Research

21 pages, 15858 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Formation Control of Swarming Vessels Using a Virtual Matrix Approach and ISOT Guidance Algorithm

by Su-Rim Kim, Hyun-Jae Jo, Jung-Hyeon Kim and Jong-Yong Park

Processes 2021, 9(9), 1581; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9091581 - 03 Sep 2021

Cited by 3 | Viewed by 2031

The formation control for the effective operation of multiple vessels is discussed. First, a virtual matrix approach is proposed to improve the formation robustness and transform performance during swarm operations, which is created based on the virtual leader vessel location, and agents composing [...] Read more.

The formation control for the effective operation of multiple vessels is discussed. First, a virtual matrix approach is proposed to improve the formation robustness and transform performance during swarm operations, which is created based on the virtual leader vessel location, and agents composing the formation follow cells in the matrix to maintain formation. This approach is affected by the virtual leader vessel location. The virtual leader vessel location is defined by two cases: matrix center and geometric center; furthermore, robustness and efficiency comparison simulations are performed. The simulation results show that in most formations, the geometric center is better in terms of efficiency and robustness. Second, the isosceles triangle guidance algorithm is proposed to improve the “go-back behavior” of certain agents during excessive maneuvering. Through a waypoint-following simulation, the algorithm is confirmed to be superior to the line-of-sight guidance algorithm. The swarm simulation on the virtual map verifies the performance of the proposed formation control and guidance algorithm. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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15 pages, 3809 KiB

Open AccessArticle

A Numerical Study on Axial Pump Performance for Large Cavitation Tunnel Operation

by Jung-Kyu Choi, Hyoung-Tae Kim, Chang-Sup Lee and Seung-Jae Lee

Processes 2021, 9(9), 1523; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9091523 - 27 Aug 2021

Cited by 4 | Viewed by 2241

Abstract

In this paper, a numerical investigation was carried out on the performances of a designed axial flow pump for a large cavitation tunnel. From this, the flow characteristics, force, and torque performance of the axial flow pump were investigated, and the rotating speeds [...] Read more.

In this paper, a numerical investigation was carried out on the performances of a designed axial flow pump for a large cavitation tunnel. From this, the flow characteristics, force, and torque performance of the axial flow pump were investigated, and the rotating speeds of the impeller satisfying the test section speed performances required in the large cavitation tunnel were estimated. The axial flow pump was modeled such that the impeller, stator, and nacelle were located in a cylindrical tunnel. The calculations were carried out for incompressible steady-state turbulent flow considering the impeller rotating. The performance of the pump was confirmed, finding that the head gain was caused by the pressure jump downstream of the pump. The performance of the stator was confirmed to be good enough to refine the tangential flow due to the impeller rotating. To investigate the operating performance of the large cavitation tunnel, the head loss of the entire tunnel without the pump was obtained from a numerical analysis. The operating points were estimated from the specific speed–head coefficient curves, and it was found that the present numerical results were in good agreement with the experiments. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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17 pages, 3968 KiB

Open AccessArticle

Platform Motions and Mooring System Coupled Solver for a Moored Floating Platform in a Wave

by Sang Chul Lee, Seongjin Song and Sunho Park

Processes 2021, 9(8), 1393; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9081393 - 11 Aug 2021

Cited by 7 | Viewed by 2716

Abstract

In advance of building moored floating offshore platforms, in recent years, there has been a greater demand for two-way coupled simulations between a motion solver based on the viscous flow theory and a mooring line model, including cable dynamics. This paper introduces open-source [...] Read more.

In advance of building moored floating offshore platforms, in recent years, there has been a greater demand for two-way coupled simulations between a motion solver based on the viscous flow theory and a mooring line model, including cable dynamics. This paper introduces open-source libraries such as MoorDyn (the lumped-mass mooring line model) and OpenFOAM (the computational fluid dynamics libraries). It describes the methods by which they can be coupled bi-directionally. In each time step, the platform motions calculated by OpenFOAM are transferred to MoorDyn as the boundary conditions for the mooring system analysis. In contrast, MoorDyn calculates the restoring force and moment due to the mooring system and transfers them to OpenFOAM. The restoring force and moment act on the platform as the external force and moment for the platform motions in the next time step. The static tension and profile of the mooring system, dynamic tension of the mooring system, and free decay motions of the floating buoy in the still water were simulated to check the accuracy of OpenFOAM and MoorDyn. The coupled solver was used to produce simulations of the moored decay motions of the floating buoy in the still water and the moored motions with the Stokes 5th order wave. All simulation results were compared and showed good agreement with the numerical solution and experiment results. In addition, the characteristics of each solver were investigated. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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21 pages, 27203 KiB

Open AccessArticle

CFD Simulation for Estimating Efficiency of PBCF Installed on a 176K Bulk Carrier under Both POW and Self-Propulsion Conditions

by Dong-Hyun Kim, Jong-Chun Park, Gyu-Mok Jeon and Myung-Soo Shin

Processes 2021, 9(7), 1192; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9071192 - 09 Jul 2021

Cited by 5 | Viewed by 2765

Abstract

In this paper, the efficiency of Propeller Boss Cap Fins (PBCF) installed at the bulk carrier was estimated under both Propeller Open Water (POW) and self-propulsion conditions. For this estimation, virtual model-basin tests (resistance, POW, and self-propulsion tests) were conducted through Computational Fluid [...] Read more.

In this paper, the efficiency of Propeller Boss Cap Fins (PBCF) installed at the bulk carrier was estimated under both Propeller Open Water (POW) and self-propulsion conditions. For this estimation, virtual model-basin tests (resistance, POW, and self-propulsion tests) were conducted through Computational Fluid Dynamics (CFDs) simulation. In the resistance test, the total resistance and the wake distribution according to ship speed were investigated. In the POW test, changes of thrust, torque coefficient, and open water efficiency on the propeller according to PBCF installation were investigated. Finally, the International Towing Tank Conference (ITTC) 1978 method was used to predict the effect of PBCF installation on self-propulsive coefficient and brake horsepower. For analyzing incompressible viscous flow field, the Reynolds-Averaged Navier–Stokes (RANS) equation with SST k-ω turbulence model was calculated using Star-CCM+ 11.06.010-R8. All simulation results were validated by comparing the results of model tests conducted at the Korea Research Institute of Ships and Ocean Engineering (KRISO). Consequently, for the self-propulsion test with the PBCF, a 1.5% reduction of brake horsepower was estimated in the simulation and a 0.5% reduction of the brake horsepower was estimated in the experiment. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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21 pages, 7274 KiB

Open AccessArticle

Study on Hull Optimization Process Considering Operational Efficiency in Waves

by Beom-Soo Kim, Min-Jae Oh, Jae-Hoon Lee, Yong-Hwan Kim and Myung-Il Roh

Processes 2021, 9(5), 898; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9050898 - 19 May 2021

Cited by 4 | Viewed by 2832

Abstract

This study investigates the optimization of the hull form of a tanker, considering the operational efficiency in waves, in accordance with the recent Energy Efficiency Design Index regulation. For this purpose, the total resistance and speed loss of the ship under representative sea [...] Read more.

This study investigates the optimization of the hull form of a tanker, considering the operational efficiency in waves, in accordance with the recent Energy Efficiency Design Index regulation. For this purpose, the total resistance and speed loss of the ship under representative sea conditions were minimized simultaneously. The total resistance was divided into three components: calm water resistance, added resistance due to wind, and to waves. The first two components were calculated using regression formulas, and the last component was estimated using the strip theory, far-field method, and the short-wave correction formula. Next, prismatic coefficient, waterline length, waterplane area, and flare angle were selected as design variables from the perspective of operational efficiency. The hull form was described as a combination of cross-sectional curves. A combination of the method shifting these sections in the longitudinal direction and the Free-Form Deformation method was used to deform the hull. As a result of applying the non-dominated sorting genetic algorithm to a tanker, the hull was deformed thinner and longer, and it was determined that the total resistance and speed loss were reduced by 3.58 and 10.2%, respectively. In particular, the added resistance due to waves decreased significantly compared to the calm water resistance, which implies that the present tendency differs from conventional ship design that optimizes only the calm water resistance. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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17 pages, 9904 KiB

Open AccessArticle

Numerical Analysis of Hydrodynamic Loads on Passing and Moored Ships in Shallow Water

by Ji-Yong Park, Bo Woo Nam and Yonghwan Kim

Processes 2021, 9(3), 558; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9030558 - 22 Mar 2021

Cited by 4 | Viewed by 2294

Abstract

In this study, hydrodynamic interactions between passing and moored ships were studied by applying a time-domain numerical simulation method. The boundary value problem for a fluid domain was formulated based on a potential flow theory. A numerical method was developed based on a [...] Read more.

In this study, hydrodynamic interactions between passing and moored ships were studied by applying a time-domain numerical simulation method. The boundary value problem for a fluid domain was formulated based on a potential flow theory. A numerical method was developed based on a finite element method with an efficient re-mesh algorithm. Regarding the free-surface boundary conditions, both double-body and free-surface models were considered for examining the free-surface effect on the hydrodynamic forces due to the passing ship. First, numerical results were validated by comparison with the model test results of Kriebel et al. (2005), where generic Series 60 hulls were considered as the target model for the passing and moored ships. In addition, hydrodynamic pressure fields and force time-series were investigated to understand the passing ship problem. Second, a series of numerical simulations were performed to study the effects of the passing ship speed, separation distance, water depth, and relative vessel size, which were used to compare the peak values of hydrodynamic forces. The applicability and limitations of the double-body and free-surface models are discussed for predicting passing ship loads. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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18 pages, 6842 KiB

Open AccessFeature PaperArticle

Study on Nonlinear Stochastic Process of Deck Slamming on Floating Offshore Platform

by Hyun-Seung Nam and Yonghwan Kim

Processes 2021, 9(2), 231; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9020231 - 26 Jan 2021

Viewed by 1232

Abstract

In this paper, a semi-analytic method is introduced to predict the deck-slamming probability and corresponding loads. This method is based on a nonlinear statistical approach that takes into account the linear and second-order components of the relative wave elevation up to the second [...] Read more.

In this paper, a semi-analytic method is introduced to predict the deck-slamming probability and corresponding loads. This method is based on a nonlinear statistical approach that takes into account the linear and second-order components of the relative wave elevation up to the second order. The linear and second-order wave elevation is assumed to be a two-term Volterra series. The joint probability density function of the relative wave elevation and velocity are formulated using the Hermite-moment method, and the probability distributions of the wave crest and relative wave velocity are calculated. These probability distributions are verified using the data sampled from the linear and second-order relative wave elevation. Based on this formulation, the probabilities of deck slamming and slamming-induced loads are estimated. This method is applied to a tension leg platform (TLP) model, and the effects of the second-order component of the relative wave elevation on the deck slamming are investigated. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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21 pages, 8028 KiB

Open AccessArticle

Numerical Study on Unsteady Pressure Distribution on Bulk Carrier in Head Waves with Forward Speed

by Kyung-Kyu Yang, Beom-Soo Kim, Yonghwan Kim, Masashi Kashiwagi and Hidetsugu Iwashita

Processes 2021, 9(1), 171; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9010171 - 18 Jan 2021

Cited by 3 | Viewed by 1720

Abstract

This study deals with wave-induced unsteady pressure on a ship moving with a constant forward speed in regular head waves. Two different numerical methods are applied to solve wave–ship interaction problems: a Rankine panel method which adopts velocity potential, and a Cartesian-grid method [...] Read more.

This study deals with wave-induced unsteady pressure on a ship moving with a constant forward speed in regular head waves. Two different numerical methods are applied to solve wave–ship interaction problems: a Rankine panel method which adopts velocity potential, and a Cartesian-grid method which solves the momentum and mass conservation equations under the assumption of inviscid and incompressible fluids. Before comparing l1ocal pressure distributions, the computational methods are validated for global quantities, such as ship motion responses and added resistance, by comparison with available experimental data. Then, the computational results and experimental data are compared for hydrodynamic pressure, particularly focusing on the magnitude of the first-harmonic component in different sections and vertical locations. Furthermore, the Cartesian-grid method is used to simulate the various wave-amplitude conditions, and the characteristics of the zeroth-, first-, and second-harmonic components of wave-induced pressure are investigated. The nonlinearity of pressure distribution is observed mostly from the pressure near the still-water-level of the ship bow and the normalized first-harmonic component of wave-induced pressure decreases as the wave steepness increases. Lastly, to understand the local characteristics of wave-induced unsteady pressure, the time-averaged added pressure and added local force are analyzed. It is found that the major contribution of the time-averaged added local force that occurs around the ship stem above the design waterline. Full article

(This article belongs to the Special Issue Theoretical and Numerical Marine Hydrodynamics)

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