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1
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.
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Qin, Jin Qi. "Seismic Response Analysis on Non-Proportional Damped System by Using Perturbation Technique." Advanced Materials Research 639-640 (January 2013): 917–21. http://dx.doi.org/10.4028/www.scientific.net/amr.639-640.917.
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A simple method for seismic response analysis on multi-degree-of-freedom (MDOF) system with non-proportional damping is proposed. Based on the real modal theory, transforming the system from physical coordinates to modal coordinates, the damping matrix is a relatively small amount compared with the mass matrix and the stiffness matrix, so the damping matrix may be denoted as a small amount. The approximate analytical solution of the non-proportional damped system can be obtained by using the perturbation technique which can be used as a reference of seismic response analysis of complicated structures.
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Minas, C., and D. J. Inman. "Matching Finite Element Models to Modal Data." Journal of Vibration and Acoustics 112, no. 1 (January 1, 1990): 84–92. http://dx.doi.org/10.1115/1.2930103.
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A technique is proposed which systematically adjusts a finite element model of a structure to produce an updated model in agreement with measured modal results. The approach suggested here is to consider the desired perturbations in stiffness and damping matrices as gain matrices in a feedback control algorithm designed to perform eigenstructure assignment. The improved stiffness and damping matrices combined with the analytical mass matrix, more closely predict the modal test results. The technique is applicable to undamped, proportionally damped, as well as non-proportionally damped models. The proposed method assumes that the analytical mass, damping and stiffness matrices are known and that vibration test data is available in the form of natural frequencies, damping ratios, and mode shapes.
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Halimi, Behrouz, Hamidreza Saba, Saeid Jafari MehrAbadi, and Saeid Saeidi Jam. "Laboratory study and measurement of stiffness and compaction of unsaturated clay soil by using the innovative rebound hammer." Nexo Revista Científica 34, no. 02 (June 7, 2021): 710–32. http://dx.doi.org/10.5377/nexo.v34i02.11557.
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Defining soil behavioral parameters, which eventually results in predicting every short-term and long-term soil behavior, has continually been one of the interests of soil mechanics and has been of exceptional value. To this end, in this study, a novel method has been reviewed to determine the compressive behavior of fine-grained soils in the laboratory and the field, without sampling by the patented electronic device. In the lab, homogeneous materials of the intended soil underwent the compaction test, mechanical and physical tests, direct shear test, and impacts of the innovative rebound hammer in the horizontal and vertical directions in the test-box. The impact shear waves produce resistance and voltage output by force and dislocation sensors with high-sensitivity proportional to the pressure based on the soil surface stiffness. The obtained voltages are then converted to digital by an analog-to-digital converter and a microcontroller. Next, a number is shown on display by the "CodeVision" program. Then, by solving a quasi-dynamic equation (Viscoelastic spring-damper model) by MATLAB software and with the aid of laboratory-field results and correlation equations, a fitting connection between all effective mechanical soil parameters has been estimated to an acceptable extent. The effective mechanical parameters of the soil include the compaction percentage, specific gravity, and frequency of the system in the damped and non-damped states, the energy imposed on the soil, and the plastic stage strain in the range of less than 15% humidity. The results determine that increased hammering numbers are directly related to increased soil compaction and stiffness. In more detail, the reading of hammer numbers less than 2 corresponds to compaction of less than 75%, while the reading of hammer numbers greater than 3 in the vertical and 2.94 in the horizontal directions on clay surfaces designates compaction of 90%.
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Zhang, J. X. "Study of Static Fluid Forces in a Squeeze Film Damper with a Circumferential Groove." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 209, no. 4 (December 1995): 263–74. http://dx.doi.org/10.1243/pime_proc_1995_209_437_02.
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Approximate expressions are obtained for static fluid pressure and force for a centrally grooved squeeze film damper (SFD) resting at an equilibrium position without vibration. The analysis shows that, to some extent, grooved SFDs may share some characteristics with hydrostatic bearings, due to the existence of the lubricant supply pressure. Thus static fluid force and hence oil stiffness may exist in SFDs, in addition to the conventional inertial and damping coefficients for SFDs. This paper is solely focused on the static fluid forces and oil stiffness generated in an SFD with a finite length groove. Flow continuity is used at the centre of the groove, which takes into account the effects of the inlet oil flowrate and oil supply pressure. This use of flow continuity differs substantially from the traditional use of constant pressure in the central groove, and it provides better results. At the interface between the groove and the thin film land, a step bearing model with ignored fluid inertia is employed. It is verified by both the theory and previous experiments that the static fluid force and stiffness are linearly proportional to both the lubricant supply pressure and the eccentricity ratio of the SFD journal.
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Kaouk, Mohamed, David C. Zimmerman, and Todd W. Simmermacher. "Assessment of Damage Affecting All Structural Properties Using Experimental Modal Parameters." Journal of Vibration and Acoustics 122, no. 4 (May 1, 2000): 456–63. http://dx.doi.org/10.1115/1.1310328.
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Recently, the authors proposed computationally attractive algorithms to determine the location and extent of structural damage for undamped and damped structures assuming damage results in a localized change in a subset (not full set) of the property matrices (mass, stiffness and damping matrices). The algorithms make use of a finite element model and a subset of measured eigenvalues and eigenvectors. The developed theories approach the damage location and extent problem in a decoupled fashion. First, a theory is developed to determine the location of structural damage. With location determined, a damage extent theory is then developed. The damage extent algorithm is a minimum rank perturbation, which is consistent with the effects of many classes of structural damage on a finite element model. In this work, the concept of the Minimum Rank Perturbation Theory (MRPT) is adopted to simultaneously determine the damage extent of all property matrices of undamped and proportionally damped structures. Note that the property matrices are the mass, stiffness and damping matrices. Illustrative examples are presented to show the performance of the proposed theory. [S0739-3717(00)01904-8]
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Rasa, Ahmad Yamin, and Mehmet Hamit Özyazıcıoğlu. "Determination of the exact mode frequencies of multi-storey structures by state-space method and a comparison with mode superposition method." Challenge Journal of Structural Mechanics 7, no. 1 (March 12, 2021): 1. http://dx.doi.org/10.20528/cjsmec.2021.01.001.
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A comparative research has been carried out for obtaining the time-consuming exact solution (state-space) and approximate solution (mode superposition) of transient and steady-state vibrations of linearly damped linear frame buildings. In the mode superposition method, the proportional damping matrix has been constructed by different approaches such as modal combination of mass and stiffness matrixes (Rayleigh) and disregarding the off-diagonal elements of the non-classical damping matrix, while in the state-space method the non-proportional damping matrix is constructed in exact situation. These observations are individually investigated, which the most suitable parameter to render the approximate results as close as possible to the exact results. Harmonic forces are applied on the different storeys of three and five storey frame buildings, and the responses are displayed in comparative tables and figures. The maximum responses are calculated by square root of sum of the squares (SRSS) method. A MATLAB code is generated and the equations of exact and approximate methods are solved.
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Winter, David A., Aftab E. Patla, Francois Prince, Milad Ishac, and Krystyna Gielo-Perczak. "Stiffness Control of Balance in Quiet Standing." Journal of Neurophysiology 80, no. 3 (September 1, 1998): 1211–21. http://dx.doi.org/10.1152/jn.1998.80.3.1211.
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Winter, David A., Aftab E. Patla, Francois Prince, Milad Ishac, and Krystyna Gielo-Perczak. Stiffness control of balance in quiet standing. J. Neurophysiol. 80: 1211–1221, 1998. Our goal was to provide some insights into how the CNS controls and maintains an upright standing posture, which is an integral part of activities of daily living. Although researchers have used simple performance measures of maintenance of this posture quite effectively in clinical decision making, the mechanisms and control principles involved have not been clear. We propose a relatively simple control scheme for regulation of upright posture that provides almost instantaneous corrective response and reduces the operating demands on the CNS. The analytic model is derived and experimentally validated. A stiffness model was developed for quiet standing. The model assumes that muscles act as springs to cause the center-of-pressure (COP) to move in phase with the center-of-mass (COM) as the body sways about some desired position. In the sagittal plane this stiffness control exists at the ankle plantarflexors, in the frontal plane by the hip abductors/adductors. On the basis of observations that the COP-COM error signal continuously oscillates, it is evident that the inverted pendulum model is severely underdamped, approaching the undamped condition. The spectrum of this error signal is seen to match that of a tuned mass, spring, damper system, and a curve fit of this “tuned circuit” yields ωn the undamped natural frequency of the system. The effective stiffness of the system, K e , is then estimated from K e = Iω2 n, and the damping B is estimated from B = BW × I, where BW is the bandwidth of the tuned response (in rad/s), and I is the moment of inertia of the body about the ankle joint. Ten adult subjects were assessed while standing quietly at three stance widths: 50% hip-to-hip distance, 100 and 150%. Subjects stood for 2 min in each position with eyes open; the 100% stance width was repeated with eyes closed. In all trials and in both planes, the COP oscillated virtually in phase (within 6 ms) with COM, which was predicted by a simple 0th order spring model. Sway amplitude decreased as stance width increased, and K e increased with stance width. A stiffness model would predict sway to vary as K −0.5 e . The experimental results were close to this prediction: sway was proportional to K −0.55 e . Reactive control of balance was not evident for several reasons. The visual system does not appear to contribute because no significant difference between eyes open and eyes closed results was found at 100% stance width. Vestibular (otolith) and joint proprioceptive reactive control were discounted because the necessary head accelerations, joint displacements, and velocities were well below reported thresholds. Besides, any reactive control would predict that COP would considerably lag (150–250 ms) behind the COM. Because the average COP was only 4 ms delayed behind the COM, reactive control was not evident; this small delay was accounted for by the damping in the tuned mechanical system.
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Tortorelli, D. A. "Sensitivity Analysis for the Steady-State Response of Damped Linear Elastodynamic Systems Subject to Periodic Loads." Journal of Mechanical Design 115, no. 4 (December 1, 1993): 822–28. http://dx.doi.org/10.1115/1.2919274.
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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 period 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 separately 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 nonproportional 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.
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Phu and Choi. "A New Adaptive Fuzzy PID Controller Based on Riccati-Like Equation with Application to Vibration Control of Vehicle Seat Suspension." Applied Sciences 9, no. 21 (October 25, 2019): 4540. http://dx.doi.org/10.3390/app9214540.
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A new controller based on the modified Riccati-like Equation is developed in this paper. The interval type 2 fuzzy model is applied and embedded in the controller to ensure the robustness to parameter uncertainties and also to support calculation progress. The proposed input control includes equivalent control and robustness control. The equivalent control is found from the conventional analysis with the sliding surface, but this control is not sufficient to resolve the uncertainties and disturbances such as error approximation of the fuzzy model. Thus, a proportional-integral-derivative (PID) controller and matrices of the traditional model of Riccati equation are utilized to ensure the robustness. In the synthesis of this control part, the H infinity technique is adopted and the stability of the system is proved using Lyapunov stability. Subsequently, to validate the effectiveness of the proposed controller, it was applied to vibration control of a vehicle seat suspension with a magnetorheological (MR) damper subjected to stiffness variation due to the magnitude of the input current. In this problem, two types of road conditions, bump and random step wave, were adopted and control performance was evaluated in both simulations and experiments. Based on these evaluations, the proposed controller provides high control performances, effectively controlling the acceleration and displacement at the driver position.
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Starek, L., and D. J. Inman. "A Symmetric Inverse Vibration Problem for Nonproportional Underdamped Systems." Journal of Applied Mechanics 64, no. 3 (September 1, 1997): 601–5. http://dx.doi.org/10.1115/1.2788935.
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This paper considers a symmetric inverse vibration problem for linear vibrating systems described by a vector differential equation with constant coefficient matrices and nonproportional damping. The inverse problem of interest here is that of determining real symmetric, coefficient matrices assumed to represent the mass normalized velocity and position coefficient matrices, given a set of specified complex eigenvalues and eigenvectors. The approach presented here gives an alternative solution to a symmetric inverse vibration problem presented by Starek and Inman (1992) and extends these results to include noncommuting (or commuting) coefficient matrices which preserve eigenvalues, eigenvectors, and definiteness. Furthermore, if the eigenvalues are all complex conjugate pairs (underdamped case) with negative real parts, the inverse procedure described here results in symmetric positive definite coefficient matrices. The new results give conditions which allow the construction of mass normalized damping and stiffness matrices based on given eigenvalues and eigenvectors for the case that each mode of the system is underdamped. The result provides an algorithm for determining a nonproportional (or proportional) damped system which will have symmetric coefficient matrices and the specified spectral and modal data.
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Kıral, Zeki. "Harmonic response analysis of symmetric laminated composite beams with different boundary conditions." Science and Engineering of Composite Materials 21, no. 4 (September 1, 2014): 559–69. http://dx.doi.org/10.1515/secm-2013-0194.
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AbstractThis study deals with the determination of the harmonic response of symmetric laminated composite beams by the finite element method. The structural stiffness of the composite beam is determined by the classical laminated plate theory. Four different ply orientations, namely, [0]2s, [0/90]s, [45/-45]s, and [90]2s are used to examine the effect of the stacking sequence on the harmonic response of the beam. Proportional damping is used to model the structural damping, and the damped harmonic responses of the composite beams are obtained to show the effect of the damping on the harmonic response. The effect of the boundary conditions on the harmonic response is also investigated. The displacement maps calculated for varying excitation points are obtained for different boundary conditions and damping ratios at different vibrational modes. The numerical results presented in this study show that the magnitudes of the harmonic response of the composite beam increase as the flexural rigidity decreases, and the vibration magnitudes reduce considerably with damping. The vibration patterns created for varying excitation and observation locations change as the damping ratio and excitation frequency change.
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Shahi, Mohammad, Mohammad Reza Sohrabi, and Sadegh Etedali. "Seismic Control of High-Rise Buildings Equipped with ATMD Including Soil-Structure Interaction Effects." Journal of Earthquake and Tsunami 12, no. 03 (August 12, 2018): 1850010. http://dx.doi.org/10.1142/s1793431118500100.
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The seismic behavior of the structures equipped with ATMD is often investigated based on the rigid base assumption without considering soil-structure interaction (SSI) effects. The SSI effects significantly modify the dynamic characteristics of the structures, while these changes may be ignored in the design process of the controllers. The present paper aims to address the issue of the SSI effects on the seismic behavior of the structures and performance of the adopted controllers. For this purpose, a mathematical model is developed for the time domain analysis of tall building equipped with ATMD including SSI effects. Considering the fixed base case and three types of ground states, namely soft, medium and dense soil, the numerical studies are carried out on a 40-story structure subjected to different earthquake excitations. Two well-known controllers, proportional-integral-derivative (PID) and linear-quadratic regulator (LQR) controllers, are employed for tuning control force of ATMD in different conditions of ground state. A particle swarm optimization (PSO) algorithm is used for the optimum design of Tuned mass damper (TMD) parameter and the gain matrices of the controllers in both cases without and with SSI effects. It is found that TMDs are more effective for the higher soil stiffness and their efficiencies are degraded in soft soils. Furthermore, the SSI significantly affects on the optimum design of the PID and LQR controllers. The adopted controllers are significantly able to mitigate the peak top floor displacement of the tall building. In addition that the PID controller is a simple strategy with design variables much less than LQR controller, it performs better than the LQR controller in most earthquakes for different conditions of ground state. The performance of the controllers decreases with increasing soil softness, so that ignoring the SSI effects may result in incorrect and unrealistic results of the seismic behavior of the structures.
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Huang, Xiuchang, Zhiwei Su, Sen Wang, Xinsheng Wei, Yong Wang, and Hongxing Hua. "High-frequency disturbance force suppression mechanism of a flywheel equipped with a flexible dynamic vibration absorber." Journal of Vibration and Control 26, no. 23-24 (March 16, 2020): 2113–24. http://dx.doi.org/10.1177/1077546320915340.
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Flywheels generate speed-related disturbances and induce micro-vibrations that influence the performance of high-sensitivity instruments on board. This study addresses dynamic modeling and disturbance force suppression of the flywheels due to its inherent characteristic structural modes. The disturbance force transmission of a rotating flywheel due to a unit radial force applied at the rim of the wheel body is reported using the three-dimensional finite element method and frequency response function–based substructuring method. The characteristic structural modes for the radial and axial disturbance forces are identified. The axial deformation–dominated flapping mode and the radial deformation–dominated transverse mode will contribute most to the axial and radial disturbance forces, respectively. A flexible ring structure, which is rested on the arms of the wheel body through independent viscoelastic pads and simultaneously in contact with the inner rim of the wheel body by independent resilient cushion members, is proposed to function as a damped dynamic vibration absorber. The modes of the dynamic vibration absorber and the modes of the flywheel equipped with the dynamic vibration absorber are analyzed. It is shown that the dynamic vibration absorber is effective to suppress both the radial and axial disturbance forces at the characteristic structural modes under different rotational speeds, provided that the loss factor of the complex elastic modulus for the viscoelastic pads is larger than 0.2 and the proportional damping constant for the stiffness matrix is larger than 6 Ns/m. Experimental analyses are conducted on a flywheel with a well-designed dynamic vibration absorber to validate the theoretical findings. Modal tests and disturbance force measurements are carried out for the flywheel with/without the dynamic vibration absorber. It is shown that the identified characteristic structural modes will contribute remarkable peaks for the radial and axial disturbance forces. The proposed dynamic vibration absorber is capable to suppress the high-frequency disturbance forces efficiently under different rotational speeds.
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"Seismic Analysis of Rcc Structure with Different Types of Dampers." Regular 9, no. 12 (October 10, 2020): 205–10. http://dx.doi.org/10.35940/ijitee.l7933.1091220.
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In the present Era escalation of multi-storey high rise building is very common because of rapid urbanization in the entire world also innovation in the field of Engineering, science and Technology. Also Engineers have sophisticated designing software. As height of the building increases building response to the wind and seismic load increases. It means that forces and displacement of the structure is directly proportional to the height of the structure. Many research studiesare going on to reduce the structural instability due to high speed winds and earthquakes. During the earthquake the multi-storey high rise structures are failed to resist the seismic loads and it become the catastrophic disaster for human life’s and for the country. It is most important that structure should be able to withstand against external excitation forces. This can be achieved by building structure more flexible.During the time of earthquake multistorey structures are swing and large deformation is occurred and vibrations are transferred in the structure through the ground which causes instability in structure. Thus the use of damper is resists lateral forces (wind load, earthquake load) and providing stability to the structure. Dampers are the mechanical devices which dissipate energy which is facilitate in multi-storey structure to reduce the displacement, buckling of beams and columns and increases the structural stiffness. There is lot of various types of dampers are used in RC multi-storey building. This study deals with performance and selection of suitable type of damper which will be more resistant to earthquake for the selected multi-storey building and different seismic parameters like time period, story stiffness, story displacement, story drift and base shear are checked out. In this study seismic behavior of multi-story RCC building with various types of dampers like fluid viscous damper, friction damper and tuned mass damper is carried out.
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Jabbar, Shahad Nazar. "ENHANCING STRUCTURAL RESPONSE USING INERTER DAMPERS." JOURNAL OF MECHANICS OF CONTINUA AND MATHEMATICAL SCIENCES 16, no. 1 (January 26, 2021). http://dx.doi.org/10.26782/jmcms.2021.01.00008.
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This paper deals with one kind of dampers which is inerter damper, Inerter is a new mechanical element proposed by Professor Malcolm C. Smith from Cambridge University, which is defined as a mechanical two-terminal, one-port device with the property that the equal and opposite force applied at the terminals is proportional to the relative acceleration between the terminals the principle work of inerter damper is how to convert the linear motion into rotational motion to mitigation the external excitation. Theoretical analysis was presented first part is the analytical study which made modeling for the damping structure proposed and get the equation of motion for the inerter behavior, secondly numerical analysis where the program (ANSYS WORK-Bench 18.2) was adopted, and study the parameters which effected on the damping behavior of inerter structure proposed that is (stiffness, coefficient of friction and mass of flywheel). Where it was found that when the stiffness of the springs increased gradually from (0.2, 0.3, 0.4, 0.6 and 0.8) Kn/mm the amplitude reduced from (25.791, 17.194, 12.896, 8.5974 to 6.4482) mm respectively for each stiffness reading, also the mass of inerter when increased gradually (200,400,600,800 and 1000) g with a constant coefficient of friction and constant stiffness 0.4, 0.6 Kn/mm respectively, the amplitude decrease from 6.3525 to 4.036290. Finally, to study the effect inerter mass on the structures, the mass of inerter increased from (200,400,600,800 to 1000) g gradually to the constant cantilever mass structure equal to 130g. The ratio of the inerter mass to the threshold mass is approximately 1.5 to 7.5 As results obtained from the previous study, the amplitude obtained for each mass (1.0778, 1.069, 1.0509, 0.9514 to 0.872) respectively
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Wang, Haifei. "A modeling method for a rotor system with an active floating ring squeeze film damper." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, July 5, 2020, 095440622093911. http://dx.doi.org/10.1177/0954406220939112.
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It is essential to optimize the support structures in rotating machinery to reduce the vibration, (i.e. decreasing forces transmitted to the whole dynamic system). Lots of vibration alleviation methods were applied in rotary machines, such as squeeze film dampers were used in aero-engine. In this paper, a theoretical model of an active floating squeeze film damper was studied in a vibration control field. The change of fluid stiffness and damping was allowed in the design of active floating squeeze film damper. In this model, it is assumed that an active magnetic bearing and a squeeze film damper were used, and oil film forces and magnetic forces were obtained. A lumped mass model and a finite element model were established with an active floating squeeze film damper. Explicit Newmark- β was used to solve the responses of the lumped mass model and the combination of explicit Newmark- β and implicit Newmark- β were used to calculate the responses of the finite element rotor system. The simulation shows that vibration frequencies will be shifted by adjusting the proportional gain kp, but the uncertain phenomenon can be seen in the amplitude’s reductions by adjusting the derivative gain kd as the relative changing position of rotor’s node and force acting points of active magnetic bearing for different modes, and the nonlinear strength of floating ring squeeze film damper were different in the complex rotor system. It shows that active floating squeeze film dampers can suppress rotor’s vibration effectively by varying magnetic bearing parameters.
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Dib, Antoine, Michele Palermo, Luca Pieraccini, Stefano Silvestri, Giada Gasparini, and Tomaso Trombetti. "EXPERIMENTS ON CRESCENT SHAPED BRACES." Proceedings of International Structural Engineering and Construction 2, no. 1 (November 2015). http://dx.doi.org/10.14455/isec.res.2015.130.
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Different design strategies, within the Performance Based Design framework, have been proposed through the years in order to design a structure of high seismic performances, including seismic isolation, viscous dampers and hysteretic dampers. A new lateral-resisting device, referred to as Crescent Shaped Brace (CSB), has been recently proposed to be used for the story isolation of multi-story frame structures. The main property of the CSB is that its lateral stiffness is uncoupled from its yield strength so that the practical designer may choose them independently, unlike conventional diagonal braces whose lateral stiffness is directly proportional to the yield strength. Past studies were devoted to the development of analytical formula for the design of such devices and to the study (through numerical simulations) of their non-linear response. In the present paper, the main results of experimental tests conducted on scaled CSB specimens (monotonic tests, cyclic tests, pseudo-static tests) are presented in order to assess the seismic behavior of such devices. The results of the experimental tests are compatible with the analytical predictions.
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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." Journal of Engineering for Gas Turbines and Power 142, no. 1 (December 12, 2019). http://dx.doi.org/10.1115/1.4044994.
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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 subambient 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-end 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 gas volume fraction (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 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 through 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 (CCO) 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 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. "Forced Response Prediction of Constrained and Unconstrained Structures Coupled Through Frictional Contacts." Journal of Engineering for Gas Turbines and Power 131, no. 2 (December 23, 2008). http://dx.doi.org/10.1115/1.2940356.
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In this paper, a forced response prediction method for the analysis of constrained and unconstrained structures coupled through frictional contacts is presented. This type of frictional contact problem arises in vibration damping of turbine blades, in which dampers and blades constitute the unconstrained and constrained structures, respectively. The model of the unconstrained/free structure 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 free structure is not artificially constrained. When modeling the contact surfaces between the constrained and free structure, discrete contact points along with contact stiffnesses are distributed on the friction interfaces. 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 normal force acting on the contact interfaces, quasistatic 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 normal load. 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, are in proportion to the number of modes employed. Therefore the number of contact points used is irrelevant. The developed method is applied to a bladed-disk system with wedge dampers where the dampers constitute the unconstrained structure, 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. Moreover, the effect of partial slip in the forced response analysis and the effect of the number of harmonics employed by the harmonic balance method are examined. Finally, the prediction for a test case is compared with the test data to verify the developed method.
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Hemmatian, Masoud, and Abdolreza Ohadi. "Sliding Mode Control of Flexible Rotor Based on Estimated Model of Magnetorheological Squeeze Film Damper." Journal of Vibration and Acoustics 135, no. 5 (June 18, 2013). http://dx.doi.org/10.1115/1.4024609.
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By using magnetorheological (MR) fluid as the lubricating oil in a traditional squeeze film damper (SFD), one can build a variable-damping SFD, thereby controlling the vibration of a rotor by controlling the magnetic field. This study aims to control the vibration of a flexible rotor system using a magnetorheological squeeze film damper (MR-SFD). In order to evaluate the performance of the damper, the Bingham plastic model is used for the MR fluid and the hydrodynamic equation of MR-SFD is presented. Usually, the numerical methods are necessary for solving this equation. These methods are too costly and time consuming, especially in the simulation of complex rotors and the implementation of model-based controllers. To fix this issue, an innovative estimated equation for pressure distribution in MR-SFD is presented in this paper. By integration of this explicit expression, the hydrodynamic forces of MR-SFD are easily calculated as an algebraic equation. It is shown that the pressure and forces, which are calculated from the introduced expression, are consistent with the corresponding results of the original equations. Furthermore, considering the structural and parametric uncertainties of the system, proportional-integral-furthermore controller (PID) and sliding mode controllers are chosen for reducing the vibration level of the flexible rotor system, which is modeled by the finite element method. The time and frequency responses of a flexible rotor in the presence of these controllers show a good performance in reducing vibration of the shaft's midpoint, although near the rotor's critical speed the results of the sliding mode controller (SMC) are better than the corresponding results of the PID controller. The last part of this article is devoted to an analysis of the system's uncertainties. The results of the open loop system indicate that changes in the stiffness coefficient of the elastic foundation and the temperature of the MR fluid (two uncertainties of the system) strongly affects the outputs while using the controllers well increases the robustness of the system. The obtained results indicate that both the PID and sliding mode controllers have good performance against the uncertainty of the stiffness coefficient, but for changes in the MR fluid's temperature, the SMC presents better outputs compared to the PID controller, especially for high rotational speeds.
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Li, Zhigang, Jun Li, and Zhenping Feng. "Numerical Investigations on the Leakage and Rotordynamic Characteristics of Pocket Damper Seals—Part I: Effects of Pressure Ratio, Rotational Speed, and Inlet Preswirl." Journal of Engineering for Gas Turbines and Power 137, no. 3 (September 30, 2014). http://dx.doi.org/10.1115/1.4028373.
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Effects of pressure ratio, rotational speed and inlet preswirl on the leakage and rotordynamic characteristics of a eight-bladed fully partitioned pocket damper seal (FPDS) were numerically investigated using proposed three-dimensional (3D) transient computational fluid dynamics (CFD) methods based on the multifrequency elliptical whirling orbit model. The accuracy and availability of the multifrequency elliptical whirling orbit model and the transient CFD numerical methods were demonstrated with the experimental data of frequency-dependent rotordynamic coefficients of the FPDS at two rotational speeds with high preswirl conditions. The frequency-dependent rotordynamic coefficients of the FPDS at three pressure ratios (three inlet pressures and three outlet pressures), three rotational speeds, three inlet preswirls were computed. The numerical results show that changes in outlet pressure have only weak effects on most rotordynamic coefficients. The direct damping and effective damping slightly increase in magnitude with decreasing outlet pressure at the frequency range of 20–200 Hz. The effect of inlet pressure is most prominent, and increasing inlet pressure for the FPDS results in a significant increase in the magnitudes of all rotordynamic coefficients. The magnitudes of the seal response force and effective damping are proportional to pressure drop through the seal. Increasing rotational speed and increasing inlet preswirl velocity both result in a significant decrease in the effective damping term due to the obvious increase in the magnitude of the destabilizing cross-coupling stiffness with increasing rotational speed or increasing preswirl velocity. The crossover frequency of effective damping significantly increases and the peak magnitude of effective damping decreases with increasing rotational speed or increasing preswirl velocity. The destabilizing cross-coupling stiffness is mainly caused by the circumferential swirl velocity generating from high rotational speed and inlet preswirl. Reducing swirl velocity (such as swirl brake) can greatly enhance the stabilizing capacity of the FPDS.
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Li, Zhigang, Zhuocong Li, Jun Li, and Zhenping Feng. "Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals Operating in Supercritical CO2 Turbomachinery." Journal of Engineering for Gas Turbines and Power 143, no. 10 (June 17, 2021). http://dx.doi.org/10.1115/1.4051104.
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Abstract The balance piston seal in multiple-stage centrifugal compressors and axial turbines sustains the largest pressure drop through the machines and therefore plays an important role in successful full load operation at high rotational speed. This is especially true for power dense turbomachines in supercritical CO2 power cycles that generate or expend higher fluid pressures (above the critical value 7.3 MPa) and density (close to water 1000 kg/m3), because the fluid forces generated by the balance piston seals are directly proportional to the fluid density and the pressure drop across the seal. This paper presents a comprehensive assessment and comparison on the leakage and rotordynamic performance of three types of annular gas seals for application in a 14 MW supercritical CO2 turbine. These three seals represent the main seal types used in high-speed rotating machines at the balance piston location in efforts to limit internal leakage flow and achieve rotordynamic stability, including a labyrinth seal (LABY), a fully partitioned pocket damper seal (FPDS), and a hole-pattern damper seal (HPS). These three seals were designed to have the same sealing clearance and similar axial lengths. To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake was also designed and employed at seal entrance for each type seal to reduce the seal inlet preswirl velocity. Numerical results of leakage flow rates, rotordynamic force coefficients, cavity dynamic pressure, and swirl velocity developments were analyzed and compared for three seal designs at high positive inlet preswirl (in the direction of shaft rotation), using a proposed transient computational fluid dynamic (CFD)-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the National Institute of Standards and Technology reference fluid properties database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions. Results show that the inlet swirl brake can significantly reduce the preswirl velocity at seal entrance, lowering the effective damping crossover frequency fco (or even fco = 0) to maximize the full operational frequency range of the machines. In stability analysis phase of a MW-scale supercritical CO2 turbine/compressor, the seal stiffness effects on the rotor mode shape must be evaluated carefully, where the seal stiffness is sufficiently large (comparable to the bearing stiffness). From a rotordynamic viewpoint, the HPS seal with entrance swirl brake is a better seal concept for the balance piston seal in supercritical CO2 turbomachinery, which possesses the largest positive effective damping throughout the entire subsynchronous frequency range.