Hull Plate Research Articles

Vibration of High-speed Ship Frames

Impact testing of a typical high-speed ship section has shown that the mode of vibration most likely to fall in the frequency range of excitation resulting from propeller or rotor blade passing is that where the ship frame rocks in a fore and aft direction about its base connection to the hull plate. This vibration has significant amplitude to either side of the keel and it is found that connection between the inboard and outboard sides is weak. As a consequence, vibration can occur in two modes in which the opposite sides of the hull either move together or in antiphase. This leads to the structural strain energy in the two modes being slightly different, the mode with rather less strain energy having slightly lower frequency. Because the frequencies of the two modes are close together, the transient response exhibits beating in which vibration energy is exchanged between the two sides of the hull at the low beat frequency. Vibration of the ship frames in this manner appears to have been the cause of minor weld cracking where the top of stiffeners pass through cutouts in the web of the ship frames within the fuel tank areas of the hull.

Development of process design program for manufacture of desired shapes using line array roll set (LARS) process

The line array roll set (LARS) process is a continuous process in which a flat metal plate is formed into a singly or doubly curved plate through successive passes of forming rolls. In the process, the plate is deformed incrementally as the deformation proceeds simultaneously in longitudinal and transverse directions in a stepwise manner. For the industrial application of this process, the forming information (such as bending radii) must be determined considering the springback phenomenon that is inevitable in the sheet metal forming process. In the present study, the process design program calculating forming information for the manufacture of doubly-curved plates is proposed. The calculation program using the iterative scheme has been implemented with Visual C++ language. To check the validity of the developed program, experiments were carried out. From the experimental results, it has been demonstrated that the cold roll forming system has the general applicability for the manufacture of ship hull plates.

Design of Acoustic Emission Monitoring System for Defects of Hull Plate

An acoustic emission (AE) monitoring system has been developed for micro cracks of hull plate, which has a human-machine interface (HMI) designed by Labview, with functions of signal acquisition, storage and replay, key parameters extraction. With the powerful signal processing capabilities of MATLAB, defects can be rapidly and accurately located.

다중 슬릿 구조화 광원을 이용한 곡판 측정장치 개발

The measurement in the manufacturing process of curved ship hull plates still depends on wooden templates as a standard instrument. The metrology-enabled automation in the shipbuilding process has been challenged instead of line measurement with wooden templates. The developed measurement system consists of a CCD camera, multiple structured laser sources and 3-DOF motion device. The system carries out measurement of curved profiles for large scale plates by an optical triangulation method. The results of experiment conducted in a manufacturing shop demonstrate the accurate and robust performance.

Effect of forming factors on surface temperature and residual deformation of the plate in line heating

Parameters of line heating input are key factors which determine temperature field and deformation field in line heating for ship hull plate manufacturing. Two coupling variables named as qs (average energy input per unit area), qs·t (average energy input per unit area and time) are constructed with line heating input parameters to describe relations between final deformation of plate and acetylene flux, heating velocity, heat source radius, heat source efficiency, and length of heating line in line heating. The relation between the new variables and residual deformation is revealed via numerical simulation. The results show that the new variables can reflect the relation between heating parameters and final residual deformation.

Optimum subdivision of curved hull plates for efficient ship manufacture using minimum strain energy

In this article, a novel hull subdivision method is presented. Hull subdivision is a process to subdivide the hull shape into smaller pieces, each of which can be fabricated individually. It is an important step since the fabrication time and cost depend on how the hull shape is subdivided. This process, however, has been done heuristically using experienced workers’ know-how, which makes it difficult for automation due to the difficulty of quantifying the workers’ expertise in an objective manner. Furthermore, the performance evaluation of the subdivision work has not been conducted. In this work, the subdivision process has been analysed using mechanical and mathematical theories considering strain energy and welding length of a plate, and a systematic procedure to perform subdivision using the differential evolution method, a combinatorial optimisation scheme, is proposed. The proposed method is tested with examples obtained from an existing ship, which demonstrates that the proposed method has the potential for replacing the current manual subdivision process.

A procedure for optimizing laterally loaded stiffened panels (the “Bubnov in Monte Carlo” algorithm)

The main objective of this paper is to develop a closed, programmable algorithm for optimizing laterally loaded stiffened panels. To overcome the main obstacle to using present-day sophisticated optimization software tools for that purpose, i.e., the lack of a general formulation of the relations between the load and the response parameters of such models, which are necessary to define programmable failure calculations, an attempt is made to use Bubnov's quasi-analytical formulae, developed for analysing ship hull plating grillages more than a century ago. They are incorporated in a Monte Carlo optimization algorithm, forming a “Bubnov in Monte Carlo” procedure for optimizing laterally loaded stiffened panels. The performance of the algorithm is tested on a number of examples, alternatively analysed using the finite element method. Although a comparison of the results is not entirely straightforward, due to the assumptions and simplifications made in Bubnov's method, the essential criterion of assessment – a general judgment on the occurrence of failures, is found to be satisfied.

선박의 장비 공기소음이 수중소음에 미치는 영향

In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.

무금형 다점 펀치를 사용한 선체외판의 분할 성형 가공 정보 계산 시스템 개발

As a forming method for curved hull plates more efficient than the flame bending, mechanical bending using multi point press forming and die-less forming is discussed in this paper. the mechanical forming is a flexible manufacturing system for automatically forming of hull parts. It is especially suited to varied curved parts. This paper discusses a multiple point pressing machine composed of a pair of reconfigurable punches in order to achieve the rapid forming of curved hull plates using division forming and presents how forming information is obtained from the given design surface. Although the mechanical forming can be efficient in the metal forming, spring back after pressing is a phenomenon which must be carefully considered when quantifying the process variables. If the spring back is not accurately controlled, the fabricated shell plate cannot meet assembly tolerance. This paper describes the principles to calculate the proper stroke of each punch at the divided areas. the strokes are determined by an iterative process of sequential pressing and spring back compensation from an unfolded flat shape to its given design surface. FEA(finite element analysis) is used to simulate the spring back of the plate and the IDA(iterative displacement adjustment) method adjusts the offset of pressing punches from the deformation results and the design surface. The shape deviations of two surfaces due to spring back are compensated by integrated system using FEA and IDA method. For the practical application, It is aimed to develop an integrated system that can automatically perform the compensation process and calculate strokes of punches of the double sides' reconfigurable multiple-press machine and some experimental results obtained with mechanical bending are presented.

Numerical Simulation and Analysis on Bending Forming of Hull Plate

Bending process is one of the important methods to form thick hull plate, whose accuracy is directly related to the quality of hull plate forming.In this paper, bending process of thick hull plate is simulated by using finite element software ANSYS, and some simulation results on bending deformation of thick hull plate such as the deformation of meshes in deformation zone, the distributions of the Von Mises stress and effective strain are obtained.

The effects of storms and diving activities on the corrosion rate across the SS Yongala (1911) site in the Great Barrier Reef

The initial assessment of the condition of the wreck of the SS Yongala (1911) took place in 2005 and was followed with additional in-situ measurements on three field trips in 2007. Analysis of the corrosion potential, pH and plate perforation data confirmed that the superstructure, deck and hull plates are highly corroded and that the most extensive corrosion is on the port side gunwale. The high corrosion rates found at the forward end hull/forecastle deck level and at the stern near the rudder are consistent with the exposed locations which lie proud of the seabed and are subject to significant water movement across the site. Comparison of the original structure and its present condition with site records from previous visits suggest that the wreck is following the Riley waterline theory with the port side frames eventually collapsing and the bow and or stern section breaking off from the vessel. This collapse could happen at or near hold 3 and or around holds 1 and 2. Currently the bow is corroding at a higher rate than the stern end. Changes in the souring of the site and past practices of tying up to the wreck have been significant factors in accelerating the corrosion of this historically significant iron shipwreck.

APDL Based Vibration Optimization of a Ship Foundation

Based on the structural dynamics optimization theory, a vibration optimization design method of a ship foundation by APDL language is presented in this paper. Structural dynamic optimization design of a ship foundation under the constraint of gross weight of a ship cabin is performed by ANSYS to minimize the vibration of ship hull plating. Optimization shows that the thickness of webs has considerable influence on the vibration isolation performance of ship foundation, while changes of the thickness of base panels and brackets have insignificant influence. Optimal thickness combination of webs, panels and brackets of the foundation is obtained through the optimization. Study also provides reference for practical engineering as well as enriches theories and methodologies of novel vibration isolation for ship foundation design.

Technical Parameter Analysis of High-Frequency Induction Heating Applied to Steel Plate Bending

This paper describes the study of hull plate forming by high-frequency induction heating. A finite element model of static large-scale heating is performed and verified by experiments. It can be proposed to be a powerful alternative tool to the actual induction heating process. Parameters influencing the temperature and deformation are deduced.

Increased accuracy of SHPB test apparatus to better evaluate naval steels

The use of high strength steel alloys for shipbuilding applications has increased in recent years in an effort to decrease costsassociated with the manufacture (i.e. material and welding costs) and operation (i.e. fuel economy) of naval vessels. The use ofthinner hull plate has implications for many design criteria, including high strain rate (impact and shock loading) performance.Increasingly, numerical modeling is being used to simulate high strain rate loading events on naval vessels, such as collisions and weapons attacks, with a goal of assessing operational limits. Accurate and reliable high strain rate material data must be used to ensure the accuracy of the numerical models. Confidence in measured data can only be achieved if the potential sources of errorin the measurement system have been eliminated, minimized or characterized. The mechanical behavior of three naval alloys, MIL S-16216K (HY-80), ASTM A517 grade F and CSA G40-21 350WT cat 5 were quantified under high strain rate (103s-1) compression using a Split Hopkinson Pressure Bar (SHPB) apparatus. A systematic error analysis was conducted on the SHPB apparatus to identify potential sources of error in the test set-up, data acquisition and data processing. The identified sources of error were then eliminated, minimized or compensated for, in order to improve the accuracy of the testing apparatus. SHPB compression data are compared to quasi-static tensile behavior. Metallography was conducted before and after high strain rate testing in order to investigate the deformation mechanisms that occurred in the alloys during the high strain rate loading events.

Model-based structural health monitoring of naval ship hulls

The present paper reports on results from an ongoing research program at Cornell University aimed at employing model-based structural health monitoring techniques within new and existing naval hull structures. The techniques discussed involve the solution of inverse problems, formulated using both optimization-based and Bayesian approaches. The forward modeling capability is handled using a specially developed hull structural analysis tool, CU-BEN, while the solution of the inverse problem is handled using stochastic search methods that are part of a dedicated inverse solution algorithm “toolbox,” CU-PSST. Results from the application of these tools to problems of detecting section loss in hull plating due to corrosion, and isolating damaged framing due to an internal blast, are discussed.

Development of High Strength Hull Plate by Normal Hot Rolling and High Rate Cooling Process

This paper investigates the effects of normal hot rolling and high rate cooling (NHR+HRC) on microstructure and mechanical properties of the rolled EH 36 hull plate. Double-hit tests were carried out to study the effect of process parameters such as the deformation temperature and soaking time on microstructures of the tested steel, and explore optimal processing parameters. Single-hit compression with various parameters was developed and the microstructures of the tested steel are analyzed to determine the cooling rate and the final cooling temperature of the normal hot rolling and high rate cooling. This study will provide experimental and theoretical base on high-temperature rolling control system. Industrial trial was performed to produce regular products. The results show that the NHR+HRC is an effective and promising method to improve the product quality of high-strength hull plate.

Residual stress characterization of a fabrication weld from the VICTORIA-Class submarine pressure hull: revealing the Unseen Special issue on Neutron Scattering in Canada.

Explicit understanding of the residual-stress character of primary submarine pressure hull weldments will improve the fidelity of numerical analysis and experimentation supporting operational envelope and design life. A length of circumferential-seam closure weld was contained within a section of hull plate removed from the HMCS VICTORIA during the extended docking work period (EDWP) refit operations. This has provided a rare opportunity for detailed characterization of the as-received condition of this common weld-type from original vessel assembly. In collaboration with the Canadian Neutron Beam Centre of the National Research Council (NRC), a program was conducted to study this weld using neutron diffraction. Neutron diffraction is able to survey nondestructively through the section thickness, providing a three-dimensional characterization, while leaving the specimen intact for complementary study by other methods. Results indicate tensile stress peaks of up to 80% of the base-material yield stress. Understanding the three-dimensional behaviour of residual stress in this type of weld provides a valuable resource to the numerical modelling community. The results can also support fatigue and fracture experimental work and serve to confirm and improve the interpretation of the existing body of “surface-only” work conducted on similar welds.

Ultimate strength assessment of hull structural plate with pitting corrosion damnification under biaxial compression

It is well known that pitting corrosion occurring on surface of hull structural plate will surely result in a significant degradation of the ultimate strength of the hull structural plate. This report aims at development of an assessing formula for ultimate strength of hull plate with pitting corrosion damage under the biaxial in-plane compression loading. The ultimate strength assessment model that is in terms of the corroded volume loss was deduced in theory, and which was then completed through numerical experiment by employing nonlinear finite element analyses for series of corroded plate models. Meanwhile, pitting corrosion in actual ship hull was analyzed and simulated, which ensured that all the assumptions for the finite element model parameters were in accord with the actual hull plate with pitting corrosion damage. Furthermore, the effects of plate slenderness, the linear factors at the plate edges and the ratio between the transverse and the longitudinal in-plane stresses on the ultimate strength reduction related to the corroded volume loss were discussed. The ultimate strength assessment formula being in terms of corroded volume loss developed in this research is expected to be applicable to assess the ultimate strength of the hull structural plate with pitting corrosion damage.

Geometrical approach for flame forming of single curved ship hull plate

Ship hull plate forming by flame torch plays an important role in shipbuilding process. In shipyards, the line heating method is one of the major processes carried out by workers to form the plates into desired shapes. Since this process depends on the skilled workers’ experiences and knowhow, there is a lot of variation in the products. There also could be some difficulties in communicating with each other. Hence, it is necessary to develop an automation system to increase not only the plate forming productivity, but also product quality. For automated plate forming, it is required to know where and how much to heat on the plate. Thus, the inverse problem should be solved to obtain process parameters such as torch travel speed and the heating positions. In this study, the deformed curve shape by flame heat was geometrically considered so that the appropriate geometrical parameters can be obtained. Then, the relationship between the bending angle and the radius of the curvature of the deformed curve shape were established. In addition, the process parameters were obtained by using the relationship between geometrical parameters and process parameters. Lastly, experiments of the two-dimensional plate forming considering deformed curve shape with the curvature were performed. The results of the formed shape were similar to the target shape.

Stress analysis on Canadian naval platforms using a portable miniature X-ray diffractometer

Strain field distribution in a naval platform under dry-dock conditions is complex and represents the cumulative response from residual stress (“locked in” during fabrication of materials and formation of the structure) and static loading stress (e.g., dry-dock loading). The magnitude and distribution of stress fields are a significant concern for the Canadian Navy, where the superposition of applied stresses on residual stresses may adversely affect the performance, safe operational envelope, and service life of naval platforms. Stress analysis was conducted on Canada’s VICTORIA Class submarines using a portable miniature X-ray diffractometer (mXRD) under dry-dock conditions. This paper introduces the concept of “residential stress” as it applies to submarine platforms and discusses the methodology for performing stress analysis with a portable mXRD. The evolution of residential stress during routine pressure hull repairs to Canada’s VICTORIA Class submarines is discussed. In particular, the recent replacement of the diesel exhaust hull and back-up valves on one of the submarines, as well as a pressure hull plate extraction-insertion-weld procedure on another, is discussed.