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Investigation of hydroelastic effect in analysis of high-speed craft
, Article Ships and Offshore Structures ; 2014 ; ISSN: 1754212X ; Seif, M. S ; Tabeshpur, M. R ; Yaakob, O ; Sharif University of Technology
Abstract
Hydroelastic effect in bottom slamming problem of high-speed craft is one of the most challenging issues in structural design. In this paper, numerical method is used to investigate the hydroelastic effect in bottom-water impact analysis of high-speed monohull craft. Slamming with two viewpoints of rigid and elastic structures (hydroelastic effect) is modelled by coupled computational fluid dynamic (CFD) and finite element method (FEM) techniques. The results showed that considering hydroelastic effect, especially in high-impact speed, reduces the structural deformations and stresses compared with quasi-statistic analysis. The effect of different parameters, such as boundary condition, plate...
New constrained initialization for bearing-only SLAM
, Article Proceedings - 2013 IEEE International Conference on Control System, Computing and Engineering, ICCSCE 2013 ; 2013 , Pages 95-100 ; 9781479915088 (ISBN) ; Arbabmir, M. V ; Asl, H. G ; Sharif University of Technology
2013
Abstract
In this paper we present a new landmark initialization technique for Bearing-Only Simultaneous Localization and Mapping (SLAM) algorithm. The initialization scheme is a type of the delayed constrained initialization method and is different from previous approaches. In our work, it is shown that the angle between sequential observations measured by a bearing-only sensor such as pan-tilt camera and the distance between the vehicle and landmark plays an important role in landmark localization accuracy. Considering this fact, a proper constrained function that utilizes the rotation angle of the camera is applied between multiple landmark location estimates and the best estimate is selected. The...
Investigation of wedge water-entry under symmetric impact loads by experimental tests
, Article Latin American Journal of Solids and Structures ; Volume 14, Issue 5 , 2017 , Pages 861-873 ; 16797817 (ISSN) ; Yaakob, O. B ; Seif, M. S ; Koto, J ; Sharif University of Technology
Brazilian Association of Computational Mechanics
2017
Abstract
One of the main challenges for engineers in designing high-speed crafts is the evaluation of hydrodynamic loads during the impact of hull to wave’s surface. This paper presents an experimental investigation on the pressure distribution on three wedge-sections with 15°, 20° and 30° deadrise during water-entry. Assessment of pressure distribution on the effects of parameters such as drop heights, deadrise angles and the weights of the models had done. Time histories of impact pressure were recorded. It was showed that, the maximum pressure for 20° wedge had increased 2.4 times in comparison with 30° wedge while this number is 1.23 time for the 15° wedge. But the effects of weight and drop...
Application of β-unzipping method in offshore system reliability analysis under changing load pattern
, Article 22nd International Conference on Offshore Mechanics and Arctic Engineering; Safety and Reliability Pipeline Technology, Cancun, 3 June 2001 through 13 June 2001 ; Volume 2 , 2003 , Pages 77-83 ; Makouie, S. H ; Sharif University of Technology
2003
Abstract
This paper is concerned with the reliability assessment of a fixed platform operating in intermediate water depth under extreme environmental conditions. The structure is modelled by two-dimensional frame structure and subjected to quasi-static loads. Extreme wave loads acting on the platform in the unidirectioal mode are estimated together with their probabilistic characteristics. Fully plastic capacities of the members are also treated as random variables. The structure is modelled as a plane truss by using beam-column models and the plastic collapse of the structure is evaluated by using a linearized plasticity condition of the section under effect of axial force to generate the safety...
Integration of image de-blurring in an aerial Mono-SLAM
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Vol. 228, issue. 8 , May , 2014 , p. 1348-1362 ; Gholampour, P ; Malaek, S. M. B ; Sharif University of Technology
Abstract
In this article, we discuss the possibility of integrating image de-blurring techniques in an aerial simultaneous localization and mapping by a single camera (monocular simultaneous localization and mapping (Mono-SLAM)). We use an integrated aerial virtual environment together with a six-degree-of-freedom aircraft flight simulator to show the effectiveness of the approach to generate three-dimensional flight trajectories via integration of image de-blurring in the associated loop of the Mono-SLAM. The objective is to increase the overall performance of a flying mission over an unknown area by means of a vision-only method. The integrated aerial virtual environment produces and collects...
Investigation on Effects of Slamming on High Speed Craft Motions and the Crew
, M.Sc. Thesis Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor) ; Rad, Manoochehr (Supervisor)
Abstract
Regarding the increasing application of fast boats in the world, studying the motions and dynamic performances of these boats is consequently effective and vital.Vast activities take place in all over the world yearly. General performances hull tests occur in marine laboratories such as Wave maker and carriage. Model hull test is one of effective branches of the naval architecture engineering. This method is also based on dimensional analysis. In this thesis,after understanding the waves and the methodology, a computer program was developed to predict motions of a high speed craft in regular and irregular waves (Heave and Pitch). Slamming is one of the most important parameters on a high...
Investigation of hydroelastic effect in analysis of high-speed craft
, Article Ships and Offshore Structures ; Volume 11, Issue 1 , 2016 , Pages 16-24 ; 17445302 (ISSN) ; Seif, M. S ; Tabeshpur, M. R ; Yaakob, O ; Sharif University of Technology
Taylor and Francis Ltd
2016
Abstract
Hydroelastic effect in bottom slamming problem of high-speed craft is one of the most challenging issues in structural design. In this paper, numerical method is used to investigate the hydroelastic effect in bottom-water impact analysis of high-speed monohull craft. Slamming with two viewpoints of rigid and elastic structures (hydroelastic effect) is modelled by coupled computational fluid dynamic (CFD) and finite element method (FEM) techniques. The results showed that considering hydroelastic effect, especially in high-impact speed, reduces the structural deformations and stresses compared with quasi-statistic analysis. The effect of different parameters, such as boundary condition, plate...
A unified computational method for simulating dynamic behavior of planing vessels
, Article China Ocean Engineering ; Volume 23, Issue 3 , 2009 , Pages 517-528 ; 08905487 (ISSN) ; Jahanbakhsh, E ; Panahi, R ; Karimi, M. H ; Sharif University of Technology
2009
Abstract
High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of integration of the two-phase viscous flow induced stresses over the hull, acting loads (forces and moments) are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time...
Indoor Office Environment Mapping Using a Mobile Robot with Kinect Sensor
, M.Sc. Thesis Sharif University of Technology ; Jamzad, Mansour (Supervisor)
Abstract
In recent years with advancement of Robotics, the applications of wide scale use of robots in our homes is not as far-fetched as it was before. One of the important problems for an indoor robot is moving inside a new and unknown environment. To achieve this, the robot should, with the help of its sensors, not only calculate its location; but should also build a map of the environment for later use. Additionally, the robot must be able to explore this unknown environment. The most important drawbacks of the classical solutions to these problems are long computation times, heavy memory usage and absence of precision. In recent years, large amount of research effort has put on solving these...
Design and Construction of Arash Social Robot for Pediatric Cancer Hospitals Part III: Position Estimation in Populated Environments Comprising Simultaneous Localization and Mapping Technique and a Multi-person Tracking Module
, M.Sc. Thesis Sharif University of Technology ; Meghdari, Ali (Supervisor) ; Alemi, Minoo (Co-Supervisor)
Abstract
Simultaneous Localization And Mapping (SLAM) is regarded as one of the most significant advances in robotics in recent decades. It enables robots to map their surrounding environments without the need for external equipment and simultaneously determine their position on this map. In the present study, this technique was implemented on Arash social robot to enable it to estimate its position in the environment with decent accuracy and potentially be able to automatically move towards the targets determined on the map using a path planning algorithm. At first, Arash robot mechanically was redesigned for this technique, and then the hardware and software needed to high-level and low-level...
Combined Optical flow Algorithm and Simultaneous Localization and Mapping for Localization Robust to Surface Texture Variations
, M.Sc. Thesis Sharif University of Technology ; Vosoughi, Gholamreza (Supervisor) ; Moradi, Hamed (Supervisor)
Abstract
The research field of localization with high precision (precision of 10 micrometers) has greatly attracted attentions in recent years. Optical flow sensor is one of the inexpensive solutions for the localization of robot, which have been used in computer mice. The most important application of this thesis is to localize walking micro robot. The main challenge of previous research is the fact that sensor's precision is highly dependent on the surface texture. The aim of this research is to implement an appropriate algorithm on optical flow sensor in order to increase the robustness of sensor's precision to surface texture. In this regard, firstly experimental hardware has been designed and...
Hull Form Optimization of Floating Body for Maneuvering
, M.Sc. Thesis Sharif University of Technology ; Sayyaadi, Hassan (Supervisor)
Abstract
This paper was directed to recognize maneuver equations perfectly, and with regard to CFD method maneuver simulation is going to be done in form of two and three dimensional. Today, since CFD methods have been exerted in different works, further and more actual development of floating body's maneuver is going to be our special need. As numerical methods for floating body's maneuver simulation by RANS method are developing, more researches are being done about this field as well. This thesis is going to simulate primitively maneuver of one floating body by Smoothed Particle Hydrodynamic(SPH) method in order to be as the beginning of maneuver simulation by this method in which with regard to...
Safety Enhancement using SLAM Assisted Flight Control System (SAFCS)in Low-Level Flights
, M.Sc. Thesis Sharif University of Technology ; Malaek, Mohammad Bagher (Supervisor)
Abstract
Ultralight aircraft (VLA category) are usually piloted by novice pilots under Visual Flight Rules (VFR). In this work, we demonstrate how newly developed techniques in robotics could be used to enhance flight safety in this category of aircraft, especially during landing around sunset. In this research we have investigated the ability of Simultaneous Localization And Mapping (SLAM) algorithms in low level flight just before touch-down. Different case-studies show that SLAM algorithm is efficient in detecting the runway threshold. Comparing five different methods of parameterizations for landmarks detection including: (1) Plucker, (2) Anchored Plucker, (3) Homogeneous, (4) Anchored...
Optimum Camera Position for UAV Vertical Plane Maneuvers
,
M.Sc. Thesis
Sharif University of Technology
;
Malaek, Mohammad Bagher
(Supervisor)
Abstract
This work presents the methodology to investigate Optimum Camera Installation Angle (OCIA)while employing the so called?Vision Based Navigation (VBN)? in urban areas.The approach is suitable for future general aviation aircraft as envisioned in Small Air Transportation System (SATS) as well as Unmanned Aerial Vehicles (UAV).Due to practical constraints, the work is limited to the maneuvers in the vertical plane while conducting Simultaneous Localization and Mapping (SLAM) technique.This technique was originated in robotics and is commonly used to guide both ground based and low speed aerial robots in unknown environments involving different types of obstacles. A variety of camera...
A hybrid computer simulation-genetic algorithm for scheduling optimisation of cargo trains with time and queue limitations
, Article International Journal of Industrial and Systems Engineering ; Volume 8, Issue 2 , 2011 , Pages 157-174 ; 17485037 (ISSN) ; Izadbakhsh, H. R ; Mohammadhosseinzad, M ; Raissifard, M. R ; Sharif University of Technology
2011
Abstract
This paper presents the scheduling optimisation of cargo trains by hybrid computer simulation (CS) and genetic algorithm. Scheduling cargo trains is based on the timetable of passenger trains that have priority in relation to cargo trains. System modelling is accomplished by Visual SLAM by considering time limitations, queue priority and limited station lines. Time limitations define that a cargo train is permitted to travel from station i to j if scheduled passenger trains have completed the travel from station i to j. Queue priority means that passenger trains have priority over cargo trains. In addition, each station has a limited storage track. In addition, all repair, maintenance,...
Semantic Visual SLAM in Dynamic Environments
, M.Sc. Thesis Sharif University of Technology ; Meghdari, Ali (Supervisor) ; Nemati Estahbanati, Alireza (Supervisor) ; Taheri, Alireza (Co-Supervisor)
Abstract
Most of the existing visual SLAM methods heavily rely on a static world assumption and easily fail in dynamic environments. One solution is to eliminate the influence of dynamic objects by introducing deep learning-based semantic information to SLAM systems. In this project, we propose a real-time semantic RGB-D SLAM (built upon RTAB-Map) system for dynamic environments that is capable of detecting moving objects and maintaining a static map for robust camera tracking. Furthermore, we augment the semantic segmentation process using an Extended Kalman filter module to detect temporarily static moving objects by adding centroids to each found dynamic object and calculating their velocity. We...
Augmenting Inertial Motion Capture with SLAM Using EKF and SRUKF Data Fusion Algorithms
, M.Sc. Thesis Sharif University of Technology ; Salarieh, Hassan (Supervisor)
Abstract
Inertial motion capture systems widely use low-cost IMUs to obtain the orientation of human body segments, but these sensors alone are unable to estimate link positions. Therefore, this research used a SLAM method in conjunction with inertial data fusion to estimate link positions. SLAM is a method that tracks a target in a reconstructed map of the environment using a camera. This paper proposes quaternion-based extended and square-root unscented Kalman filters (EKF & SRUKF) algorithms for pose estimation. The Kalman filters use measurements based on SLAM position data, multi-link biomechanical constraints, and vertical referencing to correct errors. In addition to the sensor biases, the...
An integrated virtual environment for feasibility studies and implementation of aerial MonoSLAM
, Article Virtual Reality ; Volume 16, Issue 3 , September , 2012 , Pages 215-232 ; 13594338 (ISSN) ; Malaek, S. M. B ; Sharif University of Technology
2012
Abstract
This work presents a complete framework of an integrated aerial virtual environment (IAVE), which could effectively help implementing MonoSLAM (single-camera simultaneous localization and mapping) on an aerial vehicle. The developed system allows investigating different flight conditions without using any preloaded maps or predefined features. A 3D graphical engine integrated with a full 6 DOF aircraft dynamic simulator together with its trajectory generator completes the package. The 3D engine generates and accumulates real-time images of a general camera installed on the aerial vehicle. We effectively exploit C++ to develop the 3D graphics engine (3DGE) and all its associated visual...
Towards simulation of 3D nonlinear high-speed vessels motion
, Article Ocean Engineering ; Volume 36, Issue 3-4 , 2009 , Pages 256-265 ; 00298018 (ISSN) ; Jahanbakhsh, E ; Seif, M. S ; Sharif University of Technology
2009
Abstract
A numerical simulation algorithm based on the finite volume discretisation is presented for analyzing ship motions. The algorithm employs a fractional step method to deal with the coupling between the pressure and velocity fields. The free surface capturing is fulfilled by using a volume of fluid method in which the interface between the liquid (water) and gas (air) phases are computed by solving a scalar transport equation for the volume fraction of the liquid phase. The computed velocity field is employed to evaluate the acting forces and moments on the vessel. Using the strategy of boundary-fitted body-attached mesh and calculating all six degrees-of-freedom of motion in each time step,...