• Journal of Korean Society of Steel Construction
• /
• v.16 no.5 s.72
• /
• pp.713-724
• /
• 2004

A fatigue crack found at the coped stringer of the old dismantled Dangsan Subway Bridge was numerically simulated. A model of a single span of the plate girder bridge with its beam elements was created and analyzed in order to obtain the nominal stress history caused by trains. A detailed FEM analysis of the coped stringer was conducted using a shell element model. A fracture mechanical model was used to estimate crack propagation. The stress intensity factors were calculated using the J-Integral method. The simulation with some reasonable assumptions showed that the calculated crack lengths were comparable to those found on the site.

• Journal of Korean Society of Steel Construction
• /
• v.19 no.3
• /
• pp.281-290
• /
• 2007

In this paper, the dynamic behavior of a 12m plate girder railway bridge is analyzed using the commercial FEM program. A time history load is applied to a standard train load via the shape function ofthe beam element. In addition, lateral behavior characteristics were simulated using the Klingel sine movement. A feasibility study of the FEM program and an analysis were performed by comparing the displacement and the acceleration, from the experimental data and the results of the FEM analysis. the time history of the lateral and vertical displacements are reflected in the experimental results. Six kinds of reinforcements were studied from the effects of the displacement and the acceleration. The RF-1 model that was applied to the upper lateral bracing system, and the RF-3 model that reinforced the plate, turned out to be the most effective reinforcement methods with respect to weight limits and construction simplification.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.1
• /
• pp.31-36
• /
• 2014

This paper shows the feasibility of using carbon-fiber-reinforced polymer (CFRP) composite materials for manufacturing automotive coil springs. For achieving weight reduction by replacing steel with composite materials, it is essential to optimize the material parameters and design variables of the coil spring. First, the shear modulus of a CFRP beam model, which has $45^{\circ}$ ply angles for maximum torsional stiffness, was calculated and compared with the test results. The diameter of the composite spring was predicted to be 17.5 mm for ensuring a spring rate equal to that when using steel material. Finally, a finite element model of the composite coil spring with $45^{\circ}$ ply angles and 17.5 mm wire diameter was constructed and analyzed for obtaining the static spring rate, which was then compared with experimental results.

• Korean Journal of Medicinal Crop Science
• /
• v.26 no.3
• /
• pp.240-247
• /
• 2018

Background: Saline soil has negative effects on the growth of most crops. Sodium is the main element that causes salt accumulation in soil. Organic materials such as cow and poultry manure, are frequently used during the preparation stage, which causes an increase in the rate of salt accumulation in the soil. Methods and Results: To investigate the influences of sodium on ginseng, $NaH_2PO_4$, $Na_2SO_4$, and NaCl were used to adjust the sodium concentrations at 0, 12.5, 25, 50, 75 and 100 mM in nutrient solution. In a 2-year-old ginseng, toxic symptoms appeared when the sodium treatment exceeded 50 mM. The sodium concentration in the leaves was 3.33%, which is more than twice as high as that of the control treated at 50 mM. As the sodium concentration increased, the root weight significantly decreased. In the 100 mM treatment, the weight decreased by 28% when compared to that of the control. The Amount of ginsenoside significantly increased with an increase in sodium concentrations. Conclusions: These results suggest that the growth of 2-year-old ginseng is negatively affected when sodium exceeds 50 mM. This result can be used for a as basis in diagnosing the physiological disorders of ginseng.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.7
• /
• pp.29-36
• /
• 2004

In this work, the effect of composite couplings on hub loads of a hingeless rotor in forward flight is investigated. The hingeless composite rotor blade is idealized as a laminated thin-walled box-beam. The nonclassical effects such as transverse shear, torsional warping are considered in the structural formulation. The nonlinear differential equations of motion are obtained by applying Hamilton's principle. The blade response and hub loads are calculated using a finite element formulation in space and time. The aerodynamic forces acting on the blade are calculated by quasi-steady strip theory. The theory includes the effects of reversed flow and compressibility. The magnitude of elastic couplings obtained by MSC/NASTRAN is compared with the classical pitch-flap $({\delta}3)$ or $pitch-lag({\alpha}1)$ coupling. It is found that the elastic couplings have a substantial effect on the behavior of $N_b/rev$ hub loads. Nearly 10 to 40% of hub loads is reduced by appropriately tailoring the fiber orientation angles in the laminae of the composite blade.

• Journal of Sensor Science and Technology
• /
• v.26 no.4
• /
• pp.235-238
• /
• 2017

In this study, the design of a tri-axis micromachined gyroscope is proposed and the vibration characteristic of the structure is analyzed. Tri-axis vibratory gyroscopes that utilize Coriolis effect are the most commonly used micromachined inertial sensors because of their advantages, such as low cost, small packaging size, and low power consumption. The proposed design is a single structure with four proof masses, which are coupled to their adjacent ones. The coupling springs of the proof masses orthogonally transfer the driving vibrational motion. The resonant frequencies of the gyroscope are analyzed by finite element method (FEM) simulation. The suspension beam spring design of proof masses limits the resonance frequencies of four modes, viz., drive mode, pitch, roll and yaw sensing mode in the range of 110 Hz near 21 kHz, 21173 Hz, 21239 Hz, 21244 Hz, and 21280 Hz, respectively. The unwanted modes are separated from the drive and sense modes by more than 700 Hz. Thereafter the drive and the sense mode vibrations are calculated and simulated to confirm the driving feasibility and estimate the sensitivity of the gyroscope. The cross-axis sensitivities caused by driving motion are 1.5 deg/s for both x- and y-axis, and 0.2 deg/s for z-axis.

• Structural Engineering and Mechanics
• /
• v.59 no.3
• /
• pp.503-526
• /
• 2016

In-plane and out-of-plane free vibration analysis of Timoshenko curved beams is addressed based on the isogeometric method, and an effective scheme to avoid numerical locking in both of the two patterns is proposed in this paper. The isogeometric computational model takes into account the effects of shear deformation, rotary inertia and axis extensibility of curved beams, and is applicable for uniform circular beams, and more complicated variable curvature and cross-section beams as illustrated by numerical examples. Meanwhile, it is shown that, the $C^{p-1}$-continuous NURBS elements remarkably have higher accuracy than the finite elements with the same number of degrees of freedom. Nevertheless, for in-plane or out-of-plane vibration analysis of Timoshenko curved beams, the NURBS-based isogeometric method also exhibits locking effect to some extent. To eliminate numerical locking, the selective reduced one-point integration and $\bar{B}$ projection element based on stiffness ratio is devised to achieve locking free analysis for in-plane and out-of-plane models, respectively. The suggested integral schemes for moderately slender models obtain accurate results in both dominated and non-dominated regions of locking effect. Moreover, this strategy is effective for beam structures with different slenderness. Finally, the influence factors of structural parameters of curved beams on their natural frequency are scrutinized.

• Steel and Composite Structures
• /
• v.19 no.5
• /
• pp.1115-1144
• /
• 2015

Current climate conditions along with advances in technology make further design and verification methods for structural strength and reliability of wind turbine towers imperative. Along with the growing interest for "green" energy, the wind energy sector has been developed tremendously the past decades. To this end, the improvement of wind turbine towers in terms of structural detailing and performance result in more efficient, durable and robust structures that facilitate their wider application, thus leading to energy harvesting increase. The wind tower industry is set to expand to greater heights than before and tapered steel towers with a circular cross-section are widely used as more capable of carrying heavier loads. The present study focuses on the improvement of the structural response of steel wind turbine towers, by means of internal stiffening. A thorough investigation of the contribution of stiffening rings to the overall structural behavior of the tower is being carried out. These stiffening rings are placed along the tower height to reduce local buckling phenomena, thus increasing the buckling strength of steel wind energy towers and leading the structure to a behavior closer to the one provided by the beam theory. Additionally to ring stiffeners, vertical stiffening schemes are studied to eliminate the presence of short wavelength buckles due to bending. For the purposes of this research, finite element analysis is applied in order to describe and predict in an accurate way the structural response of a model tower stiffened by internal stiffeners. Moreover, a parametric study is being performed in order to investigate the effect of the stiffeners' number to the functionality of the aforementioned stiffening systems and the improved structural behavior of the overall wind converter.

• Korean Journal of Optics and Photonics
• /
• v.10 no.2
• /
• pp.107-113
• /
• 1999

Low-aberration holographic scanners that eliminate the need for lenses and mirrors promise to greatly reduce the cost of laser printers and image scanners. In this study, a holographic optical element that can simultaneously scan and focus a laser beam is designed with analytic ray tracing method. An analytic and experimental work is conducted in which we investigated the hologram structure and hologon configuration for linear aberration-free scanning. For a prototype scanner, a He-Ne laser is used to manufacture and reconstruct the hologram, and the measured bow is about $\pm$133$\mu\textrm{m}$ and spot size(half-intensity beamwidth) in under 100$\mu\textrm{m}$ for a 300 mm scan length without using a correcting lens or mirror. The diffraction efficiency is about 55$\pm$5%, which is acceptably flat. The experimentally measured results agrees with the computed values. From this fact, we can conclude that the computed results using ray tracing method are practical and useful values, and have a potential for use in high resolution laser printers.

• Journal of the Korean Society for Railway
• /
• v.18 no.3
• /
• pp.212-222
• /
• 2015

The characteristics of noise emission from tram systems should be investigated in order to design and construct an urban tram network that raises fewer environmental noise problems. In this paper, the characteristics of rolling noise from a tram were studied and a desired stiffness of the rail supports was proposed using a noise prediction model. The mobilities of embedded rails and resilient wheels were predicted using the Timoshenko beam model and the finite element model, respectively. The predicted mobilities were compared with the measured results. Compared with the measured values, the calculated noise level near the track showed small errors for frequencies higher than 300 Hz. Then, the source strengths of rail and wheel components were examined by varying the rail supporting stiffness and the slab supporting stiffness so that suitable stiffness values could be estimated that would reduce noise radiated from rails and wheels but that would not greatly increase the ground vibration.