Displacement RMS Research Articles

Stability control method of double crystal monochromator based on hybrid control algorithm

The Bragg angle stability of the DCM (double crystal monochromator) in synchrotron radiation facilities is critical for beam position, flux and resolution of hard X-ray beam lines. Generally, the vibration caused by LN2 cooling system is the most critical factor affecting the stability of DCM. In this paper, aiming at the stability of DCM, we propose the stability control method of double crystal monochromator base on hybrid control algorithm. The numerical results show that the stability of the DCM in the pitch direction can be greatly improved by this active vibration control method under LN2 mode. The angular displacement RMS value in the pitch direction decreased from about 358.52 nrad to about 0.071nrad, which decreased by 99.98%. Proposed method is of great significance to the research of ultra-high stability DCM in synchrotron radiation facilities all over the world.

Development of a novel tuned liquid multiple columns gas damper under wave and earthquake incidence

A developed tuned liquid multiple columns gas damper, introduced as a TLMCGD damper, is proposed in this study and its capability is assessed on an offshore jacket platform under regular and irregular waves and also earthquake incidence. The proposed damping system includes a combination of performance of both tuned liquid multiple columns damper (TLMCD) and tuned liquid column gas damper (TLCGD). The number of multiple columns and gas pressure are defined as of the main parameters of the damper and their performance are investigated through various values under earthquake. According to the results, a passive optimum TLMCGD system can decrease the structural response of the system up to 22, 60, and 55 percent under regular wave, irregular wave, and earthquake, respectively. The whole structural response of the system reduces as the number of columns and the value of gas pressure increases up to a certain amount. To investigate the effectiveness of gas pressure in performance of the damper, various gas pressure values are considered for different 4 to 10-column TLMCGD dampers. By increasing the value of the gas, the displacement RMS reduces significantly. The highest decrement occurs as 50 to 100 bar gas pressure is specified for the gas springs of the dampers. Still more investigation is required to evaluate other key parameter of the system within an experimental study which is left for future studies.

Experimental study on characteristics of vortex-induced vibration of a twin-box girder and damping effects

To investigate the characteristics of vortex-induced vibration (VIV) of the twin-box girder, we carried out the VIV wind tunnel tests. The VIV of the twin-box girder occurs in the range of 4.680≤Ur≤6.113, with the maximum dimensionless VIV displacement RMS(y)/D=0.03308 at reduced velocity at Ur=5.949. It is interesting that the VIV suddenly disappears at Ur=6.276 at the loading stage, and the large amplitude VIV does not occur at the unloading stage, which indicates that the vibration trajectory with the variation of reduced wind velocity shows significant asymmetry characteristic. In the lock-in region, as the aerodynamic lift force increases, both the phase lag and the VIV displacement show an increasing tendency with the reduced velocity. Flow visualization results show that strong alternately shedding vortex generates around the gap during the VIV. Under the effects of the vortex in the gap, the size of the separation bubble increases with the increase of vibration amplitude, and the wake width becomes wider. As the damping ratio increases, the amplitude of VIV displacement shows a decreasing tendency, the lock-in region becomes narrower and the reduced velocity corresponding to the max VIV displacement decreases. Moreover, the maximum RMS displacement of vertical VIV decays exponentially as the damping ratio increases.

Triggered afterslip on the southern Hikurangi subduction interface following the 2016 Kaikōura earthquake from InSAR time series with atmospheric corrections

The 2016 Mw 7.8 Kaikōura earthquake represents an extremely complex event involving over ten major crustal faults, altering conventional understanding of multi-fault ruptures. Although evidence for coseismic slip on the Hikurangi subduction interface is controversial, we present afterslip on the subduction zone beneath Marlborough using 13 months of Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) observations. The spatially and temporally correlated atmospheric errors in SAR interferograms are problematic, and hence a new InSAR time series approach, combining the Generic Atmospheric Correction Online Service (GACOS) with a spatial-temporal Atmospheric Phase Screen (APS) filter to facilitate the InSAR time series analysis, is developed. For interferograms with over 250 km spatial extent, we achieve a 0.77 cm displacement RMS difference against GPS, improving 61% from the conventional InSAR time series method (TS). Comparisons between the overlapping region of two independent tracks show an RMS difference of 1.1 cm for the TS-GACOS-APS combined method, improving 54% from the TS method and 27% from using TS with an APS filter only. The APS filter reduces the short wavelength residuals substantially, but fails to remove the long wavelength error even after the ramp removal, revealing that the GACOS correction has played a key role in mitigating long wavelength atmospheric effects. The resultant InSAR displacements, together with the GPS displacements, are used to recover the time-dependent afterslip distribution on the Hikurangi subduction interface, which provides insights for reviewing the co-seismic slip sources, the present status of the subduction plate boundary and future seismic hazards.

Integrated bi-directional vibration control and energy harvesting of monopile offshore wind turbines

Offshore wind turbines (OWTs) subjected to combined wind and wave loadings experience excessive bi-directional vibrations that adversely influence the system performance and the structural integrity. The present paper utilizes a three-dimensional pendulum tuned mass damper (3d-PTMD) to mitigate the bi-directional vibrations as well as harvest the kinetic energy using a linear electromagnetic energy harvester. The proposed energy harvester consists of magnets and coil assemblies which are connected with the pendulum to convert the kinetic energy of the pendulum into electricity. An analytical model of the offshore wind turbine coupled with the 3d-PTMD is established using Euler-Lagrangian equation. The mathematical model of the linear electromagnetic energy harvester is established and integrated with the wind turbine model. The optimum design of the electromagnetic energy harvester to minimize the nacelle displacement RMS as well as to maximize the energy output is determined via a numerical search method. The NREL 5 MW baseline wind turbine model is utilized to evaluate the performance of the 3d-PTMD and the energy harvester. Results show that the 3d-PTMD can reduce the bi-directional vibrations induced by misaligned wind and wave loadings. Additionally, electrical energy in orders of magnitude of kilowatts can be harnessed via using the energy harvester.

Improving Seismic Behavior of MRFs by U-shaped Hysteretic Damper Along Diagonal Brace

This paper presents seismic assessment of a U-shaped hysteretic damper as an enhancement system, in moment resisting frames. The proposed system is consisted of a damping box at the middle of a diagonal brace. The box includes U-shaped steel plates welded to the side plates. When a transverse load, like earthquake, is exerted to the building, relative displacement between the stories forms and will be transmitted to the braces where energy dissipation will be achieved by adding a displacement-dependent U-shaped damper. For this purpose, the system is applied to a 2D 2-span 3-story frame to which by applying eight different earthquake records, far-field, near-field and mid-field, seismic response are evaluated. The responses are the roof displacement, inter-story drifts, root mean squared of roof displacement and base shear. Result verification is carried out via calibrating characteristics of this damper with an experimental work on a somewhat similar device conducted at the University of Toronto. The results showed that by using this system, the roof maximum displacement decreased 38.9, 40.0 and 37.1% and the maximum base shear decreased 36.5, 28.5 and 39.5% respectively under near-field, mid-field and far-field records, averagely. Similar results were observed in inter-story drifts and roof displacement RMS.

Wind Tunnel Study on Wind-Induced Vibration Responses of a UHV Transmission Tower-Line System

This paper presents an experimental investigation on the wind-induced vibration of a transmission tower-line system. A discrete stiffness method is applied to design the aero-elastic model on the basis of similarity theory. The dynamic characteristics of the single tower and the tower-line system are identified and the displacement responses at different positions are obtained under a variety of wind speeds. The mean and the RMS of the displacements as well as their spectra are discussed. Moreover, the test results and the codal specifications are compared in terms of the wind-induced vibration coefficient. The first natural frequency of the single tower is slightly larger than that of the tower-line system. But the damping ratio of the former is smaller than that of the latter, especially in the direction normal to the conductors. At the wind attack angle of 90°, the conductors significantly increase the longitudinal and lateral displacement RMS as well as the longitudinal mean displacement. And more complicated forms of vibration are aroused by the conductors, especially in the lateral direction. The wind-induced vibration coefficient show a notable rise at the position of cross arm, which cannot be characterized by Chinese code. Besides, the wind-induced vibration coefficient specified by the code is much smaller than test results thus the codal value seems to be unsafe for the UHV transmission tower.

Development and testing of a general amber force field.

We describe here a general Amber force field (GAFF) for organic molecules. GAFF is designed to be compatible with existing Amber force fields for proteins and nucleic acids, and has parameters for most organic and pharmaceutical molecules that are composed of H, C, N, O, S, P, and halogens. It uses a simple functional form and a limited number of atom types, but incorporates both empirical and heuristic models to estimate force constants and partial atomic charges. The performance of GAFF in test cases is encouraging. In test I, 74 crystallographic structures were compared to GAFF minimized structures, with a root-mean-square displacement of 0.26 A, which is comparable to that of the Tripos 5.2 force field (0.25 A) and better than those of MMFF 94 and CHARMm (0.47 and 0.44 A, respectively). In test II, gas phase minimizations were performed on 22 nucleic acid base pairs, and the minimized structures and intermolecular energies were compared to MP2/6-31G* results. The RMS of displacements and relative energies were 0.25 A and 1.2 kcal/mol, respectively. These data are comparable to results from Parm99/RESP (0.16 A and 1.18 kcal/mol, respectively), which were parameterized to these base pairs. Test III looked at the relative energies of 71 conformational pairs that were used in development of the Parm99 force field. The RMS error in relative energies (compared to experiment) is about 0.5 kcal/mol. GAFF can be applied to wide range of molecules in an automatic fashion, making it suitable for rational drug design and database searching.

Suppression of vortex-excited vibration of tall buildings using tuned liquid dampers

The objective of this paper is to study the control effects of rectangular TLDs installed on a tall building that vibrates due to vortex excitation. Optimal design properties of these TLDs and their control performance are first obtained using the characteristic equation of the TLD-building system. Wind tunnel experiments are performed on a scaled-down building model equipped with rectangular TLDs of various sizes. The liquid heights of the TLDs are varied to determine an optimal TLD's frequency range for this building model under vortex-induced vibration. A total of 34 test cases that correspond to different TLD geometries are performed for wind speeds ranging from 1.5 to 4.2 m/s. It is found that the rectangular TLD is quite effective in reducing the vortex-excited vibration of a building, especially when its frequency is tuned to within the optimal range. The top displacement RMS value reduces to only one-sixth of that of the original building model without a TLD when the generalized mass ratio equals to 2.3%. The optimal frequency of the TLD range between 0.9 and 1.0 of that of the building model which is consistent with the analytical derivation.