• Journal of Ocean Engineering and Technology
• /
• v.36 no.2
• /
• pp.91-100
• /
• 2022

In general, the effect of roll motion is not considered in the study on maneuverability in calm water. However, for high-speed twin-screw ships such as the DTMB 5415, the coupling effects of roll and other motions should be considered. Therefore, in this study, the estimation of maneuverability using a 4-degree-of-freedom (DOF; surge, sway, roll, yaw) maneuvering mathematical group (MMG) model was conducted for the DTMB 5415, to improve the estimation accuracy of its maneuverability. Furthermore, a study on the change in turning performance according to the fin angle was conducted. To accurately calculate the lift and drag forces generated by the fins, it is necessary to consider the three-dimensional shape of the wing, submerged depth, and effect of interference with the hull. First, a maneuvering simulation model was developed based on the 4-DOF MMG mathematical model, and the lift force and moment generated by the side fins were considered as external force terms. By employing the CFD model, the lift and drag forces generated from the side fins during ship operation were calculated, and the results were adopted as the external force terms of the 4-DOF MMG mathematical model. A 35° turning simulation was conducted by altering the ship's speed and the angle of the side fins. Accordingly, it was confirmed that the MMG simulation model constructed with the lift force of the fins calculated through CFD can sufficiently estimate maneuverability. It was confirmed that the heel angle changes according to the fin angle during steady turning, and the turning performance changes accordingly. In addition, it was verified that the turning performance could be improved by increasing the heel angle in the outward turning direction using the side fin, and that the sway speed of the ship during turning can affect the turning performance. Hence, it is considered necessary to study the effect of the sway speed on the turning performance of a ship during turning.

• Industrial Engineering and Management Systems
• /
• v.7 no.2
• /
• pp.160-170
• /
• 2008

This paper proposes a mathematical model for converting conveyor assembly line to cellular manufacturing in complex production environments. Complex production environments refer to the situations with multi-products, variant demand, different batch sizes and the worker abilities varying with work stations and products respectively. The model proposed in this paper aims to determine (1) how many cells should be formatted; (2) how many workers should be assigned in each cell; (3) and how many workers should be rested in shortened conveyor line when a conveyor assembly line should be converted, in order to optimize system performances which are defined as the total throughput time and total labor power. We refer the model to a new production system. Such model can be used as an evaluation tool in the cases of (i) when a company wants to change its production system (usually a belt conveyor line) to a new one (including cell manufacturing); (ii) when a company wants to evaluate the performance of its converted system. Simulation experiments based on the data collected from the previous documents are used to estimate the marginal impact that each factor change has had on the estimated performance improvement resulting from the conversion.

• Research in Mathematical Education
• /
• v.12 no.4
• /
• pp.251-258
• /
• 2008

This paper deals with factors discriminating mathematically gifted and non-gifted students. Discussion of some characteristics of mathematically gifted students is done in the first session. Several factors distinguish mathematically gifted from the non-gifted students. High mathematical creativity, high intelligence and opinion of teachers are some of the key factors that can be used for discriminating mathematically gifted and non-gifted students. Research studies have revealed that cognitive as well as affective factors will enhance giftedness. In this study the investigator wishes to look in detail about the characteristics of mathematically gifted students and how they can be identified. Anyway, teachers can change environmental factors and maximum outcome of giftedness can be ensured."

• Journal for History of Mathematics
• /
• v.29 no.6
• /
• pp.353-363
• /
• 2016

In mathematical population ecology which is an academic field that studies how populations of biological species change as times flows at specific locations in their habitats, PDE models have been studied in many aspects and found to have different properties from the classical ODE models. And different approaches to PDE type models in mathematical biology are still being tried currently. This article investigate various forms to express diffusion effects and review the history of PDE models involving diffusion terms in mathematical ecology. Semi-linear systems representing the spatial movements of each individual as random simple diffusion and quasi-linear systems describing more complex diffusions reflecting interspecific interactions are studied. Also it introduce a few of important problems to be solved in this field.

• Bulletin of the Korean Mathematical Society
• /
• v.44 no.4
• /
• pp.795-806
• /
• 2007

We investigate F-traceless component of the conformal curvature tensor defined by (3.6) in $K\ddot{a}hler$ manifolds of dimension ${\geq}4$, and show that the F-traceless component is invariant under concircular change. In particular, we determine $K\ddot{a}hler$ manifolds with parallel F-traceless component and improve some theorems, provided in the previous paper([2]), which are concerned with the traceless component of the conformal curvature tensor and the spectrum of the Laplacian acting on $p(0{\leq}p{\leq}2)$-forms on the manifold by using the F-traceless component.

• East Asian mathematical journal
• /
• v.32 no.1
• /
• pp.139-152
• /
• 2016

Inflammatory Bowel Disease(IBD) is chronic, relapsing, immune mediated disorder. The exact cause of IBD is still unknown. The immune system is known to play important role in the dynamics of IBD. We focus on relation between T cells and cytokines in immune system that leads to IBD. In this paper, we propose a mathematical model describing IBD under considering immune mediated disorder by using ordinary differential equations. The existence and stability of the model are established, where an applicable basin of attraction are calculated and examined. Some numerical simulations are presented to verify the proposed results and as changing parameter values given by sensitivity analysis, we show how to change dynamic behaviors of the model.

• Education of Primary School Mathematics
• /
• v.19 no.4
• /
• pp.261-276
• /
• 2016

This study was to investigate the effects of peer mentoring on students' mathematical characters and mathematics achievements in mathematics class. The participants were twenty four 6th grade elementary students at the S school in Sungbuk-Gu, Seoul, Korea. They were divided into 4 groups according to the combination of groups. The researchers analyzed the experimental group and the control group with covariances on the sub-factors of the mathematical characters such as respect, caring, sharing, and openness. However, there were no statistically significant changes. However, with the help of the two analyses on the mathematical logs and the worksheets which had been carried out in advance by the quantitative and qualitative research methods, the researchers investigated how the peer mentoring-applied instructions would change the mathematical characters for each sub-factor in detail. In conclusion, the peer mentoring-applied instructions makes a positive contribution to the students' mathematical character and mathematical academic achievements. We suggest that peer mentoring in mathematics lessons should be adopted in various mathematical ability levels of students.

• Research in Mathematical Education
• /
• v.19 no.1
• /
• pp.19-41
• /
• 2015

Previous studies indicated that students tended to hold less satisfactory beliefs about the discipline of mathematics, beliefs about themselves as learners of mathematics, and beliefs about mathematics teaching and learning. However, only a few studies had developed curricular interventions to change students' beliefs. This study aimed to examine the effect of a problem-solving curriculum (i.e., Mathematical Problem Solving for Everyone, MProSE) on Singaporean Grade 7 students' beliefs about mathematical problem solving (MPS). Four classes (n =142) were engaged in ten lessons with each comprising four stages: understand the problem, devise a plan, carry out the plan, and look back. Heuristics and metacognitive control were emphasized during students' problem solving activities. Results indicated that the MProSE curriculum enabled some students to develop more satisfactory beliefs about MPS. Further path analysis showed that students' attitudes towards the MProSE curriculum are important predictors for their beliefs.

• Communications of Mathematical Education
• /
• v.26 no.1
• /
• pp.29-50
• /
• 2012

The purpose of this study is a comparison of proficient level and below basic level students' mathematical achievement in the National Achievement Evaluation and Assessment(NAEA). For the purpose, this study compared the proficient level and below basic level students' ratios, students' mathematical achievement of contents area and behavioral area in 6th, 9th, and 11th grades. This study found the change of proficient level and below basic level students' ratios, and the proficient level and below basic level students' characteristics on mathematical achievement of contents area and behavioral area in 6th, 9th, and 11th grades.

• Bulletin of the Korean Mathematical Society
• /
• v.48 no.3
• /
• pp.475-489
• /
• 2011

In this paper, we use a generalized Brownian motion to define a generalized analytic Feynman integral. We then obtain some results for the generalized analytic Feynman integral of bounded cylinder functionals of the form F(x) = $\hat{v}$(($g_1,x)^{\sim}$,..., $(g_n,x)^{\sim}$) defined on a very general function space $C_{a,b}$[0,T]. We also present a change of scale formula for function space integrals of such cylinder functionals.