Browsing by Author "Rao, Subba"

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Damage Level Prediction of NonReshaped Berm Breakwater using Soft Computing Techniques
(National Institute of Technology Karnataka, Surathkal, 2014) N, Harish.; Rao, Subba; Mandal, Sukomal
Tranquility condition inside the port and harbor has to be maintained for loading cargo and passengers. In order to maintain calm condition inside the port and harbor, breakwater has to be constructed to dissipate wave energy that is coming inside. The alignment of the breakwater must be carefully considered after examining the predominant direction of approach of waves and winds, degree of protection required, magnitude and direction of littoral drift and the possible effect of these breakwaters on the shoreline. In general these studies are invariably conducted in a physical model test where various alternatives are studied and the final selection will be based on performance consistent with cost. Considering the coastal boundary and depth variation, field analysis of wave structure interaction, determination of stability and damage level of berm breakwater structure is difficult. Mathematical modeling of these complex interactions is difficult while physical modeling will be costly and time consuming. Hence one has to depend on physical model studies which are expensive and time consuming. Soft computing techniques, such as, Artificial Neural Network (ANN), Support Vector Machine (SVM),Adaptive Neuro-Fuzzy Inference System (ANFIS) and Particle Swarm Optimization (PSO) have been efficiently proposed as a powerful tool for modeling and predictions in coastal/ocean engineering problems. For developing soft computing models in prediction of damage level of non-reshaped berm breakwater, data set are obtained from experimental damage level of non-reshaped berm breakwater 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 the other for testing. The input parameters that influence the damage level (S) of nonreshaped berm breakwater, such as, relative wave steepness (H/L0), surf similarity (ζ), slope angle (cotα) relative berm position by water depth (hB/d), relative armour stone weight (W50/W50max), relative berm width (B/ L0) and relative berm location (hB/L0) are considered in developing soft computing models for prediction damage level. The ANN model is developed for the prediction of damage level of non-reshaped berm breakwater. Two network models, ANN1 and ANN2 are constructed based on the parameters which influence the damage level of non-reshaped berm breakwater. The seven input parameters that are initially considered for ANN1 model are (H/L0), (ζ), (cotii α), (hB/d), (W50/W50max), (B/ L0) and (hB/L0). The ANN1 model is studied with different algorithm namely, Scaled Conjugate Gradient (SCG), Gradient Descent with Adaptive learning (GDA) and Levenberg-Marquardt Algorithm (LMA) with five numbers of hidden layer nodes and a constant 300 epochs. LMA showed good performance than the other algorithms. Also, influence of input parameters is evaluated using Principal Component Analysis (PCA). From PCA study, it is observed that cotα is the least influencing parameter on damage level. Based on the PCA study, least influencing parameter is discarded and ANN2 model is developed with remaining six input parameters. Training and testing of the ANN2 network models are carried out with LMA for different hidden layer nodes and epochs. The ANN2 with LMA 6-5-1 with 300 epochs gave good results. It is observed that the correlation of about 88% between predicted and observed damage level values by the ANN2 network models and measured values are in good agreement Furthermore, to improve the result of prediction of damage level of non-reshaped berm breakwater, SVM model was developed. 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. This model was developed based on statistical learning theory. The basic idea of SVM is to map the original data x into a feature space with high dimensionality through a nonlinear mapping function and construct an optimal hyper-plane in new space. SVM models were constructed using different kernel functions. In order to study the performance of each kernel in predicting damage level of non-reshaped berm breakwater, SVM is trained by applying these kernel functions. Performance of SVM is based on the best setting of SVM and kernel parameters. Correlation Coefficient (CC) of SVM (polynomial) model (CC Train = 0.908 and CC Test = 0.888) is considerably better than other SVM models. To avoid over-fitting or under-fitting of the SVM model due to the improper selection of SVM and kernel parameters and also the performance of SVM, hybrid particle swarm optimization tuned support vector machine regression (PSO-SVM) model is developed to predict damage level of non-reshaped berm breakwater. The performance of the PSOSVM models in the prediction of damage level is compared with the measured values using statistical measures, such as, CC, Root mean Square Error (RMSE) and Scatteriii Index (SI). PSO-SVM model with polynomial kernel function gives realistic prediction when compared with the observed values (CC Train = 0.932, CC Test = 0.921). It is observed that the PSO-SVM models yield higher CCs as compared to that of SVM 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 were developed with different membership namely Triangular-shaped built-in membership function (TRIMF), Trapezoidal-shaped built-in membership function (TRAPMF), Generalized bell-shaped built-in membership function (GBELLMF), and Gaussian curve built-in membership function (GAUSSMF) to predict damage level of non-reshaped berm breakwater. The performance of the ANFIS models in the prediction of damage level is compared with the measured values using statistical measures, such as, CC, RMSE and SI. ANFIS model with GAUSSMF gave realistic prediction when compared with the observed values (CC Train = 0.997, CC Test = 0.938). It is observed that the ANFIS models yield higher CCs as compared to that of ANN models. The different soft computing models namely, ANN, SVM, PSO-SVM and ANFIS results are compared in terms of CC, RMSE, SI and computational time. The hybrid models in both (ANFIS and PSO-SVM) cases showed better results compared to individual models (ANN and SVM). When the hybrid models are compared, ANFIS model gives higher CC and lower RMSE. But considering computational time, ANFIS has taken more time than PSO-SVM model. Hence PSO-SVM is computationally efficient as compared to ANFIS. ANFIS and PSO-SVM models perform better and similar to observed values. Hence, ANFIS or PSO-SVM can replace the ANN, SVM for damage level prediction of nonreshaped berm breakwater. ANFIS or PSO-SVM can be utilized to provide a fast and reliable solution in prediction of the damage level prediction of non-reshaped berm breakwater, thereby making ANFIS or PSO-SVM as an alternate approach to map the wave structure interactions of berm breakwater.
Numerical Model Studies to Predict the Wind-Wave Climate Considering Climate Change Effects
(National Institute of Technology Karnataka, Surathkal, 2021) K, Sandesh Upadhyaya.; Rao, Subba; Manu
The waves propagating over an area under the action of the wind is termed as wind waves. The disturbances on the ocean surface by the wind are restored to a calm equilibrium position by the action of gravity. The fundamental element in the wind-wave generation is the interaction between air and ocean. During this interaction, there is an energy and momentum transfer between the atmosphere and ocean. The climate change affects the atmospheric temperature which in turn alters the wind patterns. The wave conditions change according to the wind pattern. Studies on global climate changes and extreme weather events have fascinated researches all over the world. Climate change, a global phenomenon, is a consequence of ever-increasing greenhouse gas concentration and is considered a serious threat to mankind. Climate change is a phenomenon triggered by natural and anthropogenic activities, which is one of the most discussed topics in the research community today. An increase in global sea level, changes in wind pattern and an increase in the frequency of extreme wave events which is caused by climate change have critical impacts on the coastal population around the world. Indian coast measures about 7500 km along with the nine coastal states which host marine and coastal biodiversity. Thirteen major ports and associated activities play a prominent role in coastal population concentration of about 14% along the Indian coast. The coastal and offshore structures are typically designed for the significant wave height (HS) corresponding to a specific return period and it is, therefore, necessary to know possible changes in their magnitudes at different locations of interest. Structures built in the sea are traditionally designed according to historical climate observations or hindcasted data. For structural safety, consideration of such climate change effects is highly desirable. Computational advancements in recent times have resulted in various General Circulation Models being developed and effectively used for assessing the atmospheric and ocean circulation. The performance of these modelled result can be compared with the in-situ measurements of shorter duration. Forecast of the climate parameters incorporating climate change effects are developed. These data products can be used to develop numerical wave models for long term analysis of wind and wave patterns which will aid in the design of coastal and offshore structures. i i In the present study, hindcasting from 1980 for the Indian domain is performed from reanalysed gridded global wind speed dataset called ERA-Interim. The performance of this global dataset is assessed by comparing it with in-situ measurements recorded at the east and west coast of India. As the ERA-Interim dataset showed a good match with the in-situ records these long-term wind speeds are used as an input to the numerical wave model. MIKE 21 SW numerical wave model is developed for the Indian domain with coordinates - 4º to 30º N 40º to 95ºE. Significant wave heights from this wave model driven by ERA-Interim wind speeds are extracted at locations nearshore to Karwar and offshore OB03 location for validation. After validation, the numerical model is used to perform longterm wave analysis, shoreline analysis, assessment of wind-wave climate along the Indian coast and wave climate predictions along Karnataka coast for the near future. The numerical model output depends on the input which is global wind speed dataset. Wind speed analysis is initially performed before using it in the numerical model. As ERA-Interim dataset does not provide forecasts, global wind speeds provided by the CMIP5 database is considered in this study. Wind speed projections from 38 different CMIP5 global models are compared against ERA-Interim global wind speeds for the Indian domain. The performance of datasets is graphically evaluated based on Taylor plots. Initially, statistical analysis of monthly wind speeds from 1980 to 2005 is performed to arrive at four best performing datasets for the Indian domain. Further, a nowcast study on daily wind speeds from 2006 to 2018 considering the four climate change scenarios termed as Representative Concentration Pathways (RCPs) is carried out. From the nowcast analysis, an Italian CMIP5 dataset called CMCC-CM for RCP 4.5 matched well with the real-time reanalysed wind speeds provided by ERA-Interim. Hence in the present study, wave climate predictions for the Indian domain is based on wind speeds driven by CMCC-CM RCP 4.5. The long-term analysis is performed based on the five probability distributions such as Log-normal distribution, Gumbel distribution, Fretchet distribution, Exponential distribution, and Weibull distributions to arrive at significant wave height with 10 and 50 year return period for New Mangaluru port location. Initially, long-term analysis is performed on in-situ records measured for 5 years near New Mangaluru Port. From this analysis, Weibull distribution with α=1.3 showed good performance and is used to arrive at significant wave heights with 10 and 50 year return period. The same approach is extended on the MIKE 21 simulated significant wave heights from 38-year ERA-Interim hindcast. The results showed 2.6% and 5.44% increase in significant wave height with 10 year and 50 year return period at the location studied. ii i A shoreline analysis is performed using LITPACK tool along the coast adjacent to the New Mangaluru Port. The volume of sediment transport is analysed and the shoreline changes from 1980 to 2015 is studied to understand the erosion and accretion patterns. The performance of the numerical model matched well with the satellite measurements. In an attempt to explore the renewable energy potential along the Indian coast the numerical wave model is also used to assess the wind-wave climate based on ERA-Interim wind speed data of 38 years. The results showed amongst the locations studied off Goa, Karnataka, Kerala, Tamil Nadu, and Andhra Pradesh had good potential to extract offshore wind energy from offshore wind turbines. MIKE numerical model driven by wind speeds from CMCC-CM RCP 4.5 up to the year 2070 is used to simulate the wave climate along the Karnataka coast. The monsoon wave climate is studied to arrive at wave parameters with 10 and 50 year return period at six locations along the Karnataka coast.
Parametric Studies on Stability of Reshaped Berm Breakwater with Concrete Cubes as Armor Unit
(National Institute of Technology Karnataka, Surathkal, 2014) J, Prashanth.; Rao, Subba; Shirlal, Kiran G.
The breakwater construction in deeper waters requires heavier armor units due to larger wave loads. Such large stones are uneconomical to quarry or transport or may not be available nearby. Another problem is uncertainty in the design conditions resulting in breakwater damage due to increased wave loads. The structural stability and economy in construction of breakwater are the need of hour. Under these circumstances, berm breakwaters can be a solution. For an economical solution, the quarry yield may be judiciously used and berm breakwater may be constructed with small size armor units. The present research work involves a detailed experimental study of influence of various sea states and structural parameters on the stability of statically stable reshaped berm breakwater made of concrete cubes as primary armor. Initially, a 0.70 m high of 1:30 scale model of conventional breakwater of 1V:1.5H slope and trapezoidal cross section is constructed on the flume bed with concrete cubes of weight 106 g as primary armor. This is designed for a non-breaking wave of height 0.10 m. This model is tested for armor stability with regular waves of heights 0.10 m to 0.16 m and periods 1.6 s to 2.6 s in water depths of 0.30 m, 0.35 m and 0.40 m. In the second phase, a 1V:1.5H sloped and 0.70 m high berm breakwater with varying size of concrete armor cubes, berm widths, thickness of primary layer is tested for stability with same test conditions. Based on the study of conventional and reshaped berm breakwater model the following conclusions are drawn. Damage level (S) was found increasing with the increase in stability number (Ns) in conventional breakwater. In conventional breakwater damages were in the range of 4.62 to 5.69 (intermediate), 9.75 to 11.46 (failure) and 9.46 to 10.22 (failure) in the depths of 0.3m, 0.35m and 0.4m respectively. Considering the complete iranges of Ho/gT2 and d/gT2, the maximum relative run-up Ru/Ho and relative run-down Rd/Ho were respectively 1.2 and 1.25. The stability of the berm breakwater is largely influenced by the storm duration. It was observed that relative berm position (hb/d) has a greater influence on berm recession than wave run-up and run-down. As relative berm position (hb/d) parameter increases from 1.00 to 1.50, the berm recession decreased by up to 77% while the wave run-up and run-down decreases by 7% and 14% respectively. The surface elevation of the water in front of the berm influences the recession and eroded area of the berm. Some of the available equations for berm recession, wave run-up over estimated the values for the considered conditions. The damage is reduced by about 47% in the present model when compared to stone armored berm breakwater. The wave runup and run-down are reduced by 34% and 49% compared to conventional cube armored breakwater respectively. The economic analysis showed that the cube armored berm breakwater is about 8% and 4% economical than the conventional cube armored breakwater and stone armored berm breakwater for the same design conditions. The design equations for berm recession, wave run-up and wave run-down are derived. Finally, it was found that 25% reduction in armor weight with 0.40 m berm width and 2 no. of primary armor layers is safe for the most of conditions considered during the study except for extreme waves of 0.16 m height and 1.6 s period. However, same breakwater with 3 armor layers was safe for the entire range of test conditions. In terms of safety as well as economy 25% reduction in armor weight with 0.40 m berm width and 2 no. of primary layer was cheaper compared to all other models studied.
Soft computing techniques in the prediction of performance of semicircular breakwaters
(National Institute of Technology Karnataka, Surathkal, 2020) Kundapura, Suman.; Rao, Subba; Hegde, Arkal Vittal.
In the dynamic environment of the coast maintaining the harbor tranquility is possible only with the planning of proper protection structures. Breakwaters are one among the several coastal protection structures. Breakwaters could either run into the water linking to the shore or placed independently parallel to the shore. The former will lead to the accretion on up drift side and erosion on the down drift side of the structure but the latter provides shore protection without adversely affecting the longshore transport. Breakwaters attenuate the wave, slow the littoral drift and produces sediment deposition. To provide a basis for evaluating the effects of breakwater installation a comprehensive study on the hydrodynamic response of breakwaters needs to be investigated. Physical models could be used in the laboratory to assess the same however, it is expensive, laborious and time-consuming which involves many variables that affect the shape, strength, alignment, base stability and other phenomena. There are several empirical formulae but developed on limited data. Also, though numerical models are good option, it involves numerous assumptions not withstanding faster computing resources, most of which are time-consuming, tend to overestimate the hydraulic responses. The Computational Intelligence (CI) techniques can be made use to overcome some of these shortcomings. As they are capable of replicating the outcome of a numerical model with better accuracy. Among the several breakwaters available, the emerged semicircular breakwater is found advantageous and also the study on this type of breakwater is limited. Hence the present study is taken up to predict the hydraulic responses like reflection coefficient, relative wave runup, stability parameter, of emerged seaside perforated semicircular breakwater using different soft computing techniques. The soft computing techniques used are Artificial neural network (ANN), Adaptive neuro-fuzzy inference system (ANFIS), Genetic algorithm based adaptive neuro fuzzy inference system (GA-ANFIS) and Particle swarm optimization based adaptive neuro fuzzy inference system (PSO-ANFIS). The prediction is done using conventional data segregation method. Also, a methodology of segregating the lower ranges of wave height data, and not using it for training the network and then predicting the hydraulic responses purely for this segregated data is done successfully and it is namedii as ‘below the range’ predictions. Similarly, a prediction for purely higher ranges of wave height data not used in training the network, has been carried out and it is named as ‘beyond the range’ prediction. The study shows the possibility of prediction of the hydrodynamic characteristics like reflection coefficient, relative run-up parameter and stability parameter of the semicircular breakwater using the soft computing techniques for both dimensional as well as non-dimensional input parameters. In both the cases the predicted outputs the reflection coefficient, relative run-up parameter and stability parameter was good in the conventional data segregation case. Also, below the data range approach gave reasonably good results in both set of input parameters for the prediction of reflection coefficient. Whereas, in the case of beyond the data range predictions the results are good in the case of dimensional input parameters but not for non-dimensional input parameters in the prediction of reflection coefficient. The relative wave run-up parameter prediction for below and beyond the range predictions did not give satisfactory results for both set of input parameters. In the present study the stability parameter of emerged seaside perforated semicircular breakwater is predicted for a dataset of 389 data sets. The results found are good for both the set of input parameters in the case of conventional data segregation method. As the available dataset is only 389 data sets, the below the data range and beyond the data range approach was not done for stability parameter prediction. From the performance of four different models in several cases considered, the prediction made by GA-ANFIS gave better results in maximum number of cases. The ANN also predicted the output parameter well, though it is an individual model. But, the disadvantage here is the number of neurons in the hidden layer is chosen based on trial and error method, depending on thumb rules. In the case of ANFIS method the FIS could be generated by grid partitioning, subtractive clustering or fuzzy cmeans clustering. In the present study since the number of inputs in dimensional as well as nondimensional case is more than 5 the grid partitioning method has not been employed as it suffers the curse of dimensionality. In such cases the subtractive clustering or fuzzy c-means clustering can be employed. In the study it is found that the prediction made by fuzzy c-means clustering-ANFIS gave better results in maximum number of cases of reflection coefficient prediction compared to subtractive clustering-ANFIS with dimensional input parameters. Hence for all the remaining cases FCM-ANFIS is employed. The performance of PSO-ANFIS model is not as good as GA-ANFIS in the different cases considered. Arriving at the optimal parameters of the hybrid model costs time.iii However, these soft computing techniques can be adopted as an alternate technique to predict the hydraulic response of semicircular breakwaters by coastal engineers when similar site conditions are available.
Studies on Caisson Type Breakwater – A Physical and Numerical Approach
(National Institute Of Technology Karnataka Surathkal, 2023) V., Kumaran; ., Manu; Rao, Subba
The design and construction of coastal structures such as breakwaters, at greater water depths is rapidly increasing as a result of the increasing draught of large vessels and off-shore land reclamations. Vertical caisson-type breakwaters may be the best alternative compared to ordinary rubble mound breakwaters in larger water depths, in terms of performance, total costs, environmental aspects, construction time and maintenance. To fulfil the functional utility and impact of the structure on the sea environment, it is necessary to study the hydraulic performance of such breakwaters. In the present project, the hydrodynamic performance of caisson breakwater with various geometric configurations are studied in detail. In the first phase, a physical model approach is carried out extensively to study the stability of toe protection for vertical caisson breakwater. The determination of the size of the toe armour units and their cross-section for the stable design are investigated. The applicability of the Brebner and Donnelly (Coast Eng Proc 1: 24, 1962) design curve for depth-limited conditions is validated for a certain fixed relative foundation depth (d1/d). In the second phase, an investigation of the non-perforated caisson type breakwater is performed considering different wave conditions. The variation of dynamic wave pressure, wave force, wave run-up, and wave reflection are determined for this structure. The maximum wave force on the caisson breakwater is calculated from measured pressure values and is compared with the wave forces calculated by Goda’s and Sainflou wave theories. The comparison of results illustrate that the Goda’s formula provides a good estimation of wave force distribution compared with the experimental findings. In the third phase, a numerical model of caisson breakwater is developed to study its performance using the computational fluid dynamics (CFD) approach using Ansys- Fluent and validated the same using experimental data. In the fourth phase, the experimental investigations are carried out on non-perforated vertical wall breakwater with the presence of a vertical and horizontal slotted barrier. In the fifth phase, the perforations (i.e 8 %, 10%, 13%, 15%, 20%) are introduced in the front face of the caisson breakwater to analyse the hydraulic performance to arrive at better perforations in reducing the wave forces, wave reflection and wave runup.
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.
Tidal Energy Potential Estimation and Impacts on Hydrodynamics around Tidal Power Systems along the Indian Coast
(National Institute of Technology Karnataka, Surathkal, 2021) Mendi, Vikas; Rao, Subba; Seelam, Jaya Kumar
Tidal energy is the energy derived using the tides. Most of the tidal energy feasibility studies are conducted for barrage method of tidal energy extraction. In Indian scenario, the observed conditions and the methods proposed are mostly for the barrage method mainly in the states of Gujarat in the west and West Bengal in the east where the tidal range is maximum. Assessment of energy extraction from barrage method has not been carried out in the southern parts of India due to low to medium tidal range. The first objective mainly focuses on tidal energy resource availability and the energy that can be harnessed from tides along the coast of India. Two methods are considered viz. tidal barrage and tidal stream energy. Out of 471 tidal inlets identified in 9 maritime states along the Indian coast, 130 inlets are shortlisted considering a threshold of 2.53 Mm3 tidal prism and potential energy was estimated. Total potential energy estimate considering 130 inlets is 2254.906 MW. Further 107 inlets are shortlisted considering both tidal prism greater than 2.53Mm3 and inlet throat width greater than 63m and the corresponding potential energy is estimated as 2127.281 MW. The Kinetic energy estimated was 11.68kW, 5.60kW and 25.64kW at Chapora, Mandovi and Zuari respectively. The second objective intends to study the impact of tidal energy of local hydrodynamics.The turbines are placed at the locations where highest tidal currents were observed as presented in objective 1. Five cases were considered where the simulations were carried for different locations of the tidal turbine. Total energy generated by 0.5m diameter turbine was estimated to be 118kW. Whereas the 1m diameter turbine increased the energy to 409.35kN. The total energy estimates for the turbines in parallel and turbines in tandem considering 0.4 m/s threshold for current speeds was approximated to 417.5kW and 409.35kW respectively. The morphodynamics were simulated and the sea bed morphology of Zuari creek was studied. The results of the coupled model proved that the location chosen for tidal energy extraction does not exhibit sediment transport and longer durations of simulations are required. In the third objective, tidal lagoons are established and the morphodynamics due the energy extraction are studied. A tidal lagoon can be constructed either on an existing natural rock/headland or completely by artificial means. It can either be constructed nearshore adjacent to the coast of in the tidal reservoir where conditions are feasible. Locations for the construction of tidal lagoons are identified along in Maharashtra (Jaigad 1 and Jaigad 2). The potential energy that can be extracted from the established tidal pools is estimated to be 3.69MW and 1.3MW respectively. Results of morphodynamic study for 20 days are analyzed. The bed level changes observed at Jaigad 1 and Jaigad 2 prove less sensitive to hydrodynamics. Bed level changes observed are of the order 0.04m (in 20 days) due to the construction of tidal barrage.