Browsing by Author "Hegde, Arkal Vittal"

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Computational Intelligence in Prediction of Wave Transmission for Horizontally Interlaced Multi-layer Moored Floating Pipe Breakwater
(National Institute of Technology Karnataka, Surathkal, 2013) Govind, Patil Sanjay; Hegde, Arkal Vittal; Mandal, Sukomal
Energy dissipation process of Horizontally Interlaced Multi-layer Moored Floating Pipe Breakwater (HIMMFPB) depends on various factors like pipe interference effect, the spacing between the pipes and number of layers. As the effect of all these factors on transmission is not clearly understood, it will be extremely difficult to quantify them mathematically. Furthermore, it is a complex problem, and till now there has not been available a simple mathematical model to predict the wave transmission through HIMMFPB by considering all the boundary conditions, and hence one has to depend on physical model studies which are expensive and time consuming. Computational Intelligence (CI) techniques, such as, Artificial Neural Network (ANN), Adaptive Neuro-Fuzzy Inference System (ANFIS), Support Vector Machine Regression (SVMR), Genetic Programming (GP) and Genetic Algorithm (GA) have been efficaciously proposed as an efficient tool for modelling and predictions in coastal/ocean engineering problems. For developing CI models in prediction of wave transmission for HIMMFPB, data set were obtained from experimental wave transmission of HIMMFPB using regular wave flume at Marine Structure Laboratory, National Institute of Technology, Karnataka, Surathkal, Mangalore, India. These data sets are divided into two groups, one for training and other for testing. The input parameters that influence the wave transmission Kt  of floating breakwater, such as, relative spacing to pipesS D, relative breakwater widthW L, ratio of incident wave height to water depthHi d, incident wave steepness Hi L are considered in developing CI models for prediction of wave transmission past HIMMFPB. In the present work, five layer pipes with S / D of 2, 3, 4 and 5 are considered. The ANN model is developed for prediction of wave transmission for HIMMFPB. Two network models, ANN1 and ANN2 are constructed based on the parameters which influence the wave transmission of floating breakwater. The input parameters of ANN1 model areW / L , Hi / d and Hi / L . To study over a range of spacing of pipesiv S / D on Kt , an input parameter, S / D is added to form ANN2 model. Training and testing of the network models are carried out for different hidden nodes and epochs. It is observed that the correlation (above 90%) between predicted wave transmission values by the network models and measured values are in good agreement. Furthermore, to improve the result of prediction of wave transmission of HIMMFPB, recently developed technique such as SVMR is used. This technique works on structural risk minimization principle that has greater generalization ability and is superior to the empirical risk minimization principle as adopted in conventional neural network models. Support vector machines (SVMs) are based on statistical learning theory. The basic idea of support vector machines is to map the original data x into a feature space with high dimensionality through a non-linear mapping function and construct an optimal hyper-plane in new space. Six SVMR models are constructed using kernel functions. In order to study the performance of each kernel in predicting wave transmission of HIMMFPB, SVMR is trained by applying these kernel functions. Performance of SVMR is based on the best setting of SVMR and kernel parameters. Correlation Coefficient (CC) of SVMR (b-spline) model (CC Train = 0.9779 and CC Test = 0.9685) is considerably better than other SVMR models. However, it is noticed that ANN model in isolation cannot capture all data patterns easily. Adaptive neuro-fuzzy inference system (ANFIS) uses hybrid learning algorithm, which is more effective than the pure gradient decent approach used in ANN. ANFIS models are developed to predict wave transmission of HIMMFPB. The performance of the ANFIS models in the prediction of Kt is compared with the measured values using statistical measures, such as, CC, Root mean Square Error ( RMSE ) and Scatter Index ( SI ). All the ANFIS models have shown CCs higher than or equal to 0.9510, with RMSE less than or equal to 0.051074 and SI less than or equal to 0.102296. ANFIS5 model predictions are very realistic when compared with the measured values (CC Train = 0.9723, CC Test = 0.9635). It is also observed that an S D plays an important role to train ANFIS5 model to map an input-output relation. Furthermore influence of input parameters is assessed using Principalv Component Analysis (PCA). It is observed that Hi / L is the least influential parameter Based on the PCA study discarding the least influential parameters, ANFIS6 model is developed. It is observed that the ANFIS models yield higher CCs as compared to that of ANN models. To improve the performance of SVMR and better selection of SVMR and kernel parameters, hybrid genetic algorithm tuned support vector machine regression (GASVMR) model is developed to predict wave transmission through HIMMFPB. Furthermore, parameters of both linear and nonlinear SVM models are determined by GA. The results are compared with ANN, SVMR and ANFIS models in terms of CC, RMSE and SI . Performance of GA-SVMR is found to be reliably superior. CI models can be utilized to provide a fast and reliable solution in prediction of the wave transmission for HIMMFPB, thereby making GA-SVMR as an alternate approach to map the wave structure interactions of HIMMFPB.
Integrated vulnerability assessment of Karnataka Coast, India: A Geospatial approach
(National Institute of Technology Karnataka, Surathkal, 2017) B. J, Akshaya; Hegde, Arkal Vittal
Coastal environments are important ecological hotspot for all living organisms. Coastal environments support a large species of indigenous fauna and vegetation with a high biological diversity. Even the human population density in coastal areas is estimated to be three times the global mean. In recent times, increased and the rapid development at the coastal regions has strained the coastal ecosystems in the form of destruction and degradation. Change in globe’s atmospheric conditions has also increased the frequency of coastal hazards such as floods, hurricanes and storm surges. The sea level rise due to the global warming, along with the frequent storms, forms a looming threat to our coastlines. Mitigation of a potential disaster requires a detailed knowledge about vulnerability of the places to various hazards. Such vulnerabilities may be associated with natural or social hazards, or sometimes a combination of both. A systematic vulnerability may be carried out only if the various dimensions involving a hazard are considered. Vulnerability studies generally undertaken skip a very important aspect of human interaction with the nature. Researchers have insisted on inclusion of human interaction as a socio-economic variable in assessment studies. Most of the studies have been carried out using physical variables; Shoreline change rate, Sea-level change rate, Coastal slope, Significant wave height, Tidal range, Coastal regional elevation, Coastal geomorphology and very few studies have been carried out by combining socioeconomic variables along with the physical variables. Also very few studies have evaluated the effect of Tsunami and storm surge as variables for determining CVI. Most often CVI is calculated using the USGS equation. However, researchers have highlighted that the equation has a disadvantage for usage as equal weights has been assigned to all the variables even when the influence of one variable is more than that of the other variable. On the other hand, assigning random weights to variables can also be logically a mistake as weights are influenced by discretion of the individual researcher. In addition, it was found that the CVI calculated using USGS equation underestimates the risk of certain stretch of coast, which is highly prone to erosion. Hence, in the present study, an opinion survey of experts from ocean and coastalii engineering discipline was carried out and a weight scheme was formulated using the principles of Analytical Hierarchical Process (AHP). Tsunami vulnerability for regional scale using GIS was also carried out in the present study. Four geospatial variables, viz., topographic elevation, topographic slope, coastal proximity and vegetation were used to create a tsunami vulnerability map. It was found that Karnataka coast has 71.92 km length of coast in ‘very high vulnerability’ category, while 71.25 km was under ‘high vulnerability’ category. The extent of ‘moderate vulnerability’ and ‘low vulnerability’ was 71.20 km and 80.69 km, respectively. An overlay of the landuse classification on the tsunami vulnerability map showed that habitation (206.403 km2) and cropland (181.103 km2) are the two major classes of the study area, which are in high-risk category. It was also noticed that coast of Udupi and Magaluru talukas were most vulnerable coast of the study area. In addition, the use of AHP for assignment of weights to variables has provided the realistic scenario for the vulnerability assessment. The MCVI developed in the present study evaluated the level of risk on different segments of the coast. The maps developed in the present study are useful to identify areas where physical changes are most likely to occur in case of a coastal hazard, and as well in planning, managing and protecting resources in the study area.
Studies on the effects of an emerged impermeable and seaside perforated quarter circle breakwater on nearfield hydrodynamics
(2017) S, Binumol; Rao, Subba; Hegde, Arkal Vittal
Breakwaters are structures which are mainly used for the purpose of withstanding and dissipating the dynamic energy of ocean waves and thereby provide tranquility conditions on the lee side. Breakwaters are constructed either shore connected or detached to the coast. The main function of breakwaters is to create a tranquil medium on its leeside by reflecting the waves and also dissipating the wave energy arriving from seaside, resulting in ease of maneuverability to boats or ships to their berthing places. In modern times breakwaters are constructed for the purpose of protecting structures near to the coast and offshore, shoreline stabilization, forming an artificial harbour with a water area so protected from the ocean waves as to provide safe accommodation for ships and for preventing the siltation of river mouths. Different types of breakwaters have been developed in the past for the harbour development and protection of valuable coastal property, commercial activity and beach morphology. Among these, rubble mound breakwaters are the most common and provide good wave attenuation. In the beginning, primitive reefs and dykes of gentle slopes were built with natural stones. Later to save the material, steeper sloped structures with rubble mound, concrete block mound, rock fill over mound, caisson type etc. were tried. However, with time breakwaters with a variety of caisson designs have been proposed and developed. Later with development of technology various innovative types of breakwaters such as semicircular breakwater and quarter circle breakwater have been developed. Quarter circle breakwater (QBW) is a new-type breakwater first proposed by Xie et al. (2006) on the basis of semicircular breakwater. Quarter circle breakwater is usually placed on rubble mound foundation and its superstructure consists of a precast reinforced concrete quarter circular surface facing incident waves, a horizontal bottom slab and a rear vertical wall. A series of experiments are conducted in a two dimensional monochromatic wave flume on impermeable and seaside perforated quarter circle breakwater model. The present study investigates the wave reflection, loss characteristics, wave runup,ii wave rundown and sliding stability on an emerged seaside perforated quarter circle breakwater of three different radii 0.55 m, 0.575 m and 0.60 m with ratio of spacing to diameter of perforations (S/D) equal to 5, 4, 3, 2.5 and 2 for different water depths and wave conditions. A 1:30 scale model of quarter circle breakwater of 0.55 m radius is fabricated using Galvanized Iron (GI) sheet of 0.002 m thickness. The sheet is fixed to the slab with the help of stiffeners made up of flat plates of cross section 0.025 m x 0.005 m. The model is then placed over the rubble mound foundation of thickness 0.05m and stones weighing from 50 to 100 grams. Initially, impermeable quarter circle breakwater of different radius is tested for wave reflection and loss characteristics using regular waves of heights 0.03 m to 0.18 m and periods 1.2 s to 2.2 s in water depths of 0.30 m, 0.35 m and 0.40 m. Then runup and run down height on the curved QBW surface is noted and the vertical distance above and below the still water level is estimated. Later tests were conducted for determining minimum weight to be added to the QBW structure to prevent sliding. All the models were tested in the predetermined QBW dimensions as mentioned earlier. In the second phase, perforated QBW with different S/D ratios were tested to determine the reflection, loss characteristics, runup, rundown and stability with the same wave conditions and using the same structural parameters. Based on the experiments conducted, it was found that the reflection coefficient (Kr) increases but the loss coefficient (Kl) decreases with increase in incident wave steepness (Hi/gT2). The minimum Kr and the maximum Kl observed are 0.5054 and 0.8629 respectively for QBW of radius equal to 0.55 m at Hi/gT2 = 9.439 x10-4. The results shows that the value of K r decreases but Kl increases as the relative water depth (d/hs) increases for all values of Hi/gT2 and S/D ratio. The maximum percentage reduction in the value of Kr is observed for QBW of 0.55 m radius S/D= 2.5 and varies from 31.66% to 44.50% when the water depth increases from 0.35 m to 0.45 m. For seaside perforated QBW with d/hs= 0.732, percentage reduction iniii K r for S/D equal to 5, 4, 3, 2.5, 2 varies from 47% to 49%, 54% to 58%, 60% to 71%, 72% to 86% and 68% to 84% when compared to impermeable QBW. For all d/h s and Hi/gT2, the values for relative wave runup (Ru/Hi) and relative wave rundown (Rd/Hi) decreases with decrease in S/D ratio. But in the case of seaside perforated QBW with S/D = 2 the values of Ru/Hi and Rd/Hi are found to slightly more than that of S/D = 2.5 due to back propogation of waves from inside the chamber. Finally based on the studies on the sliding stability characteristics, it was observed that for all values of d/h s and S/D ratio, stability parameter (W/γHi2) decreases with increase in Hi/gT2. The minimum values for W/γHi2 for QBW of radius 0.55 m, 0.575 m and 0.60 m with S/D = 2.5 are 2.110, 1.998 and 1.967 respectively for Hi/gT2= 6.241 x10-3 and at 0.35 m water depth.