Hull Structure Research Articles

Load identification for fatigue life assessment in ship hull structural elements

The harsh and uncertain operational profile that characterizes the service life of a ship vessel demands for developing robust methods able to monitor the degrada-tion of its structural integrity. Load recognition is a central part in condition moni-toring of ship hull structures and when realized both diagnostic and prognostic ca-pabilities will be enabled. In this work a structural health monitoring framework is proposed under the conceptual basis of digital twining. The present approach em-phasizes the inverse identification of loads acting on the ship’s hull by exploiting readings from strain sensors and is cast in a Bayesian setting. The loading profile is then applied to the numerical model of the subject vessel for the estimation of the stress field at critical areas prone to fatigue damage, i.e. hot spots. The pro-posed framework is evaluated by synthetic strain data derived from a finite ele-ment (FE) model of a containership. The results demonstrate the feasibility of the proposed approach for addressing the load identification problem and acts as a starting point for the development of a structural digital twin that will allow for monitoring fatigue accumulation in ship hull structures.

Comprehensive hull structures diagnostics using a distributed fiber-optic sensors system

The possibility of constructing real-time systems that provide vibration diagnostics and acoustic diagnostics of complex man-made objects hull structures based on distributed fiber-optic sensors is substantiated. The problem of detecting and localizing sources of acoustic emission using a fiber-optic measuring system placed on a surface housing structure is considered. When solving the detection problem, the flow of acoustic emission signals is characterized by a statistically average pulse repetition rate, their amplitude and time distribution. All parameters of emission signals are random variables with a priori unknown characteristics. To solve the detection problem, the sequential Wald analysis algorithm is used according to the “M out of N” detection criterion. A fiber-optic measuring system has been developed and manufactured, combining the capabilities of vibration diagnostics and acoustic diagnostics of the hull structure. To increase the noise immunity of a fiber-optic measuring system, it is proposed to interrogate it with a broadband signal, for example, a signal with linear frequency modulation.

Lake Environmental Data Harvester (LED) for Alpine Lake Monitoring with Autonomous Surface Vehicles (ASVs)

This article introduces the Lake Environmental Data Harvester (LED) System, a robotic platform designed for the development of an innovative solution for monitoring remote alpine lakes. LED is intended as the first step in creating portable robotic tools that are lightweight, cost-effective, and highly reliable for monitoring remote water bodies. The LED system is based on the Shallow-Water Autonomous Multipurpose Platform (SWAMP), a groundbreaking Autonomous Surface Vehicle (ASV) originally designed for monitoring wetlands. The objective of LED is to achieve the comprehensive monitoring of remote lakes by outfitting the SWAMP with a suite of sensors, integrating an IoT infrastructure, and adhering to FAIR principles for structured data management. SWAMP’s modular design and open architecture facilitate the easy integration of payloads, while its compact size and construction with a reduced weight ensure portability. Equipped with four azimuth thrusters and a flexible hull structure, SWAMP offers a high degree of maneuverability and position-keeping ability for precise surveys in the shallow waters that are typical of remote lakes. In this project, SWAMP was equipped with a suite of sensors, including a single-beam dual-frequency echosounder, water-quality sensors, a winch for sensor deployment, and AirQino, a low-cost air quality analysis system, along with an RTK-GNSS (Global Navigation Satellite System) receiver for precise positioning. Utilizing commercial off-the-shelf (COTS) components, a Multipurpose Data-Acquisition System forms the basis for an Internet of Things (IoT) infrastructure, enabling data acquisition, storage, and long-range communication. This data-centric system design ensures that acquired variables from both sensors and the robotic platform are structured and managed according to the FAIR principles.

Methodic of design of technological complexes. Design of tools for high-speed machining

Within the framework of the developed methodic for designing of non-stationary technological complexes, a further decomposition of the tool development block is carried out with the workup of its structural design for the slipway processing of grooves for welding in the hull structures of underwater shipbuilding products. Keywords:non-stationary technological complexes, groove for welding, mathematical model, design methodology, components of cutting forces, tool diagram s.rusanovskiy@narfu.ru, m.khudyakov@narfu.ru

Причины повреждений корпусных конструкций в носовой оконечности судов

The operation of marine vessels, especially large-tonnage ones, is accompanied by the occurrence of serious damage to hull structures within bow in stormy conditions. A new mechanism to explain the catastrophic destruction of the side grillages of large-tonnage ships in the area of the bow is proposed. Simulation of the process of flow around the fore end when it is digged in a wave using SPH technology showed that when the flow speeds around the fore end occur when the vessel moves in developed waves, there is a sharp drop in pressure in certain areas of the bow end. This circumstance can lead to the occurrence of cavitation that is confirmed by modeling the process of flow around the fore end using ANSYS FLUENT software. During stall cavitation, a cavitation cavern of considerable size may arise, the collapse of which is accompanied by the occurrence of hydrodynamic loads that can destroy hull structures. A calculation method is proposed that allows one to estimate the magnitude of hydrodynamic loads acting on the ship’s hull during the collapse of a cavitation cavern. To prevent damage to the bow in storm conditions, a number of constructive measures have been proposed. One of the options for solving the problem is to install a deck fairing in the bow that eliminates the negative influence of structural cavitators in the traditional design when the bow is digged in the wave. It is also possible to install a compressed air supply system to those areas of the bow where vacuum occurs when a liquid flows around when digged in a wave.

A Study on Crack Initiation and Propagation of Welded Joints under Explosive Load

Welded joints in naval ship hull structures are weak areas under explosive load, but there are relatively few studies investigating the failure characteristics of welded joints through dynamic fracture and explosion tests. In order to explore and predict the failure characteristics of welded joints under explosive load, instrumented Charpy impact tests, explosion tests, and numerical simulations were carried out. The dynamic fracture toughness of ultra-high strength ship hull structural steel welded joints was obtained, and the dynamic stress intensity factors, together with the correlation between stress wave and crack propagation at different positions, were acquired. The results showed that the stress state at the crack tip of a Charpy impact specimen was consistent with that of a welded joint under explosive loads, and the crack initiated when the dynamic stress intensity factor exceeded the dynamic fracture toughness. The results indicated that the dynamic fracture toughness obtained by instrumented Charpy impact tests could be used to predict the crack initiation characteristics of welded structures under explosive load, and the stress wave at the crack tip was basically perpendicular to the crack propagation surface and promoted the rapid propagation of cracks.

The influence of lateral pressure on ultimate strength of ship structure

ABSTRACT The lateral pressure influences the ultimate strength of double-bottom structure. In the midship section of bulk carrier, upward bottom local loads typically exceed downward loads, resulting in increased longitudinal thrust in the outer bottom plating and a reduction in the ultimate strength of the hull girder during hogging conditions. In the present research, the typical stiffened plate and double bottom structures of the Kamsarmax type bulk carrier are taken as the research objects. The nonlinear finite element method is considered to analyze the collapse behaviour of the stiffened plate and double-bottom structure under the longitudinal thrust/bending and lateral pressure, respectively. The influence of lateral pressure on buckling modes, stress distribution, collapse mode and ultimate strength is systematically demonstrated and analyzed. This research contributes significantly to the safety design of hull structures.

Notch corrosion fatigue behaviour and simplified strain energy density-based notch fatigue life assessment of Grade-A shipbuilding steel

Corrosion fatigue is a key challenge in lifecycle management of ship hull structures. Although sea wave fatigue stresses are linear-elastic, highly-damaging elastic–plastic conditions occur at geometrical discontinuities or notches. Estimation of notch stress-strains to characterize notch fatigue behaviour conventionally requires large computational efforts. Also, constant strain energy density (SED), as a driving force, is far more effective in realistic applications versus constant stress and strain fatigue life approaches. Identified research gaps were the development of a simplified SED approach for fatigue life assessment of hole-notched structures. Fatigue studies were conducted on hole-notched specimens of Grade-A shipbuilding steel in air and corrosion mediums. Strong synergistic interactions of corrosion and fatigue damage mechanisms were studied by scanning electron microscope (SEM) fractography. Notch corrosion fatigue life was reduced by 70% from notch air fatigue life due to environmental effect. Two new parameters are proposed to improve the efficiency of notch fatigue life assessment, namely “fatigue notch strain energy density concentration factor (K_SED) and “fatigue notch toughness”. This improved fatigue life assessment method was demonstrated as equally reliable but much simpler to implement, eliminating the complex computational analysis. This improved method has promising applications in real-time structural health monitoring (SHM) of ship hull structures.

Experimental study and mathematical modelling of face milling forces of high-strength high-viscosity shipbuilding steel

Mechanical processing of hole edges in large-size hull structures of single and double curvature for welding saturation parts into them is an urgent task of shipbuilding. A considerable amount of such machining has to be performed directly on the slipway on a fully assembled structure. To perform such works non-stationary technological machining complexes are used, which have reduced rigidity in comparison with stationary equipment. The article summarizes the results of mathematical modeling of cutting forces during face milling of a workpiece made of high-strength high-viscosity shipbuilding steel. The application of high-speed face milling in order to reduce the value and non-uniformity of cutting forces is theoretically substantiated. Recommendations for selection of technological cutting modes and tool geometry are determined. The obtained experimental data confirm the possibility and expediency of high-speed face milling of hull structures made of hard-to-machine materials under conditions of a low-rigid technological system.

A rational approach for the scantling design of GRP pleasure crafts

In various fields of industrial engineering, including naval architecture, structural design is considered one of the most challenging steps by designers as it shall accommodate all other design aspects, likely already defined in earlier steps. Moreover, structures need to comply with specific requirements, i.e. limit states, while also performing in accordance with user's demands in terms of mission profile. In a goal-based design perspective, limit state criteria have to be defined accounting for both, structural robustness, functional and operational demands. Construction feasibility is an issue as well, further constraining the scantling design. Balancing construction needs, ship performances and structural aspects is not always an easy task.The environment in which a ship operates is indeed complex and verification of safety and robustness is usually carried out in accordance with classification societies and other rules, possibly applying direct calculations whenever applicable rules do not provide suitable solutions. At the same time, the asset needs to fulfill various attributes specified by the owner. As a matter of facts, the scantling design is mathematically a multivariate and over-constrained problem whose feasible solutions are in fact rather few. In the case of composite pleasure craft hull structures, while the number of design variables increases, feasibility constraints also largely reduce the design space.To address these challenges, designers may nowadays exploit new procedures able to reduce structural weight, though ensuring that the asset performs safely and adequately meeting client's requirements. To achieve this, designers may combine a more rational design philosophy with currently available numerical problem-solving applications to obtain a rational trade-off among all actually feasible solutions, which are relatively few.Thus, the objective of this study is to present a dependable numerical method for determining the scantling while reducing the weight of hull composite structures of pleasure crafts. This method aims to provide the most suitable, high-performing, and safe layout in the quickest and easiest possible manner. It turns out that counterintuitive, yet feasible and fit-for-purpose, structural lay-outs can be obtained.

ROV-Based Autonomous Maneuvering for Ship Hull Inspection with Coverage Monitoring

Hull inspection is an important task to ensure sustainability of ships. To overcome the challenges of hull structure inspection in an underwater environment in an efficient way, an autonomous system for hull inspection has to be developed. In this paper, a new approach to underwater ship hull inspection is proposed. It aims at developing the basis for an end-to-end autonomous solution. The real-time aspect is an important part of this work, as it allows the operators and inspectors to receive feedback about the inspection as it happens. A reference mission plan is generated and adapted online based on the inspection findings. This is done through the processing of a multibeam forward looking sonar to estimate the pose of the hull relative to the drone. An inspection map is incrementally built in a novel way, incorporating uncertainty estimates to better represent the inspection state, quality, and observation confidence. The proposed methods are experimentally tested in real-time on real ships and demonstrate the applicability to quickly understand what has been done during the inspection.

Design of an add-on ceramic composite armour against 14.5 × 114 mm API/B32 projectile for the armoured vehicles and investigation of the ballistic performance of the armour

Abstract A ceramic/composite add-on armour system with innovative ceramic geometry (cylindrical) against 14.5 × 114 mm API/B32 projectile was developed and ballistic performance of the armour was investigated both experimentally and numerically. Numerical analysis was used to calculate exit velocities of the projectile after passing through the ceramic/composite layer (before penetrating the Armox 500T which simulates hull structure of an armoured vehicle) and also contributed to the selection of optimum ceramic thickness. The calculated projectile velocity-time curves (from numerical analysis) for three different ceramic thicknesses are given comparatively in the study. The curve characteristics are the same for three different analyses. The duration of the total absorption of the projectile energy is about 0.2 microseconds (ms). There were differences in the transmission of the stress wave and the delamination in the Ultra-High-Molecular-Weight Polyethylene (UHMWPE) layers differed as ceramic thickness increases. The separation between the layers varied with the change in projectile energy. As a result of the ballistic test, the armour prevented 14.5 × 114 mm API/B32 ammunition with desired damage mechanisms. In the x-ray image taken after the shootings, it was seen that the ceramic damage was local which enhanced multi-hit resistance capability and the geometry of the cylindrical alumina played an important role in the localization of the ceramic zone damage during the projectile penetration process. Due to this cylindrical ceramic geometry, the projectile moving on after the moment of impact constantly encounters a curved and new surface, and thus it is deflected and exposed to more wear. The areal density of the armour was also reduced by using the UHMWPE (which is one of the composite material whose fibres have the lowest density and good mechanical properties) composite plate as the backing plate.

Mechanical, metallurgical, and corrosion investigations on wire arc additively manufactured low carbon steel

Current global 3D metal printing research is focused on powder bed fusion and direct energy deposition. Several materials are presently under research to assess their post-additive manufacturing properties, and to process them in industries using advanced manufacturing techniques. This study investigates the electrochemical, mechanical, and metallurgical properties of wire arc additively manufactured (WAAM) ER70S-6 alloy walls on AISI S235 plates, emphasizing ship component fabrication. The corrosion resistance of both materials is assessed through Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization testing in a 3.5% NaCl solution. Surface and cross-sectional morphologies are analyzed using optical microscopy and scanning electron microscopy, while energy dispersive spectroscopy is employed to study the chemical composition of the corrosion products. Moreover, the hardness of the WAAM-deposited ER70S6 wall is found to be highest in the uppermost layers of deposition due to the presence of acicular ferrite and ferritic-bainite microstructure. Tensile and Charpy impact strength for AISI S235 and WAAM-deposited ER70S-6 exhibit similar performance at room and low temperatures. Interestingly, the WAAM sample demonstrates a 60% higher elongation than the AISI S235 sample. Hence, the findings from this experimental work suggest that WAAM-deposited carbon steel exhibits favourable corrosion resistance and comparable mechanical properties to AISI S235. Consequently, WAAM is emerging as a promising alternative to conventional manufacturing techniques for fabricating ship components, repairing and modifying hull structures, manufacturing nozzles, propeller blades, fin-like structures, structural components, and more.

Application of Machine Learning (ML)-based multi-classifications to identify corrosion fatigue cracking phenomena in Naval steel weldments

Corrosion fatigue (CF) crack detection in welded ship hull structures is quite crucial as well as challenging for ensuring their structural integrity. This is conventionally done by offline ship hull survey and inspection methods, which have large time and cost implications. Data-driven approaches of ship hull crack detection are promising in this regard. Corrosion fatigue crack growth rate (CFCGR) behaviour of shipbuilding steel was studied for its base metal (BM), fatigue-prone heat affected zones (HAZs) of Submerged Arc Welding (SAW), and shielded metal arc welding (SMAW) joints of Naval-grade steel. The results indicated the highest CFCGR for BM, intermediate for SAW, and smallest for SMAW welds. This was attributed to 44% lath martensite observed in the SMAW HAZ microstructure as compared to 33% in SAW HAZ. A novel ML-based method has been proposed for CF crack location identification by a multi-classification approach using CFCGR data for structural health monitoring (SHM) applications. Prediction of crack location (either BM, SMAW HAZ, or SAW HAZ) was investigated using K-nearest neighbour (KNN), linear support vector machine classifier (LSVC), Naïve Bayes (NB), decision tree (DT), random forest (RF), and artificial neural network (ANN) models. DT and RF models were found to perform very well even without scaling and hyper-parameter tuning operations and exhibited 98–99% classification accuracy. Scaling and tuning operations resulted in significant improvements in accuracy of KNN models from 43% to 84% (minmax scaling) and 98% (standard scaling). Significant improvement in the accuracy from 37% to 98% ANN model was achieved by standard scaling. The proposed method shall be useful in data-driven real-time crack location identification in ship hull structures.

Underwater implosion behavior of 3D-printed polymer structures

This study experimentally investigates the failure behavior of 3D-printed polymer tubes during underwater implosion. Implosion is a prevalent failure mechanism in the underwater domain, and the adaptation of new technology, such as 3D printing, allows for the rapid manufacturing of pressure vessels with complex geometries. This study analyzes the failure performance of 3D-printed polymer structures to aid the future development of 3D-printed pressure vessels. The 3D-printed tube specimens analyzed were fabricated using digital light synthesis (DLS) technology and included four different case geometries. The geometries consist of three cylindrical shells of varying diameter and thickness and one double hull structure with a cylindrical gyroid core filler. These specimens were submerged in a pressure vessel and subjected to increasing hydrostatic pressure until implosion failure occurred. High-speed photography and Digital Image Correlation (DIC) were employed to capture the collapse event to obtain full-field displacements. Local dynamic pressure histories during failure were recorded using piezoelectric transducers. The findings highlight that the 3D-printed polymers underwent significant deformation and failed at localized points due to material failure. The fracture of the specimens during failure introduced inconsistencies in pressure and impulse data due to the chaotic nature of the failure. Notably, the energy flow analysis revealed that the proportion of energy released via the pressure pulse was lower than in traditional aluminum structures. These findings contribute to our understanding of the behavior of 3D-printed polymers under hydrostatic pressure conditions.

A Two-Stage Optimisation of Ship Hull Structure Combining Fractional Factorial Design Technique and NSGA-II Algorithm

The intricate nature of ships and floating structures presents a significant challenge for ship designers when determining suitable structural dimensions for maritime applications. This study addresses a critical research gap by focusing on a three-cargo hold model for a multipurpose cargo ship. The complex composition of these structures, including stiffening plates, deck plates, bottom plates, frames, and bulkheads, necessitates thorough structural analysis to facilitate effective and cost-efficient design evaluation. To address this challenge, the research utilises FEMAP-integrated NX NASTRAN software (2021.2) to assess hull girder stress. Furthermore, a novel approach is introduced, integrating the Design of Experiments (DOE) principles within Minitab 21.4.1 software to identify critical parameters affecting hull girder stress and production costs. This method determined the top five key parameters influencing hull girder stress: Hatch coaming plate, Hatch coaming top plate, Main deck plate, Shear strake plate, and Bottom plate, while also highlighting key parameters that impact production costs: the inner bottom plate, Inner side shell plate, Bottom plate, Web frame spacing, and Side shell plate. Ship design optimisation is then carried out by incorporating regression equations from Minitab software into the Non-dominated Sorting Genetic Algorithm II (NSGA-II), which is managed using Python software (PyCharm Community Editon 2020.3.1). This optimisation process yields a significant 10% reduction in both ship weight and production costs compared to the previous design, achieved through prudent adjustments in plate thickness, web frame positioning, and stiffener arrangement. The optimally designed midship section undergoes rigorous validation to ensure conformity with industry standards and classification society regulations. Necessary adjustments to inner bottom plates and double bottom side girders are made to meet these stringent requirements. This research offers a comprehensive framework for the structural optimisation of ship hulls, potentially enhancing safety, sustainability, and competitiveness within the maritime engineering industry.

Reliability of river fleet vessels hull elements

Improving the process of fault detection of metal ship hull elements by using a probabilistic approach is considered in the paper. The most labor-intensive part of the defect detection report, namely, measurement and assessment of hull structures individual elements wear, accounting for more than 90 % of the total measurements, is reviewed. Defect detection of a ship hull means the examination, measurement and assessment of defects in each element of the ship hull in order to establish method and volumes of repairs that ensure its reliable operation until the next survey under specified operating conditions. The necessity of carrying out a preliminary calculation stage for defect detection is substantiated. It allows you to significantly reduce the number of measurements of hull structures elements, which will have a positive effect on reducing the cost of repair both due to a smaller number of measurements and the duration of repairs. It has been proved that using the probability approach to predict the residual thickness of individual elements also takes into account the effect on the total strength, which guarantees the reliability of the ship hull in operation. Tables to assess the technical condition of individual hull elements based on their level of wear have been developed, and a method for filling them has improved. The tables are made in two versions, namely, paper and electronic, the most convenient for a specific user — the designer of the defect detection report tables. A test example of using the electronic tables for assessing technical condition by wear level, which proves that the predicted residual thicknesses obtained by calculation will in all cases, be less, than similar ones obtained from measurements results, is carried out using a representative vessel. This proves the reliability and feasibility of using the preliminary defect detection stage, which is essentially an analogue of the concept of the zero stage in ship repair. Using the probability approach to determine the residual thicknesses will allow you not only to reduce the costs of defect detection of the hull itself, but also at early stages (before placing the ship on a slip or dock) to reduce the volume of hull structures repairs, and to choose the most appropriate and effective method of repair.

Acoustic emission diagnostics of a hull structures by a system of integrating fiber-optic sensors for the aircraft and spacecraft safe operation

A variant of aircraft and spacecraft state of hull structures acoustic emission diagnostics method based on a system of distributed fiber-optic sensors is considered. Such systems can be sources of information for a technical means of ensuring safety at aerospace facilities. The Green's function for a single sensor is found, and the features of its operation under the influence of pulsed acoustic emission signals are considered. The capabilities of the sensor system under consideration in estimating the coordinates and parameters of acoustic emission signals are determined. The results of experimental studies demonstrating the possibility of detecting emission signals under conditions of specific interference are reported.

Construction High Precision Neural Network Proxy Model for Ship Hull Structure Design Based on Hybrid Datasets of Hydrodynamic Loads

In this work, we constructed a neural network proxy model (NNPM) to estimate the hydrodynamic resistance in the ship hull structure design process, which is based on the hydrodynamic load data obtained from both the potential flow method (PFM) and the viscous flow method (VFM). Here the PFM dataset is applied for the tuning, pre-training, and the VFM dataset is applied for the fine-training. By adopting the PFM and VFM datasets simultaneously, we aim to construct an NNPM to achieve the high-accuracy prediction on hydrodynamic load on ship hull structures exerted from the viscous flow, while ensuring a moderate data-acquiring workload. The high accuracy prediction on hydrodynamic loads and the relatively low dataset establishment cost of the NNPM developed demonstrated the effectiveness and feasibility of hybrid dataset based NNPM achieving a high precision prediction of hydrodynamic loads on ship hull structures. The successful construction of the high precision hydrodynamic prediction NNPM advances the artificial intelligence-assisted design (AIAD) technology for various marine structures.

Electric Propulsion Applied for Research Vessel

In the present work a research boat or specifically for geography was developed where the electric propulsion was chosen, for the reason that advantages of electric propulsion in this type of vessel. The dimension the power necessary to propulsion the ship is necessary to account the wholly weight of the ship and her navigation velocity. In this work the weight of the every part of the ship were considerate, as: electric equipment, mechanic equipment, hull structure, and crane, etc. Then the preliminary design of the hydrographic boat was developed where a group of the three engineers was constituted for realize this work.