Browsing by Author "Dagli, BY"

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    Application of a Statistical Regression Technique for Dynamic Analysis of Submarine Pipelines
    Dagli, BY
    This study employs a statistical regression technique to investigate the maximum displacement, stress, and natural vibration frequencies of a submarine pipeline subjected to hydrodynamic wave forces. Eighteen pipeline models are designed, varying in wall thickness from 10 mm to 30 mm and diameter from 500 mm to 1000 mm. The hydrodynamic drag and inertia forces are performed by using the Morison equation. Computer-aided Finite Element Analysis is employed to simulate the complex interactions between the fluid and structure in 18 pipelines. Multiple Regression technique is used to evaluate the reliability metrics, considering uncertainties in geometrical properties affecting pipeline performance. Full Quadratic models are developed for expressing more effective and concise mathematical equations. Analysis of Variance (ANOVA) is performed to determine the adequacy of the model in representing the observed data. The Coefficient of Determination (R2), Mean Square Error (MSE), and Mean Absolute Error (MAE) are calculated to assess the equation's predictive accuracy and reliability. The results confirm the suitability of the suggested regression technique for analyzing the relationships between predictor variables and the response variable.
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    Estimation of Natural Frequencies of Pipe-Fluid-Mass System by Using Causal Discovery Algorithm
    Dagli, BY; Ergut, A; Çiftçioglu, AÖ
    This paper employs a novel approach to investigating the dynamic behavior of a pipe conveying fluid and the relationship between the variables that influence it, based on causal inference. The pipe is modeled as a beam with Rayleigh beam theory and Hamilton's variation principle is demonstrated to obtain the equation of motion. Concentrated mass at various locations is introduced using the Dirac delta function. The fluid in the pipe has no compression properties and no viscosity. The non-dimensional equations of motion of the pipe-fluid-mass system are achieved by using the approach of the fluid-structure interaction problem. The non-dimensional partial differential equations of motion are converted into matrix equations and the values of natural frequencies are obtained by using the Finite Differences Method. The relationship between the variables is investigated by causal discovery using the produced natural vibration frequencies dataset. Moreover, the Bayesian Network's probability distribution is fitted to the discretized data using the structural model created through causal discovery, resulting in trustworthy predictions without the need for sophisticated analysis. The findings highlighted that the proposed causal discovery can be an alternative practical way for real-time applications of pipe conveying fluid systems.
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    Prediction of natural frequencies of Rayleigh pipe by hybrid meta-heuristic artificial neural network
    Dagli, BY; Ergut, A; Turan, ME
    This paper focuses on determination of the natural frequencies in slenderness pipe flows by considering fluid-structure interaction approach. Rayleigh beam theory is used to model the pipe. The fluid in the pipe is assumed as ideal, steady and uniform. Hamilton's variation principle is demonstrated to obtain the equation of motion of pipe-fluid system. The dimensionless partial differential equations of motion are converted into matrix equations, and the values of natural frequencies of first three modes are archived with the analytical method. The results are arranged to be a data set for hybrid meta-heuristic artificial neural network (ANN) method. Three different meta-heuristic algorithms are used to train the ANN: particle swarm optimization (PSO) and artificial bee colony (ABC) and grey wolf optimizer (GWO). The comparison is presented to find a suitable algorithm based on accuracy for determining the natural frequency of the Rayleigh pipe conveying fluid. The results show that the PSO algorithm outperforms the other meta-heuristics in terms of performance indicators in prediction analysis. However, all algorithms and models can predict the natural frequencies with rate with satisfactory accuracy.
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    Evaluation of the technical feasibility aspects of the fishing structures: a case study of Izmir coast
    Dagli, BY; Uncu, DY; Gökkus, Ü
    This paper was conducted by considering 28 fishing structures in Izmir Coast based on three aspects: inter relation with the fishing ground, technical aspects and market accessibility to determine technical requirements about infrastructure and superstructure facilities. The questionnaires and personal interviews with the main stakeholders were utilized to determine current situation of the fishing structures. The field observation covered the activities such as catch unloading, handling, auction, distribution and marketing of the catching fish. The data of fishing structures were evaluated by using Quality Function Deployment (QFD) Method. 13 customer requests and 19 technical requirements were considered for designing House of Quality (HoQ) matrix consisting of 7 sections. A mathematical model represented the relationship between fishing structure and boats was obtained by using Queuing Theory. The suitability of the model with Poisson arrival distribution and negative exponential service time distribution was checked using Chi-Square goodness of fit test. In the conclusion, the most important technical criteria were discussed. The features were identified which need to be improved most.
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    Behaviour of Large Cylindrical Offshore Structures Subjected to Wave Loads
    Dagli, BY; Yigit, ME; Gökkus, Ü
    Spar-type and monopole substructures consisting of a large-diameter, single vertical cylinders have been used as wind turbine towers, oil storage platforms, tankers and wave energy converters at deepwater region in the sea. These towers and platforms are exposed to environmental forces such as wind, wave and current. Wave force is the most effective force in the total environmental force. The body disturbs the incident wave and Diffraction Theory is used for computing the pressure distribution for designing the structure. Therefore, this study aims to present the effect of structural design of towers on dynamic behavior due to wave actions. Two different cases of structural models are selected to employ bidirectional fluid structure interaction (FSI) analysis. Diffraction Theory is utilized to investigate wave forces. Solid and fluid domains are modeled in Abaqus finite elements program. Behaviors of various types of offshore structures are evaluated and compared according to the significant stresses and displacements. The hydrodynamic pressure on the cylindrical structure surface and the diffraction forces acting on structures are presented. Mode shapes, first three natural frequencies are comparatively given.
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    Evaluation of Offshore Wind Turbine Tower Dynamics with Numerical Analysis
    Dagli, BY; Tuskan, Y; Gökkus, Ü
    A dynamic behaviour of a cylindirical wind tower with variable cross section is investigated under environmental and earthquake forces. The ground acceleration term is represented by a simple cosine function to investigate both normal and parallel components of the earthquake motions located near ground surface. The function of earthquake force is simplified to apply Rayleigh's energy method. Wind forces acting on above the water level and wave forces acting on below this level are utilized in computations considering earthquake effect for entire structure. The wind force is divided into two groups: the force acting on the tower and the forces acting on the rotor nacelle assembly (RNA). The drag and the inertial wave forces are calculated with water particle velocities and accelerations due to linear wave theory. The resulting hydrodynamic wave force on the tower in an unsteady viscous flow is determined using the Morison equation. The displacement function of the physical system in which dynamic analysis is performed by Rayleigh's energy method is obtained by the single degree of freedom (SDOF) model. The equation of motion is solved by the fourth-order Runge-Kutta method. The two-way FSI (fluid-structure interaction) technique was used to determine the accuracy of the numerical analysis. The results of computational fluid dynamics and structural mechanics are coupled in FSI analysis by using ANSYS software. Time-varying lateral displacements and the first natural frequency values which are obtained from Rayleigh's energy method and FSI technique are compared. The results are presented by graphs. It is observed from these graphs that the Rayleigh model can be an alternative way at the prelimanary stage of the structural analysis with acceptable accuracy.
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    Dynamics of fluid conveying pipes using Rayleigh theory under non-classical boundary conditions
    Dagli, BY; Ergut, A
    The dynamic behavior of fluid conveying pipe has been investigated by using Rayleigh theory to present the effect of non-classical boundary conditions on natural frequencies. The assumption of ideal fluid is used for acquiring the equation of motion for a uniform Rayleigh pipe. The ideal fluid moves in the vertical direction with pipe and the pipe makes small oscillations by Hamilton's variation principle. Euler equation is adopted for the modeling of the flow behavior in the pipe. Accordingly, the dimensionless partial differential equations of motion are converted into matrix equations and solved for two different set of non-classical boundary conditions. The natural frequencies are obtained depending on fluid velocity and stiffnesses of boundary conditions by using Rayleigh Theory. The effect of mass ratio and slenderness ratio on vibration frequency is examined for the first three modes. The one-way FSI (Fluid-Structure Interaction) technique is used by ANSYS software to determine natural frequencies of pipe. The results of first natural frequency based on the numerical solution performed by using ANSYS-FSI are compared with the results of analytical solution for Rayleigh pipe. (C) 2019 Elsevier Masson SAS. All rights reserved.