• International Journal of Automotive Technology
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• 제5권1호
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• pp.61-67
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• 2004

This paper suggests two simple two-degree-of-freedom models to describe the dynamical interaction between the pad and the disc of a disc brake system. Separate models for in-plane and out -of-plane vibration are described. Although a brake pad and disc have many modes of vibration, the interaction between a single mode of each component is considered as this is thought to be crucial for brake noise. For both models, the pad and the disc are connected by a sliding friction interface having a velocity dependent friction coefficient. In this paper, it is shown that this friction model acts as negative damping in the system that describes the in-plane vibration, and as negative stiffness in system that describes the out-of-plane vibration. Stability analysis is performed to investigate the conditions under which the systems become unstable. The results of the stability analysis show that the damping is the most important parameter for in-plane vibration, whereas the stiffness is the most important parameter for the out-of-plane vibration.

• Computers and Concrete
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• 제30권3호
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• pp.175-183
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• 2022

To study the working mechanism and size effect of an innovative dovetail UHPC joint originated from the 5th Nanjing Yangtze River Bridge, a large-scale testing subject to negative bending moment was conducted and compared with the previous scaled specimens. The static responses, i.e., the crack pattern, failure mode, ductility and stiffness degradation were analyzed. It was found that the scaled specimens presented similar working stages and working mechanism with the large-scale ones. However, the post-cracking ductility and relative stiffness degradation all decrease with the enlarged length/scale, apart from the relative stiffness after flexural cracking. The slab stiffness at the flexural cracking stage is 90% of the initial stiffness while only 24% of the initial stiffness reserved in the ultimate stage. Finite element model (FEM) was established and compared with the experiments to verify its effectiveness in exploring the working mechanism of the innovative joint. Based on this effective method, a series of FEMs were established to further study the influence of material strength, pre-stressing level and ratio of reinforcement on its deflection-load relationship. It is found that the ratio of reinforcement can significantly improve its load-carrying capacity among the three major-influenced factors.

• Smart Structures and Systems
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• 제21권3호
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• pp.359-371
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• 2018

Strong seismic events commonly cause large drift and deformation, and functionality failures in the superstructures. One way to prevent functionality failures is to design structures which are ductile and flexible through yielding when subjected to strong ground excitations. By developing forces that assist motion as "negative stiffness forces", yielding can be achieved. In this paper, we adopt the weakening and damping method to achieve a new approach to reduce all of the structural responses by further adjusting damping phase. A semi-active control system is adopted to perform the experiments. In this adaptation, negative stiffness forces through certain devices are used in weakening phase to reduce structural strength. Magneto-rheological (MR) dampers are then added to preserve stability of the structure. To adjust the voltage in MR dampers, an inverse model is employed in the control system to command MR dampers and generate the desired control forces, where a velocity control algorithm produces initial required control force. An extensive numerical study is conducted to evaluate proposed methodology by using the smart base-isolated benchmark building. Totally, nine control systems are examined to study proposed strategy. Based on the numerical results of seven earthquakes, the use of proposed strategy not only reduces base displacements, base accelerations and base shear but also leads to reduction of accelerations and inter story drifts of the superstructure. Numerical results shows that the usage of inverse model produces the desired regulated damping, thus improving the stability of the structure.

• 한국자동차공학회논문집
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• 제18권2호
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• pp.114-121
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• 2010

As a vehicle speed increases, more vibration energy is transmitted from chassis to a driver. Current isolation system for the driver's seat by damping control can reduce the transmitted vibration energy near resonance area. But in higher frequency region than natural frequency multiplied by $\sqrt{2}$, the vibration energy transmitted to the driver has a tendency to be increased. Therefore, the method by natural frequency reduction of the system is preferred to increase the effectiveness of the anti-vibration. However, the natural frequency could not be freely reduced due to the nature of the isolation system structure. A new passive suspension system to reduce the natural frequency is proposed. The theoretical analysis and experimental results show better vibration attenuation compared with the current isolation system.

• 대한의용생체공학회:의공학회지
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• 제34권4호
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• pp.218-225
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• 2013

In this paper hair bundle feature model and integration method for hair cell models were proposed. The proposed hair bundle feature model was based on spring-damper-mass model. Input of integrated vestibular hair cell model was frequency and output was interspike interval of hair cell that was reflected the feature of hair bundles. Irregular afferents that had a great gain variation showed reduction of negative stiffness section. Regular afferents that had a small gain variation, however, showed same feature with base negative stiffness feature. As a result, integrated vestibular hair cell model showed almost the same modeling data with experimental data in the modeled eleven frequency bands. It is verified that the proposed model is a good model for hair bundle feature modeling.

• Steel and Composite Structures
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• 제47권2호
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• pp.239-251
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• 2023

The stiffness evaluation of cracked base metal is of great guidance to fatigue crack reinforcement. By carrying out fatigue tests and numerical simulation of typical cracking details in steel box girder, the strain-degradation law of cracked base metal was analyzed and the relationship between base metal stress and its displacement (stiffness) was explored. The feasibility of evaluating the stress of cracked base metal based on the stress field at the crack tip was verified. The results demonstrate that the stiffness of cracked base metal shows the fast-to-slow degradation trend with fatigue cracking and the base metal at 50mm or more behind the crack tip basically lose its bearing capacity. Drilling will further accelerate stiffness degradation with the increase of hole diameters. The base metal stress has a negative linear relation with its displacement (stiffness), The stress of cracked base metal is also related to stress intensity factor and its relative position (distance, included angle) to the crack tip, through which the local stiffness can be effectively evaluated. Since the stiffness is not uniformly distributed along the cracked base metal, the reinforcement patch is suggested to be designed according to the stiffness to avoid excessive reinforcement for the areas incompletely unloaded.

• Steel and Composite Structures
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• 제42권6호
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• pp.765-777
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• 2022

Ultra high performance concrete (UHPC) can be used in the UHPC-steel composite structures especially for bridge structures to achieve high stiffness and high fatigue resistance with low self-weight. The structural performances of UHPC-steel composite slabs subjected to hogging moment have a significant influence on the global stiffness and durability of UHPC-steel composite structures. In order to study the structural behaviors of non-steam-cured UHPC-steel composite slabs subjected to negative moment, five composite slabs combined the thin UHPC layers to steel plates via shear stud connecters with the diameter of 16mm were fabricated and tested under negative moment. The test program aimed to investigate the effect of stud spacing and longitudinal reinforcement ratios on the failure mode, load-deflection behaviors, cracking patterns, bond-slips, and carrying capacities of composite slabs subjected to negative moment. In addition, direct tensile tests for the dog-bone UHPC specimens with longitudinal reinforcement bars were carried out to study the effect of reinforcement bars on the tensile strength of UHPC in the thin structure members. Based on the experimental results, analytical models were also developed to predict the cracking load and ultimate load of UHPC-steel composite slabs subjected to negative moment.

• 한국운동역학회지
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• 제27권2호
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• pp.109-116
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• 2017

Objective: This study aimed to investigate the relationship between leg stiffness and kinematic variables according to load while running. Method: Participants included eight healthy men (mean age, $22.75{\pm}1.16years$; mean height: $1.73{\pm}0.01m$; mean body weight, $71.37{\pm}5.50kg$) who ran with no load or a backpack loaded with 14.08% or 28.17% of their body weight. The analyzed variables included leg stiffness, ground contact time, center of gravity (COG) displacement and Y-axis velocity, lower-extremity joint angle (hip, knee, ankle), peak vertical force (PVF), and change in stance phase leg length. Results: Dimensionless leg stiffness increased significantly with increasing load during running, which was the result of increased PVF and contact time due to decreased leg lengths and COG displacement and velocity. Leg length and leg stiffness showed a negative correlation (r = -.902, $R^2=0.814$). COG velocity showed a similar correlation with COG displacement (r = .408, $R^2=.166$) and contact time (r = -.455, $R^2=.207$). Conclusion: Dimensionless leg stiffness increased during running with a load. In this investigation, leg stiffness due to load increased was most closely related to the PVF, knee joint angle, and change in stance phase leg length. However, leg stiffness was unaffected by change in contact time, COG velocity, and COG displacement.

• 한국소음진동공학회논문집
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• 제21권4호
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• pp.352-356
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• 2011

The isolation performance of a linear vibration isolator is limited to the ratio of stiffness to mass it supports. The stiffness of the isolator must be large enough to hold the weight. This results in the deterioration of the isolation performance. Recently, to overcome this fundamental limitation, the HSLDS(high-static-low-dynamic-stiffness) magnetic vibration isolator was introduced and its isolation characteristic was investigated theoretically. In this paper, the isolation performance of the HSLDS magnetic isolator is examined experimentally. Considerable amount of experiments are performed by carefully considering nonlinear characteristics. The experimental results verify the practical usability promisingly and agree with the theoretical studies, i.e. its performance is largely dependent on the key design parameter.

• Steel and Composite Structures
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• 제20권1호
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• pp.57-70
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• 2016

The predominant type of buckling that I-steel concrete composite beams experience in the negative moment area is distortional buckling. The key factors that affect distortional buckling are the torsional and lateral restraints by the bottom flange. This study thoroughly investigates the equivalent lateral and torsional restraint stiffnesses of the bottom flange of an I-steel concrete composite beam under negative moments. The results show a coupling effect between the applied forces and the lateral and torsional restraint stiffnesses of the bottom flange. A formula is proposed to calculate the critical buckling stress of the I-steel concrete composite beams under negative moments by considering the lateral and torsional restraint stiffnesses of the bottom flange. The proposed method is shown to better predict the critical bending moment of the I-steel composite beams. This article introduces an improved method to calculate the elastic foundation beams, which takes into account the lateral and torsional restraint stiffnesses of the bottom flange and considers the coupling effect between them. The results show a close match in results from the calculation method proposed in this paper and the ANSYS finite element method, which validates the proposed calculation method. The proposed calculation method provides a theoretical basis for further research on distortional buckling and the ultimate resistance of I-steel concrete composite beams under a variable axial force.