Transverse Bulkheads Research Articles

Wave responses of rectangular plates having uniform flexural rigidities floating on shallow water

This paper shows wave responses of very large floating rectangular plates under the thin plate and shallow water theory. First, the summary of wave response analysis method is briefly introduced. Next, numerical results of wave response of rectangular plates are shown and discussed for various parameters, incident wavelength and incident angle of incident shallow water waves, and flexural rigidity and aspect ratio of the plates. The characteristics of wave response of rectangular plates on shallow water are summed up. Wave induced maximum response values of shear force, bending moment and torsional moment are estimated. From these results the thickness of stiffened deck and bottom plate, and the minimum separation of longitudinal and transverse bulkhead to be needed can be estimated for initial structural design.

A Probabilistic Model of Flooding Loads on Transverse Watertight Bulkheads in the Event of Hull Damage

Watertight bulkheads (WTBs) are crucial to ship survivability in the event of hull damage. Current design standards for WTBs are empirical and prescriptive in nature. However, damage-causing events and damaged ship response exhibit significant variabilities and uncertainties. Hence, the design and assessment of WTBs should be performed in a probability-based format. This paper outlines, as an essential input to reliability analysis, the development of a physically based probabilistic model of transverse WTB loads. Poisson arrival is assumed for damage events, and the maximum life-time load effect envelope on the WTB in damaged condition is derived. The emphasis of this paper is on the probabilistic modeling of loads; hence, simple phenomenological expressions of load components are used to underline the cause and extent of randomness in WTB loads. A response surface type approach is suggested for determining ship-specific model parameters. A large RO/RO vessel with side shell breach below the waterline is used for illustrating the application of the proposed methodology; randomness is considered in ship hydrostatic properties, damage location, length of breach, occurrence and duration of damage events, the environment, curve fitting, and modeling errors. Probabilistic estimates of the maximum load components are obtained through Monte Carlo simulations. These are compared with available code-prescribed design values.

Finite element modelling and strength analysis of hold No. 1 of bulk carriers

Bulk carriers are subject to SOLAS regulations concerning the structural integrity of hold No. 1. SOLAS Chapter XII Regulation 6 mandates that the transverse watertight bulkhead between the two foremost holds and double bottom of the foremost hold shall have sufficient strength to withstand flooding of the first hold. This regulation applies to all single-skin bulk carriers of 150 m in length and upwards constructed before 1 July 1999. IACS provides rules for the construction of these areas of such vessels in order to comply with SOLAS Chapter XII. This paper presents a methodology for modelling hold No. 1 of bulk carriers using finite elements in order to assess the structural integrity of these areas under the loads prescribed by IACS. Results from respective nonlinear analyses using IACS loads are also presented.

상하부 스툴을 고려한 파형 격벽 최적 설계에 관한 연구

Design of the corrugated watertight bulkhead for a bulk carrier is principally determined by the permissible limit of Classification requirements. As the weight of upper and lower stool has considerable portion of the total weight of the transverse bulkhead, optimum design including the stool geometry and size will play an important role on economic shipbuilding. The purpose of this study is focused on the minimization of steel weight using the design variables, which are the shape and the size of the corrugation as well as the upper and lower stools. Discrete variables are used as design variables for the practical design. In this study, the evolution strategies (ES), which can highly improve the possibility of leaching the global minimum point, are selected as an optimization method. Usefulness of this study is verified by comparison with the proven type ship design. As objective function, total weight of the transverse bulkhead including the upper and lower stools is used.

Product-Oriented Optimum Structural Design of Double-Hull Oil Tankers

A convenient interactive structural design system (ISSMID), which consists of a structural arrangement module, a scantling module, and an interface module, has been developed for the optimum design of double-hull oil tankers. The structural arrangement module defines the configuration and properties of the longitudinal, transverse, and transverse bulkhead members. The scantling module determines the scantling of the longitudinal, transverse, and transverse bulkhead members to obtain the minimum structural weight and fabrication cost. The interface module generates the data for the structural analysis (ANSYS/NASTRAN) and the CAD system (TRIBON/AUTOKON). This paper describes a new structural cost model developed by considering welding technique, welding poses, and assembly stages to manage the fabrication man-hour and process. Also, a multi-objective function method (random search method) is developed to find the minimum structural weight and fabrication cost. Several optimum structural designs are produced based on the Pareto optimal set obtained by the random search method. The design results are compared with existing ships.

Vibration of air-coupled transverse bulkheads of a submarine

Vibration of a submarine's watertight compartments, lined up in the rigid cylindrical pressure shell, in which adjacent bulkheads (treated as thin plates) are coupled weakly through air cavities, is investigated by theoretical methods. Such air coupling separates the natural frequencies of each plate, and for each set of split modes, the frequency difference increases as the cavity depth is decreased. The system-level modes in which plates in the array vibrate in- or out-of-phase with each other are at closely spaced frequencies. Compared to each mode of a single plate, there exist one in-phase mode and N−1 combinations of out-of-phase system modes for a N-plate array. A vibration model comprising N classical thin plates that are coupled through the three dimensional acoustic fields established in the circular cavities between the plates is developed, and its results are shown in splitting the natural frequencies. In order to solve for the system modes, plate- and air-alone expansion functions are obtained in advance by considering a clamped circular plate and a rigid cylindrical acoustic cavity, separately.

Wave-induced stress analysis for detailed structural members on a very large floating structure (Mega-Float)

The estimation of wave-induced response of a very large floating structure has been calculated by a coupled structure fluid interaction program. The evaluation of the calculated responses is mainly carried out on amplitude of motions, such as vertical displacements, accelerations. Although the nominal stress on the structure can be calculated by the program, it is very hard to obtain a detailed structural stress because the scale ratio of the detailed structure to whole floating structure is very large.This paper is concerned in the wave-induced stress response calculation procedure for the detailed vstructure on a very large floating structure. The calculation method consists of two steps. First step; Internal loads such as wave-induced bending moment and shear force and external load such as wave -induced water pressure, Aikc, s(ω, χ;x, y), are calculated by 3D coupled structure-fluid interaction program. Second step ; When these loads act in the same time on the structure, wave-induced stress for the detailed structure, σikc, s (ω, χ;x, y), can be calculated by using stress factor, kj.σi, s (ω, χ;x, y)=∑Nj=1kjAijc, s (ω, χ:x, y)To verify the procedure, we conduct a full scale measurement of 200×100m scale floating structure for 2 months. The estimated stress of detailed structure, for example stress around scallop at transverse bulkhead, shows very good agreement with measured stress.

Optimum structural design of double hull bulk carriers in comparison with conventional single hull types

In recent years, bulk carrier casualties have increased dramatically, Most of the damaged bulk carriers were totally destroyed by the structural failures of the weak structures such as the single side structure and the corrugated transverse bulkhead. The double hull bulk carrier will be a solution to improve the situation. It is a more rigid, efficient and safer structure than the conventional single hull type but it has disadvantages of weight and cost. In this study, the optimum structural design of bulk carriers with double side skin was performed to minimise the structural weight. This study shows that the weight of the optimised double hull bulk carriers can be reduced to a reasonable amount in comparison with the existing single hull types, not optimised.

The KBXM Tanker Hull Structure Details

paper deals with the structural details and defines the reasoning of the side, deck and bottom structure. structure consists of 5 (6) longitudinal girders connected mutually by the transverse bulkheads stools. orthrotropic composite plates (panels) of double bottom, double side and deck are supported by the girder system brought about in a mentioned way, which flows between the peaks. In the composite plate structure the longitudinal elements are performed without break and they flow continuously throughout the ship. paper is the instalment of the paper The KBXM Ship Hull Structure (ODRA'99) aiming at researching main structural details.

Fibre reinforced composite–steel connections for transverse ship bulkheads

The structural performance of a symmetric steel to composite bonded joint has been examined. Numerical predictions and experimental results on the mechanical strength of the joint are presented. The experimental data and the findings from this study provide useful guidelines to ship designers for using large composite structural components in steel ships.

Optimisation procedure for X-80 steel blast tolerant transverse bulkheads

An optimisation procedure to be used to develop optimised X-80 steel blast tolerant transverse bulkheads is described. Three different structural arrangements have been investigated and optimised. This work has been stimulated by the increased interest in naval platform survivability over the past decade and the development of X-80 steel.

A Method of Structural Analysis for Mega-Float subject to Wave Loads

When carrying out stress analyses of a Mega-Float structure subject to wave loads, it is in many cases difficult to make an all-in-one program containing both of hydroelastic analysis and stress analysis because of capacity and processing time of computers. To cover such situation, a practical two-step method is proposed in which separately obtained first step output of hydroelastic analysis is given to the second step of stress analysis, where the static analysis program for Mega-Float is used.The stress analysis is done for each of the real part and the imaginary part of the hydroelastic solution to obtain two typical simultaneous set of stresses, and then, calculations of amplitude distributions for experienced maximum stresses while waves pass are done using the two parts.The method is applicable to plane grillage models and also three-dimensional finite element models based on common skeleton consisting of the lines of longitudinal and transverse bulkheads and girders. Hence, flexible application can be done according to various stages of design work.Results of trial analysis are shown for the cases of head sea and diagonal sea applied to the grillage model and the finite element model. From those results, it has been found that the method proposed here can be used as a useful analytical tool for structural design of Mega-Float.

Natural Frequecy of Multi-Tiered Tank Structure Subjected to Thermal Stress

It is sometimes reported that the heated tank structures in engine room are suffered from serious vibration, in particular fuel oil service tank or fuel oil settling tank. That phenomenon is quite strange, since the tank structure is designed so as to avoid resonance with exciting forces. However the reason of that resonance has not always been clarified in many cases.Heavy vibration of tank panels occurred in a heavy fuel oil settling tank in VLCC. The tank panels vibrated at 6.30Hz to 7.12Hz frequencies with 1.13mm of maximum single amplitude, although the natural frequency of tank panel had been designed to be more than 23.3Hz. The reason of the vibration is investigated on the basis of theoretical analysis and FEM analysis, consequently following facts are clarified : 1) In case of multi-tiered of tanks, oscillation of adjacent tank panels, in particular upper and lower panels, caused the pressure increase due to interference. That pressure reduced the natural frequency of panel due to the increased added mass of fluid.2) The thermal stress due to the tank heating caused compressive stress in tank panel, since the extension of tank structure was restricted by engine flats, transverse and longitudinal bulkheads of normal temperature. The compressive stress reduced the natural frequency of tank panel.3) The combination of the above two factors decreased natural frequency of tank panel to 1/4 of the original one and induced the resonance between the reduced natural frequency and the exciting frequency of main engine.This investigation can provide the designers helpful suggestions to avoid the vibration problem of multi-tiered and heated tank structures.

On the Application of Response Surface Methodology to the Optimization of Ship Structural Design

In this paper, the applicability of response surface methodology (RSM) to the design of ship structures is examined. One of the principal features of RSM is to rationally minimize the number of response evaluations by using the technique of experimental design. RSM also allows easy estimation of the change of response associated with the change of the design parameters on the obtained response surface. This is particularly effective in ship structural designs wherein trade-offs between design parameters are everyday occurrences. However, before RSM is applied to the actual design, the degree of the approximate polynomial equation that represents the response surface, and the necessary number of response evaluations, etc., must be examined. Thus, the optimization of the transverse bulkhead structure of a crude oil tanker is performed as an example of the application of RSM, wherein the method's effectiveness together with the results of above-mentioned basic examinations are shown.

Damage Stability Characteristics of Model RO/RO Ferries

The paper reports on experimental investigations which have been made on four model RO/RO ferries. One of these was based on a 1/100th scale model of the Herald of Free Enterprise. Two of the other models were modified versions of the Herald of Free Enterprise, which were so modified that they did not decrease the efficient concept of the vehicle throughput of a conventional vessel. The tests revealed that the capsize times of these modified RO/RO vessels were increased by 350% for one vessel and 500% for the other vessel. The modified vessels should meet SOLAS 90 + 50 regulations. A fourth model was fitted with two equally spaced transverse bulkheads. This model also had good damage stability characteristics. The paper also summarizes the history of some of the past RO/RO ferry disasters.

Time Domain Computer Simulation Of SloshingIn Ship Tanks Due To Irregular Wave Excitation

A direct approach to pressure determination in partially filled ship tanks subjected to irregular sea action is the subject of the paper. The approach presented, based on the design sea method and time domain sloshing simulation, is performed using PRS-developed TANK computer program. CTO-developed pre-processor is used to determine random time history of tank acceleration due to assumed wave energy spectrum, that is needed for fluid excitation. The calculations confirm, that severe sloshing loads of rather a local nature can occur as a result of impact between liquid and a tank ceiling in the regions close to transverse bulkheads. It is also concluded that wave modal period rather than excitation amplitude influence most the fluid impact pressure. Also impact pressure forecast is possible, that accounts both for impact pressure and wave excitation randomness. The work was done in the framework of an applied research project financially supported by The State Committee for Scientific Research.

Analysis of the accident of the MVNakhodka. Part 2. Estimation of structural strength

In the early morning of January 2, 1997, a Russian tanker, the MVNakhodka, broke in two in the Sea of Japan. The fore part of the vessel drifted and was stranded on the coast of Japan, and the aft part sank. The coast of Japan was seriously polluted by spilled heavy oil. Following this disaster, the Japanese Government established a Committee for the Investigation of the Causes of the Casualty of theNakhodka. This paper deals with the structural strength of MVNakhodka at the time of the accident. First the structural characteristics of theNakhodka are described, and the reduction in thickness of the structural members are estimated based on the data measured on the fore part of the vessel which drifted ashose. Then the ultimate longitudinal strength of the hull girder at the time of the accident is evaluated by applying Smith's method, and the possibility of break-up collapse due to excess loads is discussed. The mechanism of fracture at the bottom plate is also discussed based on the observed fracture surfuce of the cross section. Finally an FEM (finite element method) simulation of the break-up of the hull girder is performed. It is shown that buckling/plastic collapse took place at the deck plate near Fr.153, which was followed by the successive buckling collapse of the side shell plate of the hull girder. Right after the collapse of the deck structure, the bottom plate fractured just in front of the transverse bulkhead at Fr.153.

Finite element comparative study of ship structural detail

Abstract A comparative study of the finite element analysis of the local stresses in a ship structural detail has been carried out by the members of Technical Committee II.1 of ISSC ’97. An experimental model for the intersection structure of longitudinal stiffeners and a transverse bulkhead was selected as the analysis object. Finite element analysis results of eight shell element models and two solid element models were collected for this comparative study. It is found that the results of shell element models for local stresses have high correlation with each other, but give significantly lower stresses than the experimental results. The results of the solid element model, on the other hand, agreed well with the experimental results at the weld toe. A possible interpretation of the results of shell element models, in the practical procedures of hot spot stress evaluation, is discussed.

Ship grounding on rock—I. Theory

This paper presents a set of analytical expressions which can be used to calculate the reaction force on a ship bottom deformed by a conical rock with a rounded tip. Closed-form solutions are given for the resistance of inner and outer bottom plating, longitudinal stiffeners, girders and bulkheads and transverse frames, floors and bulkheads. The expressions are derived by use of an energy method or a type of ‘upper bound’ method which rigorously takes into account the effects of large plastic deformations, friction and fracture. A high level of generality for the methodology has been optained by postulating a global mode of deformation for the structure around the rock with one free parameter, the plate split angle, related to the shape of the deformation mode. It is assumed that intersections between structural components stay intact during the entire deformation process so the resistance of the individual structural members are derived according to the global deformation mode. The resistance of the entire structure is found by minimizing the energy dissipation from all the deformed members with respect to the plate split angle. In a subsequent paper (B.C. Simonsen, Ship grounding on rock—II. Validation and application, Marine structures 10 (1997) 563–584) it is shown that the theoretical model predicts the damage of four large scale tests and an accidental grounding with errors less than 10%. Moreover, it is illustrated by an example that the model evaluation of a grounding scenario is sufficiently fast to be used in a probabilistic framework in a Formal Safety Assessment.

Discrete Optimization of Ship Structures from the Viewpoint of Practical Design

In practical design of ship structures, it is obvious that some structural elements, for instance, longitudinals, must be chosen from a given set of standard discrete values being available commercially. Furthermore, some integer parameters such as the number of transverse web frames in the midship segment should be considered as the design variables to be optimized. In view of those facts, we investigate especially how to deal with the above kinds of discrete design variables in this paper. A cargo ship with large hatch opening is taken as the numerical example. The structural construction cost of hold length between two transverse bulkheads is chosen as the objective function to be minimized by genetic algorithms. Besides the conventional variable design parameters, some particular parameters such as the serial number of standard shaped steel for longitudinals and for transverse frames, the number of longitudinals in a given length, the number of transverse web frames in the midship segment, etc., are also selected as the design variables from the viewpoint of practical design. For each design variable, we describe it by a specific length binary string with a corresponding relationship to its available discrete values. Through the numerical analyses, it shows that the present method is a simple yet efficient method to deal with the discrete optimization of ship structures. The search efficiency of some genetic strategies such as the elitist preserving selection, the multi-point crossover and the uniform crossover is also investigated in this paper.