• International Journal of Highway Engineering
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• v.17 no.4
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• pp.25-31
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• 2015

PURPOSES: Implementation and verification of the simple linear cohesive viscoelastic contact model that can be used to simulate dynamic behavior of sticky aggregates. METHODS: The differential equations were derived and the initial conditions were determined to simulate a free falling ball with a sticky surface from a ground. To describe this behavior, a combination of linear contact model and a cohesive contact model was used. The general solution for the differential equation was used to verify the implemented linear cohesive viscoelastic API model in the DEM. Sensitivity analysis was also performed using the derived analytical solutions for several combinations of damping coefficients and cohesive coefficients. RESULTS : The numerical solution obtained using the DEM showed good agreement with the analytical solution for two extreme conditions. It was observed that the linear cohesive model can be successfully implemented with a linear spring in the DEM API for dynamic analysis of the aggregates. CONCLUSIONS: It can be concluded that the derived closed form solutions are applicable for the analysis of the rebounding behavior of sticky particles, and for verification of the implemented API model in the DEM. The assumption of underdamped condition for the viscous behavior of the particles seems to be reasonable. Several factors have to be additionally identified in order to develop an enhanced contact model for an asphalt mixture.

• Structural Engineering and Mechanics
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• v.83 no.1
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• pp.31-43
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• 2022

A nonlinear gas-spring tuned mass damper is proposed to mitigate the seismic responses of the multi-degree-of-freedom (MDOF) structure, in which the nine-story benchmark model is selected as the controlled object. The nonlinear mechanical properties of the gas-spring are investigated through theoretical analysis and experiments, and the damper's control parameters are designed. The control performance and damping mechanism of the proposed damper attached to the MDOF structure are systematically studied, and its reliability is also explored by parameter sensitivity analysis. The results illustrate that the nonlinear gas-spring TMD can transfer the primary structure's vibration energy from the lower to the higher modes, and consume energy through its own relative movement. The proposed damper has excellent "Reconciling Control Performance", which not only has a comparable control effect as the linear TMD, but also has certain advantages in working stroke. Furthermore, the control parameters of the gas-spring TMD can be determined according to the external excitation amplitude and the gas-spring's initial volume.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.6
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• pp.578-586
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• 2010

This paper describes a theoretical model and acoustic analysis of hysteresis of contacting surfaces subject to compression pressure. Contacting surfaces known to be nonlinear and hysteretic is considered as a simple spring that has a complex stiffness connecting discontinuous displacements between two solid contact boundaries. Mathematical formulation for 1-D interfacial wave propagation between two contacting solids is developed using the complex spring model to derive the dispersion relation between the interface wave speed and the complex interfacial stiffness. Existence of the interface wave propagating along the hysteretic interface is studied in theory and discussed by investigating the solution to the dispersion equation. Unlike the linear interface without hysteresis, there can exist only one distinct mode of interface waves for the hysteretic interface, which is anti-symmetric motion. The anti-symmetric mode of interface wave propagates with the velocity faster than the Rayleigh surface wave but less than the shear wave depending on the interfacial stiffness. If the contacting surfaces are compressed so much that the linear interfacial stiffness is very high, the hysteretic stiffness does not affect the interface wave velocity. However, it has an effect on the speed of interface wave for a loosely contact surfaces with a relatively low linear stiffness. It is also found that the phase velocity of anti-symmetric wave mode converges to the shear wave velocity in despite of the linear stiffness value if the hysteretic stiffness approaches 0.5.

• Journal of Drive and Control
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• v.16 no.1
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• pp.7-13
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• 2019

The objective of this study was to present a damped pneumatic suspension, a bike fork suspension, which can adapt itself to incoming road excitations is presented in this paper. It consists of a hydraulic damper and a pneumatic spring in parallel with a linear spring. The study also proposed a variable and switchable orifice, in the hydraulic damper, to select appropriate damping property. Hydraulic-pneumatic circuit model for the bike fork suspension was established based on AMESim, in order to predict its performance. In addition, elastic-damping characteristics of the fork such as spring constant and viscous damping coefficient were computed and compared, for validation, with those evaluated by experiment using the universal test machine. Through simulation analysis and test, it was established that the hydraulic-pneumatic circuit model is effective and practical for development of future MTB suspensions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.289-294
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• 2001

Three kinds of viscoelastic damper model, which has a non-linear spring as an element is studied analytically and numerically. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by a non-linear constitutive equation and an additional equation of motion. Harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurrences of such non-linear phenomena.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.1
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• pp.57-64
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• 2002

Three kinds of viscoelastic damper model, which has a non-linear spring as an element is studied analytically and numerically The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by a non-linear constitutive equation and an additional equation of motion. Harmonic balance method is applied to get analytical solutions of the system. The frequency-response curves sallow that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurrences of such non-linear Phenomena.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.53-63
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• 1993

A numerical modeling technique is proposed for computer simulations of high speed valve train dynamic terms in the valve spring reaction forces are calculated using linear vibration theory for given kinematic valve motions. Because the spring dynamics are analyzed before the time stepping integration, spring surge phenomena can be included without using additional computer time. In addition to that, steady state response of the valve dynamics can be obtained by just one cycle simulation. Consequently, valve train dynamics can be simulated very quickly without noticeable errors in accuracy. The experimental result prove the computer model developed here is accurate and also computationally efficient. The model is especially useful for cam profile optimizations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.5
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• pp.475-481
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• 2004

This paper presents a force model of the clean tube system, which was developed as a means of transferring air-floated wafers inside a closed tube filled with super clean air. The recovering force from the holes for floating wafers is modeled as a linear spring and thus the wafers motion is modeled as a mass-spring-damper system. The propelling forces are modeled as linear along with the wafer location. The paper also proposes a control method to emit and stop a wafer at the center of a control unit. It reveals the minimum value of the propelling force to leave from the control unit. In order to stop the wafer, it utilizes the exact time when the wafer arrives at the position to activate the propelling force. Experiments with the clean tube system built for the 12 inch wafer shows the validity of the proposed model and the algorithm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.459-462
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• 2003

This paper presents a force model of the clean tube system, which was developed as a means for transferring the air-floated wafers inside the closed tube filled with the super clean air. The recovering force from the holes for floating wafers is modeled as a linear spring and thus the wafer motion is modeled as a mass-spring-damper system. The propelling forces are modeled as linear along with the wafer location. The paper also proposes the control method to emit and stop a wafer at the center of a control unit. It shows the minimum value of the propelling force to leave from the control unit. In order to stop the wafer, it utilizes the exact time when a wafer arrives at the position to activate the propelling force. Experiments with the clean tube system built for 12 inch wafer shows the validity of the proposed model and the algorithm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.28-33
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• 2005

Nonlinear aeroelastic characteristics of a two dimensional typical section model with bilinear plunge spring are investigated. Doublet-point method(DPM) is used for the calculation of supersonic unsteady aerodynamic forces which are approximated by using the minimum-state approximation. For nonlinear flutter analysis structural nonlinearity is represented by an asymmetric bilinear spring and is linearized by using the describing function method. The linear and nonlinear flutter analyses indicate that the flutter characteristics are significantly dependent on the frequency ratio. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a wide range of air speeds below or above the linear flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are investigated.