Dynamics of a Flexible Beam Contacting a Linear Spring at Low Frequency Excitation: Experiment and Analysis

2002 ◽  
Vol 124 (2) ◽  
pp. 237-249 ◽  
Author(s):  
Karen J. L. Fegelman ◽  
Karl Grosh
Keyword(s):  
Low Frequency ◽  
Theoretical Models ◽  
Model System ◽  
Degree Of Freedom ◽  
Flexible Beam ◽  
High Frequencies ◽  
Linear Spring ◽  
Frequency Excitation ◽  
The Impact ◽  
Period Motion

A detailed study of one-, two-, and three-impact per period motion of a vibro-impacting, pinned beam is presented involving experimental results, as well as one- and multi-degree-of-freedom theoretical models. The details of the impact event are examined and correlated to the qualitative appearance of the frequency response. In addition, it is noted that the multi-degree-of-freedom model is necessary in order to predict response at high frequencies. This study is unique in that the model system includes a pinned boundary condition, the forcing frequency is considerably lower than the fundamental in-contact natural frequency, and the frequency analysis extends into a range important for acoustic predictions.

Permeability and borehole Stoneley waves: Comparison between experiment and theory

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 66-75 ◽  
Author(s):  
Kenneth W. Winkler ◽  
Hsui‐Lin Liu ◽  
David Linton Johnson
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Theoretical Models ◽  
Oil Field ◽  
Stoneley Wave ◽  
Biot Theory ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
High Frequencies ◽  
Theoretical Predictions

We performed laboratory experiments to evaluate theoretical models of borehole. Stoneley wave propagation in permeable materials. A Berea sandstone and synthetic samples made of cemented glass beads were saturated with silicone oils. We measured both velocity and attenuation over a frequency band from 10 kHz to 90 kHz. Our theoretical modeling incorporated Biot theory and Deresiewicz‐Skalak boundary conditions into a cylindrical geometry and included frequency‐dependent permeability. By varying the viscosity of the saturating pore fluid, we were able to study both low‐frequency and high‐frequency regions of Biot theory, as well as the intermediate transition zone. In both low‐frequency and high‐frequency regions of the theory, we obtained excellent agreement between experimental observations and theoretical predictions. Velocity and attenuation (1/Q) are frequency‐dependent, especially at low frequencies. Also at low frequencies, velocity decreases and attenuation increases with increasing fluid mobility (permeability/viscosity). More complicated behavior is observed at high frequencies. These results support recent observations from the oil field suggesting that Stoneley wave velocity and attenuation may be indicative of formation permeability.

scholarly journals Implementation and Comparison of Contact Models Within PIRAT for Nuclear Reactivity Control Systems

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Matthew S. Bonney ◽  
Maxime Zabiégo
Keyword(s):  
Control Systems ◽  
Seismic Event ◽  
Nuclear Reactor ◽  
Low Frequency ◽  
Assessment Tools ◽  
Single Frequency ◽  
Maximum Displacement ◽  
Contact Models ◽  
Linear Spring ◽  
Frequency Excitation

Abstract The reactivity control system is a vital safety system for a nuclear reactor. One of the most challenging aspects in the design of these systems is the operation during critical situations, in particular during earthquakes to safely shut-down the reactor. To study these situations, the toolbox python Implementation for Reliability Assessment Tools (PIRAT) is used to model two types of excitation: single frequency and realistic. The main focus of this work is the comparison of the implementation of the contact models used to describe the interaction between the subsystems. For the dynamic tool in PIRAT (dynamic Euler–Bernoulli for seismic event (DEBSE)), this is done with a two-stage linear spring or Lankarani and Nikravesh-based models. For the sine excitation, the results show four distinct response types with the maximum displacement varying between the models. Low-frequency excitation showed little variance while higher frequency excitation showed large variations. The realistic excitation, however, did not show these variations and showed nearly identical results for the contact models tested. This gives confidence in the simulations since the user selected contact model did not greatly affect the simulation results for a realistic excitation.

The Dynamics of an Impact Print Hammer

1988 ◽  
Vol 110 (2) ◽  
pp. 193-200 ◽  
Author(s):  
P. C. Tung ◽  
S. W. Shaw
Keyword(s):  
Period Doubling ◽  
Cycle Period ◽  
Flexible Beam ◽  
Qualitative Behavior ◽  
Periodic Motions ◽  
Chaotic Motions ◽  
Linear Spring ◽  
The Stability ◽  
Energy Type ◽  
The Impact

A mathematical model is developed to describe the characteristic behavior of an impact print hammer of the stored energy type. The armature of the impact print hammer is represented by a rigid mass held against a backstop by a preloaded linear spring with negative stiffness which characterizes the net effect of a permanent magnet and a prestressed flexible beam acting on the armature. Periodic sine pulses are adopted to represent currents which release the armature to strike the ribbon and paper which is represented by a linear spring and a linear viscous dashpot. A coefficient of restitution is employed to characterize the instantaneous behavior of impact and rebound at the backstop. In this paper, periodic motions with n impacts against the backstop per forcing cycle, period doubling bifurcations, and chaotic motions are found. The stability of the periodic motions is investigated as is the influence of various parameters on the performance of the impact print hammer. With this simple model we can predict much of the qualitative behavior of the actual physical system.

scholarly journals Observed Evidences of Frequency-Dependent Site Spectral Amplification due to Strong Structural Control of Active Reverse Faults at Different Three Localities in Japan

2021 ◽  
Author(s):  
Mostafa Thabet
Keyword(s):  
Fault Zone ◽  
Structural Control ◽  
Active Fault ◽  
Low Frequency ◽  
Fault Zones ◽  
Low Velocity ◽  
Frequency Dependent ◽  
Near Surface ◽  
High Frequencies ◽  
The Impact

Abstract In the present study, observed active fault zone related site amplification is calculated based on Fourier acceleration spectrum (FAS) at three different localities in Japan. For this purpose, the FASs are calculated using 26432 earthquakes recorded at 126 K-NET and KiK-net seismic stations, which are distributed on the fault zones and upthrown and downthrown sides. This observed amplification is strongly frequency-dependent because of the presence of the near-surface low-velocity flower fault structure and the deeper fault zone. Moreover, the amplification patterns at each study area are tectonic-specific patterns. Sources inside the active fault zones could produce amplification at high frequencies at stations on both fault zone and far away from the fault zone. This is because of the impact of the near-surface fault zone. Sources outside the active fault zones could not produce significant amplification at high frequencies, whereas remarkable high amplification at low frequencies exhibits a gradual increase through stations on hanging walls, fault zones, and footwalls. Remarkably, low-frequency amplification due to sources outside the active fault zones at stations on footwalls is much higher than those observed on hanging walls. Interestingly, the peaks of the low-frequency amplification are corresponding to wavelengths that approximately equalize the width of the fault zone. Diffuse field theory inversion using earthquake horizontal-to-vertical spectral ratio (EHVSR) could successfully detect the presence of fault zone low-velocity layers. However, analyzing the fault zone related site effects using HVSR is not effective because of the strong amplification related structural control of the active fault zones on the ground motions.

The Effects of Employment Protection legislationon Personnel Policies: A Review of Theoretical Modelsand Empirical results

2014 ◽  
pp. 126-140
Author(s):  
O. Mironenko
Keyword(s):  
Personnel Selection ◽  
Selection Criteria ◽  
Theoretical Models ◽  
Employment Protection ◽  
Empirical Results ◽  
Protection Legislation ◽  
Labour Contracts ◽  
Hiring And Firing ◽  
The Impact ◽  
Personnel Policies

Employers incur costs while fulfilling the requirements of employment protection legislation. The article contains a review of the core theoretical models and empirical results concerning the impact of these costs on firms’ practices in hiring, firing, training and remuneration. Overall, if wages are flexible or enforcement is weak, employment protection does not significantly influence employers’ behavior. Otherwise, stringent employment protection results in the reduction of hiring and firing rates, changes in personnel selection criteria, types of labour contracts and dismissal procedures, and, in some cases, it may lead to the growth of wages and firms’ investments to human capital.

USING FIELD DATA FOR THE EVALUATION OF THE IMPACT OF ULTRA-LOW FREQUENCY MOTIONS ON THE FATIGUE OF MOORING LINES

2019 ◽  
Author(s):  
Guilherme Borzacchiello ◽  
Carl Albrecht ◽  
Fabricio N Correa ◽  
Breno Jacob ◽  
Guilherme da Silva Leal
Keyword(s):  
Field Data ◽  
Low Frequency ◽  
Mooring Lines ◽  
The Impact

scholarly journals Rheology of rounded mammalian cells over continuous high-frequencies

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gotthold Fläschner ◽  
Cosmin I. Roman ◽  
Nico Strohmeyer ◽  
David Martinez-Martin ◽  
Daniel J. Müller
Keyword(s):  
High Frequency ◽  
Mammalian Cells ◽  
Mechanical Response ◽  
Cell Mass ◽  
Low Frequency ◽  
Mass Measurements ◽  
High Frequencies ◽  
Polymer Relaxation ◽  
Continuous Frequency ◽  
Rheological Experiments

AbstractUnderstanding the viscoelastic properties of living cells and their relation to cell state and morphology remains challenging. Low-frequency mechanical perturbations have contributed considerably to the understanding, yet higher frequencies promise to elucidate the link between cellular and molecular properties, such as polymer relaxation and monomer reaction kinetics. Here, we introduce an assay, that uses an actuated microcantilever to confine a single, rounded cell on a second microcantilever, which measures the cell mechanical response across a continuous frequency range ≈ 1–40 kHz. Cell mass measurements and optical microscopy are co-implemented. The fast, high-frequency measurements are applied to rheologically monitor cellular stiffening. We find that the rheology of rounded HeLa cells obeys a cytoskeleton-dependent power-law, similar to spread cells. Cell size and viscoelasticity are uncorrelated, which contrasts an assumption based on the Laplace law. Together with the presented theory of mechanical de-embedding, our assay is generally applicable to other rheological experiments.

scholarly journals Evaluation of P-Band SAR Tomography for Mapping Tropical Forest Vertical Backscatter and Tree Height

2021 ◽  
Vol 13 (8) ◽  
pp. 1485
Author(s):  
Naveen Ramachandran ◽  
Sassan Saatchi ◽  
Stefano Tebaldini ◽  
Mauro Mariotti d’Alessandro ◽  
Onkar Dikshit
Keyword(s):  
Tropical Forest ◽  
Vertical Profile ◽  
Mean Squared Error ◽  
Low Frequency ◽  
Tree Height ◽  
Canopy Layer ◽  
Local Maxima ◽  
Slope Correction ◽  
Compensation Approach ◽  
The Impact

Low-frequency tomographic synthetic aperture radar (TomoSAR) techniques provide an opportunity for quantifying the dynamics of dense tropical forest vertical structures. Here, we compare the performance of different TomoSAR processing, Back-projection (BP), Capon beamforming (CB), and MUltiple SIgnal Classification (MUSIC), and compensation techniques for estimating forest height (FH) and forest vertical profile from the backscattered echoes. The study also examines how polarimetric measurements in linear, compact, hybrid, and dual circular modes influence parameter estimation. The tomographic analysis was carried out using P-band data acquired over the Paracou study site in French Guiana, and the quantitative evaluation was performed using LiDAR-based canopy height measurements taken during the 2009 TropiSAR campaign. Our results show that the relative root mean squared error (RMSE) of height was less than 10%, with negligible systematic errors across the range, with Capon and MUSIC performing better for height estimates. Radiometric compensation, such as slope correction, does not improve tree height estimation. Further, we compare and analyze the impact of the compensation approach on forest vertical profiles and tomographic metrics and the integrated backscattered power. It is observed that radiometric compensation increases the backscatter values of the vertical profile with a slight shift in local maxima of the canopy layer for both the Capon and the MUSIC estimators. Our results suggest that applying the proper processing and compensation techniques on P-band TomoSAR observations from space will allow the monitoring of forest vertical structure and biomass dynamics.

scholarly journals Transport Properties of Natural and Artificial Smart Fabrics Impregnated by Graphite Nanomaterial Stacks

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1018
Author(s):  
Carola Esposito Corcione ◽  
Francesca Ferrari ◽  
Raffaella Striani ◽  
Antonio Greco
Keyword(s):  
Electrical Conductivity ◽  
Transport Properties ◽  
Low Cost ◽  
Empirical Relationship ◽  
Theoretical Models ◽  
Expandable Graphite ◽  
Easy Method ◽  
Textile Materials ◽  
Fabric Materials ◽  
The Impact

In this work, we studied the transport properties (thermal and electrical conductivity) of smart fabric materials treated with graphite nanomaterial stacks–acetone suspensions. An innovative and easy method to produce graphite nanomaterial stacks–acetone-based formulations, starting from a low-cost expandable graphite, is proposed. An original, economical, fast, and easy method to increase the thermal and electrical conductivity of textile materials was also employed for the first time. The proposed method allows the impregnation of smart fabric materials, avoiding pre-coating of the fibers, thus reducing costs and processing time, while obtaining a great increase in the transport properties. Two kinds of textiles, cotton and Lycra®, were selected as they represent the most used natural and artificial fabrics, respectively. The impact of the dimensions of the produced graphite nanomaterial stacks–acetone-based suspensions on both the uniformity of the treatment and the transport properties of the selected textile materials was accurately evaluated using several experimental techniques. An empirical relationship between the two transport properties was also successfully identified. Finally, several theoretical models were applied to predict the transport properties of the developed smart fabric materials, evidencing a good agreement with the experimental data.

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