Effect of the nonuniform grid on the two-dimensional transport equation was investigated in terms of theoretical analysis and finite difference method (FDM). The nonuniform grid having a typical structure of the numerical weather forecast model was incorporated in the vertical direction, while the uniform grid was used in the zonal direction. The staggered and non-staggered grid were placed in the vertical and zonal direction, respectively. Time stepping was performed with the third-order Runge Kutta scheme. An error analysis of the spatial discretization on the nonuniform grid was carried out, which indicated that the combined effect of the nonuniform grid and advection velocity produced either numerical diffusion or numerical adverse-diffusion. An analytic function is used for the quantitative evaluation of the errors associated with the discretized transport equation. Numerical experiments with the non-uniformity of vertical grid were found to support the analysis.

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Compared to conventional sheet forming processes, ISF is of a clear advantage in manufacturing small batch or customized parts. ISF needs die-less machine alone, while conventional sheet forming requires highly expensive facilities like dies, molds, and presses. This equipment takes long time to get preparation for manufacturing. However, ISF does not need the full facilities nor much cost and time. Because of the facts, ISF is continuously being used for small batch or prototyping manufacturing in current industries.However, spring-back induced in the process of incremental forming becomes a critical drawback on precision manufacturing. Since sheet metal, being a raw material for ISF, has property to resilience, spring-back would come in the case.It is the research objective to investigate how geometrical shaping parameters make effect on shape dimensional errors. In order to analyze the spring-back occurred in the process, this study experimented on Al 1015 material in the ISF. The statistical tool employed experimental design with factors. The table of orthogonal arrays of L8 (27) are used to design the experiments and ANOVA method are employed to statistically analyze the collected data. The results of the analysis from this study shows that the type of shape and the slope of bottom are the significant, whereas the shape size, the shape height, and the side angle are not significant factors on dimensional errors. More error incurred on the pyramid than on the circular type in the experiments. The sloped bottom showed higher errors than the flat one.

Incremental sheet metal forming is a manufacturing process to produce thin parts using sheet metals by a series of small incremental deformation. The process rarely needs dedicated dies and molds, thus, preparation time for the process is relatively short as to be compared to conventional metal forming. Spring back in sheet metal working is very common, which causes critical errors in dimensions. Incremental sheet metal forming is not fully investigated yet. Hence, incremental sheet metal forming frequently produces inaccurate parts. This paper proposes a method to minimize dimensional errors to improve shape accuracy of products manufactured by incremental forming. This study conducts experiments using an exclusive incremental forming machine and the material for these experiments are sheets of aluminum AL1015. This research defines a process parameter and selects a few factors for the experiments. The parameters employed in this paper are tool feed rate, tool diameter, step depth, material thickness, forming method, dies applied, and tool path method. In addition, their levels for each factor are determined. The plan of the experiments is designed using orthogonal array L8 (27) which requires minimum number of experiments. Based on the measurements, dimensional errors are collected both on the tool contacted surfaces and on the non-contacted surfaces. The distances between the formed surfaces and the CAD models are scanned and recorded using a commercial software product. These collected data are statistically analyzed and ANOVAs (analysis of variances) are drawn up. From the ANOVAs, this paper concludes that the process parameters of tool diameter, forming depth, and forming method are the significant factors to reduce the errors on the tool contacted surface. On the other hand, the experimental factors of forming method and dies applied are the significant factors on the non-contacted surface. However, the negative forming method always produces better accuracy than the positive forming method.

최근 기후변화의 영향으로 대규모 집중호우와 예측이 어려운 국지성 호우가 증가함에 따라 침수로 인한 피해가 증가하고 있다. 이러한 피해가 증가하면서 치수사업의 중요성이 대두되고 있으며, 예산사용 대비 효율적인 치수사업을 시행하기 위해서는 치수사업 전후의 비용과 편익을 비교한 정확한 경제성 분석이 필수적이다. 치수사업의 경제성을 분석하는 방법으로는 간편법, 개선법, 다차원법 등이 있으며 산간지역, 공업지역, 농업지역, 상업 및 주거지역의 특성을 고려해 피해액을 산정할 수 있어 정확도가 높은 다차원법을 실무에 가장 많이 사용하고 있다. 하지만 다차원법을 이용해 추정한 피해액과 재해연보의 실제피해액의 차이가 여전히 큰 것으로 나타나, 경제적 편익 및 투자비 회수 등의 문제점이 야기될 수 있다. 이러한 문제점을 해소시키기 위해서 군산시의 과거 침수피해액 자료를 이용하여 실제피해액에 의한 침수피해액 곡선과 다차원법의 결과값을 이용한 침수피해액 곡선을 비교하여 다차원법의 정확도를 파악하였다. 본 연구는 실측자료 기반의 침수피해 곡선을 이용하여 피해액 산출의 정확도를 개선시킬 뿐만 아니라 합리적인 비용-편익 분석을 통한 치수사업을 실시하는데 도움이 될 것으로 예상된다.