scholarly journals How to Experimentally Monitor the Fatigue Behaviour of Vibrating Mechanical Systems?

2020 ◽  
Vol 66 (10) ◽  
pp. 557-566
Author(s):  
Filippo Cianetti
Keyword(s):  
Mechanical System ◽  
Fatigue Damage ◽  
Time Domain ◽  
Residual Life ◽  
Numerical Models ◽  
A Priori ◽  
Mechanical Systems ◽  
Signal Amplitude ◽  
Fatigue Behaviour ◽  
Operational Life

Fatigue damage and, in general, fatigue behaviour is not simple to observe or estimate during the operational life of a generic vibrating mechanical system. There are a lot of theoretical or numerical methods that allow to evaluate it or by knowing a priori the loading conditions and obtaining output stress states by adopting numerical models of the mechanical system or by directly experimentally measuring and acquiring stress/strain states. A few examples of instruments (e.g. rain flow recorders) or measurement chains dedicated to estimate it in time domain or frequency domain are found in the literature but none that fully both observes the system dynamic behaviour and estimates the related actualized cumulated damage, and, thus, none that can estimate the residual life of the system itself. In this paper, a simple time-domain method, designed to monitor the instantaneous fatigue behaviour by definition of the instantaneous and cumulated potential damage or of equivalent damage signal amplitude is presented, based on rain-flow counting method and a damage linear cumulation law and starting from system dynamics signals. This methodology was designed to overestimate real damage to alert the system manager before any crack starts and to be simply translated into electronic boards that can be mounted on generic mechanical systems and linked to one of the sensors that usually monitor system functionality. Keywords: fatigue; damage; rain flow counting; random loads

Modified HHT Method for Vehicle Vibration Analysis in Time Domain Utilisation

2013 ◽  
Vol 486 ◽  
pp. 396-405 ◽  
Author(s):  
Juraj Gerlici ◽  
Tomáš Lack
Keyword(s):  
Mechanical System ◽  
Time Domain ◽  
Vibration Analysis ◽  
Mechanical Systems ◽  
Dynamical Analysis ◽  
Vehicle Design ◽  
Negative State ◽  
Eigen Frequencies ◽  
Dynamical Properties

The analysis of mechanical systems (for example the mechanical systems of vehicles) vibration is permanently very topical. The vehicle dynamical properties are determined with the help of this analysis during a new vehicle design, or renewal of an older existing vehicle. The Eigen frequencies are characteristic for a vehicle construction. A vehicle mechanical system is excited with various types of loads in the operation and this is the reason why its individual parts oscillate. The aim of a dynamical analysis is not only to judge the influence of an excitation on the mechanical system, but also on the base of that analysis, to propose and to perform the construction changes of a vehicle for the detected negative state elimination or improvement.

scholarly journals DIRECT HAMILTONIZATION — GENERALIZATION OF AN ALTERNATIVE HAMILTONIZATION

2012 ◽  
Vol 22 (06) ◽  
pp. 1250135
Author(s):  
MARIA LEWTCHUK ESPINDOLA
Keyword(s):  
Dynamical Systems ◽  
Mechanical System ◽  
Equations Of Motion ◽  
A Priori ◽  
Mechanical Systems ◽  
Hamiltonian Function ◽  
Analytical Mechanics ◽  
Principal Change

A new procedure named direct Hamiltonization presents an alternative foundation to Analytical Mechanics, since in this formalism the Hamiltonian function can be obtained for all mechanical systems. The principal change proposed in this procedure is that the conjugate momenta cannot be defined a priori, but are established as a consequence of a canonical description of the mechanical system. The direct Hamiltonization is a generalization of the alternative one, where the usual Hamiltonization and momenta are recovered whenever they exist. Also this procedure assures the existence of a Hamiltonian function without any constraints for any mechanical system, therefore the usual quantization is always allowed. This procedure can be applied to non-Lagrangian, Nambu, nonholonomic and dynamical systems since there are no restrictions in this formalism as, for example, the number of equations of motion.

Tribo-Fatigue

Tribology ◽  
2005 ◽  
Author(s):  
Leonid A. Sosnovskiy ◽  
Veniamin I. Senko
Keyword(s):  
Fatigue Strength ◽  
Mechanical System ◽  
Fatigue Damage ◽  
Contact Interaction ◽  
Mechanical Systems ◽  
Simultaneous Reduction ◽  
Active Systems ◽  
Basic Ideas ◽  
Material Expenditure

By the end of the last century it was realized that most critical units of any machine are the ones which are called active systems, i. e. any mechanical system that operates in the conditions of contact interaction of elements (during sliding, rolling, slippage, etc.) and transmits cycle load simultaneously. In these cases complex wear-fatigue damage of materials takes place. Such systems and processes of their damage became the main object of studies in tribo-fatigue — the science that emerged on the verge of fatigue strength, tribology and the theory of reliability of mechanical systems. Practically the development of tribo-fatigue opens new ways for solving problems of improving lifetime and reliability of machines on main criteria of workability with simultaneous reduction of labour, means and material expenditure for their manufacture and operation. The basic ideas of tribo-fatigue and its interrelation with related disciplines (tribology, fatigue strength, reliability of mechanical systems) are presented in the report [1,2]. In the present work we will give a very brief report of some basic results obtained in tribo-fatigue.

scholarly journals Research on Hydroelastic Response of an FMRC Hexagon Enclosed Platform

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1110
Author(s):  
Wei-Qin Liu ◽  
Luo-Nan Xiong ◽  
Guo-Wei Zhang ◽  
Meng Yang ◽  
Wei-Guo Wu ◽  
...  
Keyword(s):  
Time Domain ◽  
Numerical Models ◽  
Structural Response ◽  
Deep Ocean ◽  
Surface Model ◽  
Large Area ◽  
Floating Structure ◽  
Small Depth ◽  
Response Amplitude Operators ◽  
Hydroelastic Response

The numerical hydroelastic method is used to study the structural response of a hexagon enclosed platform (HEP) of flexible module rigid connector (FMRC) structure that can provide life accommodation, ship berthing and marine supply for ships sailing in the deep ocean. Six trapezoidal floating structures constitute the HEP structure so that it is a symmetrical very large floating structure (VLFS). The HEP has the characteristics of large area and small depth, so its hydroelastic response is significant. Therefore, this paper studies the structural responses of a hexagon enclosed platform of FMRC structure in waves by means of a 3D potential-flow hydroelastic method based on modal superposition. Numerical models, including the hydrodynamic model, wet surface model and finite element method (FEM) model, are established, a rigid connection is simulated by many-point-contraction (MPC) and the number of wave cases is determined. The load and structural response of HEP are obtained and analyzed in all wave cases, and frequency-domain hydroelastic calculation and time-domain hydroelastic calculation are carried out. After obtaining a number of response amplitude operators (RAOs) for stress and time-domain stress histories, the mechanism of the HEP structure is compared and analyzed. This study is used to guide engineering design for enclosed-type ocean platforms.

The Control of Vibration Transmissibility Using an Electrodynamic Actuator –Close-Loop Solution

2013 ◽  
Vol 436 ◽  
pp. 166-173
Author(s):  
A. Mihaela Mîţiu ◽  
Daniel Constantin Comeagă ◽  
Octavian G. Donţu
Keyword(s):  
Mathematical Model ◽  
Control System ◽  
Mechanical System ◽  
Closed Loop ◽  
Mechanical Systems ◽  
Vibration Transmissibility ◽  
Technical Solutions ◽  
The Mathematical Model

In this paper are presented some aspects of transmissibility control of mechanical systems with 1 DOF so that the effects of vibration on their action to be minimized. Some technical solutions that can be used for this purpose is analyzed. Starting from the mathematical model of an electro-mechanical system with 1 DOF, are identified the parameters which influence the effectiveness of the transmissibility control system using an electrodynamic actuator who work in "closed loop".

Controlled Arming of Mechanical Systems Embedded into Embarked Electrical Systems

2014 ◽  
Vol 555 ◽  
pp. 209-216
Author(s):  
Gheorghe Negru
Keyword(s):  
Kalman Filter ◽  
Mechanical System ◽  
High Speed ◽  
Mechanical Systems ◽  
Electrical Systems ◽  
General Motion

The paper presents an application of the Kalman filter to achieve the controlled arming of mechanical system embedded into embarked electrical systems (FMES). The solution of FMES which contain mechanical subsystems electronically controlled could significantly reduce the influence, on their functioning, of the general motion of high speed object (HSO) .

The Method for Determining the Vibration-Damping Elements for the Mechanical System to Obtain the Desired Amplitude Value

2014 ◽  
Vol 657 ◽  
pp. 644-648 ◽  
Author(s):  
Andrzej Dymarek ◽  
Tomasz Dzitkowski
Keyword(s):  
Mechanical System ◽  
Dynamic Characteristics ◽  
Vibration Reduction ◽  
Mechanical Systems ◽  
Vibration Damping ◽  
Displacement Velocity ◽  
Synthesis Methods ◽  
Resonance Frequencies

The paper presents the use of synthesis methods to determine the parameters of passive vibration reduction in mechanical systems. Passive vibration reduction in a system is enabled by units called dampers whose values are determined on the basis of the method formulated and formalized by the authors. The essence of the method are, established at the beginning of a task, dynamic characteristics in the form of the resonance and anti-resonance frequencies, and amplitudes of displacement, velocity or acceleration of vibration.

Synconvergent and coherent (ultra)high-pressure crustal rock exhumation

2021 ◽  
Author(s):  
Lorenzo G. Candioti ◽  
Joshua D. Vaughan-Hammon ◽  
Thibault Duretz ◽  
Stefan M. Schmalholz
Keyword(s):  
Numerical Models ◽  
A Priori ◽  
Western Alps ◽  
Ultrahigh Pressure ◽  
Plate Motion ◽  
Crustal Rock ◽  
Plate Boundaries ◽  
Crustal Rocks ◽  
Natural Data ◽  
The Alps

<p>Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.</p><p> </p><p>Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called mélanges. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.</p><p> </p><p>Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.</p><p> </p><p>The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.</p>

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