• Smart Structures and Systems
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• v.31 no.1
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• pp.89-100
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• 2023

This paper conducts a parametric study of a new tuned mass damper with pre-strained superelastic SMA helical springs (SMAS-TMD) on the vibration reduction effect. First, a force-displacement relation model of superelastic SMA helical spring is presented based on the multilinear constitutive model of SMA material, and the tension tests of the six SMA springs fabricated are implemented to validate the mechanical model. Then, a dynamic model of a single floor steel frame with the SMAS-TMD damper is set up to simulate the seismic responses of the frame, which are testified by the shaking table tests. The wire diameter, initial coil diameter, number of coils and pre-strain length of SMA springs are extracted to investigate their influences on the seismic response reduction of the frame. The numerical and experimental results show that, under different earthquakes, when the wire diameter, initial coil diameter and number of coils are set to the appropriate values so that the initial elastic stiffness of the SMA spring is between 0.37 and 0.58 times of classic TMD stiffness, the maximum reduction ratios of the proposed damper can reach 40% as the mass ratio is 2.34%. Meanwhile, when the pre-strain length of SMA spring is in a suitable range, the SMAS-TMD damper can also achieve very good vibration reduction performance. The vibration reduction performance of the SMAS-TMD damper is generally equal to or better than that of the classic optimal TMD, and the proposed damper effectively suppresses the detuning phenomena that often occurs in the classic TMD.

• Earthquakes and Structures
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• v.14 no.5
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• pp.459-465
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• 2018

Reducing response of buildings during earthquakes by mass dampers, has been examined in many articles and books. Nowadays, many researchers are trying to realistically examine this type of dampers by new methods of performance. In this paper, for the better study of tuned mass damper (TMD), two schematic models are presented for a passive TMD with softening stiffness (softening TMD) and a passive TMD with hardening stiffness (hardening TMD). Then by modeling and analysis of the damper on a single degree of freedom (SDOF) structure and an 11-story steel building, the dampers performance was evaluated. State space was used for damper and structure modeling and to solve nonlinear equations, the Newton-Raphson method was used. The results show that when the structure is subjected to the Chi-Chi earthquake, response of the sixth floor in the system without TMD reduces 54.0% in comparison to the structure with softening TMD. This percentage of reduction for hardening TMD is 55.0%. Also for the Tabas earthquake, reduction in the RMS acceleration of the sixth floor in the system with hardening TMD is 96.2% more than the structure without TMD. This percentage of reduction for hardening TMD is 96.3%.

• Structural Engineering and Mechanics
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• v.75 no.2
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• pp.229-237
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• 2020

The steel slit shear wall (SSSW), made by cutting vertical slits in a steel plate, is increasingly used for the seismic protection of building structures. In the domain of thin plate shear walls, the out-of-plane buckling together with the potential fracture developed at slit ends at large lateral deformation may result in degraded shear strength and energy dissipation, which is not desirable in view of seismic design. To address this issue, the present study proposed a new type of SSSW made by intentionally introducing initial out-of-plane folding into the originally flat slitted plate. Quasi-static cyclic tests on three SSSWs with different amplitudes of introduced out-of-plane folding were conducted to study their shear strength, elastic stiffness, energy dissipation capacity and buckling behavior. By introducing proper amplitude of out-of-plane folding into the SSSW fracture at slit ends was eliminated, plumper hysteretic behavior was obtained and there was nearly no strength degradation. A method to estimate the shear strength and elastic stiffness of the new SSSW was also proposed.

• Tribology and Lubricants
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• v.32 no.4
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• pp.107-112
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• 2016

This paper presents a rotordynamic analysis of the reduction gear system applied to the 250 kW super critical CO₂ cycle. The reduction gear system consists of an input shaft, intermediate shaft, and output shaft. Because of the high rotating speed of the input shaft, we install tilting pad bearings, rolloer bearings support the intermediate and output shafts. To predict the tilting pad bearing performance, we calculate the applied loads to the tilting pad bearings by considering the reaction forces from the gear. In the rotordynamic analysis, gear mesh stiffness results in a coupling effect between the lateral and torsional vibrations. The predicted Campbell diagram shows that there is not a critical speed lower than the rated speed of 30,000 rpm of the input shaft. The predicted modes on the critical speeds are the combined bending modes of the intermediate and output shaft, and the lateral vibrations dominate when compared to the torsional vibrations. The damped natural frequency does not strongly depend on the rotating speeds, owing to the relatively low rotating speed of the intermediate and output shaft and constant stiffness of the roller bearing. In addition, the logarithmic decrements of all the modes are positive; therefore all modes are stable.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.818-823
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• 2012

Assessment of the dynamics properties, like damping, dynamic stiffness and resonance sharpness is essential for the development of a robust system, specifically for the reduction of a traction motor noise. A practical method for identifying dynamic characteristics of a traction motor hosing for an electric vehicle is proposed. Assembling using interference fit of the components of the motor is attributed to the main cause of strong nonlinearity. It is well known that nonlinearity of a structure makes it difficult to assess damping properties or dynamic characteristics of the system. This research presents a practical damping or dynamic stiffness identifying procedures for a nonlinear system according to the boundary condition between assembled components. Based on the simple idea that impact forces of modal tests are highly affected on the condition of the hammer tip, Auto Power Spectrum of the impact forces are used to assess the assembling condition and dynamic characteristics of the system, especially, damping of the system.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.153-160
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• 2002

A new system identification method based on tunnel deformation data is proposed to find the damage in the lining structure. For this, an inverse problem in which the deformation data and dead load of concrete lining are known a priori is introduced to estimate the degree and location of the damages. Models based on uniform reduction of stiffness and homogenized crack concept are individually employed to compare the applicability and relative advantages of the models. Numerical analyses are peformed for the idealized tunnel structure and the effect of white noise, common in most measurement data, is also included to better understand the suitability of the proposed models. As a result, model 1 based on uniform stiffness reduction method is shown to be relatively insensitive to the noise, while model 2 with the homogenized crack concept is proven to be easily applied to the field situation since the effect of stiffness reduction is rather small.

• Korean Journal of Exercise Nutrition
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• v.23 no.3
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• pp.39-44
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• 2019

[Purpose] Weight loss can reduce obesity-induced arterial stiffening that is attributed to decreased inflammation. Angiopoietin-like protein 2 (ANGPTL2) is a pro-inflammatory adipokine that is upregulated in obesity and is important in the progression of atherosclerosis and cardiovascular disease. The purpose of this study is to investigate the effects of dietary modification on circulating ANGPTL2 levels and arterial stiffness in overweight and obese men. [Methods] Twenty-two overweight and obese men (with mean age of 56 ± 2 years and body mass index of 28.6 ± 2.6 kg/m²) completed a 12-week dietary modification program. We measured the arterial compliance and β-stiffness index (as the indices of arterial stiffness) and serum ANGPTL2 levels before and after the program. [Results] After the 12-week dietary modification, body mass and daily energy intake were significantly reduced. Arterial compliance was significantly increased and β-stiffness index was significantly decreased after the 12-week dietary modification program. Serum ANGPTL2 levels were significantly decreased. Also, the changes in arterial compliance were negatively correlated with the changes in serum ANGPTL2 levels, whereas the changes in β-stiffness index were positively correlated with the changes in serum ANGPTL2 levels. [Conclusion] These results suggest that the decrease in circulating ANGPTL2 levels can be attributed to the dietary modification-induced reduction of arterial stiffness in overweight and obese men.

• Structural Engineering and Mechanics
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• v.88 no.1
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• pp.53-65
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• 2023

With the gradual implementation of long-span suspension bridges into high-speed railway operations, the main beam's bending stiffness contribution to the live load response permanently grows. Since another critical control parameter of railway suspension bridges is the beam-end rotation angle, it should not be ignored by treating the main beam deflection as the only deformation response. To this end, the current study refines the existing method of the main cable shape and simply supported beam bending moment analogy. The bending stiffness of the main beam is considered, and the main beam's analytical expressions of deflection and rotation angle in the whole span are obtained using the cable-beam deformation coordination relationship. Taking a railway suspension bridge as an example, the effectiveness and accuracy of the proposed analytical method are verified by the finite element method (FEM). Comparison of the results by FEM and the analytical method ignoring the main beam stiffness revealed that the bending stiffness of the main beam strongly contributed to the live load response. Under the same live load, as the main beam stiffness increases, the overall deformation of the structure decreases, and the reduction is particularly noticeable at locations with original larger deformations. When the main beam stiffness is increased to a certain extent, the stiffening effect is no longer pronounced.

• Composites Research
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• v.17 no.5
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• pp.39-46
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• 2004

In this study, the strength of spatially reinforced composites (SRC) are predicted by using stiffness reduction for each structural element composed of a rod stiffness in each direction and a matrix stiffness proportional to its rod volume fraction. Maximum failure strain criteria is applied to rod failure, and modified Tsai-Wu failure criteria to matrix failure. The material properties composed of the tensile failure strain of a rod, the compressive failure strain of 3D SRC, the tensile and compressive strength of the 3D SRC in the $45^{\cir}$ rotated direction from a rod and the shear strength of the 3D SRC are measured to predict the SRC strength. The strength distributions of the 3D/4D SRC in rod and off-rod direction have the largest and the smallest values, respectively. A variable load step is selected to increase an efficiency of strength distribution calculation. Uniform load step is applied when a load history is needed. The results of compressive strength from analysis and experiment show the 18 % difference though the initial slop is coincident with each other.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.797-803
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• 2019

This study was carried out to reduce the lateral vibration of high-speed electric multiple units. In the study, the high-speed electric multiple unit prototype (HEMU-430X) has a high lateral vibration at low equivalent conicity regardless of the wheel profiles (XP55, GV40, S1002). As wheel wear progresses and the equivalent conicity increases, the lateral vibration tends to decrease. The reason is that a combination of the suspension characteristics causes the body and bogie to resonate at a frequency of 1.4 Hz when the equivalent conicity is low, resulting in body hunting. An investigation of the lateral vibration of overseas high-speed trains showed that a decrease in the hydraulic stiffness of the yaw damper could improve the vibration. The series stiffness of the yaw damper is a combination of the hydraulic stiffness and elastic joint. In this study, an attempt was made to improve the lateral vibration by lowering the stiffness of the elastic joint. The series stiffness of the adjusted yaw damper was approximately 60% compared to the original one. The on track test results showed improvement in the lateral vibration for both running directions. The vibration reduction method of this study can be used for EMU-250 and EMU-320 in future commercial operations.