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An experimental study of interceptor's effectiveness on hydrodynamic performance of high-speed planing crafts
, Article Polish Maritime Research ; Volume 20, Issue 2 , 2013 , Pages 21-29 ; 12332585 (ISSN) ; Seif, M. S ; Abbaspoor, M ; Sharif University of Technology
2013
Abstract
Trim control mechanisms such as interceptors and trim flaps have been widely used in recent years in highspeed crafts for ride and trim control. In spite of their extensive application, a few studies investigating the impact of interceptors on planing craft performance, have been published. In the present study, the impact of interceptors on planing crafts hydrodynamic quality is investigated through application of an experimental method. Two scaled-down models of high-speed planing mono-hull and catamaran are tested with and without interceptors in calm water at different heights of the interceptors to investigate the effect of interceptors on drag reduction of the models. The first one is...
Comparison final velocity between sailing boat with a rigid airfoil and cloth sail
, Article 2006 ASME International Mechanical Engineering Congress and Exposition, IMECE2006, Chicago, IL, 5 November 2006 through 10 November 2006 ; 2006 ; 08888116 (ISSN); 0791837904 (ISBN); 9780791837900 (ISBN) ; Rad, M ; Fakhraee, A ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2006
Abstract
The powering requirement of a ship is one of the most important aspects of naval architecture. Traditionally, ships have been tested for hull resistance using hydrodynamic tank testing. But it is very time consuming, expensive, and has inherent scaling errors. Because of these reasons, today many vessels are sold on the market without any model testing. Another set of design tools are Computational Fluid Dynamics and parametric prediction. Computational Fluid Dynamics (CFD) codes are not yet wholly proven in its accuracy. Parametric predictions contain acquired data for a specific family of hull forms and use key hull parameters to evaluate a particular design. This tool is absolutely...
Parametric study of buckling and post-buckling behavior for an aluminum hull structure of a high-aspect-ratio twin hull vessel
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 234, Issue 1 , 2020 , Pages 15-25 ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
SAGE Publications Ltd
2020
Abstract
Metal plates are essential parts of structures such as ship hulls and offshore oil platforms. These plates are typically under compressive axial forces. Hence, one of the main mechanisms for failure and collapse of such structures is buckling of plates. Thus, for safe and secure design, buckling strength of plates should be evaluated. Finite element analysis techniques are perfect tools for this purpose because of the accuracy and flexibility for performing simulations with different variables. In this study, the strength of aluminum plates has been studied using finite element analysis software and it was tried to study the influence of variables such as initial imperfections, plate...
Numerical study on a heeled one-stepped boat moving forward in planing regime
, Article Applied Ocean Research ; Volume 96 , 2020 ; Tavakoli, S ; Kohansal, A ; Khosravani, R ; Ghassemzadeh, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Stepped planing hulls have the potential to reach high-speeds in the sea. The step on the bottom of these vessels influence the pressure distribution and thus stability of the vessel, especially in transverse plane. Understanding the behavior of these vessels in a non-zero heel condition is fundamental in the early stage design. In the current paper, numerical simulation of the viscous flow field around a heeled one-stepped planing hull is performed to evaluate influences of the asymmetric planing on the performance of the vessel. The numerical model is validated in two steps. At the first step, performance of a heeled stepless planing hull operating in calm water is simulated using the...
Experimental investigation of the wetted surfaces of stepped planing hulls
, Article Ocean Engineering ; Volume 187 , 2019 ; 00298018 (ISSN) ; Nowruzi, H ; Karami, M ; Javanmardi, H ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
In the current study, experimental tests are conducted to evaluate the hydrodynamic characteristics and the bottom wetted surfaces of the planing hulls equipped by one transverse step. For this purpose, total resistance, dynamic trim angle, dynamic sinkage, reattachment lengths of the separated flow and forebody and aftbody wetted areas are quantitatively measured at different geometrical parameters of the step and hull velocities. Moreover, the bottom wetted surfaces are qualitatively investigated by analyzing the underwater photographs. Our experimental results are also compared by archival data with good accordance. Based on our experimental observations, dynamic trim angle and dynamic...
Ship hull drag reduction using bottom air injection
, Article ASME 2007- 26th International Conference on Offshore Mechanics and Arctic Engineering 2007, OMAE2007, San Diego, CA, 10 June 2007 through 15 June 2007 ; Volume 4 , 2007 , Pages 283-292 ; 0791842703 (ISBN); 9780791842706 (ISBN) ; Rad, M ; Amini, H ; Rishehri, M ; Sharif University of Technology
2007
Abstract
Air cavity ship concept has received some interest due to its potential on viscous resistance reduction for high speed craft. Air-cavity ships (ACS) are advanced marine vehicles that use air injection at the wetted hull surfaces to improve a vessel's hydrodynamic characteristics. Air is supplied through nozzles under a profiled bottom to generate an air cavity beneath such a ship, so that a steady air layer separates a part of the bottom from contact with water, consequently reducing hydrodynamic resistance. Resistance tests were conducted with two forms: first of which was planning catamaran hull form, and second one was an alternative form with an air cavity injection under its bottom...
Design and Optimization of Positioning System for Hull Crawling Robot
, M.Sc. Thesis Sharif University of Technology ; Khorasanchi, Mahdi (Supervisor) ; Tabeshpour, Mohammad Reza (Supervisor)
Abstract
The hulls of various ships are exposed to the problem of biofoulings on the hull after a period of time due to use in the salt water environment of the sea and the existence of suitable conditions for the growth of marine plants, so that the ship after about one month of stopping in the port, in order to start the activity again, it is necessary to clean the hull from these biofoulings. The ship will be transported to the dry dock for cleaning only when it is heavily involved in biofoulings on the hull, and in the meantime, it must be periodically cleaned in water by other systems, including the diver and robotic systems.Using a robotic system to perform this operation has various...
Nonparametric frontier analysis models for efficiency evaluation in insurance industry: A case study of Iranian insurance market
, Article Neural Computing and Applications ; Vol. 24, issue. 5 , April , 2014 , pp. 1153-1161 ; ISSN: 09410643 ; Barati, B ; Majazi Dalfard, V ; Hatami-Shirkouhi, L ; Sharif University of Technology
Abstract
Performance evaluation and efficiency analysis is considered to be one of the critical responsibilities of the management department. This paper investigates and assesses the efficiency and performance of Iranian insurance companies through nonparametric frontier analysis (FA) models. The two well-known nonparametric FA models, data envelopment analysis (DEA) and free disposal hull, are utilized to separate the efficient companies from the inefficient companies, and two well-known super-efficiency analysis models are utilized to rank the efficient units. For the further analysis, critical inputs are also identified for inefficient companies using DEA sensitivity analysis which is a powerful...
Numerical investigation of a stepped planing hull in calm water
, Article Ocean Engineering ; Volume 94 , January , 2015 , Pages 103-110 ; 00298018 (ISSN) ; Ashrafizaadeh, M ; Esfahan, R. K ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Stepped planing hulls enable the feasibility of running at relatively low Drag-Lift ratio by means of achieving more optimal trim angle at high speeds. Currently, there is no precise method to analyze these hulls over the full range of operating speeds. In this study, a three-dimensional computational fluid dynamics (CFD) model using volume of fluid (VOF) approach is presented for examining the characteristics of a planing hull having one transverse step. A procedure is presented to transform a series of fixed-position simulations into a free to heave and pitch simulation. Resistance, lift, running draft, dynamic trim angle, and wetted area are compared with available experimental data and...
Numerical study and acoustic analysis of propeller and hull surface vessel in self-propulsion mode
, Article Ships and Offshore Structures ; 2021 ; 17445302 (ISSN) ; Norouzi Keshtan, M ; Malek Jafarian, M ; Bagheri, M. R ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
In this article, the hydrodynamic analysis and noise of the propeller and the surface vessel hull were examined. The model selected in this study is a KRISO Container Ship (KCS) with a five-bladed propeller. Initially, the hydrodynamic analysis of the propeller in open water mode and then in self-propulsion mode was investigated using computational fluid dynamics. Simulations were carried out using a commercial solver, STAR-CCM+ (RANS equations with FVM and VOF model). Finally, the emitted noise from the propeller and the vessel hull was investigated using Fox William Hawkins equations. The pressure distribution and hydrodynamic performance (thrust, torque, efficiency) of the propeller in...
Numerical study and acoustic analysis of propeller and hull surface vessel in self-propulsion mode
, Article Ships and Offshore Structures ; Volume 17, Issue 11 , 2022 , Pages 2488-2497 ; 17445302 (ISSN) ; Norouzi Keshtan, M ; Jafarian, M. M ; Bagheri, M. R ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
In this article, the hydrodynamic analysis and noise of the propeller and the surface vessel hull were examined. The model selected in this study is a KRISO Container Ship (KCS) with a five-bladed propeller. Initially, the hydrodynamic analysis of the propeller in open water mode and then in self-propulsion mode was investigated using computational fluid dynamics. Simulations were carried out using a commercial solver, STAR-CCM+ (RANS equations with FVM and VOF model). Finally, the emitted noise from the propeller and the vessel hull was investigated using Fox William Hawkins equations. The pressure distribution and hydrodynamic performance (thrust, torque, efficiency) of the propeller in...
Evaluating of Geometric Factors Effects on Seakeeping Performance of HARTH Vessels
, M.Sc. Thesis Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor)
Abstract
Performing research and development in the field of modern vessel types which serve several functions is considerably necessary because of their importance and rapid development. HARTH vessel is considered one of the important ships which has been recently attracted much attention from the world. In this respect, a full investigation of its performance could make a big contribution to its optimum design and appropriate exploitation.“HARTH” ship is the abbreviation for “High Aspect Ratio Twin Hull” is included in the catamaran vessel category with a high aspect ratio with respect to their underwater cross-section’s ratio of length to width.A host of crucial issues should be considered for...
White space regions
, Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 22 January 2011 through 28 January 2011, Novy Smokovec ; Volume 6543 LNCS , 2011 , Pages 226-237 ; 03029743 (ISSN) ; 9783642183805 (ISBN) ; Fazli, M ; Ghodsi, M ; Safari, M ; Saghafian, M ; Tavakkoli, M ; Sharif University of Technology
2011
Abstract
We study a classical problem in communication and wireless networks called Finding White Space Regions. In this problem, we are given a set of antennas (points) some of which are noisy (black) and the rest are working fine (white). The goal is to find a set of convex hulls with maximum total area that cover all white points and exclude all black points. In other words, these convex hulls make it safe for white antennas to communicate with each other without any interference with black antennas. We study the problem on three different settings (based on overlapping between different convex hulls) and find hardness results and good approximation algorithms
Improved linear cryptanalysis of reduced-round SIMON-32 and SIMON-48
, Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 6 December 2015 through 9 December 2015 ; Volume 9462 , December , 2015 , Pages 153-179 ; 03029743 (ISSN); 9783319266169 (ISBN) ; Alizadeh, J ; Alkhzaimi, H. A ; Aref, M. R ; Bagheri, N ; Gauravaram, P ; Biryukov A ; Goyal V ; Sharif University of Technology
Springer Verlag
2015
Abstract
In this paper we analyse two variants of SIMON family of light-weight block ciphers against variants of linear cryptanalysis and present the best linear cryptanalytic results on these variants of reducedround SIMON to date. We propose a time-memory trade-off method that finds differential/ linear trails for any permutation allowing low Hamming weight differential/ linear trails. Our method combines low Hamming weight trails found by the correlation matrix representing the target permutation with heavy Hamming weight trails found using a Mixed Integer Programming model representing the target differential/linear trail. Our method enables us to find a 17-round linear approximation for SIMON-48...
Performance of high-speed planing hulls accelerating from rest under the action of a surface piercing propeller and an outboard engine
, Article Applied Ocean Research ; Volume 77 , 2018 , Pages 45-60 ; 01411187 (ISSN) ; Najafi, S ; Amini, E ; Dashtimanesh, A ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In this paper, a mathematical model for performance prediction of a high-speed planing hull in forward acceleration motion has been developed. Three degrees of freedom have been considered for solving the problem. Utilizing previous empirical equations of displacement ships, motion of the vessel in displacement regime has been simulated. In order to model pre-planing and planing regimes, 2D + T theory has been used. Equations for prediction of performance of a surface piercing propeller (SPP) and an engine have been presented. Validity of the proposed method has been assessed by comparing its results against previous experimental data, and good agreement between experimental and mathematical...
Convex Hull Problem in the Uncertain Models
, M.Sc. Thesis Sharif University of Technology ; Ghodsi, Mohammad (Supervisor)
Abstract
Many geometric problems have algorithms that exist on paper for them, such as the Convex Hull problem [1], Minimum Spanning Tree [2], Voronoi Diagram [3], Closest Pair of Points [4], Largest Empty Circle [5], Smallest Enclosing Circle [6], and more. In all of these problems, the assumption is that a certain number of points are given as input, and we must perform various operations on these points based on the nature of the problem. Furthermore, a stronger assumption is that these points are given to us precisely, but in reality, this is not the case, and for various reasons, it is not possible to determine the exact locations of these points. Therefore, it can be said that we are dealing...
Experimental evaluation of ship squat in shallow waters
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Vol. 36, Issue. 3 , 2014 , pp. 559-569 ; ISSN: 1806-3691 ; Seif, M. S ; Sharif University of Technology
Abstract
Enlargement of ship size in recent decades and no change in the harbors and approach channels have resulted in global attention toward navigation in shallow and confined waters. A phenomenon which restricts ship navigation in shallow waters is reduction of under-keel clearance in terms of sinkage and dynamic trim, which is called squatting. Due to the complexity of flow around the ship hull, one of the best methods for predicting the ship squat is the experimental approach based on systematic model tests in the towing tank. In this study, model tests for tanker ship model and traditional Persian Gulf and Oman Sea vessel called dhow had been performed in the towing tank and the squat of the...
A new design for floating offshore platforms
, Article Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE ; Volume 1 , 2012 , Pages 529-537 ; 9780791844885 (ISBN) ; England, G. L ; Moradkhan, E ; Valikhani, A. R ; Bahadori, M. R ; Sharif University of Technology
2012
Abstract
While for shallow waters the use of old offshore jackets still seems efficient and justifiable, for deep and ultra-deep waters such platforms cannot be used. During the past few decades the old generation of fixed offshore platforms was succeeded by the new floating platforms and new designs such as FPSOs. A new family of floating offshore platforms has been developed. These should be able to respond to size, weight and space for operating equipment, i.e. they can be constructed to have a wide range of load-bearing capacities. Use is made of the old concept of Life Saving Tubes, which in their simplest form can be a toroidal shaped tyre inner tube. The Torus-shaped idea can be further...
DeFining and Critical Sets of Graphs and Latin Squares
, M.Sc. Thesis Sharif University of Technology ; Mahmoodian, Ebadollah (Supervisor)
Abstract
Since critical and defining sets have been examined in various fields of combinatorics, including Latin squares and different branches of graph theory, we aim to present a portion of the obtained results con-cerning defining sets in diverse fields of graph theory, and provide a survey on them.In the present dissertation, we examine defining sets of vertex coloring,edge coloring, total coloring and forcing sets of orientation of graphs,perfect matching, hull and geodetic sets. Since complete graphs’ col-oring defining sets and Latin squares’ critical sets are closely related,we shall discuss them in a coloring framework. Furthermore, for dif-ferent graph families, including regular graphs,...
Unsupervised Pattern Recognition in DATA Strams
, M.Sc. Thesis Sharif University of Technology ; Zarei, Alireza (Supervisor)
Abstract
Pattern recognition in data streams using bounded memory and bounded time is a difficult task. There are many techniques for recognizing patterns but when we talk about data streams these algorithms became useless since there are no enough memory to store all data. In data stream model the entire data is not available at any time and we don’t have enough time processing each data.
In this thesis we consider current methods for recognizing patterns from a data streams. The goal pattern in this study was the minimum total area of k convex polygons encloses all data
In this thesis we consider current methods for recognizing patterns from a data streams. The goal pattern in this study was the minimum total area of k convex polygons encloses all data