• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.8
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• pp.849-855
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• 2008

An experimental method based on contact resonance is developed to extract the contact parameters of mechanical joints under various clamped conditions. Mechanical joint parameters of shear contact stiffness and damping were extracted for different physical joint parameters such as surface finish of the mating surfaces, the presence of lubrication, the effect of the clamping pressure, and shear load. It was found that the shear contact stiffness values decreased with increasing clamping load and increased with increasing shear loading. Contact damping ratio values were almost constant with clamping load, but decreased with increasing shear load. Moreover, rough surfaces exhibited the highest shear stiffness and contact damping compared to smooth surfaces.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.3
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• pp.209-217
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• 1997

Effect of Co content on the microstructure and damping capacity of Fe-23%Mn-X%Co alloy was studied. The volume fraction of ${\varepsilon}$ martensite of the alloy was increased with increasing Co content. The hardness was increased with lowering cooling temperature and increasing Co content in Fe-23%Mn-X%Co alloy, which is ascribed to the increase in ${\varepsilon}$ martensite content. The damping capacity of Fe-23%Mn-X%Co alloy was linearly increased with increasing the strain amplitude, and was constant regardless of Co content at the same volume fractions of ${\varepsilon}$ martensite when the low strain amplitudes ($1{\sim}3{\times}10^{-4}$) were applied, while the damping capacity with large strain amplitudes ($4{\sim}6{\times}10^{-4}$) became higher with increasing Co content at all valume fractions of ${\varepsilon}$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.1
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• pp.75-82
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• 2016

In this study, a cross-damped low vibration controller was developed to reduce vibration in ultra-precision dual stage driven by master/slave principle. In master-slave structure, the master stage leads the driving motion and the slave stage follows it so as to maintain a constant gap between two stages. In this structure, a small perturbation of master stage makes big oscillations in slave servoing stage, so a low damped master stage composed of voice coil motor makes a long vibration in settling area after driving motion profile. In this research, an effective feedback damping algorithm for increase the damping characteristics of the dual stage was developed. The designed velocity damping algorithm improves the system stability and reduces the settling time of the whole system. Simulation and experimental results show that the developed algorithm reduces settling time and improves the regulating performance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.35-38
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• 2011

Damping characteristic according to acoustic cavity's geometries was investigated to control the high frequency combustion instability occurring in the Liquid Rocket Combustion Chamber by experimental test and linear analysis. Its diameter was determined as a design parameter and its orifice length and diameter were appointed as fixed parameter in this study. Result shows that the damping capacity has been almost constant through all the experiments despite using the same orifice and helmholtz resonators which have different volume.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.12
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• pp.866-873
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• 2015

The transverse vibration of the deploying beam from rigid hub was analyzed by simulation and experiment. The linear governing equation of the deploying beam was obtained using the Euler-Bernoulli beam theory. To discretize the governing equation, the Galerkin method was used. After transforming the governing equation into the weak form, the weak form was discretized. The discretized equation was expressed by the matrix-vector form, and then the Newmark method was applied to simulate. To consider the damping effect of the beam, we conducted the modal test with various beam length. The mass proportional damping was selected by the relation of the first and second damping ratio. The proportional damping coefficient was calculated using the acquired natural frequency and damping ratio through the modal test. The experiment was set up to measure the transverse vibration of the deploying beam. The fixed beam at the carriage of the linear actuator was moved by moving the carriage. The transverse vibration of the deploying beam was observed by the Eulerian description near the hub. The deploying or retraction motion of the beam had the constant velocity and the velocity profile with acceleration and deceleration. We compared the transverse vibration results by the simulation and experiment. The observed response by the Eulerian description were analyzed.

• Advances in Computational Design
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• v.2 no.3
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• pp.123-141
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• 2017

Solving a system of linear or non-linear equations is required to analyze any kind of structures. There are many ways to solve a system of equations, and they can be classified as implicit and explicit techniques. The explicit methods eliminate round-off errors and use less memory. The dynamic relaxation method (DR) is one of the powerful and simple explicit processes. The important point is that the DR does not require to store the global stiffness matrix, for which it just uses the residual loads vector. In this paper, a new approach to the DR method is expressed. In this approach, the damping, mass and time steps are similar to those of the traditional method of dynamic relaxation. The difference of this proposed method is focused on the method of calculating the damping. The proposed method is expressed such that the time step is constant, damping is equal to zero except in steps with maximum energy and the concentrated damping can be applied to minimize the energy of system in this step. In this condition, the calculation of damping in all steps is not required. Then the volume of computation is reduced. The DR method for form-finding of membrane structures is employed in this paper. The form-finding of the three plans related to the membrane structures with different loading is considered to investigate the efficiency of the proposed method. The numerical results show that the convergence rate based on the proposed method increases in all cases than other methods.

• Structural Engineering and Mechanics
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• v.39 no.4
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• pp.465-498
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• 2011

Concrete structures are generally cracked in flexural tension at working loads. Concrete beams with asymmetric section details and crack patterns exhibit different flexural rigidity depending upon the sense of the applied flexural moment. In this paper, three different models, having the same natural period, of such SDOF bilinear dynamical systems have been proposed. The Model-I and Model-II have constant damping coefficient, but the latter is characterized by two stiffness coefficients depending upon the sense of vibration amplitude. The Model-III, additionally, has two damping coefficients as well. In this paper, the dynamical response of Model-III to sinusoidal loading has been investigated and compared with that of Model-II studied earlier. It has been found that Model-III exhibits regular and irregular sub-harmonics, jump phenomena and strong sensitivity to initial conditions, forcing frequency, system period as well as the sense of peak sinusoidal force. The constant sustained load has been found to affect the natural period of the dynamical system. The predictions of Model-I have been compared with those of the approximate linear model adopted in present practice. The behaviour exhibited by different models of the SDOF cracked elastic concrete structures under working loads and the theoretical and practical implications of the approach followed have been critically evaluated.

• Journal of Korean Association for Spatial Structures
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• v.17 no.4
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• pp.123-132
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• 2017

A smart tuned mass damper (TMD) was developed to provide better control performance than a passive TMD for reduction of earthquake induced-responses. Because a passive TMD was developed decades ago, optimal design methods for structural parameters of a TMD, such as damping constant and stiffness, have been developed already. However, studies of optimal design method for structural parameters of a smart TMD were little performed to date. Therefore, parameter studies of structural properties of a smart TMD were conducted in this paper to develop optimal design method of a smart TMD under seismic excitation. A retractable-roof spatial structure was used as an example structure. Because dynamic characteristics of a retractable-roof spatial structure is changed based on opened or closed roof condition, control performance of smart TMD under off-tuning was investigated. Because mass ratio of TMD and smart TMD mainly affect control performance, variation of control performance due to mass ratio was investigated. Parameter studies of structural properties of a smart TMD was performed to find optimal damping constant and stiffness and it was compared with the results of optimal passive TMD design method. The design process developed in this study is expected to be used for preliminary design of a smart TMD for a retractable-roof spatial structure.

• Steel and Composite Structures
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• v.25 no.2
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• pp.141-155
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• 2017

This paper presents an investigation into the magneto-thermo-mechanical vibration and damping of a viscoelastic functionally graded-carbon nanotubes (FG-CNTs)-reinforced curved microbeam based on Timoshenko beam and strain gradient theories. The structure is surrounded by a viscoelastic medium which is simulated with spring, damper and shear elements. The effective temperature-dependent material properties of the CNTs-reinforced composite beam are obtained using the extended rule of mixture. The structure is assumed to be subjected to a longitudinal magnetic field. The governing equations of motion are derived using Hamilton's principle and solved by employing differential quadrature method (DQM). The effect of various parameter like volume percent and distribution type of CNTs, temperature change, magnetic field, boundary conditions, material length scale parameter, central angle, viscoelastic medium and structural damping on the vibration and damping behaviors of the nanocomposite curved microbeam is examined. The results show that with increasing volume percent of CNTs and considering magnetic field, material length scale parameter and viscoelastic medium, the frequency of the system increases and critically damped situation occurs at higher values of damper constant. In addition, the structure with FGX distribution type of CNTs has the highest stiffness. It is also observed that increasing temperature, structural damping and central angle of curved microbeam decreases the frequency of the system.

• Earthquakes and Structures
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• v.26 no.6
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• pp.449-461
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• 2024

The vertical reinforcement connection between the precast reinforced concrete shear wall and the cast-in-place reinforced concrete member is vital to the performance of shear walls under seismic loading. This paper investigated the structural behavior of three precast reinforced concrete shear walls, with different levels of connection (i.e., full connection, partial connection, and no connection), subjected to quasi-static lateral loading. The specimens were subjected to a constant vertical load, resulting in an axial load ratio of 0.4. The crack pattern, failure modes, load-displacement relationships, ductility, and energy dissipation characteristics are presented and discussed. The resultant seismic performances of the three tested specimens were compared in terms of skeleton curve, load-bearing capacity, stiffness, ductility, energy dissipation capacity, and viscous damping. The seismic performance of the partially connected shear wall was found to be comparable to that of the fully connected shear wall, exhibiting 1.7% and 3.5% higher yield and peak load capacities, 9.2% higher deformability, and similar variation in stiffness, energy dissipation capacity and viscous damping at increasing load levels. In comparison, the seismic performance of the non-connected shear wall was inferior, exhibiting 12.8% and 16.4% lower loads at the yield and peak load stages, 3.6% lower deformability, and significantly lower energy dissipation capacity at lower displacement and lower viscous damping.