• Steel and Composite Structures
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• v.50 no.4
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• pp.403-418
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• 2024

In this paper, vibration and energy absorption characteristics of a nanostructure which is composed of two embedded porous annular/circular nanoplates coupled by a viscoelastic substrate are investigated. The modified couple stress theory (MCST) and the Gurtin-Murdoch theory are applied to take into account the size and the surface effects, respectively. Furthermore, the structural damping effect is probed by the Kelvin-Voigt model and the mathematical model of the problem is developed by a new hyperbolic higher order shear deformation theory. The differential quadrature method (DQM) is employed to obtain the out-of-phase and in-phase frequencies of the structure in order to predict the dynamic response of it. The acquired results reveal that the vibration and energy absorption of the system depends on some factors such as porosity, surface stress effects, material length scale parameter, damping and spring constants of the viscoelastic foundation as well as geometrical parameters of annular/circular nanoplates. A bird's-eye view of the findings in the research paper offers a comprehensive understanding of the vibrational behavior and energy absorption capabilities of annular/circular porous nanoplates. The multidisciplinary approach and the inclusion of porosity make this study valuable for the development of innovative materials and applications in the field of nanoscience and engineering.

• Wind and Structures
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• v.38 no.5
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• pp.355-366
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• 2024

Severe natural multi-hazard events can cause damage to infrastructure and economic losses of billions of dollars. The challenges of modeling these losses include dependency between hazards, cause and sequence of loss, and lack of available data. This paper presents and explores multi-hazard loss modeling in the context of the combined wind and rain vulnerability of mid/high-rise buildings during hurricane events. A component-based probabilistic vulnerability model provides the framework to test and contrast two different approaches to treat the multi-hazards: In one, the wind and rain hazard models are both decoupled from the vulnerability model. In the other, only the wind hazard is decoupled, while the rain hazard model is embedded into the vulnerability model. The paper presents the mathematical and conceptual development of each approach, example outputs from each for the same scenario, and a discussion of weaknesses and strengths of each approach.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.2
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• pp.63-72
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• 2016

An expected-discounted cost model based on RRP(Renewal Reward Process), referred to as a stochastic decision model, has been developed to estimate the optimal period of in-depth inspection which is one of critical issues in the life-cycle maintenance management of harbor structures such as rubble-mound breakwaters. A mathematical model, which is a function of the probability distribution of the service-life, has been formulated by simultaneously adopting PIM(Periodic Inspection and Maintenance) and CBIM(Condition-Based Inspection and Maintenance) policies so as to resolve limitations of other models, also all the costs in the model associated with monitoring and repair have been discounted with time. From both an analytical solution derived in this paper under the condition in which a failure rate function is a constant and the sensitivity analyses for the variety of different distribution functions and conditions, it has been confirmed that the present solution is more versatile than the existing solution suggested in a very simplified setting. Additionally, even in that case which the probability distribution of the service-life is estimated through the stochastic process, the present model is of course also well suited to interpret the nonlinearity of deterioration process. In particular, a MCS(Monte-Carlo Simulation)-based sample path method has been used to evaluate the parameters of a damage intensity function in stochastic process. Finally, the present stochastic decision model can satisfactorily be applied to armor units of rubble mound breakwaters. The optimal periods of in-depth inspection of rubble-mound breakwaters can be determined by minimizing the expected total cost rate with respect to the behavioral feature of damage process, the level of serviceability limit, and the consequence of that structure.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.29-41
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• 2007

Structural design, like other complex decision problems, involves many trade-offs among competing criteria. Although mathematical programming models are becoming increasingly realistic, they often have design limitations, that is, there are often relevant issues that cannot be easily captured. From the understanding of these limitations, a decision-support system is developed that can generate some useful alternatives as well as a single optimum value in the optimization of steel frame structures. The alternatives produced using this system are "good" with respect to modeled objectives, and yet are "different," and are often better, with respect to interesting objectives not present in the model. In this study, we created a decision-support system for designing the most cost-effective moment-resisting steel frame structures for resisting lateral loads without compromising overall stability. The proposed approach considers the cost of steel products and the cost of connections within the design process. This system makes use of an optimization formulation, which was modified to generate alternatives of optimum value, which is the result of the trade-off between the number of moment connections and total cost. This trade-off was achieved by reducing the number of moment connections and rearranging them, using the combination of analysis based on the LRFD code and optimization scheme based on genetic algorithms. To evaluate the usefulness of this system, the alternatives were examined with respect to various design aspects.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.1
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• pp.11-26
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• 1984

The aim of this study is to establish a synthetical optimal method that simultaneously analyze and design reinforced concrete flat slab-column structures involving multi-constraints and multi-design variables. The variables adopted in this mathematical models consist of design variables including sectional sizes and steel areas of frames, and analysis variable of the ratio of bending moment redistribution. The cost function is taken as the objective function in the formulation of optimal problems. A number of constraint equations, involving the ultimate limit state and the serviceability limit state, is derived in accordance with BSI CP110 requirements on the basis of limit state design theory. Both objective function and constraint equations derived from design variables and an analysis variable generally become high degree nonlinear problems. Using SLP as an analytical method of nonlinear optimal problems, an optimal algorithm is developed so as to analyze and design the structures considered in this study. The developed algorithm is directly applied to a few reinforced concrete flat slab-column structures to assure the validity of it and the possibility of optimization From the research it is found that the algorithm developed in this study is applicable to the optimization of reinforced concrete flat slab column structures and it converges to a optimal solution with 4 to 6 iterations regardless of initial variables. The result shows that an economical design can be possible when compared with conventional designs. It is also found that considering the ratio of bending moment redistribution as a variable is reasonable. It has a great effect on the composition of optimal sections and the economy of structures.

• Journal of Korea Water Resources Association
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• v.44 no.7
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• pp.511-522
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• 2011

Two-dimensional shallow water model based on the cut cell and the adaptive mesh refinement techniques is presented in this paper. These two mesh generation methods are combined to facilitate modeling of complex geometries. By using dynamically adaptive mesh, the model can achieve high resolution efficiently at the interface where flow changes rapidly. The HLLC Reimann solver and the MUSCL method are employed to calculate advection fluxes with numerical stability and precision. The model was applied to simulate the extreme urban flooding experiments performed by the IMPACT (Investigation of Extreme Flood Processes and Uncertainty) project. Simulation results were in good agreement with observed data, and transient flows as well as the impact of building structures on flood waves were calculated with accuracy. The cut cell method eased the model sensitivity to refinement. It can be concluded that the model is applicable to the urban flood simulation in case the effects of sewer and stormwater drainage system on flooding are relatively small like the dam brake.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.663-670
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• 2020

A study on mechanical property characterization and modeling technique was carried out to approximate the behaviour of structures with 2.5D C/SiC material. Several tensile tests were performed to analyze the behaviour characteristics of the 2.5D C/SiC material and elastic property was characterized by applying a mathematical homogenization and a modified rule of mixture. SiC matrix representing the elasto-plastic behavior approximates as a bilinear function. Then the equivalent yield strength and equivalent plastic stiffness were calculated by minimizing errors in experiment and approximation. RVE(Representative Volume Element)was defined from the fiber and matrix configuration of 2.5D C/SiC and a process of calculating the effective stiffness matrix by applying the modified rule of mixture to RVE was implemented in the ABAQUS User-defined subroutine. Finite element analysis was performed by applying the mechanical properties of fiber and matrix calculated based on the proposed process, and the results were in good agreement with the experimental results.

• Communications of Mathematical Education
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• v.23 no.1
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• pp.109-128
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• 2009

This study aimed to investigate students' learning process by examining their perception process of problem structure and mathematization, and further to suggest an effective teaching and learning of mathematics to improve students' problem-solving ability. Using the qualitative research method, the researcher observed the collaborative learning of two middle school students by providing problem-posing activities of five lessons and interviewed the students during their performance. The results indicated the student with a high achievement tended to make a similar problem and a new problem where a problem structure should be found first, had a flexible approach in changing its variability of the problem because he had advanced algebraic thinking of quantitative reasoning and reversibility in dealing with making a formula, which related to developing creativity. In conclusion, it was observed that the process of problem posing required accurate understanding of problem structures, providing students an opportunity to understand elements and principles of the problem to find the relation of the problem. Teachers may use a strategy of simplifying external structure of the problem and analyzing algebraical thinking necessary to internal structure according to students' level so that students are able to recognize the problem.

• The Mathematical Education
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• v.59 no.1
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• pp.17-29
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• 2020

The purpose of this study is to analyze the teacher's discourse structure of teachers according to the interaction pattern between teacher and student in the process of mathematization. To achieve this goal, we observed a semester class (44 lessons) of an experienced teacher who had practiced teaching methods for promoting student engagement for more than 20 years. Among them, one lesson case would be match the teacher's intention and the student's response and the other one lesson case would be to mismatch between the teacher's intention and the student's response was analyzed. In other words, in the process of mathematization based on students' engagement, the intention of the teacher and the reaction of the student was determined according to the cases where students did not make an error and when they made an error. A methodology used to develop a theory based on data collected through classroom observations(grounded theory). Because the purpose of the study is to identify the teacher's discourse structure to help students' mathematization, observe the teacher's discourse and collect data based on student engagement. Based on the teacher's discourse, conceptualize it as a discourse structure for students to mathematization. As a result, teacher's discourse structure had contributed to the intention of the teacher and the reaction of the student in the process of mathematization. Based on these results, we can help the development of classroom discourse for mathematization by specifying the role of the teacher to help students experience the mathematization process in the future.

• Communications of Mathematical Education
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• v.35 no.1
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• pp.75-96
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• 2021

This study aims to drive the implications for the structure of mathematics curriculum documents in Korea, exploring the coherence in the documental structure of the IB DP mathematics curriculum, which is gaining international attention. The documents of the IB DP mathematics curriculum were analyzed based on the coherence of external and internal structures. First, the curriculum was consistently described by subject and topic, presenting the table of contents and structure of the documents in the same format. Second, the descriptions of the curriculum between subjects and within the subjects were consistent through the same composition of the subject and assessment methods, the presentation of big ideas, and 'Guidance, clarification and syllabus links'. Third, in 'Connections', the curriculum documents were described with coherence through linking with other subjects by describing the connection plan with the real-world contexts, other subjects, and the 'Theory of Knowledge' in the IB curriculum. Based on these findings and implications for the concreteness and consistency of the components in mathematics curriculum documents, we propose the coherence between the presentation of subject areas and assessment methods of the revised curriculum, and the implementation of coherence in documental structure through links with other subjects.