Now showing 1 - 10 of 21
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    Enhancing the material properties of carbon fiber epoxy composite by incorporating electrospun polyacrylonitrile nanofibers
    (01-01-2022)
    Vijay Kumar, Vishnu
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    Ramakrishna, Seeram
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    Composite materials are a superior class of material used in almost every field of engineering like construction, military, aerospace, ocean structures, communication, and various other high-performance applications owing to their high specific strength and modulus, increased design flexibility, desirable thermal expansion characteristics good resistance to fatigue and corrosion, and economic efficiency. However, their ply-by-ply nature makes them susceptible to delamination, which originates from the propagation of microcracks in the weak resin-rich layers. Many attempts have been made to address the lack of mechanical properties of this weak interlaminar region. A particularly promising approach involves the incorporation of nanofibers between the reinforcement layers as the composite is laid up. This work involves studying the property improvements in carbon fiber epoxy composite by interleaving electrospun polyacrylonitrile (PAN) nanofibers. Experimental testing involving Tensile, Izod, Charpy and high velocity impact tests showed improved material properties for the PAN nano-interleaved composite. These improvements achieved by nanofiber interleaving shows a greater potential in addressing major concerns for critical application of composite materials in future.
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    Publication
    On the water entry problem of 2D wedges and bow flare section
    (01-01-2021)
    Peddamallu, Pravallika
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    Menon, Aravind K.
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    Slamming is a phenomenon that results from the relative motion between a ship hull and water surface in rough seas. It is associated with high impact loads and whipping which may result in structural failure. Hence accurate estimation of slamming loads is important during the structural design of ships, particularly containerships with pronounced bow flare. This paper presents the numerical analysis of the slamming loads acting on triangular wedge sections by the application of Computational Fluid Dynamic (CFD) techniques using a commercial software. The water entry of 2D sections are simulated by modelling a free surface using Eulerian multiphase and VOF method. The body is kept stationary and the free surface is moved relative to the body by solving the flow equations using unsteady implicit time marching scheme. The phenomenon is numerically simulated in in-viscid, laminar, and turbulent flow regimes by solving Euler equations, Navier-Stokes equations, and Reynolds Average Navier-Stokes equations respectively using a commercial CFD tool star-CCM+ . This methodology is applied to 2D wedge sections and bow flare section and results are compared with existing literature. The effect of viscosity on the water entry of wedge sections with various dead rise angles and bow flare section is analyzed.
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    Investigation of bottom slamming on ships in irregular waves
    (01-01-2018)
    Wang, Shan
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    Guedes Soares, C.
    The bottom slamming of a chemical tanker and a LNGcarrier advancing in irregular waves is investigated numericallyand compared with experiments. The probability of slammingoccurrence on longitudinal locations and the slamming inducedpressures on the bottom of two ships are discussed. It isconsidered that slamming occurrence at a point is dependentupon two conditions: the relative vertical motion at the samelongitudinal position of the ship being larger than the verticaldistance from the still water to the concerned position, and theentry velocity exceeding some threshold velocity.Ship motions in irregular waves predicted by a time domainseakeeping code and measured from the model tests are used tocalculate the slamming occurrence statistically based on the twoconditions mentioned above. Only heave and pitch motions areconsidered in the calculations. The seakeeping code combinesbody linear radiation and diffraction forces with body nonlinearFroude-Krylov forces, hydrostatic forces and shipping of greenwater on the bow. The effects of body nonlinearity areconsidered by a simplified method: the memory functions,infinite frequency added masses and the radiation restoringcoefficients are assessed at each time instant as function of theinstantaneous wetted surface. A similar procedure is used tocalculate the diffraction forces.The experimental data of the wave-induced loads on thesetwo vessels in different sea states are analyzed statistically.Probability of exceedance of entry velocities and pressure peaksfor the sections at the bow and stern are computed for variousirregular sea states. The results of the slamming occurrence onlongitudinal locations and wave induced loads on these twotypes of ships are discussed.
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    Efficient Ship Detection in Synthetic Aperture Radar Images and Lateral Images using Deep Learning Techniques
    (01-01-2022)
    Nambiar, Athira
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    Vaigandla, Ashish
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    Over the past few decades, Synthetic Aperture Radar (SAR) imagery has become a primary means for high-resolution earth observation and a monitoring solution well suited for maritime surveillance. Ship detection (selecting the bounding boxes corresponding to ships) in SAR images plays a significant role in marine monitoring and in disaster relief. In the past, classical machine learning algorithms have been used towards this goal. Recently, in the field of object detection, the accuracy and detection speed have been significantly improved with the advent of deep learning (DL) techniques. However, such DL methods are less explored in the area of ship detection. In this paper, a salutary approach for improving ship detection in SAR images using advanced deep learning techniques is proposed. Various state-of-the-art benchmark models i.e. Faster-RCNN, YOLOv5, G-CNN and SSD are compared to assess their detection performance in various publicly available SAR datasets. Additionally, the best one among the trained models is used to detect lateral images of ships in real-time scenarios. The study is performed on a new custom-made Lateral Ship Detection Dataset (LSDD) developed in-house. Further, the best detection model is deployed in real-time tracking by integrating it with deepSORT tracking algorithm. The experimental results show the effectiveness of the DL models in ship detection and tracking applications in the wild.
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    Enhancing the properties of Carbon fiber thermoplastic composite by nanofiber interleaving
    (01-01-2022)
    Kumar, Vishnu Vijay
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    Ramakrishna, Seeram
    Thermoplastic composites have growing significance due to the rising demand for cost-effective and lightweight materials with high structural endurance and recyclability. The composition of composites is altered to enhance their overall properties. Electrospun Polyacrylonitrile nanofiber interleaving in Carbon fiber thermoplastic composite is investigated in this paper. Material properties are estimated using Tensile, Izod, Charpy, and Ballistic testing. Experimental results suggest that the nanofiber interleaving resulted in a composite with enhanced properties. The study can be further extended in investigating the effect of nanofibrous addition in various composites.
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    Hydroelastic effects on the vertical bending moment of a container ship in head and oblique seas
    (01-10-2023)
    Vijith, P. P.
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    Large-sized ships like Ultra large container ships (ULCS) experience severe hydroelastic vibrations like springing and whipping. This study numerically investigates the performance of a time domain method to assess the effect of structural vibration in calculating of vertical bending load of an ULCS. The proposed 2-D body nonlinear time-domain numerical method comprises a seakeeping solver based on potential flow theory and a structural solver based on Timoshenko beam theory. The simulations are carried out in the head and oblique waves for various forward speed conditions. The solver captures the effects of high-order springing and whipping in vertical bending. The numerical method identifies the whipping effect based on the slamming associated with the relative motion of the ship. The vertical bending moment is calculated in both regular and irregular waves, and the results are compared with the experimental results. The statistical evaluations of available results for irregular waves are carried out and presented. The numerical results are in good agreement with the experimental ones for most of the analyzed cases.
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    ESTIMATION OF VERTICAL, HORIZONTAL AND TORSIONAL RIGID BODY LOADS OF AN ULTRA-LARGE CONTAINER SHIP (ULCS) IN REGULAR WAVES
    (01-01-2022)
    Vijith, P. P.
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    Predicting hull responses and structural loads is essential for the robust design of ships. The Ultra Large Container Ships (ULCS) are subjected to non-linear wave loads due to the low block coefficient and pronounced bow flare. They are highly susceptible to torsional loads because of the large open cross-section which is subjected to unsymmetrical hydrodynamic loading. A time domain method based on strip theory is developed for estimating the coupled rigid body motions and wave-induced loads acting on an Ultra large containership. A 2D-Panel method is followed to calculate the added mass and damping coefficients. A body-nonlinear approach is followed to capture the major source of non-linearity in the structural load estimation due to Froude-Krylov and restoring forces. Case studies are conducted for an Ultra-large container ship in small amplitude regular waves. Motions and structural load (vertical, horizontal, and torsional load) RAOs are being investigated for various wave headings, and the results are compared with the published experimental results. The proposed method is computationally efficient to capture coupled rigid body responses and sectional loads, including torsion.
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    Surf-riding and Broaching—A Numerical Investigation on the Vulnerability of Ships
    (01-01-2021) ;
    Ameer Hassan, A. S.
    International Maritime Organization’s (IMO) recent discussion on the development of second-generation intact stability criterion has emphasized on the instability problems like surf-riding and broaching of ships. Surf-riding and broaching occur when a ship rides in astern seas with the ship velocity close to the wave celerity. It results in loss of stability, sometimes even leading to capsizing. Rudder becomes ineffective in these conditions and ship may lose its manoeuvring abilities. A ship’s vulnerability towards surf-riding and broaching is investigated using a numerical method. The numerical method based on strip theory calculates the Froude–Krylov and hydrostatic force for instantaneous wave profile. The numerical study is conducted on the ITTC A2 fishing vessel in regular astern waves and is compared with the measured ones available from the literature.
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    On the performance of different Deep Reinforcement Learning based controllers for the path-following of a ship
    (15-10-2023)
    Sivaraj, Sivaraman
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    Dubey, Awanish
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    A set of continuous state-action space-based deep reinforcement learning algorithms are used for the path following of a ship in calm water and waves. The mathematical model of a KVLCC2 tanker represents the ship dynamics. The mathematical model includes the hull force, rudder force, propulsion force, and external wave forces. Look ahead distance-based guidance algorithm called Line of Sight (LOS) is used for computing the Cross Track Error (CTE) and Heading Error (HE). The reward function is designed based on HE and CTE. The created Environment is trained with four different Deep Reinforcement Learning (DRL) agents named Proximal Policy Optimization (PPO), Deep Deterministic Policy Gradients (DDPG), Twin-Delayed Deep Deterministic Policy Gradients (TD3), and Soft-Actor Critic (SAC). Common Neural Network architecture is used for all four agents. Yaw rate, HE, and CTE serve as input to the Neural Network, and the rudder deflection rate (δ°) corresponds to the action space (output). Computation time, average cross-track error, and rudder actuation are computed and compared for path-following scenarios. DDPG performs better with a minimum average CTE for all the simulated cases. However, SAC demands minimum rudder control effort to achieve the tasks. Finally, the trained agents are validated using Hardware In-Loop (HIL) simulation.
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    A time-domain method for analyzing the ship roll stabilization based on active fin control
    (01-01-2021)
    Patil, Neha
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    The present work focuses on the development of a numerical body nonlinear time-domain method for estimating the effect of active roll fin stabilizers on ship roll motion in both regular and irregular seaway. The time-domain analysis aims at providing fast and accurate ship responses that will be useful during the design process through accurate estimation of the environmental loads. A strip theory-based approach is followed where the Froude-Krylov and hydrostatic forces are calculated for the exact wetted surface area for every time step. The equations of motions are formulated in the body frame and consider the six degrees of coupled motions. The active fin, rudder, and propeller modules are included in the simulation. This leads to accurate modeling of the system dynamics. The numerical unstabilized roll motion is validated with experimental seakeeping simulations conducted on a Coastal Research Vessel (CRV). The phenomena of Parametric Rolling (PR) is identified during the numerical investigation of the candidate vessel. Besides, a nonlinear PID (NPID) control technique and LQR method is implemented for active roll motion control and its performance is observed in regular as well as irregular waves. The proposed numerical approach proves to be an effective and realistic method in evaluating the 6-DoF coupled ship motion responses