• Smart Structures and Systems
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• v.26 no.5
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• pp.619-629
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• 2020

Solar towers, which often has a large aspect ratio and low fundamental natural frequency, were extremely prone to large amplitude of wind-induced vibrations, especially Vortex-Induced Vibration (VIV). A tiny Tuned Mass Damper (TMD) with conveniently adjustable eddy current damping was specially designed and manufactured for elastic wind tunnel tests of a solar tower. A series of numerical simulations by using the COMSOL software were conducted to determine three key parameters, including the thickness of the back iron plate and the conductive plate (T_b and T_c), the distance between the magnet and the conductive plate (T_d). Based on the results of numerical simulations, a tiny TMD was manufactured and its structural parameters were experimentally identified. The optimized values of the tiny TMD can be conveniently realized. The tiny TMD was installed at the top of the elastic test model of a 243-meter-high solar tower, and a series of wind tunnel tests were carried out to examine the effectiveness of the TMD in suppressing wind-induced responses of the test model. The results showed that the wind-induced responses could be obviously reduced by the TMD, especially in the cross-wind direction. The cross-wind RMS and peak responses at the critical wind velocity can be reduced by about 86% and 75%, respectively. However, the maximum reduction of the responses at the design wind velocity is about 45%, obviously less than that at the critical wind velocity.

• Wind and Structures
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• v.9 no.5
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• pp.345-356
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• 2006

It is well known that cylinder steel stacks are heavily impacted by vortex-induced vibration. However, the wind-induced vibration behaviors of tower-supported steel stacks are not clarified due to a lack of observation. We studied a stack's response to strong winds over a long period of time by observing the extreme wind-induced vibration of a 200 m-high tower-supported steel stack. This experiment aimed to identify the wind-induced vibration properties of a tower-supported steel stack and assess the validity of the vibration control method used in the experiment. Results revealed a trend in wind-induced vibration behavior. In turn, an effective measure for controlling such vibration was defined by means of increasing the structural damping ratio due to the effects of the tuned mass damper to dramatically decrease the vortex-induced vibration of the stack.

• Journal of Drive and Control
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• v.13 no.2
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• pp.10-18
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• 2016

A front-end loader (FEL) mounted on an agricultural tractor is one of the most commonly used implements to mechanize routine agricultural tasks. When the FEL is used with a loaded bucket, careful operation is required to maintain safety and avoid spillage when the tractor passes a bump because a change in the gravity center of the tractor due to varied loadings can affect the stability of the tractor. Use of a boom suspension system consisting of accumulators and orifice dampers can be instrumental in reducing pitching vibrations while increasing the handling performance of the FEL-mounted tractor. The objective of this research was to reduce bump shocks by adding an orifice and a flow control valve to the original hydraulic circuit composed solely of accumulators. A simulation study was performed using the SimulationX program to investigate the effects of an accumulator and an orifice-throttle damper on bump shocks. Results showed that the peak pressure on a boom cylinder and the vertical acceleration of a bucket were significantly affected by use of both an accumulator and an orifice damper. In a field test conducted with a 75-kW tractor, the peak pressure of the boom cylinder, and the root mean square (RMS) vertical acceleration of the bucket and seat were reduced by on average, 23.0, 42.2, and 44.9% respectively, as compared to those measured with the original accumulator system, showing that an improved design for the accumulator hydraulic circuit can reduce bump shocks. Further studies are needed to design a tractor suspension system that includes the effects of cabin suspension and tires as well as dynamic analysis.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.7-14
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• 2011

Numerical simulations were performed for the evaluation of wave and current loads on a fixed cylindrical substructure model for an ocean wind turbine using the ANSYS-CFX package. The numerical wave tank was actualized by specifying the velocity at the inlet and applying momentum loss as a wave damper at the end of the wave tank. The Volume-Of-Fluid (VOF) scheme was adopted to capture the air-water interface. An accuracy validation of the numerical wave tank with a truncated vertical circular cylinder was accomplished by comparing the CFD results with Morison's formula, experimental results, and potential flow solutions using the higher-order boundary element method (HOBEM). A parametric study was carried out by alternately varying the length and amplitude of the wave. As a meaningful engineering application, in the present study, three kinds of conditions were considered, i.e., cases with current, waves, and a combination of current and progressive waves, passing through a cylindrical substructure model. It was found that the CFD results showed reasonable agreement with the results of the HOBEM and Morison's formula when only progressive waves were considered. However, when a current was included, CFD gave a smaller load than Morison's formula.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.81-89
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• 2009

Dancer systems are typical equipment for attenuation of tension disturbances. Lately, demands for high speed roll-to-roll machines are rising but it is prior to attenuate the tension variation on the web entering into the printing zone to achieve the speed increment. Maintaining a constant tension before the first printing cylinder is the key of high speed, high quality printing. Dancer has been researched in two ways, whether it is controlled or not. The first one is active dancer and the other one is passive dancer. In the active dancer, a position of idle roll of dancer is measured and the roll is moved by external hydraulic cylinder to control tension disturbances. While the passive one composed with spring, damper and idle roll has no external actuator to position the idle roll. The tension disturbance causes movement of dancer roll and the displacement of the roll regulates the tension variation. On the other hand a composite type of dancer is applied for roll-to-roll printing machines. It has same apparatus as passive dancer. The displacement of roll is measured and front(or rear) driven roller is controlled to position the roll. In this paper, it is presented an analysis of pendulum dancer including position feedback PI control and logic for PI gain tuning in roll-to-roll machines. Pole-zero map and root locus with varying system parameters gives a design method for control of the dancer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.181-186
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• 2009

The objective of this study is ensuring safety of cabin when the blade impacts into a obstacle by verifying safety of the rotor mast and the transmission using impact loads calculated from the simulation. The rotor mast shall not fail and the transmission shall not be displaced into occupiable space when the main rotor composite blade impact into a 8 inch rigid cylinder in diameter on the outer 10% of the blade at operational rotor speed. To calculate the reaction loads at the spherical bearing and lead-lag damper, blade impact analysis was performed with FE model consist of composite blade, tree(or rigid cylinder) using elastic-plastic with damage material and several contact surfaces which were created to describe a progress of actual failure. Also, the reaction loads were investigated in change of blade rotation speed and pitch angle.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.3
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• pp.563-572
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• 2001

With the results of calculation for natural frequencies the reponses of forced coupled vibration of propulsion shafting system were investigated by the modal analysis method. For the forced vibration response analysis, the axial exciting forces, the axial damper/detuner, propeller exciting forces and damping coefficients were extensively considered. As the conclusion of this study, some items are cleared as follows.-The torsional vibration amplitudes are not influenced by the radial excitation forces of the crank shaft. -The axial vibration amplitudes are influenced by the tangential exciting forces as well as the radial exciting forces of the crank shaft. The increase of the amplitudes is observed in the speed range at the neighbourhood of any torsional critical speed. 1The closer the torsional and axial critical speed. the larger coupling effect becomes. -The axial exciting force of propeller is relatively strong comparing with axial exciting forces of cylinder gas pressure and oscillating inertia of reciprocating mechanism. Therefore, the following conclusions are obtained. -Torsional vibration calculation with the classical one dimensional model is still valid. -The influence of torsional excitation at each crank upon the axial vibration is improtant. especially in the neighbourhood of a torsional critical speed. That means that the calculation of axial vibration with the classical one dimensional model is inaccurate in most of cases.

• Ocean Systems Engineering
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• v.3 no.3
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• pp.203-217
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• 2013

A PTO (power-take-off) mechanism by using relative heave motions between a floating buoy and its inner mass (magnet or amateur) is suggested. The inner power take-off system is characterized by a mass with linear stiffness and damping. A vertical truncated cylinder is selected as a buoy and a special station-keeping system is proposed to minimize pitch motions while not affecting heave motions. By numerical examples, it is seen that the maximum power can actually be obtained at the optimal spring and damper condition, as predicted by the developed WEC(wave energy converter) theory. Then, based on the developed theory, several design strategies are proposed to further enhance the maximum PTO, which includes the intentional mismatching among heave natural frequency of the buoy, natural frequency of the inner dynamic system, and peak frequency of input wave spectrum. By using the intentional mismatching strategy, the generated power is actually increased and the required damping value is significantly reduced, which is a big advantage in designing the proposed WEC with practical inner LEG (linear electric generator) system.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.11a
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• pp.99-107
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• 2000

With the results of calculation for natural frequencies, the forced reponses of coupled vibration of propulsion shafting were analysed by the modal analysis method. For the forced response analysis, axial exciting forces, axial damper/detuner, propeller exciting forces and damping coefficients were extensively investigated. As the conclusion of this study, some items are cleared as next. - The torsional amplitudes are not influenced by the radial excitation forces. - The axial vibrational amplitudes are influenced by the tangential exciting forces. An increase of amplitude is observed for the speed range in the neighbourhood of any torsional critical speed. - The coupling effect becomes larger if torsional and axial critical speed are closer together. - The axial exciting force of propeller is relatively strong, comparing with those of axial forces of cylinder gas pressure and oscillating inertia of reciprocating mechanism. Therefore, as a resume one can say, that- Torsional vibration calculation with the classical one dimension model is still valid. - The influence of torsional excitation at each crank upon the axial vibration is impotent, especially in the neighbourhood of a torsional critical speed. That means that the calculation of axial vibration with the classical one dimension model is insufficient in most of cases. - The torsional exciting torque of propeller can be neglected in most of cases. But, the axial exciting forces of propeller can not be neglected for calculating axial vibration of propulsion shafting.

• Journal of Power System Engineering
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• v.12 no.1
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• pp.41-46
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• 2008

The primary objective of this study is to truly understand exciting forces of the in-line 4 cylinders engine. Exciting forces of the engine apply a source of the vehicle NVH(Noise, Vibration, Harshness). To understand exciting forces, first was governed theoretical equations for single cylinder engine. And this theoretical equations was programming using MATLAB software. To compare theoretical analysis value, was applied MSC.ADAMS software. To determined the specification of engine(2,000cc, in-line 4) was applied ADAMS/Engine module. And this specification for engine was applied ADAMS/View and MATLAB software. The geometry model for ADAMS/View analysis was produced by the 3-D design modeling software. After imported 3-D model, each rigid body was jointed suitable. Under idle speed for engine, was analysed. The results of analysis are fairly well agreed with those of three analysis method. Using MATLAB software proposed in this study, engine exciting fores can be predicted. Also using ADAMS/Engine module and ADAMS/View software, engine exciting forces can be predicted.