrangian formulation for a discrete – continuous system. The variation formulation for this system is possible, considering the continuous system as one-dimensional. The generalized formulation for one dimensional continuous rotary shaft with discrete external damper has been obtained through principle of variation. Using this extended formulation, the invariance of umbra-Lagrangian density through extended Noether’s theorem is achieved. Rayleigh beam model is used to model the shaft. Amplitude equation of rotor is obtained theoretically and validated through simulation results. The simulation results reveal the important phenomena of limiting dynamics of the rotor shaft, which is due to an imbalance of material damping and stiffness of the rotor shaft. The regenerative energy in the rotor shaft, induced due to elasticity/stiffness of the rotor shaft, is dissipated partially through the in-span discrete damper and also through the dissipative coupling between drive and the rotor shaft. In such cases, the shaft speed will not increase with increase in excitation frequency of the rotor but the slip between the drive and the shaft increases due to loading of drive.

A Vectorial-Wave Method for free and forced vibration analysis of extra thin cylindrical shells with boundary discrete damping

The Vectorial-wave method (VWM) is developed to study free and forced vibrations of cylindrical shells in the presence of dampers at supports. In modeling the issue, a circular cylindrical shell is considered with two ended supports, including separate springs and viscous dampers in the possible directions. Accordingly, based on Flugge thin shell theory and by considering the wave vectors going in the opposite direction along with the shell axis, reflection and transmission matrices are determined to satisfy the shell continuity as well as the boundary conditions. The proposed method is verified through comparing its results with the available literature and the numerical results calculated by Finite element method (FEM). Employing VWM, the viscous characteristics of the applied supports on natural frequencies of the shell are investigated. Furthermore, frequency responses of the shell, which are affected by point-load excitation, are obtained. Finally, the results show that several tandem resonance picks can be eliminated via accurate setting of the support damping.

Elemental damping formulation: an alternative modelling of inherent damping in nonlinear dynamic analysis

To date, nonlinear dynamic analysis for seismic engineering predominantly employs the classical Rayleigh damping model and its variations. Though earlier studies have identified issues with the use of this model in nonlinear seismic analysis, it still remains the popular choice for engineers as well as for software providers. In this paper a new approach to modelling damping is initiated by formulating the damping matrix at an elemental level. To this regard, two new elemental level discrete damping models adapted from their global counterparts are proposed for its application in nonlinear dynamic analysis. Implementation schemes for these newly proposed models using Newmark incremental method and revised Newmark total equilibrium method is outlined. The performance of these proposed models, compared to existing models, is illustrated by conducting nonlinear dynamic analyses on a four story RC frame designed to Eurocodes. The incremental dynamic analysis study presented in the paper illustrates the fact that both the proposed models seem to produce more reliable results from an engineering perspective in comparison to the global models. It is also shown that the proposed elemental damping models lead to smaller and more realistic damping moments in the plastic hinges. Furthermore, these models could be easily included in existing software frameworks without adding noticeably to the computational effort. The computation time required for these models is approximately equivalent to the one required when using the tangent Rayleigh damping matrix with constant coefficients.

Control Engineering Analysis of Mechanical Pitch Systems

With the help of a local stability analysis the coefficient range of a discrete damper, used for centrifugal forced, mechanical pitch system of small wind turbines (SWT), is gained for equilibrium points. – By a global stability analysis the gained coefficient range can be validated. An appropriate approach by Takagi-Sugeno is presented in the paper.

Idealisation and Formulation in Structural Dynamics Using Modal Analysis

The crux feature of this paper is the equations of motion in a structural dynamics with respect to single reference frame that can be easily derived, and the results are well defined and converged. However, problem occurs, when the analysis of any complex, complicated structure is considered and its equation of motion is extracted with respect to single reference frame. The results are indecipherable, ambiguous and less converged. Thus, for such a complex structure, the results obtain with respect to multiple reference frames. In present study, an approximated model with a set of lumped masses, properly interconnected, along with discrete spring and damper elements are in consideration for continuous vibrating system. This results in dynamic equilibrium, which in turn results in formulation and idealization. As, rightly said by scientist Steve Lacy- “To me, there is spirit in a reed. It is a living thing, a weed, really and it does not contain spirit of sort. It’s really an ancient vibration”

Nonlinear momentum transfer control of a gyrostat with a discrete damper using neural networks

An adaptive feedback linearization technique combined with neural networks is addressed for the momentum transfer control of a torque-free gyrostat with an attached spring-mass-dashpot damper. The neural network is used to adaptively compensate for the model error uncertainties of internal dynamics. The total spacecraft angular momentum component of the wheel spin axis is selected as an output function for the feedback linearization. Thus, a desired output function is predefined for which the total angular momentum of the spacecraft is absorbed into the wheel spin direction at the steady state with nutation angle converging to zero. The ultimate boundedness of the tracking error is proved by the Lyapunov stability theory. We also investigate the effect of rotor misalignment on the steady spin of the spacecraft and the initial stability condition to overcome the inverted turn due to unstable mass moment of inertia configuration. The effectiveness of the proposed control law is verified through a simulation study.

Nonlinear three-dimensional wagon–track model for the investigation of rail corrugation initiation on curved track

A nonlinear wagon–track model on curved track has been developed to characterize rail corrugation formation due to self-excitation of the wheel–rail stick–slip process. In this model, wagon movements were described using up to 78 degrees of freedom (DOFs) to model a three-piece freight bogie. Innovatively, the wheelset movements are described using nine DOFs, including torsional and bending modes about the longitudinal and vertical directions. The track modelling is considered as a one-layer structure (two rail beams on discrete spring and damper elements). The wheel sliding after creepage saturation is considered in the wheel–rail interface modelling. Simulation of a case study shows that the frequencies of the wheel stick–slip process are composed of the basic frequency, which might come from the combined effect of sleeper-passing frequency and one-third of the combined torsional and bending frequency of the wheelset, and the double and triple basic frequencies, which form the wavelengths of rail corrugation at different situations.

Bifurcations of relative equilibria of an oblate gyrostat with a discrete damper

We investigate relative equilibria of an oblate gyrostat with a discrete damper. Linear and nonlinear methods yield stability conditions for simple spins about the nominal principal axes. We use analytical and numerical methods to explore other equilibria, including bifurcations that occur for varying rotor momentum and damper parameters. These bifurcations are complex structures that are perturbations of the zero rotor momentum case. We use Lyapunov–Schmidt reduction to determine an analytic relationship between parameters to determine conditions for which a jump phenomenon occurs.

Numerical analysis and experimental verification of vehicle trajectories

The paper presents research results of a study, in which computational mechanics was utilized to predict vehicle trajectories upon traversing standard Florida DOT street curbs. Computational analysis was performed using LS-DYNA non-linear, finite element computer code with two public domain, finite element models of motor vehicles: Ford Festiva and Ford Taurus. Shock absorbers were modeled using discrete spring and damper elements. Connections for the modified suspension systems were carefully designed to assure proper range of motion for the suspension models. Inertia properties of the actual vehicles were collected using tilt-table tests and were used for LS-DYNA vehicle models. Full-scale trajectory tests have been performed at Texas Transportation Institute to validate the numerical models and predictions from computational mechanics. Experiments were conducted for Ford Festiva and Ford Taurus, both for two values of approach angle: 15 and 90 degrees, with impact velocity of 45 mph. Experimental data including accelerations, displacements and overall vehicles behavior were collected by high-speed video cameras and have been compared with numerical results. Verification results indicated a good correlation between computational analysis and full-scale test data. The study also underlined a strong dependence of properly modeled suspension and tires on resulting vehicle trajectories.

Relative Equilibria of a Prolate Gyrostat with a Discrete Damper

We investigate the possible equilibria for a torque-free gyrostat with an attached springmass damper. The equations of motion are presented, and we develop explicit stability conditions for simple steady spins about principal axes using Routh-Hurwitz and Liapunov stability analyses. Numerical continuation determines additional equilibria using rotor momentum as the bifurcation parameter. Multiple equilibria are identified and characterized, including some interesting stable equilibria corresponding to steady spins about non-principal axes. Pitchfork bifurcations from the nominal-spin state are examined analytically using Liapunov-Schmidt reduction, which produces conditions on system parameters for avoiding a jump phenomenon. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the US Government.

Momentum Transfer Dynamics of a Gyrostat with a Discrete Damper

Thestabilityofmotionofattitudemaneuversofatorque-freerigidgyrostatwithadiscretedamperisinvestigated. The equations of motion are presented in dimensionless form. Conditions for equilibrium motions and for their stability aredeveloped.Bifurcation diagramsareused toillustratethestableand unstablebranchesofsteady spins, and these bifurcation diagrams are interpreted in the slow state space of the rotor momenta and the unperturbed systemHamiltonian. Theeffectof thedampermechanismisillustratedusing a perturbed version ofthebifurcation diagram. A class of rotational maneuvers is developed based on maintaining a stationary-platform condition. This class of maneuvers maintains a small angularvelocity, which has the effect of reducing the excitation of the e exible component.

Discrete string damper for a guitar

A guitar string damper device includes six discrete damper arms for selectively dampening each string individually. The device universally fits most guitars because it attaches to a standard guitar nut. Employing a staggered arrangement for the damper arms and levers allows a musician to quickly dampen and release individual strings while still playing.

A real transformation for modal analysis of flexible damped spacecraft

Modal approach is widely used for the analysis of dynamics of flexible structures. However, space analysts yet lack an intimate modal analysis of current spacecraft which are rich with flexibility and possess both structural and discrete damping. Mathematical modeling of such spacecraft incapacitates the existing real transformation procedure, for it cannot include discrete damping, demands uncomputable inversion of a modal matrix inaccessible due to its overwhelming size and does not permit truncation. On the other hand, complex transformation techniques entail more computational time and cannot handle structural damping. This paper presents a real transformation strategy which averts inversion of the associated real transformation matrix, allows truncation and accommodates both forms of damping simultaneously. This is accomplished by establishing a key relation between the real transformation matrix and its adjoint. The relation permits truncation of the matrices and leads to uncoupled pairs of coupled first order equations which contain a number of adjoint eigenvectors. Finally these pairs are solved to obtain a literal modal response of forced gyroscopic damped flexibile systems at arbitrary initial conditions.