Browsing by Author "Gökkus, Ü"

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    Multimethod simulation approach for capacity design of a truck parking area in city ports
    Yildirim, MS; Aydin, MM; Gökkus, Ü
    The port induced freight can cause traffic congestion problems in city ports if road freight transportation is used. The secondary congestion problem arises from the pooling of the trucks at the port gates because of the delays of the port operations. The absence of the truck parking areas inside the port causes additional truck trips between the port and auxiliary truck servicing areas around the port. For reducing the impacts of the associated problems of the port induced truck traffic, truck parking areas can be used as buffer zones between the port and city. The purpose of this study is to develop a Decision Support System (DSS) with using multimethod simulation and cost optimization model for the capacity design of a truck parking area for a city port. The preliminary design of the parking area is used to estimate the development cost and outputs of the simulation model is coupled for the capacity optimization for truck arrival scenarios. The methodology is implemented for a case study of the Izmir city port in Turkey. The results of the study indicated that significantly different parking area capacities are required for different truck dwell times for the time restricted and unrestricted truck arrivals.
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    Scheduling of the Shuttle Freight Train Services for Dry Ports Using Multimethod Simulation-Optimization Approach
    Yildirim, MS; Karasahin, M; Gökkus, Ü
    This paper introduces a simulation-optimization method for addressing scheduling problems for shuttle freight trains (SFTs) in a shared railway corridor between a seaport and dry port. We use dispatching delays for scheduling the SFT trips so as to not disturb the existing scheduled regular train (SRT) paths. The method employs a multi-method microscopic simulation model and an optimization framework. A swarm-based optimization algorithm is used for finding the best dispatching delays to preserve SRT paths. The method is demonstrated for a railway corridor between the Alsancak seaport and a close-distance dry port. The railway corridor is modeled using a simulation model considering single and double railway tracks, stations, and schedules. By running the simulation-optimization, the SFT freight transport capacity and the quality of the SFT and SRT operations were compared using key performance indicators (number of completed trips and station stops, average trip delay, and average station delay) addressing the throughput and punctuality after the application of dispatching delays. The results show that, by preserving the existing SRT paths, freight transport capacity decreased by 11.1% (from 18 to 16 completed SFT trips) and 13.8% (from 36 to 31 completed SFT trips) for single and couple SFT scenarios, respectively. The methodology also decreased the average SFT station delays by 45.2% and 45.6% for the single and couple SFT scenarios comparing with the unoptimized SFT trips. However, the number of SFT station stops increased by 12.5% and 57.1% for the single and couple SFT scenarios for prioritizing the SRTs. Also after the optimization, the average SFT trip delays decreased by 30.7% and 0.58% for the single and couple SFT scenarios. This study successfully demonstrates that the proposed method can be used for scheduling the SFT trips inside a congested railway corridor and can be implemented as a capacity assessment tool for cyclic SFT service using a series of key performance indicators addressing throughput and punctuality.
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    Simulation optimization of the berth allocation in a container terminal with flexible vessel priority management
    Yildirim, MS; Aydin, MM; Gökkus, Ü
    Solving the berth allocation problem (BAP) in ports is not trivial where the berth resources are limited and various sizes of vessels arrive with dramatically dissimilar loads. Especially in real scenarios, arriving vessels are accepted for a berth with the first come first served (FCFS) priority rule. This study proposes a decision support system coupled with a simulation optimization module based on the swarm-based Artificial Bee Colony optimization algorithm for solving the BAP. The proposed methodology was implemented for the Izmir port in Turkey. To investigate the influences of the vessel priorities on the BAP, four different experimental scenarios based on the single (SQM) and multiple queue models (MQM) were coupled with FCFS and proposed hybrid queue priority (HQP) rule. The results indicated that SQM scenarios were superior to MQM scenarios in a manner of minimizing the average vessel waiting times and the implementation of a dynamic berth allocation strategy for the MQM significantly decreases the vessel waiting times. Results of the SQM also imply that utilization of the HQP approach further minimizes the average vessel waiting times and increases the berth utilization and port throughput without yielding excessive waiting times for the larger vessels compared with the FCFS priority rule.
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    Estimation of Container Traffic at Seaports by Using Several Soft Computing Methods: A Case of Turkish Seaports
    Gökkus, Ü; Yildirim, MS; Aydin, MM
    Container traffic forecasting is important for the operations and the design steps of a seaport facility. In this study, performances of the novel soft computing models were compared for the container traffic forecasting of principal Turkish seaports (Istanbul, Izmir, and Mersin seaports) with excessive container traffic. Four forecasting models were implemented based on Artificial Neural Network with Artificial Bee Colony and Levenberg-Marquardt Algorithms (ANN-ABC and ANN-LM), Multiple Nonlinear Regression with Genetic Algorithm (MNR-GA), and Least Square Support Vector Machine (LSSVM). Forecasts were carried out by using the past records of the gross domestic product, exports, and population of the Turkey as indicators of socioeconomic and demographic status. Performances of the forecasting models were evaluated with several performance metrics. Considering the testing period, the LSSVM, ANN-ABC, and ANN-LM models performed better than the MNR-GA model considering overall fitting and prediction performances of the extreme values in the testing data. The LSSVM model was found to be more reliable compared to the ANN models. Forecasting part of the study suggested that container traffic of the seaports will be increased up to 60%, 67%, and 95% at the 2023 for the Izmir, Mersin, and Istanbul seaports considering official growth scenarios of Turkey.
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    Irregular Wave Effects on Dynamic Behavior of Piles
    Gücüyen, E; Erdem, RT; Gökkus, Ü
    The paper presents computer-aided numerical analyses which are utilized to investigate the dynamic behavior of piles under wind-generated irregular wave loads. A pile is modeled as a single-degree-of-freedom system. The equation of motion of the system is numerically integrated using a fourth order Runge-Kutta method. The equation of motion includes shape function that is obtained approximately. It is needed to compare the solutions with another method to determine the approximation leads whether significant differences or not. For this purpose the dynamic behavior of structure is modeled by the Time History Tool of SAP 2000 and the results compared with those found by a single-degree-of-freedom system. Irregular wave is represented with equivalent regular waves with two different approaches; based on either superimposed multi-sinusoidal wave (Loading I) or significant wave (Loading II), utilizing the energy spectrum. Wave forces are obtained from Morrison Equation. The analyses account for a soil-pile interaction in a simplified way. As the lateral ground pressure changes by delving deep into the ground, soil spring stiffness also changes. Those forces are calculated separately for different depths and taken into account in both analyses. Lateral displacement of the employed pile varying with the time is obtained from analyses for Loading I and Loading II. Critical results are obtained from which loading is determined. Finally, the frequencies of the external loads and natural frequency of pile are compared to examine whether the resonance came true or not.
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    Dry port integrated port development with microsimulation method for solving port-city conflict: a case of Alsancak Port
    Yildirim, MS; Gökkus, Ü
    In this research, we have developed a dry port integrated development scenario for a city port with a port-city conflict problem and evaluated the economic benefits of the integration compared with the 'port-only' development. Discrete event simulation was used for developing intermodal port simulation models with (IPSM-2) and without dry port (IPSM-1). A port development cost model was developed for economic comparison of the scenarios considering the port storage area requirement and traffic predictions in 20-foot equivalent units (TEU). The model results indicated that for the year of 2019, IPSM-2 decreased the port storage area up to 87% and IPSM-2 ($101/TEU) was 47% more economical compared to the IPSM-1 ($191/TEU) considering the handling rate. The study concludes that dry port integration can yield sustainable and more economic port development and can be used for solving port-city conflict for land usage.
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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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    NUMERICAL MODELLING OF SUDDEN CONTRACTION IN PIPE FLOW
    Gücüyen, E; Erdem, RT; Gökkus, Ü
    In the present work, full-scale numerical simulations of incompressible fluid flow through different locations of sudden contractions are studied according to Computational Fluid Dynamics (CFD) technique. Finite Elements Method is used to numerically solve governing equations via the commercial program ABAQUS including CFD code. Four different locations of contraction zone are utilized to determine the effect of location changes on sudden contraction head loss coefficients (K-c). Twelve area ratios (sigma) are performed for all zones. Three different Reynolds numbers, remain in laminar flow boundaries, are adopted to determine effects of Reynolds number, as well as location effects. The graphs are constituted by results from computing 48 models for each Reynolds number and the study is concluded with 144 models in the end. In this manner, contraction ratio varying coefficients are obtained for four configurations. According to results, the pressure drop values of the same model for varying contraction locations are different. Maximum values of pressure drops are obtained for the second geometry (G(2)). Combination of maximum pressure drops and minimum velocity values leads to maximum contraction coefficients for G(2). While the area coefficients increase, decreasing values of contraction coefficients of different contraction locations (G) converge in connection with the changing values of velocities and pressure drops. It is necessary to entrain to this remark, for increasing area coefficients. It is stated that K-c-sigma curves vary due to location change. It is recommended to consider the location varying coefficients while modelling different located contracting flows especially for side contracting flows.
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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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    FSI ANALYSIS OF SUBMARINE OUTFALL
    Gücüyen, E; Erdem, RT; Gökkus, Ü
    In the scope of this study, main pipe of the diffuser, risers, ports, internal and external environments forming the discharge system which is used in application are modelled by Finite Elements Analysis (FEA) program to obtain discharge and structural behaviour. The last two spans of the system (20 m) and four ports on these spans are investigated. While the diameter and geometry of the risers and ports remain constant, the diffuser pipe is modelled in three different ways. These are constant sectioned (Model 1), contracting with sharp edge entrance sectioned (Model 2) and gradually contracting sectioned (Model 3) respectively. Among them, only Model 1 is treated as Single Degree of Freedom (SDOF) system and it is simulated by FEA to verify FEA solver in the first place. After structural suitability is confirmed, rest of the models are analysed to determine reaction forces and stresses. The discharge is performed as unsteady external flow as well as steady external flow assumption which is widely used in external flow model in the literature. The discharge analyses are performed in two different ways to verify FEA program. Iterative method is accompanying to FEA program. As a result of this study, proper model for structural and discharge behaviour and external flow effects on discharge velocities are obtained.