• Journal of the Korean Wood Science and Technology
• /
• v.44 no.2
• /
• pp.274-282
• /
• 2016

This aims of this study were to investigate the relationship between non-destructive evaluation (NDE) and actual bending properties of particleboard, and to predict the bending properties of three-layer particleboard. Three kinds of raw materials, i.e. Hinoki (Chamaecyparis obtusa Endl.) strand, knife-milled Douglas-fir (Pseudotsuga manziesii (Mirb) Franco), and hammer-milled matoa (Pometia spp.) obtained from wooden industry, were utilized as furnish for experimental panel with methylene diphenyl diisocyanate (MDI) resin as binder. The NDE test was conducted by hit sounds using an FFT analyzer according to the spectrum peak of wave frequency, while the static bending test was conducted according to JIS A-5908. The results reveal that the dynamic Young's modulus as an NDE test has a potential for being used to predict the elastic bending of particleboards by a specific equation for adjusting its proper values. The values of NDE and static test are significantly different with a deviation range at 3-20%. The bending stiffness of three-layer particleboards manufactured from different wood species is predictable by observing the bending stiffness of two elements based on the thickness of its layers. The predicted values of bending stiffness and static test are significantly different with a deviation range at 5-24%.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.14 no.4
• /
• pp.21-27
• /
• 2015

Induction bending is a method that allows the bending of any material that conducts electricity. This technology applies a bending force to a material that has been locally heated by an eddy current induced by a fluctuating electromagnetic field. Induction bending uses an inductor to locally heat steel through induction. This results in a narrow heat band in the shape to be bent. In general, the reduction of thickness attenuation of a large-diameter steel pipe is not allowed to exceed 12.5%. In this paper, in order to meet the standard of thickness attenuation reduction, a non-uniform heating temperature jump-bending process was investigated. As a result, the developed bending technique meets the requirements of thickness attenuation reduction for large-diameter steel pipes.

• Journal of the Korean Society for Precision Engineering
• /
• v.25 no.10
• /
• pp.99-106
• /
• 2008

5kWh FESS(Flywheel Energy Storage System) using AMB(Active Magnetic Bearing) has been under development and 1st trial system has been finished and run the operating test. Unfortunately, the test result was not satisfactory because FESS could increase the rotational speed up to 9,000 rpm only although the target rotational speed is 18,000rpm. It's because 1st bending mode frequency of flywheel shaft was too low and imbalance response was too big. To achieve the target speed, 1st bending mode and imbalance response must be improved and the whole FESS needed to be designed again. This paper presents the newly designed FESS and what has been changed from the 1st trial FESS to improve 1st bending mode and imbalance response. The experimental results to see how much 1st bending mode frequency was improved are presented, too.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.3
• /
• pp.77-85
• /
• 2020

In this study, we proposed a method to replace the solid finite element model of the boiler membrane wall for coal-fired power plants using an equivalent shell model. The application of a bending load to the membrane wall creates greater displacement at both ends of the central portion when compared with the middle when an isotropic elastic constant is used in the shell model. This is inconsistent with the results of the solid model where the central portion is uniformly deformed. Here, we presented a method to determine the orthotropic elastic constants of the shell model in terms of bending stiffness and vibration characteristics to solve this problem. Our analysis of the orthotropic shell model showed that the error ratio was 0.9% for the maximum displacement due to the bending load, 0.3% for the first natural frequency, and 2.5% for the second natural frequency when compared with the solid model. In conclusion, a complicated boiler membrane wall composed of a large number of pipes and fins can be replaced with a simple shell model that shows equivalent bending stiffness and vibration characteristics using our proposed method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.05a
• /
• pp.955-962
• /
• 2002

According to the trends of construction of large size vessel with high power, the natural frequencies of the bending modes of propeller blades have been lower than the past. Therefore, it is expected that the noise and vibration problems of the marine propeller are frequently occurred. As main issue of the propeller noise and vibration problem, the cavitation noise and singing noise due to the flow induced excitation of the bending modes of propeller blade in the high frequency range has been studied by the hydrodynamic researchers in the view point of the excitation force reduction. In this paper, the vibration mode characteristics of propeller with a large diameter in very large vessel are investigated by the vibration analysis of the finite element method using MSC/Nastran and the vibration measurement by the impact test on the propeller blade. According to the results, the natural frequencies of various blade bending modes in water entrained condition could be estimated from the natural frequencies taken by the measurement and free vibration analysis in the dry condition, and it could be estimated how the high frequency noise such as singing is generated from the blade bending modes.

• Special Issue of the Society of Naval Architects of Korea
• /
• 2005.06a
• /
• pp.97-106
• /
• 2005

According to the trends of construction of large size vessel with high power the natural frequencies of the bending modes of propeller blades have been lower than the past. Therefore, it is expected that the noise and vibration problems of the marine propeller are frequently occurred. As main issue of the propeller noise and vibration problem, the cavitation noise and singing noise due to the flow induced excitation of the bending modes of propeller blade in the high frequency range has been studied by the hydrodynamic researchers in the view point of the excitation force reduction. In this paper, the vibration mode characteristics of propeller with a large diameter in very large vessel are investigated by the vibration analysis of the finite element method using MSC/Nastran and the vibration measurement by the impact test on the propeller blade. According to the results, the natural frequencies of various blade bending modes in water entrained condition could be estimated from the natural frequencies taken by the measurement and free vibration analysis in the dry condition, and it could be estimated how the high frequency noise such as singing is generated from the blade bending modes.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.21 no.2
• /
• pp.169-177
• /
• 2011

In this paper, the natural frequency of a cracked cantilever L-beams with a coupled bending and torsional vibrations is investigate by theory and experiment. In addition, a method for detection of crack in a cantilever L-beams is presented based on natural frequency measurements. The governing differential equations of a cracked L-beam are derived via Hamilton's principle. The two coupled governing differential equations are reduced to one sixth order ordinary differential equation in terms of the flexural displacement. Futher, the dynamic transfer matrix method is used for calculation of a exact natural frequencies of L-beams. The crack is assumed to be in the first mode of fracture and to be always opened during vibrations. In this study, the differences between the actual and predicted positions and sizes of crack are less than about 10 % and 39.5 % respectively.

• Structural Monitoring and Maintenance
• /
• v.9 no.4
• /
• pp.305-321
• /
• 2022

Bridge structural health monitoring with the aim of continuously assessing structural safety and reliability represents a topic of major importance for worldwide infrastructure managers. In the last two decades, due to their potential economic and operational advantages, drive-by approaches experienced growing consideration from researcher and engineers. This work addresses two technical topics regarding indirect frequency estimation methods: bridge and vehicle dynamics overlapping, and bridge expansion joints impact. The experimental campaign was conducted on a mixed multi-span bridge located in Lombardy using a Ford Galaxy instrumented with a mesh of wireless accelerometers. The onboard time series were acquired for a number of 10 passages over the bridge,performed at a travelling speed of 30 km/h, with no limitations imposed to traffic. Exploiting an ad-hoc sensors positioning, pitch vehicle motion was compensated, allowing to estimate the first two bridge bending frequencies from PSD functions; moreover, the herein adopted approach proved to be insensitive to joints disturbance. Conclusively, a sensitivity study has been conducted to trace the relationship between estimation accuracy and number of trips considered in the analysis. Promising results were found, pointing out a clear positive correlation especially for the first bending frequency.

• Steel and Composite Structures
• /
• v.45 no.1
• /
• pp.119-131
• /
• 2022

Due to the complexity of the structure and the limits of classical SEA, a combined SEA approach is employed, with angle-dependent SEA in the low- and mid-frequency ranges and advanced SEA (ASEA) considering indirect coupling in the high-frequency range. As an important component of the steel box girder, the dynamic response of an L-junction periodic ribbed plate is calculated first by the combined SEA and validated by the impact hammer test and finite element method (FEM). Results show that the indirect coupling due to the periodicity of stiffened plate is significant at high frequencies and may cause the error to reach 38.4 dB. Hence, the incident bending wave angle cannot be ignored in comparison to classical SEA. The combined SEA is then extended to investigate the vibration properties of the steel box girder. The bending wave transmission study is likewise carried out to gain further physical insight into indirect coupling. By comparison with FEM and classical SEA, this approach yields good accuracy for calculating the dynamic responses of the steel box girder made of periodic ribbed plates in a wide frequency range. Furthermore, the influences of some important parameters are discussed, and suggestions for vibration and noise control are provided.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.12
• /
• pp.188-193
• /
• 1998

This paper describes static and dynamic weak point analysis of spindle systems to eliminate high concentrated bending point on spindle and improve total stiffness of spindle systems. The weak point analysis is based on the evaluation of bending curves of spindles. For static weak point analysis the bending curve is derived from static deflection curve and for dynamic weak point analysis it is derived from the mode shape curves in consideration of the transfer function at exciting point. The validity of the weak point search methodology is verified by comparison of the static deflection, the natural frequency and the dynamic compliance between the original and the improved spindle.