scholarly journals SIMULATION OF A MULTI-FREQUENCY STOCKBRIDGE VIBRATION DAMPER OSCILATIONS WITH ENERGY SCATTERING HYSTERESIS

2020 ◽  
Vol 16 (4) ◽  
pp. 29-37
Author(s):  
Alexander Danilin ◽  
Alexey Kurbatov ◽  
Sergey Zhavoronok
Keyword(s):  
Experimental Data ◽  
Limit Cycle ◽  
Solid Body ◽  
Spatial Configuration ◽  
Hysteresis Loops ◽  
Linear Formulation ◽  
Vibration Damper ◽  
Kinematic Equation ◽  
Energy Scattering

Spatial vibrations of a system containing a cable and a mass (solid body of arbitrary spatial configuration) are modeled. The problem is solved in a geometrically linear formulation, taking into account the hysteresis of energy scattering that is based on the kinematic equation. Identification of its parameters is carried out on the basis of experimental data on hysteresis loops of the limit cycle.

scholarly journals Metaecosystem dynamics drive community composition in experimental multilayered spatial networks

2019 ◽  
Author(s):  
Eric Harvey ◽  
Isabelle Gounand ◽  
Emanuel A. Fronhofer ◽  
Florian Altermatt
Keyword(s):  
Experimental Data ◽  
Community Composition ◽  
Spatial Configuration ◽  
Spatial Networks ◽  
Resource Exchange ◽  
Ecosystem Boundaries ◽  
Dendritic Networks ◽  
Regional Dynamics ◽  
Lattice Network ◽  
Local Ecosystem

AbstractCross-ecosystem subsidies are studied with a focus on resource exchange at local ecosystem boundaries. This perspective ignores regional dynamics that can emerge via constraints imposed by the landscape, potentially leading to spatially-dependent effects of subsidies and spatial feedbacks. Using miniaturized landscape analogues of river dendritic and terrestrial lattice spatial networks, we manipulated and studied resource exchange between the two whole networks. We found that community composition in dendritic networks depended on the resource pulse from the lattice network, with the strength of this effect declining in larger downstream patches. In turn, this spatially-dependent effect imposed constraints on the lattice network with populations in that network reaching higher densities when connected to more central patches in the dendritic network. Consequently, localized cross-ecosystem fluxes, and their respective effects on recipient ecosystems, must be studied in a perspective taking into account the explicit spatial configuration of the landscape.Statement of authorshipEH, IG, EAF and FA designed the research; EH conducted the lab experiment with support from IG, EAF and FA, processed the experimental data with methodological developments from IG, and carried out the analysis of experimental data; all authors participated in results interpretation; EH wrote the first draft of the manuscript; All authors significantly contributed to further manuscript revisions.

Underplatform Dampers for Turbine Blades: Theoretical Modeling, Analysis, and Comparison With Experimental Data

1998 ◽  
Vol 123 (4) ◽  
pp. 919-929 ◽  
Author(s):  
K. Y. Sanliturk ◽  
D. J. Ewins ◽  
A. B. Stanbridge
Keyword(s):  
Experimental Data ◽  
Theoretical Model ◽  
Normal Load ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Hysteresis Loops ◽  
Modeling Analysis ◽  
Modes Of Vibration ◽  
Opening And Closing ◽  
Distinct Features

This paper describes a theoretical model for analyzing the dynamic characteristics of wedge-shaped underplatform dampers for turbine blades, with the objective that this model can be used to minimize the need for conducting expensive experiments for optimizing such dampers. The theoretical model presented in the paper has several distinct features to achieve this objective including: (i) it makes use of experimentally measured contact characteristics (hysteresis loops) for description of the basic contact behavior of a given material combination with representative surface finish, (ii) the damper motion between the blade platform locations is determined according to the motion of the platforms, (iii) three-dimensional damper motion is included in the model, and (iv) normal load variation across the contact surfaces during vibration is included, thereby accommodating contact opening and closing during vibration. A dedicated nonlinear vibration analysis program has been developed for this study and predictions have been verified against experimental data obtained from two test rigs. Two cantilever beams were used to simulate turbine blades with real underplatform dampers in the first experiment. The second experiment comprised real turbine blades with real underplatform damper. Correlation of the predictions and the experimental results revealed that the analysis can predict (i) the optimum damping condition, (ii) the amount of response reduction, and (iii) the natural frequency shift caused by friction dampers, all with acceptable accuracy. It has also been shown that the most commonly used underplatform dampers in practice are prone to rolling motion, an effect which reduces the damping in certain modes of vibration usually described as the lower nodal diameter bladed-disk modes.

scholarly journals Experimental Investigations on the Dynamic Behaviour of O-Type Wire-Cable Vibration Isolators

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Hong-Xia Wang ◽  
Xian-Sheng Gong ◽  
Fei Pan ◽  
Xue-Jiang Dang
Keyword(s):  
Experimental Data ◽  
Hysteresis Loops ◽  
Iterative Algorithms ◽  
Experimental Investigations ◽  
Loading Frequency ◽  
Restoring Force ◽  
Mass System ◽  
Cable Vibration ◽  
Vibration Isolators ◽  
Deformation Curves

A series of periodic loading experiments were carried out on the O-type wire-cable vibration isolators. The isolators were loaded under shear, roll, and tension-compression loadings. When subjected to shear and roll loads, the restoring force-deformation curves generated by the isolators formed symmetric hysteresis loops. However, when the isolators were loaded with tension-compression loads, the isolator produced asymmetric hysteresis loops. It is found through the experiment that the dynamic characteristics of the isolator are determined by the loading amplitude as well as the geometric parameters of the isolator while they are almost independent of loading frequency within the testing frequency range. Based on the experimental data, the dynamic response of the isolator was modeled by a modified normalized Bouc-Wen model. The parameters of this model were identified through an identification procedure that does not involve any nonlinear iterative algorithms. Comparison between the identification results and the experimental data suggests that the identification method is effective. With the model and the identified parameters, the frequency response of an O-type wire-cable vibration isolator-mass system was evaluated. Typical nonlinear response behaviors were found when the isolator was used in tension-compression mode while the response appears to be similar to that of a linear system when the isolator was used in shear and roll mode.

How to prevent undesired oscillation in NC rotary table

2015 ◽  
Vol 23 (20) ◽  
pp. 3490-3503
Author(s):  
Ali Ghaffari ◽  
Ebrahim Mohammadiasl
Keyword(s):  
Experimental Data ◽  
Limit Cycle ◽  
Operating Conditions ◽  
Rotary Table ◽  
Describing Function ◽  
Rotary Axis ◽  
Milling Operations ◽  
Complete Set ◽  
Simulation Results ◽  
Real Experimental Data

Heavy lathe-mill and turn-mill machine tools with both turning and milling operations are usually equipped with a frictional brake system to mitigate the effect of the mechanical backlash on the gear driven rotary table. In this paper the simultaneous effects of the coupled nonlinear frictions and backlashes on the positioning of the rotary axis have been investigated theoretically and empirically. Using the describing function method, it is shown that the undesired oscillations of the system are due to the existence of a limit cycle in the nonlinear closed-loop trajectory pattern of the rotary axis. Some simple practical rules are proposed for parameters adjustment of the rotary table, to assure that limit cycle is not created, and the multi-function machine does not oscillate improperly. The proposed rules can be used both at the designing stage and also during the maintenance of the machine. In order to verify the simulation results, a complete set of experimental data in a heavy lathe-mill machine has been utilized. It is shown that the deviation between the simulation results and the real experimental data at different operating conditions are quite small.

Plastic Energy Required for Fatigue Failure of Specimens Containing Cracks

1975 ◽  
Vol 97 (2) ◽  
pp. 172-178 ◽  
Author(s):  
Thang Bui-Quoc ◽  
Andre Biron
Keyword(s):  
Experimental Data ◽  
Crack Propagation ◽  
Hysteresis Loops ◽  
Mean Value ◽  
Repeated Loading ◽  
Plastic Energy ◽  
Propagation Law ◽  
The Mean ◽  
Damage Rule ◽  
Propagation Stage

A study is conducted to determine the plastic energy absorbed by a material subjected to cyclic loading during the crack propagation stage. The analysis is based on Liu’s elastoplastic solution for calculating the plastic energy around the crack tip combined with a modified crack propagation law. The plastic energy per cycle Δw is found to be dependent upon the fatigue crack length and therefore varies with the number of applied cycles. The mean value of this energy corresponds to the plastic energy obtained by measuring the area within the stress-strain hysteresis loops of the material under repeated loading. If fatigue damage is based on plastic energy, the trend of variation of Δw with the applied cycles in the present analysis shows that the application of the linear damage rule (such as Miner’s law) should be more successful in the low-cycle region than in the high-cycle region. This is consistent with experimental data.

scholarly journals A multifractal approach to characterize cumulative rainfall and tillage effects on soil surface micro-topography and to predict depression storage

2010 ◽  
Vol 7 (10) ◽  
pp. 2989-3004 ◽  
Author(s):  
E. Vidal Vázquez ◽  
J. G. V. Miranda ◽  
J. Paz-Ferreiro
Keyword(s):  
Experimental Data ◽  
Multifractal Analysis ◽  
Spatial Configuration ◽  
Vertical Component ◽  
Soil Surface ◽  
Data Sets ◽  
Natural Rainfall ◽  
Cumulative Rainfall ◽  
Disc Level ◽  
Micro Topography

Abstract. Most of the indices currently employed for assessing soil surface micro-topography, such as random roughness (RR), are merely descriptors of its vertical component. Recently, multifractal analysis provided a new insight for describing the spatial configuration of soil surface roughness. The main objective of this study was to test the ability of multifractal parameters to assess in field conditions the decay of initial surface roughness induced by natural rainfall under different soil tillage systems. In addition, we evaluated the potential of the joint use of multifractal indices plus RR to improve predictions of water storage in depressions of the soil surface (MDS). Field experiments were performed on an Oxisol at Campinas, São Paulo State (Brazil). Six tillage treatments, namely, disc harrow, disc plough, chisel plough, disc harrow + disc level, disc plough + disc level and chisel plough + disc level were tested. In each treatment soil surface micro-topography was measured four times, with increasing amounts of natural rainfall, using a pin meter. The sampling scheme was a square grid with 25 × 25 mm point spacing and the plot size was 1350 × 1350 mm (≈1.8 m2), so that each data set consisted of 3025 individual elevation points. Duplicated measurements were taken per treatment and date, yielding a total of 48 experimental data sets. MDS was estimated from grid elevation data with a depression-filling algorithm. Multifractal analysis was performed for experimental data sets as well as for oriented and random surface conditions obtained from the former by removing slope and slope plus tillage marks, respectively. All the investigated microplots exhibited multifractal behaviour, irrespective of surface condition, but the degree of multifractality showed wide differences between them. Multifractal parameters provided valuable information for characterizing the spatial features of soil micro-topography as they were able to discriminate data sets with similar values for the vertical component of roughness. Conversely, both, rough and smooth soil surfaces, with high and low roughness values, respectively, can display similar levels of spectral complexity. Although in most of the studied cases trend removal produces increasing homogeneity in the spatial configuration of height readings, spectral complexity of individual data sets may increase or decrease, when slope or slope plus tillage tool marks are filtered. Increased cumulative rainfall had significant effects on various parameters from the generalized dimension, Dq, and singularity spectrum, f(α). Overall, micro-topography decay by rainfall was reflected on a shift of the singularity spectra, f(α) from the left side (q>>0) to the right side (q>0) to the left side (q

Dependence of the Hysteresis Characteristics of Co-Au Core-Shell Nanoparticles on the Size of the Particles

2015 ◽  
Vol 233-234 ◽  
pp. 554-557
Author(s):  
Maria A. Chernova ◽  
Leonid L. Afremov ◽  
Ilia G. Iliushin
Keyword(s):  
Experimental Data ◽  
Saturation Magnetization ◽  
Coercive Field ◽  
Hysteresis Loops ◽  
Core Shell ◽  
Residual Saturation ◽  
Shell Nanoparticles ◽  
Core Shell Nanoparticles ◽  
Hysteresis Characteristics ◽  
Good Agreement

Hysteresis loops were plotted and dependence of coercive field, residual saturation magnetization and saturation magnetization on size of the Co-Au core-shell nanoparticles were calculated within the developed model. It was shown that decrease in the size of nanoparticles leads to decrease of the abovementioned characteristics. Calculated values of the hysteresis characteristics ​​are in good agreement with the experimental data.

Estimation of Non-Linear Damping Parameters in a Normal Triangular Array Subject to Fluidelastic Instability

2006 ◽  
Author(s):  
Craig Meskell ◽  
Petr Eret
Keyword(s):  
Experimental Data ◽  
Limit Cycle ◽  
Triangular Array ◽  
Working Fluid ◽  
Structural Damping ◽  
Non Linear ◽  
Fluidelastic Instability ◽  
Linear Damping ◽  
Predicted Values ◽  
Good Agreement

The non-linear damping parameters associated with a coupled fluidelastic system have been extracted using the non-linear decrement method. The response of a single flexible tube in a five row normal triangular tube array (P/d = 1.32) was recorded over a range of freestream velocities with air as the working fluid. The structural damping has been set so as to avoid fluidelastic instability. The linear and cubic fluidelastic damping parameters have been obtained. Using these identified quantities, the limit cycle amplitudes for the system at lower structural damping levels have estimated. Good agreement between the predicted values and the experimental data is achieved.

Computational Fluid Dynamics Analysis of a Hydrokinetic Turbine Based on Oscillating Hydrofoils

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Thomas Kinsey ◽  
Guy Dumas
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Numerical Simulations ◽  
Spatial Configuration ◽  
Operating Conditions ◽  
Power Extraction ◽  
Numerical Predictions ◽  
Hydrokinetic Turbine ◽  
Computational Fluid Dynamics Analysis

The performance of a new concept of hydrokinetic turbine using oscillating hydrofoils to extract energy from water currents (tidal or gravitational) is investigated using URANS numerical simulations. The numerical predictions are compared with experimental data from a 2 kW prototype, composed of two rectangular oscillating hydrofoils of aspect ratio 7 in a tandem spatial configuration. 3D computational fluid dynamics (CFD) predictions are found to compare favorably with experimental data especially for the case of a single-hydrofoil turbine. The validity of approximating the actual arc-circle trajectory of each hydrofoil by an idealized vertical plunging motion is also addressed by numerical simulations. Furthermore, a sensitivity study of the turbine’s performance in relation to fluctuating operating conditions is performed by feeding the simulations with the actual time-varying experimentally recorded conditions. It is found that cycle-averaged values, as the power-extraction efficiency, are little sensitive to perturbations in the foil kinematics and upstream velocity.

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