Comparison between M5′ model tree and neural networks for prediction of significant wave height in Lake Superior

Prediction of wave height is of great importance in marine and coastal engineering. Soft computing tools such as artificial neural networks (ANNs) are recently used for prediction of significant wave height. However, ANNs are not as transparent as semi-empirical regression-based models. In addition, neural networks approach needs to find network parameters such as number of hidden layers and neurons by trial and error, which is time consuming. Therefore, in this work, model trees as a new soft computing method was invoked for prediction of significant wave height. The main advantage of model trees is that, compared to neural networks, they represent understandable rules. These rules can be readily expressed so that humans can understand them. The data set used for developing model trees comprises of wind and wave data gathered in Lake Superior from 6 April to 10 November 2000 and 19 April to 6 November 2001. M5′ algorithm was employed for building and evaluating model trees. Training and testing data include wind speed (U₁₀) as the input variable and the significant wave height (H_s) as the output variable. Results indicate that error statistics of model trees and feed-forward back propagation (FFBP) ANNs were similar, while model trees was marginally more accurate. In addition, model tree shows that for wind speed above 4.7 m/s, the wave height increases nonlinearly by the wind speed.     

Numerical simulation of local scour around two pipelines in tandem using CFD–DEM method

In the field of offshore oil and gas engineering, the arrangement of multiple pipelines are becoming more common, the spacing between the pipelines and the incoming stream velocity will significantly affect the scouring process around the pipelines. In this study, the effect of space ratio (G/D) and the stream velocity on the scouring process around two pipelines in tandem are investigated using the coupled approach of computational fluid dynamics (CFD) and discrete element method (DEM). Here G is the spacing between the pipelines and D is the diameter of the pipeline. Specifically, the effect of space ratio and the stream velocity are discussed by simulating the gap ratio (G/D) between two pipelines ranging from 1 to 3 with an interval of 1, under the stream velocity U = 0.5,1 and 2 m/s, The results indicate that when G/D ≤ 2, the equilibrium scour depth below the upstream pipeline (S1) is slightly larger than that under the downstream pipeline (S2), S1 and S2 slightly increase as the gap ratio increases. Whereas for G/D > 2, the equilibrium scour depth beneath the upstream pipeline is slightly smaller than that under the downstream pipeline, S1 and S2 slightly decrease as the gap ratio increases. Furthermore, the scour depths are highly dependent on and positively related to the incoming stream velocity, the equilibrium bed profiles are similar under the same incident stream velocity with different gap ratios.     

Determination of the chlorophyll “a” concentration using a combined method based on measurements with a modified photometer

A method of chlorophyll ??a?? determination based on fluorescence and optical density measurements with a compact photometer is described. Our modification of the method allows one to determine the chlorophyll ??a?? with a simple instrument in the field with acceptable accuracy. The results of the calibration and validation of the method obtained from conventional spectrophotometric determinations in Antarctic waters are shown.     

Lower bound limit loads of ship structure components using the mα-tangent method based on single linear elastic analysis

Limit loads for ship structure components are determined in this paper based on a single linear elastic finite element analysis by invoking the concept of kinematically active reference volume in conjunction with the m_α-tangent method. The method enables rapid determination of lower bound limit loads for ship structure components by taking their kinematically inactive volume into consideration. This method is applied to a number of ship structure components possessing different percentages of inactive volume. Results are compared with the corresponding inelastic finite element results, and available analytical solutions.     

Measurement of 224Ra, 226Ra and 228Ra in seawater using Mn-fiber adsorption-γ spectrum method

I~IOXThe half-lives of natural radioactive nuclides "'Ra, 226Ra and 228Ra are 3. 66 d, 5. 76 a,1600 a respectively, hence, the marine process with various time scales can be researched by taking these nuclides as tracers. Because these nuclides can be determined by measuring them or theirdaughters' a,g, y-rays, they have been applied extensively in oceanography research. Huang(1996), Huang et al. (1996 a,b) and Chen (1996) have given reviews on it.Since the contents of "'Ra, 226Ra and 228…