• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.519-527
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• 1987

Simple procedures have been formulated to compute approximate natural frequency of nonlinear systems by the use of variational principle. These procedures are applicable to motion of large amplitudes, even to systems which are not linearizable. The results obtained by these procedures have been found to have good agreements with computer solutions and exact solutions for systems having piece-wise linear springs and polynomial springs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.963-968
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• 2004

Free vibration analysis of helical spring with crack was studied. Natural frequency changes due to the crack was analyzed with respect to crack locations. The effect of crack on natural frequency was decreased as crack location is further from the fixed end of a spring. The frequency change was larger in rectangular-shaped spring than that in circular-shaped spring. It was found that experiment may not be appropriate to determine the presence of crack because no significant natural frequency change can be shown by experiment.

• Journal of KSNVE
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• v.10 no.6
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• pp.1067-1074
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• 2000

Numerical methods for calculating both the natural frequencies and buckling loads of columns with the multiple elastic springs are developed. In order to derive the governing equations of such columns, each elastic spring is modeled as a discrete elastic foundation with the finite longitudinal length. By using this model, the differential equations governing both the free vibrations and buckled shapes, respectively, of such columns are derided. These differential equations are solved numerically. The Runge- Kutta method is used to integrate the differential equations, and the determinant search method combined with Regula-Falsi method is used to determine the eingenvalues. namely natural frequencies and buckling loads. In the numerical examples, the clamped-clamped. clamped-hinged, hinged-clamped and hinged-hinged end constraints are considered. Extensive numerical results including the frequency parameters, mode shapes of free vibrations and buckling load parameters are presented in the non-dimensional forms.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.870-875
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• 2003

This paper deals with the free vibrations of horizontally curved beams with the general boundary condition, which consists of translational and rotational springs. The equations of general boundary condition of such beams are derived, while the ordinary differential equations governing free vibrations are adopted from the literature. The parabola as the curved beam's curvilinear shape is considered in numerical examples. For calculating the natural frequencies, the governing equations are solved by numerical methods. The Runge-Kutta and Determinant Search Methods are used for integrating the differential equations and for calculating the natural frequencies, respectively. for validation purpose, the numerical results obtained herein are compared to those obtained from the SAP 2000. With regard to numerical results, the relationships between frequency parameters and various beam parameters are presented in the forms of Table and figures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.629-635
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• 2000

Vibrational characteristics and tension fluctuation of a translating wire in WEDM are the main problems to deteriorate the cutting accuracy and processing performance. In this paper, we analyze natural frequencies of the wire used in WEDM, both theoretically and experimentally. To reduce the tension variation of the wire. which directly affects cutting performance. we have designed a simply tension reduction device using springs and rollers. It is shown that tension fluctuation is reduced about 25% using the passive tension controller.

• Journal of Microbiology and Biotechnology
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• v.24 no.9
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• pp.1280-1290
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• 2014

In order to obtain the cellulolytic bacterial consortia, sediments from Great Basin hot springs (Nevada, USA) were sampled and enriched with cellulosic biomass as the sole carbon source. The bacterial composition of the resulting anaerobic ethanol-producing celluloytic bacterial consortium, named SV79, was analyzed. With methods of the full-length 16S rRNA library-based analysis and denaturing gradient gel electrophoresis, 21 bacteria belonging to eight genera were detected from this consortium. Clones with closest relation to the genera Acetivibrio, Clostridium, Cellulosilyticum, Ruminococcus, and Sporomusa were predominant. The cellulase activities and ethanol productions of consortium SV79 using different agricultural residues (sugarcane bagasse and spent mushroom substrate) and energy crops (Spartina anglica, Miscanthus floridulus, and Pennisetum sinese Roxb) were studied. During cultivation, consortium SV79 produced the maximum filter paper activity (FPase, 9.41 U/ml), carboxymethylcellulase activity (CMCase, 6.35 U/ml), and xylanase activity (4.28 U/ml) with sugarcane bagasse, spent mushroom substrate, and S. anglica, respectively. The ethanol production using M. floridulus as substrate was up to 2.63 mM ethanol/g using gas chromatography analysis. It has high potential to be a new candidate for producing ethanol with cellulosic biomass under anoxic conditions in natural environments.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.244-252
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• 2004

The theoretical method is developed to investigate the vibration characteristics for the partially fluid-filled continuous cylindrical shells with the intermediate supports. The intermediate supports are simulated by two types of artificial springs : the translational spring for the translation for each direction and the rotational spring for a rotation. The springs are continuously distributed along the circumferential direction. By allowing the spring stiffness to become very high compared to the stiffness of the structure, the rigid intermediate supports are approximated. In the theoretical procedure, the Love's thin shell theory is adopted to formulate the theoretical model. The frequency equation of the continuous cylindrical shell is derived by the Rayleigh-Ritz approach based on the energy method. Comparison and convergence studies are carried out to verify and establish the appropriate number of series term and the artificial spring stiffness to produce results with an acceptable order of accuracy. The effect of intermediate supports, their positions and fluid level on the natural frequencies and mode shapes are studied.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.179-189
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• 2006

Recently the electrostatic 2-axis MEMS stages have been fabricated f3r the purpose of an application to PSD (Probe-based Storage Device). However, all of the components (platform, comb electrodes, springs, anchors, etc.) in those stages are placed in-plane so that they have low areal efficiencies such as a few percentage, which is undesirable as data storage devices. In this paper, we present a novel structure of an electrostatic 2-axis MEMS stage that is characterized by having a large areal efficiency of about 25%. For obtaining large area efficiency, the actuator part consisting of mainly comb electrodes and springs is placed right below the platform. The structure and operational principle of the MEMS stage are described, followed by a design and analysis, the fabrication and measurement results. Experimental results show that the driving ranges of the fabricated stage along the x and y axis were 27$\mu$m, 38$\mu$m at the supplied voltages of 65V, 70V, respectively and the natural frequencies along x and y axis were 180Hz, 310Hz, respectively. The total size of the stage is about 5.9$\times$6.8mm$^2$ and the platform size is about 2.7$\times$3.6mm$^2$.

• Advances in nano research
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• v.15 no.6
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• pp.551-565
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• 2023

Coupled porous curved beams, due to their low weight and high flexibility, have many applications in engineering. This study investigates the vibration behavior of coupled porous curved beams in different boundary conditions. The system consists of two curved beams connected by a mid-layer of elastic springs. These beams are made of various materials, such as homogenous steel foam, and composite materials with PMMA (polymethyl methacrylate) and SWCNT (single-walled carbon nanotube) used as the matrix and nanofillers, respectively. To obtain equivalent material properties, the role of mixture (RoM) was employed, followed by the implementation of the porosity function. The system's governing equations were obtained by employing FSDT and Hamilton's law. To investigate thermal vibration, temperature was implemented as a load in the governing equations. The GDQ method was used to solve these equations. To demonstrate the applicability of the GDQ method in calculating the frequencies of the system and the correctness of the developed program, a validation study was conducted. After validation, numerous examples were presented to investigate the behavior of single and coupled curved beams in various material properties and boundary conditions. The results indicate that the frequencies of the curved beams and the system depend highly on the amount of porosity (n) and the distribution pattern. The system frequencies decreased with an increase in the porosity coefficient. The stiffness of the springs had no effect on the first mode frequency but increased frequencies of other modes in a specific range. The frequencies of the system decreased with an increase in environmental temperature.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.27-33
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• 1998

The powertrain is a system of exciters which are connected by vibration transmitters and noise radiators. The powertrain has infinite natural frequencies. If the engine explosion, excites a certain natural frequency, then the powertrain system seriously vibrates. The torsional vibration arises from here. Torsional vibration like this can cause various noises as rattle and booming. In this study, the simulation models of multiple degrees of freedom were developed to reduce the torsional vibration of the powertrain. These models are combined mass moment of inertias with torsional springs. The free and forced vibration analyses were carried out by these models; and the validity of the simulation models were checked by the field test. The reduction effect of the torsional vibration along the driveline design factor is presented by the analytical results.