Numerical modeling of seawater flow through the flooding system of dry docks

A. Najafi-Jilani,A. Naghavi 대한조선학회 2009 International Journal of Naval Architecture and Oc Vol.1 No.2

Numerical simulations have been carried out on the flooding system of a dry located at the south coasts of Iran. The main goals of seawater flow haracteristics in the intake channels conditions of the flooding system are imposed in the modeling. The upstream boundary condition is the tidal fluctuations of sea water level. At the downstream, the gradually rising water surface elevation in the dry described in a transient boundary condition. The numerical results are compared with available laboratory a good agreement is obtained. The seawater discharge through the flooding system and the required time to filling up the dry dock is determined at the worst case. The water current velocity and pressure on the rigid boundaries are discussed.

Simulating three dimensional wave run-up over breakwaters covered by antifer units

A. Najafi-Jilani,M. Zakiri Niri,Nader Naderi 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.2

The paper presents the numerical analysis of wave run-up over rubble-mound breakwaters covered by antifer units using a technique integrating Computer-Aided Design (CAD) and Computational Fluid Dynamics (CFD) software. Direct application of Navier-Stokes equations within armour blocks, is used to provide a more reliable approach to simulate wave run-up over breakwaters. A well-tested Reynolds-averaged Navier-Stokes (RANS) Volume of Fluid (VOF) code (Flow-3D) was adopted for CFD computations. The computed results were compared with experimental data to check the validity of the model. Numerical results showed that the direct three dimensional (3D) simulation method can deliver accurate results for wave run-up over rubble mound breakwaters. The results showed that the placement pattern of antifer units had a great impact on values of wave run-up so that by changing the placement pattern from regular to double pyramid can reduce the wave run-up by approximately 30%. Analysis was done to investigate the influences of surface roughness, energy dissipation in the pores of the armour layer and reduced wave run-up due to inflow into the armour and stone layer.

Robust Periodic Vehicle Routing Problem with Time Windows under Uncertainty: An Efficient Algorithm

A. Salamatbakhsh-Varjovi,R. Tavakkoli-Moghaddam,M. Alinaghian,E. Najafi 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.11

In a competitive environment, distributors engage in intense rivalry to meet the customers’ demands and accordingly earn maximum profits. Due to changes in customers’ demands, changes in a planned combination of customers to be visited in various days, traffic changes, etc., a sequence of visiting customers by competitors will be changed. So, planning for serving customers ahead of competitors will be uncertain. On the other hand, total transportation costs are also of high importance in distribution of goods. By keeping this issue in mind, we develop a bi-objective mathematical model to evaluate a Periodic Vehicle Routing Problem (PVRP) with time windows under uncertainty for companies competing to provide services to customers. The model is established using an improved scenario-based robust optimization approach. Given that the PVRP is an NP-hard problem, an Improved Differential Evolution (IDE) algorithm is used to identify efficient solutions for the model. The results on small-scale problems were compared with those obtained using the CPLEX solver. To evaluate the performance of the proposed IDE algorithm, a few sample tests on large-scale problems are conducted, and the results are compared with those derived using two other differential evolution algorithms. The findings show that the IDE algorithm exhibits suitable accuracy and performance in solving the presented model.

Simulating three dimensional wave run-up over breakwaters covered by antifer units

Najafi-Jilani, A.,Niri, M. Zakiri,Naderi, Nader The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.2

The paper presents the numerical analysis of wave run-up over rubble-mound breakwaters covered by antifer units using a technique integrating Computer-Aided Design (CAD) and Computational Fluid Dynamics (CFD) software. Direct application of Navier-Stokes equations within armour blocks, is used to provide a more reliable approach to simulate wave run-up over breakwaters. A well-tested Reynolds-averaged Navier-Stokes (RANS) Volume of Fluid (VOF) code (Flow-3D) was adopted for CFD computations. The computed results were compared with experimental data to check the validity of the model. Numerical results showed that the direct three dimensional (3D) simulation method can deliver accurate results for wave run-up over rubble mound breakwaters. The results showed that the placement pattern of antifer units had a great impact on values of wave run-up so that by changing the placement pattern from regular to double pyramid can reduce the wave run-up by approximately 30%. Analysis was done to investigate the influences of surface roughness, energy dissipation in the pores of the armour layer and reduced wave run-up due to inflow into the armour and stone layer.

Numerical modeling of seawater flow through the flooding system of dry ocks

Najafi-Jilani, A.,Naghavi, A. The Society of Naval Architects of Korea 2009 International Journal of Naval Architecture and Oc Vol.1 No.2

Numerical simulations have been carried out on the flooding system of a dry located at the south coasts of Iran. The main goals of seawater flow haracteristics in the intake channels conditions of the flooding system are imposed in the modeling. The upstream boundary condition is the tidal fluctuations of sea water level. At the downstream, the gradually rising water surface elevation in the dry described in a transient boundary condition. The numerical results are compared with available laboratory a good agreement is obtained. The seawater discharge through the flooding system and the required time to filling up the dry dock is determined at the worst case. The water current velocity and pressure on the rigid boundaries are discussed.

Numerical solution of non-Fourier heat transfer during laser irradiation on tooth layers

S. Falahatkar,A. Nouri-Borujerdi,M. Najafi,A. Mohammadzadeh 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.12

This study reports on the simulation of temperature distribution of human tooth under a laser beam based on non-Fourier models. The temperature in the tooth depth that directly results from the conduction heat transfer process is caused by the lengthy thermal relaxation time in the tooth layers. A detailed tooth composed of enamel, dentin, and pulp with unstructured shape, uneven boundaries, and realistic thicknesses was considered. A finite difference scheme was separately adopted to solve time-dependent equations in solid layers and soft tissue of the tooth. In this study, a dual-phase-lag non-Fourier heat conduction model was applied to evaluate temperature distribution induced by laser irradiation. Results show that for the laser-irradiated tooth, the phase lag time of heat flux (τ q ) greatly affects the temperature of the early stage, whereas the phase lag time of the temperature gradient (τ T ) significantly influences the temperature of the later stage. Prediction of temperature profile in the tooth based on this investigation is more real using the non-Fourier model (i.e., τ q = 16 and τ T = 2 millisecond) compared with experimental studies. Meanwhile, the Fourier model (τ q = τ T ) or classical Fourier form (τ q = τ T = 0) and the thermal wave model (τ q = 16 and τ T = 0) led to unreal heated point on the enamel. The effects of laser parameters, such as laser exposure time and laser intensity on the pulp, were also investigated. Increasing the laser duration and simulation time after laser irradiation was a logical approach to pulp ablation compared with increasing the laser intensity.

Effect of Ce Addition on the Tribological Behavior of ZK60 Mg-Alloy

S. M. Banijamali,Y. Palizdar,S. Najafi,A. Sheikhani,M. Soltan Ali Nezhad,P. Valizadeh Moghaddam,H. Torkamani 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

The present work aims to study the tribological behavior of an extruded ZK60 alloy in the presence of Ce; in a previous study, among ZK60 alloys with diferent Ce addition rates, an alloy with 3 wt% of Ce was found to exhibit the mostpromising mechanical (e.g., hardness and strengths) properties, while its wear behavior remained unknown. The results ofmicrostructural examinations by optical and electron microscopes show that Ce addition reduces the grain size from 6.1 to2.0 μm. Besides, in addition to the precipitates already distributed in the base alloy (Mg7Zn3), Ce could promote the formation of a new precipitate (MgZn2Ce), increasing the total fraction of the precipitates. These microstructural evolutionsenhance the strengths of the studied ZK60 alloy, as the yield and tensile strengths increase from 212 to 308 MPa and from297 to 354 MPa, respectively. A pin on disc tribometer was employed to study the wear behavior of the developed alloyunder diferent normal loads (5, 20, 40, and 60 N). The results show that the base and Ce-added alloys exhibit almost asimilar frictional behavior, while the wear resistance of the Ce-added alloy is higher within the load ranges applied: (i) inlow load conditions (5 and 20 N), where the abrasive wear is the active mechanism, the precipitates in the Ce-added alloycould enhance the wear resistance. (ii) Under the load of 40 N, oxidative wear is also an operative wear mechanism, leadingto a sharp increase in the wear rate of the alloys. In this condition, Ce could provide a protective oxide layer, which couldimprove the wear resistance of the alloy. (iii) At a load of 60 N, both studied alloys exhibit a similar wear rate due to a severeoxidation condition. Therefore, beyond this loading condition, the microstructural evolutions (e.g., change in precipitationbehavior) caused by Ce addition can no longer contribute to the enhancement of wear resistance.

Order of N Complexity Transform Domain Adaptive Filters : Software and Hardware Implementation

A. Najafi,B. Farhang Boroujeny,G. S. Samudra 대한전자공학회 1993 JTC-CSCC : Joint Technical Conference on Circuits Vol.- No.-

Development of integrated marine monitoring network on southern coastline of Caspian sea

A. Najafi-Jilani,A. Nik-Khah 대한조선학회 2011 International Journal of Naval Architecture and Oc Vol.3 No.2

Monitoring of water surfaces through permanent measurement of hydrodynamic and meteorological data is one of the main requirements in safe and sustainable water management. The Caspian Sea, the major surface water body in Iran, significantly affects more than 600 km of urban and industrial coastline. In the present work, an integrated marine monitoring network for the entire southern coastline of the Caspian Sea was developed. The main design concerns centered on the network measuring components and data recording, checking, filtering, gap recognition, and transferring systems. Four coastal monitoring stations were assigned, along with two regional collecting stations and one central data station for gathering, checking and delivering recorded data at different access levels. Applicable guidelines on selection of measuring devices for both shallow and deep water zones are presented herein.

Numerical investigation of floating breakwater movement using SPH method

A. Najafi-Jilani,A. Rezaie-Mazyak 대한조선학회 2011 International Journal of Naval Architecture and Oc Vol.3 No.2

In this work, the movement pattern of a floating breakwater is numerically analyzed using Smoothed Particle Hydrodynamic (SPH) method as a Lagrangian scheme. At the seaside, the regular incident waves with varying height and period were considered as the dynamic free surface boundary conditions. The smooth and impermeable beach slope was defined as the bottom boundary condition. The effects of various boundary conditions such as incident wave characteristics,beach slope, and water depth on the movement of the floating body were studied. The numerical results are in good agreement with the available experimental data in the literature The results of the movement of the floating body were used to determine the transmitted wave height at the corresponding boundary conditions