Naval Architects Research Articles

Design of an Autonomous Underwater Maintenance Dredger: A teaser to the maritime industry

A hopper dredger was chosen as a first autonomous concept design, since dredgers, next to Offshore and Passenger Vessels, are part of C-Job Naval Architects’ main market segments. By submerging a Trailing Suction Hopper Dredger (TSHD) a major benefit was identified in ship’s resistance and required vacuum for the dredge pump. The first aspect due to reduction in wave making and -breaking resistance, the second due to reduced suction depth relative to the pump. In addition, an increased part of the ship’s volume would generate displacement resulting in additional payload and a new arrangement of the vessel could be created resulting in a reduction in overall hull girder loads and reduced steel weight. To prove these insights, a comparative study was performed between a conventional, manned TSHD and the Autonomous Underwater Maintenance Dredger (AUMD). During this study the following aspects were quantified: hydrodynamic resistance, power requirements, sustainable power supply, general arrangement, redundancy / maintenance. The operational profile of the conventional TSHD, was used as a reference for the new concept. The developed concept showed very promising, both from operational as well as sustainability point of view. Some of the key benefits of the design are reduced dredge pump power (2x175 kw versus 2x675 kW), reduced propulsion power (2x575 kW versus 2x1100 kW), low OPEX, zero emission power supply and reduced hull girder loads. Amongst others, based on this concept design, C-Job feels strongly that Autonomous vessels have an enormous potential on (operational) improvements for ship operators. Not only by omitting the ship’s crew, but by fully utilizing the opportunities this presents.

Codesign Case Study of a Planing Craft with Active Control Systems

This case study presents a novel insight into the design of a codesigned planing craft with an active control system (ACS), along with its potential advantages and disadvantages when compared with a traditionally designed vessel (i.e., a vessel whose geometry is first selected, and then its ACS is implemented). This work has three purposes:present tools a designer can use to codesign a planing craft with its ACS,use these tools to expand the design space and further explore the potential of codesign, andinvestigate the feasibility of having a planing craft with ACS designed to the codesign results found in 2) and compare it with a traditionally designed vessel. The vessel particulars that are numerically optimized are the beam, dead rise, longitudinal center of gravity (lcg), and two tuning parameters for the ACS's linear quadratic regulator. In the case study, the codesigned vessel had 4% lower drag at the design speed and Sea State (SS) 3, but on lower SS's it had drag savings of 10% and seakeeping improvements of around 40% for the investigated seakeeping metric. The case study suggests that although the codesigned vessel is technically feasible, it would require unconventional hull/deck design—a result which emphasizes the importance of considering the coupling between a planing craft and its ACS early in the concept design. 1. Introduction In search for a better performing planing craft, a naval architect could consider using an active control system (ACS) on their designs. Although they will encounter published research confirming performance improvements when an ACS is used (Wang 1985; Savitsky 2003; Xi & Sun 2006; Kays et al. 2009; Engle et al. 2011; Hughes & Weems 2011; Rijkens et al. 2011; Shimozono & Kays 2011; Rijkens 2013), literature addressing the concept design process of a planing craft that will have an ACS is, to the best of the authors' knowledge, limited only to the previous work by the authors (Castro-Feliciano et al. 2016, 2018). The work by Castro-Feliciano et al. (2016, 2018) suggests that the benefit from codesigning (as opposed to sequentially designing the vessel geometry and later adding an ACS) can be significant and should be the design methodology followed when designing a planing craft that will have an ACS.

Stratification Technology of the English Shipbuilding Sublanguage Lexical Units

The study of shipbuilding sublanguage, development and systematic description of its vocabulary are not only of great theoretical, but also of practical importance. The sublanguage of shipbuilding consists of complex terminological systems to be studied and unified by the joint efforts of linguists, sociolinguists and naval architects. The aims of the present research are the following: a) to study classification of ships and their systems from various aspects of shipbuilding science, b) to consider principles of building a terminological shipbuilding dictionary, including multicomponent terms and models they are formed of, c) to analyse processes of terminalisation or reterminalisation of lexical units d) to analyse how lexical units belonging to the so-called general scientific usage and special vocabulary function in this branch of science, i.e. to stratify lexemes according to the degree of their terminalisation, and to create a lexical minimum for students specialising in this field of knowledge. The research was carried out on the basis of structural-probability analysis, using the concept of distribution vocabulary, developed by prof. N.D. Andreev.

Feature identification using acoustic signature of Ocean Researcher III (ORIII) of Taiwan

Feature identification using acoustic signature of Ocean Researcher III (ORIII) of Taiwan

Danish Modernist Architecture and Furniture Design in Passenger Ship Interiors 1935–1965

Since the 1960s Denmark has become internationally renowned for its architecture and design output. The work of Danish modernist architects and designers working on terra firma is very well known, but very little has been written about their influence on the design of merchant ships. This article examines the manifestation of Danish architectural modernism in the interior design of Danish and other Scandinavian-owned passenger ships built between the mid-1930s and the mid-1960s. It explains how the Danish Modern Movement in architecture and design had distinct characteristics from other avant-gardes in visual culture of the early-to-mid twentieth century and argues that its respect for tradition was advantageous when engaging with ship owners, naval architects and shipbuilders. It focuses in particular on ship interiors designed by the architects Kay Fisker, Palle Suenson and Kay Kørbing and shows how their designs became ‘floating ambassadors’ for Danish and Scandinavian modernism more generally.

Heave and Pitch Motion Performances of a Ship Towing System Incorporated with Symmetrical Bridle Towline Model

An investigation on vertical motion characteristics of a ship towing system incorporated with symmetrical bridle towline configuration set a real challenge for the naval architect engineer. This paper presents a Computational Fluid Dynamic (CFD) approach to analyse heave and pitch motion performances in waves. Several towing parameters such as various towline length and towing’s velocity have been taken into account. Here, 1B (barge) is employed in the simulation; and designated as a towed ship. The results revealed that the subsequent increase of the towline lengths has been basically proportional with the increase of her heave motion; while inversely decrease in pitch motions. In addition, the effect of the extending towline length = 1.0 to 3.0 resulted in insignificant effect to the towline tension. However, the increase of the towing’s velocity from 0.509 m/s to 0.728 m/s has led to significantly increase her heave motion and the towline tension by 40.46% and 24%, respectively; meanwhile, the pitch motion barge has sufficiently decreased by 35.94%. This simulation has been beneficial for the towing operator to ensure a higher level of the safety navigation of ship towing system.

Allied Maritime Forces Transformation: Towards a Defence Planning Process That Includes Adaptable Warships

Warships have long service lives. During the life of a warship the types of operations that will be assigned to the ship will change (this happened for example at the end of the Cold War), the technology behind the installed systems will advance (e.g., radar performance and miniaturisation) and new technologies will emerge. New technologies are likely to require changes in the way operations are presently conducted (e.g., off-board systems for conducting mine countermeasures operations) and can deliver new operational capabilities to the ship (e.g., directed-energy weapon systems). For these reasons, warships can only maintain maximum operational relevance through-life if their operational capabilities can be augmented and adapted to meet changing user requirements. NATO nations and partners, and also their peer competitors, are designing and building more adaptable warships. A common characteristic of these ships is that mission essential systems can be added to and removed from the ship in a relatively short time period. Warship roles can thus be reconfigured. The future of this trend is transforming the NATO defence planning process so that the future structure of the allied maritime forces will include an appropriate mix of adaptable warships and up-to-date mission packages that can respond to constantly changing operational tasking. The naval architect is already aware that traditional warship design features must be re-worked to accommodate modular, in addition to—or even to replace—organic systems. This paper considers the transformation from the engineering and management of mission packages, their deployment and integration into new warship designs towards a new maritime defence planning philosophy and process.

When is the Adaptable or Multi-Role Ship the Right Answer?

The rise of the multi-role ship, often envisaged with modular bolt on capabilities, has been the stable of conferences for most of this decade. Similarly, adaptability is an increasingly common theme in presenting new designs and concepts. However, the question for the naval architect is “do these represent the right solution for a given individual project” or has the concept been overstated as a vision of the future and used as the template which is not quite the panacea that it promises. After several decades involved in a wide range of projects, the authors offer their thoughts on the opportunities and realism of multi-role ships and adaptability. The paper explores some of the lessons learnt in delivering multi-role and modular designs. The underlying themes that are fuelling the interest in multi-role ships along with the typical roles considered are also discussed.

New interactive method to determine parameters for large motor yachts stability

The stability of a ship is the most important safety criteria to be considered during the design process, in fact an error in the design of the hull. An error in the stability evaluation has two different levels of danger, each one related to the other: the loss of stability leads to the loss of the ship, and this loss usually happens suddenly and quickly, causing a serious danger for the passengers. At the same time, in last decades, yachts have been changing significantly, increasing their dimensions from “boat” to “ships”, and the Rules have followed this change setting different criteria to be met. This has led to a different approach to motor yacht design, and to the way of building yachts, considering new materials, manufacturing, etc. For a designer ‘managing the stability of a yacht’ is the capability to have control over the trim and heel when an inclining cause occurs. This capability is strictly related to the hull shape and the weight distribution in three-dimensional space; the criteria of stability for motor yachts have been raising especially in last 2 decades, becoming more and more strict, but this request has to fight with the development of the market and the design that requests always larger superstructures, creating a serious conflict for the naval architects. Considering the importance of stability, undoubtedly considered as mandatory, we can underline the relevance of a method for an immediate evaluation of the parameters involved, especially at the beginning of the project, in order to foresee the stability of a motor yacht and operate in an interactive way with the production department. The suggested method aims at filling a void in the available documentation, referring to a methodology already known and used in Naval Architecture for the evaluation of the residual resistance of the various hulls, with the creation of a systematic database, but this methodology has net yet been applied to stability. The search for the stability parameters is usually done applying a direct weight estimation, considering the weight of each items, like shell plates, girders, single machinery etc. and the position of the center of gravity and then, once, estimated the center of gravity of the ship, verify if the stability criteria are satisfied. But the interactivity concept contained in the proposal is to have already a target to aim, in terms of position of center of gravity G, and constantly adjusting the distribution of each item to come close to that value, similarly to the already mentioned method to aim at values of geometrical parameters regarding the resistance. The present work, in order to provide this method for the stability, will examine a series of various motor yachts, with their inclining experiment and data, in order to create a methodological criteria to foresee the performances in terms of stability and the main design criteria that can be adopted. The method will give values and tendencies of main stability parameters to be aimed before starting the project, without having to follow the complete process of a preliminary calculation, with an important saving of time.

ABİDİN DÂVER UNDER THE LIGHT OF HIS LABOUR IN TURKISH PRESS FOR ALMOST A HALF CENTURY

Abidin Dâver had been active as a journalist for almost a half century. The starting point of this article is defined as the examination of Abidin Dâver’s literary life with respect to his written works inthe history of maritime and the naval history. Born in 1886, Abidin Dâver (d.1954) had been amongst the journalists, passionate with the sea, and dedicated his life to the ships and the naval history as well as the understanding of foreign cultures within the framework of travels abroad. His long literary life had reflected a high gusto. Known as the “civil or little admiral” along with some other titles referring to his high interests on the military affairs, Abidin Dâver had also been amongst the founders of the Galatasaray Sports Club. Aside from his works such as the Oppressed Prince Zizim (1909,) The Ship (1932), The Sea (1932), Turkish Maritime (1947), Barbaros Hayreddin Pacha (1954), he had also written a novel entitled as “The Novel of the Lieutenant”. The study had applied to the periodicals such as Her Hafta (Every Week), Hollywood Dunyasi (Hollwood World), Av ve Deniz (Hunt and the Sea), Deniz Mecmuasi (The Sea Journal), Deniz Nakliyati T.A.O. Bulteni (The Sea Transport Bulletin), the publication of the Chamber of Turkish Naval Architects and Marine Engineers, Gemi Mecmuasi (the Ship Journal). and the daily Cumhuriyet (Republic) and Ikdam newspaper as well as the digitalized archives of Taha Toros and Salt Research.

Combined stochastic lateral and in-plane loading of a stiffened ship panel leading to collapse

With harshening ocean environments and the push to extend the service life of vessels and platforms, lifetime structural design performance is an increasingly important factor to differentiate between design options. But despite many advancements in structural modeling, reliability analysis may still be too time consuming and computationally expensive to be employed for local design choices. Reliability analysis for stiffened ship panels is additionally complicated as the collapse mechanism is due to combined stochastic lateral and in-plane loading effects [1]. This paper employs the non-linear Design Loads Generator (NL-DLG) process [2] to efficiently estimate the probability of stiffened ship panel collapse while retaining the wave profiles which lead to lifetime responses. This information allows a direct comparison between panel options and highlights critical panel parameters which are strongly related to design robustness. The resulting ensemble of short NL-DLG wave profiles lead to similar statistical characteristics of the panel designs as do brute-force Monte Carlo Simulations, but reduce the required simulation time by a factor of nearly 87,000 for the same number of simulations. These directed wave profiles offer naval architects the opportunity to efficiently examine rare complex structural responses by linking high-fidelity structural and hydrodynamic models. The potential of the NL-DLG process is that relevant information about complex marine structures, even those with limit surfaces excited by combined non-Gaussian loading, can be obtained efficiently and in earlier stages of the design process via low-order surrogate models.

THE LIFE PLATFORM: LEVERAGING A VIRTUOUS CIRCLE DESIGN

The end of 2018 saw the delivery of the motor yacht Bravo Eugenia. She is built by Oceanco based on the LIFE platform developed in collaboration with Lateral Naval Architects. This study defines the LIFE platform (i.e. Long, Innovative, Fuel efficient, Eco conscious) its key features and outlines its fundamental design pillars. The relative merits of main parameters are assessed against a typical similar sized yacht by use of baseline fleet data. LIFE’s low weight in relation to length and reduced powering requirements combined with a hybrid propulsion system result in a virtuous circle at which the centre is the single tier engine room. The benefits of the single tier layout such as the higher flexibility in designing the accommodation spaces and the improved balance between technical and luxury areas are outlined. In this context, various designers’ LIFE platform interpretations are provided as examples for discussion. The LIFE hybrid propulsion system is presented and the various modes of operations for which the hybrid system is conceived are discussed.

Numerical simulation of the slamming phenomenon of a wave-piercing trimaran in the presence of irregular waves under various seagoing modes

Trimaran vessels have been of great interest to naval architects, due to their large deck space, low resistance at high speeds and stability. Meanwhile, determination of their slamming forces in the presence of highly nonlinear waves has always been a challenge for the structural designers. However, because of novelty and complexity of their hulls, there is insufficient information in this regard, which necessitates suitable effort in filling this gap. Accordingly, in this article, using Flow-3D, a commercial computational fluid dynamics code, seakeeping of a wave-piercing trimaran is simulated in the presence of irregular waves via standard Bretschneider spectrum in sea state 5 in various seagoing modes. These modes include two speeds and two waves with encountering angles of head sea and bow quartering sea. For validation purposes, seakeeping of a trimaran vessel and water entry of a wedge-shaped section are investigated and numerical results are compared against experimental and analytical data. Good compliance of the results confirms the accuracy of the proposed numerical model. In the slamming analysis of the considered trimaran, using the relative vertical velocity of the bow section from the seakeeping analysis, the water entry problem is investigated for the most severe slamming mode. Pressure distribution caused by water entry and instantaneous impact pressure, known as structural design pressure, is computed. The exerted slamming pressure on the bottom and bow flare region is determined to be 4300 and 2100 Pa, respectively. Results indicate that during slamming phenomenon, the maximum pressure exerted on the vessel’s floor occurs at the time of impact at which the pressure coefficient is 4.4. Accurate assessment of the vessel’s vertical velocity from the start of water entry until the water surface rise-up, and the utilized technique considered for slamming phenomenon in more realistic sea condition, can be considered as important features of this study.

Improving SWATH Seakeeping Performance using Multi-Fidelity Gaussian Process and Bayesian Optimization

We construct a multi-fidelity framework for statistical learning and global optimization that is capable of effectively synthesizing seakeeping predictions having two different levels of modeling fidelity, namely a strip theory and a boundary element method based on potential flow assumption. The objective of this work is to demonstrate that the multi-fidelity framework can be used efficiently to discover optimal small waterplane area twin hull shapes having superior seakeeping performance using a limited number of expensive high-fidelity simulations combined with a larger number of inexpensive low-fidelity simulations. Specifically, we employ multi-fidelity Gaussian process regression and Bayesian optimization to build probabilistic surrogate models and efficiently explore a 35-dimensional design space to optimize hull shapes that minimize wave-induced motions and accelerations, and satisfy specific requirements in terms of displacement and metacentric height. Our results demonstrate the superior characteristics of this optimization framework in constructing accurate surrogate models and identifying optimal designs with a significant reduction in the computational effort. 1. Introduction During the past decades, estimating the seaworthiness of a ship in the early design stages has become a primary concern for naval architects. Increased requirements in terms of comfort and ergonomics have steered the research in developing innovative hull forms, with the specific target of decreasing motions in waves. From a safety point of view, extreme accelerations can exert harmful dynamic loads (on the vessel, cargo, or equipment), slamming, or green water effects that can severely damage the structural integrity of the vessel or lead to stability losses. When ship behavior in waves becomes a quantity of interest in the hull-form optimization process, seakeeping performance needs to be predicted with numerical models able to combine high fidelity and high computational efficiency. Nowadays, ship motion predictions mainly rely on three families of numerical models, here sorted by increasing level of fidelity: 2-D strip theories, 3-D boundary element methods (BEM), both developed under the assumption of potential flow, and unsteady fully viscous nonlinear 3-D methods in which ship motions are simulated in six Degrees of Freedom (DOF) for incident regular or irregular waves (see Fig. 5). In this article, we introduce a probabilistic method for constructing surrogate models using multi-fidelity training datasets that allows to increase the accuracy of the model with significant savings in computational resources. For the purpose of demonstration of the multi-fidelity framework, the training datasets used in this article are composed of classical 2-D and 3-D potential flow predictions; for this reason, we will refer to 2-D strip theories as low-fidelity models and a more accurate 3-D BEM as high-fidelity models. In the present study, our goal is to demonstrate the ability of the multi-fidelity framework in efficiently discovering hull forms with superior seakeeping characteristics by using simplified prediction models. Although in the present study, we do not include any viscous effects, the methodology is general and can combine any type of high-fidelity simulations or experimental data with low-fidelity simulations, experimental data, or even empirical correlations.

A wake field design system utilizing a database analysis to enhance the performance of energy saving devices and propeller

The purpose of this paper is to propose the wake field design system which outputs a bare hull form generating a desired input wake distribution, and to demonstrate capability and effectiveness of this system through a practical hull form design project considering the interference effect of ESD and propeller. Our proposed wake field design system outputs a hull form which achieves desired input wake distribution utilizing hull form and wake field database. In the system, the database is analyzed by a method for the first time proposed in the present study, that is, a scheme using the Euclidean distance and hull form blending (morphing). To validate our system, the one-leave-out cross validation is performed, which is widely used for the validation of the database analysis. There, it is confirmed that the proposed method has practical accuracy. A practical demonstration is also performed in this paper, where a 749 gross tonnage cargo ship is selected as object ship. The initial (original) hull form in this research was developed in a project of the Japan society of naval architects and ocean engineers as a considerably promising bare hull form. This hull form is defined as the original design in this study, then we try to further modify the design to reduce delivered horse power in a condition of hull with duct type ESD. Importantly, we design a new hull form to improve wake field suitable for the duct along with the consideration of reduction of cavitation. To confirm the effectiveness of our proposed system, the towing tank test is conducted to measure the wake distribution, using 2 model ships (original and new design) with 6.8 m ship length. It is proved that our proposed system is capable to efficiently design desired wake field for the given hull form without trial and error, and provide equivalent to or more precise results than the expert designer’ design. Additionally, we also confirm that the propulsive performance of the new design hull form is improved. In our careful comparison of the effectiveness of the ESD, it is indicated that the new design shows 2.2% reduction of horsepower compared to the original hull form both for ESD installed case.

Ultimate Strength of Hull Plates under Monotonic and Cyclic Uniaxial Compression

As the most fundamental structural components of the ship hull, the hull plates' ultimate strength not only affects their own load bearing capacity, but also contributes to the ultimate strength of the whole ship hull. Through the literature survey of the ultimate strength of hull plates, it can be found that most of the ultimate strength research studies focused on the ultimate strength behavior of hull plates under monotonic increasing loading. Considering the motion and deformation of hull girders among sea waves, the ultimate bearing capacity research of the hull structures under cyclic loading maybe more in line with reality. In this article, the local instability tests of plates under cyclic uniaxial loading carried out by Fukumoto and Kusama is reanalyzed. Based on the tests carried out by Fukumoto and Kusama, some fundamental behaviors about the ultimate strength and unloading and reloading paths of the plates under cyclic uniaxial compression are summarized. Then, a simple approach to construct the average stress-average strain relationship of the hull plates exposed to cyclic compression is proposed. Finally, tests on six square-column models are carried out to simulate the collapse behavior of the hull plates under cyclic uniaxial compression. The present study shows that the average stress-average strain relationship of hull plates under cyclic compression can be constructed by a simple approach conveniently and accurately. Meanwhile, the ultimate strength behavior of the hull plates under cyclic uniaxial compression can also be reflected well by the simple approach. 1. Introduction Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. An appropriate level of the ultimate strength of a ship hull is perhaps its most important guarantee of structural safety. Accurate assessment of the ultimate strength and/or residual ultimate strength of a ship is pertinent not only for the initial design, but also for the operation, maintenance, repair, and even disaster management, rescue, and salvage assessment of the ship hulls in accident situations. The first attempt to calculate the ultimate hull girder strength was developed by Caldwell (1965), who applied "Rigid Plastic Mechanism Analysis" to evaluate the ultimate strength of the hull girder. From then on, the ultimate strength of ship structures (including plates, stiffened plates, and hull girders) was widely studied by numerous scholars. Certainly, a great deal of developments have made naval architects obtain a clearer understanding of the ultimate strength behaviors of ship structures. However, because of the complexity and importance of the problems related to the ultimate strength, they still need to be explored more deeply. As described in the report of 19th International Ship and Offshore Structures Congress (ISSC 2015), "with these developments ultimate strength assessment is now becoming a more important issue to ensure the safety of ship structures."

Waterjet Modeling to Calculate High Speed Vessels’ Performance

Similar to the matching process between the main engine and propeller in a conventional vessel, there is a basic necessity to match main engine and waterjet in a high speed craft. Unlike the ability of the naval architect to review the overall impact of the engine and propeller selection in terms of thrust, delivered power, fuel consumption and vessel range, when coming to match a waterjet to a particular vessel, the performance data presented by the waterjet manufacturers is in some ways simplistic and does not contribute to the naval architect's effort to assess the complete performance picture of the propulsion system. In this article, a simple parametric modeling of the waterjet is presented which is common to all waterjets and enables the naval architect to match and assess the interaction between main engine and waterjet much like the process when matching main engine to a propeller. It will be shown that the constant power lines for thrust and rotational speed of a waterjet can in fact be consolidated into a single nondimensional set of curves similar to the nondimensional KT/KQ/ηo of a conventional propeller. This process will allow in fact the overall assessment of the matching problem between the main engine and the waterjet. Some waterjet manufacturers provide data for different impeller designs in which case this process can provide the naval architect a tool to choose the optimal impeller. Unlike the graphical nature of the performance assessment of the conventional data presented by the waterjet manufacturers, this method of modeling allows the digital/analytical solution in any intermediate speed and power setting. For the sake of simplicity, this article does not deal with the cavitation phenomena and the loss of thrust when the waterjet is cavitating although these are important issues that should be considered when assessing waterjet performance.

Resistance calculation of a composite material structure for leisure crafts using finite element method

A naval architect is choosing the material taking into account various factors, some of them being the dimensions, weight, area of navigation, costs and impact strength. For leisure craft vessels, materials which are made of are mainly fibre reinforced composite materials. The composites show many advantages, being light, resistant to corrosion, resistant to impact, capable of vibration reduction and of course, it is very easy to use them in the construction process, to maintain and to repair. There are numerous general use programs which include finite element intended for calculation of the structures of which a composite is made of. Elements of the analysed structure are linear if they do not admit yielding of the layers and nonlinear if they admit yielding of the layers. Using finite element analysis, it was modelled and calculated the structure resistance of a power driven leisure craft with a length less than 24 m and will be compared with the “DNV GL Rules for Classification: High Speed and Light Craft” in force since 1 July 2016. Based on the mentioned rules, there were calculated the design loads, pressures and forces. It is noticed that the results achieved using finite element analysis are within DNV GL limits.

Numerical study on the dynamic response of the large containership's bow structure under slamming pressures

The dynamic behaviors of the large containership's bow structures subjected to slamming pressures with different influence parameters are studied based on 3D finite element method. The slamming pressure is characterized as symmetrical and non-symmetrical half sine impact load, traveling over the side shell of the bow at a constant speed. The yield failure criterion is used to determine the critical slamming pressures of the bow structure under slamming pressures in the present paper. Various influence parameters which are relevant to the dynamic response of the bow structure are discussed, including the amplitude of slamming pressures, impact duration, rise time of slamming pressures, load attenuation coefficient, the position of maximum slamming pressures and traveling speed of the slamming pressures over side shell of the bow flare. The results show that the maximum stress responses of the bow structure increase with the increase of slamming pressures amplitude and with the decrease of the load attenuation coefficient, the other parameters also have a great influence on the dynamic response of bow structure. The safety margin coefficient is presented to evaluate the safety performance of large container ships under slamming pressures. The obtained results contribute to help the naval architect to design a ship which has a stronger capacity of resisting slamming.

Ultimate Strength Assessment of Hull Girder under Cyclic Bending Based on Smith’s Method

Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. Accurate assessment of the (residual) ultimate strength of a ship hull is important not only for the initial design, but also for the operation, maintenance, repair, and even for disaster management, rescue, and salvage assessment of the ship hulls. In fact, under ocean wave conditions, the hull girder is likely to withstand extreme cyclic bending. In this article, a simplified method based on Smith's method is proposed to assess the ultimate strength of the ship hulls under extreme cyclic bending. To obtain the nonlinear average stress-average strain relationship (σ-ε curve) of the basic structural element (consisting of a stiffener with its attaching plating) under cyclic in-plane compression and tension, systematic calculations are carried out by using a combination of the Beam-Column analysis and the nonlinear finite element method (NLFEM). By introducing the cyclic σ-ε curves of basic structural elements to a simplified calculation program, which is developed by the authors and based on Smith's method, the ultimate strength of hull girders exposed to extreme cyclic bending is subsequently determined. The ultimate strength of three box girder models and an actual ship are obtained under cyclic bending by using the authors' developed procedures including the simplified calculation program and are compared with the corresponding results from NLFEM calculations and also the box girder experiments. 1. Introduction Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. An appropriate level of the ultimate strength of a ship hull is perhaps its most important guarantee of structural safety. Accurate assessment of the ultimate strength and/ or residual ultimate strength of a ship is pertinent not only for the initial design, but also for the operation, maintenance, repair, and even for disaster management, rescue, and salvage assessment of the ship hulls in accidental situations. Perhaps the first attempt to calculate ship hull girder ultimate strength was by Caldwell (1965), who applied a type of rigid plastic mechanism analysis to evaluate strength. Since then, naval architects have gradually realized various technology developments and advances of importance to the ultimate strength assessment of ship structures. Over the last two decades, the ultimate bearing capacity of ship structures (including plates, stiffened plates, and hull girders) in their many different modes of possible behavior has been widely studied, and a great deal of results developed, which have made possible an increasingly clearer understanding of the ultimate strength behavior of ship structures. However, because of the complexity and importance of the problem, and the need for continuing development is still felt, for example, as described in the 19th International Ship and Offshore Structures Congress (ISSC) report, which emphasizes that (even) "with these developments ultimate strength assessment is now becoming a more important issue to ensure the safety of ship structures."