In order to allow for the numerical modeling of impacts for the design of live fire facilities commonly used by military and law enforcement personnel against next generation and environmentally friendly ammunition currently in development, constitutive models for novel target materials must be developed. Many existing facilities are constructed from AR500 steel, coupled with a layer of cellular rubber to reduce impact velocities and contain projectile fragments. High strain rate models, such as the commonly used Johnson-Cook constitutive model, are widely available to characterize AR500 steel, but calibrated models do not currently exist to characterize the cellular rubber. This project seeks to address this shortfall and provide a suitable material model for designers of these facilities in order to ensure the safety of users and the public. Appropriate constitutive models that account for the large strain, high strain rates, and temperature effects experienced during ballistic events and the porosity of the material were researched and a plan developed for future materials testing. Three suitable models were selected for further analysis — A Non-Linear Elastic Model described by Johnson in his work with polyurethane coupled with a Mie-Gruneisen equation of state to account for the porosity of the material, an Osborn-Hull model developed for use with crushable solids, and the Holmquist-Johnson-Cook Model commonly used for cementitious materials.

Bending curved metal plate is an important process for many heavy industries such as shipbuilding. It is a basic process to manufacture hull surface. The conventional method is the so-called line heating method, which is not only labor intensive but also inefficient and error-prone. We have presented a new method of incremental bending. In this paper the incremental bending system is explained from its hardware and software. A kind of curved metal plate is formed by experiment and finite element simulation. The manufactured workpiece is of high quality with smooth surface. The presented method can be successfully used to form curved metal plate. It is a highly flexible forming method. It would have a wide application in industry.

In this work, a bow thruster is proposed to be used onboard small and medium-size watercraft, like motor yachts, fishing boats, patrol boats, ocean exploration vessels etc. with conventional or unconventional hull designs including displacement hull, planing hull, catamarans, SWATHs, SES, and so on. As oftentimes the case, a magnetic coupling is employed. Specifically, magnetic coupling is used to transfer torque from a brushless motor’s stator to its rotor through a magnetic field rather than a physical mechanical connection. Such magnetic coupling is very convenient for liquid pumps and as, in our case, propeller systems, since a static, physical barrier can be placed between the stationary and rotating part of the system to separate the fluid from the electrically supplied stator operating in air. Therefore, magnetic couplings preclude the use of shaft seals, which eventually wear out and fail from the sliding of two surfaces against each other. In this work, a system identification process of a rim driven bow thruster is implemented employing data series obtained by tests on a prototype scale model. System Identification leads to a black-box model of the system. The model derived can be extrapolated by grey-box modeling techniques for further design improvements. A control system for the proposed thruster is developed and validated through both computer and hardware-in-the-loop simulation, after its implementation onboard a broadly used industrial Programmable Logic Controller (PLC). The mathematical model of the bow thruster mechanism is developed and the performance is analysed by using Matlab/Simulink.

Rapid deployment of marine structures is of growing importance to U.S. naval forces. Surface-based inflatable structures including Rigid Inflatable Boats (RIBs), inflatable causeways and bridging, and launch and recovery systems provide unique solutions for temporary structures during sea-based missions. When performance specifications demand minimal weight and stowage, rapid deployability and temporary rigidity, solutions are limited to inflatable structures constructed of flexible materials. Driven by air pressure, today’s inflatables provide significant load-carrying capacities per unit weight (or stowed volume) utilizing technical textiles, elastomers or “soft” composites. Overloading of inflatable structures produces unique fail-safe behaviors (reversible wrinkling) that allow the structures to assume rigidity and load-carrying capacity upon load removal. Design standards are virtually nonexistent for inflatable structures involving shapes constructed of spheres, beams, arches and most recently flat panels using 3D woven drop-stitch panels. Predictive performance tools (analytical and numerical) for static applications lag significantly behind those for conventional structures. Nonlinear system behaviors (material and geometric), thermo-mechanical coupling and fluid-structure interactions (FSI’s) pose significant challenges when applying existing design tools to inflatable structures. This gap is further exacerbated for dynamic applications as inflatable structures exhibit pressure-dependent natural frequencies and mode shapes. Surface-based structures must be designed with consideration given to operational sea state frequencies and wave periods so that the onset of structural instabilities (wrinkling, buckling) and loss of load-carrying capacities can be prevented. The present research establishes the validity of physics based models using the Ideal Gas Law as an equation of state (EOS) to predict the natural frequencies and corresponding mode shapes of air-inflated drop-stitch fabric panels as functions of inflation pressure. Particular concern is given to the breathing modes for inflation pressures ranging from 5.0 to 30.0 psig. The presence of breathing modes can negatively impact the riding performance of RIBs vessels constructed with drop-stitch fabric hulls by amplification of the panel’s skin separation displacements and vertical accelerations, and are not seen in this material system for the pressures considered. Both numerical and experimental methods are pursued; the results of laboratory modal experiments are used to validate the numerical models. Predicted and experimental natural frequencies and mode shapes are compared and excellent correlation was observed. Increasing inflation pressures produced increasing in-plane and through-thickness normal stresses and modal frequencies of the drop-stitch fabric panels.

The bending of complex curved sheet metals of ship hull has long been a challenge in shipbuilding yard on account of some inherent defects of the traditional forming processes such as the line heating. This paper presents a novel incremental bending process based on punching to obtain complex curved steel plates in order to take the place of those inefficient traditional forming processes of ship hull. The presented incremental bending process is carried out by a series of stepping punches, so it is also defined as incremental punching in this work. By means of this process, the blank plate that is fixed and held by a flexible supporting system can incrementally be bent to the target shape by a press tool with a planned tool trajectory one step after another. Meanwhile, in order to improve geometric accuracy of the formed work-piece, a 3D scanning feedback system is applied to measure the deformation of the work-piece during the forming process. Three dimensional shape of the formed work-piece can be imaged and rebuilt with a large amount of point cloud data by the 3D scanning feedback system. Then the difference between the rebuilt model of the formed work-piece and the target CAD-model can be acquired, which can be used for feedback control of the forming accuracy if necessary. To validate the presented forming process, an original incremental punching prototype was designed and manufactured, which is mainly composed of a 3-axis CNC machine, a flexible supporting system and a 3D scanning feedback system. A forming experiment of a gradual curvature steel plate was carried out using this prototype and is discussed in detail in this paper in order to demonstrate the feasibility of the proposed incremental bending process of complex curved steel plate.

Recently, there has been an interest in aluminum alloys by many industrial areas as an environmentally-friendly material reducing environment pollution. Now, especially for maritime industries aluminum alloys are in the spotlight for ship construction instead of fiber reinforced plastics (FRP) or even stainless steel. Aluminum alloy ships are fast, lightweight, and exhibit a great load capacity when compared to traditional steel hulls. The Navy’s number one problem is maintenance due to corrosion impact. Annual combined costs of corrosion for army ground vehicles and navy ships range around $6.14B/year. Corrosion impacts the readiness of most Navy systems and is a major factor contributor to life cycle cost. Hence the vision for corrosion technologies is to develop and implement corrosion control and prevention technologies to minimize the impact of material deterioration and maintenance costs. Stress corrosion cracking (SCC) and environment-induced cracking (EIC) has been extensively investigated using various methods to improve performance, designs, and service life for these structures. Present interested research areas are advanced smart coatings technologies for corrosion control and prevention of its effects under sea water and marine environments. With the rapid development of modern technology, foil metals have found applications in a variety of areas. The mechanical behavior of these materials may be different from that of bulk materials due to size effects. Therefore, models and conclusions for bulk characterization might not be applicable when analyzing foil materials. The purpose of this experiment is to describe and examine the susceptibility of aluminum alloy foil to stress corrosion cracking under 3.5% w.t NaCl solution. Mechanical properties of aluminum specimens were investigated using slow strain rate tests of 0.001 mm/min under load control while inside an environmental chamber at a flow rate of 150 ml/min. Smooth specimen samples with thickness of 0.0508 mm were subjected to monotonic tensile tests until fracture in ambient air and under corrosive solution environment. Scanning electron microscopy (SEM) was used to analyze stress corrosion cracking and crack propagation observing the different microstructural and intergranular fracture deformations. A digital microscope camera was used to observe and perform an analysis on the corroded specimen surface. A comparison of stress, strain, and time results of fracture between air and 3.5% NaCl solution at room temperature were calculated to demonstrate the susceptibility of the aluminum material to SCC. Test standards regarding stress corrosion cracking in metal foils are still limited.

In this study an academic CFD code, named Galatea-I , is presented, capable for simulating inviscid, viscous laminar and viscous turbulent incompressible fluid flows. It employs the RANS (Reynolds-Averaged Navier-Stokes) approach along with the SST (Shear Stress Transport) turbulence model to predict turbulent flow phenomena, such as recirculations and separations of flow, on three-dimensional unstructured hybrid grids, composed of prismatic, tetrahedral and pyramidal elements. Discretization of the governing equations is obtained with a node-centered finite-volume scheme. Parallel processing and agglomeration multigrid scheme are implemented for the acceleration of the numerical process. As the title of this paper reveals, the solver is validated against the test cases of the DARPA SUBOFF program; in particular, flows over the SUBOFF bare hull submarine geometry at two incident angles and the SUBOFF hull with fairwater configuration are examined. The obtained results, compared to available in open literature experimental data as well as results computed by reference solvers, indicate the proposed methodology’s potential to accurately simulate complex fluid flows.

In this paper, we fit we explore three different model approximation schemes in order to determine a representative model of measured data. As in many experimental settings where complex phenomenon is challenging to capture, limited sampled points of the physical process are known. However, there is knowledge of an upper and lower bounding solution. In the case where only the sampled points are known, a polynomial fit of order four (with only 5 known sampled points) produces a very crude fit with the largest amount of error. An average of the bounding solutions is able to provide a more accurate fit but still moderately crude. Finally, it is shown that the convex hull of the bounding solution with the sampled points is able to provide a fit with the least amount of error. We demonstrate this by predicting the target strength of an unknown acoustically scattering rigid sphere which is sampled at equally spaced frequencies over a vast range of frequency values.

A simulation model for planing-hull watercraft propulsion consisting of a 3ph induction motor as prime mover, direct shaft drive, surface piercing propeller as thruster and speed controller was developed, tested, and operated demonstrating the ability to analyze the entire system numerically. The modularity of the model allows for the user to easily substitute different or more advanced modules, or add additional ones to obtain greater level of detail or simulate more complex interactions. Trends indicate an interest in all electric ship design as well as the use of surface piercing propellers for small craft. All-electric drive plants offer distinct advantages due to their flexibility in arrangements, ability to eliminate reduction gears in many cases, and wide range of available sizes. Of particular interest is the ability to apply electric drive to small craft with planing-hull, which achieve significantly higher velocities and where arrangements and maneuverability are of high concern. The accurate control of speed combined with the ability to output fairly constant torque across a wide range of speeds allows application of non-conventional thrusters such as surface piercing propellers to small craft. Due to the availability of towing tank data from a surface piercing propeller, a methodology to translate measured performance data for non-conventional thrusters as a computer simulation block needed to be developed. The derived modeling block of the surface piercing propeller, which took the form of a neural net, was integrated with an AC induction motor prime mover module, detailed dynamic propulsion shaft module and Proportional-Integral (PI) control module. The modules were finally augmented with a block implementing Savitsky’s method for planing-hull modeling. Simulations were conducted using full-scale real-world conditions for a hull Bayliner 170 Bowrider boat the hull of which can be adjusted to accommodate for a 50HP electric motor and a surface-piercing propeller. The runs conducted demonstrated the model functionality and level of detail.

Automated equipment is used for the ship fabrication process to obtain its higher productivity. However, in the final assembly stage of ship structures, automatic welding system has some constraints on application because of angled and curved surfaces. In order to overcome these constraints, wall climbing mechanism which has mobility and strong adhesion force is necessary. This paper presents an autonomous mobile platform designed for climbing on ferrous 3-D surfaces with welding head. The switchable permanent magnets are used for adhesion, which are capable of adjusting a maximum adhesion force if a variation in the magnetic field strength is required. The mechanism of mobile platform has identical twin bodies, link, flexible rail and sensing devices. Experimental results on the test block verified that the proposed mechanism was feasible and suitable for mobile platform of welding head.

Fabrication of large composite structures, such as recreational yacht hulls and wind turbine blades, is a cost intensive and high-risk operation, which must be carefully controlled to meet demanding design specifications and reduce defects. In this study, the goal was to develop an intelligent resin delivery system that can easily be integrated into the existing traditional setup in production environment and without any modifications to the mold. A prototype system with two resin supply lines and 16 optical sensors was developed. The system automatically monitors and adjusts resin flow in the mold in real-time using a controller. The effect of process setup parameters on the resin flow was investigated with the design of experiments technique to identify the best settings. The results showed that the automatic system can successfully control the resin flow, hence can be a potential future option in composite manufacturing.

A jack up rig, such as those used for oil drilling in the Gulf of Mexico, is a dynamic sensitive system subjected to random and periodic environmental loads (wave, wind, current, etc.), in which the inertia forces cannot be ignored. However, a static load analysis approach can be justified only if an extra inertial load set, due to the dynamic effect response, is included in the analysis. The Society of Naval Architects and Marine Engineers, SNAME T&R 5-5A, “Guidelines for Site Specific Assessment of Mobile Jack-Up Units”[1], addresses the calculation of the inertial load set by using the classical Single Degree of Freedom (SDOF) analogy to calculate such dynamic effect. This study evaluates how far apart crucial structural members’ stresses/loads obtained by using the SDOF analogy method are from those values obtained from a more realistic modal dynamic analysis. The analysis is performed for wave loads at different heights and frequencies such as those existing on extreme or severe design conditions as a storm. Although a jack up rig structure presents some non-linearities, especially in the legs-hull contact areas and the spud-cans interaction with the soil; a modal superposition analysis can be used if proper linearization is considered. The results of this study for a jack show that the SDOF analogy method tends to underestimate the base shear loads for high wave periods and conversely overestimate some stresses on crucial members, such as the legs’ chords close to the hull for all the wave periods. This study shows that the stresses on one of the legs’ chord of the most loaded leg, due to the dynamic effect produced by the harmonic loads calculated with the SDOF analogy developed in this study tend to be overestimated as the wave period decreases. Conversely, the calculation of the base shear of the structure employing a quasi-static analysis with inertial load set (ILS) as calculated in this study shows that the base shear forces difference between the modal dynamic analysis and the quasi static analysis tends to decrease as the periods of the wave decreases.

The exact calculation of the added resistance in waves is a seakeeping problem of high interest due to economic effect on ship exploitation. In this paper an open uniform B-spline based method is developed to calculate added resistance. Initially this method applied to calculate velocity potential and Kochin functions that are necessary for calculation of the added resistance by Kashiwagi’s formula. For this purpose the source strength and potential are distributed over body surface and described Open-uniform B-spline basic function. Computations are performed for different hull forms then results are validated by comparing them with practical results. The present method shows a good agreement in contrast to published results.

The current study presents a numerical study of co-firing chunk coal and one kind of light weight biomass, oat hulls, in a stoker boiler. First, a standard combustion model was applied to simulate coal combustion in a real size three dimensional boiler; the results were compared with the temperatures measured at different locations of the stoker boiler to assess the accuracy of heat sink and heat transfer model. Once a good accuracy was achieved, a devolatilization model for oat hulls was derived from experimental data and was matched with this combustion model to simulate combustion in a co-firing stoker boiler. The results showed that light biomass burns in suspension, similar to pulverized coal by following the air flow. Also, the peak temperature inside the furnace inversely varies with the increase of co-firing percentage of oat hulls. This numerical study reveals thermal and economic potential of using unprocessed light weight biomass on the existing combustion facility.

Automated equipment is used for the ship fabrication process for higher productivity. However, in final assembly stage of ship structures, automatic welding system has the constraints for application because of inclination and curvature of the hull block. In order to solve these problems, an automatic welding system which has special mechanism to travel on the flexible rail has been studied. This paper describes the essential characteristics of the new automatic welding system equipped with the proper mechanism for flexible rail and continuously adjustable welding torch slider.

This paper demonstrates use of thermal imaging for nondestructive defect detection in a composite boat hull which covers a large area. There is a strong demand in the boat industry for a non-destructive method that can detect defects such as delamination, voids of air or fluid, cracks, acid, dry mat, and carbon fiber. These defects are always difficult to detect as they occur inside the walls of the boat. Currently, ultrasound and manual inspection methods are used to identify these defects. The manual checking technique is unscientific; furthermore the ultrasound method is not acceptable due to unsatisfactory results. Thermal imaging involves detecting infra-red radiation from a hot body; this is captured by a thermal imaging camera. A thermal heat gun is used to heat the walls of the boat hull. After heating for a specific time period, the walls of the boat start emitting radiation. Dry void attains the highest peak intensity value for short time heating followed by Acid. Other defects like carbon fiber, delamination, and dry mat took longer time to attain higher intensity value. The decay of radiations is also different for various types of defects. The maximum intensity decay occurs for dry void as compared to other defects. From the results obtained so far, it can be inferred that thermal imaging can distinctly differentiate the different kinds of defects, as well as the unaffected areas of the boat wall.

The market of LNG (Liquefied Natural Gas) carrier is continuously in a prosperous condition, and a lot of LNG vessels are being built in many shipyards. Membrane-type MARK-III LNG CCS (Cargo Containment System) is used more and more in the construction of LNG carrier, and it has already taken considerable market share among the various LNG CCS products. This paper deals with a study on structural safety of LNG carrier whose inner hull structure is affected by cryogenic temperature of LNG. If the primary and secondary barriers are failed simultaneously, the inner hull structure comes to be in direct contact with LNG. It is well known that the cryogenic temperature exposes the inner hull structure to fatal risk of structural failure due to brittle fracture, but nevertheless it is quite difficult to find a precedent research which explains the degree of risk and severity with due consideration of the consequence caused by structural failure of inner hull. The heat transfer test has been performed using the specimen appropriate to realize test scenario while considering cryogenic liquid flow from primary and secondary barrier into inner hull structure, and at the same time, the specimen has been tested by applying proper deformation so as to examine the structural behavior of inner hull structure under cryogenic condition. The heat transfer analysis has been performed to simulate and verify the heat transfer test, and consequently it is possible to obtain actual distribution of temperature in the inner hull structure exposed to cryogenic temperature. The structural analysis has been performed to evaluate the damage of inner hull structure and as a result to assess overall decrease of hull girder strength of LNG carrier. Finally, consequence of the decrease of global strength has been discussed.

Line spectra in the radiated noise of marine vessels are the most visible signs, which can be detected, tracked and identified by enemy’s passive sonar, and hence it is of great significance to reduce the line spectra for improving the acoustic stealth of marine vessels. Insertion of resilient isolators between the machinery and the base is one of the most common methods for controlling unwanted vibration of the hull of submarine. Isolators in service are usually assumed to be linear and almost all the vibration isolation-n systems (VIS) are designed with linear theory, which satisfies engineering requirements in most situations. However, the nonlinear dynamical characteristics of VIS have attracted increasing attention in recent years due to the facts that onboard machinery trends towards more powerful and lighter, and that the demands in engineering for reducing vibration become more rigorous. Furthermore, some distinguishing features of nonlinear systems can be applied to achieve some special functions, among which the most important one is using chaos to reduce line spectra in the radiated noise of submarines based on the fact that response spectrum of a nonlinear system under harmonic excitation is a continuous one when chaos occurs. In this paper, a chaos synthesis method based on tracking control is prososed for a vibration isolation system (VIS) of on board machinery to make the chaotic motion in nonlinear VIS persistent. In this way, the line spectra in the radiated noise can be reduced effectively because the response spectrum of a chaotic system under harmonic excitations is a continuous and reduced one. Numerical simulations were carried out and the results showed that utilizing this method the nonlinear VIS not only possesses an excellent isolation performance of vibration and line spectra, but also reduces the amplitude of the isolated equipment notably.

The purpose of this study is to design the initial shape of doubly curved hull surfaces. In this paper, the development method of the hull surfaces was suggested by minimizing potential energy between initial and final shapes. In order to do this, the values of strains and stresses were defined through finite element analysis and genetic algorithm was used to estimate the initial shape which is the state of minimum potential energy. Validity of the prediction method was verified by comparing the estimated contour lengths with those obtained by the commercial software for sheet metal forming. It was founded that the established prediction method using genetic algorithms would enable to determine the initial contour of the doubly curved surfaces with maximum deviation of 0.7%.

Metal-composite joints between steel ribs and advanced fiber-polymer composites are an effective structural system for hybrid ship hulls. Similar joints are of interest for fuel-efficient aircraft. The current designs of such joints are generally based on the strength criterion, which ignores fracture mechanics. Aimed at an efficient and reliable design, this study investigates the size effect on the strength of these joints theoretically, numerically and experimentally. The analytical formulation of the size effect is asymptotically anchored at the large-size limit in linear elastic fracture mechanics (LEFM). The bi-material corner of the joint is shown to have a singular stress field with complex singularity. The strength of the joint is determined by the energy criterion for the macrocrack initiation at the corner, from which the large-size asymptote of the size effect law has been derived. A general approximate size effect law, spanning all sizes and various joint angles, is further derived via asymptotic matching. Numerical analysis with cohesive fracture model is used to design the experiments. Experimental studies involve the testing of geometrically similar hybrid joint specimens with the size ratio of 1 : 4 : 12. The analytical, numerical and experimental studies all indicate that the strength of bimaterial metal-composite joints is subjected to a strong size effect.