• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.706-713
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• 2019

In this study, basic research was conducted to provide guidelines for selecting printers and materials suitable for each application case by analyzing 3D printing method and surface characteristics of materials suitable for microfluidic system. We have studied the surface characteristics according to the materials for the two typical printing methods: The most commonly used method of Fused Deposition Modeling (FDM) printing and the relatively high resolution method of Stereolithography (SLA) printing. The FDM prints exhibited hydrophilic properties before post - treatment, regardless of the material, but showed hydrophobic properties after post - treatment with acetone vapor. It was confirmed by the observation of surface roughness using SEM that the change of the contact angle was due to the removal of the surface structure by post-treatment. SLA prints exhibited hydrophilic properties compared to FDM prints, but they were experimentally confirmed to be capable of surface modification using hydrophobic coatings. It was confirmed that it is impossible to make a transparent specimen in the FDM method. However, sufficient transparency is secured in the case of the SLA method. It is also confirmed that the electroporation chip of the digital electroporation system based on the droplet contact charging phenomenon was fabricated by the SLA method and the direct application to the microfluidic system by demonstrating the electroporation successfully.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.189-207
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• 2023

In the present study, the thermoshearing experiment on a rough rock fracture were modeled using a three-dimensional grain-based distinct element model (GBDEM). The experiment was conducted by the Korea Institute of Construction Technology to investigate the progressive shear failure of fracture under the influence of thermal stress in a critical stress state. The numerical model employs an assembly of multiple polyhedral grains and their interfaces to represent the rock sample, and calculates the coupled thermo-mechanical behavior of the grains (blocks) and the interfaces (contacts) using 3DEC, a DEM code. The primary focus was on simulating the temperature evolution, generation of thermal stress, and shear and normal displacements of the fracture. Two fracture models, namely the mated fracture model and the unmated fracture model, were constructed based on the degree of surface matedness, and their respective behaviors were compared and analyzed. By leveraging the advantage of the DEM, the contact area between the fracture surfaces was continuously monitored during the simulation, enabling an examination of its influence on shear behavior. The numerical results demonstrated distinct differences depending on the degree of the surface matedness at the initial stage. In the mated fracture model, where the surfaces were in almost full contact, the characteristic stages of peak stress and residual stress commonly observed in shear behavior of natural rock joints were reasonably replicated, despite exhibiting discrepancies with the experimental results. The analysis of contact area variation over time confirmed that our numerical model effectively simulated the abrupt normal dilation and shear slip, stress softening phenomenon, and transition to the residual state that occur during the peak stress stage. The unmated fracture model, which closely resembled the experimental specimen, showed qualitative agreement with the experimental observations, including heat transfer characteristics, the progressive shear failure process induced by heating, and the increase in thermal stress. However, there were some mismatches between the numerical and experimental results regarding the onset of fracture slip and the magnitudes of fracture stress and displacement. This research was conducted as part of DECOVALEX-2023 Task G, and we expect the numerical model to be enhanced through continued collaboration with other research teams and validated in further studies.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.108-108
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• 2017

In this study, biocomposite filaments with agricultural by-products can be used in extrusion-based 3D (Three-dimensional) printing. Extrusion-based 3D printing stands as a promising technique owing to its versatility. We hypothesized that bio-filament composite consisted of something derived from agricultural by-products could be used as 3D printing materials that could overcome the drawbacks of PCL (poly-caprolactone). Bio-filament mixed with PCL and agricultural by-products was defined as r-PCL in this study. In order to find it out the optimal mixing ratio of filaments, we had investigated PCL, r-PCL 10%, r-PCL 20%, r-PCL 50% separately. The morphological and chemical characteristics of the filaments were analyzed by FE-SEM (Field emission scanning electron microscope) and EDX (Energy-dispersive X-Ray spectroscopy), and the mechanical properties were evaluated by stress-strain curve, water contact angle, and cytotoxicity analysis. Results of this study have been shown as a promising way to produce eco-friendly bio-filaments composite for FDM (Fused deposition modeling) method based 3D printing technology. Thus, we could establish biomimetic scaffolds based on bio-printer filaments mixed with agricultural by-product.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.33-38
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• 2012

EMB is considered as the next generation braking mechanism because it has simple structure and is environment friendly. However, as other brake mechanisms, EMB should be operated reliably for any operating conditions. EMB should be designed with fail-safe and fault-tolerant control concepts which require robust fault detection algorithms for various possible faults. In the design of fault detection algorithms, it is very difficult to construct faulty conditions in real EMB and thus, simulations are often used to emulate the faulty conditions. In this paper, a simulation tool is developed using the commercial software to emulate gear faults in the EMB mechanism. A backlash compensation algorithm is introduced based on contact point detection because screw backlash causes a delay in clamping force response time.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.89-100
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• 2016

Given the unpredictability of the space environment, satellite communications are manually performed by exchanging telecommands and telemetry. Ground support for orbiting satellites is given only during limited periods of ground antenna visibility, which can result in conflicts when multiple satellites are present. This problem can be regarded as a scheduling problem of allocating antenna support (task) to limited visibility (resource). To mitigate unforeseen errors and costs associated with manual scheduling and mission planning, we propose a novel method based on a genetic algorithm to solve the ground support problem of multiple satellites and antennae with visibility conflicts. Numerous scheduling parameters, including user priority, emergency, profit, contact interval, support time, remaining resource, are considered to provide maximum benefit to users and real applications. The modeling and formulae are developed in accordance with the characteristics of satellite communication. To validate the proposed algorithm, 20 satellites and 3 ground antennae in the Korean peninsula are assumed and modeled using the satellite tool kit (STK). The proposed algorithm is applied to two operation modes: (i) telemetry, tracking, and command and (ii) payload. The results of the present study show near-optimal scheduling in both operation modes and demonstrate the applicability of the proposed algorithm to actual mission control systems.

• Journal of Korea Foundry Society
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• v.21 no.5
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• pp.290-295
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• 2001

We fabricated test samples containing various shape elements and surface roughness checking points for the jewelry cast master patterns by employing the 3D computer aided design (CAD), selective laser sintering (SLS) rapid prototype (RP) with the DuraForm powders. We varied the alignment angle from $0^{\circ}$ to $10^{\circ}$ at a given layer thickness of 0.08 and 0.1mm, respectively, in RP operation. Dimensions of the shape elements as well as values of surface roughness are characterized by an optical microscope and a contact-scanning profilometer. Surface roughness values of the top and vertical face increased as the alignment angle increased, while the other roughness values and shape elements variation were not depending on the alignment angle. The resolution of the shape realization was enhanced as the layer thickness became smaller. The minimum diameter of the hole, common in jewelry design, was 1.2 mm, and the shrinkage became 12% at the 1.6 mm-diameter hole, Our results implied that we face down the proposed design elements with $0^{\circ}$ alignment angle, and consider the shrinkage effect of each shape element in DuraForm RP jewelry modeling.

• International Journal of Automotive Technology
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• v.5 no.4
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• pp.247-255
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• 2004

The majority of real world frontal collisions involves partial overlap (offset) collision, in which only one of the two longitudinal members is used for energy absorption. This leads to dangerous intrusions of the passenger compartment. Excessive intrusion is usually generated on the impacted side causing higher contact injury risk on the occupants compared with full frontal collision. The ideal structure needs to have extendable length when the front-end structure is not capable to absorb crash energy without violating deceleration pulse requirements. A smart structure has been proposed to meet this ideal requirement. The proposed front-end structure consists of two hydraulic cylinders integrated with the front-end longitudinal members of standard vehicles. The work carried out in this paper includes developing and analyzing mathematical models of two different cases representing vehicle-to-vehicle and vehicle-to-barrier in full and offset collisions. By numerical crash simulations, this idea has been evaluated and optimized. It is proven form numerical simulations that the smart structures bring significantly lower intrusions and decelerations. In addition, it is shown that the mathematical models are valid, flexible, and can be used in an effective way to give a quick insight of real life crashes.

• IE interfaces
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• v.18 no.4
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• pp.361-369
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• 2005

Postal address information is basis for customer contact channel as well as for the postal logistics such as sorting and dispatching, and the management system has been prepared. It should manage not only address itself but also information of delivery districts and sequences. It is necessary to consider geographic information system (GIS) to be included for intuitive and efficient manipulation. In order to construct a integrative system that could manage and utilize the standardized postal address information, we analyze various user requirements, define required GIS information, and present some results of data and process modeling. In addition, we explain several main functions with screen-shots of the implemented system. The GIS-enabled system, which is constructed after this study, is planned to be used to build and manage a database of nationwide postal addresses. It would make it possible to present other postal information systems with the address information and to provide various customer services.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1663-1666
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• 2007

The finite element method is applied to analyze the deformation mechanisms in the closed-cell Al foam under the compression. The modeling of the real cellular structure proceeds with the concept of the reverse engineering. First of all, the small, $10{\times}\;10{\times}\;10mm^3$ sized specimens of the closed-cell Al foam are prepared. The micro focus X-ray CTsystem of SHIMADZU Corp. is used to scan the full structures of the specimens. The scanned structures are converted to the geometric surfaces and solids through the software for 3-D scan data processing, RapidFormTMof INUS Tech. Inc. Then the solid meshes are directly generated on the converted geometric solids for the finite element analysis. The large elastic-plastic deformation and 3-D contact problems for the Al cellular material are considered. The clear and successful analysis for the deformation mechanisms in the closed-cell Al foam is carried out through the comparison of the numerical results in this research with the referred experimental ones.

• International Journal of Automotive Technology
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• v.8 no.6
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• pp.723-730
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• 2007

The typical design of automotive driveshafts generally utilizes Constant Velocity(CV) joints as a solution to NVH. CV joints are an integral part of vehicles and significantly affect steering, suspension, and vehicle vibration comfort levels. Thus, CV joints have been favored over universal joints due to the constant velocity torque transfer and plunging capability. Although CV joints are common in vehicle applications, current research works on modeling CV joint friction and assumes constant empirical friction coefficient values. However, such models are long known to be inaccurate, especially under dynamic conditions, which is the case for CV joints. In this paper, an instrumented advanced CV joint friction apparatus was developed to measure the internal friction behavior of CV joints using actual tripod-type joint assemblies. The setup is capable of measuring key performance of friction under different realistic operating conditions of oscillatory speeds, torque and joint installation angles. The apparatus incorporates a custom-installed triaxial force sensor inside of the joint to measure the internal CV joint forces(including friction). Using the designed test setup, the intrinsic interfacial parameters of CV joints were investigated in order to understand their contact and friction mechanisms. The results provide a better understanding of CV joint friction characteristics in developing improved automotive driveshafts.