Identification of hydrodynamic coefficients in ship maneuvering equations of motion by Estimation-Before-Modeling technique

Estimation-Before-Modeling (EBM) technique (or the two-step method) is a system identification method that estimates parameters in a dynamic model. Given sea trial data, the extended Kalman filter and modified Bryson–Frazier smoother can be used to estimate motion variables, hydrodynamic force, and the speed and the direction of current. And using these estimated data, we can use the ridge regression method to estimate the hydrodynamic coefficients in a model. An identifiable state space model is constructed in case that current effect is included and the maneuvering characteristics of a ship are analyzed by correlation analysis. To better identify hydrodynamic coefficients, we suggest the sub-optimal input scenario that considers the D-optimal criterion. Finally, the algorithm is confirmed against real sea trial data of 113K tanker.     

Formation rate of water masses in the Japan sea

Water masses in the subsurface and the intermediate layer are actively formed due to strong winter convection in the Japan Sea. It is probable that some fraction of pollution is carried into the layer below the sea surface together with these water masses, so it is important to estimate the formation rate and turnover time of water masses to study the fate of pollutants. The present study estimates the annual formation rate and the turnover time of water masses using a three-dimensional ocean circulation model and a particle chasing method. The total annual formation rate of water masses below the sea surface amounted to about 3.53 ± 0.55 Sv in the Japan Sea. Regarding representative intermediate water masses, the annual formation rate of the Upper portion of the Japan Sea Proper Water (UJSPW) and the Japan Sea Intermediate Water (JSIW) were estimated to be about 0.38 ± 0.11 and 1.43 ± 0.16 Sv, respectively, although there was little evidence of the formation of deeper water masses below a depth of about 1500 m in a numerical experiment. An estimate of turnover time shows that the UJSPW and the JSIW circulate in the intermediate layer of the Japan Sea with timescales of about 22.1 and 2.2 years, respectively.     

Assessment of the volcanic hazard of Mt. Paektu explosion to international air traffic using South Korean airspace

Natural Hazards - A volcanic eruption is one of the most critical natural hazards in air transportation. In the European region, the Eyjafjallajökull eruption in 2010 triggered extensive...     

Wintertime suspended sediment simulation in the Huanghai and East China Seas

A simulation of suspended sediment movement relating to tidal and wave forcing during a winter monsoon in November 1983 in the Huanghai and East China Seas continental shelf is attempted by using the model describing the cohesive/non-cohesive sediment resuspension generated by interactions between currents and waves.model simulation showed that sediment concentration was increased by resuspension at shallow depths during the strong storm conditions due to high bottom stress interacted between currents and waves. This result is in general agreement with observations in horizontal distribution of suspended sediment distribution.At three current meter mooring positions off the southern Shandong Peninsula resuspension occurred only at a depth of 22m,nearest coastal position and at deeper parts at depths of 51 and 80m wave-current interaction effects were not significant. It has shown that the present model simulation demonstrated the capability of reproduction of suspended sediment movement under wintertime extreme event reasonably well.     

Factors controlling groundwater chemistry in an agricultural area with complex topographic and land use patterns in mid‐western South Korea

Shallow and bedrock groundwater from granitic aquifers were investigated for the hydrogeochemistry of major and minor constituents in an agricultural area. Nitrate concentrations were observed up to 49 mg/l as NO₃‐N, with 22% of samples exceeding the drinking water standard, which could pose a significant threat because most residents rely on groundwater as their drinking water source. Principal component analysis revealed three principal components (PCs): (1) nitrate contamination, contributed by major cations, Cl^?, SO and NO , (2) reduction processes positively involving Fe, Mn and B, and negatively involving dissolved oxygen and NO and (3) natural mineralization, involving HCO and F^?. Cluster analysis, performed on the PC scores, resulted in seven sample groups, which were successfully identified by total depth, elevation and land use. The nitrate‐contaminated groups had mixed land uses, with locally concentrated residential areas. Uncontaminated groundwater groups were found in the natural environment, including high‐altitude spring water and bedrock groundwater with a higher degree of natural mineralization. Shallow groundwater groups in paddy fields in lowlands were affected by reducing environments, of which one group was characterized by high Fe, Mn and B, and negligible nitrate. Groundwater with intermediate nitrate and lower Cl^? and SO was found primarily in hilly terrains with orchards and vegetable gardens, indicating lower contaminant loadings than lowland areas. Higher concentrations of F^? and nitrate were observed in the nitrate‐contaminated water, which seemed unlikely to be explained by groundwater mixing. The strong acidity generated from nitrification may infiltrate deeper into the aquifer, induce accelerated weathering of bedrock and result in the coexistence of F^? and nitrate, which may be an evidence of intense nitrate loading, leading to soil acidification. Multivariate statistical analysis successfully delineated hydrochemical characteristics of groundwater attained by natural and anthropogenic processes in an agriculturally stressed area with complex topographic land use patterns. Copyright © 2009 John Wiley & Sons, Ltd.     

Monitoring of suspended sediment variation using Landsat and MODIS in the Saemangeum coastal area of Korea

Suspended sediment concentration (SS) is an important indicator of marine environmental changes due to natural causes such as tides, tidal currents, and river discharges, as well as human activities such as construction in coastal regions. In the Saemangeum area on the west coast of Korea, construction of a huge tidal dyke for land reclamation has strongly influenced the coastal environment. This study used remotely sensed data to analyze the SS changes in coastal waters caused by the dyke construction. Landsat and MODIS satellite images were used for the spatial analysis of finer patterns and for the detailed temporal analysis, respectively. Forty Landsat scenes and 105 monthly composite MODIS images observed during 1985-2010 were employed, and four field campaigns (from 2005 to 2006) were performed to verify the image-derived SS. The results of the satellite data analyses showed that the seawater was clear before the dyke construction, with SS values lower than 20 g/m(3). These values increased continuously as the dyke construction progressed. The maximum SS values appeared just before completion of the fourth dyke. Values decreased to below 5 g/m(3) after dyke construction. These changes indicated tidal current modification. Some eddies and plumes were observed in the images generated from Landsat data. Landsat and MODIS can reveal that coastal water turbidity was greatly reduced after completion of the construction.     

Biomass and trophic structure of the plankton community in subtropical and temperate waters of the northwestern Pacific Ocean

This study examined the biomass structure of autotrophic and heterotrophic plankton along a trophic gradient in the northwestern Pacific Ocean in an attempt to understand planktonic food web structure. Autotrophic biomass exceeded that of heterotrophic organisms in all sampling regions, but with lesser contribution to total planktonic biomass at stations of higher phytoplankton biomass, including the northern East China Sea, compared to the regions of lower phytoplankton biomass. The proportion of the biomass of heterotrophic bacteria, nanoflagellates (HNF), and dinoflagellates (HDF) relative to that of phytoplankton was all inversely related to phytoplankton biomass, but positive relationships were observed for both ciliates and mesozooplankton. Mesozooplankton biomass inclined greater than phytoplankton along the gradient of phytoplankton biomass, with biomass rise being most closely associated with ciliate and HDF biomass and, to a lesser degree, with large phytoplankton (>3?μm). Both bacteria and picophytoplankton were significantly and positively related to the biomass ratio of mesozooplankton to the sum of HDF and ciliates (i.e., proxy of mesozooplankton predation on protozoans), but no positive relationship was apparent either for HNF or for large phytoplankton. Such relationships may result from predation relief on lower food webs associated with mesozooplankton feeding on protistan plankton.     

Effective periods and seismic performance of steel moment resisting frames designed for risk categories I and IV according to IBC2009

In current seismic design, structures that are essential for post‐disaster recovery, and hazardous facilities are classified as risk category IV and are designed with higher importance factors and stringent drift limits. These structures are expected to perform better in an earthquake event because a larger base shear and more stringent drift limit are used. Although this provision has been in the seismic design code over the last three decades, few studies have investigated the performance of essential structures. The aim of this study is to quantify the impact of higher importance factors and stringent drift limits on the seismic performance of steel moment resisting frames. A total of 16 steel structures are designed for Los Angeles and Seattle. Different risk categories are used for the design. The effects of the risk categories on the structural periods, and thus on the seismic force demand, are investigated. A suite of inelastic time history analyses are carried out to understand the probability of exceeding a specified limit state when the structures are subjected to different levels of earthquake events. The results show that the periods of the structures in risk category IV decrease by a factor of 0.5 to 0.8, and the strengths increase by a factor of 1.5 to 3.2. Seismic fragility analysis shows that the structures in risk category IV generally satisfy the probabilistic performance objectives. Copyright © 2014 John Wiley & Sons, Ltd.