Journal of Marine Science and Technology

 This article describes the results of hydraulic model tests of the elastic response of a very large floating structure (VLFS) moored inside a reef in an isolated island. The distributions of strains and vertical displacements due to the elastic response of the VLFS were measured. The response characteristics were strongly affected by deformed nonlinear waves inside the reef. A two-step analytical method to compute the elastic response of a VLFS is proposed, and its validity is verified using the results of the hydraulic model tests.

This paper proposes a mathematical model for intermodal chains with seaborne transport, in which the optimization of a multi-objective model enables conflicting objectives to be handled simultaneously. Through the assessment of ‘door-to-door’ transport in terms of costs, time, and environmental impact, the most suitable maritime route and the optimized fleet are jointly proposed to maximize the opportunities for success of intermodal chains versus trucking. The NSGA-II algorithm is applied to resolve the model. The Pareto fronts obtained not only permit decision-making in the short-term but also enable long-term strategies to be defined according to the behaviour of these frontiers when sensitivity analysis is undertaken. A real-life case in Chile is studied to test the usefulness of the model. Aside from identifying the most suitable Motorway of the Sea with its optimized fleet for Chile, the application case has provided several significant findings to promote the intermodal option regardless of its location.

In order to prevent the spread of marine compartment fires, it is necessary to understand the governing factors or characteristics of fire-spread phenomena. We present a pseudofield model approach to this problem. We first described a field model of turbulent heat convection based on a standard k − Ε turbulence model. Two-dimensional numerical simulations of a two-linked compartment fire were carried out in order to predict the turbulent convection flow induced by the heat released from the fire. Then a more complicated fire-spread problem of multilinked compartment fires was analyzed by means of a zone model, in which the amounts of oxygen consumption and gas generation were solved by a gas-balance equations system. The effect of threshold conditions on fire propagation and the effect of the thickness of the heat insulation were investigated with numerical simulations.

This article discusses the dynamic responses of a coastal cargo ship that consists of unit modules with advance forward speed in waves. We introduce a simple way of connecting the modules that has enough capability to link the modular parts of the ship as a unified whole. The flexible connection consists of male and female rubber fenders with additional pretensioned ropes. This kind of connection system is proposed for use in coastal regions with relatively calm waters wherein the modular ship can move at a moderate speed. The modules are assumed to be rigid compared to the connections. Computations were performed to investigate the vertical elastic responses of four modules connected end-to-end with the assumption that in the simple hinge, no gaps occur in the flexible rubber connections between adjacent modules. A simple method, which is an extension of the computational analysis we reported previously, is presented to study the hydroelasticity and rope tension forces of the modular ship with forward speed in waves. Experiments with a three-dimensional model at Froude numbers of 0 and 0.16 in head waves were performed to evaluate the effectiveness of the calculation method. In the experiments, deflections for each part were measured using calibrated potentiometers. Force transducers were used to measure the rope tension force between the modules of the articulated cargo ship. Some slight differences were observed, but generally the calculated results showed the same trends as the experimental values.

In moving-ship type CO2 ocean sequestration, liquid CO2 is discharged into a domain in a water column. Since the maximum CO2 concentration that is reached depends on the horizontal shape of the water column and the depths of release, it is very important to optimize these parameters for each injection site in order to minimize the biological impact. We conducted numerical experiments using an offline Oceanic General Circulation Model with a horizontal resolution of 0.1 degree × 0.1 degree. Experiments using a different horizontal site shape show that a site elongated in the meridional direction is effective to reduce the CO2 concentration. This is because CO2 has a tendency to be transported in a zonal direction. Optimization of the vertical distribution of CO2 injections is inherently determined by the balance of the following two factors; (1) dilution effect by eddy activity which decreases with depth, and the (2) predicted no effect concentration (PNEC), a criterion concentration causing no effect on biota, which increases with depth. Based on superposition of simulated CO2 concentration, we determined the optimized vertical distribution of CO2 injection which keeps the ratio of a simulated maximum CO2 concentration to PNEC constant.

Ocean sequestration of the CO2 captured from fossil-fuel burning is a possible option to mitigate the increase in CO2 concentration in the atmosphere. It can isolate huge amounts of CO2 from the atmosphere for a long time at relatively low cost, if it is acceptable from the viewpoint of the environmental impact on the ocean. The concept of CO2 dispersion in the ocean depths by ships is a promising method for efficient dilution. That is, liquefied CO2 is delivered to the site and injected into the ocean at depths of 1000–2500 m with a suspended pipe towed by a slowly moving ship. In addition to the horizontal movement of the release point, the vertical journey of CO2 droplets until they disappear by dissolution is effective for the dilution of CO2 in seawater. In this paper, the possibility of the generation of relatively large-sized droplets from a moving nozzle is investigated experimentally. In addition, the terminal velocity of CO2 droplets in deep-sea circumstances is measured in a large high-pressure tank to investigate the influence of the hydrate film formed on the surface of the droplet. Finally, it is shown by simulation that an initial dilution ratio of one to some ten thousandths is possible on a realistic engineering scale in the moving ship type of CO2 ocean sequestration.

Drillships are used for exploratory drilling operations in a water depth above 3000 m. Design variants in the new-generation drillships include flexible internal storage and payload capacity. While their operations are quite satisfactory in moderate weather conditions, response under metocean hurricane conditions to preserve operation versatility poses challenges. The design and operation of drillships, which are intricate and domain-specialized vessels, need attention. This study examines the motion characteristics of a drillship for different sea states and environmental conditions. Their stability across critical sea states is also assessed. Based on the numerical studies, it is seen that they experience a modest degree of instability due to excessive roll and pitch under extreme environmental loads. While preliminary checks under mild heave motion showed that the coupled heave–pitch motion dominates the design shear and longitudinal bending, they are critically influenced by the pitch motion. The forces of second-order steady drift in the far field and the near field are compared in the frequency domain. This study identifies parameters that influence its strength and stability, and the results are useful for improving the operational safety and reliability of drillships under challenging offshore conditions.

In this paper a radial-basis-function neural network is used to localize acoustic emission events in ship hulls. It is shown that using a tiny network configuration and a small set of robust features, selected automatically by the K-means algorithm from a superset of 90 signal parameters, the location of a single event can be classified efficiently into three typical areas found in ship hulls. In simulation experiments, where a stiffened plate model is partially sunk into the water, the localization rate of acoustic emission events in a noise-free environment is 100% using four sensors and only four features per sensor. In the proposed method, the feature set is adapted and estimated automatically in cases of noisy environments. Robust acoustic emission localization rates, greater than 90%, are achieved using less than ten features per sensor in case of additive white Gaussian noise at 0 dB SNR or more.

We concentrate our attention on developing a meshfree flat-shell formulation for evaluating linear buckling loads and mode shapes (modes) of structural plates employing an eigen value analysis. A Galerkin-based shear deformable flat-shell formulation for that purpose is proposed. The in-plane and out-of-plane deformations are interpolated using the reproducing kernel particle method (RKPM), while the two membrane deformations, and the three deflection and rotational components are, respectively, approximated through a plane stress condition and Mindlin–Reissner plate theory. The meshfree discretization by which, as a consequence, constructs five degrees of freedom per node. A generalized eigenvalue problem for the solution of buckling loads and modes of the structural plates is then described. The stiffness matrices of the linear buckling analysis are numerically integrated based on the stabilized conforming nodal integration (SCNI) and sub-domain stabilized conforming integration (SSCI). The RKPM and SCNI/SSCI based on Galerkin meshfree formulation, i.e., stabilized meshfree Galerkin method, can overcome the shear locking problem by imposing the Kirchhoff mode reproducing condition. In addition, a singular kernel (SK) function is included in the meshfree interpolation functions to accurately impose the essential boundary conditions. The merits of the developed formulation are demonstrated through numerical buckling experiments of several examples of plates, by which the accuracy and performance of the proposed method are investigated and discussed in detail. It indicates from our numerical results of buckling loads and modes that the proposed meshfree formulation is accurate and useful in the simulation of buckling problems of structural stiffened plates.