Papers by Keyword: Damping Ratio

Abstract: The shear modulus and damping ratio are two important index in equivalent nonlinear model which is widely used in seismic response analysis. GDS resonant-column is used to study the shear modulus and damping ratio of highly weathered granite by controlling the consolidation confining pressure and pore water pressure. Variation of resonant frequency, shear modulus and damping ratio can be observed when different effective stress which is changed with confining pressure and pore water pressure applied on the sample. Hadin-Drnevich fitting curves are given on the basis of experimental data, and damping mechanism of highly weathered granite is discussed by making use of frictional theory. We can conclude from the results that there is a positive correlation between resonance frequency and shear strain, while there is a negative correlation between samples damping ratio and shear strain. The effective stress impact both samples shear modulus and damping ratio. However, pore water pressure can only act on damping ratio.

Abstract: Dynamic test has been carried out to completed road bridge of Nanjiang Port inTianjin. When cars were passing through the bridge, the dynamic deflections, the maximum amplitudes, the relation between amplitude and velocity, the Natural frequency and the damping ratio were gained. Dynamic modulus, vibration characteristics and crack condition of the bridge were determined so as to ascertain the reliability of the bridge.

Abstract: Damping ratio is a very important parameter for building structures in the analysis of dynamic response. Story-adding RC structure of light-weight steel is composed by two different material stories. If all the modal damping ratios are defined as the same, as to the dynamic analysis for that structure, the results of analysis will be inappropriate. This paper made some response spectrum analysis on a six-story story-adding RC structure of light-weight steel by finite element analysis software Midas Gen through defining the Rayleigh damping. In the meanwhile, compared the results based on different Rayleigh damping parameters with the results by using the method of strain energy proportional, and got the rule of the definition of Rayleigh damping.

Abstract: The shear modulus and damping ratio of soil are important factors for soil layer seismic response analysis, people have done a lot of research. Currently, the method to measure soil shear modulus and damping ratio have bending element test method, resonant column test, dynamic triaxial test and so on. This article describes the British GDS company developed a new resonant column GDS-RCA's main features, technical indicators and working principle, compared the IEM original GZ-1 resonant column test results with GDS-RCA resonant column test results, the compared results are as follows: both damping ratio results in somewhat different, but in 10^-6-10^-4 low strain shear modulus ratio between the range of test results are consistent, GDS-RCA resonant column testing machine can by low-frequency torsional mode, expand the soil strain measurement extended to 10^-6-10^-2, and the small strain to large strain test results are in good connection.

Abstract: The majority of aircrafts structure cracks due to fatigue are thin gage metallic structures and secondary support structures. Beside lower fatigue strength, they may also occur due to mechanical defects, especially at weak area and for areas exposed to high repetitive force such as vibration, friction, acoustic load and tensile force. Normally, the Original Equipment Manufacturer (OEM) recommended the aircraft operator to repair the crack by typical patch or doublers repair technique which is formally known as Non-Flush Patch Repair Scheme. However, the crack tends to reappear and tend to be more severe. The natural frequency and damping ratio of a structure which is treated with Typical Non-Flush Patch Repair, with and without Passive Damping Treatment (PDT) are studied using impulse based technique. Experimental data are presented to demonstrate the difference of damping ratio (ζ) among the test specimens. The cracked structure which has been treated with PDT on Non-Flush Repair Scheme has a better damping ratio and resonates at a different natural frequency. The experiment data generated from this study can be used as a basis to further the study on aircrafts structural repair scheme.

Abstract: In this paper based on the foundation construction of Datong Xian high-speed railway, a large number of test samples have been taken. The order and contribution rate of every experiment factor like cement commingle ratio, depths, water dipping conditions, compacting factor and vibration frequency on the dynamic characteristics of cement-improved loess such as dynamic elastic modulus, dynamic deformation, damping ratio by dynamic triaxial test, which orthogonal test method has been applied to. The dynamic load was calculated according to the train vibration attenuation rule of different depth. The dynamic characteristics of cement-improved loess such as dynamic deformation, dynamic elastic modulus, damping ratio were got form the dynamic tests of long time and large number of cycles. The results showed that with the increase of cement ratio, the dynamic characteristics of cement-improved loess are more better, there is no optimal ratio of cement.

Abstract: With the scale of the wind farm growing fast, its impact on the power system has become increasingly apparent. So the research has a significant meaning on the characteristics of dynamic stability of the power system which contains wind farms, and the stable operation of the large area interconnected power grid. In this paper it realized the application of the double-fed wind turbine grid model by using power system analysis software PSD-BPA. The analysis of the generator power Angle curve which indicate the state after the failure of N-1 shows as follows: with the wind farms integration on the grid, the damping ratio is decreased slightly but little change after the system failure of N-1, which is still live up to the standard of grid stability.

Abstract: For the good vibration alleviating properties, polymer concrete (PC) has attracted much attention in the field of elementary machine components. In order to get more excellent mechanical properties, the forming process and mechanical properties of PC were concerned. In this research, glass fiber and carbon fiber were applied to improve the mechanical properties of PC. A series of PC and fiber reinforced polymer conctete (FRPC) specimens were prepared basing on the orthogonal tables for property test. Compression strength test was carried out. It is obvious that FRPC is better than PC as far as compression strength is concerned, and carbon fiber reinforced polymer concrete (CFRPC) is better than glass fiber reinforced polymer concrete (GFRPC). Trend curves about the relationship between fiber length and compression strength, as well as that between fiber dosage and compression strength were drawn. Relationship between the considered factors and compression strength is analyzed basing on the experiment results and the trend curves. Strengthening fibers would bear most of the internal stress when the specimen is faced to outer loads. Thus, FRPC has much better properties than PC. Mechanical properties of CFRPC are relatively better than that of GFRPC, for the strength of carbon fiber is better than that of glass fiber. It could be concluded that glass fiber is the proper strengthening fiber for PC considering both technical and economical factors.

Abstract: The results of the experimental tests, in dynamic regime, on antiseismic elastomeric devices, evidenced the fact that the internal damping represents a significant parameter tightly related to the specific shearing deformation of the elastomeric elements. Consequently, based on the final obtained results, correlation curves were raised meant to represent the variation of the equivalent critical damping ration (dynamic system of order I).

Abstract: The present study examines the characteristics of rectangular and circular tuned liquid dampers, which control wind-induced vibration in tall buildings, according to the natural frequency. The tuned liquid dampers (TLD) were of frequencies: 0.44Hz, 0.55Hz, 0.64Hz and 0.73Hz. The tuning feature of TLD water tanks was better in circular water tanks than in rectangular water tanks. Excitation amplitude affected the damping ratio based on energy dissipation capacity. At low excitation (below 5mm) and low natural frequency (0.44Hz), circular water tanks were advantageous over rectangular water tanks. However, at high excitation (over 5mm) and high natural frequency (over 0.55Hz), rectangular water tanks were advantageous over circular water tanks.