• Journal of the Society of Naval Architects of Korea
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• v.56 no.6
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• pp.488-496
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• 2019

The estimation of block erection work time at a dock is one of the important factors when establishing or managing the total shipbuilding schedule. In order to predict the work time, it is a natural approach that the existing block erection data would be used to solve the problem. Generally the work time per unit is the product of coefficient value, quantity, and product value. Previously, the work time per unit is determined statistically by unit load data. However, we estimate the work time per unit through work time coefficient value from series ships using machine learning. In machine learning, the outcome depends mainly on how the training data is organized. Therefore, in this study, we use 'Feature Engineering' to determine which one should be used as features, and to check their influence on the result. In order to get the coefficient value of each block, we try to solve this problem through the Ensemble learning methods which is actively used nowadays. Among the many techniques of Ensemble learning, the final model is constructed by Stacking Ensemble techniques, consisting of the existing Ensemble models (Decision Tree, Random Forest, Gradient Boost, Square Loss Gradient Boost, XG Boost), and the accuracy is maximized by selecting three candidates among all models. Finally, the results of this study are verified by the predicted total work time for one ship among the same series.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.2
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• pp.185-196
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• 2006

Statement of problem: The researches on the influence of design variables on the stress distribution in cortical and trabecular bones and on optimal design for implant system were limited. Purpose: The purpose of this study is to identify the sensitivities of design parameters and to suggest the optimal parameters for designing the onebody type implant system. Material and methods: Stresses arising in the implant system were obtained by finite element analysis using a three dimensional model. An onebody type implant system[Oneplant (Warrantec. Co. Ltd., Korea)] was considered in this study. Vortical load(150 N) was applied on the top of the abutment along the axial direction. The initial design variables set for sensitivity analysis were radius of fixture, numbers of micro thread, numbers of power thread, height of micro thread, future length, tapered angle of future, inclined angle of thread, width of micro thread and width of power thread. The statistical technique of Design of Experiments(DOE) was applied tn the simulation model to deduce effective design parameters on stress distributions in bones. The deduced design parameters were incorporated into a fully automated design tool which is coupled with the finite element analysis and numerical optimization to determine the optimal design parameters. Results: 1. The result of sensitivity analysis showed six design variables - radius of future, tapered angle of fixture, inclined angle of thread, numbers of power thread, numbers of micro thread and height of micro thread - were more influential than the others. 2. The optimal values of design variables can be deduced by coupling finite element analysis (FEA) and design optimization tool(DOT).

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.825-831
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• 2007

The use of high-strength aluminum alloys for ship and offshore structure generally has many benefits compared to the structural steels. These materials are used widely in a variety of fields, especially in the hull and deck of high speed craft, box-girder of bridges, deck and side plates of offshore structure. The structural weight can be reduced using these aluminum structure, which can enable high speed The characteristics of stress-strain relationship of aluminum structure are fairly different from the steel one, because of the influence of Heat Affected Zone(HAZ) by the welding processing. The HAZ of aluminum is much wider than that of steel with its high heat conductivity. In this paper, the ultimate strength characteristics of aluminum stiffened panel subjected to axial loading, such as the relationship between extent of HAZ and the behavior of buckling/ultimate strength, are investigated through the Finite Element Analysis with varying its range.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.80-85
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• 2016

Carbon fiber-reinforced composite materials have been widely used in various industrial fields, but there are limits to increasing their strength and stiffness, because of the short-length fibers that are impregnated in them. In this study, a lab-scale small extruder system was developed with the capability to perform the carbon fiber impregnation and extrusion process in order to evaluate the properties of long-length carbon fiber reinforced thermoplastic composite materials molded by the LFT-D method. Specimens were made with the small extruder to press-mold long-length carbon fiber composite materials and evaluate their material properties. As a result, it was found that the carbon fiber length, press load and carbon fiber contents have a considerable influence on the strength and stiffness. Additional studies on such factors as the mixing screw design and coating of the carbon fiber are needed in order to improve the mechanical properties of carbon fiber composite materials.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.411-417
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• 2013

The moment responses of electric pole foundations for a railroad were investigated using real-scale load tests. Large overturning moments were applied to two square rigid piles with a 1.1 m width and a 2.2 m embedded depth. Two different installation methods-with and without a form-were applied to evaluate the influence of the form work on the moment capacities of the foundations. The reduction of ground strength caused by the excavation without a form is more pronounce than the decrease of frictional strength due to the smooth concrete surface with a form. From the test results, it is found that the current design method which applies a proportional coefficient to consider the effect of a form work is not appropriate. When the normal and frictional stressed is considered separately, the effect of a form work can be estimated reasonably by reducing the friction angle between soil and foundation by 20%.

• Restorative Dentistry and Endodontics
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• v.19 no.1
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• pp.231-254
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• 1994

Fracture of cusp, on posterior teeth, especially those carious or restored, is major cause of tooth loss. Inappropriate treatments, such as unnecessarily wide cavity preparations, increase the potential of further trauma and possible fracture of the remaining tooth structures. Fracture potential may be directly related to the stresses exerted upon the tooth during masticatory function. The purpose of this study is to evaluate the fracture resistance of tooth, restored with composite resin inlay. In this study, MOD inlay cavity prepared on maxillary first premolar and restored with composite resin inlay. Three dimensional finite element models with eight nodes isoparametric solid element, developed by serial grinding-photographing technique. These models have various occlusal isthmus and depth of cavity, 1/2, 1/3 and 1/4 of isthmus width and 0.7, 0.85 and 1.0 of depth of cavity. The magnitude of load was 474 N and 172 N as presented to maximal biting force and normal chewing force. These loads applied onto ridges of buccal and lingual cusp. These models analyzed with three dimensional finite element method. The results of this study were as follows : 1. There is no difference of displacement between width of occlusal isthmus and depth of cavity. 2. The stress concentrated at bucco-mesial comer, bucco-disal comer, pulpal line angle and the interface area between internal slopes of cusp and resin inlay. 3. The vector of stress direct to buccal and lingual side from center of cavity, to tooth surface going on to enamel. The magnitude of vector increase from occlusal surface to cervix. 4. The crack of tooth start interface area, between internal slop of buccal cusp and resin inlay. It progresses through buccopulpal line angle to cervix at buccomesial and buccodistal comer. 5. The influence with depth of cavity to fracture of tooth was more than width of isthmus. 6. It would be favorable to make the isthmus width narrower than a third of the intercuspal distance and depth of cavity is below 1 : 0.7.

• Journal of the Korea Institute of Building Construction
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• v.10 no.2
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• pp.105-113
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• 2010

Method or work type improvement is needed in relation to reducing cost and increasing efficiency by ensuring construction quality and reducing labor in the form work process. This would have a great influence on the entire construction process, and make the process of adopting materials and methods more rational and economic. Hence, this study aimed to develop a Synthetic Resins Euroform that could improve durability, water-proofing, sophistication, and organizational unity through the use of injection modeling. Accordingly, this paper first investigated various performance requirements and necessary techniques, and then verified feasibility by evaluating the physical safety and technical validity when it is applied to construction field. In addition, this study evaluated the constructability, safety performance, environmental performance, and systemic excellence in terms of maintaining convenience of Synthetic Resins Euroform. Moreover, to verify feasibility in the construction field, this study analyzed and evaluated the maximum stress by measuring the load and deformation of the space of the horizontal furring, which is attached to Euroform as an armature.

• Tribology and Lubricants
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• v.32 no.3
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• pp.101-105
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• 2016

Trap effect of groove is evaluated in a lubricating system using computational fluid dynamics (CFD) analysis. The simulation is based on the standard k-ε turbulence model and the discrete phase model (DPM) using a commercial CFD code FLUENT. The simulation results are also capable of showing the particle trajectories in flow field. Computational domain is meshed using the GAMBIT pre-processor. The various grooves are applied in order to improve lubrication characteristics such as reduction of friction loss, increase in load carrying capacity, and trapping of the wear particles. Trap effect of groove is investigated with variations in cross-sectional shape and Reynolds number in this research. Various cross-sectional shapes of groove (rectangular, triangle, U shaped, trapezoid, elliptical shapes) are considered to evaluate the trap effect in simplified two-dimensional sliding bearing. The particles are assumed to steel, and defined a single particle injection condition in various positions. The “reflect” boundary condition for discrete phase is applied to the wall boundary, and the “escape” boundary condition to “pressure inlet” and “pressure outlet” conditions. The streamlines are compared with particles trajectories in the groove. From the results of numerical analysis in the study, it is found that the cross-sectional shapes favorable to the creation of vortex and small eddy current are effective in terms of particle trapping effect. Moreover, it is found that the Reynolds number has a strong influence on the pattern of vortex or small eddy current in the groove, and that the pattern of the vortex or small eddy current affects the trap effect of the groove.

• Restorative Dentistry and Endodontics
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• v.39 no.4
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• pp.310-318
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• 2014

Objectives: This study examined the influence of the resin thickness on the polymerization of silorane- and methacrylate-based composites. Materials and Methods: One silorane-based (Filtek P90, 3M ESPE) and two methacrylate-based (Filtek Z250 and Z350, 3M ESPE) composite resins were used. The number of photons were detected using a photodiode detector at the different thicknesses (thickness, 1, 2 and 3 mm) specimens. The microhardness of the top and bottom surfaces was measured (n = 15) using a Vickers hardness with 200 gf load and 15 sec dwell time conditions. The degree of conversion (DC) of the specimens was determined using Fourier transform infrared spectroscopy (FTIR). Scratched powder of each top and bottom surface of the specimen dissolved in ethanol for transmission FTIR spectroscopy. The refractive index was measured using a Abbe-type refractometer. To measure the polymerization shrinkage, a linometer was used. The results were analyzed using two-way ANOVA and Tukey's test at p < 0.05 level. Results: The silorane-based resin composite showed the lowest filler content and light attenuation among the specimens. P90 showed the highest values in the DC and the lowest microhardness at all depth. In the polymerization shrinkage, P90 showed a significantly lower shrinkage than the rest two resin products (p < 0.05). P90 showed a significantly lower refractive index than the remaining two resin products (p < 0.05). Conclusions: DC, microhardness, polymerization rate and refractive index linearly decreased as specimen thickness linearly increased. P90 showed much less polymerization shrinkage compared to other specimens. P90, even though achieved the highest DC, showed the lowest microhardness and refractive index.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.133-140
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• 2010

Five strengthened columns and an unstrengthened column were tested under constant axial load and cyclic lateral loads to examine the seismic performance of the unbounded strengthening procedure using wire ropes and T-plates. Main variables considered were the presence of mortar cover for strengthening steel element and anchorage method of T-plate. Test results clearly showed that T-plates having a proper anchorage contribute to transfer of applied moment as well as enhancement of ductility of reinforced concrete columns. However, T-plate not anchored fully into a column base can seldom transfer the externally applied moment, though it highly improves the ductility of column. The presence of mortar cover for strengthening steel elements is significantly effective in enhancing the initial stiffness and flexural capacity of the strengthened columns, but has an adversely effect on enhancing the ductility. The ultimate moment strength predicted from the extended section laminae method in better agreement with test results compared with predictions obtained using stress black specified in ACI 318-05.