The Influence of Support Hardware and Piping System Seismic Response on Snubber Support Damping

1997 ◽  
Vol 119 (4) ◽  
pp. 451-456 ◽  
Author(s):  
C. Lay ◽  
O. A. Abu-Yasein ◽  
M. A. Pickett ◽  
J. Madia ◽  
S. K. Sinha
Keyword(s):  
Seismic Response ◽  
Fundamental Frequency ◽  
Damping Ratio ◽  
Damping Coefficient ◽  
Piping System ◽  
Nodal Displacement ◽  
Damping Coefficients ◽  
Fundamental Frequencies ◽  
Piping Systems

The damping coefficients and ratios of piping system snubber supports were found to vary logarithmically with pipe support nodal displacement. For piping systems with fundamental frequencies in the range of 0.6 to 6.6 Hz, the support damping ratio for snubber supports was found to increase with increasing fundamental frequency. For 3-kip snubbers, damping coefficient and damping ratio decreased logarithmically with nodal displacement, indicating that the 3-kip snubbers studied behaved essentially as coulomb dampers; while for the 10-kip snubbers studied, damping coefficient and damping ratio increased logarithmically with nodal displacement.

Seismic Response Reduction in Piping Systems Using Plastic Deformation of Pipe Support Structures

2012 ◽  
Author(s):  
Tsuneo Takahashi ◽  
Akira Maekawa
Keyword(s):  
Plastic Deformation ◽  
Seismic Response ◽  
Damping Ratio ◽  
Damping Coefficient ◽  
Piping System ◽  
Initial Stiffness ◽  
Support Structure ◽  
Modal Damping Ratio ◽  
Modal Damping ◽  
Piping Systems

This study describes inelastic seismic design of piping systems considering the effect of plastic deformation of a pipe support structure. The damping coefficient of a piping system is focused on, and the relation between seismic response of the piping system and elastic-plastic behavior of the support structure was studied using nonlinear time history analysis and complex eigenvalue analysis. The analysis results showed that the maximum seismic response acceleration of the piping system decreased largely in the area surrounded by pipe elbows including the support structure which allowed plastic deformation. Furthermore, modal damping coefficient increased a maximum of about seven-fold. The increase ratio of the modal damping coefficient was proportional to the size of the effective mass ratio, when a relatively large increase was seen in the increase ratio of the modal damping coefficient. On the other hand, the amount of the initial stiffness of the support structure made a difference in the increasing tendency of the modal damping ratio. In the case of relatively small initial stiffness, the modal damping ratio of only one vibration mode increased. The increment of the modal damping ratio was proportional to the effective mass ratio in the case of large initial stiffness. In the viewpoint of the inelastic seismic design, the seismic response of the piping system was little affected by the plastic deformation of the support structure with 10% variation of the secondary stiffness to the initial stiffness. The result suggested that the seismic response of the piping system with the support structure can be estimated by using only the support model which has the elastic perfectly plastic property even if there are various shapes of steel type of support structures.

scholarly journals Computation of Rayleigh Damping Coefficients for the Seismic Analysis of a Hydro-Powerhouse

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Zhiqiang Song ◽  
Chenhui Su
Keyword(s):  
Seismic Response ◽  
Seismic Analysis ◽  
Damping Ratio ◽  
Least Square Method ◽  
Least Square ◽  
Dynamic Responses ◽  
Damping Coefficients ◽  
Rayleigh Damping ◽  
Damping Matrix ◽  
Fundamental Frequencies

The mass and stiffness of the upper and lower structures of a powerhouse are different. As such, the first two vibration modes mostly indicate the dynamic characteristics of the upper structure, and the precise seismic response of a powerhouse is difficult to obtain on the basis of Rayleigh damping coefficients acquired using the fundamental frequencies of this structure. The damping ratio of each mode is relatively accurate when the least square method is used, but the accuracy of the damping ratios that contribute substantially to seismic responses is hardly ensured. The error of dynamic responses may even be amplified. In this study, modes that greatly influence these responses are found on the basis of mode participation mass, and Rayleigh damping coefficients are obtained. Seismic response distortion attributed to large differences in Rayleigh damping coefficients because of improper modal selection is avoided by using the proposed method, which is also simpler and more accurate than the least square method. Numerical experiments show that the damping matrix determined by using the Rayleigh damping coefficients identified by our method is closer to the actual value and the seismic response of the powerhouse is more reasonable than that revealed through the least square method.

Numerical Study on Inelastic Seismic Design of Piping Systems Using Damping Effect Based on Elastic–Plastic Property of Pipe Supports

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Akira Maekawa ◽  
Tsuneo Takahashi
Keyword(s):  
Seismic Response ◽  
Seismic Design ◽  
Plastic Property ◽  
Damping Coefficient ◽  
Seismic Load ◽  
Piping System ◽  
Elastic Plastic ◽  
Damping Effect ◽  
Modal Damping ◽  
Piping Systems

This study describes inelastic seismic design of piping systems considering the damping effect caused by elastic–plastic property of a pipe support which is called an elastic–plastic support. Though the elastic–plastic support is proposed as inelastic seismic design framework in the Japan Electric Association code for the seismic design of nuclear power plants (JEAC4601), the seismic responses of the various piping systems with the support are unclear. In this study, the damping coefficient of a piping system is focused on, and the relation between seismic response of the piping system and elastic–plastic behavior of the elastic–plastic support was investigated using nonlinear time history analysis and complex eigenvalue analysis. The analysis results showed that the maximum seismic response acceleration of the piping system decreased largely in the area surrounded by pipe elbows including the elastic–plastic support which allowed plastic deformation. The modal damping coefficient increased a maximum of about sevenfold. Furthermore, the amount of the initial stiffness of the elastic–plastic support made a difference in the increasing tendency of the modal damping coefficient. From the viewpoint of the support model in the inelastic seismic design, the reduction behavior for the seismic response of the piping system was little affected by the 10% variation of the secondary stiffness. These results demonstrated the elastic–plastic support is a useful inelastic seismic design of piping systems on the conditions where the design seismic load is exceeded extremely.

The Influence of Higher Modes and Support Gaps on the Seismic Response of Piping Systems Containing Snubbers

1997 ◽  
Vol 119 (4) ◽  
pp. 444-450 ◽  
Author(s):  
O. A. Abu-Yasein ◽  
C. Lay ◽  
M. A. Pickett ◽  
J. Madia ◽  
S. K. Sinha
Keyword(s):  
Seismic Response ◽  
Fundamental Frequency ◽  
Support System ◽  
Fundamental Mode ◽  
Support Condition ◽  
Higher Modes ◽  
Nodal Displacement ◽  
Piping Systems

In this study of flexible piping systems (0.6 to 6.6 Hz), it was shown that the fundamental mode was not always the most significant mode of vibration. This study also concluded that variations in support condition do not significantly influence response in terms of nodal stress, fundamental frequency, and contribution of higher modes. In terms of support stiffness, the ratio of the magnitude of the gap (the total of all the mechanical tolerances and deadbands in the snubber support system) to the magnitude of the support nodal displacement was found to be more important than the actual magnitude of the gap. Additionally, when the magnitude of the nodal displacement exceeded the gap magnitude by a factor of about five or more, support stiffness was found to remain relatively constant.

Pulsation suppression in a reciprocating compressor piping system using a two-tank element

2017 ◽  
Vol 232 (4) ◽  
pp. 427-437 ◽  
Author(s):  
Quyang Ma ◽  
Zhenhuan Wu ◽  
Guoan Yang ◽  
Yue Ming ◽  
Zheng Xu
Keyword(s):  
Theoretical Model ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Wave Theory ◽  
Damping Coefficient ◽  
Piping System ◽  
Pressure Pulsations ◽  
Surge Tank ◽  
Piping Systems ◽  
Gas Pulsations

Gas pulsations excited by reciprocating compressors could introduce severe vibrations and noise in piping systems. When pulsating gas flows through the reducers, the changes in flow characteristics, such as velocity and damping coefficient, will affect the pressure pulsations. To circumvent these constraints, a two-tank element is introduced to control the gas pulsation that is still strong in the piping system with a surge tank. Installing another surge tank to form a two-tank element is more flexible and costs lower than replacing the original surge tank with a larger one. In this work, a theoretical model based on the wave theory was proposed to study the transferring mechanism of gas pulsations in the pipeline with the two-tank element. By considering the damping coefficient and the Mach number, the distributions of the pressure pulsations were predicted by the theoretical model and agreed with the three-dimensional fluid dynamics transient analysis. Three experiments were conducted to prove that the suppression capability of the two-tank element is as good as that of a single-tank element (surge tank) with the same surge volume. The volume optimization of the two-tank element is implemented by selecting the best allocations of the two tanks’ volumes to achieve larger reductions of pressure pulsations. Assuming that the total surge volume is constant, we found that the smaller the volume of the front tank (near the cylinder) is, the lower the pulsation levels are. The optimized result proves that in some conditions the two-tank element could control pulsations better than the single-tank element with the same surge volume.

Response Characteristics of Piping System Supported by Visco-Elastic and Elasto-Plastic Dampers

1990 ◽  
Vol 112 (1) ◽  
pp. 34-38 ◽  
Author(s):  
T. Chiba ◽  
H. Kobayashi
Keyword(s):  
Energy Dissipation ◽  
Seismic Design ◽  
Damping Ratio ◽  
The Other ◽  
Piping System ◽  
Response Level ◽  
Response Characteristics ◽  
Damping Effect ◽  
Component Test ◽  
Piping Systems

Improving the reliability of the piping systems can be achieved by eliminating the mechanical snubber and by reducing the response of the piping. In the seismic design of piping system, damping is one of the important parameters to reduce the seismic response. It is reported that the energy dissipation at piping supports contributes to increasing the damping ratio of piping system. Visco-elastic damper (VED) and elasto-plastic damper (EPD) were developed as more reliable, high-damping piping supports. The dynamic characteristics of these dampers were studied by the component test and the full-scale piping model test. Damping effect of VED is independent of the piping response and VED can be modeled as a complex spring in the dynamic analysis. On the other hand, damping ratio of piping system supported by EPD increases with the piping response level. So, these dampers are helpful to increase the damping ratio and to reduce the dynamic response of piping system.

Simplified Seismic Response Analysis Method Using Reduced Model of Piping System

2018 ◽  
Author(s):  
Michiya Sakai ◽  
Ryuya Shimazu ◽  
Shinichi Matsuura ◽  
Ichiro Tamura
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Seismic Response ◽  
Degrees Of Freedom ◽  
Response Analysis ◽  
Piping System ◽  
Element Analysis ◽  
Mass System ◽  
Piping Systems ◽  
Low Degrees

In the seismic response analysis of piping systems, finite element analysis is performed with analysis method guidelines [1]–[4] established based on benchmark analysis. However, since it takes a great deal of effort to carry out finite element analysis, a simplified method to analyze the seismic response of complex piping systems is required. In this research, we propose a method to reduce an equivalent spring-mass system model with low degrees of freedom, which can take into account the main mode of the complicated piping system. Simplified seismic evaluation is carried out using this spring mass system model with low degrees of freedom, and the accuracy of response evaluation is confirmed by comparison with finite element analysis.

PWR Fuel Assembly Damping Characteristics

2006 ◽  
Author(s):  
Roger Y. Lu ◽  
David D. Steel
Keyword(s):  
Fuel Assembly ◽  
Temperature Effect ◽  
Damping Ratio ◽  
Damping Coefficient ◽  
Low Flow ◽  
Published Data ◽  
Viscous Damping ◽  
Flowing Water ◽  
Damping Coefficients ◽  
Flow Velocities

PWR fuel assembly damping is a key parameter in seismic/LOCA safety analysis. The damping coefficients of a fuel assembly in air, still water and flowing water are significantly different. Several researchers and engineers have published their results and methods in the past. With this paper, PWR fuel assembly damping was studied and tested in air, still water, and flowing water (including flowrate and temperature variation). The damping coefficients were obtained by the initial displacement and first response method. The coefficients are also compared with published data. Several conclusions are obtained. • The damping obtained from the tests in air gives the damping component of assembly structure damping. From the comparison of the damping in air with still water the amount of viscous damping can be determined. The viscous damping component is the effect of still water on damping. The amount of viscous damping is represented by the increase in the damping ratio from air to still water at room temperature. The results show that damping in still water is approximately two times the damping in air. • The temperature effect on damping in still water is minimal. In flowing water, the results show a very slight effect of temperature, as the damping slightly decreases with an increase in temperature. This temperature effect is much smaller than the data scatter observed in most damping measurement tests under the same test conditions. • The damping is significantly affected by flowing water. For relatively low flow velocities, compared to in-core conditions, the damping coefficient is around two times the damping in still water. For intermediate to high flow velocities, all damping coefficients are 2.5 times higher than that in still water. For high velocities and large displacement, the damping coefficient can be over 3 times higher than that in still water. The flow velocity appears to be acting on the system by suppressing the motion of the assembly. Additional damping due to flowing water is called hydraulic damping, which is generated by hydraulic force. When a fuel assembly vibrates in flowing water, the assembly is trying to change the flow direction and momentum, but the flow mass wants to retain its pure axial direction which suppresses the motion of the assembly.

Optimal Distribution of Damping Coefficients for Viscous Dampers in Buildings

2017 ◽  
Vol 17 (04) ◽  
pp. 1750054 ◽  
Author(s):  
Tzu Kang Lin ◽  
Jenn Shin Hwang ◽  
Kuan Hui Chen
Keyword(s):  
Damping Ratio ◽  
Optimization Method ◽  
Design Guidelines ◽  
Damping Coefficient ◽  
Optimal Distribution ◽  
Viscous Dampers ◽  
Moment Frame ◽  
Practical Applications ◽  
Soft Story ◽  
Damping Coefficients

Design guidelines for implementing viscous dampers to buildings have been broadly included in seismic design codes worldwide. Although the relationship between the damping coefficient of viscous dampers and the added damping ratio to the structure has been theoretically studied, the process of distributing the damping coefficient onto each story of a building has not been regulated by the codes. For practical applications, some distribution methods have been previously proposed. However, no comparison has been made between these proposed methods considering the controllability and design economy. In this paper, two search methods based on the genetic algorithms (GAs) are adopted to examine the optimal distribution of damping coefficients. The results are then compared with a variety of existing distribution methods. A comparison is made for the distribution methods assuming the same added damping ratio for the structure. Three two-dimensional frames are adopted in the comparison: a regular moment frame, a moment frame with a soft-story, and a setback building. The results indicated that similar seismic response reduction can be achieved by using different distribution methods if the supplemental damping ratio is the same, while the optimal story damping coefficient can be obtained by using the proposed optimization method. Moreover, the “story shear strain energy to efficient stories” (SSSEES) method, among others, offers advantages in terms of seismic reduction efficiency, economical design, and practical application simplicity.

Hybrid Seismic Response Evaluation Method for Wall Thinning Piping System

2013 ◽  
Author(s):  
Michiya Sakai ◽  
Shinichi Matsuura ◽  
Fumio Inada
Keyword(s):  
Seismic Response ◽  
Evaluation Method ◽  
Low Cycle Fatigue ◽  
Shaking Table ◽  
Piping System ◽  
Shaking Table Tests ◽  
Seismic Safety ◽  
Pipe Model ◽  
Wall Thinning ◽  
Piping Systems

Pipe wall thinning is a one of the major degradation mechanisms in aged nuclear power plants (NPPs). In Japan, the seismic safety of wall thinning piping system during earthquake must be evaluated in aged NPPs. Seismic safety of piping systems with wall thinning had been investigated by other researchers using shaking table tests of reduced scale and numerical analyses. However, there exist the limitations such as the scale effect of pipe model for shaking table tests and the limit of the evaluation for numerical analysis concerning the criteria of pipe integrity. By the way, elbow can be one of the most important elements to evaluate the seismic safety of piping system. So, in order to evaluate seismic safety of piping systems with wall thinning elbow, hybrid tests have been conducted, in which the seismic response of the whole piping system is treated as a numerical model, and the real piping is used only for the element on which the transformation and damage locally concentrated. The through-wall crack only occurred in the case of a uniform thinning model although cracks didn’t penetrate in the non thinning model and the local thinning model. In the experimental condition, the failure mode of wall thinning elbow under seismic loadings had been low cycle fatigue, and effectiveness of this evaluation method has been demonstrated.

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