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INCAS Bulletin , 2009, DOI: 10.13111/2066-8201.2009.1.1.12
Abstract: The low frequency damper is an autonomous equipment for damping vibrations with the 1-20Hz range.Its autonomy enables the equipment to be located in various mechanical systems, without requiring special hydraulic installations.The low frequency damper was designed for damping the low frequency oscillations occurring in the circuit controls of the upgraded IAR-99 Aircraft.The low frequency damper is a novelty in the aerospace field ,with applicability in several areas as it can be built up in an appropriate range of dimensions meeting the requirements of different beneficiaries. On this line an equipment able to damp an extended frequency range was performed for damping oscillations in the pipes of the nuclear power plants.This damper, tested in INCAS laboratories matched the requirements of the beneficiary.The low frequency damper is patented – the patent no. 114583C1/2000 is held by INCAS.
Analysis of Magneto Rheological Fluid Damper  [PDF]
Md. Sadak Ali Khan,A.Suresh,N.Seetha Ramaiah
International Journal of Engineering and Advanced Technology , 2012,
Abstract: Control of seismic, medical and automobile vibrationsrepresents a vast area of research that is growing rapidly. Magnetorheological (MR) dampers are a new class of devices that match wellwith the requirements and constraints of applications, including thenecessity of having very low power requirements. The performanceof MR damper depends on its magnetic and hydraulic circuit design.In this paper a finite element model is used to examine andinvestigate the 2- D axi-symmetric MR damper. Nine differentconfigurations of piston for MR damper are simulated in order toinvestigate how the profile of the piston affected the maximumpressure drop that the damper could provide. The piston velocity andthe input current to the coil are varied to evaluate the resultingchange in magnetic flux density (B) and pressure drop (ΔP). Thesimulation results of the different configuration of piston show thatthe performance of single coil with filleted piston ends was betterthan that of other configurations for the same magnitude of inputcurrent and piston velocity.
Developing Hydraulic Sensitivity Equations for Baffle Modules and Determining the Effects of Sensitivity Index Quantity Variations on Operating Conditions  [cached]
A. Montazar,S. Kouchakzadeh,A. Liaghat,M. H. Omid
Journal of Science and Technology of Agriculture and Natural Resources , 2004,
Abstract: The operation of an irrigation network is the result of a decision-making system in which three elements, i. e. the physical condition of the structures, control capacity, and hydraulic behavior of canal system, have important roles. The impact of these components is incorporated in the hydraulic sensitivity concept. For this purpose, the sensitivity of structures could be considered as the most important factor in the hydraulic characteristics of a system. The sensitivity analysis approach is one of the flow analysis methods that is used to forecast the flow behavior in several irrigation networks. Baffle Modules are one of the most suitable structures for flow regulating and delivery. In this paper, hydraulic sensitivity equations are presented for this type of structure. Also, the quantitative variations of the sensitivity index have been evaluated under operating conditions and compared with those of theoretical conditions. Then the influence of the sensitivity index variations on the performance of structures has been studied. This study was carried out on some modules of the Qazvin network. The results indicated that the hydraulic sensitivity of these off-takes varies under operating conditions. In some cases, variations were estimated to be more than 100%. The range of discharge variations was twice the predefined acceptable value (20%) in some offtakes.
Application Research on Load Allocation of Hydraulic Unit based on Multi-objective Optimized Methods  [cached]
Li-ying Wang,Wei-guo Zhao,Jian-xi Wang
Journal of Software , 2010, DOI: 10.4304/jsw.5.11.1224-1227
Abstract: Stratified Genetic algorithm was used in the optimized calculation of Wanjiazhai Hydropower Station, a multi-objective optimized model was established , two sub-populations of independent parallel were used to compute, the calculated values of network model and test values were compared, results showed that the two values are matched, the value of optimized load pressure fluctuation deviates from the average in 3mH2O ,the actual power flow is also less ,it is propitious to improve economic efficiency of the Hydropower station.
Case Study of Variable Orifice Damper for Seismic Protection of Structures  [PDF]
Septimiu-George Luca,Cristian Pastia
Bulletin of the Polytechnic Institute of Jassy, Constructions, Architechture Section , 2009,
Abstract: The seismic protection is, without any doubt, a worldwide priority, and that is why one of the main preoccupations of the researchers in the field is finding some innovative concepts concerning the seismic protection of the structures. The aim of the paper consists in the analytical and numerical study of the variable orifice damper implemented in a single degree of freedom (SDOF) structure in order to increase people’s safety and reduce the seismic risk. The variable orifice damper is the common semi-active hydraulic device which may be utilized as part of seismic isolation system or within the lateral bracing of a structure. The semi-active control strategy is realized using on-off clipping control algorithm. It is concluded that the variable orifice damper afforded a substantial reduction of the displacement response of a SDOF system in comparison to the response with passive control fluid device.
Dynamic Analysis of Stockbridge Damper  [PDF]
Nilson Barbieri,Renato Barbieri
Advances in Acoustics and Vibration , 2012, DOI: 10.1155/2012/659398
Abstract: In this work a machine cam with five different profiles was used to investigate the linear and nonlinear dynamical behavior of asymmetric Stockbridge damper with excitation frequencies in the range of ?Hz. The experimental vibration signals were acquired through accelerometers placed along the sample. The loss factor and the Young's modulus were estimated through approximation of the experimental and numerical results using Genetic Algorithms (GAs). Linear and nonlinear mathematical models were used to adjust the data. The two parameters are dependent on the excitation frequency and the amplitude of the base displacement. The results are validated comparing typical impedance curves obtained in conventional testing using an electromechanical shaker. 1. Introduction The Stockbridge damper is presently the most common type of transmission line damper. In general, the absorber consists of two weights attached to the end of stranded cables, which are known as messenger wires. A detailed mathematical description of conductor motion is difficult due to the stranded construction of a conductor. An example of this problem is the study carried out by Nawrocki and Labrosse [1], where the cable is modeled using each individual wire model and all possible contacts are investigated. However, in order to get good results for the static analysis, this model was not applied for dynamic problems and the dynamic friction between the individual wires of the cable was also not studied. In Stockbridge dampers of transmission line, mechanical energy is dissipated in wire cables “damper or messenger cables”. The damping mechanism is due to statical hysteresis resulting from Coulomb (dry) friction between the individual wires of the cable undergoing bending deformation. In order to test this dynamical model of Stockbridge damper, the typical experimental impedance curves are compared with numeric results. This procedure was used by [2] who uses the masing model for modeling the nonlinear damping behavior of the damper cable of the Stockbridge damper. Zhu and Meguid [3–5] analyzed the behavior of cables considering curved beam models. Due to difficulties in modeling the hysteretic damping, the standard Rayleigh damping was used. The numerical and experimental results presented good approximation. López and Venegas [6] analyzed the dynamic behavior of Stockbridge dampers through dynamic and fatigue tests and showed that the damping ratio decreases linearly with the excitation motion amplitude. In this work, the physical parameters are adjusted through the comparison between
Application of Magneto-Rheological Damper for Car Suspension Control  [PDF]
M.M. Rashid,M.A. Hussain,N. Abd. Rahim
Journal of Applied Sciences , 2006,
Abstract: The MR damper is a control device that consists of a hydraulic cylinder filled with magnetically polarizable particles suspended in a liquid. MR dampers dissipate vibration by absorbing energy. Magnetorheological (MR) fluids dampers are very effective to control vibration, which use MR fluids to produce controllable damping force and provide both the reliability of passive systems and the facility of active control systems with small power supply. Due to their mechanical simplicity, high dynamic range, low power requirements, large force capacity and robustness, offer an attractive means of vibration protection. The objective of this study are understanding the characteristics of the MR damper to provide effective damping for the purpose of suspension isolation or suppression car body. In this study, fuzzy logic controller is used to control semiactive car suspension system.
Nonlinear dynamic analysis of an optimal particle damper  [PDF]
Martín Sánchez,C. Manuel Carlevaro
Physics , 2011, DOI: 10.1016/j.jsv.2012.09.042
Abstract: We study the dynamical behavior of a single degree of freedom mechanical system with a particle damper. The particle (granular) damping was optimized for the primary system operating condition by using an appropriate gap size for a prismatic enclosure. The particles absorb the kinetic energy of the vibrating structure and convert it into heat through the inelastic collisions and friction. This results in a highly nonlinear mechanical system. Considering linear signal analysis, state space reconstruction, Poincar\'e sections and the determination of maximal Lyapunov exponents, the motion of the granular system inside the enclosure is characterized for a wide frequency range. With the excitation frequency as control parameter, either regular and chaotic motion of the granular bed are found and their influence on the damping is analyzed.
Hydraulic calculation of pressure pipes  [cached]
M.A. Mikhalev
Magazine of Civil Engineering , 2012,
Abstract: In the present time there is only one classic method for hydraulic calculation of pressure pipes. In it fluid flow velocity and pipeline diameter are considered as given values.The paper proposes a procedure for physical modeling and hydraulic calculation of pressure pipes, based on the theory of similarity. Methods for obtaining similarity criteria from combinations of similarity numbers were discussed. Similarity numbers and criteria and criteria equations were defined.
Gas Turbine Blade Damper Optimization Methodology  [PDF]
R. K. Giridhar,P. V. Ramaiah,G. Krishnaiah,S. G. Barad
Advances in Acoustics and Vibration , 2012, DOI: 10.1155/2012/316761
Abstract: The friction damping concept is widely used to reduce resonance stresses in gas turbines. A friction damper has been designed for high pressure turbine stage of a turbojet engine. The objective of this work is to find out effectiveness of the damper while minimizing resonant stresses for sixth and ninth engine order excitation of first flexure mode. This paper presents a methodology that combines three essential phases of friction damping optimization in turbo-machinery. The first phase is to develop an analytical model of blade damper system. The second phase is experimentation and model tuning necessary for response studies while the third phase is evaluating damper performance. The reduced model of blade is developed corresponding to the mode under investigation incorporating the friction damper then the simulations were carried out to arrive at an optimum design point of the damper. Bench tests were carried out in two phases. Phase-1 deals with characterization of the blade dynamically and the phase-2 deals with finding optimal normal load at which the blade resonating response is minimal for a given excitation. The test results are discussed, and are corroborated with simulated results, are in good agreement. 1. Introduction The friction damping concept is widely applied in turbomachinery applications, especially at hot end parts, to reduce resonance stresses. A typical application of this in gas turbines. They are popularly called as “friction damper,” “cottage-roof damper” or “under platform damper.” This damper is loaded by centrifugal force against the underside of the platforms of two adjacent blades. The main design criterion for such devices is to determine the optimum damper configuration or the damper mass or both in order to reduce the dynamic stresses to maximum possible extent. For example, if the damper mass is too small for a given configuration, the friction force will not be large enough to dissipate sufficient energy. On the other hand, if the damper mass is too large, it will get into “stick” condition, thereby limiting the relative motion across the interface and hence the amount of energy dissipation. In both cases, the friction damper will be inefficient, and between these two extremes there exists an optima. A good review of the friction damping concept in turbomachinery applications is given by Griffin [1]. Theoretical analysis and the optimization of this simple device is difficult because of marked nonlinearity and assumptions about the contact characteristics and damper behavior. Several friction damper models and analysis
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