Hull Structure Research Articles

Theoretical and experimental studies of effects of non-axisymmetric inner structures on vibration signatures of axisymmetric submarine hulls

A unified hybrid analytical-numerical method is proposed for vibration analysis of stiffened hulls coupled with non-axisymmetric internal structures. The coupled system is firstly decomposed into the submarine hull and internal structures. Then, the stiffened hull is further divided into ring stiffeners, bulkheads and shell segments, including conical and cylindrical shell segments. The shell strips and axisymmetric reinforcements are uniformly described by the Flügge formula and power series method. For non-axisymmetric interior structures, finite element method is utilized to establish the motion equations owing to their irregular shapes. To synthesize the shell and non-axisymmetric internal structures, the receptance functions at coupling nodes are respectively deduced by condensing the global stiff matrices of the hull and interior substructures. A precise coupling method fully considering all 6 DOFs at coupling nodes, rather than just 3 or 4 DOFs in previous literature, is proposed to synthesize the receptance functions. To verify the validity of this approach, a stiffened conical-cylindrical-spherical shell coupled with two foundations is manufactured and the forced vibration characteristics of this coupled model subjected to multiple types of excitations are tested. Results obtained by semi-analytical method are simultaneously compared with the ones measured from this experiment and calculated through finite element method (FEM). Effects of the inner structures and different external excitations on forced vibrations are discussed by experiment. Furthermore, how non-axisymmetric internal structures modify wave propagation and conversion characteristics of axisymmetric hulls is investigated through the present method.

Analysis and Experimental Research on Vibration Characteristics of Pressure Shell Structure

The vibration and sound radiation characteristics of the submarine pressure hull structure are important performance indicators for the acoustic design of the submarine structure. In this paper, the spectral element method is used to analyze the vibration of the shell structure. Combined with the periodic structure theory, the theoretical calculation method of the periodic ribbed shell structure is deduced, and the analytical method that can be used to calculate the vibration of the pressure shell structure is established. The feasibility of applying the spectral element method to the vibration calculation of the pressure shell structure is verified by comparing the analytical calculation and the finite element simulation. The vibration characteristics test experiment of the actual submarine pressured hull structure is carried out. The results show that the theoretical analysis is correct.HighlightsThe vibration and sound radiation characteristics of the submarine pressure hull structure have an important influence on the radiated noise of the submarine.A theoretical analysis method of vibration characteristics of pressure hulled based on spectral element method and periodic structure theory is proposed.The experimental study on vibration characteristics and active control of line spectrum of the pressure hull is carried out.

Development of fishing boat collision models in extreme weather using computer simulation

The incidence of fishing boat accidents in Indonesia is very worrying, with 342 people dying during 2018–2020. Based on this, it is crucial to investigate the construction strength of fishing vessels against the possibility of a collision. In this study, the fishing boat due to the impact load was investigated in extreme weather conditions using Finite Element Method (FEM) analysis. Traditional fishing boat was constructed by measuring the thickness of the hull, deck, keel, frames, and longitudinal structure of the fishing boat. The collision model is carried out with an impactor in the form of a mooring pole during extreme weather with a wave height of 6 meters and wind speeds 30 knots. Variations in velocity and frame spacing as in actual conditions are modeled to obtain differences in deformation, absorption energy values, and plasticity of boat construction due to collisions. The collision speed of 30 and 20 knots are set on the extreme weather conditions, while the collision speed of 7 knots is set on operating speed. Frame spacing of 0.5 and 0.6 meters is built according to the boat's frame spacing in the field. Computer simulation is carried out using application software ANSYS Research License. The fishing boat material used is mahogany wood with tested by using impact test with a toughness value of 39.1 kJ/m2. Based on the simulations results, the impact velocity has an effect deformation wider crash area and hull stress value. The speed of the ship collision was 7 knots, the collision did not damage the hull, but the construction failed at speeds of 20 and 30 knots. The closer of frame spacing, the higher collision performance of structure to withstand impact are indicated by the higher energy absorption. At a ship collision speed of 30 knots, the absorption energy of the construction at 0.5-meter frame spacing is 49.8 kJ, greater than 0.6-meter frame spacing with a value of 29.6 kJ

Low Temperature Effect on the Mechanical Properties of EH36 with Strain Rates

With the expansion of the Arctic route, the safety of ship crossing the area in light of the low temperature and ice has become of focus, especially with regards to the ship’s structure. The mechanical properties of the material making up the ship’s structure may not be suitable for the Arctic environment. A series of quasi-static and dynamic tests were performed to investigate the behaviour of EH36 steel, which is used to build Arctic ships, at temperatures ranging from 20 °C to −60 °C. The yield and ultimate tensile stress increased more than 10% as the temperature decreased from 20 °C to −60 °C, whereas the toughness decreased as the temperature decreased. A formula was derived to illustrate the relationship between the temperature reduction and the yield strength by fitting the experimental data. Four common constitutive rigid-perfectly plastic, elastic-perfectly plastic, bilinear elastic-plastic, and multi-linear elastic plastic models were fitted to simulate the hull structure under static loading and low temperature. Additionally, the strain rate effect of EH36 steel at low temperatures was illustrated by quasi-static and high-speed impact tests. A constitutive model including the low temperature and strain rate was introduced based on a modified Cowper-Symonds model, in which the coefficients of the constitutive model are fitted by the test results. It is improved by an iterative numerical method used to obtain more accurate coefficients using a series of numerical analyses. Detailed finite element simulations of the experiment conditions revealed that the constitutive model accurately predicts the dynamic response at low temperatures.

Insight into the underwater implosion mechanisms of thin-walled metallic cylindrical shells

Underwater hollow structures are prone to implosion due to high hydrostatic pressure and structural imperfections. The implosion deformation patterns and induced shock wave impulses are quite involved, and the underlying mechanisms are still not clear. This paper presents an investigation of the implosion mechanisms of metallic cylindrical tubes. The finite element model is first established and validated by the existing experimental results. Numerical simulations are then performed for the aluminum alloy (6061-T6) cylindrical tubes with different length diameter and wall thickness. The deformation features, as well as the induced implosion shock wave characteristics, are analyzed, and the boundaries for the switch of deformation modes are derived. Furthermore, a comparison between the implosion of the cavity and that of the cylindrical shells is implemented. Results show that with the variation of geometrical dimensions, three deformation modes are developed for the cylindrical shells. The implosion shock wave pressure is non-uniformly distributed in the nearby fluid field, and the higher peak is generated in the area around the valleys of the deformed shells. The finding of this work can help understand the implosion mechanics and facilitate the design of underwater hull structures.

CFD-FEM simulation of water entry of a wedged grillage structure into Stokes waves

The fluid-structure interaction problem and the slamming loads on a wedged grillage structure free-falling into 5th order Stokes plane progressive wave under gravity effect is investigated by a partitioned CFD-FEM two-way coupled numerical method. Verification and validation of the CFD-FEM coupled method using calm water entry results of the wedge are first conducted, which indicates that the numerical method is feasible and reliable. Then, the slamming loads and structural stresses on the wedge, considering hydroelasticity effects, are investigated during the entry on Stokes waves for different wedge-wave relative positions and are also compared with calm water results. Moreover, the influence of horizontal and rotation degree-of-freedom motions on the vertical water wave entry results is also investigated. This study provides some insights into the slamming behaviour of ship hull structure impact with sea waves, which is useful for ship hull grillage structure design and strength assessment.

Evaluation of high cycle fatigue behavior of flux cored arc welded naval grade DMR249 A grade steel joints for ship hull structures

DMR 249A is a micro-alloyed high strength low alloy (HSLA) steel particularly designed for shipbuilding structures due to its excellent strength-to-weight ratio. In this investigation, the rotating-beam fatigue test was performed on the flux-cored arc welded (FCAW) butt joints of DMR 249A steel. And the fatigue test results compared to mechanical properties and microstructural characteristics. The transverse tensile, microhardness, impact, and fatigue properties were evaluated from across the butt weld. The S-N curve was constructed from the experimental data for the stress ratio R = -1. The evaluated fatigue life of the FCAW joint and parent metal was 366 MPa and 394 MPa, respectively. The maximum achieved transverse tensile strength and impact energy absorption of the FCAW joint was 578 MPa &174 J. The weld region contains an acicular ferrite microstructure, which exhibited improved properties of strength, toughness, and fatigue crack resistance. From the results, the fatigue strength of FCAW is 92.8% that of the parent metal and 62.8% equal to the tensile strength of the FCAW joint.

Risk-Based Hybrid Light-Weight Ship Structural Design Accounting for Carbon Footprint

The study aims to develop an integrating risk-based formulation and cost-benefit analysis for identifying an optimal ship hull structural design solution where the steel cargo holds aluminium honeycomb sandwich panels to replace inner side shells. The risk of progressive structural failure includes hazards related to environmental pollution due to accidental fuel and oil spills, possible loss of cargo, crew members and ship during operations, and air pollution during shipyard construction and ship voyages. The structural failure incorporates progressive time-dependent structural degradation coupled with ship hull load-carrying capacity in predicting structural integrity during the service life. The ship hull structural failure and associated risk are estimated over the ship’s service life as a function of the design solution. The carbon footprint and cost to mitigate the impact for the entire steel and hybrid ship hull structural solution implemented as a sustainable life cycle solution are analysed where the steel ship hull structure is built through primary construction. The cost of structural measures accounts for redesigning the ship structure and implementing aluminium honeycomb composite panels instead of steel plates, reducing steel weight, environmental pollution and cost and increasing the transported cargo and corrosion degradation resistance. It has been found that design solutions AHS1 and AHS2, in which aluminium honeycomb panels replace the inner steel shell plates, enhance the corrosion degradation resistance, and reduce the ship hull’s lightweight, reflecting a better beta-reliability index at the time of the first repair with a lower repair cost and more transported cargo. The cost of the ship associated with the design solutions AHS1 and AHS2 is about 11% lower than the steel solutions.

Primjena sendvič panel sustava na 155 m barži (teglenici): konfi guracija konstrukcijskog sustava, smanjenje težine i procjena dinamičkih karakteristika

The SPS application in ship structure is an innovative breakthrough that provides an excellent strength-to-weight ratio. SPS application for new construction is crucial to ensure the proposed design has better static and dynamic behavior than conventional design. The study aims to evaluate the weight savings and dynamic characteristics of different proposed framing systems of 155 m barge due to the application of various SPS types in the deck, ship hull, and bottom structures. A total of three proposed construction systems: longitudinal, transverse, and mixed framing systems, are investigated under different plate configurations, material types, and scantling sizes. In addition, the free vibration analysis is used to evaluate the influence of damage occurrence on the structural characteristics. Several damage parameters, including damage size, location, shape, and depth, are investigated using ABAQUS software. The promising result of weight saving indicates SPS application results in about 9-13%. Moreover, the debonding assessment reveals that eigenvalue decreases with increasing debonding size, where the damaging effect in higher modes is more substantial. The stiffness loss due to debonding causes a high local deformation in the debonded area. Moreover, interfacial debonding reduces eigenvalues significantly, particularly in localized debonding shapes. It can be found that several damage parameters, including damage size, location, depth, and shape, influence the eigenvalue shifts.

On the Resistance of Cruciform Structures during Ship Collision and Grounding

This paper presents an experimental, numerical, and analytical study of a novel specimen subjected to local in-plane load, to investigate its crushing deformation and resistance. The specimen was designed and fabricated to simplify the cruciform structure in double-hulled vessels subjected to external loads during collision and grounding incidents. The study results will provide reliable insights into grounding scenarios as well as side collision scenarios of double-hulled vessels. A quasi-static indentation test and related numerical research showed good agreement regarding deformation mode and force–displacement response. On the basis of the experimental and numerical results, an analytical method is proposed to derive the deformation energy, the instantaneous resistance, and the mean resistance of the deformed structure. The analytical method was verified with recorded test data and a nonlinear finite element analysis. It enables a rapid assessment of the response of the structure under accidental loads, which is a guideline for the design of crashworthy hull structures and the assessment of their crashworthiness.

Bayesian based updating of hull and mooring structure parameters of semi-submersible platforms using monitoring data

The parameters of hull structures and mooring systems of offshore platforms will change during their long service lives at sea. Therefore, if assessments of platforms are based on the original design parameters, they will become less accurate over time. As sensor technology and data analysis methods have advanced, it has become possible to update hull body and mooring parameters based on field monitoring data. However, simultaneously updating the many parameters of the hull and mooring system of semi-submersible platform is complex and computationally demanding, and underwater structure monitoring is difficult, therefore this paper proposes a parameter updating method based on floating platform response monitoring data. First, the method conducts a sensitivity analysis based on the hydrodynamic theory of semi-submersible platforms and the parameters to be updated and an objective function for the semi-submersible platform is determined. Then, updating methods for hull structure parameters and mooring parameters are established using Bayesian theorem and surrogate models. Finally, the parameters of hull and mooring structure of a semi-submersible platform in the South China Sea were updated using monitoring data and the results assessed. The proposed method effectively reduced the statistical error between measured and simulated 6-DOF motion values by more than 20% compared with the model before updating. The updated platform model was used to re-evaluate the hydrodynamic responses of the platform under multi-year return period environmental loads. The evaluation showed that during the multi-year service of the platform, the displacement of the platform had decreased by 10%, which was the main reason for the changes in wave frequency responses of the platform.

Stress–Strain Assessment of Honeycomb Sandwich Panel Subjected to Uniaxial Compressive Load

The ship hull structure is composed of plates and stiffened panels. Estimating the maximum load-carrying capacity, or the ultimate strength, of these structural components is fundamental. One of the main challenges nowadays is the implementation of new materials and technologies to enhance the structural integrity, economy, safety and environmentally friendly design of the ship’s hull structure. A new design solution may be represented by aluminium alloy honeycomb sandwich structures, both as plane panels or stiffened ones, which are characterised by excellent impact-absorption capabilities and a high stiffness-to-weight ratio. Still, their response to some conditions typical of ship structural design needs to be deeply investigated. Axial compressive loading is one of the most critical conditions that could impact the structural integrity of such light-weight solutions. Hence, the uniaxial compressive behaviour of aluminium honeycomb sandwich structures has to be deeply investigated to promote their integration in ship structural design. Within this context, the present work performs an experimental and numerical study of a honeycomb sandwich panel subjected to uniaxial compressive loads. The results will help develop models for predicting the uniaxial compressive load-carrying capacity of hybrid honeycomb sandwiches of aluminium alloy design.

Risk-Based Integrity Management System of Oil Tanker Hull Structure due to Corrosion

The ship hull construction suffers a decrease in strength performance over its life cycle due to corrosion and fatigue. Therefore, the risk of structural failure also rises during the extended service life if maintenance is not performed properly. The budget, on the other hand, limits these activities. As a result, it is critical for ship owners to plan an optimal maintenance program. The idea of this research is to find the best way to keep the hull's structural integrity due to corrosion. A time dependent corrosion model has been developed for failure prediction purposes, based on the historical data of plate thickness reduction. Failure scenarios are carried out on local, global and fatigue strength. This research adopted a semi-quantitative risk assessment along with reliability analysis to give strategic maintenance planning by lowering the risks that would be encountered. Hence, ensuring uninterrupted service of the ship throughout the service life. Finally, this study will be very useful as reference to establish risk informed program to evaluate the risk level of components of hull that guides to adjust inspection intervals without avoiding safety requirements.

The Mortella II Wreck, a Genoese Merchantman Sunk in 1527 in Corsica (Saint-Florent, France): A Preliminary Assessment of the Site, Hull Structures and Artefacts

This article presents the results of a preliminary archaeological operation carried out in 2021 on the Mortella II wreck. It was designed as a continuation and complement to the excavation of the Mortella III wreck that was performed between 2010 and 2019 and to which it is historically linked: both ships were Genoese merchantmen sailing together, which sank in 1527 in the context of the 7th Italian War between France and Spain. The paper takes up the main outcomes of the lines of research on shipbuilding and artefacts (anchors and artillery). It discusses their characteristics, comparing them to other wrecks of similar Mediterranean origin. In this way, this work seeks to contribute to the knowledge of Mediterranean shipbuilding and the material culture of the Renaissance, which is currently little known.

Friction Characteristics Analysis of Rubber Bushing with a Bionic Flexible Contact Surface Based on the Convex Hull Structure.

Inspired by the convex hull structure of the dung beetle head's surface, we extracted the non-smooth surface morphology of its head and designed a rubber bushing with a representative structure according to the bionics principle. According to the fitting results of the test data, Ogden N3-Prony N3 was selected as the hyper-viscoelastic constitutive model of the rubber material. Then, the two-direction (radial, axial) motion characteristics of the flexible friction pair in the rubber bushing were systematically analyzed from the aspects of stress, strain and thermal effect through the combination of numerical simulation and experimental research. Finally, the bionic design with the best drag reduction and wear resistance was determined.

Assessment of Fatigue Life Prediction on Gas Metal Arc Welded DMR249A Steel Joints for Ship Hull Structure

Assessment of Fatigue Life Prediction on Gas Metal Arc Welded DMR249A Steel Joints for Ship Hull Structure

Drawing deviation assessment of ship plate marking lines using progressive target extraction

In the construction of large marine structures such as ships, the precise assembly of parts is imperative for ensuring the overall structure's strength and functionality. Currently, construction workers still use marking lines to assist with ship part assembly tasks, and conventional measuring tools are used to draw marking lines throughout the whole assembly process. Unfortunately, there is not yet a method for accurately assessing marking line errors. Hence, this article proposes a method for evaluating the marking line accuracy of a hull part. A progressive sampling method is applied to extract the edge point set and marking lines. An optimised marking evaluation can be obtained while preserving the details of the as-built model. In the proposed method, geometric features are used to extract edge elements from the as-built model and then register it with its as-designed counterpart instead of using the overall data for registration. In addition, the marking lines are extracted in HSV colour space instead of RGB colour space. Using the most common panels in a ship hull structure, we evaluated the accuracy of the marking lines for each hull plate and demonstrated the effectiveness of the proposed method. The proposed method has the potential to reduce the need for rework and increase the speed of ship fabrication.

Algorithms for the Recognition of the Hull Structures’ Elementary Plate Panels and the Determination of Their Parameters in a Ship CAD System

The article deals with some issues of geometric modeling of ship hull structures in specialized CAD system. Stiffened shells and platings should be idealized as a set of elementary plate panels for the purpose of structural design using local strength and buckling requirements. In the process of geometric modeling and creating the database for calculation, a special searching algorithm for closed loops of every panel should be used. This algorithm is to have good performance and versatility. In this paper, the authors suggest an original algorithm used in CADS-Hull software developed in SMTU. It is based on a regular field of points generation within the large contour of the considered structure. A series of rays is built from every point to find intersections. It is shown that this algorithm is quite good for structures (expansions, decks, bulkheads, etc.) with non-orthogonal boundaries. Some tasks for logical operations with found panels are also discussed. One of them is the clipping of a panel or plate polygon by boundaries of a considered structure (expansion contour, hull lines). The authors developed a generic method of polygons clipping. It is based on a rotation of clipping convex polygons together with the clipped polygons. All faces of the latter that are in the negative half-plane are removed. Some problems of collecting data for every found panel are discussed. An original algorithm of smaller and larger size definition for irregular and triangular panels is also given in this paper.

Design and Manufacturing Process of a New Type of Deep-Sea Spherical Pressure Hull Structure

Spherical shell structures are the most suitable shape for deep-sea pressure hulls because they have ideal mechanical properties for handling symmetrical pressure. However, the shape accuracy requirement for a hull in a spherical shell structure subjected to deep-sea pressure is extremely high. Even minor asymmetry can significantly degrade its mechanical properties. In this study, a new type of spherical deep-sea pressure hull structure and its integral hydro-bulge-forming (IHBF) method are proposed. First, 32 flat metal plate parts are prepared and welded along their straight sides to form a regular polygonally shaped box. Next, water pressure is applied inside the preformed box to create a spherical pressure vessel. We performed a forming experiment using a spherical pressure vessel with a design radius of 250 mm as a verification research object. The radius of the spherical pressure vessel obtained from the forming experiment is 249.32 mm, the error from the design radius is 0.27%, and the roundness of the spherical surface is 2.36 mm. We performed a crushing analysis using uniform external pressure to confirm the crushing and buckling characteristics of the formed spherical pressure vessel. The results show that the work-hardening increased the crushing and buckling load of the spherical pressure vessel, above that of the conventional spherical shell structure. Additionally, it is established that local defects and the size of the weld line significantly and slightly affected the crushing and buckling load of the spherical pressure hull, respectively.

A Verification and Validation Study on a Loosely Two-Way Coupled Hydroelastic Model of Wedge Water Entry

_ The interaction between the structural response and hydrodynamic loading (hydroelasticity) must be considered for design and operation purposes of high-speed planing craft made of composites that are prone to frequent water impact (slamming). A computational approach was proposed to study the hydroelastic slamming of a flexible wedge. The computational approach is a loose two-way coupling between a Wagner-based hydrodynamic solution and a linear finite element plate model. Verification and validation (V&V) was performed on this coupled model. It was found that the model overpredicts rigid-body/spray root kinematics by <15% and hydrodynamic loading/ structural response by <26%. Introduction One of the primary constraints on the operational envelope of high-speed craft is slamming (water impact). Slamming occurs between the hull body and the water surface when a portion/whole of the craft exits the water and then reenters at high-enough velocity (Lloyd 1989; Faltinsen 2005). The frequent water impacts, which work like “water hammers,” along with their induced acceleration pose great jeopardy on hull structures as well as crew and instrument on-board (Yamamoto et al. 1985; Ensign et al. 2000; Hirdaris et al. 2014). With the growing use of lightweight materials, the interaction between the structural deformation and the hydrodynamic loading (hydroelasticity) becomes more prevalent. The current design criteria of high-speed craft are based on empirical procedures with no regard to hydroelasticity due to the lack of understanding of this complex phenomenon (DNV 2013; ABS 2016). Therefore, a better comprehension of hydroelastic slamming is the first step to designing more high-performance craft (Fu et al. 2014; Judge et al. 2020).