Transverse Bulkheads Research Articles

Analysis of Residual Stresses in Curved Cutouts of Steel Box Girder Transverse Diaphragms

In order to analyze the characteristics of cutting residual stress distribution at the arc‐shaped cutout of steel box girder diaphragm and to study its fatigue cracking mechanism. Taking Xia Zhang Bridge as the engineering background, this paper proposes a systematic method for calculating the residual stress field at the arc‐shaped cutout of the diaphragm. First, a mathematical model of the cutting heat source was established for predicting the temperature field changes during the cutting process of the diaphragm. Then, a 3D thermoelastic‐plastic finite element model was established using Abaqus to parametrically analysis the residual stresses during the fabrication of the transverse spacer. The results show that the cutting heat source creates a “thermal stagnation” effect at the curved notch, which leads to the local metallurgical transformation of the metal surface layer, which is unfavorable to its fatigue performance. The residual stresses are mainly concentrated near the cutting line, and the transverse residual stresses are lower at the free edge of the cutting line, which is easy to crack, and higher in the middle of the arc section of the arc notch. Inside the transverse bulkhead, at 14.5 mm from the free edge of the cut, in addition to the existence of high longitudinal residual tensile stress, its transverse residual tensile stress is also high, with a peak value of 199.3 MPa. Thermal cutting produces high residual tensile stress at the free edge, and the tensile stress cycle formed under the combined effect of wheel load is one of the reasons for the formation of initial fatigue cracks.

Floodable length analysis of a container vessel using computer aided design

The floodability of a container vessel is investigated to determine the maximum volume of compartments that can be flooded without causing the container vessel to capsize. In this project, Maxsurf modeler was used for the hull design and Maxsurf stability enterprise for the floodable length analysis of a container vessel at several displacements, number of transverse water tight bulkheads and its positions from AP to FP and a constant permeability value for the compartments. Floodable length is the preliminary check on damage survival. It is used at the initial concept design phase because it is faster than a full damage stability analysis, it checks if the vessel has sufficient buoyancy to sustain damage and stop from sinking straight to the bottom. Maxsurf Enterprise marine design software is used to determine the results. The output of the analysis shows a floodable length curve and the curves that represent different displacements, if a displacement line is below the allowable floodable length of a compartment then the vessel will not survive damages but if the line is above the allowable floodable length then the vessel will survive damages. The result also shows that it is easier for the vessel to survive heavily loaded conditions with more compartments.

Bulkheads’ Position Optimisation in the Concept Design of Ships under Deterministic Rules

The position of the transverse bulkheads is the most important aspect in determining the internal subdivision of the ship and has a strong impact on the general arrangement, weight distribution and capacity of the ship. Nowadays, deterministic rules still apply to various types of ships such as gas carriers, naval ships, icebreakers, etc. For these vessels a new floodable length can be defined as the extent of the ship that can be flooded, still assuring compliance with the damage stability criteria. The main objective of this paper is using the floodable lengths to optimize the position of bulkheads. The proposed methodology maximises the margin between the floodable length and the actual flooded length, which consists of two lost contiguous compartments. This method, applicable in the framework of multi-attribute decision-making techniques for ship concept design, allows identification of the minimum number of bulkheads a ship requires, quantification, and maximisation of the safety margin for compliance with deterministic damage stability criteria. This margin ensures maximum flexibility for changes that may be required in the next design phases. The proposed method, based on a multi-stage optimization, is tested on a compressed natural gas carrier to define the minimum number and position of the transverse bulkheads dividing the cargo holds.

Numerical Study on the Sagging Damage of the Simplified Hull Girder Subjected to Underwater Explosion Bubble

The pulsation of the bubbles resulting from underwater explosions can lead to severe damage to the structure of the ship’s hull, and even to its sinking. To study the damage mechanism of a simplified hull girder (SHG) subjected to near-field underwater explosion bubble, the Coupled Eulerian–Lagrangian (CEL) method based on verifications of the calculation accuracy was used to simulate 11 SHG structures. The sagging bend mechanism of SHGs was analyzed from the perspective of plastic hinge lines. Moreover, the length formula of the potential bend zone was studied through the assumed plastic hinge lines. The influence of transverse bulkheads on bending mode and total longitudinal strength was investigated. The results show that SHGs’ sagging damage is composed of regular plastic hinge lines, mainly depending on side plates’ folding—W-shaped in this paper. When facing the near-field underwater explosion bubble, the distant transverse bulkheads influence the total longitudinal strength and do not always play a positive role.

Cooling Potential of Ship Engine Intake Air Cooling and Its Realization on the Route Line

A fuel efficiency of a ship engine increases with cooling inlet air. This might be performed by the chillers, which transform the heat of engine exhaust gas and scavenge air for refrigeration. The effect gained due to cooling depends on the intake air temperature drop and the time of engine operation at decreased intake air temperature. Thus, the cooling degree hour (CDH) number, calculated as air temperature depression multiplied by the duration of engine operation at reduced intake air temperature, is used as a primary criterion to estimate the engine fuel efficiency enhancement due to intake air cooling over the ship routes. The engine intake air cooling potential is limited by its value, available according to engine exhaust heat and the efficiency of heat conversion to refrigeration in the chiller, evaluated by the coefficient of performance (COP). Therefore, it should be determined by comparing both the needed and available values of CDH. The ejector chiller (ECh) was chosen for engine exhaust gas heat recovery to refrigeration as the simplest and cheapest, although it has a relatively low COP of about 0.3 to 0.35. However, the ECh generally consists of heat exchanges which are mostly adapted to be placed in free spaces and can be mounted on the transverse and board side bulkheads in the ship engine room. The values of sucked air temperature depression and engine fuel consumption reduction at varying temperatures and humidity of ambient air on the route were evaluated.

DESIGN FOR AN ALL-ELECTRIC DESIGN FOR SUPPORT IN INITIAL DESIGN USING THE NETWORK BLOCK APPROACH: A SUBMARINE EXAMPLE

The layout of the Distributed Ship Service Systems (DS3) can be a major constraint both on the location of hull berth unit and of transverse bulkheads, with implications for conducting maintenance and so contribute to submarine Sustainability. This paper proposes a new early-stage ship design (ESSD) approach that would aid the designer to consider DS3 features physically and logically much earlier in the design process. The approach is termed the Network Block Approach and combines the advantages of the UCL 3D physically based ship synthesis Design Building Block (DBB) approach and the network-based approach for distributed ship service systems (DS3) synthesis already proposed for naval combatants. The proposed Network Block Approach enables modelling of individual spaces to locate and zone various DS3 components and take account of hull unit boundaries and major bulkheads. The paper discusses the importance of DS3 routing to warship Sustainability through the complexity of a submarine design example and shows how the proposed approach enables this to be explored in ESSD.

Проектирование доковых стоек поперечных переборок корабля

Object and purpose of research. The paper is concerned with interaction of the docking stanchion and the transverse bulkhead plating when a ship is docked. Involvement of the bulkhead plating and vertical pillars closest to the docking stanchion in sustaining the response of the keel track is assessed. The purpose of the study is updating the classical design procedure for docking stanchion where such interaction is ignored. Materials and methods. A plane steel transverse bulkhead of traditional type is considered. Loads on a dry-docked ship are estimated. Finite element method is used. Main results. Studies were conducted using two finite element models: a 2D bulkhead model and a 3D model of ship hull part incorporating bulkhead. Results of calculation by both models are generally in good agreement. It is shown that along with the docking stanchion the keel track response is sustained partly by the bulkhead plating and vertical struts closest to the docking stanchion. Conclusion. The classical design method of docking stanchions was updated, which made it possible to reduce the weight and size of docking stanchions. The formula used to assess the buckling of docking stanchions was corrected.

PARAMETRIC FORMULATION OF THE FLOODABLE LENGTH CURVE: APPLICATION CASE TO OFFSHORE PATROL VESSELS

The residual buoyancy of vessels after damage has a fundamental role in their survivability and it is implemented through adequate ship internal subdivision. Traditionally the number and the position of transverse watertight bulkheads are selected for most ships early in the design phase by means of the “floodable length curve” coupled with the concept of “margin line”. However, for naval vessels, it is more and more common during the acquisition process to explore a wide domain of feasible ships, identified with the assistance of automated processes and assessed also in terms of capabilities, among which is survivability. The generation and the comparison of a considerable number of different ship configurations is very time consuming. Therefore recourse to a parametric expression of the floodable length curve is considered to be a very efficient approach and would thus enable characterisation of the ship, in terms of survivability performance. In this paper such an approach is presented, using an offshore patrol vessel (OPV) as the case study.

Influence of different topological variants on optimized structural scantlings of passenger ship

For a multi-deck ships with extensive superstructures (such as passenger and cruise ships, RoPax, mega yachts, etc.) the global structural response can be particularly complex. The influence of the superstructure to the primary strength for those multi-deck ships must be considered from an early design phase. Main global topological parameters (e.g. size of side openings, position and stiffness of longitudinal and transverse bulkheads, etc.) have dominant influence on the shape of hull girder stress distributions over the ship height. The Taguchi concepts and techniques (FFE, orthogonal arrays, ANOVA, etc.) could be used to systematically study influence of multiple topological parameters on the global structural response obtained by FEM analysis. It also enables rational identification of the most dominant parameters and provide designer with the near-optimal level of each topological parameter for the defined design objective. It has been demonstrated how different topological variants can lead to different optimal structural scantlings w. r.t chosen design objectives (mass, VCG, etc.), using simplified full ship 3D FE model of passenger ship as an example. Structural design software MAESTRO and in-house developed framework for the design support system DeMak – OCTOPUS Designer were used as a structural optimization tool. This paper aim to extend the standard scantling optimization by introducing topological aspects as a first STEP in overall optimization procedure.

Combined backbone application on numerical simulations and a model experiment of a 20,000 TEU container ship

For the large-scale development and large opening characteristics of container ships, the characteristics of springing in waves has become more complex. It is thus urgent to find reasonable equivalent principles to solve the dilemma of simultaneously simulating vertical, horizontal and torsional vibrations in model tests. Meanwhile, to avoid the complexity and time-consuming nature of full three-dimensional modelling, a large-scale combined beam model is adopted to simulate three-dimensional coupled vibrations and the positions of the neutral axis and torsion centre. Combined with the finite element method, a 3D equivalent modelling method of the combined model is analysed in detail, and the stiffness influence of transverse bulkheads on the coupled vibrations mode is revealed. Furthermore, the elastic modal responses, vibration principles and waves load in the fluid-structure interaction vibrations are assessed and investigated by the three-dimensional linear hydroelastic mechanics method in the frequency- and time-domains. Then, the scheme and load measurement method in the model test in the wave basin are put forward, and the experimental data and numerical calculation results are compared and found to be consistent. The proposed the equivalent combined beam model is of great significance for model tests and numerical analyses of very large container ships.

A Study on Preventive Measures for Fatigue Cracking at Welded Joints in Cargo Tank Structure of Chemical Tanker

In the cargo tank structure of the chemical tanker, fatigue cracking at the cruciform welded joint between the transverse bulkhead and the double bottom, which is the most important part under severe stress conditions, can lead to a serious accident.

Учет изгиба килевой балки в расчетах общей и местной прочности корабля при доковании в сухом доке

This paper presents an approximate method for taking into account finite stiffness of bottom grillages in strength calculations of ship installed on one keel track in the dry dock. It compares the approximate method and FEM results for the docking of a 600 t barge platform. The results have shown good correlation. It has been demonstrated that local stresses in the keel near transverse bulkheads might become quite significant.

Fatigue assessment of FPSO hull side shell longitudinals using component stochastic and full spectral method

The emphasis of this work is on comparison of fatigue damage capacity at the bulkhead and web frame connections of side shell longitudinals under the effect of vertical and horizontal bending in combination. Fatigue analysis methods adopted such as component stochastic and full spectral consider an FPSO of 325 m length, selecting side shell longitudinal structural elements connected to the typical transverse bulkhead and web frame at mid ship area. The analyses are being performed in accordance with three loading conditions such as fully loaded, intermediate and ballast condition. This research uses spectral fatigue analysis to create a function of stress transfer that in turn helps generate the power spectral density function by the bending moment transfer function. The combination of spectral moments with the Palmgren-Miner law results in the FPSO's accumulated fatigue damage. The findings provide insight into the changes in fatigue damage of the structural component under the effect of vertical and horizontal bending moments. Not only acting global loads and local pressure are important on the side shell longitudinal elements, but also relative deflections of webs influence the stress response due to additional stiffener bending are required. Due to the large amount of intersection details of side shell longitudinals at transverse web frame and bulkhead and due to high repair costs in case of damage, a sound structural design is thus necessary. The findings and insights developed from the present work are discussed in detail.

Parametric Formulation of the Floodable Length Curve: Application Case to Offshore Patrol Vessels

The residual buoyancy of vessels after damage has a fundamental role in their survivability and it is implemented through adequate ship internal subdivision. Traditionally the number and the position of transverse watertight bulkheads are selected for most ships early in the design phase by means of the “floodable length curve” coupled with the concept of “margin line”. However, for naval vessels, it is more and more common during the acquisition process to explore a wide domain of feasible ships, identified with the assistance of automated processes and assessed also in terms of capabilities, among which is survivability. The generation and the comparison of a considerable number of different ship configurations is very time consuming. Therefore recourse to a parametric expression of the floodable length curve is considered to be a very efficient approach and would thus enable characterisation of the ship, in terms of survivability performance. In this paper such an approach is presented, using an offshore patrol vessel (OPV) as the case study.

Dimensional precision controlling on out-of-plane welding distortion of major structures in fabrication of ultra large container ship with 20000TEU

Ultra large container ship as an essential role during international trade, is required for precision fabrication due to highly efficient TEU loading and unloading. In this study, two major structures, so called watertight transverse bulkhead structure and torsion box structure of ultra large container with 20000TEU were examined for out-of-plane welding distortion prediction and mitigation with measurement and computational analysis. Based on the welding inherent deformation theory, typical welded joints of two major structures were systematically classified with the different material, thickness, welding condition and joining form; and the relationships between welding heat input and inherent deformations were also presented. Elastic FE analysis with shell elements model and welding inherent deformation as input loading was employed for welding distortion prediction. Not only the distributions but also the magnitudes of predicted out-of-plane welding distortions of considered major structures have a good agreement comparing to the measurements. Furthermore, welding sequence influence was considered for dimensional precision controlling during the watertight transverse bulkhead structure fabrication, and welding groove optimization of thick plate was examined for out-of-plane welding distortion mitigation during the torsion box structure fabrication. Computational results show that welding distortions of both ship block structures can be significantly reduced for requirement of fabrication precision.

An automated computational tool for offshore supply vessels’ structural preliminary design

This work presents the application of the rules of the Classification Society American Bureau of Shipping (ABS) for steel vessels in a development of an Excel computational tool that allows to speed up the preliminary structural design calculation process, from several days to minutes, with no precision loss, based on the main particulars and a few structural characteristics, automating everything that does not depend on decision-making. This tool is intended to be a first of a few to perform the required calculations for the preliminary structural design, in this case, applied to Offshore Support Vessels. Once the frame type, the selection of the commercial steel type, and manufacturer are prescribed by the user, all the rules are automatically calculated, all the thicknesses are computed and presented, and rounded up to the commercial values and which reinforcements need to be dimensioned are defined. The user then should dimension these structural elements by selecting the profile type, thickness and height of the web, and thickness and length of the flange, such as stiffeners and/or girders of the bottom, double bottom, sides, double sides, decks, and bulkheads; solid and open floor, side stringers, frames, bottom and deck girders, deck transverses, bulkhead girders, and webs. Besides verifying if the structural strength values are in accordance with the classification society rules in each and every step of the dimensioning process, the program also shows a sketch of the Midship Section that is redrawn at each decision change of the user. The program also verifies the global structural resistance; calculates the steel area, the hull girder section modulus, and moment of inertia; compares these values with the minimum rules requirements; and analyzes if the ship fulfills the longitudinal resistance. Soon after, based on the midship section, the sectional area and the transverse bulkheads positions, the program estimates the steel weight, and center of gravity of the ship. Finally, the user can generate a detailed Report that contains all the information produced by the program, as well as the calculation memory. An application example is presented.

О расчетах прочности и жесткости килеватых днищевых перекрытий и выборе доковых стоек поперечных переборок корабля

This paper explains how to calculate the correction factor for keel inertia moment due to the dead rise of grillage and how to consider bulkhead plating in calculation of dock strut response to keel cribbing. The solutions described in this study are different from the commonly used ones. New formulas have been obtained for taking into account inertia moment of grillages with dead rise, as well as for calculation of Euler stresses in dock struts, and their design algorithm has also been updated. The results offer more accurate calculations of grillages with dead rises and more accurate design of transverse bulkheads in terms of conventional beam models and methods of structural mechanics.

Improvement of the structure of floating docks based on the study into the stressed­deformed state of pontoon

We have investigated the stressed-deformed state of reinforced concrete slabs of the composite dock pontoon with a reduced number of framing sets. A refined estimation scheme was applied in the calculation of bending plates of the slipway-deck and pontoon bottom, which accounts for the work of reinforcement structure in both directions. Accounting for the work of reinforcement structures in both directions makes it possible to accurately estimate the structural strength and provide recommendations on their design in terms of material consumption and optimal size. When modeling work of concrete, we took into consideration that concrete at stretching has a less rigidity for stretching than for compression. It has been shown that the developed design and construction technology of the composite dock with a reduced number of framing sets in the pontoon makes it possible to expand the technological capabilities of dock construction. The results derived from the calculations of cumulative stresses in the slabs of the dock's pontoon stack-deck showed that the actual safety factors meet the requirements for strength. Given that the structure of concrete slabs perceives the moment of resistance that is several times larger than that of steel, it becomes possible to increase the span of a slab and to erect less supports-bulkheads. The result would be the reduced material costs and the decreased labor intensity of operations at dock construction. We have proposed a structure and a construction technology for a composite dock with a reduced number of framing sets in the pontoon. It has been shown that the erection of transverse bulkheads between the inner boards in 4 quadrats, that is, in 3 meters, as well as the absence of lack frames, and floors and beams, in concrete towers, makes it possible to reduce the amount of materials, as well as bring down the labor intensity of dock construction. This paper lists features for the selection of shipbuilding concrete intended to withstand extreme operating conditions of marine reinforced-concrete structures

Application of Neural Network and Genetic Algorithm in Subdivision Optimization

It is complicated and time consuming to evaluate the anti-wind capability of a damaged ship. This paper tries to find a way to estimate the ship’s anti-wind capability after damage comprehensively with some simplified conditions. The index representing anti-wind capability of damaged ship comprehensively is named “Average Anti-wind Capability”. When the change of watertight bulkheads’ position is not big, with a series of data calculated by NAPA and programs developed by author, Artificial Neural Network improved by genetic algorithm is applied to study the nature of functional dependency between the“Average Anti-wind Capability” and the positions of transverse watertight bulkheads. Then, genetic algorithm is also employed to find the best combination of watertight bulkhead, making the ship have the best anti-wind capability after damage. This method is verified to be feasible and effective by example calculation.

Analysis of Corrugated Bulkhead against Transverse Plane Bulkhead in a Tanker Ship

Ship is built from thousands of integrated construction materials. The selection of a strong and efficient construction material is significant since it directly affects the weight of the ship. For a watertight bulkhead in a tanker ship, there are two kinds of bulkhead construction which are transverse plane bulkhead and corrugated bulkhead. The selection of these two bulkhead constructions for watertight bulkhead is based on the bulkhead strength analysis as well as bulkhead weight. The analysis was conducted using an engineering structural analysis software by comparing the bulkhead structural configurations which has the same von Misses tension. For corrugated bulkhead, corrugation angle was simulated between 45°- 90° while for transverse plane bulkhead, the range of stiffener distances was simulated between 400-1400 mm. The result shows that minimum corrugated bulkhead weight which is 41.18 ton can be obtained on the corrugation angle of 60o with the structural efficiency ratio of 1.79% - 30.91% while for transverse plane bulkhead, minimum weight of bulkhead which is 71.175 ton can be obtained on the stiffeners distance of 600 mm with structural efficiency ratio of 2.62% - 60.25%. It can be seen that for the same von Misses tension, corrugated bulkhead construction is more efficient in terms of bulkhead weight and cost with the difference weights of almost 30 ton.