• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.2
• /
• pp.130-135
• /
• 2015

Recently, as a result of the application of large and multi-blade propellers with high efficiency for large vessels, the vertical bending stiffness of propulsion shafting system tends to be declined. For some specific vessels, the shaft arrangement leads to the forward stern tube bearing to be omitted, decreasing vertical bending stiffness. In this respect, decreased vertical bending stiffness causes the problem which is the blade order resonance frequency to be placed within the operational rpm range of propulsion shafting system. To verify whirling vibration, the measurement should be carried out covering from operating rpm up to target rpm, however, the range is un-measurable generally. In order to resolve the measurement issue, this study shows the measuring method and the assessment method of relevant natural frequency of whiling vibration by using measured harmonic order component of whirling vibration.

• Explosives and Blasting
• /
• v.15 no.4
• /
• pp.11-17
• /
• 1997

Impulsive vibration velocity is monitored at the surface and the boundary surface of rocks as various impulsive forces of horizontal and vertical directions were given to rocks which had difference in uniaxial compressive strength for investigate to the vibration velocity of rocks according to the impulsive direction and the monitoring site. The vibration velocity of the boundary surface of rocks was about 2.9 times or much larger than that of the surface at the same scaled distance in the case of horizontal impulsive forces, and was above 4.2 times in the case of vertical impulsive forces. The attenuation exponents of the vibration velocity equations in the surface and the boundary surface of rocks make a vast difference with the impulsive directions, but is makes little difference in the case of the same impulsive direction. The ratio of vibration constants of the surface to the boundary surface of rocks is that square and cube root scaled equation is a range of 2.7∼3.0 and 4.9∼5.0 respectively in the case of horizontal impulsive forces, and is a range of 4.2∼5.7 and 7.7∼11.5 respectively in the case of vertical impulsive forces.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.522-528
• /
• 2000

Dynamic characteristics of seated human body were investigated by measuring apparent masses of eight different seating subjects exposed to vertical vibration. Two types of vibration signals - one is random signals over 1 to 30Hz having flat spectral density and the other is signals measured on seat rail in passenger car under driving conditions - were employed. It was found that the apparent masses are highly dependent on vibration level rather than type of the vibration signals. Based on the apparent mass measurements, a mathematical model of the human body in seating posture was developed by using genetic algorithm. Three-degree-of-freedom model was satisfactory in describing apparent mass of seated human body.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.241-245
• /
• 2003

When considering the effects of whole-body vertical vibration, it is valuable to have an understanding of the mechanical characteristics (mechanical impedance and apparent mass) of the body. This paper addresses experimental results carried out to investigate the characteristics of apparent masses fer 41 Korean. The apparent masses of the seated human body in vertical direction were measured during different experimental conditions, such as vibration excitation level (0.5-2 ms$\^$-2/ r.m.s). frequency range (1-50Hz), and upper body posture (relaxed, normal and backrest-upright). We showed the average of all subjects and all conditions and compared the results with ISO5982/DIS (2000).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.766-771
• /
• 2005

To compare blasting vibration at blasting construction field in urban area, the vibration level (dB(V)) and vibration velocity (cm/sec) on the ground and the structure of buildings due to the differences of the measuring sites from the blasting source is investigated and the difference between the measured vertical vibration level and the calculated vibration level by using vibration velocity PVS and the correlation between vibration velocity and vibration level and is studied in the thesis.

• Proceedings of the KSR Conference
• /
• 2011.05a
• /
• pp.1242-1247
• /
• 2011

This study investigates vertical vibration control method for railway structure by using vertical vibration control device. The device consists of high stiffness polyurethane spring and friction damper recognized by National Center for Earthquake Engineering Research of USA for durability. To confirm the capacity of vertical vibration control, at first, behavior equation is established by considering correlation among the components. Then, hysteresis curve is drawed from behavior equation. By considering both dynamic behaviors and material nonlinearities, more reasonable behavior of the device can be simulated. After that, the Validity of the vibration control trend is proved by FEM(Finite Element Method).

• Transactions of the Korean Society of Automotive Engineers
• /
• v.3 no.5
• /
• pp.100-110
• /
• 1995

The human subject perception response according to vertical vibration and pitching was analyzed with a five degree of freedom model. The vehicle dynamic system with the delayed colored noise excitation and the passenger perception response was arranged as an integrated viration system and could be analyzed simultaneously for seven different combination of vehicle suspension. ISO2631 and BS6841 was adapted for analyzing the passenger perception reponse. Simulation results shows that passenger feel relatively less discomfort due to pitching compared to vertical vibration and road type was not necessary to be considered as a design parameter in view of comfort analysis.

• Structural Engineering and Mechanics
• /
• v.10 no.6
• /
• pp.603-619
• /
• 2000

Analysis of a framed structure for vertical vibration requires a lot of computational efforts because large number of degrees of freedom are generally involved in the dynamic responses. This paper presents an efficient modeling technique for vertical vibration utilizing substructuring technique and super elements. To simplify the modeling procedure each floor in a structure is modeled as a substructure. Only the vertical translational degrees of freedom are selected as master degrees of freedom in the inside of each substructure. At the substructure-column interface, horizontal and rotational degrees of freedom are also included considering the compatibility condition of slabs and columns. For further simplification, the repeated parts in a substructure are modeled as super elements, which reduces computation time required for the construction of system matrices in a substructure. Finally, the Guyan reduction technique is applied to enhance the efficiency of dynamic analysis. In numerical examples, the efficiency and accuracy of the proposed method are demonstrated by comparing the response time histories and the analysis time.

• Journal of the Korean housing association
• /
• v.17 no.3
• /
• pp.61-69
• /
• 2006

Vertical vibrations on the slab of buildings are affected by types of vibration sources, transfer paths, and the material property and the size of members. Among these parameters, the vibration sources and the transfer path can not be controlled, but the property and the size of members can be controlled in the phase of design the members. In this study, the vibration responses according to the property and size of members were obtained by using a prediction program based on dynamic-stiffness matrix. Three parameters which are not usually considered as major factors for architecral planning were selected fur these analyses. They are the strength of materials, the thickness of wall and the thickness of slab. The ground vibration source located near a building was used as vibration input data in the analyses. This study has its originality on presenting appropriate property and size of structural members in order to reduce vertical vibration of slab in shear-wall structures. Analysing the results from the vibration estimation program according to the variations of parameters, the appropriate ratio among the sizes of structural members were proposed. From these results, the vibration level on the slab which is not constructed yet would be predicted and the vibration peak level can be reduced or shifted into the desirable frequency range. Therefore, the vertical vibration could be controlled in the phase of designing buildings.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.33-44
• /
• 2003

This paper introduces attempts to obtain the'representative'characteristics of the apparent mass and mechanical impedance of seated Korean subjects under vertical vibration. Individual responses of the apparent mass and driving-point mechanical impedance obtained from forty-one Korean subjects are illustrated. Four kinds of vibration levels and three different sitting postures are selected to collect the responses of each subject. Those individual responses are used to estimate the 'mean' mechanical impedance, which may be expected to be a representative model to Korean subjects. Several interesting features of the estimated mechanical impedance are suggested and compared to those of ISO 5982.