• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.7 s.100
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• pp.865-870
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• 2005

Torque fluctuation of the engine and angular velocity variation of propeller shaft is the main excitation source for torsional vibration in the vehicle driveline. Experimental model for engine system is constructed with 4 cylinder 4 cycle diesel engine including Motor-Propeller Shaft-Axle-Wheel system. The angular velocity is measured by magnetic pickup and FV converter at the engine flywheel and propeller shaft. This paper presents the theoretical mechanism of these excitation sources and it is identified by the experimental methods.

• Transactions of the Society of Information Storage Systems
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• v.10 no.1
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• pp.23-26
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• 2014

In this paper, we present a novel approach for tuning the resonant frequency of torsionally driven vertical comb actuators. The tuning unit composed of thermal actuator, scissor mechanism and V-shape shaft enables continuous and reversible resonant frequency tuning. The proposed method is based on the stiffness alteration of the V-shape shaft. It is experimentally verified that the resonant frequency of the torsional microscanner is shifted up to 1.59 kHz from 1.51 kHz showing the maximum tuning ratio of 5.29%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.261-267
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• 2011

This study reveals the longitudinal vibration mechanism of tendon embedded in a prestressed concrete. The extensional and torsional displacements of the strand are coupled, and the applied prestress level of tendon affects not only axial rigidity but also torsional rigidity. Measuring the elastic wave velocity of tendon, the applied prestress level of tendon could be evaluated. This is because the elastic wave velocity is a function of extensional and torsional rigidity. Using the experimental results for the six prsteressed concrete beams with different prestress levels, the longitudinal vibration mechanism and the effect of prestress level have been examined. To estimate the system ridigities of tendon, a system identification algorithm has been newly developed. The estimated system rigidities have been compared with the available results of related previous study.

• Wind and Structures
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• v.15 no.5
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• pp.423-439
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• 2012

Three common medium- rise building forms were physically tested to study their overall wind induced structural response. Emphasis was placed on the torsional response and its correlation with other peak responses. A higher correlation was found between the peak responses than between the general fluctuating parts of the signals. This suggests a common mechanism causing the peak event, and that this mechanism is potentially different to the mechanism causing the general load fluctuations. The measurements show that about 80% of the peak overall torsion occur simultaneously with the peak overall along wind drag for some generic building shapes. However, the peak torsional response occurs simultaneously with only 30%-40% of the peak overall drag for the rectangular model. These results emphasise the importance of load combinations for building design, which are often neglected in the design of medium sized rigid buildings for which the along-wind drag is dominant. Current design wind loading standards from around the world were evaluated against the results to establish their adequacy for building design incorporating wind-induced torsion effects. Although torsion is frequently neglected, for some structural systems it may become more important.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.591-592
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• 2008

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.3
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• pp.149-155
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• 2006

This paper presents a torsional micromirror detached from PZT actuators (TMD), whose rotational motion is achieved by push bars in the PZT actuators detached from the micromirror. The push bar mechanism is intended to reduce the bending, tensile and torsional constraints generated by the conventional bending bar mechanism, where the torsional micromirror is attached to the PZT actuators (TMA). We have designed, fabricated and tested prototypes of TMDs for single-axis and dual-axis rotation, respectively. The single-axis TMD generates the static rotational angle of $6.1^{\circ}$ at 16 VDC, which is 6 times larger than that of single-axis TMA, $0.9^{\circ}$. However, the rotational response curve of TMD shows hysteresis due to the static friction between the cover and the push bar in the PZT actuator. We have shown that 63.2% of the hysteresis is due to the static friction caused by the initial contact force of the PZT actuaor. Without the initial contact force, the rotational response curve of TMD shows linear voltage-angle characteristics. The dual-axis TMD generates the static rotational angles of $5.5^{\circ}$ and $4.7^{\circ}$ in x-axis and y-axis, respectively at 16 VDC. The measured resonant frequencies of dual-axis TMD are $2.1\pm0.1$ kHz in x-axis and $1.7\pm0.1$ kHz in y-axis. The dual-axis TMD shows stable operation without severe wear for 21.6 million cycles driven by 16 Vp-p sinusoidal wave signal at room temperature.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.1018-1025
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• 2003

The diesel engine is often a serious excitation source in ships. Both the varying cylinder gas forces and the reciprocating and rotating mass forces associated with the crank and the connecting rod mechanism produce ample possibilities for excitation of the engine structure itself, the shafting, the surrounding substructures as well as the hull girder. This paper presents a guide for optimization of excitation forces produced by the marine propulsion 2-stroke diesel engine. The computational program for predicting the excitation forces is developed and applied to 2-stroke in-line engines. The object function is defined as the work done by every cylinder excitation force which is related to the mode shape of the diesel engine system, especially in the torsional vibration of the shafting. As a practical application of the presented method, the crank angle of 7 cylinder 2-stroke engine is optimized to reduce torsional vibration stresses on the shafting. Compared with the regular firing angle, about 60% of the 4th order torsional vibratory stress on the propeller shaft can be reduced by optimizing the crank angle irregularly. The usefulness of the presented optimization method is confirmed by the measurements.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.709-717
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• 2004

The diesel engine is often a serious excitation source in ships. Both the varying cylinder gas forces and the reciprocating and rotating mass forces associated with the crank and the connecting rod mechanism produce ample possibilities for excitation of the engine structure itself, the shafting, the surrounding substructures as well as the hull girder. This paper presents a guide for optimization of excitation forces produced by the marine propulsion 2-stroke diesel engine. The computational program for predicting the excitation forces is developed and applied to 2-stroke in-line engines. The object function is defined as the work done by every cylinder excitation force which is related to the mode shape of the diesel engine system, especially in the torsional vibration of the shafting. As a practical application of the presented method. the crank angle of 7 cylinder 2-stroke engine is optimized to reduce torsional vibration stresses on the shafting. Compared with the regular firing angle, about 60 ％ of the 4th order torsional vibratory stress on the propeller shaft can be reduced by optimizing the crank angle irregularly. The usefulness of the presented optimization method is confirmed by the measurements.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1021-1027
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• 2006

Torque fluctuation of an engine and angular velocity variation of a propeller shaft are the main excitation sources in the vehicle driveline. This paper presents brief mechanism of these excitation sources. Equivalent models of these systems are construced to simulate the excitation source. The computer simulation was carried out by ARLA Simul v 6.7 and ARLA-Simstat v 2.3. Results of the simulations show the characteristics of torsional excitation source of the driveline. Experimental setups for engine system and propeller shaft system are constructed with component of the vehicle. Torque fluctuation of the flywheel and angular velocity of the propeller shaft were measured from this experimental setups. Experimental results are compared with simulation results. The results from experimental analysis agree with those from theoretical results.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.4
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• pp.339-345
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• 1992

Estimates of maximum amplitudes of conductor galloping are needed in order to determine appropriate phase-to-phase clearances on the overhead lines. One approach to obtaining these estimates is through the use of mathematical models of conductor galloping. Unfortunately, the models that consider both vertical conductor motion (Den Hartog type) and torsional conductor motion are often too complex for practical use. However, the estimates of maximum amplitude obtained from galloping models that assume only vertical (Den Hartog type) conductor motion tend to be too conservative. This paper presents the DF method to obtain the estimates of the amplitude and the frequency of galloping limit cycle, along with the wind pressure at which they occur, from a nonlinear dynamic model that considers both Den Hartog type and torsional conductor motion. From these results, the useful data for the line design guide and further insight into the mechanism of the conductor galloping are obtained.