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Hydroelastic slamming is a phenomenon that occurs when there is a fully coupled interaction between the water surface and a deformable structure, and it has a significant effect on the local and global loads of the structure during high impact velocities in rough seas. Estimating the simultaneous structural responses caused by hydrodynamic loads during high impact water entry is a challenging task. This article, which is Part I of a two-part companion paper, deals with the experimental studies of the impact-induced loads and structural responses of a three-dimensional non-prismatic aluminium wedge with stiffened panel during free-fall water entry. Two different plates were considered on the bottom of the wedge in order to study the influence of flexural rigidity on hydroelastic slamming. A description of the experimental conditions, including the geometry of the wedge, material properties, and the test plan is provided. The effects of water impact velocity, deadrise angle, mass of the wedge, and bending stiffness on the slamming pressures and structural responses are discussed in detail. It is shown that the maximum strain and deformation occur during the partially wetted phase of the slamming problem. The study concludes that the hydroelasticity effects on slamming responses generally increase at lower deadrise angles and higher impact velocities. The importance of FSI simulation is assessed using a hydroelasticity factor (R F), which is found to have a significant effect on the unstiffened bottom for all impact velocities studied. For a stiffened bottom panel, hydroelasticity is only significant at high impact velocities.

An experimental study was carried out to examine the impact-induced loads and structural responses of a three-dimensional non-prismatic aluminium wedge. The findings of the experimental study were presented in the first part of this publication, entitled “Slamming loads and responses on a non-prismatic stiffened aluminium wedge: Part I. Experimental study.” This paper describes the second part of the study, which deals with numerical simulations of slamming loads acting on the wedge and its dynamic responses. Two different two-way coupling methods are assessed and compared to simulate the water entry problem. Initially, an explicit nonlinear finite element method with a Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) solver is employed to evaluate the elastic response of the structure following a free-fall water impact. Subsequently, the hydroelastic slamming problem is modelled using a two-way coupled technique with a k-ε turbulence model and implicit unsteady solver for both the fluid and structural domains (Star-CCM+/ABAQUS). The effect of viscosity on slamming loads and responses was examined, and numerical results are compared with experimental data. To investigate the effect of rigidity on structural response and bottom deflection, the wedge was designed with bottom plates of varying thickness. The computed results from the two numerical models and the experimental data are in good agreement. The study concluded that the bottom plates deformation affects hydrodynamic loads during slamming. It is also observed that impact-induced loads depend on the water impact velocity and the flexibility of the bottom plates. This suggests that the slamming pressure increases with an increase in impact velocity and decreases when the structures become more flexible. According to this study, both numerical models are suitable for accurate and efficient computations of hydroelastic slamming; however, the MMALE method results in larger numerical fluctuations.

Society is concerned about maritime accidents since pollution, such as oil spills from ship accidents, adversely affects the marine environment. Operational and strategic pollution preparedness and response risk management are essential activities to mitigate such adverse impacts. Quantitative risk models and decision support systems (DSS) have been proposed to support these risk management activities. However, there currently is a lack of computationally fast and accurate models to estimate oil spill consequences. While resource-intensive simulation models are available to make accurate predictions, these are slow and cannot easily be integrated into quantitative risk models or DSS. Hence, there is a need to develop solutions to accelerate the computational process. A fast and accurate metamodel is developed in this work to predict damage and oil outflow in tanker collision accidents. To achieve this, multiobjective optimization is applied to three metamodeling approaches: Deep Neural Network, Polynomial Regression, and Gradient Boosting Regression Tree. The data used in these learning algorithms are generated using state-of-the-art engineering models for accidental damage and oil outflow dynamics. The multiobjective optimization approach leads to a computationally efficient and accurate model chosen from a set of optimized models. The results demonstrate the metamodel’s robust capacity to provide accurate and computationally efficient estimates of damage extents and volume of oil outflow. This model can be used in maritime risk analysis contexts, particularly in strategic pollution preparedness and response management. The models can also be linked to operational response DSS when fast, and reasonably accurate estimates of spill sizes are critical.

This paper examines the hydroelastic problems of a two-dimensional symmetric flexible wedge water entry through free-fall motion. Water entry is numerically investigated by coupled Finite Volume Me...

The interaction of sea ice with offshore structures is an important engineering concern in ice-infested areas. This paper presents a procedure to evaluate ice loads acting at the sloping offshore wind turbines in the Estonian territorial waters at the Baltic Sea, where the waters are seasonally covered by ice. Region-specific characterization of ice thickness and ice days is done with the help of assessing ice maps from a period of 15 years. For each year, the number of days with ice coverage and thickness are determined. The extreme value probability distribution for annual maximum ice thickness is determined by fitting an asymptotic extreme value distribution to the maximum annual ice thickness. For ice-structure interaction, a numerical ice model suitable for the Baltic Sea ice is implemented. The ice is treated as an isotropic, brittle material described by stress-strain curves for compression and tension. Numerical assessment is conducted to evaluate the ice load history, load maxima, and variations for a selected wind turbine foundation design.

The paper presents a method for the assessment of residual strength of a ship hull damaged in a grounding accident. The strength assessment is based on a coupled beam (CB) method that allows time-e...

The objective of this paper is to present the application of equivalent single layer (ESL) approach for the ultimate strength assessment of ship hull girder in the context of numerical finite element (FE) simulations. In the ESL approach, the stiffened panel is replaced with a single plate, which has the equivalent stiffness of the original panel. Removal of tertiary stiffening elements from the numerical model facilitates time-savings in pre-processing and FE analysis stage. The applicability of ESL approach is demonstrated with two case studies, one compartment model and full-sized double hull tanker model in intact and damaged conditions. The damage extents are determined based on the international association of classification societies from common structural rules (IACS-CSR) for oil tanker. Ship hull girder is exposed to distributed pressure with the sinusoidal shape that bends the hull girder. This pressure load is applied separately to bottom and side structures to obtain the vertical and horizontal bending moments of the hull girder, respectively. Ultimate strength predictions obtained from ESL approach are compared to full three-dimensional finite element method (3D FEM) and IACS incremental-iterative method. The comparison between different methods is provided in terms of longitudinal bending moment and cross sectional stress distribution. Overall, ESL approach yields good agreement compared to the 3D FEM results in predicting the ultimate strength of ship hull girder while providing up to 3 times computational efficiency and ease of modeling.

This paper introduces first results of a joint research project between Taltech University and Industrial partners. The goal was to develop a universal autonomous surface vessel (ASV) that has readiness for the following applications: pollution detection, water environment monitoring and small cargo transportation. The paper describes the design and structure of the mechanical, electrical and control system. The open water tests and first mission are described.

This paper presents a benchmark study on the ultimate limit state analysis of a stiffened plate structure subjected to uniaxial compressive loads, initiated and coordinated by the ISSC 2022 technical committee III.1-Ultimate Strength. The overall objective of the benchmark is to establish predictions of the buckling collapse and ultimate strength of stiffened plate structures subjected to compressive loads. Participants were asked to perform ultimate strength predictions for a full-scale reference experiment on a stiffened steel plate structure utilizing any combination of class rules, guidelines, numerical approaches and simulation procedures as they saw fit. The benchmark study was carried out blind and divided into three phases. In the first phase, only descriptions of the experimental setup, the geometry of the reference structure, and the nominal material specifications were distributed. In the second phase, the actual properties of the reference structure were included. In the third and final phase, all available information on the reference structure and measured properties were distributed, including the material properties and laser-scanned geometry. This paper presents the results obtained from seventeen submitted FE simulations as well as details on the experiment. It also presents comparisons of the force versus the displacement curve, failure modes and locations for each phase, among others, and a discussion on the participants’ ability to predict the characteristics of the reference experiment with the information that is available for the phase. The outcome of the study is a discussion and recommendations regarding the design of finite element models for the ultimate state analysis of stiffened plate structures, with emphasis on the prediction of the ultimate capacity, force-displacement curve, and failure mode and location related to access to data, uncertainties and modeling of the material properties, geometric imperfections and distortions, and residual stresses.

This paper presents a benchmark study on grounding simulations. The objective was to compare key parameters in modelling techniques and assump-tions for finite element (FE) analysis. Five contributors participated in the bench-mark study by performing numerical simulations, and results were compared with available results from experimental tests. Good agreement between experi-mental tests and numerical simulations was achieved which illustrates that non-linear finite element analysis can be used to estimate the damage extent in grounding scenarios. In addition, a sensitivity study was performed in order to investigate the effect of varying different parameters such as friction coefficient and failure strain values. For the numerical results following the guideline DNV GL-RP-C208 [5], a calibration case for mean failure strain was used in order to simulate real experimental tests (with measured yield and ultimate strength), and good agreement was achieved

V-shaped spray interceptors are a novel concept of spray deflection on planing craft. Conventional spray rails are positioned longitudinally on the bottom of the hull and detach the spray from hull deflecting it towards the sides or slightly down and aftward. The V-shaped spray interceptors, on the other hand, are located in the spray area forward of the stagnation line such that they would deflect the oncoming spray down and aftward, thereby producing a reaction force that reduces the total resistance. An experimental study reported that the V-shaped spray interceptors to reduce the total resistance at low planing speed by up to 4%. This paper features a numerical comparison of two planing craft, one equipped with a conventional setup of longitudinal spray rails and the other with a V-shaped spray interceptor. Both configurations were simulated in calm water conditions and were free to pitch and heave in a speed range of Fr∇ = 1.776 to 3.108. The numerical model was analyzed for grid sensitivity and numerical results were compared with experimental results. The two concepts were compared in terms of total resistance, lift, running position and wetted surface area. Conventional spray rails were shown to account for up to 5.6% of total lift and up to 6.5% of total resistance. The V-shaped spray interceptor was shown to reduce the total resistance by up to 8%. Since the V-shaped spray interceptor was located in the spray area forward of the stagnation line, it deflected the oncoming spray thereby producing a horizontal reaction force (-1.5% of RTM) in the direction of the craft’s motion. The rest of differences in the total resistance of the hulls equipped with the conventional spray rails and the V-shaped spray rails was due to absence of the resistance of the absent spray rails.

The present study is concerned with the numerical simulation of Fluid-Structure Interaction (FSI) on a deformable three-dimensional hydrofoil in a turbulent flow. The aim of this work is to develop a strongly coupled two-way fluid-structure interaction methodology with a sufficiently high spatial accuracy to examine the effect of turbulent and cavitating flow on the hydroelastic response of a flexible hydrofoil. A 3-D cantilevered hydrofoil with two degrees-of-freedom is considered to simulate the plunging and pitching motion at the foil tip due to bending and twisting deformation. The defined problem is numerically investigated by coupled Finite Volume Method (FVM) and Finite Element Method (FEM) under a two-way coupling method. In order to find a better understanding of the dynamic FSI response and stability of flexible lifting bodies, the fluid flow is modeled in the different turbulence models and cavitation conditions. The flow-induced deformation and elastic response of both rigid and flexible hydrofoils at various angles of attack are studied. The effect of three-dimension body, pressure coefficient at different locations of the hydrofoil, leading-edge and trailing-edge deformation are presented and the results show that because of elastic deformation, the angle of attack increases and it lead to higher lift and drag coefficients. In addition, the deformations are generally limited by stall condition and because of unsteady vortex shedding, the post-stall condition should be considered in FSI simulation of deformable hydrofoil. To evaluate the accuracy of the numerical model, the present results are compared and validated against published experimental data and showed good agreement.

This paper examines the hydrodynamic problem of a two-dimensional symmetric and asymmetric wedge water entry through freefall motion. The gravity effect on the flow is considered and because of precise simulation close to the real phenomenon, the oblique slamming is analyzed. The defined problem is numerically studied using SIMPLE and HRIC schemes and by implementing an overset mesh approach. In order to evaluate the accuracy of the numerical model, the present results are compared and validated with previous experimental studies and showed good agreement. The results are presented and compared for each symmetry and asymmetry in different deadrise angles, drop heights and heel angles. Based on a comparison of the measured vertical acceleration of the experimental wedge data, it is determined that the proposed numerical method has relatively good accuracy in predicting the slamming phenomenon and wedge response. The influence of viscous regime on water entry simulations is investigated, in according to results, effect of viscosity is negligible. Results show that the heel angle dramatically affects the wedge dynamics, pile-up evolution, and pressure distribution. These results suggest evidence for a complex interaction between geometric parameters on the water entry of rigid wedges, which could finally develop our understanding of planing vessels operating in real sea conditions.

The risk of oil spills is an ongoing societal concern. Whereas several decision support systems exist for predicting the fate and drift of spilled oil, there is a lack of accurate models for assessing the amount of oil spilled and its temporal evolution. In order to close this gap, this paper presents an online platform for the fast assessment of tanker grounding accidents in terms of structural damage and time-dependent amount of spilled cargo oil. The simulation platform consists of the definition of accidental scenarios; the assessment of the grounding damage and the prediction of the time-dependent oil spill size. The performance of this integrated online simulation environment is exemplified through illustrative case studies representing two plausible accidental grounding scenarios in the Gulf of Finland: one resulting in oil spill of about 50 t, while in the other the inner hull remained intact and no spill occurred.

Steel stiffened panels are widely used in engineering design and construction. However, numerical modeling and analysis effort for a three-dimensional (3D) stiffened panel may be notable, especially for the ultimate limit state of ship structures. Therefore, a homogenization method is outlined that transforms 3D stiffened panel into an Equivalent Single Layer (ESL) concerning the same mechanical behavior. ESL stiffnesses are obtained with a unit cell analyses based on stiffened panel where periodicity is imposed with boundary conditions based on a first-order shear deformation theory (FSDT). Stiffnesses were determined from the first derivative of a membrane force and bending moment obtained with numerical simulations. The effect of initial imperfection shape was included in the analysis to account for local and global buckling behavior. ESL with non-linear stiffness was implemented in Abaqus UGENS subroutine, allowing incremental evaluation of stiffness. Ultimate strength prediction of a steel grillage model with ESL finite element analysis was in excellent agreement with detailed 3D FEM analysis. The key in this analysis was consideration of non-linear ESL stiffness as linear analysis was unable to detect the point where ultimate strength capacity of the grillage was reached.

Hydraulic models for one- and two-layer flows are combined in different oil spill scenarios for tanker accidents. Four oil spill model versions are used to determine oil-leak quantities in six test cases. Five test cases are verified by comparison to the laboratory results of Tavakoli et al. (2011). One test case is presented as a demonstration of the modelling approach developed here. In the hydraulic modelling, it was found that a descending oil surface in the leaking tank yields a unidirectional flow, while an ascending oil-water interface shows a bidirectional flow. Oil spill volumes and durations confirm that oil outflow depends strongly on flow separation and mixing at the submerged orifices. As a corollary of this work, discharge coefficients are determined from the experimental verification of the hydraulic models. An optimisation algorithm was employed to determine the head losses of a stratified flow through the double-hull tank hole.

Groundings are among the most common and destructive maritime accidents. Sea bottom shape influences greatly what kind of damage the ship structure suffers and whether this leads to loss of water tightness. Sormunen et al. [21] presented and statistically compared rock models used in grounding damage analysis with detailed bottom shape data from two Finnish harbour fairways. The results were promising in terms of statistical fit especially for the binormal rock model, which also showed a wide range of flexibility in representing different types of sea bottom shapes. However, this measure does not explicitly tell if the model rock in grounding damage analysis results in similar damage size as real rocks cause. To test this, this paper develops a framework for studying, testing and evaluating rock models in terms of resulting grounding damage. FEM is used to analyse and compare grounding damage of rock models to the actual rock using otherwise identical grounding scenarios. Analysis is performed for four different real rocks with each rock being modelled with four different analytical rock models as well. The results show that rock models with good statistical fit did not necessarily result in similar grounding energy compared to results using the real rock. Differences in energy are caused especially by the rougher surface of the real rocks. For the similarity in rock area and the damaged ship structure element volume the results are much better, especially for the binormal model. As such another criteria for evaluating rock models for grounding damage analysis is needed. The results show that the damaged material volume is strongly linearly dependent on the rock area- and volume metrics. A similar linear dependency exists between the damaged volume and the energy dissipated in grounding. Knowledge of these relationships can be used towards estimating grounding damage of ships in future investigations, but rock surface unevenness should be evaluated as well.

This paper presents a benchmark study on collision simulations that was initiated by the MARSTRUCT Virtual Institute. The objective was to compare assumptions, finite element models, modelling techniques and experiences between established researchers within the field. Fifteen research groups world-wide participated in the study. An experiment involving a rigid indenter penetrating a ship-like side structure was used as the case study. A description of how the experiment was performed, the geometry model of it, and material properties were distributed to the participants prior to their simulations. The paper presents the results obtained from the fifteen FE simulations and the experiment. It presents a comparison of, among other factors, the reaction force versus the indenter displacement, internal energy absorbed by the structure versus the indenter displacement, and analyses of the participants' ability to predict failure modes and events that were observed in the experiment. The outcome of the study is a discussion and recommendations regarding mesh size, failure criteria and damage models, interpretation of material data and how they are used in a constitutive material model, and finally, uncertainties in general.

This paper presents a set of analytical expressions for the calculation of damage opening sizes in tanker groundings. The simplified formulas were given for the grounding force, longitudinal structural damage and the opening width in the inner and outer plating of a tanker's double bottom. The simplified formulas derived are based on a set of numerical simulations conducted with tankers of different dimensions- 120, 190 and 260 m in length. The simulations were performed for five penetration depths and for several rock/ground topologies. The formula for the horizontal grounding force was derived provided the grounding force is proportional to the contact area and the contact pressure. By use of regression analysis it was shown that the contact pressure for any combination of ship and rock size can be expressed with a single normalized polynomial. The actual contact pressure was found by scaling the normalized pressure with the structural resistance coefficient. Given the formulation for the normalized contact pressure, the actual contact force for a ship can be found as a product of average contact pressure and the contact area. The longitudinal length of the damage was evaluated based on the average contact force and the kinetic energy of the ship. The damage opening widths in the outer and inner bottom of the ship were derived separately for two ranges of relative rock sizes as they have strong influence on the deformation mode. The damage widths were given as a function of rock size, penetration depth and double bottom height. To improve the prediction of the onset of the inner bottom failure, a critical relative penetration depth as a function of the ratio of the rock size and the ship breadth was established. Comparison to the numerical simulations showed that the derived simplified approach describes the horizontal grounding force and the damage length well for the penetration depths above 0.5 m. For the range of specified relative rock sizes, the damage width in the inner and outer bottom deviates from numerical simulations approximately up to 25%, which was considered sufficient for the analyses where rapid damage assessment is needed. Comparison was also made to real accidental damage data and to the results of several simplified formulas.

The maritime transportation system in the Northern Baltic Sea (NBS) is complex and operates under varying environmental conditions. The most challenging conditions relate to the presence of ice-cover, which for the NBS e.g. for the Gulf of Finland or Bay of Bothnia, can remain up to several months. The number of maritime accidents in these two areas is the highest during winter season, which can involve accidents like groundings, collisions, damages due to the ice etc. The paper presents the model to predict the ice interaction in ship-ship collision dynamics. The ice forces are included in the time-domain simulation model and also in a simplified model based on the momentum conservation. The simplified model is proposed for a rapid estimation of increase in deformation energy due to the presence of ice forces. The analysis shows that the ice influence depends strongly on the ship mass, ice thickness and collision speed. The maximum increase in the deformation energy in the studied collision scenarios was up to 19%.Copyright © 2015 by ASME