Side Shell Research Articles

Crash concepts for CFRP transport aircraft – comparison of the traditional bend frame concept versus the developments in a tension absorbers concept

ABSTRACTDue to their inherently brittle behaviour, carbon fibre reinforced plastics (CFRP) structures demand for a specific design to achieve appropriate crash energy absorption compared to classical metallic fuselage designs. In this paper, experimental as well as numerical studies on two different crashworthy designs are presented. The first concept aims to absorb the crash energy by crushing of CFRP components below a reinforced cargo cross beam in combination with further energy absorbing devices in the lower side shell. The feasibility of this concept was in the meantime proven by tests at the coupon and structural element level. An alternative crash concept making use of energy absorption in so-called tension absorbers in the passenger and cargo floor structure was developed and assessed with the focus on a reduction of structural mass in combination with improved concept robustness. This paper provides a summary of the performed research work and discusses the context of the concept development. Details on the individual research tasks can be found in further publications which are given in the references.

Development of Design Formula for Predicting Post-Buckling Behaviour and Ultimate Strength of Cylindrical Shell

Cylindrical shells are often used in ship structures at deck plating with a camber, side shell plating at fore and aft parts, and bilge structure part. It has been believed that such curved shells can be modelled fundamentally by a part of a cylinder under axial compression. From the estimations with the usage of cylinder models, it is known that, in general, curvature increases the buckling strength of a curved shell subjected to axial compression, and that curvature is also expected to increase the ultimate strength. We conduct series of elasto-plastic large deflection analyses in order to clarify the fundamentals in buckling and plastic collapse behaviour of cylindrical shells under axial compression. From the numerical results, we derive design formula for predicting the ultimate strength of cylindrical shell, based on a series of the nonlinear finite element calculations for all edges, simply supporting plating, varying the slenderness ratio, curvature and aspect ratio, as well as the following design formulae for predicting the ultimate strength of cylindrical shell. From a number of analysis results, fitting curve can be developed to use parameter of slenderness ratio with implementation of the method of least squares. The accuracy of design formulae for evaluating ultimate strength has been confirmed by comparing the calculated results with the FE-analysis results and it has a good agreement to predict their ultimate strength.

Problems in the Application of Low Voltage Circuit Breakers for Gassing Material

Polyoxymethylene (POM) and nylon 66 (PA 66) represent polymer gassing materials as arc extinguishing chamber side plate or shell were widely used in low voltage circuit breaker. During the short-circuit breaking test of the low voltage circuit breaker, the problems such as pressure, temperature, poisonous and harmful gas, etc. were found for gassing material application. In the application of low voltage circuit breaker, the existence of these problems has an effect on the performance of the low voltage circuit breaker and has the potential safety hazard. In this paper, these above problems were analyzed, the models were established, and the suggestions were put forward. That can optimize the application of gassing material in low voltage circuit breaker, and improve the performance of low voltage circuit breaker.

Application of chamfered narrow face mold technology to reduce longitudinal surface crack defects of hyperperitectic steel generated during flexible thin slab casting process

Mold wear can occur at the interface between slab and mold when slab moves downward through the mold during casting. Longitudinal surface cracks in continuous casting process of slab are closely related with inadequate amount of narrow face taper. Optimizing inner structure and adjusting taper of narrow face mold were helpful in improving contact situation between mold and solidified shell to achieve uniform solidifying shell and to avoid forming longitudinal surface cracks. A chamfered narrow face mold for flexible thin slab casting process was developed and implemented successfully in industrial production process. The relationship between wear profiles of narrow face mold and occurrence of longitudinal surface cracks has been researched. The results show that a chamfered narrow face mold can effectively compensate the narrow side shell shrinkage along slab width direction to reduce the occurrence of longitudinal surface cracks.

Design of four-beam IH-RFQ linear accelerator

The multi-beam acceleration method is an acceleration technique for low-energy high-intensity heavy ion beams, which involves accelerating multiple beams to decrease space charge effects, and then integrating these beams by a beam funneling system. At the Tokyo Institute of Technology a two beam IH-RFQ linear accelerator was developed using a two beam laser ion source with direct plasma injection scheme. This system accelerated a carbon ion beam with a current of 108mA (54mA/channel×2) from 5 up to 60keV/u.In order to demonstrate that a four-beam IH-RFQ linear accelerator is suitable for high-intensity heavy ion beam acceleration, we have been developing a four-beam prototype. A four-beam IH-RFQ linear accelerator consists of sixteen RFQ electrodes (4×4 set) with stem electrodes installed alternately on the upper and lower ridge electrodes.As a part of this development, we have designed a four-beam IH-RFQ linear accelerator using three dimensional electromagnetic simulation software and beam tracking simulation software. From these simulation results, we have designed the stem electrodes, the center plate and the side shells by evaluating the RF properties such as the resonance frequency, the power loss and the electric strength distribution between the RFQ electrodes.

Applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures

In design and operation of floating offshore structures, one has to avoid fatigue failures caused by action of ocean waves. The aim of this paper is to investigate the applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures. The applicability was investigated for Bluewaters’ FPSO (Floating Production, Storage and Offloading) which had been turret moored at Sable field for half a decade. The waves were predicted as sea-state time series consisting of one wind sea and one swell. The predicted waves were compared with wave data obtained from ERA-interim and buoy measurements. Furthermore, the fatigue calculations were also carried out for main deck and side shell locations. It has been concluded that predicted fatigue damages of main deck using WaveWatch-III are in a very good agreement regardless of differences in predicted wind waves and swells caused by differences in wave system partitioning. When compared to buoy measurements, the model underestimates fatigue damages of side shell by approximately 30 %. The reason for that has been found in wider directional spreading of actual waves. The WaveWatch-III wave model has been found suitable for the fatigue assessment. However, more attention should be paid on relative wave directionality, wave system partitioning and uncertainty analysis in further development.

Nonlinear structural behaviour and design formulae for calculating the ultimate strength of stiffened curved plates under axial compression

Cylindrically curved and stiffened plates are often used in ship and offshore structures. For example, they can be found in the cambered decks, fore and aft side shells and circular bilge parts of ships. A number of studies have investigated curved plates in which the buckling/ultimate strength is increased according to the curvature under various loading scenarios and design formulas. However, information regarding the nonlinear structural behaviour and design formulas for calculating the ultimate strength of the stiffened curved plates is currently limited. In this paper, a series of finite element analyses are performed on stiffened curved plates with varying geometric parameters. The existing curvatures are also analysed to clarify the effects of these parameters on the buckling/post-buckling characteristics and collapse behaviour under axial compression. The results are used to derive closed-form expressions to predict the ultimate compressive strength of curved stiffened plates for marine applications.

Optimization of heat transfer and pressure drop characteristics via air bubble injection inside a shell and coiled tube heat exchanger

Most recently, a couple of academic investigations have focused on air bubble injection (with a constant air flow rate) inside the shell-and-coiled-tube heat exchangers in order to increase the performance and effectiveness of these heat exchangers. However, the amount of air flow rate has great effects on these applications which have not been probed in previous studies. Moreover, in former papers, air flow has been injected inside the only shell side and not coil side of heat exchanger. Hence, in this experimental research, air bubbles is flowed inside the shell or coil side of heat exchanger with variant air flow rates to detect an optimum condition and also fill out this topic. Air flow rate was changed between 1LPM and 5LPM. Coil side water flow rate was kept at 1LPM (inlet temperature of 40°C) and shell side water flow rate was varied between 1LPM and 5LPM (inlet temperature of 15°C). Furthermore, pressure drop due to bubble injection is measured in this paper for aforesaid heat exchangers as another new parameter. Observations showed that the air flow rate and injection side (shell and coil) play key roles on the effect of bubble injection into the heat exchangers. Findings showed that, increment of air flow rate causes enhancement of overall heat transfer coefficient. Air injection into the shell side of the heat exchanger increased the overall heat transfer coefficient 6–187% depending on air flow rate.

A probabilistic approach for optimizing inspection, monitoring, and maintenance actions against fatigue of critical ship details

Fatigue is one of the main deteriorating mechanisms that affect the safety and reliability of ship structures. Fatigue cracks can appear at various locations along the ship structure and may occur at early stages in the service life of a ship. Inspection, monitoring and/or repair actions are applied to prevent sudden failures of damaged structural components and their associated consequences. However, these actions increase the operational cost of the ship and should be optimally planned during its service life. Due to the presence of significant uncertainties associated with crack initiation and propagation, the planning of such actions should be performed probabilistically. In this paper, a probabilistic approach for inspection, monitoring, and maintenance optimization for ship details under fatigue effects is proposed. Based on the stress profile and the crack geometry at the damaged location, intervention times and types are determined by solving an optimization problem which simultaneously minimizes the life-cycle cost, maximizes the expected service life, and minimizes the expected maintenance delay over the life-cycle. The life-cycle cost includes the cost of inspection, monitoring, and maintenance actions, as well as the cost of failure of the detail. The proposed approach is applied to a side shell detail of a steel ship.

Characteristics analysis of local ice load signals in ice-covered waters

The aim of this paper is to investigate the characteristics of the signal of local ice load acting on side shell in the bow part due to ice broken by an icebreaker in ice-covered waters. The Korean icebreaking research vessel “ARAON” voyaged to the Arctic Ocean during the summer of 2010, and measurements of local ice load were carried out using several strain gauges. In this study, the time history of measured signals was analyzed and the characteristic values including rising time and half-decaying time were presented using non-dimensional parameters.

FLEXURAL STRENGTH ANALYSIS OF LAMINATED BAMBOO SLATS (BAMBUSA ARUNDINACEA) FOR CONSTRUCTING A SMALL FISHING BOAT SHELLS

Because of the advantages of bamboo and the decreasing supply of teak, as a material for the construction of small Indonesian fishing boats, bamboo becomes an alternative substitute for teak as a common material to construct this type of boat. There are many bamboo species and populations in Indonesia which form the basis for selecting an advanced alternative material to construct fishing boats. This study discusses the mechanical properties of laminated bamboo slats, with a polyamide epoxy adhesive made by employing a manual cold press method. The type of bamboo used was the Bambusa Arundinacea variety that was greater than 3 years old. The bamboo laminate flexural strength was tested using the ASTM D 3043 Standard. The results of these tests revealed that the flexural strength of the laminated bamboo slats provided bending strengths of MOR and MOE values of 84.12 MPa and 18.04 GPa respectively. By using MOR and MOE values, and based on Bureau Classification of Indonesia (BKI), the shell thickness of 30 GT a fishing boat was calculated to be 25 -28 mm (bottom shell) and 19 -21 mm (side shell). These dimensions showed that the shell thickness can be reduced up to 33.3% when compared with teak (Tectona Grandis ) and the total volume of shell material to build a 30 GT of fishing boat, can be reduced by approximately 30%. The flexural strength of the bamboo slat laminate was shown to be 20% higher than 2nd class solid teak.

An analytical method for predicting the ship side structure response in raked bow collisions

As an increasing number of ships continue to sail in heavy traffic lanes, the possibility of collision between ships has become progressively higher. Therefore, it is of great importance to rapidly and accurately analyse the response and consequences of a ship's side structure subjected to large impact loads, such as collisions from supply vessels or merchant vessels. As the raked bow is a common design that has a high possibility of impacting a ship side structure, this study proposes an analytical method based on plastic mechanism equations for the rapid prediction of the response of a ship's side structure subjected to raked bow collisions. The new method includes deformation mechanisms of the side shell plating and the stiffeners attached. The deformation mechanisms of deck plating, longitudinal girders and transverse frames are also analysed. The resistance and energy dissipation of the side structure are obtained from individual components and then integrated to assess the complete crashworthiness of the side structure of the struck ship. The analytical prediction method is verified by numerical simulation. Three typical collision scenarios are defined in the numerical simulation using the code LS_DYNA, and the results obtained by the proposed analytical method and those of the numerical simulation are compared. The results correspond well, suggesting that the proposed analytical method can improve ship crashworthiness during the design phase.

Welding Hot Cracking of Side Shell of Drilling-Well Oil Storage Ship

Cracks were found in the weld metal (WM) of weld-section of side shell of drilling-well oil storage ship when performing post weld radiographic examination. The cracks were subjected to detailed metallographic analysis and the fracture surfaces were observed visually and using SEM. The results indicate that the cracks were embedded in middle of multiple beads of WM. The fracture surface reveals the dendritic solidification structure of WM, which contains impurity element sulfur and other alloy elements (Ti, Al, and O) originating from the filler core of welding wire. The embedded cracks are a type of weld hot crack, the solidification crack. The failure mechanism is identified to be welding hot cracking.

해빙과의 접촉 면적을 고려한 국부 빙압력 추정 연구

Ice loads may be conveniently categorized as local ice loads and global ice loads. Local ice loads are often defined as ice pressures acting on local areas of shell plates and stiffeners. Therefore, local ice loads are defined in all ice class rules. However, directly measuring the local ice pressure using the actual ice class vessel is a very difficult task because appropriate instruments for direct measurement must be installed on the outer hull, and they are easily damaged by direct ice contacts/impacts. This paper focuses on the estimation of the local ice pressure using the data obtained from icebreaking tests in the Arctic sea in 2010 using the Korean icebreaking research vessel (IBRV) ARAON. When she contacted the sea ice, the local deformation of the side shell was measured by the strain gauges attached to the inside of the shell. Simultaneously, the contact area between the side shell and sea ice is investigated by analyzing the distribution of the measured strain data. Finally, the ice pressures for different contact areas are estimated by performing a structural analysis.

Computational analysis and design formula development for the design of curved plates for ships and offshore structures

In general, cylindrically curved plates are used in ships and offshore structures such as wind towers, spa structures, fore and aft side shell plating, and bilge circle parts in merchant vessels. In a number of studies, it has been shown that curvature increases the buckling strength of a plate under compressive loading, and the ultimate load-carrying capacity is also expected to increase. In the present paper, a series of elastic and elastoplastic large deflection analyses were performed using the commercial finite element analysis program (MSC.NASTRAN/PATRAN) in order to clarify and examine the fundamental buckling and collapse behaviors of curved plates subjected to combined axial compression and lateral pressure. On the basis of the numerical results, the effects of curvature, the magnitude of the initial deflection, the slenderness ratio, and the aspect ratio on the characteristics of the buckling and collapse behavior of the curved plates are discussed. On the basis of the calculated results, the design formula was developed to predict the buckling and ultimate strengths of curved plates subjected to combined loads in an analytical manner. The buckling strength behaviors were simulated by performing elastic large deflection analyses. The newly developed formulations were applied in order to perform verification analyses for the curved plates by comparing the numerical results, and then, the usefulness of the proposed method was demonstrated.

Finite element crack propagation analysis of shear loaded buckling panels

Purpose – In former work, test results of cracks in aluminium panels under cyclic shear buckling showed that cracks in the tensile stress field of a buckle propagate. The main influencing factor for the crack growth rate is the maximum principle stress. A simplified approach for crack propagation analyses based on this finding showed limitations for application on larger cracks because it disregarded the increasing out-of-plane deformation for larger cracks as well as stress redistributions. The purpose of this paper is to improve the results of the simplified approach with the help of finite element method (FEM). Design/methodology/approach – An approach for crack propagation based on FEM is presented taking into account the mutual interaction of cracks and buckling. The finite element (FE) model, which is described in detail, respects the boundary conditions of the test-set-up. Different initial crack positions, loads and panel thicknesses are analyzed. Results of the stress intensity factors KI calculated by the ABAQUS® FE model provide a function which is used to run a crack propagation analysis based on Forman law. Findings – The results of the FE-based crack propagation solution are in good agreement with test results and improve the prediction of the simplified approach. It is not restricted in terms of panel thickness, crack position or applied shear load. Research limitations/implications – Limitations of the FE-based crack propagation solution compared to the experimental results are discussed. These are, the sensitivity of crack propagation analyses to initial crack length and deviations of the experimental settings from the ideal FE model. Originality/value – The interaction of cracks and buckling in aluminium shells is mainly disregarded both in research and industrial work, but can be of interest considering, accidental damages in fuselage side shells. Cracks propagate under shear load as it was shown in former work. The FE modeling of the tests presented in this paper proves the mutual interactions of crack propagation and buckling deformation.

북극해에서의 쇄빙시 국부 빙하중 계측 신호에 대한 파형 분석

The aim of this study is to investigate the characteristics on the profile of local ice load acting on side shell of port side in bow part due to broken ice during icebreaking of ships in ice covered waters. The first Korean icebreaking research vessel `ARAON` had a sea ice field trial in the Arctic Sea during early August, 2010, and the signals due to local ice impact measured from several strain gauges installed at bow part were gathered. It is known that these data with structural response characteristics due to local ice impact have some different characteristics with a typical hydraulic impact pressure - time history. In this study, the time history on the measured signals was analyzed and the characteristic values were presented using non-dimensional parameters.

Calculated and prescribed stress concentration factors of ship side longitudinal connections

Stress concentration factors (SCFs) of typical details of the connection of the side shell longitudinals and the web frame stiffeners are among the most important issues of ship fatigue analysis. Classification societies propose pre-defined values of SCFs, obtained by experimental analysis and a limited number of finite element (FE) calculations on similar details. In this paper, SCFs are calculated by the FE method, using shell elements and are then compared with their prescribed values according to the rules of classification societies. FE analysis is performed for various configurations of the detail that may appear in practice. A simplified procedure for calculating fatigue life is employed and discrepancies in calculated fatigue life caused by differences in SCFs are assessed. The methodology of calculating SCFs is verified based on the FE analysis of details with derived target hot spot stress and corrected SCFs are thus obtained. Influence of the correction of SCFs on the fatigue life is discussed. Different procedures for extrapolating stresses to the weld toe are considered and the resulting SCFs are compared with the values proposed by rules of classification societies. The results of the study may be used in the harmonization process of ship structural rules and within fatigue reliability analyses. Another obvious motivation for this paper is that nowadays a detailed FEA can be carried out in most design offices and the presented results may help to enhance such applications.

Fatigue damage assessment of corroded oil tanker details based on global and local stress approaches

Fatigue damage assessment of double hull oil tanker structural details is performed, based on global and local structural finite element models. The wave-induced vertical and horizontal bending moments, as well as local pressure loads are accounted for in the fatigue damage calculations. Local stress analyses are considered based on the notch stress approach. Time-dependent stresses as a function of corrosion deterioration are analyzed based on nonlinear corrosion wastage during the design life of ship. The effective notch stress approach is applied for analyzing the stress distributions and the fatigue damage of the welded joint at two hotspots. The hotspots are located between the flat bar stiffener of a transverse web frame and the flange of a longitudinal stiffener at the side shell of a tanker ship hull. The details under consideration are modeled separately in a fine mesh employing the sub model techniques. Finally the fatigue damage assessment accounting for corrosion deterioration of the considered hotspots is analyzed.

Study on Casting Speed and the Speed of on-Line Mould Width Adjustment of Slab Continuous Casting

Starting from the analysis of stresses on narrow side shell, based the principle that the stresses of narrow side shell will be less than the hot strength of cast steel grade, the maximum rate of displacement in course of freely bulging under hydrostatic pressure is deduced in this paper. And the speed of width adjustment is set based on which. Meanwhile the strain on wide side shell in width adjustment process is calculated. According to critical strain hypothesis, after investigation a proper casting speed is set to make the strain of wide side shell less than the critical strain and so to ensure the shell thickness in exit of mold meeting with production requirements.