Series Damping Research Articles

Muscle short-range stiffness behaves like a maxwell element, not a spring: Implications for joint stability.

Muscles play a critical role in supporting joints during activities of daily living, owing, in part, to the phenomenon of short-range stiffness. Briefly, when an active muscle is lengthened, bound cross-bridges are stretched, yielding forces greater than what is predicted from the force length relationship. For this reason, short-range stiffness has been proposed as an attractive mechanism for providing joint stability. However, there has yet to be a forward dynamic simulation employing a cross-bridge model, that demonstrates this stabilizing role. Therefore, the purpose of this investigation was to test whether Huxley-type muscle elements, which exhibit short-range stiffness, can stabilize a joint while at constant activation. We analyzed the stability of an inverted pendulum (moment of inertia: 2.7 kg m2) supported by Huxley-type muscle models that reproduce the short-range stiffness phenomenon. We calculated the muscle forces that would provide sufficient short-range stiffness to stabilize the system based in minimizing the potential energy. Simulations consisted of a 50 ms long, 5 Nm square-wave perturbation, with numerical simulations carried out in ArtiSynth. Despite the initial analysis predicting shared activity of antagonist and agonist muscles to maintain stable equilibrium, the inverted pendulum model was not stable, and did not maintain an upright posture even with fully activated muscles. Our simulations suggested that short-range stiffness cannot be solely responsible for joint stability, even for modest perturbations. We argue that short-range stiffness cannot achieve stability because its dynamics do not behave like a typical spring. Instead, an alternative conceptual model for short-range stiffness is that of a Maxwell element (spring and damper in series), which can be obtained as a first-order approximation to the Huxley model. We postulate that the damping that results from short-range stiffness slows down the mechanical response and allows the central nervous system time to react and stabilize the joint. We speculate that other mechanisms, like reflexes or residual force enhancement/depression, may also play a role in joint stability. Joint stability is due to a combination of factors, and further research is needed to fully understand this complex system.

Vibration control for a semi-submersible floating offshore wind turbine with optimal ultra-low frequency electromagnetic tuned inerter-mass dampers

The platform of a semi-submersible floating offshore wind turbine is prone to large ultra-low frequency pitch motion in a complex marine environment. To address this problem, this study proposes the application of multiple ultra-low frequency electromagnetic tuned inerter-mass dampers (UF-ETIMDs) inside the offset columns to mitigate the pitch motion of the platform. An UF-ETIMD is achieved by replacing the viscous damping of the classical tuned mass damper (TMD) with an electromagnetic inerter damper in series with a tuning spring, which will tune the inerter's resonant frequency. A constant-force spring is added in parallel with the main spring to neutralize the gravity force of the mass damper that can effectively reduce static elongation of the main spring while tuning the resonant frequency of the mass to ultra-low frequency of the pitch motion. Thus UF-ETIMDs can achieve a double-tuned electromagnetic damping system to enhance the vibration mitigation performance of the platform. The parametric optimization of the UF-ETIMDs is conducted based on the H∞ optimization criteria, whose target is to minimize the peak value of platform pitch in the frequency domain. To analyze the performance of the UF-ETIMD on the semi-submersible FOWT, a 20-degree-of-freedom (DOF) analytical model has been developed for the semi-submersible FOWT coupled with three UF-ETIMDs, retrofittable inside the platform. The performance of the UF-ETIMDs is examined and compared with the classical TMDs under different combinations of wind and wave loadings and in both operational and parked conditions. Results found that UF-ETIMDs can achieve a better performance than TMDs in mitigating the platform pitch of the semi-submersible FOWT. The potential powers in the UF-ETIMDs system that could be converted from vibrations to usable electricity are also examined.

Experimental and numerical investigations of a staged energy dissipation device

Energy-dissipating devices (EDDs) are widely used in building structures to mitigate seismic disasters. This study designed a fully assembled friction-metal series damper which is one kind of the staged energy dissipation devices (SEDD). Quasi-static tests were conducted to examine the behaviour of the SEDDs. The influence of factors such as the configurations of the restrainers, pre-tightening force, and material of the metal strip module was investigated. The work behaviour of the SEDD consists of three stages: elastic, frictional energy dissipation, and metallic elastic–plastic energy dissipation stages. The experimental results verified the effectiveness of the predicted working mechanism and showed that the bearing capacity and energy dissipation of the SEDD increased with the configuration of the restrainers, pre-tightening force, and yield strength of the metal strip module. The experiment also showed that the rotation of the outer plates caused an unexpected force mode in the metal strip module. Subsequently, numerical models of the test specimens were built, and good agreement was observed between the numerical simulations and test results for the hysteresis performance, loading capacity, and stress distribution. To further improve the mechanical properties of the SEDD, an optimised model was established and studied. The SEDDs with optimised strip shapes and constraint conditions of the outer plate exhibited better mechanical performance, and their load capacities increased by 11 % and 41 %, respectively.

A hybrid buckling-restrained brace for enhancing the seismic performance of steel moment resisting frames

Buckling-restrained braces (BRBs) are effective and widely used devices to enhance the seismic performance of steel moment resisting frames (SMRF), but they might fail to prevent significant structural damage or structural collapse under unexpectedly high seismic loads. To address this issue, a novel hybrid BRB (HBRB) composed of a conventional BRB and a friction damper in series is proposed, where the activated force/displacement of the friction damper could be adjusted to protect the HBRB from failure. The paper begins by providing a detailed explanation of the configuration and working principle of the proposed HBRB. The cyclic behavior of the HBRB is thoroughly analyzed both theoretically and numerically. Building on this, a performance-based design approach is developed, focusing on enhancing the seismic response of SMRF using the HBRB. To assess the effectiveness of the proposed HBRB and design method, two typical SMRFs, one with 9 stories and the other with 20 stories, are enhanced with the HBRB. Comprehensive numerical models are established, considering the bare SMRFs, HBRB-enhanced SMRFs, and conventionally BRB-enhanced SMRFs. Nonlinear static and dynamic analyses are conducted to evaluate the seismic performance of these steel frames. Special attention is given to the performance comparison between HBRB-enhanced SMRFs and conventionally BRB-enhanced SMRFs, specifically under the extremely rare earthquake (ERE) scenario. The results highlight that the HBRB can achieve comparable energy dissipation capacity to conventional BRB while displaying superior energy dissipation efficiency. Moreover, the proposed design method achieves the predefined seismic performance objectives for the enhanced SMRFs in a straightforward and time-efficient manner. Furthermore, the HBRB proves effective in eliminating the failure risk associated with conventional BRB under ERE conditions, effectively mitigating structural damage and preventing collapse.

Topological Optimization of Vehicle ISD Suspension under Steering Braking Condition

Anti-roll and anti-pitch are important directions in the comprehensive research of automobiles. In order to improve the anti-roll and anti-pitch performance of the vehicle, an inerter was applied to the vehicle suspension system, and a 14 DOF vehicle nonlinear dynamics model was established. The influence of the change in inertance in the eight kinds of improved ISD (Inerter-Spring-Damper) suspension structures on the RMS (root mean square) value of performance indexes of roll, vertical, and pitch motion of the vehicle was studied. Based on this, the vehicle’s ISD structure with better performance was selected, and the NSGA-Ⅱ algorithm was adopted to optimize the selected structural parameters. The simulation results showed that the four kinds of suspension hadbetter comprehensive performance, and their structureswere, respectively, excluding the supporting spring in parallel, (1) an inerter in series with a spring and a damper in parallel, (2) a damper in series with a spring and an inerter in parallel, (3) an inerter and a damper in series, and (4) the damper in parallel with a spring and an inerter in series. The ISD suspension structure had better comprehensive performance under step steering braking, which was obviously better than the passive suspension, and effectively improved the vehicle ride comfort, anti-roll and anti-pitch performance. Under the hook steering braking, the lateral load transfer rate was used to evaluate the vehicle’s anti-rollover ability. The results showed that the ride comfort and anti-rollover ability of ISD suspension were better than those of passive suspension. Under the condition of taking into account the anti-pitching ability, the suspension consists of a supporting spring in parallel with an inerter, and a damper in series was better.

Practical negative stiffness device with viscoelastic damper in parallel or series configuration for cable damping improvement

Negative stiffness mechanism has been found able to improve damping performance of dampers on a stay cable which otherwise is limited by the damper installation distance from a cable end. This study provides a practical negative stiffness device (NSD) with adjustable negative stiffness and experiments are performed to validate the negative stiffness effect. The NSD is then combined with a viscoelastic damper in parallel or series for cable damping improvement. Explicit design formulas are derived for optimal design with a target enhancement effect in damping considering the damper described respectively using the Kelvin model and the linear hysteretic damping model. The formulas are verified by analytical and numerical solutions. Parametric analyses show damping enhancement effects of the NSD and it is found more efficient when combined with a damper in series because both deformation amplitudes of the damper and the NSD are further increased in this configuration. Subsequently, case studies are carried out based on two cables of the Sutong Bridge respectively with a shear-type viscous damper and a high damping rubber damper. The results show that the designed NSD can fulfill practical requirements. Particularly, a 100% increase in damping can be achieved by the presented NSD when combined with the damper installed on a cable of 546.9 m long.

Seismic performance of the combined viscous-steel damping system suffering from oil leakage

The combined viscous-steel damping system is a passive energy dissipation device consisting of a fluid viscous damper and a steel yielding damper in series. However, many viscous dampers installed in structures have been suffering from severe oil leakage. This study aims to assess the influence of the leaked viscous damper on the seismic performance of the combined system. Cyclic tests were conducted on the viscous damper with different leakage levels to obtain its degraded hysteretic performance. The modeling method of the leaked viscous damper was proposed according to the experimental result. The locking behavior and seismic mitigation effectiveness of the combined system suffering from oil leakage were investigated based on a single-degree-of-freedom system. The result reveals that (i) The leaked viscous damper cannot generate damping force at the beginning of the reverse movement of its piston, which is reflected in the hysteretic curves as a “gap” phenomenon. (ii) The proposed modeling method can accurately simulate the damping characteristics of the leaked viscous damper. (iii) In spite of the leakage severity, the combined system possesses reliable locking behavior and decent vibration mitigation effectiveness under earthquakes. (iv) The combined system is superior to the viscous damper in mitigating seismic-induced displacement when suffering from oil leakage.

Experimental investigation for novel hybrid journal bearing with hydrostatic squeeze film and metal mesh damper in series

PurposeThis study aims to present a novel hydrostatic squeeze film-metal mesh journal bearing (HS-MMJB), which uses both hydrostatic squeeze film damper (HSFD) and metal mesh damper (MMD), to suppress the vibration of rotor-bearing systems.Design/methodology/approachThe lubrication equations were introduced to calculate the dynamic characteristics of HS-MMJB, and the response analyses of rotor systems were carried out. Experiments were conducted to study the vibration reduction of a rotor system with HS-MMJB. In addition, experiments for different oil supply pressures in the HS-MMJB were conducted.FindingsThe theoretical and experimental results show that the HS-MMJB exhibits excellent damping and vibration attenuation characteristics. Moreover, the stability of the rotor system can be improved by controlling the oil supply pressure.Originality/valueThere is a dearth of research on vibration characteristics of rotor system support by journal bearing combining HSFD and MMD. Moreover, the active oil pressure control is implemented to improve the stability of rotor system.

Force chains, creep and acoustic reflection in marine sediments

Marine sediments are water-saturated granular media. A feature of granular media is that the stress is not uniformly distributed but concentrated in force chains. Several force chains acting in parallel transmit external stresses through the medium. A force chain is a chain of particles through which the external stresses are concentrated and transmitted. Given that the contact stiffness between particles may be approximated as a Maxwell element, i.e. a spring in series with a damper, then the stiffness of any force chain may be modeled as several Maxwell elements in series. It is known that any number of springs and dampers in series may be reduced to just one spring and one damper in series, i.e., one equivalent Maxwell element. Therefore, several force chains in parallel may be modeled as parallel Maxwell elements. However, parallel Maxwell elements may not be reduced to one Maxwell element. The stiffness of a distribution of parallel Maxwell elements falls under the generalized creep model. This model is used to represent the skeletal frame of a larger porous medium model. The inversion of model parameters from the reflection coefficient is explored in the context of a muddy sediment. [Work supported by ONR, Ocean Acoustics Program.]

A passive negative stiffness damper in series with a flexible support: Theoretical and experimental study

Dampers with negative stiffness behavior have been widely investigated for structural vibration control due to their superior performance. In practical applications, a support in series with these dampers might have some flexibility, that is, the stiffness is positive but finite. This paper investigates the effects of that flexibility on the performance of a passive negative stiffness damper (PNSD). First, a system consisting of a PNSD in series with a flexible support is presented, and the lower limit of the support stiffness needed to keep the system stable is derived. Second, a mechanical model for the proposed system is analyzed theoretically. An equivalent model of the damping force is established. The deformation of the flexible link is illustrated, followed by a demonstration of its effect on the hysteresis loops. Finally, an experimental investigation is performed to evaluate the performance of the PNSD support system. A device that contains an oil damper and two compressed springs is utilized to provide negative stiffness and Coulomb friction behavior. One of the set of springs is then incorporated to act as a positive but finite stiffness support in series with the device. Tests are conducted to assess the hysteretic behavior of the overall system. Theoretical and experimental results indicate that a range of equivalent negative stiffness and Coulomb friction level can be achieved simply, depending upon the positive stiffness of the flexible support in series with the PNSD.

Solid-State Single-Port Series Damping Device for Power Converters in DC Microgrid Systems

In dc microgrid systems, power converters with input filters sometimes encounter unwanted input voltage and current oscillations, due to interactions among the bus impedance, filters, and converters. This paper presents a solid-state single-port series damper (“ S 3 damper”) that can deal with such oscillations. The damper, which is connected in series between the input filter and the converter, is realized by operating a transistor as an ac resistor. It lowers the quality factor of the filter and thus increases the damping effect on the interaction between the filter and the converter. It also increases the input impedance of the filter to avoid voltage and current oscillation between the filter and the bus. In addition, the transistor is regulated at a low dropout voltage to reduce power dissipation. The control mechanism is autonomous. Furthermore, the proposed damper does not require any power capacitor or inductor, favoring high compactness and reliability. Modeling, design, and comprehensive analysis of the S3 damper will be provided. A prototype damper for a commercially available 100 W dc–dc converter operated on a 48 V bus has been built and evaluated.

Improved nonlinear model of a yaw damper for simulating the dynamics of a high-speed train

The aim of this paper is to establish a simple and accurate nonlinear model of a yaw damper for the dynamic numerical simulation of high-speed trains. An improved nonlinear yaw damper model is proposed based on the traditional Maxwell model. It comprises a piecewise linear force–displacement spring and a piecewise linear force–velocity damper in series. These nonlinear inputs for the model are retrieved from the dynamic performance tests of the damper, and the force–displacement and force–velocity curves are further modified to improve the modelling accuracy according to the test results. The proposed model can accurately simulate the damper's dynamic stiffness and dynamic damping characteristics with respect to the excitation frequency or displacement, which cannot be reproduced when using the traditional Maxwell model. Both the traditional Maxwell model and the improved nonlinear model presented in this work are integrated into a multibody dynamics railway vehicle model to simulate the typical dynamic problems of a high-speed train operating at 250 km/h in northeast China. Through comparative analysis, it was found that the numerical simulations are consistent with the field measurements. It can be concluded that the proposed nonlinear damper model is more suitable for studying railway vehicle system dynamics under various operating cases. By contrast, the input parameters of the traditional Maxwell model must be modified artificially according to the vehicle responses and the dynamic characteristics of the yaw damper.

Minimization of the beam response using inerter-based passive vibration control configurations

Two inerter-based passive vibration control configurations, i.e., a mass connected to a parallel combination of a spring and a damper in series with a spring and an inerter (Case I), and a traditional dynamic vibration absorber in series with an inerter (Case II), are proposed and are successfully applied to achieve the vibration suppression of beam-type structure. The frequency response functions of system displacement and acceleration are analytically derived through the classical vibration theory. The optimization problem of minimizing the maximum value of the frequency response function in the whole range or a certain range of frequency is expressed as a min-max problem and then the optimal parameters are derived numerically. Especially, for Case II the optimal system parameters can be analytically expressed by using the fixed-point theory. Numerical results show that the inerter-based passive vibration control configurations are more efficient than the traditional dynamic vibration absorber, especially for case with a small mass ratio. The inerter-based Case I is more efficient than the inerter-based Case II for a smaller mass ratio while contrary is true for a larger mass ratio. Also, the influences of the mass ratio and the inertance-to-mass ratio on the optimal system parameters are briefly discussed.

産業施設を対象とした粘性-摩擦直列ダンパーに関する研究（ダンパーの構造と基本性能）

This study proposes a viscous-friction series damper. The series damper consists of an oil damper and a friction damper connected in series. Long period and long time seismic waves were recognized as new problems by the Great East Japan Earthquake. In the case of those seismic waves, there are risks that performance of damper decreases. For example, temperature of inner fluid of viscous dampers may increase, and fatigue failure may occur in steel dampers by such earthquakes. On the other hand, friction dampers have high durability, but they don't operate with small input. Proposed series damper compensates for these weak points. In the case of small input, only the viscous damper operates. In the case of large input, both dampers operate, so energy absorption is divided and the durability is increased. In this paper, an analysis model of the series damper is introduced, and numerical analysis is carried out in order to investigate behavior of the series damper. The target of vibration control is a boiler structure. As a result of analysis, response of the structure with the series damper was smaller than response without the damper. In addition, response of the structure with the series damper approached response with an ordinary viscous damper by increasing friction coefficient. Then test model of the series damper is fabricated, and load experiments by sinusoidal waves are conducted. As a result of the experiments, stabile performance of the series damper against various input condition was confirmed. In addition, experimental results agreed well with analysis results, so proposed analysis model is efficient.

Increasing trunk flexion transforms human leg function into that of birds despite different leg morphology.

Pronograde trunk orientation in small birds causes prominent intra-limb asymmetries in the leg function. As yet, it is not clear whether these asymmetries induced by the trunk reflect general constraints on the leg function regardless of the specific leg architecture or size of the species. To address this, we instructed 12 human volunteers to walk at a self-selected velocity with four postures: regular erect, or with 30deg, 50deg and maximal trunk flexion. In addition, we simulated the axial leg force (along the line connecting hip and centre of pressure) using two simple models: spring and damper in series, and parallel spring and damper. As trunk flexion increases, lower limb joints become more flexed during stance. Similar to birds, the associated posterior shift of the hip relative to the centre of mass leads to a shorter leg at toe-off than at touchdown, and to a flatter angle of attack and a steeper leg angle at toe-off. Furthermore, walking with maximal trunk flexion induces right-skewed vertical and horizontal ground reaction force profiles comparable to those in birds. Interestingly, the spring and damper in series model provides a superior prediction of the axial leg force across trunk-flexed gaits compared with the parallel spring and damper model; in regular erect gait, the damper does not substantially improve the reproduction of the human axial leg force. In conclusion, mimicking the pronograde locomotion of birds by bending the trunk forward in humans causes a leg function similar to that of birds despite the different morphology of the segmented legs.

Damping systems that are effective over a wide range of displacement amplitudes using metallic yielding component and viscoelastic damper in series

SUMMARYA damper system that absorbs energy over a wide range of displacement amplitudes during building vibration was proposed. This system uses a serial connection of a metallic yielding component and viscoelastic damper with a displacement limit mechanism. Three types of the system were developed and tested: a diagonal bracing type, inverted V bracing type, and wall type. The test results showed that all these systems have damping ratios higher than 8% at small vibration amplitudes on the order of 0.1 mm. For a large vibration, a displacement limit mechanism with two pins limited the displacement of the viscoelastic damper as designed. Analytical simulations established that the system reduced the acceleration and the story drift to 60–70% and 80%, respectively, during a small earthquake compared with a conventional metallic yielding damper system. Furthermore, it showed an equivalent control performance during a severe earthquake. The damper system requires that a clearance be maintained for the displacement limit mechanism. However, this may be lost through construction error, residual displacement after an earthquake, and temperature effects. The changes in the clearance due to these effects were discussed. Copyright © 2014 John Wiley & Sons, Ltd.

J1010601 長周期構造物に設置する粘性-摩擦ハイブリッドダンパに関する研究([J101-6]制振(2))

Every year, many earthquakes occur in Japan. Many high rise structures which are in a long distance from the hypocenter of the earthquake resonate with the long period ground motion. Recently, many structures require countermeasure for long period ground motion. Various viscous dampers have been developed and applied to actual structures to suppress vibration response. However, the vibration control performance decreases with the long duration time of earthquake because of a temperature rise of the viscous material. Therefore, there is concern that these viscous dampers can not suppress vibration response in case of long period ground motion. In order to solve this problem, a viscous-friction damper in series is proposed in this study. Then, in this hybrid damper, the friction damper can absorb vibration energy as well in case of the long period ground motion. In this paper, seismic response analysis is conducted to confirm performance of hybrid damper.

Suppression of Burst Oscillations in Racing Motorcycles

Burst oscillations occurring at high speed, and under firm acceleration, can be suppressed with a mechanical steering compensator. Burst instabilities in the subject racing motorcycle are the result of interactions between the wobble and weave modes under firm-acceleration at high speed. Under accelerating conditions, the wobble-mode frequency (of the subject motorcycle) decreases, while the weave mode frequency increases so that destabilizing interactions can occur. The design analysis is based on a time-separation principle, which assumes that bursting occurs on time scales over which speed variations can be neglected. Even under braking and acceleration conditions linear time-invariant models corresponding to constant-speed operation can be utilized in the design process. The influences of braking and acceleration are modeled using d’Alembert-type inertial forces that are applied at the mass centers of each of the model’s constituent bodies. The resulting steering compensator is a simple mechanical network that comprises a conventional steering damper in series with a linear spring. In control theoretic terms, this network is a mechanical lag compensator. A robust control framework was used to optimize the compensator design because it is necessary to address the inevitable uncertainties in the motorcycle model, as well as the nonlinearities that influence the machine’s local behavior as the vehicle ranges over its operating envelope.

Attenuation of a linear oscillator using a nonlinear and a semi-active tuned mass damper in series

In this paper, the behavior of a three degrees-of-freedom system is examined, consisting of a linear primary structure (PS), a tuned mass damper with a small cubic stiffness nonlinearity and a semi-active tuned mass damper (STMD) connected in series—each element with a mass approximately two orders of magnitude smaller than the previous. Using numerical simulations, it is determined that an STMD with a mass four orders of magnitude smaller than the PS is able to greatly reduce the amplitude of the PS response by acting to keep the nonlinear tuned mass damper within its linear range. Effective attenuation is dependent on appropriate selection of design parameters—selecting an appropriate STMD mass ratio given its damping, the strength of the stiffness nonlinearity, and the largest forcing amplitude expected. Using a standard tuning approach for the STMD (modulating its stiffness to match the natural frequency of the STMD to the excitation frequency) and comparing its performance with an optimal passive linear tuned mass damper (TMD), the STMD provides a wider-band frequency-response amplitude reduction but often increases the response amplitude slightly above the resonance frequency. A piecewise linear tuning approach for the STMD is proposed which combines the performance benefits of the STMD and the TMD to improve performance and further reduce power requirements.

Nonlinear Dynamic Behavior of Turbocharger Rotor-Bearing Systems With Hydrodynamic Oil Film and Squeeze Film Damper in Series: Prediction and Experiment

Current trends for advanced automotive engines focusing on downsizing, better fuel efficiency, and lower emissions have led to several changes in turbocharger bearing system design and technology. Automotive turbochargers run faster and use engine oils with very low viscosity under high oil inlet temperature and low feed pressure. The development of high performing bearing systems, marrying innovation with reliability, is a persistent challenge. This paper shows progress on the nonlinear dynamic behavior modeling of the rotor-radial bearing system (RBS) incorporating two oil films in series: a hydrodynamic one with a squeeze film damper commonly used in turbochargers. The developed fluid bearing code predicts bearing rotational speed (in the case of fully floating design), operating inner and outer bearing film clearances, effective oil viscosity, taking into account its shear effect, and hydrostatic load. A rotordynamics code uses this input to predict the nonlinear lateral dynamic response of the rotor-bearing system. The model predictions are validated with test data acquired on a high speed turbocharger RBS of a 6.0 mm journal diameter running up to 250,000 rpm (maximum speed), 5W30 oil type, 150°C oil inlet temperature, and 4 bar oil feed pressure. The tests are conducted at a rotordynamics technology laboratory using a high performance data acquisition system. Turbochargers with four combinations of inner and outer RBS clearances are tested. Prediction and measured synchronous response and total motion are in good agreement. Both demonstrate the nonlinear character of the RBS behavior, including several subsynchronous frequency components across the operating speed range. The nonlinear predictive model aids the development of high performance and optimized turbocharger RBS with faster development cycle times and increased reliability.