Large Damping Effect Research Articles

Quantitative and Intuitive VSG Transient Analysis With the Concept of Damping Area Approximation

The inherent large damping effect in virtual synchronous generator (VSG) control brings great challenges to its transient analysis. The recent studies mainly focus on qualitative explanation of damping effect, lacking an intuitive and quantitative assessment method. In this letter, the concept of damping area is introduced to visualize the transient damping energy in a tailored phase portrait, which facilitates the physical and intuitive understanding of damping effects. On top of that, the damping area approximation method is further proposed to evaluate attraction domain quantitatively, and its conservativeness for VSG control is proved in theory and validated by experiments. The proposed method evaluates the impact of damping on attraction domain quantitatively and intuitively, and it may provide some insights into the VSG transient stability analysis.

Dynamics of the Transient Negative Eddy Response to Zonal-Mean Zonal Wind Variations

Abstract Many studies have focused on the long-term positive feedback between annular mode zonal wind (U) perturbations and the eddy momentum fluxes (M). Lagged correlation analysis between U and M anomalies, however, shows that a transient period of negative eddy forcing follows the peak in zonal wind anomalies. This negative forcing is more ubiquitous than the positive feedback because it occurs for all U EOFs not just EOF1. It has been hypothesized that this response is either 1) an intrinsic feature of the eddies independent of the U or 2) caused by U-induced changes in Rossby wave reflection. Here it is shown that the response can be reproduced in a GCM by imposing a rapid change in U; therefore, mechanism 1 does not appear to be relevant. Furthermore, the transient response can be generated in a model when there are no turning latitudes; therefore, mechanism 2 does not appear to be relevant. Instead it is shown that the transient response is due to the adjustment of a preexisting eddy field to a change in the background wind. This transient effect is negative when the meridional scale of the U change is small enough compared to the waves, and vice versa. The sign of the initial response depends on the relative size of advection by U versus retrogression by the background vorticity gradient on the meridional tilt of the Rossby waves. Finally, it is shown that this transient response has a large damping effect on U variability.

Experimental Study on Application of Tuned Mass Dampers for Chatter in Turning of a Thin-Walled Cylinder

Chatter is more likely to occur during the turning process of a thin-walled cylindrical workpiece owing to the low rigidity of such workpieces. Chatter causes intensive vibration, deterioration of the surface finish accuracy, tool damage, and tool wear. Tuned mass dampers (TMD) are usually applied as a passive damping technique to induce a large damping effect using a small mass. This study experimentally investigated the effect of the mounting arrangement and tuning parameters of the TMDs on the production of chatter during the turning process of a thin-walled cylinder, wherein multiple TMDs with extremely small mass ratios were attached to the rotating workpiece. The results of the cutting tests performed by varying the circumferential and axial mounting positions of the TMDs exhibited different characteristics of the chatter suppression effect. Conclusively, the TMDs could suppress the chatter generated by the vibration mode with circumferential nodes if they were mounted on the workpiece to avoid the coincidence of the circumferential arrangement with the pitch of the vibration nodes, regardless of the extremely small mass of the TMDs.

Clutching inerters enhanced tuned mass dampers for structural response mitigation under impulsive and seismic excitations

Inerters, a type of two-terminal inertial elements, have significantly enhanced the performance of conventional control devices. The clutching inerters are especially appealing since they take energy away from the structural system without transferring back. In this study, a clutching inerter enhanced tuned mass damper (TMDCI) is proposed. First, the formation of the TMDCI is described based on a tuned mass damper inerter and two clutching flywheels. Then, the equations of motion are derived for the TMDCI on a single-degree-of-freedom (SDOF) primary structure. Subsequently, the modal properties of the TMDCI system are revealed by examining the steady-state responses under harmonic ground excitations. Afterward, performance analyses are conducted for the TMDCI on SDOF and three-DOF steel structures when subjected to initial velocities. The frequency robustness and parametric sensitivity of the TMDCI are evaluated on the SDOF structure, whereas practical concerns regarding the hosting location and stiffness demand of the TMDCI are addressed on the three-DOF structure. Finally, the seismic performance of the TMDCI is investigated on the three-DOF structure under a suite of earthquakes. The results show that the TMDCI exhibits a large damping effect which can reduce responses in both the structure and device and maintain strong robustness against frequency uncertainties. This study demonstrates the great potential of TMDCIs as an effective and affordable control strategy for the seismic protection of structures.

Anisotropic plasmons due to carrier electrons in Cs-doped hexagonal WO3 studied by momentum transfer resolved electron energy-loss spectroscopy

Cs-doped hexagonal WO3 (CWO) is used as a solar heat-shielding material for windows, in which plasma oscillation due to carrier electrons (carrier plasmon) plays an important role for near infrared scattering. Despite the hexagonal crystal structure of CWO, the anisotropic properties of the carrier plasmons have not been investigated. This study reports the momentum transfer resolved electron energy-loss spectroscopic measurements of CWO to investigate the anisotropic properties of carrier plasmons. The experimental results clarified that the two plasma oscillation modes at 1.2 and 1.8 eV have different excitation properties in CWO. One plasma oscillation at 1.2 eV was excited for q along the ab plane with a large damping effect, which indicated that electron excitations occur for the q//ab plane. Another mode at 1.8 eV was an oscillation excited for q along the c-axis with a small damping effect, i.e., a long plasmon relaxation time. These two modes can be interpreted by the anisotropic energy dispersion of the electronic states around the Fermi level of CWO. Such anisotropic properties of the carrier plasmons led to an accurate understanding of the heat-shielding mechanism.

Properties of Subhalos in the Interacting Dark Matter Scenario

One possible and natural derivation from the collisionless cold dark matter (CDM) standard cosmological framework is the assumption of the existence of interactions between dark matter (DM) and photons or neutrinos. Such a possible interacting dark matter (IDM) model would imply a suppression of small-scale structures due to a large collisional damping effect, even though the weakly-interacting massive particle (WIMP) can still be the DM candidate. Because of this, IDM models can help alleviate alleged tensions between standard CDM predictions and observations at small mass scales. In this work, we investigate the properties of the DM halo substructure or subhalos formed in a high-resolution cosmological N-body simulation specifically run within these alternative models. We also run its CDM counterpart, which allowed us to compare subhalo properties in both cosmologies. We show that, in the lower mass range covered by our simulation runs, both subhalo concentrations and abundances are systematically lower in IDM compared to the CDM scenario. Yet, as in CDM, we find that median IDM subhalo concentration values increase towards the innermost regions of their hosts for the same mass subhalos. Similarly to CDM, we find IDM subhalos to be more concentrated than field halos of the same mass. Our work has a direct application to studies aimed at the indirect detection of DM where subhalos are expected to boost the DM signal of their host halos significantly. From our results, we conclude that the role of the halo substructure in DM searches will be less important in interacting scenarios than in CDM, but is nevertheless far from being negligible.

Experimental investigation on hygrothermal performance of a bio-based wall made of cement mortar filled with date palm fibers

In the present work, the hygrothermal behavior of a wall structure made of a novel biobased material, i.e. date palm fiber reinforced concrete was investigated. In this context, a specific setup was developed which allows simulating a bi-climatic environment with separate outdoor and indoor environments. This device made it possible to apply various scenarios of static / dynamic hygrothermal loading to the outer side of wall, involving variation/cycling of temperature (T) and /or relative humidity (RH). During these experiments, resulting variations of T and RH across the wall thickness were monitored with in-situ sensors. Outstanding thermo-hygric phenomena were highlighted, such as high coupling effect between heat and moisture transfers, resulting from evaporation-condensation and sorption-desorption processes. Besides, significant thermal and hygric inertia was observed through the Date Palme Concrete (DPC) wall. The response time of this DPC wall to temperature variations remains shorter than in the case of humidity variations. Even so, large damping effect is obtained compared to outdoor boundary conditions, which make this DPC wall a good candidate for mitigating overheating during summertime and reducing interstitial condensation as well.

Q factor enhancement of Si resonator by nonlinear damping

The nonlinear damping effect of thin cantilevered Si resonators with thicknesses of 100---1500 nm is investigated from the measurements of the Q factor change versus the vibration amplitude. The Q factor of the 100 nm-thick resonator largely increases as its vibration amplitude become larger due to its large nonlinear damping effect, while the Q factor increment of the thicker resonators (400, 800, 1500 nm of thickness) becomes smaller. The surface condition of the Si resonator also has an interaction to the amplitude dependence on the Q factor. The H2 annealing increases the Q factor change with increasing the amplitude, and the Ar plasma treatment is vice versa. These results show that Si resonators exhibit the nonlinear damping effect, and the large Q factor enhancement by this effect is markedly observed in the thin resonator. The nonlinear damping constant of the 100 nm-thick Si resonator was ź1.12 × 1011 kg/m2s.

Enhancement of Microwave Properties of FeCoN Films on Mica Substrates by Control of SiO2 Underlayer Thickness

A thin SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> underlayer has been found to be effective to enhance the microwave properties of FeCoN films on mica substrates. In this study, the effect of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness on static and dynamic magnetic properties was studied. A 160 nm FeCoN film directly deposited on a mica substrate exhibited in-plane isotropy, accompanied by a large coercivity of 70 Oe. By inserting a thin SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as the underlayer, the anisotropy and coercivity were dramatically changed. When the thickness of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was 40nm, the film had well-defined in-plane anisotropy, and the coercivity greatly decreased to less than 3Oe. Correspondingly, excellent microwave properties were obtained with a strong magnetic resonance at 2.8GHz. However, both the static and dynamic magnetic properties declined rapidly with the further increase in the thickness of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , which is related to the large damping effect due to the increased surface roughness and residual stress of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer.

Dynamical density and spin response functions of two-dimensional correlated fermion systems: Self-consistent second-order perturbation theory

Dynamical density and spin responses of a two-dimensional fermion system are studied with the self-consistent second-order perturbation theory using a model Hamiltonian. Special attention is paid to the density response at a large wave vector, where it was reported that a sharp mode develops below the particle-hole continuum in two-dimensional liquid ${}^{3}$He. We find that at a large wave vector, a peak in the dynamical density structure factor shifts to lower energy as interaction sets in, but it is not sharp enough to represent a well-defined mode because of the strong damping effect of the quasiparticles. We point out that it is necessary to treat the large damping effect properly in explaining the propagating mode found in two-dimensional liquid ${}^{3}$He.

Influencing Factors on Dynamic Response of Hydrostatic Guideways

Stiffness and damping of hydrostatic guideways are calculated by small perturbation method based on Reynolds equation in dynamic regime. The hydrostatic guideway is considered as a system which consists of the mass, the spring and the damper. The effects of some main parameters on stiffness, damping and damping ratio are analyzed which include the supply pressure, the film thickness, the pad dimension, the pressure ratio, the lubricating oil volume and the lubricating oil viscosity. The relationships between the settling time of the hydrostatic guideways and these parameters are investigated under a step load. It is shown that the slide block returns to equilibrium without overshooting under a step load, and the amplitude of the block vibration has not a maximum value under a cyclic load, due to the large damping effect( ξ&gt;1). In addition, the settling time can be shorten with the increase of the supply pressure, the film thickness and the lubricating oil volume, and also with the decrease of the pressure ratio and the lubricating oil viscosity. The settling time get the shortest value when recess parameter( α) is 0.55.

Numerical Electromagnetic Analysis of Current and Voltage Distribution along Down Conductors and Towers Hit by Direct Lightning

In order to answer the practically important question of whether the down conductors of lightning protection systems to tall towers and buildings can be electrically isolated from the structure itself, this work is conducted. As a first step in this regard, it is presumed that the down conductor placed on metallic tower will be a pessimistic representation of the actual problem. This opinion was based on the fact that the proximity of heavy metallic structure will have a large damping effect. The post-stroke current distributions along the down conductors and towers, which can be quite different from that in the lightning channel, govern the post-stroke near field and the resulting gradient in the soil. Also, for a reliable estimation of the actual stroke current from the measured down conductor currents, it is essential to know the current distribution characteristics along the down conductors. In view of these, the present work attempts to deduce the post-stroke current and voltage distribution along typical down conductors and towers. A solution of the governing field equations on an electromagnetic model of the system is sought for the investigation. Simulation results providing the spatio-temporal distribution of the post-stroke current and voltage has provided very interesting results. It is concluded that it is almost impossible to achieve electrical isolation between the structure and the down conductor. Furthermore, there will be significant induction into the steel matrix of the supporting structure.

435 床下機器の高減衰弾性支持による鉄道車両の車体弾性振動低減

This report presents a simple method to reduce flexural vibrations in a railway vehicle carbody just by supporting underfloor equipments using high-damping elastic mounts. Recent studies by the authors show that on-boarding passengers have large additional damping effect on the carbody flexural vibrations. Since a human as a elastic body itself has relatively large damping coefficient, we tried to simulate the additional damping effect of passengers by supporting underfloor equipments using high-damping elastic material. Some numerical studies are firstly carried out to check the feasibity of the idea using simple single degree of freedom and two degrees of freedom systems. Then, two types of elastic mounting devices are built for actual railway vehicle. A series of excitation tests are conducted in the rolling stock testing plant in the Railway Technical Research Institute (RTRI) using a commuter type test vehicle by applying those elastic mounting devices, and good vibration reduction performances are observred by the tests.

Possibility of utilizing MCF in viscous damper of passive type

We experimentally investigated the dynamic characteristics of a viscous damper of passive damper type utilizing a newly proposed magnetically responsive fluid, MCF (magnetic compound fluid). We compared the characteristics regarding the damping and the response time of the damper's amplitude of MCF among those of MF and MR. The damping effect was also investigated as a viscous damping coefficient by employing a theoretical equation. MCF has the largest damping effect and the shortest response time. This cause can be considered the particles aggregating in chain- or necklace-shaped clusters in the fluid, as observed via light microscope.

Seismic behavior of concrete gravity dams with penetrated cracks and equivalent impact damping

The seismic behavior of concrete gravity dams with cracks that penetrate the monoliths has rarely been studied. The treatment of dynamic contact conditions at the cracks is the major difficulty. Not only all the sliding, rocking and drifting modes of motion have to be properly handled, but also specific attention should be focused on impact when the crack is closing. This study employs the FEM and adopts the IDCE (incremental displacement constraint equations) model to deal with all the modes of motion along the cracks. For impact, equivalent damping is introduced based on the concept of coefficient of restitution that is used in collision between point masses. After the IDCE damping model is verified in dynamic contact situations for rigid and flexible bodies, a typical concrete gravity dam with full reservoir water and three cases of crack is investigated under El Centro 1940 NS earthquake excitation. Calculations reveal very interesting phenomena, such as occurrence of rocking and jumping, coupling between the direction of residual sliding and the direction of peak rocking, and the large damping effect of multi-cracks on peak residual sliding, rocking and jumping.

ADDED VISCOUS DAMPERS IN SHEAR-TYPE STRUCTURES: THE EFFECTIVENESS OF MASS PROPORTIONAL DAMPING

In this paper the authors investigate the dynamic performances of multi-degree-of-freedom shear-type structures equipped with manufactured viscous dampers. The system of added viscous dampers that leads to a mass proportional damping (MPD) matrix is identified as the one providing the best overall performance in terms of minimum top-storey response variance to a Gaussian band limited white noise input within the class of classically damped systems. A performance index developed by the authors and based upon modal damping ratios confirms that, within the class of Rayleigh damping systems, the MPD limiting case provides the largest damping effect. For a 6-d.o.f. system, a comparison with results available in literature also shows that the MPD system provides better performance than optimised (as suggested by other research works) non-classical damping schemes. A physical explanation for the optimum damping performance offered by MPD systems is also provided herein, together with clear indications about how to implement MPD systems in real building structures. A check on the applicability of MPD systems to real structures and its effectiveness is also carried out successfully through the development and study of a realistic finite element model of an actual 18-storey building.

414 配管系の簡易弾塑性応答解析手法

Under extreme seismic excitation, plastic deformation occurs in piping system. It is considered that the large damping effect causes with energy dissipation by the plastic deformation. In this study, a simplified method to calculate the damping effect and maximum seismic response of piping with plastic deformation was examined. The maximum response by this method resulted in appropriate simulations of the excitation tests of the piping models.

Development of Non-Sedimentation Type Damper

We proposed a new type of viscous fluid damper of non-sedimentation type having complex fluids : MF (magnetic fluid), MR (magneto-rheological fluid), MCF (magnetic compound fluid). The damper never has the sedimentation of particles by using permanent magnet settled in a cylinder. We also used an electro-magnet by applying steady or fluctuating magnetic fields and then the damper is suitable as semi-active damper. To investigate the effect of damping, we measured displacement ratio under low frequency of the vibration. By comparing among the differences of the damping effects by three kinds of the fluids, MCF has the largest damping effect. In case of using fluctuating magnetic field, it is also larger than in that of steady magnetic field. The cause is due to the cluster of particles aggregated like a chain or necklace in the MCF.

A possible mechanism of the pseudo-gap in organic superconductor on the basis of the superconducting fluctuation

The explanation of the anomalous behavior which was revealed by the nuclear magnetic resonance experiments in κ-type (BEDT-TTF) 2X is presented. We calculate the electronic properties by using the one-loop approximation for the superconducting fluctuation. The decrease of the density of states due to the large damping effect is obtained and the one-particle spectrum has a pseudogap structure around the Fermi level. It is found that these behaviors are peculiar to the quasi-two-dimensional system and are enhanced in the incoherent metal.

A Possible Mechanism of the Pseudogap in Organic Superconductor Based on the Superconducting Fluctuation

The explanation of the anomalous behavior in κ-type (BEDT-TTF) 2 X which was revealed by the nuclear magnetic resonance experiments is presented. We calculate the electronic properties by using the one-loop approximation for the superconducting fluctuation. The decrease of the density of states due to the large damping effect is obtained and the one-particle spectrum has a pseudogap structure around the Fermi level. It is found that these behaviors are peculiar to the quasi two-dimensional system and are enhanced in the incoherent metal. The similarity between the cuprates and this compounds is discussed and an experiment to check this proposal is suggested.