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.

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.

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.

A constrained optimal Rayleigh damping coefficients for structures with closely spaced natural frequencies in seismic analysis

2016 ◽  
Vol 20 (1) ◽  
pp. 81-95 ◽  
Author(s):  
DG Pan ◽  
GD Chen ◽  
LL Gao
Keyword(s):  
Seismic Analysis ◽  
Lattice Structure ◽  
Damping Ratio ◽  
Optimization Method ◽  
Accurate Analysis ◽  
Damping Coefficients ◽  
Rayleigh Damping ◽  
Optimal Load ◽  
Parametric Studies ◽  
Response Spectral Analysis

A constrained optimization method is proposed to determine Rayleigh damping coefficients for the accurate analysis of complex structures. To this end, an objective function was defined to be a complete quadratic combination of the modal errors of a peak base reaction evaluated by response spectral analysis. An optimization constraint was enforced to make the damping ratio of a prominent contribution mode exact. Parametric studies were conducted to investigate the effects of the constraint, the cross term of modes, and weighting factors on the optimization objective. A two-story building and a real-world lattice structure were analyzed under six earthquake ground motions to understand the characteristics and demonstrate the accuracy and effectiveness of the proposed optimization method. Unlike the conventional Rayleigh damping, the optimization method provided an optimal load-dependent reference frequencies that account for varying frequency characteristics of earthquakes around the prominent contribution mode.

A Modified Optimal Design of a Vibration Absorber for Ground Motion Isolation

2014 ◽  
Author(s):  
Jimmy S. Issa
Keyword(s):  
Objective Function ◽  
Damping Ratio ◽  
Optimization Methods ◽  
Optimization Method ◽  
Design Guidelines ◽  
Vibration Absorber ◽  
Primary System ◽  
Optimal Parameters ◽  
Invariant Points ◽  
Downhill Simplex

Recently, a new vibration absorber setup was proposed where the absorber is placed between the dynamic system and its moving support. The problem was solved and design guidelines were proposed using the classical absorber design technique. In this work, the unique optimal absorber parameters are determined with the aim of minimizing the maximum of the primary system amplitude. For a given stiffness ratio of the system, the optimal mass and damping ratios are obtained analytically using an optimization method based on invariant points of the objective function. Similar to the case of the classical vibration absorber setup, these points are independent of the system damping ratio. It is shown that a trade-off relationship exists between these points, therefore the optimal mass ratio is determined first by a proper placement of the invariant points. Two suboptimal damping ratios are determined by forcing one of the two peaks of the objective function to coincide with one of the invariant points. Then, the optimal damping ratio is obtained from the average of the two suboptimal damping ratios. This approximate analytical solution is validated through comparison with the exact optimal parameters which were calculated numerically using two different numerical optimization methods. The first is based on the genetic algorithm technique and the second on the downhill simplex method. The optimal parameters are plotted and several examples are considered where the objective function is plotted in its approximate and exact optimal shapes.

A Study of the Roll Motion by Means of a Free Decay Test

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Hamid Zeraatgar ◽  
Mohsen Asghari ◽  
Firooz Bakhtiari-Nejad
Keyword(s):  
Damping Ratio ◽  
Nonlinear Damping ◽  
Damping Coefficient ◽  
Roll Motion ◽  
Damping Force ◽  
Restoring Force ◽  
Cubic Form ◽  
Damping Coefficients ◽  
Decay Test ◽  
Nonlinear Form

In this study, a method for the extraction of damping by tracing free roll decay is presented. For this purpose, in calm waters, a bulk carrier model is given a large initial roll angle and then released. Consequently, the roll motion is recorded. Restoring coefficients and virtual moments of inertia for the model are determined by means of an inclining test and recording the damped period, respectively. The linear damping coefficient is evaluated by using the damping ratio. Four different forms of combinations of restoring moment and damping coefficient are assumed in order to determine the nonlinear form of the roll motion. These equations are numerically solved for various damping coefficients and results are compared with the experimental data. By virtue of this comparison, the damping coefficients are determined for each case. It may be concluded that the use of the nonlinear restoring moment, which is an odd polynomial of the fifth order, and the cubic form for the nonlinear damping moment best fits the roll behavior for the ship model. The amount of energy dissipated by the damping moments is also calculated in the time domain. The energy method also confirms that the nonlinear form of restoring force in conjunction with the cubic form of the damping force is the best solution of the roll motion for small to large angles.

scholarly journals Longitudinally Vibrating Elastic Rods with Locally and Non-Locally Reacting Viscous Dampers

2005 ◽  
Vol 12 (2) ◽  
pp. 109-118 ◽  
Author(s):  
Şefaatdin Yüksel ◽  
Uğur Dalli
Keyword(s):  
Characteristic Equation ◽  
Mode Shape ◽  
Damping Ratio ◽  
Continuous System ◽  
Elastic Rods ◽  
Elastic Rod ◽  
Viscous Dampers ◽  
Absolute Value ◽  
Damping Coefficients ◽  
Optimal Values

Eigencharacteristics of a longitudinally vibrating elastic rod with locally and non-locally reacting damping are analyzed. The rod is considered as a continuous system and complex eigenfrequencies are determined as solution of a characteristic equation. The variation of the damping ratios with respect to damper locations and damping coefficients for the first four eigenfrequencies are obtained. It is shown that at any mode of locally or non-locally damped elastic rod, the variation of damping ratio with damper location is linearly proportional to absolute value of the mode shape of undamped system. It is seen that the increasing damping coefficient does not always increase the damping ratio and there are optimal values for the damping ratio. Optimal values for external damping coefficients of viscous dampers and locations of the dampers are presented.

Leakage, Drag Power and Rotordynamic Force Coefficients of an Air in Oil (Wet) Annular Seal

2017 ◽  
Author(s):  
Luis San Andrés ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Volume Fraction ◽  
Damping Coefficient ◽  
Liquid Volume ◽  
Pure Liquid ◽  
Test Results ◽  
Liquid Volume Fraction ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Annular Seal

Wet gas compression systems and multiphase pumps are enabling technologies for the deep sea oil and gas industry. This extreme environment determines both machine types have to handle mixtures with a gas in liquid volume fraction (GVF) varying over a wide range (0 to 1). The gas (or liquid) content affects the system pumping (or compression) efficiency and reliability, and places a penalty in leakage and rotordynamic performance in secondary flow components, namely seals. In 2015, tests were conducted with a short length smooth surface annular seal (L/D = 0.36, radial clearance = 0.127 mm) operating with an oil in air mixture whose liquid volume fraction (LVF) varied to 4%. The test results with a stationary journal show the dramatic effect of a few droplets of liquid on the production of large damping coefficients. This paper presents further measurements and predictions of leakage, drag power, and rotordynamic force coefficients conducted with the same test seal and a rotating journal. The seal is supplied with a mixture (air in ISO VG 10 oil), varying from a pure liquid to an inlet GVF = 0.9 (mostly gas), a typical range in multiphase pumps. For operation with a supply pressure (Ps) up to 3.5 bar (a), discharge pressure (Pa) = 1 bar (a), and various shaft speed (Ω) to 3.5 krpm (ΩR = 23.3 m/s), the flow is laminar with either a pure oil or a mixture. As the inlet GVF increases to 0.9 the mass flow rate and drag power decrease monotonically by 25% and 85% when compared to the pure liquid case, respectively. For operation with Ps = 2.5 bar (a) and Ω to 3.5 krpm, dynamic load tests with frequency 0 < ω < 110 Hz are conducted to procure rotordynamic force coefficients. A direct stiffness (K), an added mass (M) and a viscous damping coefficient (C) represent well the seal lubricated with a pure oil. For tests with a mixture (GVFmax = 0.9), the seal dynamic complex stiffness Re(H) increases with whirl frequency (ω); that is, Re(H) differs from (K-ω2M). Both the seal cross coupled stiffnesses (KXY and −KYX) and direct damping coefficients (CXX and CYY) decrease by approximately 75% as the inlet GVF increases to 0.9. The finding reveals that the frequency at which the effective damping coefficient (CXXeff = CXX-KXY/ω) changes from negative to positive (i.e., a crossover frequency) drops from 50% of the rotor speed (ω = 1/2 Ω) for a seal with pure oil to a lesser magnitude for operation with a mixture. Predictions for leakage and drag power based on a homogeneous bulk flow model match well the test data for operation with inlet GVF up to 0.9. Predicted force coefficients correlate well with the test data for mixtures with GVF up to 0.6. For a mixture with a larger GVF, the model under predicts the direct damping coefficients by as much as 40%. The tests also reveal the appearance of a self-excited seal motion with a low frequency; its amplitude and broad band frequency (centered at around ∼12 Hz) persist and increase as the gas content in the mixture increase. The test results show that an accurate quantification of wet seals dynamic force response is necessary for the design of robust subsea flow assurance systems.

scholarly journals An Adaptive Operation Strategy for Voltage Stability Enhancement in DMFCs

2018 ◽  
Author(s):  
Qinwen Yang ◽  
Xu-Qu Hu ◽  
Ying Zhu ◽  
Xiu-Cheng Lei ◽  
Xing-Yi Wang
Keyword(s):  
Voltage Stability ◽  
Optimization Method ◽  
Operation Strategy ◽  
Practical Applications ◽  
Operating Current ◽  
Voltage Stability Enhancement ◽  
Voltage Deviation ◽  
Adaptive Operation ◽  
Underlying Mechanisms ◽  
Stability Enhancement

An adaptive operation strategy for on-demand control of DMFC system is proposed as an alternative method to enhance the voltage stability. Based on a single-cell DMFC stack, a newly simplified semi-empirical model is developed from the uniform-designed experimental results to describe the I-V relationship. Integrated with this model, the multi-objective optimization method is utilized to develop an adaptive operation strategy. Although the voltage instability is frequently encountered in unoptimized operations, the voltage deviation is successfully decreased to a required level by adaptive operations with operational adjustments. Moreover, the adaptive operations are also found to be able to extend the range of operating current density or to decrease the voltage deviation according to ones requirements. Numerical simulations are implemented to investigate the underlying mechanisms of the proposed adaptive operation strategy, and experimental adaptive operations are also performed on another DMFC system to validate the adaptive operation strategy. Preliminary experimental study shows a rapid response of DMFC system to the operational adjustment, which further validates the effectiveness and feasibility of the adaptive operation strategy in practical applications. The proposed strategy contributes to a guideline for the better control of output voltage from operating DMFC systems.

An Energy-Based Approach to the Generalized Optimal Locations of Viscous Dampers in Two-Way Asymmetrical Buildings

2014 ◽  
Vol 30 (2) ◽  
pp. 867-889 ◽  
Author(s):  
Jui-Liang Lin ◽  
Manh-Tien Bui ◽  
Keh-Chyuan Tsai
Keyword(s):  
Strain Energy ◽  
Ground Motions ◽  
Damping Ratio ◽  
Intrinsic Property ◽  
Simple Approach ◽  
Engineering Practice ◽  
Viscous Dampers ◽  
Response Parameter ◽  
Control Target ◽  
Target Performance

This paper proposes a simple approach to the generalized optimal locations of linear viscous dampers in elastic two-way asymmetrical buildings under bi-directional ground excitations. The control target used in this optimization process is to maximize the average dissipation rate of the overall strain energy of the two-way asymmetrical building under the ground excitation of two bi-directional unit impulses. The proposed control target, referred to as the smeared damping ratio, is an intrinsic property of the building system. Two advantages of the proposed approach appeal to engineering practice. First, the proposed approach does not require a complicated optimization algorithm. Second, due to the employment of an intrinsic property rather than a certain response parameter as the target performance index, the optimal damper locations resulting from the proposed approach are generalized, which are independent on the characteristics of input ground motions.

scholarly journals Body Bias Optimization for Real-Time Systems

2020 ◽  
Vol 10 (1) ◽  
pp. 8
Author(s):  
Carlos C. Cortes Torres ◽  
Ryota Yasudo ◽  
Hideharu Amano
Keyword(s):  
Real Time ◽  
Computer Aided Design ◽  
Optimization Method ◽  
Design Guidelines ◽  
Real Time Systems ◽  
Total Energy Consumption ◽  
Aided Design ◽  
Time Systems ◽  
Parameter Constraints ◽  
Body Bias

The energy of real-time systems for embedded usage needs to be efficient without affecting the system’s ability to meet task deadlines. Dynamic body bias (BB) scaling is a promising approach to managing leakage energy and operational speed, especially for system-on-insulator devices. However, traditional energy models cannot deal with the overhead of adjusting the BB voltage; thus, the models are not accurate. This paper presents a more accurate model for calculating energy overhead using an analytical double exponential expression for dynamic BB scaling and an optimization method based on nonlinear programming with consideration of the real-chip parameter constraints. The use of the proposed model resulted in an energy reduction of about 32% at lower frequencies in comparison with the conventional model. Moreover, the energy overhead was reduced to approximately 14% of the total energy consumption. This methodology provides a framework and design guidelines for real-time systems and computer-aided design.

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