فهرست مطالب

  • Volume:7 Issue:11, 2019
  • تاریخ انتشار: 1397/12/10
  • تعداد عناوین: 6
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  • Hassan Rashidi* Pages 1-12
    The Minimum Cost Flow (MCF) problem is a well-known problem in the area of network optimisation. To tackle this problem, Network Simplex Algorithm (NSA) is the fastest solution method. NSA has three extensions, namely Network Simplex plus Algorithm (NSA+), Dynamic Network Simplex Algorithm (DNSA) and Dynamic Network Simplex plus Algorithm (DNSA+). The objectives of the research reported in this paper are to simulate and investigate the advantages and disadvantages of NSA compared with those of the three extensions in practical situations. To perform the evaluation, an application of these algorithms to scheduling problem of automated guided vehicles in container terminal is used. In the experiments, the number of iterations, CPU-time required to solve problems, overheads and complexity are considered.
    Keywords: Network Simplex Algorithm, Dynamic Network Simplex Algorithm, Optimization Methods, Dynamic Scheduling, Container Terminals
  • Esmaeel Masoudi* Pages 13-20
    Various types of floating breakwaters in different configuration and shapes are used to reduce wave height in coastal areas. The most important parameter in designing breakwaters are their shapes which determines hydrodynamic reaction to incident waves. Some cross sections are more effective and more efficient than others. In framework of numerical methods, finite element and boundary element methods are two popular and effective approaches which have been widely applied to floating body problems. In this study by using boundary element method, diffraction problem is solved for a new type of breakwater, which is called inverse T-type floating breakwater. To have a validated results, a rectangular cross section floating breakwater is analyzed and results are compared to previous researches. The final goal of this study is obtaining hydrodynamic characteristics of this new type of breakwater and comparing its response to sinusoidal waves with other conventional floating breakwaters. It is shown that in same weight, this new type of breakwater has better transmission coefficient among other conventional breakwaters and might be used as an efficient alternative.
    Keywords: Floating breakwater Rectangular cross section Transmission coefficient Reflection coefficient Inverse Ttype
  • Farhad Hosseinlou*, Hamid Hokmabady, Alireza Mojtahedi, Samira Mohammadyzadeh Pages 21-31
    A simple dynamic model of an offshore jacket platform is developed based on the scaled hydro-elastic model of the jacket to estimate the dynamic response of the system. The finite element model of the platform is updated numerically by using the experimental modal analysis (EMA) results. Dynamic characteristics of the improved simple dynamic model (SPM) and idealized model are specified based on updated model properties. The effects of the experimental test are studied to investigate the dynamic response of a scaled model of an offshore jacket platform through the SPM and idealized models. Seismic response of the jacket platform is studied by using the idealized model under an earthquake acceleration. The effects of marine growth and the corrosion are considered within the calculation process by considering the jacket mass and stiffness variation. The developed SPM and idealized model provide a feasible and effective approach for evaluating the dynamic response of the offshore jacket platform. The results indicate the importance of the experimental studies in validating the numerical results and reducing the uncertainties for the fixed marine structures.
    Keywords: Offshore jacket platform, Improved reduction technique, Simplified platform model, Dynamic response analysis, Model updating
  • Mohsen Soltani, Rouhollah Amirabadi* Pages 33-40
    This paper aims to tackle an important uncertainty which extremely affects seismic performance of wharf structures in earthquake events. According to previous studies performed for structures on land, it is shown that structures on land are highly susceptible to unknown orientation of earthquakes called as the directional uncertainty. However, for marine structures, especially pile supported wharves, research efforts are rare to assess the effect of directional uncertainty of earthquakes. Therefore, to show this effect on pile supported wharves, fragility analysis is performed based on methodology suggested by Pacific Earthquake Engineering Research Center (PEER) for the modeled pile supported wharf located in Maah-shahr port as a case study. As the first phase of this methodology, nonlinear static pushover analyses are performed for randomly chosen incident angles in order to quantitatively measure damage states suggested by marine design code. After damage states are obtained, IDA analysis are conducted in the selected incident angles to obtain nonlinear structural responses which are supposed to be used for fragility analysis as inputs. Finally, once fragility curves have been developed according to the last phase of PEER methodology, the more vulnerable directions of wharf are represented.
    Keywords: IDA, Fragility analysis, Pile-supported wharf, Directional uncertainty
  • Abbasali Rezapour*, Fazlolah Saghravani, Alireza Ahmadyfard, Mehdi Rezapour Pages 41-51
    Saltwater intrusion is a transient process that affects the coastal aquifers quality and hydrodynamics. The transient behavior of the saltwater wedge (SW) and mixing zone (MZ) due to the changes of the inland freshwater head was investigated through experimental and numerical approaches using image processing technique and the numerical code SUTRA. To acquire data in the transient conditions, automated algorithms were designed and employed for both methods. Numerical simulations were extended to a reference problem of field scale for further study of the transient aspect of the saltwater intrusion phenomena. The results demonstrated that the behavior of SW area is significantly similar to the behavior of SW toe length in transient conditions. Also, in the advancing case, the SW height reaches the steady state condition much sooner than the SW toe length and the SW area, while in the receding case, all the three indicators are stabilized almost simultaneously. Furthermore, the results showed that the MZ expanded at early stages of the receding and after a while condensed again gradually until it finally reaches to its original state at the beginning of the advancing case. Although local velocity of brackish water toward sea boundary in the dilute region of the MZ is more than in the dense region, the flushing and mixing process causes to increase the MZ in the receding case. Sensitivity analyzes showed that the speed of SW advancing or receding does not affect the MZ thickness in a steady state condition.
    Keywords: saltwater intrusion, transient condition, saltwater wedge, mixing zone, image processing, numerical modelling
  • Alireza Hosseinnajad, Mehdi Loueipour* Pages 53-59
    In this paper, a control system is designed for dynamic positioning of an ROV with unknown dynamics, subject to external disturbances using passive arm measurements. To estimate uncertain dynamics and external disturbances, a new method based on time delay estimation (TDE) is proposed. The proposed TDE, not only maintains the advantages of conventional TDE, but also eliminates its sensitivity to sensor noise and fast-varying external disturbances which in turn, results in smooth control signal. The proposed control system is considered as a nonlinear PD-type controller together with feedforward of estimated dynamics and disturbances. This structure presents good performance against uncertainties and external disturbances which is guaranteed via stability analysis presented. To evaluate the performance of proposed TDE, simulations are conducted and comparison are made with conventional TDE. Besides, the performance of the proposed control system is compared with conventional time delay controller (TDC) and PID controller to verify its performance. Simulations show high accuracy and superior performance of the proposed control system.
    Keywords: Dynamic Positioning, Passive Arm, ROV, Time Delay Estimation, Unknown Dynamics