• The Journal of the Acoustical Society of Korea
• /
• v.34 no.5
• /
• pp.371-376
• /
• 2015

In this study, we use 1:1, 1:2, and 1:4 scale zig-zag shape acoustic metamaterial structure to achieve broad and effective sound blocking at the subwavelength scale. The SPL(Sound Pressure Level) results show that the SPL loss of the scaled metamaterial slab in series is a superposition of individual SPL losses. Also, we show that the metamaterial tailors the material properties to achieve high impedance and high refractive index using effective medium theory. Our results show that broad and effective sound blocking is possible at the subwavelength scale just by scaling acoustic metamaterial.

• The Journal of the Acoustical Society of Korea
• /
• v.38 no.1
• /
• pp.67-72
• /
• 2019

In this study, we investigate the echo reduction performance of miniaturinzed Helmholtz resonators using smaller than wavelength acoustic metamaterial structures. The Helmholtz resonators are formed using air structures which exhibit large impedance mismatch with the surrounding underwater environment. Using the multi-physics software package, we find that significant reduction in the sonar signature is expected and frequency tailoring is possible by controlling the degree of space coiling and inner volume of the resonators. We find that for the basic Helmholtz resonators, up to 7 dB reduction in echo is expected at 10,000 Hz while when the miniaturized Helmoholtz resonators are used, up to 14 dB reduction in echo is expected at 5,000 Hz. In addition, frequency tailoring is demonstrated by varying the internal volume of the Helmholtz resonators and broadband characteristic is shown using superposition of various degree of space coiled structures. Through this study we investigate the effectiveness of the miniaturized Helmholtz resonators formed using air structures and the echo reduction results show promisses in the application of achieving underwater stealth.

• Journal of Engineering Education Research
• /
• v.24 no.2
• /
• pp.68-75
• /
• 2021

ABEEK recommends convergent engineering projects to nurture creative problem-solving ability for 1st year engineering students through 'Creative Engineering Design' course. However, 1st year engineering students, who have not yet studied core subjects in engineering, have difficulties understanding and coping with the challenges posed by the engineering-related projects. For this reason, the educational objectives of this course are usually frustrating to achieve by the instructor. In this paper, by using the problem-solving process and skills of critico(-creative) thinking, we prepare guidelines for creative engineering design education that allow 1st-year students to effectively participate in engineering projects without a complete understanding of the design process which is to be studied. Also, we present a case study that applies the guidelines to an on-going creative engineering design course and discusses the outcomes by showing student-generated works. The results showed that the intuitive content and everyday expression of critico(-creative) thinking education enabled the instructor to effectively guide their students through the requirements of engineering projects without relying on advanced engineering design methods, and that the application of these guidelines also helped improve students' communication skills, including presentation. We show that the guidelines for creative engineering design education utilizing the problem-solving process and skills of critico(-creative) thinking is not only contributing to achieving the educational objectives of the creative engineering design course but can also be an educational paradigm that incorporates critico(-creative) thinking education into engineering education.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.22 no.4
• /
• pp.177-188
• /
• 1989

The purpose of this study was to investigate the detoxifying effect on PSP-infested sea mussel, Mytilus edulis, by heating treatment and correlation between the PSP toxicity and the environmental conditions of shellfish culture area such as temperature, pH, salinity, density of Protogonyaulax sp. and concentration of inorganic nutrients such as $NH_4-N,\;NO_3-N,\;NO_2-N\;and\;PO_4-P$. This experiment was carried out at $Suj\u{o}ng$ in Masan, Yangdo in Jindong, $Hach\u{o}ng\;in\;K\u{o}jedo\;and\;Gamch\u{o}n$ bay in Pusan from February to June in $1987\~1989$. It was observed that the detection ratio and toxicity of PSP in sea mussel were different by the year even same collected area. The PSP was often detected when the temperature of sea water about $8.0\~14.0^{\circ}C$. Sometimes the PSP fox of sea mussel was closely related to density of Protogonyaulax sp. at $Gamch\u{o}n$ bay in Pusan from March to April in 1989, but no relationship was observed except above duration during the study period. The concentration of inorganic nutrients effects on the growth of Protogonyaulax sp., then effects of $NO_3-N$ was the strongest among them. When the PSP-infested sea mussel homogenate was heated at various temperature, the PSP toxicity was not changed significantly at below $70^{\circ}C$ for 60 min. but it was proper-tionaly decreased as the heating temperature was increased. For example, when the sea mussel homogenate was heated at $100^{\circ}C,\;121^{\circ}C$ for 10 min., the toxicity was decreased about $67\%\;and\;90\%$, respectively. On the other hand, when shellstock sea mussel contained PSP of $150{\mu}g/100g$ was boiled at $100^{\circ}C$ for 30 min. with tap water, the toxicity was not detected by mouse assay, but that of PSP of $5400{\mu}g/100g$ was reduced to $57{\mu}g/100g$ even after boiling for 120 min.