• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2003년도 추계학술대회논문집
• /
• pp.138-140
• /
• 2003

In this paper, It is introduced to electromagnetic sound by AC motor and example of application by experiments. And Through adjusting some design parameter related to Mass, Damping coefficient and Stiffness of the system, we could find best design point to reduce motor total noise as well as noise component at AC power frequency (2f).

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
• /
• pp.362-369
• /
• 2002

This paper mainly propose the new passive vibration control device, named BRV(the bridge reduced vibration), for reducing excessive traffic-induced vibration of bridges and for measuring performance of BRV numerical example was simulated. The purpose of BRV is mainly on reducing vertical acceleration and displacement of bridge. In BRV we can control the stiffness and damping coefficient to accept the performance we want. The result of simulation showed that the vertical acceleration and displacement was effectively diminished. It would be concluded that BRV can be used to improve the serviceability of bridge and fatigue life etc.

• Tribology and Lubricants
• /
• 제10권2호
• /
• pp.43-50
• /
• 1994

The hydrodynamic bearing is accepted in many rotating systems because it has a large load carrying capacity. But the anisotropic pressure distribution of the bearing can arise the unstable vibration phenomenon over a certain speed. The magnetic bearing is an active element so that the unstable phenomenon of the hydrodynamic bearing, which is induced by the anisotropic support pressure of the oil film, can be controlled if the control algorithm and the controller gains are chosen appropriately. In this study, we investigate the stabilization method of the hydrodynamic bearing system composing the hybrid bearing which is the single unit of hydrodynamic bearing and magnetic bearing. The load carrying conditions of the hybrid bearing is modelled by the sum of the stiffness and damping coefficients of the hydrodynamic and the magnetic bearings in each direction. The dynamics of the rotor is analyzed by the Finite Element Method and the stability limit is determined by the eigenvalues of the hybrid bearings and shaft system. The eigenvalue study of the system shows that the stability limit of the hybrid bearing is increased compared to that of the hydrodynamic bearing. A Small increment of the stiffness and damping coefficient of the hybrid bearings by the magnetic actuators can increase the stability limit of the system. In this paper we tried to show the design references of the hybrid bearings by using the nondimensional bearing parameters. The analysis results show the possibilities of the stability limit increment of the hydrodynamic bearing system by combining the magnetic bearing.

• Smart Structures and Systems
• /
• 제14권5호
• /
• pp.831-845
• /
• 2014

This paper proposed a discrete wavelet transform based method for time-varying physical parameter identification of shear type structures. The time-varying physical parameters are dispersed and expanded at multi-scale as profile and detail signal using discrete wavelet basis. To reduce the number of unknown quantity, the wavelet coefficients that reflect the detail signal are ignored by setting as zero value. Consequently, the time-varying parameter can be approximately estimated only using the scale coefficients that reflect the profile signal, and the identification task is transformed to an equivalent time-invariant scale coefficient estimation. The time-invariant scale coefficients can be simply estimated using regular least-squares methods, and then the original time-varying physical parameters can be reconstructed by using the identified time-invariant scale coefficients. To reduce the influence of the ill-posed problem of equation resolving caused by noise, the Tikhonov regularization method instead of regular least-squares method is used in the paper to estimate the scale coefficients. A two-story shear type frame structure with time-varying stiffness and damping are simulated to validate the effectiveness and accuracy of the proposed method. It is demonstrated that the identified time-varying stiffness is with a good accuracy, while the identified damping is sensitive to noise.

• Steel and Composite Structures
• /
• 제36권3호
• /
• pp.339-353
• /
• 2020

This study investigates the seismic performance of steel reinforced concrete (SRC) T-shaped columns under low cyclic loading tests. Based on test results of ten half-scale column specimens, failure patterns, hysteretic behavior, skeleton curves, ultimate strength, ductility, stiffness degradation and energy dissipation capacity were analyzed. The main variables included loading angles, axial compression ratios and steel ratios. The test results show that the average values of the ductility factor and the equivalent viscous damping coefficient with respect to the failure of the columns were 5.23 and 0.373, respectively, reflecting good seismic performance. The ductility decreased and the initial stiffness increased as the axial compression ratio of the columns increased. The strength increased with increasing steel ratio, as expected. The columns displaced along the web had higher strength and initial stiffness, while the columns displaced along the flange had better ductility and energy dissipation capacity. Based on the test and analysis results, a formula is proposed to calculate the effective stiffness of SRC T-shaped columns.

• Structural Engineering and Mechanics
• /
• 제74권1호
• /
• pp.19-32
• /
• 2020

Metallic energy-dissipation dampers are widely used in structures. They are comprised of an added damping and stiffness (ADAS) device with many parallel, diamond-shaped hole plates, the neck width of which is an important parameter. However, no studies have analyzed the neck width's influence on the ADAS device's performance. This study aims to better understand that influence by conducting a pseudo-static test on ADAS, with three different neck widths, and performing finite element analysis (FEA) models. Based on the FEA results and mechanical theory, a design neck width range was proposed. The results showed that when the neck width was within the specified range, the diamond-shaped hole plate achieved an ideal yield state with minimal stress concentration, where the ADAS had an optimal energy dissipation performance and the brittle shear fracture on the neck was avoided. The theoretical values of the ADAS yield loads were in good agreement with the test values. While the theoretical value of the elastic stiffness was lower than the test value, the discrepancy could be reduced with the proposed modified coefficient.

• Interaction and multiscale mechanics
• /
• 제6권4호
• /
• pp.339-356
• /
• 2013

This paper investigates the optimized parameters of Tuned Mass Dampers (TMDs) for vibration control of high-rise structures including Soil Structure Interaction (SSI). The Artificial Bee Colony (ABC) method is employed for optimization. The TMD Mass, damping coefficient and spring stiffness are assumed as the design variables of the controller; and the objective is set as the reduction of both the maximum displacement and acceleration of the building. The time domain analysis based on Newmark method is employed to obtain the displacement, velocity and acceleration of different stories and TMD in response to 6 types of far field earthquakes. The optimized mass, frequency and damping ratio are then formulated for different soil types; and employed for the design of TMD for the 40 and 15 story buildings and 10 different earthquakes, and well results are achieved. This study leads the researchers to the better understanding and designing of TMDs as passive controllers for the mitigation of earthquake oscillations.

• Interaction and multiscale mechanics
• /
• 제4권3호
• /
• pp.239-245
• /
• 2011

The dynamic mechanical behavior of silicone rubber reinforced with multi-walled carbon nanotubes (MWCNTs) has been investigated in this study. The MWCNT-reinforced nanocomposites are tested in compression mode through dynamic mechanical analysis (DMA). Multiple effects including MWCNT loading, testing frequency, dynamic strain amplitude, and pre-strain level are taken into consideration. Results show that, by adding 5 wt% of MWCNTs, the dynamic stiffness and damping coefficient of the silicone rubber are significantly enhanced. It is further observed that the dynamic mechanical properties of the nanocomposites are sensitive to dynamic strain amplitude but only slightly affected by pre-strains.

• 대한기계학회논문집A
• /
• 제37권1호
• /
• pp.17-23
• /
• 2013

지하철 전동차에는 2 차 현가장치인 공기스프링의 횡강성 저하특성을 보강하기 위해 대차와 차체 사이에 횡댐퍼를 설치하게 되는데, 이 횡댐퍼는 주행 시 차체의 횡진동을 감소시키는 역할을 수행한다. 그러나, 횡댐퍼의 감쇠력이 저하될 경우 전동차의 주행안정성과 승차감이 함께 악화되며, 차체의 횡방향 운동이 증가되는 요인으로 작용하게 된다. 본고에서는 전동차 주행 시 비정상적으로 발생하는 충격에 대하여 그 원인을 살펴보고 해결방안을 마련하고자 횡댐퍼의 감쇠력에 따른 차체의 횡변위를 동역학 시뮬레이션을 통해 검토하였으며, 그에 따라 충격에 의한 이상진동 및 소음의 발생 유무를 파악하였다. 그로부터 충격이 발생되지 않는 적정 감쇠력을 구하고자 하였다.

• 한국산학기술학회논문지
• /
• 제18권10호
• /
• pp.81-87
• /
• 2017

본 연구는 고속열차 시운전 시험과 이에 따른 주행동특성 고찰 및 개선에 관한 것이다. 고속열차 시운전 시험을 통한 선행 연구에서 도출한 요댐퍼 설치 방법에 따른 후미 진동 개선 방안을 실제 고속철도 차량의 시운전시에 적용하여 후미 진동 저감 효과가 있음을 확인하였다. 또한 전체 차량에 대한 진동저감 방안을 동역학 해석 소프트웨어를 사용하여 수치 해석적 방법으로 도출하였으며, 그 효과를 시운전 시험을 통하여 확인하였다. 개선된 설계안은 실제 2층 고속열차 객차에 적용되어 주행동특성 문제없이 시운전을 진행하였다. 차세대 고속열차 임계속도에 영향을 미치는 현가장치 파라미터들에 대한 민감도 분석을 수행하였으며, 임계속도에 크게 영향을 미치는 4개의 설계변수를 도출하였는데, 이는 1차 탄성조인트 열차진행 방향 강성, 2차 요댐퍼 시리즈 강성, 2차 횡댐퍼 댐핑계수, 차간 댐퍼 댐핑계수 순이었다. 이 설계변수에 대한 최적화를 통하여 임계속도를 23.3% 향상시키는 현가장치 파라미터를 제시하였으며, 이는 차세대 고속열차 상용화 모델의 설계에 이용될 수 있다.