• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.289-296
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• 2017

In this paper, geometrical optimization for newly designed flapping mechanism for insect-like micro air vehicle is presented. The mechanism uses strings to convert rotation of motor to reciprocating wing motion to reduce the total weight and inertial force. The governing algorithm of movement of the mechanism is established considering the characteristic of string that only tensile force can be acted by string, to optimize the kinematics. Modified pattern search method which is complemented to avoid converging into local optimum is adopted to the geometrical optimization of the mechanism. Then, prototype of the optimized geometry is produced and experimented to check the feasibility of the mechanism and the optimization method. The results from optimization and experiment shows good agreement in flapping amplitude and other wing kinematics. Further research will be conducted on dynamic analysis of the mechanism and detailed specification of the prototype.

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.547-547
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• 2003

The aim of this study was to compare the effects of three Ni-Ti instruments on leaning ability by evaluating the volumetric and morphological changes in the apical 6mm of the root canals before and after preparation, using three-dimensionally reconstructed root canals of extracted human teeth. Forty-five teeth were used in this study. They were opened the chambers and removed the all pulp remnants ultrasonically. Subsequently, the canal wall was coated with silver paste and prepared using ProTaper, ProFile and GT rotary files according to the manufacturers instructions. Before and after root canal preparation, all the specimens were scanned with micro computed tomography and examined the differences in dentine volume removed, canal straightening, the proportion of the unchanged area and canal transportation. Quantitative analysis revealed that instrumentation increased in canal volume ranging between 0.081 and $1.866{\;}\textrm{mm}^3$. On average, the large apical preparation produced by ProTaper demonstrated smaller proportions of unchanged surface areas compared to the two other instruments in small canals. But in large canals like maxillary central incisor, the preparation of ProTaper instruments was not enough. ProTaper instrument was tended to increase more in canal volume as compared with the other two instruments but unchanged area was no significant difference. These results showed that three instruments had similar preparation ability and micro computed tomography in combination with the coated wall of root canal using silver paste is a nondestructive and valuable tool to study root canal geometry and changes after preparations in detail.

• Advances in nano research
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• v.12 no.5
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• pp.467-482
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• 2022

In the current work, static and free torsional vibration of functionally graded (FG) nanorods are investigated using Fourier sine series. The boundary conditions are described by the two elastic torsional springs at the ends. The distribution of functionally graded material is considered using a power-law rule. The systems of equations of the mechanical response of nanorods subjected to deformable boundary conditions are achieved by using the modified couple stress theory (MCST) and taking the effects of torsional springs into account. The idea of the study is to construct an eigen value problem involving the torsional spring parameters with small scale parameter and functionally graded index. This article investigates the size dependent free torsional vibration based on the MCST of functionally graded nano/micro rods with deformable boundary conditions using a Fourier sine series solution for the first time. The eigen value problem is constructed using the Stokes' transform to deformable boundary conditions and also the convergence and accuracy of the present methodology are discussed in various numerical examples. The small size coefficient influence on the free torsional vibration characteristics is studied from the point of different parameters for both deformable and rigid boundary conditions. It shows that the torsional vibrational response of functionally graded nanorods are effected by geometry, small size effects, boundary conditions and material composition. Furthermore, for all deformable boundary conditions in the event of nano-sized FG nanorods, the incrementing of the small size parameters leads to increas the torsional frequencies.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.75-75
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• 2015

Strong interactions between electromagnetic radiation and electrons at metallic interfaces or in metallic nanostructures lead to resonant oscillations called surface plasmon resonance with fascinating properties: light confinement in subwavelength dimensions and enhancement of optical near fields, just to name a few [1,2]. By utilizing the properties enabled by geometry dependent localization of surface plasmons, metal photonics or plasmonics offers a promise of enabling novel photonic components and systems for integrated photonics or sensing applications [3-5]. The versatility of the nanoplasmonic platform is described in this talk on three folds: our findings on an enhanced ultracompact photodetector based on nanoridge plasmonics for photonic integrated circuit applications [3], a colorimetric sensing of miRNA based on a nanoplasmonic core-satellite assembly for label-free and on-chip sensing applications [4], and a controlled fabrication of plasmonic nanostructures on a flexible substrate based on a transfer printing process for ultra-sensitive and noise free flexible bio-sensing applications [5]. For integrated photonics, nanoplasmonics offers interesting opportunities providing the material and dimensional compatibility with ultra-small silicon electronics and the integrative functionality using hybrid photonic and electronic nanostructures. For sensing applications, remarkable changes in scattering colors stemming from a plasmonic coupling effect of gold nanoplasmonic particles have been utilized to demonstrate a detection of microRNAs at the femtomolar level with selectivity. As top-down or bottom-up fabrication of such nanoscale structures is limited to more conventional substrates, we have approached the controlled fabrication of highly ordered nanostructures using a transfer printing of pre-functionalized nanodisks on flexible substrates for more enabling applications of nanoplasmonics.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.3
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• pp.314-321
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• 2020

In this work, a preliminary design of an inlet guide vane and runner for developing a 2.5 kW hydraulic turbine was conducted by using computational fluid dynamic analysis. Three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used to analyze the fluid flow in the hydraulic turbine. The hexahedral grid system was used to construct computational domain, and the grid dependency test was performed to obtain the optimal grid system. Velocity triangle diagram considering the flow angles of the inlet guide vane and runner was analyzed to obtain a basic geometry of the inlet guide vane and runner. Through modification of the preliminary design, the hydraulic performances of the turbine have improved under overall drop conditions. Especially, the efficiency and power of the turbine increased by 0.95% and 1.45%, respectively, compared to those of the reference model.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.1
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• pp.14-19
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• 2016

Transmission error (TE) is the most important cause of gear noise and vibration because TEs affect the changes of the force and the speed of gears. TE is usually expressed as an angular deviation, or a linear deviation measured at the pitch point and calculated at successive positions of the pinion as it goes through the meshing cycle. Accurate measurement of TE for gear transmission will provide a reasonable basis for gear design, manufacturing processes and quality control. Therefore, in order to study the accuracy of the gear transmission, stability, TE, vibration and noise after gear micro-geometry modification, a gear transmission test rig is proposed in this paper, which is based on the existing technical conditions, by using reasonable testing methods, hardware and a signal processing method. All of the details and the experience can be taken into consideration in the next upgraded test rig.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.466-471
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• 2008

Structural vibration and noise are hot issues in underwater vehicles such as submarines for their survivability. Therefore, active vibration and noise control of submarine, which can be modeled as hull structure, have been conducted by the use of piezoelectric materials. Traditional piezoelectric materials are too brittle and not suitable to curved geometry such as hull structures. Therefore, advanced anisotropic piezoceramic actuator named as Macro-Fiber Composite (MFC), which can provide great flexibility, large induced strain and directional actuating force is adopted for this research. In this study, dynamic model of the smart hull structure is established and active vibration control performance of the smart hull structure is evaluated using optimally placed MFC. Actuating performance of MFC is evaluated by finite element analysis and dynamic modeling of the smart hull structure is derived by finite element method considering underwater condition. In order to suppress the vibration of hull structure, Linear-Quadratic-Gaussian (LQG) algorithm is adopted. After then active vibration control performance of the proposed smart hull structure is evaluated with computer simulation and experimental investigation in underwater. Structural vibration of the hull structure is decreased effectively by applying proper control voltages to the MFC actuators.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.156-162
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• 2005

In this paper, we study the mechanism of lead deformation by numerically simulating the stamping process by means of a commercial finite element code. It is very important to analyze effects that the lead shape makes on the lead deformation, because the lead shape is often modified in order to minimize the deformation or to increase the buckling critical load of the punch. Therefore the stamping process, first, numerically simulated by considering as a quasi-static problem. Second, the effect on the lead deformation due to the lead shape variation, a linear lead geometry and a bent lead, was numerically analyzed and discussed. Finally, the punching order was optimized fur multi-lead generating stamping process. The results show that the bent lead is little bit more shifted than the linear lead after the punching process. But the bent lead is vertically less deformed than the linear lead. The punching order to successively generate the lead is good to keep the lead space uniform. The results will be very effectively applied for the design of the blanking or punching dies in industry.

• The KSFM Journal of Fluid Machinery
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• v.9 no.2 s.35
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• pp.7-12
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• 2006

This study is to develop a system of electric power generation utilizing the wind resources available in the domestic wind environment. We tested drag-type vortical wind turbine models, which have two different types of blades: a flat plate and circular arc shape. Through a performance test, conditions of maximum rotational speed were found by measuring the rpm of wind turbine. The rotational speed was measured by a tachometer in a wind tunnel and the tunnel wind speed was by using a pilot-static tube and a micro manometer. The performance test for a prototype was accomplished by calculating power, power coefficient, torque coefficient from the measurement of torque and rpm by a dynamometer controller From the measurements for miniature turbine models with two different blades, the circular arc shape was found to Produce a maximum rotational speed for the same wind velocity condition. Based on this result, the prototype with the circular arc blade was made and tested. We found that it produces 500W at the wind velocity of 10.8 m/s and the power coefficient was 20%.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.70-75
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• 2011

Nowadays, modern gearboxes are characterized by high torque load demands, low running noise and compact design. Also durability of gearbox is specially a major issue for the industry. For the gearbox which used in wind turbine, gear transmission error(T.E.) is the excitation that leads the tonal noise known as gear whine, and radiated gear whine is also the dominant source of noise in the whole gearbox. In this paper, tooth modification for the high speed stage is used to compensate for the deformation of the teeth due to load and to ensure a proper meshing to achieve an optimized tooth contact pattern. The gearbox is firstly modeled in Romax software, and then the various combination analysis of the tooth modification is presented by using Windows LDP software, and the prediction of transmission error under the loaded torque for the helical gear pair is investigated, the transmission error, contact stress, root stress and load distribution are also calculated and compared before and after tooth modification under one torque condition. The simulation result shows that the transmission error and stress under the loads can be minimized by the appropriate tooth modification.