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Yayın Shapes and statistics of the rogue waves generated by chaotic ocean current(International Society of Offshore and Polar Engineers, 2016) Bayındır, CihanIn this study we discuss the shapes and statistics of the rogue (freak) waves emerging due to wave-current interactions. With this purpose, we use a simple governing equation which is a nonlinear Schrödinger equation (NLSE) extended by R. Smith (1976). This extended NLSE accounts for the effects of current gradient on the nonlinear dynamics of the ocean surface near blocking point. Using a split-step scheme we show that the extended NLSE of Smith is unstable against random chaotic perturbation in the current profile. Therefore the monochromatic wave field with unit amplitude turns into a chaotic sea state with many peaks. By comparing the numerical and analytical results, we show that rogue waves due to perturbations in the current profile are in the form of rational rogue wave solutions of the NLSE. We also discuss the effects of magnitude of the chaotic current profile perturbations on the statistics of the rogue wave generation at the ocean surface. The extension term in Smith's extended NLSE causes phase shifts and it does not change the total energy level of the wave field. Using the methodology adopted in this study, the dynamics of rogue wave occurrence on the ocean surface due to blocking effect of currents can be studied. This enhances the safety of the offshore operations and ocean travel.Yayın A theoretical method for the investigation of the effects of soil improvement on train induced ground-borne vibrations(Ege Üniversitesi, 2018-09-14) Bayındır, Cihan; Kesten, Ali Sercan; Etminan, EhsanGround-borne vibrations by railway trains are generated at the rail-wheel interface due to the passage of wheels and due to irregularities of wheels and tracks. These vibrations need to be predicted and controlled during the design and service of the railway for the safety and the serviceability of the railway to avoid possible vibration induced problems such as settlement and differential settlement due to their compaction effect, liquefaction and discomfort of people. While such railway vibrations are modeled by different techniques, only few studies do exist to analyze them in the case of soil improved conditions. In this study we propose a mathematical framework to study the effects of soil improvement on the ground-borne vibrations induced by the railway trains. We use an experimentally calibrated model which utilizes the evolutionary random process approach in order to model the time varying transfer functions between the axles of the train and fixed observation point. The railway is modeled as a Winkler foundation with rail pads and corresponding transfer functions are used. The target area of this study is the Eminönü-Alibeyköy Tramway Line in ˙Istanbul, which is under construction and planned to be completed in late 2018. Due to poor soil conditions at the specific stations along the proposed tramway route, soil improvement by the application of geosynthetics are performed at the site and taken into account in our model. The improvement in soil conditions are modeled as increased vertical soil stiffness in the Winkler foundation of the evolutionary random process model. To model the various tramway loading conditions, both the 5-axle and 6-axle tramway configurations with non-uniform axle spacing are considered. We show that by increasing the vertical soil stiffness ksb, the vibration velocity and acceleration levels can be reduced significantly. By implementing model proposed, we present the reduction of the vibration velocity and acceleration levels as the functions of soil improvement parameters and discuss our findings and the applicability of the model.
