Determination of Impact Damage in CFRP via PVDF Signal Analysis with Support Vector Machine.

Carbon fiber reinforced plastics (CFRPs) have high specific stiffness and strength, but they are vulnerable to transverse loading, especially low-velocity impact loadings. The impact damage may cause serious strength reduction in CFRP structure, but the damage in a CFRP is mainly internal and microscopic, that it is barely visible. Therefore, this study proposes a method of determining impact damage in CFRP via poly(vinylidene fluoride) (PVDF) sensor, which is convenient and has high mechanical and electrical performance. In total, 114 drop impact tests were performed to investigate on impact responses and PVDF signals due to impacts. The test results were analyzed to determine the damage of specimens and signal features, which are relevant to failure mechanisms were extracted from PVDF signals by means of discrete wavelet transform (DWT). Support vector machine (SVM) was used for optimal classification of damage state, and the model using radial basis function (RBF) kernel showed the best performance. The model was validated through a 4-fold cross-validation, and the accuracy was reported to be 92.30%. In conclusion, impact damage in CFRP structures can be effectively determined using the spectral analysis and the machine learning-based classification on PVDF signals.

Nutrient inputs from submarine groundwater discharge (SGD) in Masan Bay, an embayment surrounded by heavily industrialized cities, Korea.

In order to estimate the magnitude of submarine groundwater discharge (SGD) and the associated nutrient fluxes in Masan Bay on the southern coast of Korea, we measured the concentrations of 226Ra and nutrients in seawater, brackish groundwater, and stream water in May and August 2006. Gauging unidentified nutrient fluxes through SGD is very important in this bay since diatom red tides have been occurring from April to October every year since the 1980s. Based on a 226Ra mass balance model, the submarine inputs of coastal groundwater were estimated to be 4.8x10(6) and 5.7x10(6) m3 d(-1) (61 and 71 L m(-2) d(-1)) in May and August, respectively, which were approximately 840% and 540% of the surface water discharge into the bay. The fluxes of dissolved inorganic phosphorus (DIP) and silicate (DSi) through SGD were 2-3 fold higher than those via stream water, while the fluxes of dissolved inorganic nitrogen (DIN) were comparable to those from surface waters during both sampling periods. Nutrient fluxes through stream waters relative to those from SGD were more significant in the inner part of the bay, which appears to be due to the direct influence of heavily polluted stream waters. Our study shows that the large and continuous supply of inorganic nutrients through SGD may play an important role in eutrophication and the occurrence of red tides in this bay, which should be taken into consideration in the environmental management of the bay.