Horizontal Damping Research Articles

Top-Story Softening for Enhanced Mitigation of Vortex Shedding-Induced Vibrations in Wind-Excited Tuned Mass Damper Inerter-Equipped Tall Buildings

An innovative structural modification, top-story softening, is herein proposed in conjunction with an optimally tuned top-floor tuned mass damper inerter (TMDI) for improved serviceability performance in typical core-frame slender buildings with rectangular floor plan susceptible to wind-induced vortex shedding (VS) effects causing occupant discomfort. This is supported through formulating a novel optimal TMDI tuning problem in which TMDI inertial properties, i.e., attached mass and inertance, as well as the lateral top-story stiffness are design parameters aiming to minimize peak acceleration of the highest occupied floor. The optimal TMDI tuning problem is numerically solved for a wide range of design parameters for a 34-story composite core-frame building subject to stochastic spatially-correlated wind-force field accounting for VS effects. A low-order dynamical model capturing faithfully modal properties of the case-study building is developed to facilitate computational work and parametric investigation. It is found that top-story softening reduces attached TMDI mass/weight requirements and inerter force for fixed performance and inertance. It further reduces TMDI stroke and achieves increased robustness to TMDI stiffness and damping properties as well as to the assumed inherent structural damping. It is concluded that by leveraging inertance and top-story stiffness, the proposed solution can efficiently control VS-induced floor acceleration with small additional gravitational (added weight) and horizontal (inerter and damping) forces.

Control the ride comfort of soil compactor with semi-active seat suspension and cab’s horizontal damper

To control the vibration of the driver’s seat in the vertical direction and the cab shaking angle in the pitching direction, a semi-active seat suspension and cab’s horizontal damper (SSS-HD) are proposed in this study. Based on the soil compactor dynamic model established in Matlab/Simulink software, the damping coefficients us and ux of the SSS-HD are controlled via the PID-fuzzy control. The weighted root-mean-square acceleration responses of the vertical driver’s seat (awzs) and pitching cab angle (awφs) are selected as the evaluation indexes. The SSS-HD is then compared with the semi-active hydraulic mount (SHM) of the cab. The results show that the SSS-HD has a great effect in controlling the vibration of the driver’s driver in the vertical direction and cab shaking in comparison with the SHM of the cab under the same simulation conditions of the vehicle. In particular, the awzs is improved by 27.9 % under the traveling condition and the awφs is also lower 40.2 % under the compacting condition in comparison with the SHM.

Oscillating grid generating turbulence near gas-liquid interfaces in shear-thinning dilute polymer solutions

A first experimental characterization of low Reynolds number, oscillating grid generated, and near-surface turbulence in shear-thinning dilute polymer solutions is presented. Energy transfer and horizontal damping mechanisms are evidenced. The evolution of the viscous sublayer depth can be explained by both viscous and shear-thinning effects.

INS/CNS Integrated Calibration based on Speed Reference Information

CNS needs INS to provide horizon attitude information as the horizon reference. The non-damping INS on critical conditions is easy to cause error fluctuation and divergence when the accelerometer zero is changed, directly affecting horizon reference information precision of assistant CNS. Therefore, under on-board use conditions, the INS short-term high-precision characteristics are used in CNS/INS/LOG integrated system to design Kalman filter with horizontal speed damping and compensate dynamic error of INS. The calibration and readjustment technology of on-board CNS/INS integrated system is based on horizontal speed damping. The accurate reference information of CNS is used to finish correction of position error, misalignment angle and main gyro drift error. In this way, the readjustment period will be extended to realize long-time and high-precision navigation of the integrated system.

Evaluation of the vibration response of third generation nuclear power plants with isolation technology under large commercial aircraft impact

With the development of nuclear power technology, third-generation nuclear power plants (NPPs) are being built in many places. Examples include the American passive AP1000 NPP, the French EPR NPP, and China's Hualong One NPP. These will become the main reactor type for future NPP construction. Base isolation is employed as the aseismic technology in NPPs, and its design standard has been standardized according to ASCE 4–16 and other related codes. Since the 9/11 terrorist incident, large commercial aircraft impact (AI), as a beyond design-basis event, has attracted increasing attention in nuclear research. In the case of a third-generation NPP with isolation technology, it is necessary to evaluate its safety and integrity against AI. In this study, the dynamic response of a base-isolated third-generation NPP subjected to impact by a large commercial aircraft, the Airbus A340-300, is investigated. The most typical design for a third-generation NPP is to build many buildings on the same base-mat. The presence of a flexible isolation layer renders the dynamic behavior of a base-isolated NPP different from that of a non-isolated NPP under AI loads. Five key factors, including the horizontal stiffness of isolation bearings, horizontal damping of isolation bearings, total weight and weight distribution of the NPP, and AI force and direction affect the vibration characteristics of NPPs. The horizontal stiffness of isolation bearings affects the constraint effect of the foundation on the superstructure, while the damping of isolation bearings affects the dissipation of impact energy. Meanwhile, the total weight and weight distribution of the NPP affect the vibration response of different regions, and the impact force affects the vibration intensity of the NPP.

Vibration Control Technology of a Main Hall of Traditional Wooden Structure by Horizontal Viscoelastic Damper

Vibration Control Technology of a Main Hall of Traditional Wooden Structure by Horizontal Viscoelastic Damper

Study on the stiffness degradation and damping of pile foundations under dynamic loadings

This paper presents a comprehensive study on the different behaviour of batter and vertical pile foundations in terms of stiffness degradation and damping properties under dynamic loadings. Firstly, dynamic centrifuge tests were carried out and the variations of translational/rotational stiffness and the associated damping properties were identified from a series of hysteretic loops. Results show that for the rocking behaviour, the presence of batter piles causes a small decrease of the rotational stiffness and a great increase of the rotational damping; for the horizontal translation behaviour, batter pile foundation has much higher horizontal stiffness and translational damping compared to the vertical foundation. Then, a set of stiffness degradation and damping curves for the translational and rotational behaviour of batter and vertical pile foundations are proposed. Finally, the proposed stiffness degradation and damping curves were validated numerically by using equivalent linear approach. The numerical validation shows a good agreement with the experimental results.

Dynamic characteristics of a quasi-zero stiffness vibration isolator with nonlinear stiffness and damping

A quasi-zero stiffness (QZS) isolator is devised to acquire the feature of high-static-low-dynamic stiffness. Cam–roller–nonlinear spring mechanisms, where two horizontal dampers are installed symmetrically, are employed as a negative stiffness provider to connect in parallel with a vertical spring. From the static analysis, the piecewise restoring force in the vertical direction of the system is inferred considering possible separation between the cam and roller. The stiffness characteristics and parameters for offering zero stiffness at the equilibrium position are then determined. The dynamic equation is established and used for the deduction of the amplitude–frequency equation by means of the Harmonic Balance Method. The definitions of force and displacement transmissibility are introduced, and their expressions are derived for subsequent investigations of the effects of horizontal spring’s nonlinearity, excitation amplitude, horizontal damping, and vertical damping on the transmissibility performance. The comparative study is implemented on the isolation performance afforded by the QZS isolator and an equivalent linear counterpart, whose static bearing stiffness is same as the QZS isolator. Results indicate that the system with softening nonlinear horizontal spring can exhibit better performance than that with opposite stiffness spring. With the increase in horizontal damping ratio, the force transmissibility is further suppressed in resonance frequency range but increased in a small segment of higher frequencies and tends to unite in high frequency range. However, the horizontal damper deteriorates the ability to isolate the displacement excitation to a certain extent. Besides, the isolation capability of the QZS system depends on the magnitude of excitation amplitude. The quasi-zero stiffness system possesses lower initial isolation frequency and better isolation ability around resonance frequency compared with the linear system. Therefore, the quasi-zero stiffness isolator has superior low-frequency ability in isolating vibration over its linear counterpart.

Dynamic modeling and analysis of a quad horizontal damper system for transient vibration reduction in top loading washing machine

The transient horizontal vibration of top loading washing machine with large capacity has been more important because of the radius of the inner tub in the washing machine increases proportionally. In this paper, we introduce a new vibration reduction technology, namely, a quad horizontal damper system for reduction of the transient horizontal vibration of top loading washing machine. And analyzes the vibration characteristics of a top loading washing machine with a quad horizontal damper system using Newtonian mechanics. For verification and validation of the established dynamic model, the displacement of an actual top loading washing machine are obtained from six laser sensors attached at the upper part and the lower part of outer tub respectively. Optimal design was carried out to ensure sufficient strength and reliability for each component of the horizontal damper. The damping force of the horizontal damper was also optimized so that the horizontal vibration in the transient state of top loading washing machine was reduced by about 35~45 % more than the conventional top loading washing machine and no abnormal noise was generated at high spin speed.

A Novel Damping Method for Strapdown Inertial Navigation System

There are periodic oscillation errors in the strapdown inertial navigation system (SINS) when it works in pure inertial navigation mode. It seriously restricts the navigation accuracy of the system. In order to improve the accuracy of the system, the traditional idea of the external horizontal damping in the stabilized inertial navigation system is introduced into SINS. We find that they are equivalent through comparing the damping network of the stabilized inertial navigation system with the compass alignment network. According to the equivalence, the external horizontal damping network of SINS is designed. And the difference between the velocity of the system itself and the velocity of the electromagnetic log are utilized to damp the periodic oscillation. At the same time, a horizontal damping algorithm based on the external velocity is proposed on the basis of the external horizontal damping idea. The effectiveness of the algorithm is verified by the static base of the three-axis turntable, the swing base experiment, and the vehicle simulation experiment. The experiment shows that the external damping network designed in this paper can suppress the system Schuler periodic oscillation error and improve the accuracy of the system.

Damping Rotating Grid SINS Based on a Kalman Filter for Shipborne Application

The measurement error of the inertial measurement unit (IMU) significantly affects the navigation accuracy of the grid strap-down inertial navigation system (SINS) applied in polar regions. In this paper, the single-axis rotation modulation grid SINS is designed to suppress the navigation error caused by IMU constant error. Then on the basis of rotation modulation scheme, a novel external horizontal damping algorithm based on a Kalman filter is conducted to further suppress the 84.4 min Schuler oscillation caused by IMU random error. The Kalman filter is established based on the error model of shipborne grid SINS. When the reference velocity provided by Doppler velocity log is usable, the Schuler oscillation can be restrained through feedback calibration by calibrating the grid horizontal attitude errors and grid horizontal velocity errors. The simulation results demonstrate that the proposed external horizontal damping algorithm can efficiently suppress the Schuler oscillation, meanwhile compared with traditional external horizontal damping algorithm based on damping network, the proposed algorithm has the advantage of reducing the overshoot errors in the process of state switching.

Chordwise wing flexibility may passively stabilize hovering insects.

Insect wings are flexible, and the dynamically deforming wing shape influences the resulting aerodynamics and power consumption. However, the influence of wing flexibility on the flight dynamics of insects is unknown. Most stability studies in the literature consider rigid wings and conclude that the hover equilibrium condition is unstable. The rigid wings possess an unstable oscillatory mode mainly due to their pitch sensitivity to horizontal velocity perturbations. Here, we show that a flapping wing flyer with flexible wings exhibits stable hover equilibria. The free-flight insect flight dynamics are simulated at the fruit fly scale in the longitudinal plane. The chordwise wing flexibility is modelled as a linear beam. The two-dimensional Navier-Stokes equations are solved in a tight fluid-structure integration scheme. For a range of wing flexibilities similar to live insects, all eigenvalues of the system matrix about the hover equilibrium have negative real parts. Flexible wings appear to stabilize the unstable mode by passively deforming their wing shape in the presence of perturbations, generating significantly more horizontal velocity damping and pitch rate damping. These results suggest that insects may passively stabilize their hover flight via wing flexibility, which can inform designs of synthetic flapping wing robots.

Seismic Analysis for Multi-Story Building Horizontally Damped Above Basement Level

Due to the urbanization multi-story building with underground story for parking space and storage are very common in practice. Now a day, seismic energy dissipating devices are being used for various types of structures and located in basements which are difficult to maintain. The main objective is to evaluate the effectiveness of horizontal dampers in the ground floor level of the multi-story building above basement. Among different types of dampers, visco-elastic [VE] dampers are used for this numerical study. Comparing with other types of passive energy dissipating devices, visco-elastic [VE] dampers are considered most suitable. For the better understanding of the effectiveness of horizontal dampers, stiff foundation system is considered thus soil-structure interaction is omitted. In this numerical study, seismic response of different hypothetical structures analyzed having different underground stories and horizontal dampers only in the ground level. Modeling and analysis of the structures and installation of the dampers are done by using finite element modeling software [ETABS]. Time history analysis was used to simulate the response of the structures. Sabah earthquake [05/June/2015] with the PGA of 0.126g was used for the time history analysis. Different dynamics parameters such as natural time period, displacement, base shear and inter-story drift were evaluated. Changes in the results among the structures demonstrated the efficiency of horizontal dampers. Optimum locations of the horizontal dampers were also revealed in this study in the basis of the analysis results.

Analysis and suppression of a self-excitation vibration via internal stiffness and damping nonlinearity

This work concerns the usage of the internal stiffness and damping nonlinearity for vibration suppression in a van der Pol–type mechanical self-excitation system. Changing the vertical or horizontal damping could limit the growth of the flow-induced instability. Applying harmonic balance method, the energy transfer for the self-excitation vibration is investigated through the limit circle. The steady amplitude of the limit circle is a key parameter that could be used to evaluate the effectiveness of the self-excitation oscillation suppressing. Increasing horizontal damping could reduce the rate of roll on for the steady amplitude curve of the limit circle, but the critical flow velocity for the limit circle occurring is minimally affected. Increasing vertical damping could increase the critical flow velocity, but the rate of the roll on is virtually unaffected when the parameters are properly chosen.

Precast industrial buildings in Southern Europe: loss of support at frictional beam-to-column connections under seismic actions

This paper presents the evaluation of the loss-of-support conditions in frictional beam-to-column connections of industrial precast concrete buildings under seismic actions. This type of connection is widespread throughout Southern Europe in non-seismically designed industrial precast buildings. First, geometric properties of industrial precast buildings and of the frictional beam-to-column connections, together with reference values for the friction coefficient, are reviewed. Then, earthquake time histories taken from the European Strong-Motion sets and recordings of the two major shocks of the 2012 Emilia-Romagna events are presented and discussed showing the importance of the vertical component. Two dynamic models of increasing complexity are used to ascertain loss-of-support conditions under seismic action. The first model is an elastic one, representing a single frame of the industrial buildings. Results are obtained according to: (1) 2D analyses, disregarding the time correlation between the response peaks along the horizontal and vertical directions, (2) 2D analyses taking into account time correlation, and (3) 3D analyses to evaluate also directionality effects. The second model is a 2D non-linear planar frame developed within the OpenSees framework. Results show that simplified (linear) models are a good proxy to more refined (non-linear) ones. However, one must resort to non-linear models if differential displacements between beam and column are of interest. The non-linear numerical investigations show that friction coefficient, horizontal and vertical periods and damping, and column reinforcement ratio are the key variables in estimating the loss-of-support conditions.

An Adaptive Damping Network Designed for Strapdown Fiber Optic Gyrocompass System for Ships.

The strapdown fiber optic gyrocompass (strapdown FOGC) system for ships primarily works on external horizontal damping and undamping statuses. When there are large sea condition changes, the system will switch frequently between the external horizontal damping status and the undamping status. This means that the system is always in an adjustment status and influences the dynamic accuracy of the system. Aiming at the limitations of the conventional damping method, a new design idea is proposed, where the adaptive control method is used to design the horizontal damping network of the strapdown FOGC system. According to the size of acceleration, the parameters of the damping network are changed to make the system error caused by the ship’s maneuvering to a minimum. Furthermore, the jump in damping coefficient was transformed into gradual change to make a smooth system status switch. The adaptive damping network was applied for strapdown FOGC under the static and dynamic condition, and its performance was compared with the conventional damping, and undamping means. Experimental results showed that the adaptive damping network was effective in improving the dynamic performance of the strapdown FOGC.

阻尼比连续可调的捷联惯性姿态测量系统内阻尼技术

阻尼比连续可调的捷联惯性姿态测量系统内阻尼技术

Gravity Compensation Using EGM2008 for High-Precision Long-Term Inertial Navigation Systems.

The gravity disturbance vector is one of the major error sources in high-precision and long-term inertial navigation applications. Specific to the inertial navigation systems (INSs) with high-order horizontal damping networks, analyses of the error propagation show that the gravity-induced errors exist almost exclusively in the horizontal channels and are mostly caused by deflections of the vertical (DOV). Low-frequency components of the DOV propagate into the latitude and longitude errors at a ratio of 1:1 and time-varying fluctuations in the DOV excite Schuler oscillation. This paper presents two gravity compensation methods using the Earth Gravitational Model 2008 (EGM2008), namely, interpolation from the off-line database and computing gravity vectors directly using the spherical harmonic model. Particular attention is given to the error contribution of the gravity update interval and computing time delay. It is recommended for the marine navigation that a gravity vector should be calculated within 1 s and updated every 100 s at most. To meet this demand, the time duration of calculating the current gravity vector using EGM2008 has been reduced to less than 1 s by optimizing the calculation procedure. A few off-line experiments were conducted using the data of a shipborne INS collected during an actual sea test. With the aid of EGM2008, most of the low-frequency components of the position errors caused by the gravity disturbance vector have been removed and the Schuler oscillation has been attenuated effectively. In the rugged terrain, the horizontal position error could be reduced at best 48.85% of its regional maximum. The experimental results match with the theoretical analysis and indicate that EGM2008 is suitable for gravity compensation of the high-precision and long-term INSs.

Low emittance lattice design with Robinson wiggler in the arc section

Beam emittance reduction is an effective method to increase the brightness of a synchrotron light source. Robinson wiggler can play a role in the beam emittance reduction by increasing the horizontal damping partition number. A replacement of the quadrupoles in the arc section with short combined function dipoles will construct a single-periodic Robinson wiggler in the SSRF storage ring. This scheme provides a lower beam emittance, without occupying any straight section. Detailed analysis is presented in this paper.

Horizontal Stiffness and Damping of Piles in Inhomogeneous Soil

AbstractA practically oriented analytical procedure for determining the dynamic stiffness and damping (impedance coefficients) of a laterally loaded pile in soil exhibiting different types of inhomogeneity with depth, is presented. To this end, an energy method based on the Winkler model of soil reaction in conjunction with pertinent shape functions for the deflected shape of the pile are employed. A new elastodynamic model for the wave field around a pile is also introduced. The method is self-standing and free of empirical formulas or constants. Dimensionless closed-form solutions are derived for (1) the distributed (Winkler) springs and dashpots along the pile; (2) dynamic stiffness and damping coefficients at the pile head; (3) active length, beyond which the pile can be treated as infinitely long; and (4) relative contributions to the overall head stiffness and damping of the soil and the pile media. Swaying, rocking, and cross swaying-rocking impedances are considered for parabolic, exponential, and...