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 Showing 1 - 77 of 77 Journals sorted by number of followers Deep Sea Research Part II: Topical Studies in Oceanography       (Followers: 29) Deep Sea Research Part I : Oceanographic Research Papers       (Followers: 23) Estuaries and Coasts       (Followers: 23) Limnology and Oceanography       (Followers: 22) Progress in Oceanography       (Followers: 21) Journal of Marine Biology & Oceanography       (Followers: 19) New Zealand Journal of Marine and Freshwater Research       (Followers: 18) Journal of Physical Oceanography       (Followers: 18) Frontiers in Marine Science       (Followers: 17) Journal of Marine Sciences       (Followers: 17) Coastal Engineering       (Followers: 15) Advances in Oceanography and Limnology       (Followers: 15) Journal of Oceanography       (Followers: 14) Maritime Studies       (Followers: 13) International Journal of Oceanography       (Followers: 12) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 11) Atmospheric and Oceanic Science Letters       (Followers: 10) Bulletin of Marine Science       (Followers: 9) Fisheries Oceanography       (Followers: 8) Journal of Oceanography and Marine Science       (Followers: 7) Open Journal of Marine Science       (Followers: 6) Limnology and Oceanography: Methods       (Followers: 6) Journal of Operational Oceanography       (Followers: 6) Physical Oceanography       (Followers: 6) Paleoceanography and Paleoclimatology       (Followers: 5) Marine Science       (Followers: 5) Limnology and Oceanography: Fluids and Environments       (Followers: 5) Ocean Yearbook Online       (Followers: 4) Journal of Oceanology and Limnology       (Followers: 4) Limnology and Oceanography Letters       (Followers: 4) Journal of Marine Science and Engineering       (Followers: 4) African Journal of Marine Science       (Followers: 4) Oceanology       (Followers: 3) Journal of Aquatic Sciences       (Followers: 3) Limnology and Oceanography e-Lectures       (Followers: 3) Journal of Coastal Development       (Followers: 3) Ciencias Marinas       (Followers: 3) Journal of Marine Science and Application       (Followers: 3) Journal of Ocean Engineering and Marine Energy       (Followers: 3) Tropical Oceanography       (Followers: 2) Indian Journal of Geo-Marine Sciences       (Followers: 2) Mediterranean Marine Science       (Followers: 2) Regional Studies in Marine Science       (Followers: 2) Annals of Marine Science       (Followers: 2) Limnology and Oceanography: Bulletin       (Followers: 2) Annals of Limnology and Oceanography       (Followers: 2) Development and Applications of Oceanic Engineering       (Followers: 2) Journal of Ocean Engineering and Technology       (Followers: 1) Acta Aquatica : Aquatic Sciences Journal       (Followers: 1) Ocean Life       (Followers: 1) Marine Systems & Ocean Technology       (Followers: 1) Marine Life Science & Technology       (Followers: 1) Journal of Ocean University of China (English Edition)       (Followers: 1) Journal of Ocean Engineering and Science       (Followers: 1) Coastal Engineering Proceedings : Proceedings of the International Conference on Coastal Engineering       (Followers: 1) Marine Technology Society Journal       (Followers: 1) Scientia Marina       (Followers: 1) Western Indian Ocean Journal of Marine Science       (Followers: 1) Asian Journal of Fisheries and Aquatic Research Thalassas : An International Journal of Marine Sciences Oceans Aquatic Research Jurnal Kelautan Tropis Depik Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan Journal of Agricultural and Marine Sciences Turkish Journal of Maritime and Marine Sciences Arquivos de Ciências do Mar Scientific Drilling Jurnal Kelautan : Indonesian Journal of Marine Science and Technology Oceanologia Revista de Gestão Costeira Integrada Revista Ciencias Marinas y Costeras Egyptian Journal of Aquatic Research China Ocean Engineering Revista de Biología Marina y Oceanografía Latin American Journal of Aquatic Research Acta Oceanologica Sinica
Similar Journals
 Marine Systems & Ocean TechnologyNumber of Followers: 1      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1679-396X - ISSN (Online) 2199-4749 Published by Springer-Verlag  [2467 journals]
• CFD optimization of a displacement catamaran’s configuration for
minimized calm water resistance

Abstract: Abstract In this paper, a CFD simulation of the flow about a displacement catamaran model (Delft 372 catamaran model) is carried out over a range of forward speeds by solving the Reynold Average Navier–Stokes equation (RANSE). The Shear-Stress Transport (SST) turbulence model is selected, and the volume of fluid (VOF) method is adopted to capture the free surface flow about the catamaran. Results are validated by comparison with experimental data available in the literature. The aim of this study is to investigate the effect of the separation–length ratio and the non-parallel configuration of the demi-hulls on the total resistance and wave pattern generated by the catamaran over a range of forward speeds. Subsequently, the Response Surface Method for optimization is applied at a particular Froude number and over a selected range of separation–length ratios and non-parallel configurations of the demi-hulls to provide minimum total resistance. Obtained results are satisfactory with a reduction in the total resistance at about 5% as compared to that of the original configuration.
PubDate: 2023-01-03

• Oblique wave propagation through composite permeable porous structures

Abstract: Abstract In the present study, the porous breakwater system consisting of a porous block and a permeable barrier is analysed to understand the wave dissipation due to the composite porous structure. The linearised wave theory is adopted to analyse the wave interaction with three different configurations of the composite structures including (a) porous structure and fully extended vertical barrier, (b) porous structure and bottom-standing barrier and (c) porous structure and surface-piercing barrier. The eigenfunction expansion method along with orthogonal mode-coupling relation is adopted to determine the wave reflection and transmission characteristics along with wave force on the porous structure and barrier, and surface deflection in incident and transmitted region. The experimental investigation is performed for the composite breakwater system and the results obtained are compared and validated with the numerical results. The composite breakwater system is studied for various parameters such as relative water depth, porosity of structure and barrier, structural thickness to wavelength ratio, water depth to wavelength ratio and gap between the structure and barrier. Further, the comparative study is performed with the results available in the literatures. The proposed study exhibits an informative result for the wave energy attenuation by the composite breakwater system which can be designed and implemented in coastal and harbour regions for achieving the tranquillity.
PubDate: 2022-12-20

• Experimental study of an oscillating water column wave energy converter
based on regular waves

Abstract: Abstract Increasingly, marine renewable energies are taking over as one of the most relevant solutions to minimize dependence on fossil fuels. The management and exploitation of such energy requires the optimization of converters that will, later on, ensure the conversion of hydraulic energy into electrical energy; among these converters are the oscillating water column. An OWC is characterized by its simplicity and its effectiveness against turbulent ocean conditions. The performance of OWCs depends strongly on the geometrical parameters of the air chamber such as: chamber walls, width, thickness of the front wall, slope at the bottom of the chamber and size of the opening. In this sense, the manuscript presents a parametric approach to investigate, by experimental tests, the hydrodynamic properties and the performance of oscillating water column wave energy converter (OWC). The effects of some geometrical key parameters of the system are analyzed. The tests are carried out on a small‐size OWC. The work seems to be interesting in view of its experimental aspect. We have realized a prototype of an oscillating water column (OWC) which consists of a box (an air chamber) having the shape of parallelepipeds. The experimental results found by this study showed different optimums of: (a) the distance between the wave generator and the device (2 positions). (b) The depth of water in the hydraulic channel. (c) The immersion depth of the front wall of the chamber. (d) The opening at the bottom of the prototype. The results obtained show that the coupling of the geometrical parameters of the device and the conditions of installation leads to an improvement of the hydrodynamic performances of the OWC. The study also shows that the various optimums found give a considerable increase in the energy output.
PubDate: 2022-11-11
DOI: 10.1007/s40868-022-00121-2

• A comprehensive review on exploration and exploitation of offshore
geothermal energy

Abstract: Abstract World’s ocean has abundance of geothermal energy. Exploration and exploitation of the same is in nascent stage. Several exploration sensors like magnetic, optical, chemical, etc., are towed from ships to sea floor for exploration. Several researches are carried out for drilling these explored hot spots. Once the energy is exploited, the same is transferred to power plant located on land. In this paper, three different types of power plants are discussed namely onshore power plant, offshore power plant, and power generation using the thermoelectric method. This paper narrates the current status of offshore geothermal technology which also includes the technology readiness level of this method. The paper also mentions the parameters which are required for designing of offshore geothermal power plants. Along with the technical aspects of offshore geothermal exploration and exploitation, this paper also talks about the environmental impact of these techniques on marine life. Demonstrative case studies from Indonesia and Italy are presented in this paper. The technical and economic study of the case studies are also briefed. The learnings from these countries may be utilized for the exploration and exploitation of offshore geothermal hotspots of India. Through this paper, it will be easy to understand the technical, financial, and environmental aspects of offshore geothermal technology for developing countries in the field of geothermal.
PubDate: 2022-10-24
DOI: 10.1007/s40868-022-00120-3

• Two-dimensional modelling of free-surface flows in presence of a spherical
object using the Modified Volume of Fluid technique

Abstract: Abstract In this paper, a two-dimensional numerical simulation of water entry of a spherical object is achieved using the Modified Volume of Fluid (MVOF) technique. Continuity and Navier–Stokes equations along with an equation for tracking the free-surface motion are considered as the governing equations for 2D incompressible fluid flow. The free-surface deformation is modelled via integration of the fast fictitious domain method into the MVOF technique. The computational domain includes everywhere even the spherical object where the governing equations are solved. A rigid motion of the spherical object is generated by applying the linear and angular conservation laws. To exert the no-slip condition on the solid–liquid interface implicitly, the viscosity of the region arranged within the solid object is increased artificially. The numerical results obtained using the MVOF method are compared with those of the experiments in the literature and the conventional Volume of Fluid method. The results show that the effects of the artificial compression term on the free-surface deformation is very dominant for coarse meshes while this factor becomes minor for fine meshes.
PubDate: 2022-09-29
DOI: 10.1007/s40868-022-00117-y

• Retraction Note: Numerical and experimental evaluation of cavitation
flow around axisymmetric cavitators

PubDate: 2022-09-28
DOI: 10.1007/s40868-022-00119-w

• Fatigue analysis and reliability assessment of tether system of an
offshore oil and gas platform operating in extreme sea-state conditions

Abstract: Abstract The rise in energy demands has increased hydrocarbon exploration and production-related activities in deep-water and ultra-deep-water settings. In this context, Tension Leg Platforms (TLPs) play a significant role in offshore hydrocarbon exploration and production projects. They are compliant platforms that are vertically moored permanently to the seabed with the help of taut mooring lines. They are appropriate for water depths ranging from 1000 to 5000 ft. The environmental loads acting on the structure can induce dynamic variation in the tether tension, resulting in tether failure. The present study focuses on investigating the dynamic response pattern of the platform’s restraining system under extreme sea-state conditions. With the transition in sea-state condition from rough to phenomenal, a significant increase in the variation in stress cycle range and cycle average was observed. The dynamic analysis under phenomenal sea-state conditions highlighted an increase of almost 28.57% in the tether tension. Estimating fatigue damage on the tethers and predicting fatigue life were carried out. The results indicate that as the sea state intensifies, the fatigue life of the tethers tends to decrease substantially.
PubDate: 2022-09-28
DOI: 10.1007/s40868-022-00118-x

• A reduced-order model to predict the natural frequencies of offshore wind
turbines considering soil–structure interaction

Abstract: Abstract Analytical reduced-order models (ROMs) are derived aiming at determining the natural frequencies of offshore wind turbines (OWTs). Case studies based on six wind turbines are developed considering two boundary conditions, namely fixed base (perfectly clamped) and elastic base, representing soil–structure interaction (SSI). For the elastic-base boundary condition, the stiffness of the pile-soil system at the seabed is represented by a set of three springs: $$K_{\rm L}$$ (lateral spring), $$K_{\rm R}$$ (rocking spring) and $$K_{\rm LR}$$ (cross-coupling spring). The novel aspect herein is the presentation of an analytical mathematical model that allows obtaining different natural frequencies and the representation of the vibration modes. This mathematical model tackles the problem without the transformation of the beam of a variable section into a beam of a uniform section with equivalent properties that must be adjusted to each case. The different natural frequencies predicted by the ROMs are compared with those obtained by using higher-order hierarchical models using the Finite Element Method (FEM). In addition, the values of the first natural frequency of all OWTs predicted by ROMs are compared with the measured frequencies. The results show that the derived model accurately predicts the fundamental frequency of existing turbines, with errors below 8.2%. This proposed methodology can be of great interest in the early stages of the design of OWTs, provided the expeditious analysis and good accuracy in estimating natural frequencies. It also presents generality of use, since it does not require any previous definition of equivalent properties.
PubDate: 2022-08-24
DOI: 10.1007/s40868-022-00116-z

• Selection over small-scale LNG transportation model in designing an
efficient and reliable LNG supply chain using analytical network process

Abstract: Abstract Indonesia is one of the big countries, with area of about 1.9 million sq-km, of which 2/3 is covered by water, having of about 17,480 islands separated by seas that have made it as one of the world’s biggest archipelago country. Due to its vast territory and its archipelago characteristic, distribution of goods including natural gas to reach out those remote small islands surrounded by seas, is getting really challenging. The latest development of SS LNG technology has made distribution at various small sizes even possible to reach remote areas of Indonesian archipelago (de la Peña-Zarzuelo et al., Int J Oil Gas Coal Technol, https://doi.org/10.1504/IJOGCT.2019.10026342, 2020). The Indonesian government with its Ministerial of EMR Decree No. 13K/13/MEM/2020 (MEMR, 2020e) has mandated the state-owned oil & gas enterprise, i.e., PERTAMINA to establish LNG supply system to support the conversion of 52 power plants located among the islands of Indonesia. Designing & developing an efficient and reliable LNG supply chain system are the key issues to answer all of those challenges. Thus, selecting the transportation model that provide minimum logistic cost for such system is becoming the most critical decision to make amid of all its complexity. Multi-criteria decision analysis has so far been commonly used to help in a complex decision-making process. This study is going to demonstrate the use of analytical network process as one of the MCDA tools that is able to help not only in the process of selecting the best SS LNG transportation model out of the available alternatives. Yet unlike any other MCDA tools, ANP is also able to perform the sensitivity analysis to validate the decision made. The study has revealed the fact that amid few other considerations safety remains as the top priority, besides the fact that ANP has proven to be able to give a more robust output in term of consistency.
PubDate: 2022-06-14
DOI: 10.1007/s40868-022-00115-0

• Numerical study on the influence of porous baffle interface and mesh
typology on the silencer flow analysis

Abstract: Abstract The study of the internal component geometries (i.e. perforated elements) is relevant for the acoustic performance optimisation of a silencer. During the design phase, the evaluation of the properties of a silencer is performed by numerical analysis. In the literature, there is a lack of general guidelines and comparisons among different modelling strategies. So, in this study, the influence of grid type (i.e. trimmed vs tetrahedral) on the numerical prediction of the flow inside a reactive silencer is analysed. Moreover, using a porous baffle interface to model the perforated pipe is investigated, searching for a faster and easier way to model perforated elements. The simulations are carried out with the commercial CFD software STAR-CCM+. The comparison of the obtained axial velocity with a literature case study assesses the numerical model reliability. The analysis highlights that velocity and pressure predicted with both the mesh typologies does not significantly differ, but the trimmed mesh allows to save cells number, reducing the computational cost. Instead, obtain a reliable flow description using the porous baffle interface is strictly correlated to the settings of the resistance coefficient. This assumption does not provide accurate results for the analysed perforated pipe. On the other hand, using a simplified model allows to easily perform a comparison between different muffler geometries, as the holes have not to be drowned and meshed after each modification.
PubDate: 2022-05-23
DOI: 10.1007/s40868-022-00114-1

• Interaction of surface water waves with a finite dock over two-stepped
bottom profile

Abstract: Abstract Based on linear water wave theory, scattering of surface waves by a finite dock over two step-type bottom topography is examined. A matched eigenfunction expansion method is employed where both propagating as well as non-propagating modes are considered. The expansion method is applied to the evaluation of the physical quantities, namely, the reflection and transmission coefficients of monochromatic waves caused by the finite dock and the abrupt depth change. These coefficients are validated with the results available in literature for a particular case where a good agreement is achieved. The force and moment on the finite dock are obtained numerically. The effect of various parameters on the reflection coefficient, transmission coefficient, force and moment is studied through different graphs. The energy identity relation, an important factor of the study, is derived and verified. This problem is further generalized to M-steps and the comparison is made between the flat bottom, 2-step bottom and M-steps bottom. The present results are compared with the results available in the literature. In the present study, it is highlighted that the reflection is increasing with increasing the wave number, dock length and width of the step-1 whereas the transmission coefficient is decreasing for the same. Hence, the rigid dock and the two step bottom topography help to create the calm zone in the lee side of the floating rigid dock. This information will be helpful for the marine scientists and engineers while making the breakwaters.
PubDate: 2022-04-08
DOI: 10.1007/s40868-022-00112-3

• Preliminary design dimensioning of hydrofoil boats with fully submerged
and surface piercing foils

Abstract: Abstract The development of a computer program of an optimization hydrofoil design method using analytical empirical formulation is presented for dimensioning hydrofoil boats fully submerged and surface piercing foils, from a pre-designed high-speed craft. It is part of a design system coded from a methodology for high-performance craft design. The method and its coding are novel, since there are no known design methods or computer programs for hydrofoil dimensioning. The process fully integrates hull and foils, relieving the work and time spending of testing different foils and attitudes, as in CFD. It is straightforward and fast to vary foil configurations. It selects the optimum foil instead of just providing results for judgment. Results are produced in minutes, verifying several different foils, what would otherwise take days or weeks to do, with the same reliability in hydrofoil preliminary design. From the boat’s particulars, seastate, foils profile, material, and layouts, the aft and forward configurations are drawn to scale. The program determines the foils’ areas, chords, angles of attack, lift and drag forces as objective functions, subject to cavitation and structural strength constraints, solved for ranges of thickness–chord ratios and load factors. As results, several graphs and charts are presented by the program, such as the foils’ optimization, Lift and Drag, Angles of Attack vs Speed, Take-off Speed, Resistance and Power. Besides these features, the program is fully integrated with other ones of the design system. This program can help design any hydrofoil boat. A design example is shown.
PubDate: 2022-03-16
DOI: 10.1007/s40868-022-00113-2

• Improved active disturbance rejecter control for trajectory tracking of
unmanned surface vessel

Abstract: Abstract In this paper, an improved ADRC is proposed for the design of a robust trajectory tracking control of a fully actuated unmanned surface vessel in the presence of complex time-varying disturbances; parameters uncertainties; and sensors noise. The conventional extended state observer (ESO) is effective in estimating the system states and constant or slow-varying disturbances. However, they are limited while dealing with fast-varying disturbances, in addition to the effects of the measurements noise which may affect the convergence of the system in case of high gains of the ESO. In order to cope with these problems, two essential improvements have been introduced to the ESO. Firstly, a generalization of the ESO is proposed to enhance the estimation quality of a general disturbances type composed of two principle components, polynomial and harmonic. Secondly, an extension of the space of the state with another fictional state variable that will be used to decouple the sensors noise from the estimated state variables. In order to illustrate and clarify those effects, computer simulations are conducted under sinusoidal-like type disturbances and noisy output signal, and the tracking performances of the conventional and improved ADRCs are compared.
PubDate: 2022-02-23
DOI: 10.1007/s40868-021-00110-x

• Structural health monitoring of Foroozan offshore platform using a novel
modal strain energy damage index

Abstract: Abstract Being exposed to huge waves, repetitive wetting and drying as well as vessel collisions, members that are located in the splash zone of offshore platforms are prone to damage and failure. Providing the possibility of identifying and repairing these damages at an early stage, establishing a concise structural health monitoring system for these structures is of a great importance. The modal strain energy-based Stubbs index is one of the most successful vibrational methods for structural damage identification. In recent years, some modifications have been made on this method, one of which is considering natural frequencies for damage localization. By examining the original Stubbs index and an existing modified index, in this paper, a novel damage index is proposed to increase the accuracy of damage localization. Comparing the results of the Stubbs, IMSE (Improved Modal Strain Energy), and the new indices for damage localization in Foroozan platform which is located in Iran and Saudi Arabia water border in the Persian Gulf, this research shows that this novel method has been able to identify the location of hypothetical damage in the structure with higher accuracy. Also, single and multiple damages, with low and high severity, were predicted with appropriate accuracy by this method.
PubDate: 2022-02-09
DOI: 10.1007/s40868-021-00107-6

• Numerical investigation on concomitant VIV and parametric excitation in a
rigid cylinder mounted on an elastic support

Abstract: Abstract This work focuses on a numerical investigation on the response of a rigid cylinder mounted on an elastic support subjected to simultaneous vortex-induced vibration (VIV) and parametric excitation. The rigid cylinder has diameter D, mass ratio $$m^{\ast} = 2.6$$ and is immersed in a uniform flow characterized by its free-stream velocity $$U_\infty$$ . The parametric excitation is emulated by means of a time-dependent stiffness with the form $$k_{y}(t) = \overline{k_{y}} + \varDelta k_{y} \cos (\varOmega _y t)$$ . The fluid loads are modeled by means of a wake-oscillator model and only oscillations in the cross-wise direction are allowed. The main objective is to assess the influence of the parametric excitation on the VIV phenomenon, discussing the obtained results under the light of experimental and numerical data from flexible cylinders. It is shown that, contrary to observed for flexible cylinders, the parametric excitation amplifies the VIV response only in a narrow range of reduced velocities close to the peak of cylinder response. This increase in the cylinder response amplitudes follows the increase in the force coefficients. Other numerically obtained results include amplitude-modulated time histories and the enrichment of the spectral content. This latter results are confirmed by an analytical study developed using the method of multiple scales.
PubDate: 2022-01-12
DOI: 10.1007/s40868-021-00111-w

• Oil spill detection over ocean surface using deep learning: a comparative
study

Abstract: Abstract Marine pollution poses a humongous threat to oceanic life especially large scale oil spills. The paper addresses this concern by offering a comparative study of novel deep learning architectures trained on identical datasets and computational conditions. We explore the concept of dataset amplification through non-learning image manipulations techniques like Horizontal and Vertical flipping along with random rotations. The models are thoroughly attested using parameters like Mean-IoU, F1 scores and percentage accuracy. The paper concludes by showing V-Net supremacy, as it outperforms it’s fellow implementations with an accuracy of 90.65% and a Dice-Coefficient of 90.34.
PubDate: 2021-11-09
DOI: 10.1007/s40868-021-00109-4

• Coupled dynamic analysis of spar-type floating wind turbine under

Abstract: Abstract In the present study, the coupled dynamic modelling of three different configurations of spar platform is performed using time-domain aero-servo-hydro-elastic simulation. The spar platforms are coupled with 5 MW NREL floating wind turbine and mooring sub-models. The coupled aero-servo-hydro-elastic simulation is performed using the simulation tool FAST with WAMIT as the sub module to obtain frequency domain hydrodynamic characteristics. The major emphasis is given to analyse the Response Amplitude Operators (RAOs) to understand the stability of the structures. The responses are calculated for surge, sway, heave, roll, pitch and yaw motions. The study determines the performance of the structure under the wind load developed for the turbine support structure on analysing the tower base forces and moments. The analysis for three different configurations of spar platform is performed for various environmental conditions of North Sea. The studies observed that the responses of the platforms tend to increase with increase in wind speed and wave height. Further, it is observed that surge and pitch motion is dominant for all the three configurations of spar platform. The present study provides an insight into the power performance, structural integrity and dynamic motions of the floating wind turbine under various operational and survival conditions which help the designers to develop better design standards.
PubDate: 2021-09-30
DOI: 10.1007/s40868-021-00106-7

• Numerical investigations of micro bubble drag reduction effect for
container ships

Abstract: Abstract In the course of the most recent decades reduction of ship resistance and saving fuel consumption to accomplish higher speed with reduction of pollutants has been the significant subject for researchers. Micro bubble drag reduction technique is one of the most interesting thoughts in this field owing to its great advantages, such as considerable potential drag reduction, easy operations, environmental friendliness and low costs. In this study a 3-D numerical investigation into frictional drag reduction by air micro bubbles is applied on KRISO container ship model. The objective is to understand the mechanism of resistance reduction through micro bubbles injection under model ship at different Froude numbers, injection rate and of course volume fractions. The numerical simulations are performed using a commercial CFD code solving Reynolds averaged Navier–Stokes (RANS) equations. A large number of simulations has been performed to investigate the effect of injection of micro bubble under ship model hull to estimate the local coefficient of friction values along ship hull model. The results show that at all of the examined Froude’s numbers, frictional resistance reduction attained at different rates and a maximum drag reduction of 27.6% was obtained at 0.282 Froude number with 4.8% air volume fraction.
PubDate: 2021-09-10
DOI: 10.1007/s40868-021-00104-9

• Dynamic positioning of an oceanographic research vessel using fuzzy logic
controller in different sea states

Abstract: Abstract A dynamic positioning (DP) system is a computer-controlled system which maintains the positioning and heading of ship by means of active thrust. A DP system consist of sensors, observer, controller and thrust allocation algorithm. The purpose of this paper is to investigate the performance of proportional derivative type fuzzy controller with Mamdani interface scheme for dynamic positioning of an oceanographic research vessel (ORV) by numerical simulation. Nonlinear passive observer is used to filter the noise from the position and orientation. A nonlinear mathematical model of the ORV is subjected to the wave disturbance ranging from calm to phenomenal sea. Robustness and efficiency of the fuzzy logic controller is analysed in comparison with the multivariable proportional integral derivative (PID) and the linear quadratic regulator (LQR) controller. A simplified constrained linear quadratic algorithm is used for thrust allocation. The frequency response of the closed loop system with different controllers is analysed using the bode plot. The stability of controller is established using the Lyapunov criteria.
PubDate: 2021-09-10
DOI: 10.1007/s40868-021-00105-8

• Operational modal analysis of a catamaran using time and frequency domain
methods and main engine sweep test

Abstract: Abstract The use of structural health monitoring (SHM) systems in large structures is of relevant importance, as it provides data that can alert the occurrence of structural failures even in the premature phase and thus avoiding the structure’s collapse. This work aims to identify the modal parameters of a catamaran that began to present cracks in the hull’s stern region to verify the possible occurrence of resonance conditions between the hull girder and the propulsion system. For this, two techniques of the operational modal analysis were used. The catamaran’s structure was excited by varying the rotational speed of the starboard shaft line, from 225 to 695 RPM. Thus, the structure was excited in the range of 3.75 Hz to 46.3 Hz when including the propellers’ and shaft line’s first harmonics. These forces caused the structure’s natural frequencies within the range of interest, up to 50 Hz, to be excited. Thirteen (13) natural frequencies were identified, with good agreement between both methods and an average RMS difference of 6.6%. Finally, it was verified resonance conditions in the catamaran’s operating range, excited mainly by the first harmonic of the 4-bladed propellers. By changing the 4-bladed to 5-bladed propellers, resonance conditions were avoided, and the cracks stopped appearing in the catamaran’s stern region.
PubDate: 2021-09-10
DOI: 10.1007/s40868-021-00103-w

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