• Journal of the Society of Naval Architects of Korea
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• v.53 no.5
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• pp.343-352
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• 2016

In this study, a pre-swirl duct for the 180,000 DWT bulk carrier has been designed from a propulsion standpoint using CFD. The stern duct - designed by NMRI - was selected as the initial duct. The objective function is to minimize the value of delivered power in model scale. Design variables of the duct include duct angle, diameter, chord length, and vertical and horizontal displacements from the center. Design variables of the stators are blade number, arrangement angle, chord length, and pitch angle. A parametric design was carried out with the objective function obtained using CFD. Reynolds averaged Navier-Stokes equations have been solved; and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. MRF and sliding mesh models have been applied to simulate the actuating propeller. A self-propulsion point has been obtained from the results of towing and self-propelled computations, i.e., form factor obtained from towing computation and towing forces obtained from self-propelled computations of two propeller rotating speeds. The reduction rate of the delivered power of the improved stern duct is 2.9%, whereas that of the initial stern duct is 1.3%. The pre-swirl duct with one inner stator in upper starboard and three outer stators in portside has been designed. The delivered power due to the designed pre-swirl duct is reduced by 5.8%.

• Korean Journal of Computational Design and Engineering
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• v.17 no.2
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• pp.97-110
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• 2012

High performance sensors and modern data logging technology with real-time telemetry facilitate system fault diagnosis in a very precise manner. Fault detection, isolation and identification in fault diagnosis systems are typical steps to analyze the root cause of failures. This systematic failure analysis provides not only useful clues to rectify the abnormal behaviors of a system, but also key information to redesign the current system for retrofit. The main barriers to effective failure analysis are: (i) the gathered data (event) logs are too large in general, and further (ii) they usually contain noise and redundant data that make precise analysis difficult. This paper therefore applies suitable pre-processing techniques to data reduction and feature extraction, and then converts the reduced data log into a new format of event sequence information. Finally the event sequence information is decoded to investigate the correlation between specific event patterns and various system faults. The efficiency of the developed pre-filtering procedure is examined with a terminal box data log of a marine diesel engine.

• Design & Manufacturing
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• v.2 no.3
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• pp.40-44
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• 2008

Shaving in sheet metal forming is defined as a finish process to make the sheared surface clean which was blanked or pierced in the previous shearing stage. In this study the new shaving technique is applied to the progressive operation. The specimen is automatically fed by continuous movement of the strip. Which improve the positioning accuracy higher. For this study a square part which consist of blanking and piercing is selected for investigation and the progressive die which includes pre-piercing, pierce-shaving, half-blanking and blank-shaving etc is prepared for specimens of steel sheet(SPCC) and aluminum alloy sheet(AL5052). Experiments are carried out for several working variables such as shaving allowance, pre-shearing clearance and relative half-blanking depth. Consequently it was confirmed that the shaving by progressive die can be successfully employed to produce the clean parts requiring shaving process and optimum working conditions for shaving SPCC and AL5052 sheet metal are shaving allowance of 0.2mm(1.3% of thickness) and pre-shearing clearance of 5%.

• Proceedings of the Korea Society of Design Studies Conference
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• 2005.05a
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• pp.320-321
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• 2005

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.455-456
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• 2009

• Communications of Mathematical Education
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• v.36 no.1
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• pp.59-72
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• 2022

The purpose of this study is to understand the characteristics of the mathematical modeling tasks and lesson designs developed by pre-service teachers based on the inherent awareness of mathematical modeling, considering the importance of creating a task to perform mathematical modeling activity and designing a lesson. As a result, the mathematical modeling tasks developed by pre-service teachers mainly presents an appropriate amount of information using real life contexts for the purpose of learning using concepts, and it showed a tendency to develop to the level of cognitive demand that required procedures with connections to understanding, meaning, or concepts. And most of the developed modeling task-based lessons showed a tendency to design warm-up activity, model-eliciting activity, and model-exploration activity. This result is due to the lack of experience of pre-service teachers in creating mathematical modeling tasks. Therefore, it is necessary to continuously provide opportunities for pre-service teachers to learn concepts or create mathematical modeling tasks intended for exploration according to various mathematical contents, thereby actively cultivating their ability to create modeling tasks in the course of training pre-service teachers. Furthermore, it is necessary to strengthen the expertise in mathematical modeling teaching and learning by providing opportunities to actually perform the mathematical modeling-based classes designed by pre-service teachers and to experience the process of reflecting on the lessons.

• Korean Journal of Computational Design and Engineering
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• v.5 no.3
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• pp.263-275
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• 2000

Multidisciplinary design optimization(MDO) can yield optimal design considering all the disciplinary requirements concurrently. A method to implement the collaborative optimization(CO) approach, one of the MDO methodologies, is developed using a pre-compiler “EzpreCompiler”, a design optimization library “EzOptimizer”, and a common object request broker architecture(CORBA) in distributed computing environment. The CO approach is applied to a mathematical example to show its applicability and equivalence to standard optimization(SO) formulation. In a realistic engineering problem such as optimal design of a two-member hub frame, optimal design of a speed reducer and initial design of a bulk carrier, the CO yields better results than the SO. Furthermore, the CO allows the distributed processing using the CORBA, which leads to reduction of overall computation time.

• Journal of the Korean Society of Earth Science Education
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• v.7 no.3
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• pp.371-380
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• 2014

The purpose of the research was to analyze the characteristics which appeared to the process of designing experiment for pre-service elementary teachers. This study were participated 26 pre-service elementary teachers. The findings indicated that first, the researcher figured out the process elements could constructed in 12 elements such as 'states problem or question, predicts outcome or hypothesizes, lists materials needed, arranges steps in sequential order, lists more than 3 steps, Explore variables and select one or more variables, plans to control variables, plans to measure and observation, plans data collection, plans to repeat testing and tells reason, states plan for interpreting data, states plan for making conclusion based on data, states plan for making conclusion based on data' but did not figure out 2 elements such as 'defines the terms of the experiment, practice safety'. second, the characteristics of pre-service elementary teachers in the process of designing experiment were as follows; pre-service elementary teachers designed experiments unstructured process listed types and showed the superficial level of the design experiment. The results show that the programs of designing experiment activity should be constructed with the process elements which were concentrated by pre-service elementary teachers, should provide feedbacks to design experiment more accurately.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.170-180
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• 2008

Successful design, construction and maintenance of NATM tunnel demands prediction, control, stability guidelines, the estimation pre-improvement support system and monitoring of surface settlement, gradient and ground displacement with high accuracy. Moreover, urban NATM tunnel under difficult geotechnical conditions is important the estimation and necessary of pre-improvement support system. Various strategies have been proposed for the quantitative estimation of pre-improvement support system. This paper was investigated and analysed an assessment technique for the quantitative estimation of pre-improvement support system on underground space, as mountain and urban tunnel, in detail. The analysis performed on design and construction stage with field database using the proposed stability estimation index by many researcher including the critical strain and the apparent Young's modulus concept.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.183-190
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• 1998

This paper discusses the development and use of an integrated system for the design of steel box girder bridges. The system includes pre/post processors designed particularly for the ease of use by adopting GUI(Graphical User Interface). They offer convenient facilities for the management of design data and thus enable the user to draw satisfactory structural designs. In particular, ease of redesign iterations makes better structures possible in this system