Hull-form optimization of a 66,000 dwt bulk carrier in irregular wave condition

This paper deploys optimization techniques to obtain the optimum hull form of a 66,000 DWT bulk carrier in calm water and in irregular head waves at sea state 6. Parametric modification functions for the bow hull-form variation are SAC shape, section shape (U-V type, DLWL type). Multi-objective functions are applied to minimize the values of wave-making resistance in calm water and mean added resistance in waves. WAVIS version 1.3 is used to obtain wave-making resistance in calm water condition. The modified Fujii and Takahashi's formula is applied to obtain the added resistance in short waves. The added resistance in long wave is obtained from the potential-flow solver based on the 3-D panel method. And the mean added resistance in irregular head waves is obtained by linear superposition of the wave spectrum and the response function. The PSO (Particle swarm optimization) algorithm is employed for the optimization technique. The resistance and motion characteristics in calm water, in regular head waves and in irregular head waves of the two hull forms are compared. It has been shown that the optimal brings 6.8% reduction in the mean added resistance at sea state 6

Numerical Sensitivity Tests of Volatile Organic Compounds Emission to PM2.5 Formation during Heat Wave Period in 2018 in Two Southeast Korean Cities

A record-breaking severe heat wave was recorded in southeast Korea from 11 July to 15 August 2018, and the numerical sensitivity simulations of volatile organic compound (VOC) to secondarily generated particulate matter with diameter of less than 2.5 mu m (PM2.5) concentrations were studied in the Busan and Ulsan metropolitan areas in southeast Korea. A weather research and forecasting (WRF) model coupled with chemistry (WRF-Chem) was employed, and we carried out VOC emission sensitivity simulations to investigate variations in PM2.5 concentrations during the heat wave period that occurred from 11 July to 15 August 2018. In our study, when anthropogenic VOC emissions from the Comprehensive Regional Emissions Inventory for Atmospheric Transport Experiment-2015 (CREATE-2015) inventory were increased by approximately a factor of five in southeast Korea, a better agreement with observations of PM2.5 mass concentrations was simulated, implying an underestimation of anthropogenic VOC emissions over southeast Korea. The simulated secondary organic aerosol (SOA) fraction, in particular, showed greater dominance during high temperature periods such as 19-21 July, 2018, with the SOA fractions of 42.3% (in Busan) and 34.3% (in Ulsan) among a sub-total of seven inorganic and organic components. This is considerably higher than observed annual mean organic carbon (OC) fraction (28.4 +/- 4%) among seven components, indicating the enhancement of secondary organic aerosols induced by photochemical reactions during the heat wave period in both metropolitan areas. The PM2.5 to PM10 ratios were 0.69 and 0.74, on average, during the study period in the two cities. These were also significantly higher than the typical range in those cities, which was 0.5-0.6 in 2018. Our simulations implied that extremely high temperatures with no precipitation are significantly important to the secondary generation of PM2.5 with higher secondary organic aerosol fraction via photochemical reactions in southeastern Korean cities. Other possible relationships between anthropogenic VOC emissions and temperature during the heat wave episode are also discussed in this study