Large Damping Ratio Research Articles

Study on the Cyclic Shear Performance of Waste Steel Slag Mixed Soil

Clay soil has poor engineering properties such as poor permeability and low shear strength. Waste steel slag is an industrial by-product formed in the furnace during the steelmaking process which has high quality, durability, anti-slip properties, gelling, high permeability and good particle interlocking properties. Therefore, in order to improve the engineering properties of clay and increase the utilization rate of waste steel slag, the steel slag was mixed into the clay. Steel slag clay mix was used for the straight shear test, cyclic shear test and post-cyclic straight shear test. To investigate the strength characteristics, damping ratio, shear stiffness variation and mixed soil displacement at the reinforcement-soil interface under different steel slag dosing, vertical stress, moisture content and shear amplitude conditions. The test results show that steel slag can significantly improve the shear strength of the clay tendon-soil interface, and the improvement effect is better than the conventional material sand improved clay. The steel slag mix has a large damping ratio and shear stiffness, suggesting that it has good damping and energy dissipation properties. In this case, the shear strength, damping ratio and shear stiffness of the soil mix at 40% steel slag admixture are better. The shear strength of the steel slag mix is increased after cyclic loading compared to straight shear before cyclic loading. In addition, the water content has a greater effect on the shear strength parameters, shear stiffness and damping ratio of the steel slag clay mix compared to the vertical stress and shear amplitude. The test results can provide a theoretical basis for the replacement of sand by steel slag in improving clay soils.

Analysis of Cutting Stability of a Composite Variable-Section Boring Bar with a Large Length-to-Diameter Ratio Considering Internal Damping.

Chattering in composite deep-hole boring can directly affect surface processing quality and efficiency and has always been a research hotspot in machining mechanics. In this study, based on Euler–Bernoulli beam theory, the fine control equations for the cutting stability of composite variable-section boring bars were established using the Hamilton principle, in which the sectional change and internal damping of the material were considered. Next, using the Galerkin method and semi-discrete method, the effects of the taper ratio, damping ratio, length-to-diameter ratio, and ply angle on the free vibration characteristics and cutting stability were analyzed in detail. The results show that at a low damping ratio, both the first-order inherent frequency and boring stability can be enhanced with the increase in the taper ratio; at a large damping ratio, increasing the taper ratio can reduce the first-order inherent frequency and boring stability. Finally, the effects of the sectional change on the inherent frequency, displacement response, and convergence were analyzed. A numerical simulation was performed for the model reliability validation. The present research results can provide a theoretical basis and technical guidance for analyzing the cutting stability and fine control of composite variable-section boring bars with large length-to-diameter ratios.

An assessment of damper placement methods considering upfront damper cost

Previous studies have shown that earthquake repair costs can be minimised by using large levels of supplemental damping and uniform damper placement. However, it is not always feasible to achieve this damping due to structural or financial restraints. Iterative damper placement methods may be able to achieve higher levels of damping than simple methods such as uniform damping for the same total damper cost. In this work, six damper placement methods were assessed based on structural and non-structural repair costs. The total damper cost was constrained to be the same in each case. The scope of work was limited to linear fluid viscous dampers, concentric braced frames and regular structures. The iterative methods were found to provide a greater total damping coefficient to the structures than the simple methods. This resulted in a higher supplemental damping ratio and lower repair costs. If upfront funds are limited, or if architectural constraints prevent the placement of dampers in lower storeys, then iterative methods provide the most favourable total-building seismic performance. However, the conclusions should be extended cautiously. Although iterative methods are favourable when the upfront damper investment is strictly limited, in terms of total-building seismic performance, it is advantageous to provide a large damping ratio using uniform damping.

Modeling, dynamics, and parametric studies of a multi-cable-stayed beam model

To study the dynamic behavior of cable-stayed bridges, a linear multi-cable-stayed beam model is developed to investigate its in-plane and out-of-plane transverse vibrations. From the full-bridge perspective, an in-plane nonlinear single-mode discrete model is established. First, the in-plane and out-of-plane motion equations of the system and their boundary conditions are derived. Second, by employing the separation of variables method, the linear eigenvalue problems are solved. The influences of the mass ratio, stiffness ratio, and cable sag on the occurrence of global, local, and coupled vibration modes are studied. Third, frequency response, amplitude response, phase diagram, time history, and power spectrum are extracted to investigate the system’s nonlinear dynamic behaviors. The obtained results demonstrate that for the in-plane motion, the occurrence of global and local modes of the system depends on the mass and stiffness ratios between cable and beam significantly; for the out-of-plane motion, without the elastic support of the cable, the global modes occur, which can be suppressed by adjusting the mass and stiffness ratios between cable and beam but may in turn induce the cable’s local vibration modes; for the nonlinear analysis, the single-degree-of-freedom system behaves like a hardening spring. Its lower branch behaves more complicated than the higher one and has a double-periodic steady-state solution. The system with large damping ratio behaves shows weak hardening spring property.

Aeroelastic Simulation Using CFD/CSD Coupling Based on Precise Integration Method

Aeroelasticity studies the interaction between the aerodynamic loads and the flexible structures, and has gained much attention in the design of modern aircraft. Most of the existing computational fluid dynamics/computational structural dynamics (CFD/CSD) coupling approaches are based on Runge–Kutta method, central difference method, linear multi-step method and so on, which are conditionally stable and are unsuitable for the stiff problem that requires a very small time step to solve. In this paper, the precise integration method (PIM) formula is derived for the structural modal equations and then the PIM-based CFD/CSD coupling method is presented. The three-dimensional AGARD wing 445.6 and a sweptback wing are considered here for aeroelastic studies. The flutter results demonstrate that the presented method is comparable in accuracy to the traditional strong coupling method and has better numerical stability property than some exiting improved methods. For the static aeroelastic analyses, applying a large damping ratio to the structural equations helps to obtain the equilibrium quickly but may lead to the stiff problem, which was seldom discussed before. The results show that the presented PIM-based coupling method can overcome the stiff problem arising in static aeroelastic systems and is more efficient than the traditional coupling approach based on Runge–Kutta method, especially when a large damping ratio is applied.

Experimental Studies on the Dynamic Responses of Coated Superconductor Stack Levitated Above a Permanent Magnet Guideway

In this work, we experimentally investigated the dynamic responses of stacked coated conductor tapes that were levitated over an Nd-Fe-B magnet guideway. The experiments were carried out on a recently designed test rig that can simultaneously measure the acceleration and levitation force during a vibration process. We applied three typical excitations, viz., unloading, free fall, and pulsed excitation. The attenuation coefficient and damping ratio of such stack-based maglev system were analyzed by means of free vibration attenuation method. Last, the dynamic response of mechanical components of the stack-based maglev on pulsed excitation was visualized clearly. Results obtained by this study tell us that the damping ratio is relative to the intensity of external disturbance, which means a weak excitation will cause a small damping ratio and a longer convergence time; however, a larger damping ratio and a faster convergence of vibration will be presented when a stronger stimulation is imposed on. This phenomenon could be contributed by the metal components of the stack, and is promising in practical application, particularly, in construction of HTS maglev where a large damping ratio is required.

Probabilistic seismic risk assessment of modified pseudo-negative stiffness control of a base-isolated building

Pseudo-negative stiffness (PNS) control of a base-isolated structure, which has a large damping ratio at the isolation level, is used to suppress isolator displacement without large force transmission to the superstructure during extreme earthquakes. However, potential increases in floor acceleration in the superstructure are induced by the large damping ratio, especially for low-to-moderate seismic input level. In consideration of structural functionality and safety, a modified PNS (MPNS) control scheme based on the ‘ideal isolation control principle’ is proposed, considering different seismic intensity levels. The effect of the MPNS control is investigated from three aspects, namely floor acceleration, inter-storey drift and isolator displacement within a probabilistic performance-based seismic engineering framework. Comparisons are made between MPNS control, conventional PNS control and passive damping control. A benchmark base-isolated building is used as a case study. In the seismic performance evaluation, the seismic intensity measures for different response parameters are optimised. An extensive parametric study is also conducted to identify the optimal control parameter to conform to the ideal isolation control principle. Results demonstrated that the MPNS control is an effective solution to the challenging problem of improving structural functionality at low seismic intensity, as well as structural safety from collapse at extreme seismic intensity.

Experimental and numerical study on the effect due to passengers on flexural vibrations in railway vehicle carbodies

Experimental and numerical study on the effect due to passengers on flexural vibrations in railway vehicle carbodies

An Improved Force Feedback Control Algorithm for Active Tendons

An active tendon, consisting of a displacement actuator and a co-located force sensor, has been adopted by many studies to suppress the vibration of large space flexible structures. The damping, provided by the force feedback control algorithm in these studies, is small and can increase, especially for tendons with low axial stiffness. This study introduces an improved force feedback algorithm, which is based on the idea of velocity feedback. The algorithm provides a large damping ratio for space flexible structures and does not require a structure model. The effectiveness of the algorithm is demonstrated on a structure similar to JPL-MPI. The results show that large damping can be achieved for the vibration control of large space structures.

Energy dissipation in engineered sand of large damping ratio

Many geotechnical problems such as seismic resistant designs and machine vibrations require the installation of dampers or isolators to control the amplitude of vibrations. Engineered fills designed with increased capability of dissipating energy can provide a more economical approach to control excessive vibrations. This study presents a novel technique to increase the damping ratio of sand without affecting its stiffness and shear strength. The increase in damping ratio is evaluated by performing resonant column tests on the engineered sand. The damping ratio of the sand is increased by adding a controlled amount of viscoelastic material to the voids. The resonant column tests indicate that the damping ratio of the sand can be increased manifold without affecting the shear modulus. The micromechanical evaluation of the results shows a good correlation between the particle surface area in contact with the pore-mixture and the damping ratio of the sand. The suitability of engineered sand as foundation material is also evaluated by performing direct shear tests. The direct shear tests on mixtures indicate similar or better shear strength parameters compared to pure sand.

Passively controlled MR damper in the benchmark structural control problem for seismically excited highway bridge

In this paper, we propose a simple control approach to produce negative stiffness hysteretic loops for the response control of base-isolated bridges. The combination of hysteretic loops of the controller with those of the bearing results in virtually rigid perfectly plastic force–deformation characteristics possessing large damping ratio without transmitting excessive force to other structural members. The proposed approach has the potential to be implemented as a passive approach. In this paper, the application of this approach for the response control of the benchmark structural control problem for seismically excited highway bridge has been presented. Copyright © 2009 John Wiley & Sons, Ltd.

Parameterized design of nonlinear feedback controllers for servo positioning systems

Parameterized design of nonlinear feedback controllers for servo positioning systems

Application of pseudo‐negative stiffness control to the benchmark cable‐stayed bridge

AbstractThe effectiveness of a variable damper employing pseudo‐negative stiffness control on benchmark cable‐stayed bridges was studied. Combination of a pseudo‐negative stiffness hysteretic loop produced by the variable damper plus elastic stiffness of the deck‐tower connections produces a hysteretic loop that approaches rigid perfectly plastic force–deformation characteristics with a large damping ratio. The advantage is that sensors are required only at damper connections to measure relative displacements. Moreover, the small amount of sensors and simple algorithm reduce the source of errors and uncertainties. Comparisons are made between passive, pseudo‐negative stiffness, and active control for the phase II benchmark bridge. The results of pseudo‐negative stiffness control are significantly better than those of passive control and comparable to those of active control. Copyright © 2003 John Wiley & Sons, Ltd.

Passive and semi‐active seismic response control of a cable‐stayed bridge

AbstractEffectiveness of passive and semi‐active seismic response control on a cable‐stayed bridge was studied by numerical analyses. An existing cable‐stayed bridge which has fixed‐hinge connections between deck and towers is modeled and its connections were replaced by isolation bearings and dampers. The isolation bearings are of elastic and hysteretic type. The dampers are of linear and variable type. The variable damper uses semi‐active control that incorporates a pseudo‐negative stiffness algorithm. A pseudo‐negative stiffness hysteretic loop produced by the variable damper, combined with a positive stiffness curve of the deck‐tower connections, creates nearly rigid–perfectly plastic force–deformation characteristics with a large damping ratio. The damping ratio for the main mode of the bridge for both passive and semi‐active control was also calculated. Soil‐structure interaction and three‐dimensional effects on structural responses were studied. Copyright © 2002 John Wiley & Sons, Ltd.