• Smart Structures and Systems
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• v.10 no.2
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• pp.155-179
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• 2012

This paper aims at assessing the seismic performance of Tuned Mass Dampers (TMDs) based on sets of recorded ground motions. For the simplest configuration of a structure-TMD assembly, in a comprehensive study characteristic response quantities are derived and statistically evaluated. Optimal tuning of TMD parameters is discussed and evaluated. The response reduction by application of a TMD is quantified depending on the structural period, inherent damping of the stand-alone structure, and ratio of TMD mass to structural mass. The effect of detuning on the stroke of the TMD and on the structural response is assessed and quantified. It is verified that a TMD damping coefficient larger than the optimal one reduces the peak deflection of the TMD spring significantly, whereas the response reduction of the main structure remains almost unaffected. Analytical relations for quantifying the effect of a TMD are derived and subsequently evaluated. These relations allow the engineer in practice a fast and yet accurate assessment of the TMD performance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.9
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• pp.751-761
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• 2003

We performed the numerical analysis on the airflow characteristics in the two type of cleanroom systems, which are the axial fan type (AFT) and the fan filter unit (FFU). A computational fluid dynamic model was applied to investigate and compare the nonuniformity, the deflection angle and the air ventilation effectiveness of the two designs of cleanrooms when dampers are adjusted and not adjusted. And the flow-resistance models of the various components were used in this simulation. We know that the airflow characteristics of the cleanrooms are largely affected by damper adjusting And we also find out that the FFU system is superior to the AFT system through the comparison of the cleanroom performance indices.

• Smart Structures and Systems
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• v.18 no.4
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• pp.683-705
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• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.10
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• pp.947-959
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• 2001

We propose a control scheme to control the indoor zone temperature via variable air volume (VAV) unit. To control the room temperature, state space model of the conditioned zone which is partitioned into nine artificial sectional regions is derived. The nonlinearity of the damper motion and actuator are considered for the practical use in the state space system description. The temperature control of the room temperature is performed by manipulating the degree of openness of the damper in relation to the local room temperature and the supplied air flow rate. In general, since a local temperature in the conditioned zone is measured, it is required to estimate the temperature values in each regions for the precise temperature control. We thus design a state observer to estimate the regional temperature, and use these values in the controller. The overall control system consists of the state observer based state feedback with the integral control. We compared the control results of the proposed scheme with those of cascade proportional and integral (PI) control, and showed that the scheme achieved precise control of the conditioned system.

• Smart Structures and Systems
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• v.24 no.3
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• pp.403-414
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• 2019

Offshore drilling has become a key process for obtaining oil. Offshore platforms have many applications, including oil exploration and production, navigation, ship loading and unloading, and bridge and causeway support. However, vibration problems caused by severe environmental loads, such as ice, wave, wind, and seismic loads, threaten the functionality of platform facilities and the comfort of workers. These concerns may result in piping failures, unsatisfactory equipment reliability, and safety concerns. Therefore, the vibration control of offshore platforms is essential for assuring structural safety, equipment functionality, and human comfort. In this study, an optimal multiple tuned mass damper (MTMD) system was proposed to mitigate the excessive vibration of a three-dimensional offshore platform under ice and earthquake loadings. The MTMD system was designed to control the first few dominant coupled modes. The optimal placement and system parameters of the MTMD are determined based on controlled modal properties. Numerical simulation results show that the proposed MTMD system can effectively reduce the displacement and acceleration responses of the offshore platform, thus improving safety and serviceability. Moreover, this study proposes an optimal design procedure for the MTMD system to determine the optimal location, moving direction, and system parameters of each unit of the tuned mass damper.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.8
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• pp.43-52
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• 2022

The vibration characteristics of a hammer press are important parameters for machine design and production control. In this study, a counterblow hammer press was mathematically modelled as a mass-spring-damper system in order to analyze its vibration characteristics. The forging efficiency was theoretically derived as a function of the mass ratio, momentum ratio, and the coefficient of restitution And the effects of the mass ratio, momentum ratio and the restitution coefficient on the forging efficiency were also investigated for two particular cases of the unit mass ratio and unit momentum ratio. Additionally, the vibration responses of the counterblow hammer press due to the ram colliding impact were analyzed, and the force transmitted to the foundation through the mounting unit was determined.

• Structural Engineering and Mechanics
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• v.11 no.2
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• pp.133-149
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• 2001

A high-fidelity model of a tracked vehicle traversing a flexible ground terrain with a varying profile is presented here. In this work, we employed a recursive formulation to model the track subsystem. This method yields a minimal set of coordinates and hence, computationally more efficient than conventional approaches. Also, in the vehicle subsystem, the undercarriage frame is assumed to be connected to the chassis by a revolute joint and a spring-damper unit. This increase in system mobility makes the model more realistic. To capture the vehicle-ground interaction, a Winkler-type foundation with springs-dampers is used. Simulation runs of the integrated tracked vehicle system for vibrations for four varying ground profiles are provided.

• Journal of the Korean Society of Industry Convergence
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• v.20 no.5
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• pp.419-424
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• 2017

The purpose of this study is to develop a virtual testbed capable of predicting the functional performance of a linear electromagnetic actuator for a high voltage relay in order to reduce its development costs and time. The virtual testbed is defined by a multiphysics coupling approach in order to consider the complex interactions of multi-domains such as the solenoid model of electromagnets, the mass-spring-damper model of mechanical systems, the electric circuit model for an external control unit, and the thermal model for predicting temperature variations. The performances of the existing high voltage relay were estimated by the virtual testbed, and then the effectiveness and validation of the proposed testbed were discussed in comparison with the experimental test results. This study showed that the virtual testbed can be applied in design, optimization, and investigation of high voltage relays.

• Journal of KSNVE
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• v.9 no.4
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• pp.754-760
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• 1999

The valve motions of a reciprocating compressor generate the pressure fluctuation at the plenum which is a main source of noise and vibration of a compressor unit. But a cycle of a compressor process consists of complicated phenomena interacting in a short period of time. A mathematical model is developed by simplifying and idealizing the complicated phenomena to simulate the compressor process. The governing equations about the pressure and working fluid flow are developed from the unsteady Bernoulli equation. The pressure fluctuations at the plenums are derived from the Helmholz's resonator model. The valves are modeled as one degree of freedom spring-mass-damper system. This model is verified by the experimental results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.47-54
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• 2003

The rotating of rotatory unit with its structural unbalance mass and laundry is making the main vibration problem in a vertical axis washing machine. For reducing vibration problem total washing system hung on the case by its suspension system which is constitute of spring, damper and suspension bar and hydraulic balancer is attached at the upper rim of spin basket. In this paper, we make the dynamic model of washing system of its rigid body motions by 6 degree of freedoms. Hydraulic balancer is modeled by one degree of freedom like auto ball balancer. Elastic motions of washing system have found by method of analytic, experimental and FEM. And we consider first bending mode of each suspension bar and first circumferential mode of assy tub. So, the total washing system is modeled by 12 degree of freedoms. Equations of motion for total washing system have derived, and we perform the dynamic simulation tests.