Academic literature on the topic 'Stiffness Proportional Dampers'
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Journal articles on the topic "Stiffness Proportional Dampers"
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Solmazyaghobzadeh, Solmazyaghobzadeh. "Determining the Best Insertion Site of Fluid Viscous Dampers to Optimize and Reduce Incurredcosts in Adjacent Buildings." Modern Applied Science 10, no. 9 (June 7, 2016): 130. http://dx.doi.org/10.5539/mas.v10n9p130.
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In the past decade, researchers developed the idea of connecting buildings with intelligent activated, semi-active and inactivated damper systemsreduce adjacent buildings response to wind and earthquake. One of the most important damper devices in non-active control is fluid viscous damper.Fluid dampers due to viscous fluidsshow high resistance. High resistance of viscous fluidsagainst the flow is the basicfunctionof fluid viscous dampers. Deformation speed a fluid viscous damper is proportional to the acted forces. Therefore the aim of this paper is to determine the insertion site of fluid viscous dampersto optimize and reduce the consuming costs in adjacent buildings. For this purpose, four different models of connected adjacent buildings with common and different shear stiffness in the software SAP 2000 has been modeled. This study shows that it is not necessarytwo adjacent buildings connected by a damper on all floors, but the less damper in appropriate selected locations can help reduce the earthquake response. And by placing the fluid viscous dampers in selected certainfloors provides more useful structural system for reducing the effects of earthquakes.
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de Santiago, O., L. San Andre´s, and J. Oliveras. "Imbalance Response of a Rotor Supported on Open-Ends Integral Squeeze Film Dampers." Journal of Engineering for Gas Turbines and Power 121, no. 4 (October 1, 1999): 718–24. http://dx.doi.org/10.1115/1.2818532.
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Rotor vibration attenuation and structural components isolation in jet engines are achieved with squeeze film dampers, many of them supported on long elastic squirrel cages. Integral squeeze film dampers (ISFDs) are comprised of arcuate pads and wire-EDM webs rendering a compact viscoelastic support. An experimental study is conducted to evaluate the effectiveness of ISFDs in attenuating the imbalance response of a massive test rotor. Measurements of the damper structural stiffness and rotor natural frequencies are detailed. Impact tests on the test rotor supported on its dampers reveal the supporting structure to be very flexible, thus requiring the experimental evaluation of an equivalent stiffness for the damper and supports system. System damping coefficients extracted from impact load excitations vary with the lubricant viscosity and include a significant structural damping from the bearing supports. Rotor coast-down tests demonstrate the ISFDs to damp well the rotor response with peak vibration amplitude proportional (linear) to the imbalance. Viscous damping coefficients estimated from the amplitude response at the critical speeds agree reasonably well with predictions from a full-film, finite element model.
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Szary, Marek L., and Peter Weber. "The Study of Behavior of Vibrating Systems Controllable by Devices with Rheological Fluid." Archives of Acoustics 38, no. 2 (June 1, 2013): 217–22. http://dx.doi.org/10.2478/aoa-2013-0026.
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Abstract The nonlinear mathematical model of behavior of controllable viscosity fluid (CVF) under applied external field is presented. A large family of these fluids is commonly used to control responding forces of dampers in vibration control applications. The responding force of a damper with CVF has two components. The first one - uncontrollable - is proportional to the viscosity of a base fluid and velocity of its motion, the second one, which is controllable, depends on the strength of the applied external field. Both are involved in the process of dissipation of unwanted energy from the vibrating systems. An equivalent damping factor based on the principle of energy dissipated during one cycle of damper work under a constant strength external field was calculated. When mass or stiffness is variable the equivalent damping factor can be set accordingly by adjusting the strength of external field to have vibrating damped system purposely/continuously working in the critical or other chosen state. This paper also presents cases of applying periodically changing strengths of an external field synchronized with cycles of periodical motion of the vibrating system to continuously control the damping force within each cycle.
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San Andre´s, L., and D. Lubell. "Imbalance Response of a Test Rotor Supported on Squeeze Film Dampers." Journal of Engineering for Gas Turbines and Power 120, no. 2 (April 1, 1998): 397–404. http://dx.doi.org/10.1115/1.2818136.
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Squeeze film dampers (SFDs) provide vibration attenuation and structural isolation to aircraft gas turbine engines which must be able to tolerate larger imbalances while operating above one or more critical speeds. Rotor-bearing-SFD systems are regarded in theory as highly nonlinear, showing jump phenomena and even chaotic behavior for sufficiently large levels of rotor imbalance. Yet, few experimental results of practical value have verified the analytical predictions. A test rig for measurement of the dynamic forced response of a three-disk rotor (45 kg) supported on two cylindrical SFDs is described. The major objective is to provide a reliable data base to validate and enhance SFD design practice and to allow a direct comparison with analytical models. The open-ends SFD are supported by four-bar centering structures, each with a stiffness of 3.5 MN/m. Measured synchronous responses to 9000 rpm due to various imbalances show the rotor-SFD system to be well damped with amplification factors between 1.6 and 2.1 while traversing cylindrical and conical modes critical speeds. The rotor amplitudes of motion are found to be proportional to the imbalances for the first mode of vibration, and the damping coefficients extracted compare reasonably well to predictions based on the full-film, open-ends SFD. Tight lip (elastomeric) seals contribute greatly to the overall damping of the test rig. Measured dynamic pressures at the squeeze film lands are well above ambient values with no indication of lubricant dynamic cavitation as simple theoretical models dictate. The measurements show absence of nonlinear behavior of the rotor-SFD apparatus for the range of imbalances tested.
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Kayabekir, Aylin Ece, Gebrail Bekdaş, Sinan Melih Nigdeli, and Zong Woo Geem. "Optimum Design of PID Controlled Active Tuned Mass Damper via Modified Harmony Search." Applied Sciences 10, no. 8 (April 24, 2020): 2976. http://dx.doi.org/10.3390/app10082976.
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In this study, the music-inspired Harmony Search (HS) algorithm is modified for the optimization of active tuned mass dampers (ATMDs). The modification of HS includes the consideration of the best solution with a defined probability and updating of algorithm parameters such as harmony memory, considering rate and pitch adjusting rate. The design variables include all the mechanical properties of ATMD, such as the mass, stiffness and damping coefficient, and the active controller parameters of the proposed proportional–integral–derivative (PID) type controllers. In the optimization process, the analysis of an ATMD implemented structure is done using the generated Matlab Simulink block diagram. The PID controllers were optimized for velocity feedback control, and the objective of the optimization is the minimization of the top story displacement by using the limitation of the stroke capacity of ATMD. The optimum results are presented for different cases of the stroke capacity limit of ATMD. According to the results, the method is effective in reducing the maximum displacement of the structure by 53.71%, while a passive TMD can only reduce it by 31.22%.
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KOBAYASHI, Masahito, Hisashi SATO, Yuichiro HORIE, and Tadaki KOH. "A STUDY ON EARTHQUAKE RESPONSE CONTROL OF RELATIVE STORY DISPLACEMENT OF PASSIVELY VIBRATION-CONTROLLED HIGH-RISE BUILDINGS WITH NON-PROPORTIONAL DISTRIBUTION OF LINEAR MAXWELL TYPE DAMPERS : Analysis of earthquake response mechanism by frequency response function with complex stiffness." Journal of Structural and Construction Engineering (Transactions of AIJ) 72, no. 619 (2007): 57–64. http://dx.doi.org/10.3130/aijs.72.57_3.
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Angeles, J., and S. Ostrovskaya. "The Proportional-Damping Matrix of Arbitrarily Damped Linear Mechanical Systems." Journal of Applied Mechanics 69, no. 5 (August 16, 2002): 649–56. http://dx.doi.org/10.1115/1.1483832.
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The vibration of linear mechanical systems with arbitrary damping is known to pose challenging problems to the analyst, for these systems cannot be analyzed with the techniques pertaining to their undamped counterparts. It is also known that a class of damped systems, called proportionally damped, can be analyzed with the same techniques, which mimic faithfully those of single-degree-of-freedom systems. For this reason, in many instances the system at hand is assumed to be proportionally damped. Nevertheless, this assumption is difficult to justify on physical grounds in many practical applications. What this assumption brings about is a damping matrix that admits a simultaneous diagonalization with the stiffness matrix. Proposed in this paper is a decomposition of the damping matrix of an arbitrarily damped system allowing the extraction of the proportionally damped component, which, moreover, approximates optimally the original damping matrix in the least-square sense. Finally, we show with examples that conclusions drawn from the proportionally damped approximation of an arbitrarily damped system can be dangerously misleading.
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Chan, Ricky W. K., and Zhe Fei Zhao. "Mitigation of Seismic Risks to Soft-Storey Structures Using Toggle-Brace-Damper Systems." Applied Mechanics and Materials 238 (November 2012): 833–37. http://dx.doi.org/10.4028/www.scientific.net/amm.238.833.
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Soft-storey mechanism is characterized by a sudden reduction of lateral stiffness in one or more levels of a structure. Soft-storey is often observed in the ground level due to the absence of wall or cladding. With recent develop of energy dissipation systems, soft-storey mechanism can be corrected by addition of a damper-brace assembly. In particular, this paper investigates the effect of toggle-damper-brace systems on such situations. Governing equations including the magnification factor and lateral stiffness contributed by a toggle-damper-brace are formulated. It was found that a toggle-damper-brace system, if proportioned correctly, will significantly increase the travel in the damper and overall stiffness of structure can be enhanced. An illustrative example is presented using nonlinear time history analysis implemented on MATLAB.
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Li, Jiming, Ramon Aguilar, Luis San Andre´s, and John M. Vance. "Dynamic Force Coefficients of a Multiple-Blade, Multiple-Pocket Gas Damper Seal: Test Results and Predictions." Journal of Tribology 122, no. 1 (June 29, 1999): 317–22. http://dx.doi.org/10.1115/1.555360.
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Experimental rotordynamic force coefficients and leakage for a four-blade, two-four pocket gas damper seal are presented and compared to predictions based on a one control volume bulk-flow model. The test rig comprises a vertical shaft and a test seal housing and flexible structure suspended from a rigid centering frame. The experiments were conducted at increasing rotor speeds to 6000 rpm and inlet/exit pressure ratios from 1.0 to 3.0. The seal force coefficients are obtained from impact response measurements of the seal and flexible structure using a frequency domain parameter identification technique. Both measurements and predictions show the seal direct stiffness and damping coefficients are proportional to the inlet/exit pressure ratio and insensitive to rotor speed. The agreement between experimental results and analytical predictions is acceptable. Predicted cross-coupled stiffness coefficients are of small amplitude. However, the test results evidence cross-coupled stiffnesses without journal rotation due to a structural asymmetry induced by the external pressurization into the seal. [S0742-4787(00)04201-6]
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An, Feng-chen, Qiong-guan Xiao, Shuai Li, and Hong-jun Li. "Mesoscale Modelling of Bond Behavior at FRP-Concrete under Mode II Loading: Effect of Rayleigh Damping." International Journal of Polymer Science 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/6053181.
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The paper mainly focuses on the study of the effects of Rayleigh damping in the simulations of FRP-concrete bonded joints, thereby proposing an approach to determine the value of its appropriate Rayleigh damping. Specifically, the element tests under Mode I and Mode II fracture modes were first carried out to investigate the effects of the mass proportional Rayleigh damping and the stiffness proportional Rayleigh damping. An FRP-concrete bonded joint is then employed to further investigate the effects of Rayleigh damping on the simulation results under Mode II fracture mode. It is shown that low-frequency vibrations are produced in the simulations of the specimens loaded by Mode I loading and could be damped by the mass proportional Rayleigh damping, while high-frequency vibrations are produced in the simulations of the specimens loaded by Mode II loading and could only be damped by the stiffness proportional Rayleigh damping. It also shows that the stiffness proportional damping is essential to damp out the oscillations in such simulations, thereby improving the convergence. In addition, the procedure proposed in this paper can lead to a proper interval for the value of the stiffness proportional Rayleigh damping, beyond which an unreasonable simulation result may be obtained.
Dissertations / Theses on the topic "Stiffness Proportional Dampers"
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Mazza, Samuele. "Soluzioni progettuali con dissipatori viscosi per il miglioramento sismico di un edificio ospedaliero." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Nel presente elaborato si sono analizzate alcune metodologie per il miglioramento sismico dell'Istituto Ortopedico Rizzoli. In particolare sono state elaborate tre differenti soluzioni progettuali contemplanti i dispositivi di smorzamento viscoso. Le soluzioni si diversificano oltre che dal punto di vista applicativo, anche da quello teorico, in quanto gli smorzatori in una soluzione sono stati inseriti all'interno della costruzione stessa venendo quindi modellati in modo proporzionale alle masse di piano, nelle altre due soluzioni sono inseriti al di fuori della struttura, costituendo alcune torri esterne a complemento del progetto di miglioramento; in quest'ultimo caso i dispositivi vengono modellati proporzionalmente alle rigidezze laterali degli elementi verticali interpiano. Il dimensionamento degli smorzatori è stato effettuato seguendo i criteri proposti nella Five-Step Procedure proposta da Silvestri et al. nel 2010. Per ogni soluzione, si è redatto il corrispondente computo metrico estimativo al fine di confrontare i costi delle tre soluzioni.
Conference papers on the topic "Stiffness Proportional Dampers"
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Kashani, Reza. "An Air Suspension System With Adjustable Height, Damping and Stiffness Using No Viscous Dampers." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10153.
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Abstract Air suspension is gaining more and more popularity with both the auto industry and drivers. Traditionally the height adjustability aspect of air suspension systems has been their main attracting attribute. More recently, resolving the classic conflict of combining comfortable ride with sport handling in a single suspension setup has become the main attraction of air suspension. An air suspension system has been developed which in addition to height adjustment, can adjust its damping and stiffness in real time with using neither viscous dampers nor any additional actuators. This is done by real-time adjustment air flow to and from the air springs using proportional valves. Measured relative displacement and acceleration as well as estimated velocity of the sprung mass with respect to unspring mass at each corner are fedback, thru their corresponding gains, to create the control signal that adjusts the proportional valve with the goal of controlling the height, stiffness, and damping at that corner. In a numerical study followed by laboratory testing, the effectiveness of the proposed air suspension system in terms of its ability to vary the damping and stiffness as well as the height of the suspension system is demonstrated.
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de Santiago, Oscar, Luis San Andrés, and Juan Oliveras. "Imbalance Response of a Rotor Supported on Open-Ends Integral Squeeze Film Dampers." In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-006.
Full textAbstract:
Rotor vibration attenuation and structural components isolation in jet engines are achieved with squeeze film dampers, many of them supported on long elastic squirrel cages. Integral squeeze film dampers (ISFDs) are comprised of arcuate pads and wire-EDM webs rendering a compact viscoelastic support. An experimental study is conducted to evaluate the effectiveness of ISFDs in attenuating the imbalance response of a massive test rotor. Measurements of the damper structural stiffness and rotor natural frequencies are detailed. Impact tests on the test rotor supported on its dampers reveal the supporting structure to be very flexible, thus requiring the experimental evaluation of an equivalent stiffness for the damper and supports system. System damping coefficients extracted from impact load excitations vary with the lubricant viscosity and include a significant structural damping from the bearing supports. Rotor coast-down tests demonstrate the ISFDs to damp well the rotor response with peak vibration amplitude proportional (linear) to the imbalance. Viscous damping coefficients estimated from the amplitude response at the critical speeds agree reasonably well with predictions from a full-film, finite element model.
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Changsheng, Zhu, Wang Xixuan, and Fu Caigao. "Investigation on the Bistable Jump in Subcritical Speed Range of Rotor Supported on Uncentralized Squeeze Film Dampers." In ASME 1991 Design Technical Conferences. American Society of Mechanical Engineers, 1991. http://dx.doi.org/10.1115/detc1991-0255.
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Abstract This paper presents one of bistable jump phenomena observed in rotor system supported on uncentralized squeeze film dampers which occurs in the subcritical speed range of rotor. The jumping tendency of this bistable jump is jumping up in acceleration and jumping down in deceleration and is without the transposition of disk mass centre. The behaviors, especially the latter, are different from the bistable jump behaviors reported to date. The reason for occurrence of the subcritical speed bistable jump is explained by a Duffing equation with the varied stiffness and the exciting force which amplitude is proportional to the square of rotating speed of rotor.
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San Andrés, Luis, and Daniel Lubell. "Imbalance Response of a Test Rotor Supported on Squeeze Film Dampers." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-012.
Full textAbstract:
Squeeze film dampers (SFDs) provide vibration attenuation and structural isolation to aircraft gas turbine engines which must be able to tolerate larger imbalances while operating above one or more critical speeds. Rotor-bearing-SFD systems are regarded in theory as highly nonlinear, showing jump-phenomena and even chaotic behavior for sufficiently large levels of rotor imbalance. Yet, few experimental results of practical value have verified the analytical predictions. A test rig for measurement of the dynamic forced response of a three-disk rotor (45 kg) supported on two cylindrical SFDs is described. The major objective is to provide a reliable data base to validate and enhance SFD design practice and to allow a direct comparison with analytical models. The open-ends SFD are supported by four-bar centering structures each with a stiffness of 3.5 MN/m. Measured synchronous responses to 9,000 rpm due to various imbalances show the rotor-SFD system to be well damped with amplification factors between 1.6 and 2.1 while traversing cylindrical and conical modes critical speeds. The rotor amplitudes of motion are found to be proportional to the imbalances for the first mode of vibration, and the damping coefficients extracted compare reasonably well to predictions based on the full-film open-ends SFD. Tight lip (elastomeric) seals contribute greatly to the overall damping of the test rig. Measured dynamic pressures at the squeeze film lands are well above ambient values with no indication of lubricant dynamic cavitation as simple theoretical models dictate. The measurements show absence of non-linear behavior of the rotor-SFD apparatus for the range of imbalances tested. • The research program is a joint effort funded by the National Science Foundation (NSF) and the TAMU Turbomachinery Research Consortium (TRC).
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Narayanan, Madusudanan Sathia, and Venkat Krovi. "Design of Input Shaping Control for Planar Parallel Manipulators." In ASME 2013 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/dscc2013-4052.
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Parallel manipulators are well known for their superior stiffness, higher accuracy, lower inertia and faster response compared to the serial counterparts and hence is widely used for high-speed machining and heavy load applications. However, controller limitations as well as design constraints can result in un-optimized designs causing unsettling residual vibrations at the end effector and limit their applications. Though many have discussed improving the structural design, augmenting with redundant sensors/ dampers and advanced feedback control methods for serial and mobile manipulators for vibration attenuations, very few investigated such techniques for parallel manipulators (PM). In this manuscript, we evaluate a specific type of feed-forward technique for planar PM. Lagrangian based dynamic models of platform manipulators and a simple trajectory level proportional-derivative control will be used with the gains tuned to force oscillations at the end effector to ensure stability. We will then demonstrate the applicability of basic input shapers for PM based on computation of natural frequencies and damping ratio for each mode, and resulting improvements in terms of appropriate performance measures.
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Asai, Kunio, and Muzio M. Gola. "Experimental Verification of Friction Behaviors Under Periodically-Varied Normal Force by Developing a Two-Directional Friction Test System." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42318.
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In order to achieve more accurate friction damping of turbine blades equipped with shroud covers and under-platform dampers, it is necessary to clarify such friction behaviors as tangential contact stiffness, micro-slips, and dissipated energy, under periodically varied normal force instead of constant normal force. Although some analytical studies were reported on the contact mechanics under alternating normal force, only minimal research has been conducted on the experimental verification of such behaviors, as friction tests were commonly done under constant normal force. In this study, we developed an original two-directional friction test system that can apply any combination of alternating normal and tangential forces by changing the displacement-controlled loading direction. In this system, relative displacement and contact force were measured simultaneously by using a laser Doppler displacement sensor and force transducers of the strain gage type. By using our original test system, we examined the dissipated energy under constant normal force and periodically-varied normal force whose amplitude is the same as that of tangential force with no phase difference. We then obtained a new finding that dissipated energy depends on alternating normal force under the same mean normal force and alternating tangential force. More specifically, when the tangential force coefficient, defined as the ratio of the amplitude of alternating tangential force to mean normal force, is large enough to cause a macro-slip, dissipated energy under variable normal force is smaller than that under constant normal force. Conversely, when tangential force coefficient is small in the micro-slip region, dissipated energy under variable normal force is larger than that under constant normal force. This behavior was successfully reproduced by FE analysis based on a macro-slip model, where an array of macro-slip elements was used to describe micro-slip behavior. It was found that alternating normal force makes it easier to cause a micro-slip in a certain area of the contact surface under variable normal force, resulting in higher dissipated energy than at constant normal force when tangential force coefficient is small. In this study, basic friction data were also obtained regarding the tangential contact stiffness with variations in contact pressure, as well as the relation between a micro-slip and the tangential force coefficient. Tangential contact stiffness increases as contact pressure increases. In addition, tangential contact stiffness increases with the nominal contact area, but is not proportional to the area. The non-dimensional slip range (corresponding to the ratio of slip range to stick displacement) was confirmed as being described in a unified form against different contact area (6 and 18 mm2) and contact pressure ranging from 3 to 40 MPa.
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San Andrés, Luis, and Bonjin Koo. "Model and Experimental Verification of the Dynamic Forced Performance of a Tightly Sealed Squeeze Film Damper Supplied With a Bubbly Mixture." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90330.
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Abstract Practice and experiments with squeeze film dampers (SFDs) sealed with piston rings (PRs) show the lubricant exits through the PR slit, i.e. the gap made by the PR abutted ends when installed, forced as a jet during the portion of a rotor whirl cycle generating a positive squeeze film pressure. In the other portion of a whirl cycle, a sub ambient dynamic pressure ingests air into the film that mixes with the lubricant to produce a bubbly mixture. To reduce persistent air ingestion, commercial air breathing engines utilizing PRSFDs demand of a sufficiently large lubricant supply pressure (Ps), and hence a larger flow rate that is proportional to the journal squeeze velocity (vs = amplitude r × frequency of motion ω). The stringent requirement clearly limits the applicability and usefulness of SFDs. This paper presents a computational physics model for a sealed ends SFD operating with a mixture and delivers predictions benchmarked against profuse laboratory test data. The model implements a Reynolds equation adapted for a homogeneous bubbly mixture, includes temporal fluid inertia effects, and uses physics based inlet and outlet lubricant conditions through feed holes and PR slit, respectively. In the experiments for model validation, a SFD damper, 127 mm in diameter D, film land length L = 25.4 mm (L/D = 0.2), and radial clearance c = 0.371 mm, is supplied with an air in ISO VG2 oil bubbly mixture of known GVF, zero (pure oil) to 50% in steps of 10%. The mixture supply pressure varies from Ps = 2.06 bar-g (30 psig) to 6.20 bar-g (90 psig). Located in grooves at the top and bottom of the journal, a piston ring (PR) and an O-ring (OR) seal the film land. The OR does not allow any oil leakage or air ingestion; hence the supplied mixture discharges thru the PR slit into a vessel submerged within a large volume of lubricant. Dynamic load tests with a single frequency ω, varying from 10 Hz to 60 Hz, produce circular centered orbits with amplitude r = 0.2c. The measurements record the exerted forces and journal motions and an analysis delivers force coefficients, damping and inertia, representative of the exerted frequency range. The model predicts the pressure field and evolution of the gas volume fraction (GVF) within the film land and, in a simulated process replicating the experimental procedure, delivers representative force coefficients. For all Ps conditions, both predictions and tests show the SFD added mass coefficients significantly decrease as the inlet GVF (βs) increases. The experimentally derived damping coefficients do not show a significant change, except for tests with the largest concentration of air (βs = 0.5). The predicted damping differs by 10% with the test derived coefficient which does not readily decrease as the inlet GVF (βs) increases. The added mass coefficients, test and predicted, decrease with βs, both being impervious to the magnitude of supply pressure. The test PRSFD shows a quadrature stiffness due to the sliding friction between the PR being pushed against the journal. An increase in supply pressure exacerbates this unique stiffness that may impair the action of the squeeze film to dissipate mechanical energy. The comprehensive test results, first of their kind, demonstrate that accurate modeling of SFDs operating with air ingestion remains difficult as the flow process and the paths of its major components (air and liquid) are rather complex.
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Cigeroglu, Ender, Ning An, and Chia-Hsiang Menq. "Wedge Damper Modeling and Forced Response Prediction of Frictionally Constrained Blades." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27963.
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In this paper, an improved wedge damper model is presented, based on which the effects of wedge dampers on the forced response of frictionally constrained blades are investigated. In the analysis, while the blade is modeled as a constrained structure, the damper is considered as an unconstrained structure. The model of the damper includes six rigid body modes and several elastic modes, the number of which depends on the excitation frequency. In other words, the motion of the damper is not artificially constrained. When modeling the contact surfaces of the wedge damper, discrete contact points along with contact stiffness are evenly distributed on the two contact surfaces. At each contact point, contact stiffness is determined and employed in order to take into account the effects of higher frequency modes that are omitted in the dynamic analysis. Depending on the engine rpm, quasi-static contact analysis is initially employed to determine the contact area as well as the initial preload or gap at each contact point due to the centrifugal force. A friction model is employed to determine the three-dimensional nonlinear contact forces and the relationship between the contact forces and the relative motion is utilized by the Harmonic Balance method. As the relative motion is expressed as a modal superposition, the unknown variables, and thus the resulting nonlinear algebraic equations, in the Harmonic Balance method is in proportion to the number of modes employed, and therefore the number of contact points used is irrelevant. The developed method is applied to tuned bladed disk system and the effects of normal load on the rigid body motion of the damper are investigated. It is shown that, the effect of rotational motion is significant, particularly for the in-phase vibration modes.
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Frazier, Michael J., and Mahmoud I. Hussein. "Bloch-Theory-Based Analysis of Damped Phononic Materials." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65662.
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In this paper, we combine Bloch theory with familiar techniques of structural dynamics to study the effects of energy dissipation (i.e., damping) in an acoustic metamaterial. The formulation we present has the novel feature of incorporating a temporal component to wave attenuation in addition to the standard spatial component. The frequency band structure reflects the metamaterial response to the damping intensity. In the context of a lumped parameter nested mass model, increasing the magnitude of damping is shown to cause the band structure to descend the frequency range and reveal an intriguing phenomenon: branch overtaking. This effect occurs as dissipation causes the optical branch to descend below the acoustical branch. The resulting decrease in the width of the band gap would impact vibration minimization and isolation. We also examine the effective properties of the metamaterial, specifically, the effective mass and effective stiffness, and the conditions for these quantities to become negative. Finally, the aforementioned material results are shown to be related to their finite counterpart. For ease of exposition, we consider a special form of Rayleigh damping in which the damping is proportional to the stiffness. The intrinsic presence of dissipation in acoustic metamaterials and the limited scientific literature addressing damped wave propagation in periodic media in general motivates our present study.
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Tortorelli, Daniel A. "Sensitivity Analysis for the Steady-State Response of Damped Linear Elastodynamic Systems Subject to Periodic Loads." In ASME 1990 Design Technical Conferences. American Society of Mechanical Engineers, 1990. http://dx.doi.org/10.1115/detc1990-0084.
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Abstract Adjoint and direct differentiation methods are used to formulate design sensitivities for the steady-state response of damped linear elastodynamic systems that are subject to periodic loads. Variations of a general response functional are expressed in explicit form with respect to design field perturbations. Modal analysis techniques which uncouple the equations of motion are used to perform the analyses. In this way, it is possible to obtain closed form relations for the sensitivity expressions. This eliminates the need to evaluate the adjoint response and psuedo response (these responses are associated with the adjoint and direct differentiation sensitivity problems) over the time domain. The sensitivities need not be numerically integrated over time, thus they are quickly computed. The methodology is valid for problems with proportional as well as non-proportional damping. In an example problem, sensitivities of steady-state vibration amplitude of a crankshaft subject to engine firing loads are evaluated with respect to the stiffness, inertial, and damping parameters which define the shaft. Both the adjoint and direct differentiation methods are used to compute the sensitivities. Finite difference sensitivity approximations are also calculated to validate the explicit sensitivity results.