Damping Reduction Research Articles

Decoupling criterion for elastic-plastic seismic analysis of large-scale complex piping systems in nuclear power plants

This paper proposes an elastic-plastic-based decoupling criterion that can be applied to the seismic analysis of large-scale complex piping systems in nuclear power plants under beyond design basis earthquakes. First, the existing elastic-based decoupling criteria for seismic analyses were critically reviewed. Next, the effect of plasticity on the decoupling criteria was investigated by considering the equivalent damping and stiffness reduction. Finally, the decoupling criterion considering plasticity was developed based on the changes resulting from existing decoupling criteria. The validity of the proposed decoupling criterion was confirmed through its application to an analysis of a real piping system.

Machining parameter selection in milling epoxy granite composites based on AHP

Abstract Machine tool structures fabricated with new alternate material epoxy granite has been developed to enhance the damping characteristics, stability and reduction in weight. Machining of epoxy granite composites (EGCs) has been critical by considering its heterogeneous nature. An optimization problem with multiple attributes has become a critical issue in selection of optimal solution due to the varying characteristics among attributes. Decision making model, Analytical hierarchy procedure (AHP) is employed in selection of optimal machining condition in milling EGCs. Evaluation factors consisting attributes that influences machining process such as thrust force, tangential force and surface roughness are only considered. Computation from AHP method reveals that experimental run 3 is the desired optimal solution with the optimal machining conditions of speed 600 rpm; feed rate 0.09 m/min and 4% fiber content.

Dynamic impact of hydraulic systems using pressure feedback for active damping

Pressure feedback has been an effective method for active damping and oscillation reduction in hydraulic systems. However, this study reveals a dynamic impact problem of a larger velocity overshoot and slower convergence excited by an external force/torque disturbance once pressure feedback is introduced for active damping. This problem is introduced through a theoretical analysis, and then illustrated by a numerical simulation. The solutions to this problem are analysed for a hydraulic system with a symmetric cylinder. For a trade-off between the active damping effect and reduction in dynamic impact, a multi-objective optimization method is proposed to determine the control parameters (gain and time constant) of the high-pass pressure filter. The multi-objective optimization method is validated by a simulation model with the symmetric cylinder under different disturbances. Moreover, an analysis is carried out for the system with an asymmetric cylinder or hydraulic motor. The theoretical analysis shows that the mathematical forms of the two systems are similar to that of the symmetric cylinder system. Therefore, the dynamic impact problem also exists in the two systems. The proposed method is also effective for the damping improvement and mitigation of the dynamic impact.

Damping reduction equation for the equivalent linear analysis of seismic isolated structures subjected to near fault ground motions

In this study, a new damping reduction equation is proposed to obtain reasonable estimates of the actual nonlinear responses of seismic isolated structures (SIS) subjected to near fault ground motions (NFGM) with forward-rupture-directivity effect, using equivalent linear analysis (ELA) procedure. For this purpose, first, a set of 29 NFGM are selected and grouped according to their site soil classification. Then, the average response spectra of the NFGM are plotted and a smoothed design response spectrum for each set of ground motions are obtained. Next, nonlinear time history analysis (NLTHA) and ELA of SIS are performed for the selected ground motions. Subsequently, the average of the isolator displacements calculated from the NLTHA are obtained for each set of NFGM considered in the analyses. Then, the damping reduction factor required to obtain an isolator displacement equal to the average isolator displacements obtained from the NLTHA of SIS is back calculated via the ELA procedure. Next, the variation of the damping reduction factor is plotted as a function of various combinations of the parameters considered in this research in dimensionless form and nonlinear regression analyses are performed to formulate the damping reduction equation. The isolator characteristic strength, post elastic period, the corner period of the response spectrum and peak ground acceleration are found to affect the damping reduction factor and hence, the displacements obtained from ELA. The proposed damping reduction equation is found to yield more reasonable estimates of the actual nonlinear responses compared to those available in the literature and design codes.

Examination of Rail Dampers with Respect to Noise and Vibration Mitigation

Nowadays there are more and more possibilities to mitigate noise and vibration emitted by railway transport to the lower levels. Among them, rail dampers with highly viscous properties placed on the rail web, fixed with adhesives or other methods, appeared as a new element in the railway superstructure. The elements are applied to reduce noise and vibration by transforming the vibration energy of the rail web into heat, through their large internal friction. Many companies produce rail web elements and apply them with success abroad. Domestic manufacturers have already appeared in Hungary; however, the installation of these elements is still very limited. This publication is intended to introduce the rail dampers and to demonstrate their efficiency through laboratory and field measurements. Experimental modal analysis was used during the laboratory test to determine the eigenfrequencies, the damping factors and the mode shapes of an experimental rail section, thus analyzing the vibration damping and noise reduction effect of the elements. Field measurements were also carried out at a segment installed with rail web elements in Hungary and its vicinity, under standardized conditions. By averaging measured noise level values for various types of trains, comparable noise reduction of the investigated rail web element can be achieved. The laboratory and field test results confirmed that the rail web elements can be suitable for rolling noise reduction and vibration damping in most of the cases. The results of the measurements provide guidance and information for future development of the elements.

Fabrication and Experimental Investigation on Deformation Behaviour of AlSi10Mg Foam-Filled Mild Steel Tubes

Aluminium (Al) alloy foam is an engineering material which has emerged in the automobile sector where crash energy absorption, vibration and sound damping and weight reduction are required. Al-alloy foam is a lightweight material providing high strength and stiffness at relatively low density. The paper aims to study the innovative approach of manufacturing AlSi10Mg foam. The low-density and high-strength Al-alloy foam (AlSi10Mg) is fabricated using the melt route process resulting in a density of 0.70–0.90 g/cm3. After that, square mild steel thin-walled empty tubes and Al-alloy foam-filled mild steel tubes are tested to study enhanced energy absorption characteristics. The tests are carried out on universal testing machine with strain rate 10/s. Al-alloy foam, AlSi10Mg, is assessed macroscopically and microscopically using field emission scanning electron microscope and energy-dispersive X-ray analysis. The experimental results indicate that foam-filled tubes feature more energy absorption than empty tubes at strain rate 10/s.

Influence of the Primary Suspension Damping on the Ride Comfort in the Railway Vehicles

The paper features the results of a numerical study regarding the influence that the damping reduction in the primary suspension of the rail vehicle, due to the defect in a damper, has on the ride comfort. The study is based on model of rigid-flexible coupled vehicle, with seven degrees of freedom, where the carbody is modelled as an Euler-Bernoulli type equivalent beam. The results of the numerical simulations show the power spectral density of carbody vertical accceleration and the ride index comfort calculated in three carbody reference points - at the centre and against the bogies, for various cases of reduction in the damping constant of the primay suspension in the axle, compared to the reference value. As a function of velocity, due to the geometric filtering effect, the damping reduction has contrary effects upon the level of vibrations in the carbody and upon the ride comfort.

Design of the Downhill Automatic Liquid Damping Reduction Mechanism on the carbon-free car

The carbon-free car is driven by gravity potential energy, through the mechanism to complete the specific direction control and avoid obstacles, to achieve the driving purpose of the car. The event is a national science and technology innovation activity project organized by relevant departments. It is a competition that demonstrates the engineering training and comprehensive ability of college students. Based on the “S” and “8” glyphs around the pile competition, a new circular track was added, and the track was randomly set with intermittent barrier walls and up and down ramps. Small cars that do not have the ability to climb and do not have speed control on the upper and lower ramps make it difficult to complete the race. To this end, for the content of the new project, the automatic speed reduction mechanism for the carbon-free car downhill is developed. Under the condition that the gravitational potential energy of the carbon-free car on the downhill is constant, the stall phenomenon at the time of downhill is effectively solved, the safe driving speed is adjusted, avoid the problem of out of control when escaping the intermittent barrier wall on the circular track.

Design and Optimization of Damping Materials for Power Equipment Based on Material Gene Engineering Technology

Abstract On the basis of the butyl rubber system, the damping and noise reduction with strong absorptive capacity of the low frequency, good heat dissipation and good flame retardancy was designed for power equipment by the technology of material genetic engineering. Multifaceted parameters were comprehensively inspected, such as low frequency absorptive capacity, heat dissipation performance and so on. While the safety of the electric power application scene was also taken into consideration. Breaking the barrier with high damping capacity and high thermal conductivity at the same time was achieved, which promoted the green upgrading of transmission and distribution equipment. It’s a favor for practicing the energy development policy of clean and low carbon, safe and efficient. Thus the green and livable environment would be created.

Seismic duration effect on damping reduction factor using random vibration theory

Damping Reduction Factor plays a key role in scientific literature and Technical Codes, but till now existing formulations present differences and inconsistences probably because obtained by integration of real recorded events, thus sensible to specific used data. This paper investigates the relation between damping reduction factor and earthquake duration by means of random vibration theory. A stochastic process, that is non-stationary and filtered, is used to model a seismic event. The modulation function is suitably chosen to describe earthquakes characterized by different durations. The stochastic process peak theory allows to calculate damping reduction factor after the definition of the probabilistic response of a simple linear visco-elastic oscillator. The variability with seismic duration for different soil conditions and damping ratios is investigated. The study points out that damping reduction factor is more sensitive to seismic duration in the range of high period and on rigid soil with respect to other conditions. The results show that, if damping ratio or effective duration values are increased, the damping reduction factor value diminishes.

Crashworthiness performance and microstructural characteristics of foam-filled thin-walled tubes under diverse strain rate

The implementation of Aluminum Alloy Foam (AAF) has made an impact in automobile and aerospace applications where crash energy absorption, vibration and sound damping and weight reduction is obligatory. The AAF is an emerging lightweight material providing high strength and stiffness at relatively low density. This research is carried out to quantify the energy absorption of mild steel reinforced AAF having empty mild steel and foam-filled tubes for different strain rates and geometry parameters. The AAF used in the current study is AlSi10Mg foam of densities 0.45, 0.65, 0.85 g/cm3, which is produced using melt route process. The circular, square and rectangular geometries were tested at strain rates of 0.1, 1, 10 mm/s. From the obtained compressive stress-strain curves Specific Energy Absorption (SEA), Total Energy Absorption (TEA), plateau stress of the empty and filled sections were determined, which were then evaluated. AAF was assessed by both light and electron microscopy. Field Emission Scanning Electron Microscope (FESEM) and Analysis of Variance (ANOVA) technique was employed to investigate the highest contributing factor in energy absorption. It was observed that foam filled tube can absorb more energy than empty tubes before reaching densification point.

Inter‐area low‐frequency power system oscillations caused by open‐loop modal resonance

This study examines a modal condition to cause inter-area, low-frequency, electromechanical power oscillations in an interconnected power system with two subsystems. The modal condition being examined is the closeness of two electromechanical oscillation modes from each subsystem on the complex plane, which is referred to as open-loop modal resonance. The analysis in this study indicates that under the condition of open-loop modal resonance, the electromechanical oscillation modes of the interconnected power system are located at approximately opposite positions on the complex plane with respect to the resonant electromechanical oscillation modes of the subsystems. Hence, when open-loop modal resonance occurs, one electromechanical oscillation mode of the interconnected power system must have reduced damping. In this study, the damping reduction in the inter-area, low-frequency power oscillations caused by open-loop modal resonance is demonstrated using example power systems. An incident of inter-area, low-frequency electromechanical power oscillations that occurred in an actual large-scale power system in China is examined. The examination results indicate that the poorly damped, inter-area, low-frequency power oscillation incident was caused by open-loop modal resonance.

A unified N-SECE strategy for highly coupled piezoelectric energy scavengers

This paper proposes a novel vibration energy harvesting strategy based on an extension of the synchronous electric charge extraction (SECE) approach, enabling both the maximization of the harvested power and a consequent bandwidth enlargement in the case of highly coupled/lightly damped piezoelectric energy harvesters. The proposed strategy relies on the tuning of the frequency of the energy extraction events, which is either N times greater than the vibration frequency (Multiple SECE case, ) or times smaller (Regenerative SECE, ). We first prove analytically than increasing or decreasing both lead to a damping reduction. While has no impact on the system’s resonance frequency in the Regenerative case we show that this resonant frequency becomes a function of in the Multiple SECE case (). Experimental results on a highly coupled/lowly damped piezoelectric harvester demonstrates the potential of this strategy, leading to 257% harvested power improvement compared to SECE (). and the possibility to tune the resonant frequency on a range as large as 35% of the short-circuit resonant frequency of the harvester.

On the seismic response and damping capacity of low-rise plane steel frames with seesaw system

This paper summarizes estimated seismic response results from nonlinear inelastic seismic analyses of low-rise plane steel frames equipped with a seesaw system in which linear viscous dampers have been applied. More specifically, considering for each frame three different configurations of the seesaw system and two different orientations of columns, seismic response results involving height wise distributions for peak interstorey drift ratios (IDR), peak residual interstorey drift ratios (RIDR) and peak floor accelerations (PFA) have been obtained. Moreover, peak seismic demands in columns and in the steel plates of the seesaw are found. Results in terms of modal damping ratios are also provided for all frames and seesaw configurations examined. From the results presented, it can be concluded that the seesaw system provides a very attractive solution for typical low-rise steel frames offering significant damping capacity and reduction of their seismic response.

Aerodynamic Noise Separation of an EMU Trailer Bogie Area Using Train Operation Tests

The operation transfer path analysis (OTPA) technique was used to measure the vibration and noise transfer coefficient functions of wheel‐rail noise and radiated noise from an electric multiple unit (EMU) train (high‐speed train in China) trailer bogie structure to the central area of the trailer bogie for a train running at speeds of 0–5 km/h. By applying these transfer coefficient functions to the noise analysis of high‐speed train operation, the contributions of wheel‐rail noise and frame‐radiated noise to the noise of the bogie area at high speeds are obtained, and the aerodynamic noise is separated from the total noise, providing a reference for vibration damping and noise reduction in high‐speed trains. Analysis of test data shows that, in the central area of the trailer bogie of high‐speed trains, the low‐frequency noise mainly comes from the structural radiated noise of the bogie, and the mid‐ to high‐frequency noise is primarily due to aerodynamic noise. In addition, when an EMU train operates at speeds below 250 km/h, the noise in the central area of the trailer bogie is primarily caused by the structural radiated noise. When the operating speed is higher than 250 km/h, the noise in the central area of the trailer bogie is mainly due to aerodynamic noise, and the aerodynamic noise contribution increases with increase in speed.

Development and Analysis of Human Hand-Arm System Model for Anti-Vibration Isolators

The potential health injuries associated with human hand-transmitted mechanical vibration which caused during driving vehicles, and operating on hand-held power tools. In this study five Degree-of-Freedom (DOF) human hand-arm system model is developed to analyze HAS model in terms of acceleration responses. The study analysed one of the possible protective way to reduce hand-transmitted vibration by using the anti-vibration isolators to machine handle. This study presents biomechanical models consisting deflection patterns due to masses at the finger, palm-wrist and upper-arm, corresponding to different modes of vibration, subject to z-axis vibration. A MATLAB-SIMULINK based model is also developed to determine the effect of vibration transmission from machine tool handle. The anti-vibration isolators have been introduced as a gripper of machine tool handle and simulation results shows significantly better damping characteristics and reduction of the vibration transmission effect to HAS.

Active force control of structure-borne sound based on robust optimization subjected to an irregular cavity with uncertainties

This paper proposes a novel method of structure-borne sound analysis and active force control, which combines interval mathematics and robust optimization theorems, to achieve vibration damping and noise reduction for enclosed cavity systems with bounded uncertainty. By introducing the interference principle of sound wave, responses under control can be obtained by solving finite element equations of structural–acoustic coupling systems. Through synthetical considerations of parameter dispersion in practice, the interval quantitative model, which only needs limited sample data, is defined, and the interval Taylor extension approach is employed to further determine boundary rules of responses of structural vibration and acoustic noise. On this basis, a new interval-oriented robust optimization framework is established to seek the optimal secondary force to simultaneously minimize nominal and radius levels of sound pressure indexes at concerned space and frequency domains. A complicated engineering example of the 3-D bomb cavity is eventually presented, in which numerical and experimental results can demonstrate the usage, validity and effectiveness of the developed methodology.

Modal strength reduction factors for seismic design of steel moment resisting frames

Traditional seismic design of framed structures uses a single constant value for the strength reduction factor. In this work, explicit expressions for different values of strength reduction factors for the first significant modes of steel moment resisting frames including strength deterioration and panel zone effects are developed. These factors are functions of modal periods and deformation/damage and are defined for four performance levels in a performance-based seismic design framework. The above factors are obtained through extensive parametric studies involving 20 steel frames and 100 far-field ground motions and following a two steps procedure: First an equivalent linear structure with the same mass and elastic stiffness of the original non-linear one is constructed based on equivalent modal damping ratios, which substitute the non-linearities; then use of these equivalent modal damping ratios in conjunction with modal damping reduction factors leads to modal strength reduction factors. Using these factors, one can obtain the seismic design base shear of a frame through response spectrum analysis. Thus, a more accurate and rational seismic design method is established. Numerical examples are presented to illustrate the method and demonstrate its advantages against conventional seismic design methods.

13.15: Seismic design of steel moment resisting frames: Modal strength reduction factors including strength deterioration and panel zone effects

ABSTRACTTraditional seismic design of framed structures uses a single constant value for the strength reduction factor. In this work, explicit expressions for different values of strength reduction factors for the first significant modes of steel moment resisting frames including strength deterioration and panel zone effects are developed. These factors are functions of modal periods and damage and are designed for four performance levels in a performance – based seismic design framework. The above factors are obtained through extensive parametric studies involving 20 steel frames and 100 far – field ground motions and following a two steps procedure: First an equivalent linear structure with the same mass and elastic stiffness of the original non – linear one is constructed based on equivalent modal damping ratios, which substitute the non‐linearities; then use of these equivalent modal damping ratios in conjunction with modal damping reduction factors leads to modal strength reduction factors. Using these factors, one can obtain the seismic design base shear of a frame through response spectrum analysis. Thus, a more accurate and rational seismic design method is established. Numerical examples are presented to illustrate the method and demonstrate its advantages against conventional seismic design methods.

A direct design procedure for frame structures with added viscous dampers for the mitigation of earthquake-induced vibrations

A direct procedure for the seismic design of building structures with added viscous dampers is described in this paper. The procedure is applicable to regular multi-storey frame structures which are characterized by a period of vibration lower than 1.5 s. It aims at providing practical tools for the direct identification of the mechanical characteristics of the manufactured viscous dampers as well as for the structural design of the frame members’ so that a target level of performance is achieved. The design philosophy is to limit the structural damages under severe earthquakes. First, a target damping reduction factor is selected to achieve the desired reduction in the peak structural response. The linear damping coefficients of the equivalent linear viscous dampers are calculated taking advantage of modal damping ratios properties of classically damped systems. Then, simple analytical formulas for the estimation of peak inter-storey velocities are used, together with an energy criterion to identify the non-linear mechanical characteristics of the manufactured viscous dampers. Finally, the internal actions in the structural elements are estimated through the envelope of two equivalent static analyses (ESA), namely: ESA1 in which the naked structure is subjected to a first set of equivalent lateral forces, and ESA2 in which the structure, with rigid diagonal braces substituting the added viscous dampers, is subjected to a second set of equivalent lateral forces. At this preliminary stage of the research, the procedure is targeted for the preliminary design phase, since correction factors to improve the accuracy in the estimation of the peak inter-storey velocities needs to be calibrate. Therefore, for final design, non-linear dynamic analyses are recommended.