To see the other types of publications on this topic, follow the link: Effective viscous damping.
Journal articles on the topic 'Effective viscous damping'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Effective viscous damping.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Kim, Chan-Jung. "Sensitivity of the Viscous Damping Coefficient of Carbon Fiber in Carbon-Fiber-Reinforced Plastic with Respect to the Fiber Angle." Crystals 11, no. 7 (2021): 781. http://dx.doi.org/10.3390/cryst11070781.
Full textAbstract:
The variation in the viscous damping coefficient with the carbon fiber angle can be evaluated using the partial derivatives of the viscous damping coefficient with respect to the resonance frequency and modal damping ratio. However, the direct derivatives of the viscous damping coefficient were not effective solutions to the sensitivity analysis of carbon-fiber-reinforced plastic (CFRP) structures because the viscous damping from the binding matrix was not changed over the carbon fiber angle. If the identified viscous damping coefficients were assumed to be equivalent values from the parallel relationship between the binding matrix and carbon fiber, the relative error of the viscous damping coefficient of carbon fiber between the increased carbon fiber angle and reference angle could be used as the sensitivity index for the viscous damping coefficient of carbon fiber only. The modal parameters, resonance frequency, and modal damping ratio were identified from the experimental modal test of rectangular CFRP specimens for five different carbon fiber angles between 0° and 90°. The sensitivity of the viscous damping coefficient of carbon fiber was determined for two sensitivity indices: the direct derivative of the mass-normalized equivalent viscous damping coefficient and the relative error of the viscous damping coefficient of carbon fiber. The sensitivity results were discussed using the five mode shapes of the CFRP specimen, that is, three bending modes and two twisting modes.
2
Whittaker, Andrew S., Michael C. Constantinou, Oscar M. Ramirez, Martin W. Johnson, and Christis Z. Chrysostomou. "Equivalent Lateral Force and Modal Analysis Procedures of the 2000 NEHRP Provisions for Buildings with Damping Systems." Earthquake Spectra 19, no. 4 (2003): 959–80. http://dx.doi.org/10.1193/1.1622391.
Full textAbstract:
Equivalent lateral force and modal analysis procedures for yielding buildings with damping systems were developed, validated, and incorporated in the 2000 NEHRP Provisions. The technical basis for each procedure is described in the paper together with the simplifications adopted for inclusion in the Provisions. Procedures for calculating the effective damping and effective period and higher mode damping ratios for buildings equipped with yielding, viscoelastic, linear viscous, and nonlinear viscous damping devices are presented.
3
Hinze, Matthias, André Schmidt, and Remco I. Leine. "Lyapunov Stability of a Fractionally Damped Oscillator with Linear (Anti-)Damping." International Journal of Nonlinear Sciences and Numerical Simulation 21, no. 5 (2020): 425–42. http://dx.doi.org/10.1515/ijnsns-2018-0381.
Full textAbstract:
AbstractIn this paper, we develop a Lyapunov stability framework for fractionally damped mechanical systems. In particular, we study the asymptotic stability of a linear single degree-of-freedom oscillator with viscous and fractional damping. We prove that the total mechanical energy, including the stored energy in the fractional element, is a Lyapunov functional with which one can prove stability of the equilibrium. Furthermore, we develop a strict Lyapunov functional for asymptotic stability, thereby opening the way to a nonlinear stability analysis beyond an eigenvalue analysis. A key result of the paper is a Lyapunov stability condition for systems having negative viscous damping but a sufficient amount of positive fractional damping. This result forms the stepping stone to the study of Hopf bifurcations in fractionally damped mechanical systems. The theory is demonstrated on a stick-slip oscillator with Stribeck friction law leading to an effective negative viscous damping.
4
Jafari Kang, Saeed, Esmaeil Dehdashti, Vahid Vandadi, and Hassan Masoud. "Optimal viscous damping of vibrating porous cylinders." Journal of Fluid Mechanics 874 (July 9, 2019): 339–58. http://dx.doi.org/10.1017/jfm.2019.457.
Full textAbstract:
We theoretically study small-amplitude oscillations of permeable cylinders immersed in an unbounded fluid. Specifically, we examine the effects of oscillation frequency, permeability and shape on the effective mass and damping coefficients, the latter of which is proportional to the power required to sustain the vibrations. Cylinders of circular and elliptical cross-sections undergoing transverse and rotational vibrations are considered. The dynamics of the fluid flow through porous cylinders is assumed to obey the unsteady Brinkman–Debye–Bueche equations. We use a singularity method to analytically calculate the flow field within and around circular cylinders, whereas we introduce a Fourier-pseudospectral method to numerically solve the governing equations for elliptical cylinders. We find that, if rescaled properly, the analytical results for circular cylinders provide very good estimates for the behaviour of elliptical ones over a wide range of conditions. More importantly, our calculations indicate that, at sufficiently high frequencies, the damping coefficient of oscillations varies non-monotonically with the permeability, in which case it maximizes when the diffusion length scale for the vorticity is comparable to the penetration length scale for the flow within the porous material. Depending on the oscillation period, the maximum damping of a permeable cylinder can be many times greater than that of an otherwise impermeable one. This might seem counter-intuitive at first, since generally the power it takes to steadily drag a permeable object through a fluid is less than the power needed to drive the steady motion of the same, but impermeable, object. However, the driving power (or damping coefficient) for oscillating bodies is determined not only by the amplitude of the cyclic fluid load experienced by them but also by the phase shift between the load and their periodic motion. An increase in the latter is responsible for the excess damping coefficient of vibrating porous cylinders.
5
Guo, Yan, Wen Guang Liu, Jian Zhang, and Wen Fu He. "Wind-Induced Vibration Control and Analysis of Super High-Rise Structure Using Viscous Damping Walls." Applied Mechanics and Materials 488-489 (January 2014): 647–51. http://dx.doi.org/10.4028/www.scientific.net/amm.488-489.647.
Full textAbstract:
The wind-induced vibration control and analysis of a super high-rise structure located in the area of strong typhoon with viscous damping walls is introduced. Mechanical properties and design method of viscous damping wall are described, and then the arrangement scheme is put forward. The performances of structure with and without viscous damping walls under the condition of basic wind strength encountered once for 10 years are investigated in detail. The results show that the control scheme can dissipate energy of wind-induced vibration, attenuate structural dynamic response and reduce the mutation of acceleration along height direction effectively. The maximum peak acceleration can be reduced by 23.5% to 0.241m/s2, which meets 0.25m/s2 limit value stated by Technical specification for concrete structures of tall building. Therefore, the arrangement scheme is feasible and effective to control wind-induced vibration and improve structural safety and comfort.
6
Huang, Xiao, Hong Ping Zhu, and Zhi Xiang Hu. "An Improved Contact Model for Pounding Simulation of Base-isolated Highway Bridge." Advanced Materials Research 243-249 (May 2011): 3775–80. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.3775.
Full textAbstract:
A modified Hertz model with nonlinear damping (Hertz damp model) is proposed for capturing the seismic pounding response of adjacent structures. Relevant parameters in the model are theoretically derived and numerically verified. Then, this model is used to simulate pounding response of a base-isolated highway bridge subjected to near fault ground motions. At the same time, nonlinear viscous dampers are installed between bridge decks for pounding prevention. The appropriate damping coefficient of the dampers can be found by parametric studies. It is shown that nonlinear viscous dampers are effective in reducing the relative displacement between bridge decks. At last, the hysteresis curve, the maximal damper force and stroke are used to demonstrate the behavior of nonlinear viscous dampers. The results indicate that satisfied viscous dampers can be produced to eliminate pounding according to the current manufacturing skills.
7
Deng, Rui, Wenyang Duan, Shan Ma, and Yong Ma. "Numerical Research of the Viscous Effect of the Bilge Keel on the Damping Moment." Polish Maritime Research 22, s1 (2015): 67–74. http://dx.doi.org/10.1515/pomr-2015-0035.
Full textAbstract:
Abstract Bilge keels are effective passive devices in mitigating the rolling motion, and the usage of them covers almost all the sea going vessels. This paper focuses on the viscous effect of the bilge keel, ignored the effect of the free surface and the effect of the ship hull, for the general viscous characteristic of the bilge keel. In order to investigate the viscous effect of the bilge keel on the total damping moment, a special 2 dimensional numerical model, which includes a submerged cylinder with and without bilge keels, is designed for the simulation of forced rolling. Three important factors such as bilge keels width, rolling periods, as well as maximal rolling angles are taken into account, and the viscous flow field around the cylinder is simulated by some codes based on the viscous method in different conditions, in which the three factors are coupled. Verification and validation based on the ITTC method are performed for the cylinder without bilge keels in the conditions of different rolling periods and maximal rolling angles. The primary calculation of damping moment induced by the cylinder with 0mm, 4mm, and 10mm width bilge keels shows some interesting results, and a systematic analysis is conducted. The analysis of the damping moment components suggests there is phase difference between the damping moment induced by the cylinder and the bilge keels, and when the bilge keels width reaches a special size, the total damping moment is mitigated. The calculation of the damping moments induced by the cylinder with some larger bilge keels are also performed, and the results suggest that, the damping moment induced by the bilge keels is increased rapidly and becomes the dominant part in the total damping moment while the width of the bilge keels are increased, but the damping moment induced by the cylinder is not changed significantly. Some illustration of the vortices formation and shedding is included, which is the mechanism of the damping moment caused by the bilge keels. The present work shows an interesting problem, and it is useful for the bilge keel design.
8
Losanno, D., J. M. Londono, S. Zinno, and G. Serino. "Effective damping and frequencies of viscous damper braced structures considering the supports flexibility." Computers & Structures 207 (September 2018): 121–31. http://dx.doi.org/10.1016/j.compstruc.2017.07.022.
Full text
9
Yi, Jiang, Jianzhong Li, and Zhongguo Guan. "Shake Table Studies on Viscous Dampers in Seismic Control of a Single-Tower Cable-Stayed Bridge Model under Near-Field Ground Motions." Journal of Earthquake and Tsunami 12, no. 05 (2018): 1850011. http://dx.doi.org/10.1142/s1793431118500112.
Full textAbstract:
To investigate the effectiveness of viscous damper on seismic control of single-tower cable-stayed bridges subjected to near-field ground motions, a 1/20-scale full cable-stayed bridge model was designed, constructed and tested on shake tables. A typical far-field ground motion and a near-field one were used to excite the bridge model from low to high intensity. The seismic responses of the bridge model with and without viscous dampers were analyzed and compared. Both numerical and test results revealed that viscous dampers are quite effective in controlling deck displacement of cable-stayed bridges subjected to near-field ground motions. However, due to near-field effects, viscous damper dissipated most energy through one large hysteresis loop, extensively increasing the deformation and damping force demand of the damper. Further study based on numerical analysis reveals that to optimize deck displacement of cable-stayed bridges during an earthquake, a viscous damper with relatively larger damping coefficient should be introduced under near-field ground motions than far-field ones.
10
Ibrahim, R. A., and G. Latorre. "Experimental Investigation of Dynamic Parameters of Viscous Fluids in Unsteady Flow." Journal of Pressure Vessel Technology 110, no. 1 (1988): 29–35. http://dx.doi.org/10.1115/1.3265564.
Full textAbstract:
The main objective of this paper is to conduct a series of experimental investigations to measure the effective mass moment of inertia and damping coefficient of a viscous fluid due to an immersed rod fitted in a circular cylindrical container which experiences roll oscillations. This work is mainly oriented to the dynamic analysis of liquid propellant rockets. The measured results are used to examine the validity of the solution of the linearized Navier-Stokes equations. It is shown that the liquid inertia and damping are dependent upon the tank roll frequency and fairly agree with the predicted analytical results.
11
Wang, Dongqiang, and Chengjun Wu. "Vibration Response Prediction of Plate with Particle Dampers Using Cosimulation Method." Shock and Vibration 2015 (2015): 1–14. http://dx.doi.org/10.1155/2015/270398.
Full textAbstract:
The particle damping technology is a passive vibration control technique. The particle dampers (PDs) as one of the passive damping devices has found wide use in the field of aeronautical engineering, mechanical engineering, and civil engineering because it has several advantages compared with the forms of viscous damping, for example, structure simplicity, low cost, robust properties, and being effective over a wide range of frequencies. In this paper, a novelty simulation method based on multiphase flow theory (MFT) is developed to evaluate the particle damping characteristics using FEM combining DEM with COMSOL Multiphysics. First, the effects of the collisions and friction between the particles are interpreted as an equivalent nonlinear viscous damping based on MFT of gas particle. Next, the contribution of PDs is estimated as equivalent spring-damper system. Then a cantilever rectangular plate treated with PDs is introduced in a finite element model of structure system. Finally frequency response functions (FRFs) of the plate without and with particle dampers are predicted to study characteristics of the particle damping plates under forced vibration. Meanwhile, an experimental verification is performed. Simulation results are in good agreement with experiment date. It is concluded that the simulation method in this paper is valid.
12
Horton, Bryan, Marian Wiercigroch, and Xu Xu. "Transient tumbling chaos and damping identification for parametric pendulum." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 366, no. 1866 (2007): 767–84. http://dx.doi.org/10.1098/rsta.2007.2126.
Full textAbstract:
The aim of this study is to provide a simple, yet effective and generally applicable technique for determining damping for parametric pendula. The proposed model is more representative of system dynamics because the numerical results describe the qualitative features of experimentally exhibited transient tumbling chaotic motions well. The assumption made is that the system is accurately modelled by a combination of viscous and Coulomb dampings; a parameter identification procedure is developed from this basis. The results of numerical and experimental time histories of free oscillations are compared with the model produced from the parameters identified by the classic logarithmic decrement technique. The merits of the present method are discussed before the model is verified against experimental results. Finally, emphasis is placed on a close corroboration between the experimental and theoretical transient tumbling chaotic trajectories.
13
Kado, Naohiro. "Theoretical and numerical studies of semi-active friction damper showing viscous-damper-like characteristics." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, no. 10 (2017): 1778–85. http://dx.doi.org/10.1177/0954406217710304.
Full textAbstract:
To clarify the feasibility of a novel, semi-active friction damper, its damping characteristics were investigated theoretically and numerically. The proposed damper suppresses vibrations by changing the direction of the frictional force, in contrast to the conventional passive and semi-active friction dampers that only focus on the magnitude of the frictional force. The theoretical analysis indicates that the proposed damper can behave as a conventional friction damper or a viscous damper depending on the use conditions; further, its effective damping ratio can be controlled by the velocity of a friction plate moving in a direction orthogonal to the direction of the vibration. The numerical simulations clarified that damping characteristics can be controlled by the ratio of the amplitude of the excitation force to the frictional force. Finally, the design criteria of the proposed damper were derived.
14
Zhang, Xiang, Qi Wei He, and Shao Chun Ding. "Development of a New Damping Material with Oil Resistance and High Temperature Resistance." Advanced Materials Research 160-162 (November 2010): 1498–502. http://dx.doi.org/10.4028/www.scientific.net/amr.160-162.1498.
Full textAbstract:
In aerospace field and submarine field, structure vibration is ubiquity and the work environments is very bad which is oily and work temperature is high. Damping material is a kind of high molecular polymer which has elastic solid property and viscous fluid property at the same time and can attenuate bending vibration of structures and reduce radiated noise. So using damping material to control the structures vibration is an effective method. By experimentations and performance testing of 200 formulas, a new kind of excellent damping material has been successfully developed which is oil resistance and high temperature resistance. At the same time, the paper has established the formula database of damping materials which is a good base for many different engineering applications of damping material with oil resistance and high temperature resistance.
15
Garg, Deepak, Antonella Longo, and Paolo Papale. "Modeling Free Surface Flows Using Stabilized Finite Element Method." Mathematical Problems in Engineering 2018 (June 11, 2018): 1–9. http://dx.doi.org/10.1155/2018/6154251.
Full textAbstract:
This work aims to develop a numerical wave tank for viscous and inviscid flows. The Navier-Stokes equations are solved by time-discontinuous stabilized space-time finite element method. The numerical scheme tracks the free surface location using fluid velocity. A segregated algorithm is proposed to iteratively couple the fluid flow and mesh deformation problems. The numerical scheme and the developed computer code are validated over three free surface problems: solitary wave propagation, the collision between two counter moving waves, and wave damping in a viscous fluid. The benchmark tests demonstrate that the numerical approach is effective and an attractive tool for simulating viscous and inviscid free surface flows.
16
Ene, Remus Daniel, Vasile Marinca, and Bogdan Marinca. "Free Oscillations of a Nonlinear Oscillator with an Exponential Non-Viscous Damping." Applied Mechanics and Materials 801 (October 2015): 38–42. http://dx.doi.org/10.4028/www.scientific.net/amm.801.38.
Full textAbstract:
This paper deals with the nonlinear oscillations of an exponential non-viscous damping oscillator. An analytic technique, namely Optimal Homotopy Perturbation Method (OHPM) is employed to propose an analytic approach to solve nonlinear oscillations. Our procedure proved to very effective and accurate and did not require a small or large parameters in the nonlinear equation or in the initial conditions. An excellent agreement of the approximate frequencies and periodic solutions with the numerical ones has been demonstrated.
17
Carden, Lyle P., Barry J. Davidson, Tam J. Larkin, and Ian G. Buckle. "Retrofit of seismically isolated structures for near-field ground motion using additional viscous damping." Bulletin of the New Zealand Society for Earthquake Engineering 38, no. 2 (2005): 106–18. http://dx.doi.org/10.5459/bnzsee.38.2.106-118.
Full textAbstract:
Recent earthquakes have shown that a large magnitude, long period pulse is often prevalent in ground motion records at sites within a few kilometres of the active fault during an earthquake. Near-field earthquake ground motion containing forward directivity effects can result in a larger response in flexible structures, such as seismically isolated structures, compared to that predicted for conventional ground shaking. Hence, a study was performed on a number of generic seismically isolated structures designed to the 1997 Uniform Building Code, as well as a case study on the William Clayton building in Wellington, to determine the impact of near-field ground motion. In optimising the performance of the buildings for both near-field and original "design level" earthquakes, it is concluded that linear viscous dampers added to the existing isolation systems are effective in controlling the response during large magnitude near-field earthquakes with minimal impact on the design response. Additional viscous damping is more effective than hysteretic damping in limiting isolator displacements while also preventing an increase in base shear and floor accelerations for far-field "design level" earthquakes.
18
PRIEDE, JĀNIS. "Oscillations of weakly viscous conducting liquid drops in a strong magnetic field." Journal of Fluid Mechanics 671 (February 10, 2011): 399–416. http://dx.doi.org/10.1017/s0022112010005781.
Full textAbstract:
We analyse small-amplitude oscillations of a weakly viscous electrically conducting liquid drop in a strong uniform DC magnetic field. An asymptotic solution is obtained showing that the magnetic field does not affect the shape eigenmodes, which remain the spherical harmonics as in the non-magnetic case. A strong magnetic field, however, constrains the liquid flow associated with the oscillations and, thus, reduces the oscillation frequencies by increasing effective inertia of the liquid. In such a field, liquid oscillates in a two-dimensional (2D) way as solid columns aligned with the field. Two types of oscillations are possible: longitudinal and transversal to the field. Such oscillations are weakly damped by a strong magnetic field – the stronger the field, the weaker the damping, except for the axisymmetric transversal and inherently 2D modes. The former are overdamped because of being incompatible with the incompressibility constraint, whereas the latter are not affected at all because of being naturally invariant along the field. Since the magnetic damping for all other modes decreases inversely with the square of the field strength, viscous damping may become important in a sufficiently strong magnetic field. The viscous damping is found analytically by a simple energy dissipation approach which is shown for the longitudinal modes to be equivalent to a much more complicated eigenvalue perturbation technique. This study provides a theoretical basis for the development of new measurement methods of surface tension, viscosity and the electrical conductivity of liquid metals using the oscillating drop technique in a strong superimposed DC magnetic field.
19
Liu, Yi, Xing Jun Qi, Yi Jian Wang, and Shu Gang Chen. "Seismic Mitigation Analysis of Viscous Dampers for Curved Continuous Girder Bridge." Applied Mechanics and Materials 90-93 (September 2011): 1230–33. http://dx.doi.org/10.4028/www.scientific.net/amm.90-93.1230.
Full textAbstract:
The seismic response of curved girder bridge is more complex because of its irregular plane shape, therefore, the systematic study of an effective seismic mitigation method is required. In this article, the three-dimensional computational model of a double-pier curved continuous girder bridge is established and viscous dampers are added at the positions of sliding bearings. The full-bridge seismic response absorption effect is analyzed with the viscous dampers damping method under three ground motions of different frequency spectrum characteristic, and each ground motion contains three-direction. The results show that viscous dampers can reduce the difference of internal force between inner pier and outer pier in double-pier curved bridge, and it can also effectively reduce the bending and twisting coupling effect of curved bridge. But viscous dampers are sensitive to seismic spectrum to some degree, therefore seismic response absorption effect and sensitivity should be considered comprehensively when viscous dampers are selected.
20
Li, Yale, Zhouhong Zong, Bingwen Yang, Yuanzheng Lin, and Jin Lin. "Research on Longitudinal Collapse Mode and Control of the Continuous Bridge under Strong Seismic Excitations." Applied Sciences 10, no. 17 (2020): 6049. http://dx.doi.org/10.3390/app10176049.
Full textAbstract:
Bridge collapse events are common in major earthquakes around the world, among which continuous girder bridges are the most involved. In order to explore the collapse mechanism of a continuous girder bridge in an earthquake, the collapse mode of a two-span continuous girder bridge specimen which had been studied by the shaking table test was analyzed. Then, on the basis of the conventional plate rubber bearing system, the collapse control strategies which were high damping rubber bearing, fluid viscous damper, lock-up clutch control methods were discussed. It is found that high damping rubber bearing can delay the collapse time but the collapse mode remains the same; lock-up clutch has the best displacement control effect for the superstructure, but its energy consumption performance is not as good as that of a fluid viscous damper; high damping rubber bearing is quite suitable for protecting the substructure under short-period ground motion to avoid the bridge collapse caused by the failure of piers; fluid viscous damper and lock-up clutch are suitable for protecting the superstructure under long ground seismic motion to avoid the bridge non-use resulted from girder lowering; three collapse control methods can improve the anti-collapse ability of the bridge specimen, although no matter which control method is used, the bridge specimen may still collapse under strong earthquakes, but the target of postponing collapse time can be realized by means of various effective control methods.
21
Chen, Chaoyu, Junli Chen, Fengxin Sun, Huijuan Yang, and Zhaoqun Du. "Analysis of the damping property of warp-knitted spacer fabrics under damped free vibration." Textile Research Journal 88, no. 7 (2017): 790–99. http://dx.doi.org/10.1177/0040517517690628.
Full textAbstract:
The main content dealt with in this paper was to carry out a theoretical analysis of the damping property of spacer fabric used as cushion materials. A free vibration test was conducted and the corresponding model was established based on a single-degree-of-freedom (SDOF) system by considering the viscous–elastic behavior of spacer fabric during free vibration. Displacement–time curves of spacer fabric were calculated by a second-order integral of acceleration and time curves recorded by an accelerator sensor. Then, vibration indexes, including the damping ratio, damping coefficient, logarithmic decrement and free vibration period, were featured based on a SDOF model. The experimental results of damping ratio and displacement–time curves were compared with the theoretical results. It indicated that the vibration model was effective to characterize the free vibration of spacer fabric. Moreover, the effects of different structural parameters, including thickness, filament diameter, area density and inclination angle and arrangement of spacer filaments, of the spacer fabric on the damping property were also investigated. This is helpful to better design spacer fabrics with a good damping property.
22
Kong, Cuiyan, and Mervyn J. Kowalsky. "Impact of Damping Scaling Factors on Direct Displacement-Based Design." Earthquake Spectra 32, no. 2 (2016): 843–59. http://dx.doi.org/10.1193/021815eqs031m.
Full textAbstract:
Damping scaling factors (DSFs) play an important role in direct displacement-based design (DDBD) as they provide a means to establish displacement response spectra for damping values beyond 5%. Response spectra for multiple damping values are needed for DDBD as the approach relies on equivalent linearization, expressed in the form of effective stiffness and equivalent viscous damping, to establish design forces for prescribed performance limit states. In the past, DSFs based on the Eurocode have been employed for DDBD; however, recent research has resulted in more robust DSF models. This paper examines the accuracy of the current DSF equation used in DDBD across the parameters that are important for structural design. A nonlinear regression analysis is performed based on the data obtained by the Rezaeian et al. (2014) model, and a base shear adjustment factor (SAF) is proposed for application to the DDBD base shear equation.
23
Fernandez, A. L., and J. C. Santamarina. "Effect of cementation on the small-strain parameters of sands." Canadian Geotechnical Journal 38, no. 1 (2001): 191–99. http://dx.doi.org/10.1139/t00-081.
Full textAbstract:
Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.
24
Andrés, Luis San, and Adolfo Delgado. "Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal—Part I: Unidirectional Load Tests." Journal of Engineering for Gas Turbines and Power 129, no. 3 (2006): 858–64. http://dx.doi.org/10.1115/1.2436571.
Full textAbstract:
Squeeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus not generating enough damping capability. Single frequency, unidirectional load tests were conducted on a SFD test rig replicating a commercial jet-engine configuration. The damper journal is 2.54cm in length and 12.7cm in diameter, with nominal clearance of 0.127mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports, and a mechanical seal ring in contact with the damper journal. A wave spring pushes the ring ensuring tight sealing to prevent gas ingestion. The mechanical seal also serves to contain the lubricant within the squeeze film land for extended periods of time and; while in operation, to prevent contamination of the ball bearing cartridge. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and motion amplitude dependent, albeit decreasing rapidly as the motion parameters increase. Identified squeeze film force coefficients, damping and added mass, agree well with predictions based on the full film, short length damper model.
25
Chen, Shenyan, Zihan Yang, Minxiao Ying, Yanwu Zheng, Yanjie Liu, and Zhongwen Pan. "Parallel Load-Bearing and Damping System Design and Test for Satellite Vibration Suppression." Applied Sciences 10, no. 4 (2020): 1548. http://dx.doi.org/10.3390/app10041548.
Full textAbstract:
The traditional series-type satellite vibration suppression scheme significantly decreases satellite frequency, which leads to difficulty in controlling the amplitude. In the present work, a new parallel viscous damping scheme is adopted on the Payload Adaptor Fitting (PAF), which aims to integrate a load-bearing design and vibration reduction. The vibration amplitude and weight are the most important design requirements of the damping system. The Finite Element (FE) model of PAF was established. Through a series of analyses, the appropriate number and coefficient of dampers were determined. The damping force was calculated according to the damping coefficient and the relative velocity between the two ends of the damper. Based on the damping force and the installation dimensions, the damping rod was designed. The force–velocity test was carried out on the damping rod prototype, which showed its performance satisfies the requirements. With the topology optimization and sizing optimization technology, the light-weight supports were designed and manufactured. One damping rod and two supports were assembled as one set of dampers. Eight sets of dampers were installed on the PAF. Vibration tests were conducted on the damping state PAF. The results showed that the proposed system is effective at suppressing vibration and maintaining stiffness simultaneously.
26
Murakami, Katsuhide, Masato Ishii, Kentaroh Miyazaki, and Yasuhiro Tsuneki. "Proposal for an Efficient Damping System for High-Rise Buildings in Major Earthquakes." Journal of Disaster Research 11, no. 1 (2016): 106–17. http://dx.doi.org/10.20965/jdr.2016.p0106.
Full textAbstract:
Recent vibration resistant designs for buildings in Japan often adopt a vibration control structure with dampers arranged in the framework. Generally, the dampers are arranged in the building’s core in a geometry that works most effectively to protect against story shearing deformation. It is already known, however, that the above-mentioned arrangement of dampers does not provide good damping effects for the upper stories of high-rise buildings with large aspect ratios, because the protection mechanism is designed to decrease the shearing deformation components of the building’s horizontal deformation caused by its horizontal loads. A new type of dampers, called force-restricted tuned viscous mass dampers (FRTVMD), has been recently developed for such circumstances, amplifying the deformation of viscous dampers with their tuned mass effects. This paper, therefore, first presents a tuned mass damper (TMD) system, effective for high-rise buildings with large aspect ratios against great earthquakes, and then proposes a new vibration control structural system capable of generating better damping effects with FRTVMD. In addition, we review its characteristics and effects by analyzing its vibration response, as well as verify that a combined use of such vibration control structural systems will generate far greater damping effects than an individual system.
27
Moore, J. J., A. B. Palazzolo, R. Gadangi, et al. "A Forced Response Analysis and Application of Impact Dampers to Rotordynamic Vibration Suppression in a Cryogenic Environment." Journal of Vibration and Acoustics 117, no. 3A (1995): 300–310. http://dx.doi.org/10.1115/1.2874452.
Full textAbstract:
A high speed damper test rig has been assembled at Texas A&M University to develop rotordynamic dampers for rocket engine turbopumps that operate at cryogenic temperatures, such as those used in the space shuttle main engines (SSMEs). Damping is difficult to obtain in this class of turbomachinery due to the low temperature and viscosity of the operating fluid. An impact damper has been designed and tested as a means to obtain effective damping in a rotorbearing system. The performance and behavior of the impact damper is verified experimentally in a cryogenic test rig at Texas A&M. Analytical investigations indicate a strong amplitude dependence on the performance of the impact damper. An optimum operating amplitude exists and is determined both analytically and experimentally. In addition, the damper performance is characterized by an equivalent viscous damping coefficient. The test results prove the impact damper to be a viable means to suppress vibration in a cryogenic rotorbearing system.
28
Occhiuzzi, Antonio. "Additional viscous dampers for civil structures: Analysis of design methods based on effective evaluation of modal damping ratios." Engineering Structures 31, no. 5 (2009): 1093–101. http://dx.doi.org/10.1016/j.engstruct.2009.01.006.
Full text
29
Hwang, J. S., L. H. Sheng, and J. H. Gates. "Practical Analysis of Bridges on Isolation Bearings with Bi-Linear Hysteresis Characteristics." Earthquake Spectra 10, no. 4 (1994): 705–27. http://dx.doi.org/10.1193/1.1585794.
Full textAbstract:
Various equivalent elastic models specified in current bridge engineering practices for the seismic analysis of base-isolated bridges are summarized and evaluated. Two additional methods proposed by the California Department of Transportation (CALTRANS) are validated based on their predictions of the maximum inelastic seismic responses of base-isolated bridges. The CALTRANS proposed methods are implemented with an empirical model for the determinations of the effective stiffness and equivalent viscous damping ratios of isolation units and base-isolated bridges. A modal strain energy method combined with the concept of component energy ratio is utilized to formulate the “composite damping ratio” of an entire base-isolated bridge. A five-span regular bridge subjected to four design earthquakes and ten recorded ground motions is employed to investigate the accuracy of prediction using various equivalent elastic methods.
30
Wang, Zhi Hao. "Experimental Study on Multi-Mode Vibration Control of a Stay Cable with a Passive Magnetorheological Damper." Applied Mechanics and Materials 361-363 (August 2013): 1402–5. http://dx.doi.org/10.4028/www.scientific.net/amm.361-363.1402.
Full textAbstract:
Effective vibration control technology for stay cables is extremely critical to safe operations of cable-stayed bridges. For super-long cables, passive linear damper cannot provide sufficient damping since it can be only optimum for a given mode of cable, while a long cable may vibrate with several modes. This paper focuses on multi-mode vibration control of stay cables with passive magnetorheological (MR) dampers. Firstly, a 21.6m-long model cable was designed and established in the laboratory.Then, control performance of the cable with a passive MR damper was tested. The test results show that modal damping ratios of the cable in the first four modes can be improved significantly with the MR damper. It is further demonstrated that optimal tuned passively operated MR damper can outperform the passive viscous damper.
31
Xu, Wei Kai, and Wei Wang. "Single-Negative Properties Based on the Bandgaps of One-Dimensional Phononic Crystal." Applied Mechanics and Materials 105-107 (September 2011): 279–82. http://dx.doi.org/10.4028/www.scientific.net/amm.105-107.279.
Full textAbstract:
Phononic Crystals (PCs) have important potential application in engineering by the properties of bandgaps. In the paper, the bandgap characteristic of one-dimensional PCs is attributed to the results of Single-Negative (SN) properties, e.g. negative modulus or negative density. The effective parameters of the 1D PCs were predicted by the equivalent layer concept with considering viscous damping, and the results showed that during the frequency regions of the bandgaps, the negative parameters appeared. This will be a reference for the design of acoustic negative refraction metamaterials.
32
Deng, X., and M. J. Tait. "Equivalent mechanical models of tuned liquid dampers with different tank geometries." Canadian Journal of Civil Engineering 35, no. 10 (2008): 1088–101. http://dx.doi.org/10.1139/l08-044.
Full textAbstract:
This paper focuses on the development of equivalent mechanical models for tuned liquid dampers (TLDs) with rectangular, vertical-cylindrical, horizontal-cylindrical, and hyperboloid (conical) tank shapes under external excitation in the transverse direction. Potential flow theory is utilized to obtain the free-surface response amplitude and the corresponding velocity of the sloshing liquid and Lagrange’s equations are used to determine the generalized properties. Morison’s equation and the virtual work method are used to estimate an equivalent viscous damping ratio based on the screen loss coefficient. The equivalent mechanical properties derived in this paper model the fundamental sloshing mode only and are restricted to small response amplitudes. Subsequently, the equivalent mechanical properties including effective mass, natural frequency, and damping ratio of the TLDs, having different tank geometries, are compared. It is found that the effective mass values for horizontal-cylindrical and hyperboloid TLDs are larger than the effective mass values for vertical-cylindrical and rectangular TLDs. The increased effective mass values for horizontal-cylindrical and hyperboloid TLDs can result in improved tuned liquid damper performance given the same total liquid mass as that of rectangular or vertical-cylindrical TLDs.
33
RABAULT, JEAN, GRAIG SUTHERLAND, OLAV GUNDERSEN, and ATLE JENSEN. "Measurements of wave damping by a grease ice slick in Svalbard using off-the-shelf sensors and open-source electronics." Journal of Glaciology 63, no. 238 (2017): 372–81. http://dx.doi.org/10.1017/jog.2017.1.
Full textAbstract:
ABSTRACTVersatile instruments assembled from off-the-shelf sensors and open-source electronics are used to record wave propagation and damping measured by Inertial Motion Units (IMUs) in a grease ice slick near the shore in Adventfjorden, Svalbard. Viscous attenuation of waves due to the grease ice slick is clearly visible by comparing the IMU data recorded by the different instruments. The frequency dependent spatial damping of the waves is computed by comparing the power spectral density obtained from the different IMUs. We model wave attenuation using the one-layer model of Weber from 1987. The best-fit value for the effective viscosity is ν = (0.95 ± 0.05 × 10−2)m2 s−1, and the coefficient of determination is R2 = 0.89. The mean absolute error and RMSE of the damping coefficient are 0.037 and 0.044m−1, respectively. These results provide continued support for improving instrument design for recording wave propagation in ice-covered regions, which is necessary to this area of research as many authors have underlined the need for more field data.
34
Koo, Gyeong-Hoi, Jin-Young Jung, Jin-Hyeong Lee, Tae-Myung Shin, and Jin-Young Park. "Development of Small-Sized Lead Inserted Laminated Rubber Bearing for Nuclear Component Seismic Isolation." Energies 13, no. 12 (2020): 3193. http://dx.doi.org/10.3390/en13123193.
Full textAbstract:
This paper presents a design specification of the small-sized lead inserted laminated rubber bearing (LRB) for application to nuclear component seismic isolation and describes the results of test verification on design performance parameters such as effective horizontal stiffness, equivalent viscous damping ratio, design seismic isolation frequency, and ultimate shear deformation. To do this, two types of LRB, having the same vertical design load of 10 kN but with different shape factors, are designed, fabricated, and tested by the quasi-static procedures. To determine the effective horizontal stiffness and the equivalent damping value from the test results, the new method is proposed and compared with the methods of the ASCE and ISO standards in case that the tangential stiffness curve is not linear in tests. From the comparison between tests and design specifications in the performance parameters, it was found that the design specifications developed in this paper are in a good agreement with the test results. Furthermore, the target design shear deformation limits are confirmed to have sufficient design margins in ultimate shear deformation tests.
35
Chinniah, Yuvin, Richard Burton, and Saeid Habibi. "Viscous Damping Coefficient and Effective Bulk Modulus Estimation in a High Performance Hydrostatic Actuation System using Extended Kalman Filter." International Journal of Fluid Power 4, no. 3 (2003): 27–34. http://dx.doi.org/10.1080/14399776.2003.10781172.
Full text
36
Ma, Li Jun, and Jian Ming Xu. "Seismic Analysis of Urban Elevated Continuous Bridges Installed Different Damping Devices." Applied Mechanics and Materials 638-640 (September 2014): 983–86. http://dx.doi.org/10.4028/www.scientific.net/amm.638-640.983.
Full textAbstract:
Earthquakes are human recognized natural disasters, causing tremendous loss of life and property to human society, so how to strengthen the seismic capacity of the building more effectively is one of the challenges faced by scientists.While the use of a damping device is an effective method. With the rapid economic and social development, the urban transport problem is an extremely serious livelihood problem faced by all countries. To solve urban traffic congestion, in many cities setting up viaducts is a widely used way to ease urban traffic pressure, and elevated expressways are the main bridges among continuous bridges. In order to ensure the safe operation of the urban elevated road system, we must make the correct evaluation of their seismic capacity. This paper focuses on the continuous beam bridge seismic response history analysis of installing viscous dampers and lock-up devices,compared with the general scheme of continuous bridge.
37
Yao, George C., Wen-Chun Huang, and Fan-Ru Lin. "Seismic Performance of Guideway Sliding Isolator with Gap Springs for Precision Machinery." Advances in Structural Engineering 11, no. 5 (2008): 511–24. http://dx.doi.org/10.1260/136943308786412032.
Full textAbstract:
The performance of gap springs in a guideway sliding isolator (GSI) system developed to protect precision machinery against seismic motion has been studied. A spring is initially distanced from the system by a gap, causing the isolation system to exhibit nonlinear performance once the gap is closed, reducing the chance of resonance. A full-scale shaking table test of a 22-ton specimen and a numerical model simulation in SAP2000 have been performed. The study shows that springs possessing the appropriate gaps are more effective in controlling relative displacements than is a pure friction system. The optimal gap for a system subjected to far-field earthquakes was found to be 5mm. In addition, supplemental viscous damping of less than 15% of the critical damping had no significant effect on the GSI system far-field seismic response, but it did reduce the relative displacements of the system for near-fault seismic excitations.
38
Jin, Lei, Li Kou, Yanan Zeng, Chunguang Hu, and Xiaodong Hu. "Sample preparation method to improve the efficiency of high-throughput single-molecule force spectroscopy." Biophysics Reports 5, no. 4 (2019): 176–83. http://dx.doi.org/10.1007/s41048-019-00097-4.
Full textAbstract:
Abstract Inefficient sample preparation methods hinder the performance of high-throughput single-molecule force spectroscopy (H-SMFS) for viscous damping among reactants and unstable linkage. Here, we demonstrated a sample preparation method for H-SMFS systems to achieve a higher ratio of effective target molecules per sample cell by gas-phase silanization and reactant hydrophobization. Digital holographic centrifugal force microscopy (DH-CFM) was used to verify its performance. The experimental result indicated that the DNA stretching success ratio was improved from 0.89% to 13.5%. This enhanced efficiency preparation method has potential application for force-based DNA stretching experiments and other modifying procedures.
39
Sullivan, Timothy J. "Direct Displacement-Based Design of a RC wall-steel EBF dual system with added dampers." Bulletin of the New Zealand Society for Earthquake Engineering 42, no. 3 (2009): 167–78. http://dx.doi.org/10.5459/bnzsee.42.3.167-178.
Full textAbstract:
An innovative application of Direct Displacement-Based Design (DBD) is presented for a modern 8-storey dual system structure consisting of interior concrete walls in parallel to a number of large steel eccentrically braced frames, fitted with visco-elastic dampers at link positions. The innovative DBD methodology lets the designer directly control the forces in the structure by choosing strength proportions at the start of the design procedure. The strength proportions are used to establish the displaced shape at peak response and thereby establish the equivalent single-degree-of-freedom system design displacement, mass and effective height. A new simplified formulation for the equivalent viscous damping of systems possessing viscous dampers is proposed which also utilises the strength proportions chosen by the designer at the start of the process. The DBD approach developed is relatively quick to use, enabling the seismic design of the 8-storey case study structure to be undertaken without the development of a computer model. To verify the ability of the design method, non-linear time-history analyses are undertaken using a suite of spectrum-compatible accelerograms. These analyses demonstrate that the design solution successfully achieves the design objectives to limit building deformations, and therefore damage.
40
Sullivan, Timothy J. "Direct Displacement-Based Design of a RC wall-steel EBF dual system with added dampers." Bulletin of the New Zealand Society for Earthquake Engineering 44, no. 3 (2011): 167–78. http://dx.doi.org/10.5459/bnzsee.44.3.167-178.
Full textAbstract:
An innovative application of Direct Displacement-Based Design (DBD) is presented for a modern 8-storey dual system structure consisting of interior concrete walls in parallel to a number of large steel eccentrically braced frames, fitted with visco-elastic dampers at link positions. The innovative DBD methodology lets the designer directly control the forces in the structure by choosing strength proportions at the start of the design procedure. The strength proportions are used to establish the displaced shape at peak response and thereby establish the equivalent single-degree-of-freedom system design displacement, mass and effective height. A new simplified formulation for the equivalent viscous damping of systems possessing viscous dampers is proposed which also utilises the strength proportions chosen by the designer at the start of the process. The DBD approach developed is relatively quick to use, enabling the seismic design of the 8-storey case study structure to be undertaken without the development of a computer model. To verify the ability of the design method, non-linear time-history analyses are undertaken using a suite of spectrum-compatible accelerograms. These analyses demonstrate that the design solution successfully achieves the design objectives to limit building deformations, and therefore damage.
41
Matsagar, Vasant A., and R. S. Jangid. "Base-isolated building connected to adjacent building using viscous dampers." Bulletin of the New Zealand Society for Earthquake Engineering 39, no. 1 (2006): 59–80. http://dx.doi.org/10.5459/bnzsee.39.1.59-80.
Full textAbstract:
Seismic response of multi-storied base-isolated building on various isolation systems connected using viscous dampers to an adjacent dissimilar base-isolated or fixed-base building is investigated. The multi-storied buildings are modeled as a shear type structures with lateral degree-of-freedom at each floor, which are connected at different floor levels by the viscous dampers. Performance of this novel combination is studied by deriving the governing equations of motion and solving it in the incremental form using Newmark's step by-step method of integration. The variation of top floor absolute acceleration and bearing displacement under different real earthquake ground motions is computed to study the behavior and effectiveness of the connected systems. It is concluded that connecting the two adjacent base-isolated buildings with the viscous dampers is helpful in controlling large bearing displacement in the base-isolated structures; thereby, eliminating isolator damages arising due to instability at large displacement or pounding with adjacent structures during the earthquakes. Parametric studies are also performed to identify optimal parameters such as damper damping and distribution pattern of viscous dampers to achieve the maximum response reduction in the damper-linked adjacent buildings. The connection of viscous dampers to adjacent structures are found to be most effective when: (i) the adjacent base-isolated and fixed-base buildings are connected, (ii) dissimilar isolation systems are used for the two adjacent buildings, (iii) the time periods of adjacent structures are well separated, and (iv) the superstructure flexibility is higher.
42
Bai, Qingsong, and Xianhe Huang. "Using Quartz Crystal Microbalance for Field Measurement of Liquid Viscosities." Journal of Sensors 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/7580483.
Full textAbstract:
The field measurement of liquid viscosities, especially the high viscous liquids, is challenging and often requires expensive equipment, long processing time, and lots of reagent. We use quartz crystal microbalances (QCMs) operating in solution which are also sensitive to the viscosity and density of the contacting solution. QCMs are typically investigated for sensor applications in which one surface of QCM completely immersed in Newtonian liquid, but the viscous damping in liquids would cause not only large frequency shifts but also large losses in the quality factorQleading to instability and even cessation of oscillation. A novel mass-sensitivity-based method for field measurement of liquid viscosities using a QCM is demonstrated in this paper and a model describing the influence of the liquid properties on the oscillation frequency is established as well. Two groups of verified experiments were performed and the experimental results show that the presented method is effective and possesses potential applications.
43
Gabryś, Katarzyna, Emil Soból, Wojciech Sas, and Alojzy Szymański. "Material damping ratio from free-vibration method." Annals of Warsaw University of Life Sciences – SGGW. Land Reclamation 50, no. 2 (2018): 83–97. http://dx.doi.org/10.2478/sggw-2018-0007.
Full textAbstract:
Abstract One important aspect of soil dynamics is attenuation or energy loses. This inherent dynamic property is essential in the analysis of soil behavior subjected to a dynamic load. Energy absorption in soils leads to the definition of an equivalent viscous damping ratio (D). In resonant column testing there are commonly two different approaches in measuring material damping: during a steady-state vibration (SSV), when the specimen is vibrated at its first mode; and during free-vibration decay (FVD). The study reports results associated with the small to medium strain range material damping from FVD method, i.e. there is a cut off the constant vibration of the specimen at resonance and the specimen is allowed to free-vibration mode while the decay strain amplitude during free-vibration is calculated. The experiments were conducted on cohesive soils (sasiCl, Cl, clSa) from various test sites located in Warsaw, Poland. All the specimens were subjected to torsional mode of vibration at their first natural frequency, at different mean effective stress. The authors paid particular attention to the number of successive cycles after the free-vibration of the material is initiated. They examined various propositions from the literature and compare the received damping values using different number of cycles of vibration. The results showed that the most stable values of material damping ratio can be obtained by selecting each time a line of best fit on the authors’ choice of number of free-vibration cycles. However, the number of these cycles should not exceed 10.
44
Zhuravlev, V. V. "The resonant drag instability of dust streaming in turbulent protoplanetary disc." Monthly Notices of the Royal Astronomical Society 494, no. 1 (2020): 1395–410. http://dx.doi.org/10.1093/mnras/staa805.
Full textAbstract:
ABSTRACT Damping of the previously discovered resonant drag instability (RDI) of dust streaming in the protoplanetary disc is studied using the local approach to dynamics of gas–dust perturbations in the limit of the small dust fraction. Turbulence in a disc is represented by the effective viscosity and diffusivity in equations of motion for gas and dust, respectively. In the standard case of the Schmidt number (ratio of the effective viscosity to diffusivity) Sc = 1, the reduced description of RDI in terms of the inertial wave (IW) and the streaming dust wave (SDW) falling in resonance with each other reveals that damping solution differs from the inviscid solution simply by adding the characteristic damping frequency to its growth rate. RDI is fully suppressed at the threshold viscosity, which is estimated analytically, first, for radial drift, next, for vertical settling of dust, and at last, in the case of settling combined with a radial drift of the dust. In the last case, RDI survives up to the highest threshold viscosity, with a greater excess for smaller solids. Once Sc ≠ 1, a new instability specific for dissipative perturbations on the dust settling background emerges. This instability of the quasi-resonant nature is referred to as settling viscous instability (SVI). The mode akin to SDW (IW) becomes growing in a region of long waves provided that Sc > 1 (Sc < 1). SVI leads to an additional increase in the threshold viscosity.
45
Kahma, Kimmo K., and Mark A. Donelan. "A laboratory study of the minimum wind speed for wind wave generation." Journal of Fluid Mechanics 192 (July 1988): 339–64. http://dx.doi.org/10.1017/s0022112088001892.
Full textAbstract:
The minimum wind speed for wind wave generation has been investigated in a laboratory wind-wave flume using a sensitive slope gauge to measure the initial wavelets about 10 μm high. The growth at very low wind speeds was higher than predicted by the viscous shear-flow instability theory. Assuming that the growth is exponential, the inception wind speed at which the growth rate becomes positive can be defined. It occurred at (friction velocity) u* ≈ 2 cm/s, somewhat lower than the u* ≈ 4–5 cm/s predicted by shear-flow instability theory. However, the observed growth rates were close to the theory at higher wind speeds when the waves were higher than 1 mm. The effect of temperature on the wind speed at which the waves become readily visible is shown to be appreciable and in keeping with the temperature dependent viscous damping. Other sources of growth are discussed. Our estimates show that the Phillips resonance mechanism might be sufficiently effective to generate the observed growth at very low wind speeds.
46
Dong, Jian, Xiaojing Wang, Jin Zhang, and Jingjun Gu. "Experimental investigation of dynamic behavior of rotor-bearing system with nitrile rubber support." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 232, no. 12 (2018): 1502–13. http://dx.doi.org/10.1177/1350650118757067.
Full textAbstract:
Nitrile rubber (NBR) as a vibration absorber of lower elasticity modulus has a considerable contribution in the effective damping. Three kinds of journal bearings (general journal bearings, journal bearings supported on circular nitrile rubber, journal bearings supported on radial nitrile rubber) were designed and manufactured. Experiments were carried out to investigate vibration and stability of the rotor-bearing system with the above bearings. Oil whirl and the onset of instability of the system was analyzed and compared. The experimental results show that there is a significant decrease in the acceleration amplitude of the bearings embedded with nitrile rubber compared to general journal bearings. In addition, the journal bearings supported on radial nitrile rubber have better vibration damping effect than journal bearings supported on circular nitrile rubber, for there is no obvious oil whirl and asynchronous vibration, which can be verified by waterfall plots and continuous wavelet transform spectrograms. Results demonstrated that vibration energy dissipated by viscous absorbers indeed contributes to improving dynamics stability of the rotor-bearing system.
47
Chang, S. Y., Y. C. Huang, and C. H. Wang. "Analysis of Newmark Explicit Integration Method for Nonlinear Systems." Journal of Mechanics 22, no. 4 (2006): 321–29. http://dx.doi.org/10.1017/s1727719100000976.
Full textAbstract:
AbstractNumerical properties of the Newmark explicit method in the solution of nonlinear systems are explored. It is found that the upper stability limit is no longer equal to 2 for the Newmark explicit method for nonlinear systems. In fact, it is enlarged for stiffness softening and is reduced for stiffness hardening. Furthermore, its relative period error increases with the increase of the step degree of nonlinearity for a given value of the product of the natural frequency and the time step. It is also verified that the viscous damping determined from an initial stiffness is effective to reduce displacement response in the solution of a nonlinear system as that for solving a linear elastic system. All the theoretical results are confirmed with numerical examples.
48
Jeong, TG, SS Lee, and Chang-Wan Kim. "Frequency response computation of structures including non-proportional damping in a shared memory environment." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 227, no. 2 (2012): 288–98. http://dx.doi.org/10.1177/0954406212447514.
Full textAbstract:
With the increased size of the finite element model for improved accuracy, the modal frequency response analysis has been one of the common practices of evaluating the performance of vehicle dynamics. However, there is difficulty in predicting the vehicle dynamics response with non-proportional damping regarding performance. The fast frequency response analysis algorithm (FFRA) has been proved to be very effective for partially damped structural system in the modal frequency response analysis. In the fast frequency response analysis algorithm, performance depends mainly on the complex symmetric matrix eigenvalue problem. Therefore, an efficient complex symmetric matrix eigenvalue problem solver is developed in this article. This approach also uses parallel processing in a shared memory machine for more efficient analysis. Numerical examples show that the new complex symmetric matrix eigensolver provides good accuracy and high performance. Then, the fast frequency response analysis algorithm is applied to a full scale vehicle system that includes only a few viscous damping finite elements. The fast frequency response analysis algorithm significantly improves the performance of the modal frequency response analysis compared to conventional method. In addition, parallel processing improves the efficiency of the overall simulation.
49
EL-DIB, YUSRY O. "Viscous interface instability supporting free-surface currents in a hydromagnetic rotating fluid column." Journal of Plasma Physics 65, no. 1 (2001): 1–28. http://dx.doi.org/10.1017/s0022377801001003.
Full textAbstract:
The stabilization of a viscous interface stressed by an oscillating magnetic field is investigated. Account is taken of the influence of free-surface currents on the effective solidly rotating fluid column. Only azimuthal modes are considered in the linear perturbation. The dispersion relation with or without free-surface currents is obtained in the form of a linear Mathieu equation with complex coefficients. It is found that there is a nonlinear relation between the surface current density and both the stratified viscosity and the stratified azimuthal magnetic field. The surface currents disappear on the interface of the fluid column when the stratified magnetic field has the value of unity. At this value, a coupled parametric resonance occurs in the absence of angular velocity. The magnetic field plays a stabilizing role. This role increases with increasing surface currents. The angular velocity plays a destabilizing role, while the field frequency plays a stabilizing role and acts against the angular velocity. The stratified viscosity plays a damping role in the presence of the surface current density, while, in the absence of a surface current, it plays two opposite roles corresponding to the presence or absence of the field frequency. A set of graphs are used to illustrate the relation between the presence of free-surface currents and both the viscosity and the azimuthal magnetic field.
50
Abd Ghani, Kay Dora, Nor Hayati Hamid, and Muhd Salmizi Jaafar. "Load versus Displacement Validation between Ruaumoko Hysteresis Program and Experimental Work on CFRP Retrofitted Precast Beam-Column Exterior Joint." Key Engineering Materials 594-595 (December 2013): 390–94. http://dx.doi.org/10.4028/www.scientific.net/kem.594-595.390.
Full textAbstract:
This paper presented the load versus displacement curve for experimental work and validated with modeling results. A full-scale specimen which representing retrofitted precast RC beam-column exterior joint with corbels was tested in the laboratory under reversible lateral cyclic loading until ±1.75% interstorey drift. The specimen was rehabilitated by using Carbon Fiber Reinforced Polymer (CFRP) wrapping method. Modeling work was carried out using Ruaumoko Hysteres Program. A curve representing load versus displacement for beam-column exterior joint is generated using Pampanin Reinforced Concrete Beam-Column Joint Hysteresis rule with reloading slip factor. The modeling result was compared with the load versus displacement curve obtained from experimental work. It was found that the hysteresis loops exhibited good agreement between experimental and modeling results. The effective stiffness, displacement ductility and equivalent viscous damping for the specimen were also discussed and compared.