Web Frame Research Articles

선수 플레어 구조손상 해석

In rough seas, bow-flare regions of the sea-going ships are subject to high impact pressures due to the bow-flare slamming and panting. And many ships suffer structural damages in that region, even though they were built under the bow structure strengthening rules of the ship classes. So, a new design method for bow-flare structure is highly required. In this paper, bow-flare damage analysis is performed for 17 ships (total number of damage/non-damage data is 782). Based on this analysis, a new design standard and method for bow-flare structure (shell plate, frame and web frame) is proposed. 80.4% of the present damage/non-damage data were well-explained by this new design standard.

함정의 최적 구조 설계에 관한 연구

함정은 선급의 규정을 받지 않고 독자적인 기준을 가지고 설계된다. 본 연구는 함정 설계에 적용되는 가장 권위 있는 기준이라고 할 수 있는 미해군의 규정을 중심으로 그 특성과 개념을 소개하고, 개별적인 기준이 구조 설계 시에 반영되었을 때의 설계 결과에 대해 분석함으로써 설계자가 규정식 적용의 영향을 파악하는데 도움을 주고자 하였다. 또한 함정의 최적 구조 설계를 위하여 미해군 규정에 기초하고 구조 해석 이론을 접목한 최적 설계 방법을 제시하고, 실제 함정에 대해 적용하여 봄으로써 제시된 방법의 유용성을 보였다. 본 방법의 적용 결과 종보강재와 횡늑골의 간격과 같은 주요 설계 변수가 함정 중앙 단면의 설계 결과에 미치는 영향이 분석 가능하며, 최적의 중앙 단면 설계가 얻어 질 수 있었다. Naval vessels are not regulated by the class rules, but by the special regulations. This study introduces the concept and characteristics of the regulations of U.S. Navy which has been the most reliable standards in design of naval vessels in Korea, and intends to help designers to comprehend the effect of each regulation on design results. Also, an optimum structural design method combined with the structural analysis theory is proposed for naval vessels following the regulations of U.S. Navy and is applied to the design of a naval vessel. After application of the optimum design method, its validity is shown and an optimum design of midship section is obtained. In addition, the optimum spaces or longitudinals and transverse web frames are found and the effect of main design variables can be investigated.

Transverse strength analysis of catamarans

Stresses and deformations relevant for transverse strength analysis are calculated for a 60 m catamaran by a compartment model and are compared with corresponding results from a global model. It is found that the flexibility of the partial bulkheads typical for a twin-hull Ro/Ro-vessel is so large that the interaction with the surrounding structure has to be accounted for. If springs are applied, the results are sensitive to the spring stiffness. A web frame model that does not include any bulkheads, gives large errors and is not recommended.

Optimal Area Use in Orb Webs of the Spider Araneus diadematus

We studied the abilities of the garden cross spider Araneus diadematus regarding adaptation of web geometry to spatial constraints. Spiders reacted to a spatial reduction in their building site from a square-shaped frame to a slimmer, rectangular frame (side ratio 1 : 2) by maintaining overall web geometry while reducing the web area covered by the sticky capture spiral. However, when the frames were changed further to a rectangular side ratio of 1 : 3, the spiders changed specific web properties in such a way that a further reduction in the capture spiral area was prevented. Construction of the threads making up the web frame and the auxiliary spiral requires that the spider explores the spatial constraints of its building site. The geometry of both frame and auxiliary spiral threads in turn determine the geometry of the capture threads. Since in very narrow frames the spider adjusted the auxiliary to suit the subsequent capture spiral, we suggest that an initial spatial survey led to the final adaptation of overall web geometry to a web site.

The mechanical design of spider silks: from fibroin sequence to mechanical function.

Spiders produce a variety of silks, and the cloning of genes for silk fibroins reveals a clear link between protein sequence and structure-property relationships. The fibroins produced in the spider's major ampullate (MA) gland, which forms the dragline and web frame, contain multiple repeats of motifs that include an 8-10 residue long poly-alanine block and a 24-35 residue long glycine-rich block. When fibroins are spun into fibres, the poly-alanine blocks form (&bgr;)-sheet crystals that crosslink the fibroins into a polymer network with great stiffness, strength and toughness. As illustrated by a comparison of MA silks from Araneus diadematus and Nephila clavipes, variation in fibroin sequence and properties between spider species provides the opportunity to investigate the design of these remarkable biomaterials.

Spectral fatigue damage calculation in the side shells of ships, with due account taken of the effect of alternating wet and dry areas

A method for calculating the wave load induced fatigue damage in ship side shells in connections between longitudinals and transverse web frames is presented. The method is based on the Miner–Palmgren fatigue damage formulation and a spectral approach is used to determine the necessary variances of the stress processes. The traditional linear frequency domain analysis is expanded in order to incorporate the non-linear nature of the external water pressure. The pressure process is determined by use of pressure RAOs, and not as previously by relative motion RAOs. Effects of load combinations are included in the method, both combinations of the global vertical and horizontal hull girder bending and combinations of the combined global bending with the local pressure induced load process. The proposed method is used to analyze a double hull tanker, and the results show reasonable agreement with results published by other authors. Effects of load combinations are shown to be significant, and especially it is confirmed that the external pressure is very important to include in the analysis as it accounts for the majority of the calculated damage.

Fatigue Reliability of Maintained Welded Joints in the Side Shell of Tankers

A formulation is presented for the assessment of the reliability of a local ship hull structure regarding fatigue failure. The potential cracks are considered to occur in the side shell, in the connections between longitudinal stiffeners and transverse web frame. The analysis is performed for T-shaped stiffeners. The model accounts for the crack growth process applying linear elastic fracture mechanics. The long-term stress range acting on the elements is defined as a function of the local transverse pressure of internal cargo and outside water, combined with the stresses resulting from the longitudinal bending of the hull. The global hull loading is a combination of horizontal and vertical bending moments. The present paper analyzes the importance of including the transverse pressure loading for the process of the crack growth and also the distribution of the net section area of midship and location of stiffeners. The formulation has been applied to a tanker. The fatigue reliability is predicted by a time variant formulation and the effects of maintenance actions in updating the reliability assessment are shown.

Vibration Analysis of the Structure in Contact with Fluid by use of Thin Plate Boundary Element Method

This paper presents the numerical procedure for solving the fluid-structure interactive vibration of a three dimensional complicated structure such as the stiffened plate, deep girder, transverse ring and so on. So far, a classical boundary element method has been widely used for estimating the added mass effect. of the fluid surrounding the structure. However, when the plate thickness is relatively thin, the previous method may not. be applicable because the numerical error is not neglected to evaluate the fluid loading effect. on the plate. Thus, a new program code TPBEM is developed and applied to determine the distribution of the dynamic pressure on the thin circular plate and the web frame model. Some of the calculated results are compared with measured ones and the validity of the present. method is discussed.

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.

Model illuminates spider silk structure

A model for the molecular architecture of spider dragline silk—from which spiders spin their web frames—may take materials scientists a step closer to synthesizing fibers that mimic silk in tensile strength and toughness. Dragline silk outperforms rubber and rivals high-performance synthetic fibers in both mechanical properties. Spider silk contains large amounts of glycine (42%) and alanine (25%), as well as amino acid residues such as glutamine and tyrosine that have bulkier side groups. Much of the alanine is organized into repeating polypeptide sequences that adopt a β-sheet conformation. Cornell University researchers Alexandra H. Simmons, Carl A. Michal, and Lynn W. Jelinski focused on the polyalanine segments because they are believed to account for the crystalline fraction (about 30%) of dragline silk. In the group's model [ Science , 271 , 84 (1996)] the semicrystalline polymer consists of two interconnected crystal phases embedded in an amorphous matrix. 'This is the first time that the presence...

A study on the optimum structural design of surface effect ships

Abstract In this study, a method to design hull structures of surface effect ships with minimum weight is proposed, and computer programs following the method are also developed. The proposed method considers structural characteristics inherent to surface effect ships by rational structural analyses, but adopts a simplified analysis model to enhance computing efficiency during optimization process. The proposed method uses design loads and strength criteria suggested by the class rules of DnV, but the interaction effect of longitudinal girders and transverse web frames are considered by the simple and accurate grillage analysis method. As design of the midship section is accomplished through optimum design of partial structures such as stiffened plates and complex girders and frame structures, global optimization of all design variables is avoided and computing efficiency is raised. And also, the proposed method contains the simple torsional strength and analysis routine and optimization process of transverse bulkheads against pitch connection moment. Applying the proposed method to ship design, 20% reduction of hull weight was confirmed, and it can be shown that hull weight varies with the change of frame space and there exists optimum frame space.

Fatigue damage in the side shells of ships

More than 40% of the registered fatigue cracks in ship structures are observed to occur in the side shell, more specifically in the connections of longitudinals to transverse web frames. The fatigue damage is caused partly by vertical and horizontal wave-induced hull bending and partly by outside water pressure on the side shell. Due to the non-linear nature of the outside water pressure the fatigue damage of the combined stress cannot be solved via a traditional frequency domain analysis. This paper solves the combination problem by application of a realistic wave model. The proposed model is used to analyze a segregated ballast tanker, and the results are compared to previously registered fatigue cracks. The analysis shows that it is very important to include the water pressure in the fatigue analysis, as this accounts for the majority of the expected fatigue damage. The analysis is performed for both I-shaped and L-shaped stiffeners.

Strength Estimation Method of Ship Side Structures Subjected to Hard Bow Collision

In the collision of hard and sharp bows breaking of ship side structures starts from the collided point of bow, while in the collision of soft and rounded bows breaking is likely to start from the supported point such as bulkhead or transverse web frame. In the case of breaking from collided point stretching of ship side structures is followed by crack propagation, so absorbed energy should be evaluated in consideration of crack propagation.In this paper to develop an evaluation method for breaking from collided point, double hull panel models, which are typical as ship side structures of VLCC, were destructed with the indentation of rigid bow model which was pushed dynamically as well as statically. In the first crack initiation condition was investigated by FEM simulation using fine mesh solid element models and crack initiation was found to be estimated with the ductile damage parameter which consists of equivalent plastic strain and stress triaxiality. Then crack propagation condition was investigated by FEM simulation using coarse mesh shell element models. It was found that reduction of the reaction force due to crack propagation could be simulated by finding the elements adjacent to the crack and reducing the failure strain for those elements.

Residual stresses at a longitudinal stiffener — Web frame intersection and their effects on crack growth

Stress coining at geometrical discontinuities may introduce compressive residual stresses which will lower the propagation of surface cracks and thus increase the fatigue life. In a non-linear finite element analysis, the residual stresses after welding of a transverse web-frame to a ship hull plating is first estimated. Stress coining of one corner of a longitudinal cut-out in a transverse web-frame is then simulated in detail. The calculated residual compressive tangential stresses in the corner of the cut-out is seen to lower the propagation of edge cracks. Experiments performed on web-frames taken from a shipyard after manufacturing show indeed that large tensile residual stresses exist in the web-frame after welding. Stress coining is therefore believed to have a beneficial effect on the fatigue life.

Effect of Fluid in Ships Tanks on The Behavior of Double Hull VLCCs in Collision

In structural design and optimization of a double hull tanker, it is important to understand the behavior of its hull structure and energy absorption mechanism in collision and grounding accidents. It is also important to predict its hull energy absorption capacity and resulting damage in such an accident. To this purpose, numerical simulation is being increasingly used. However, due to practical reasons, i. e. model size and computer resources, ship collision simulations are carried out neglecting the fluid in cargo tanks. Fluid (liquid cargo) in cargo tanks may have an important effect on deformation configuration and failure of inner side plating. This, in turn, may affect the total energy absorbed by the struck ship until failure of inner side plating and spillage of oil.This paper reports the results of a numerical study carried out to investigate such effect of fluid in ships tanks. A structural member of a tank side structure consisting of one typical side longitudinal of a VLCC is considered together with the inner side plating adjacent to it (one longitudinal spacing, one half above and one half below the considered longitudinal). The span is taken as the distance between two successive web frames. This structure is modeled with finite shell elements. A volume of fluid representing liquid cargo adjacent to the member is modeled in an Euler mesh. Forced motion representing collision at the middle of the member is imposed. Comparisons of the behavior of the member in absence of and in presence of the fluid are carried out.The study shows that when the fluid inside a tank has enough space to move, such as in a partially filled tank, its effect on absorbed energy is small. On the hand, in a full tank, where only a small space is available for the fluid to move, normally about 2 % of the tank volume, Energy absorption capacity of side structure may be drastically reduced.

Secondary web‐flange interaction in framed‐tube buildings

AbstractIn the conventional plane‐frame model of framed‐tube buildings, only the primary interaction between the web frame and the flange frame is considered, through vertical shear transfer at corner columns. In addition to this, a secondary interaction takes place due to horizontal shear transfer at each floor level, through the floor slab having high in‐plane rigidity. This interaction causes a discrepancy in member forces of a few bottom and top storeys. A simple modification is suggested in the form of an additional cantilever column connected to the conventional plane‐frame model by axial force transfer members at every floor level. The improved model yields member forces in all the storeys that are very close to those obtained using 3D analysis.

The computation of prismatic structures, applied to naval architecture

In shipbuilding, most long vessels (barges, oil tankers, bulk carriers, etc.) are substantially prismatic in shape in the central region of their structure. These vessels have geometrical characteristics which make their calculation difficult, especially when the shell and plate panels which compose them are heavily stiffened. One of the most challenging aspects of these structures is the computation of stresses and displacements (stress analysis). Consequently, the objective of this study was to develop a tool which allows the computation of such structures, reducing to the greatest extent the simplifications and approximations related to the representation of the structural geometry, the loading and the interdependence of the various elements (such as shell plating, stiffeners, deck beams, web frames and stringers). To analyse the behaviour of each stiffened panel, the stiffened sheathing software L.B.R.-3 is presented, as well as some specific developments required for shipbuilding design. This is a new analytical method using Fourier series expansions to solve the differential equations of orthotropic prismatic shells. Using as an example the stress analysis of a tanker, the L.B.R.-3 software demonstrates its utility and efficiency in giving easily accurate stresses and displacements at every point of the structure.

Frame junction vibration transmission with a modified frame deformation model

A previous paper dealt with vibration transmission through junctions of connected frame members where the allowed frame deformations included bending, torsion, and longitudinal motions [J.A. Moore, J. Acoust. Soc. Am. 88, 2766-2776 (1990)]. In helicopter and aircraft structures the skin panels can constitute a high impedance connection along the length of the frames that effectively prohibits in-plane motion at the elevation of the skin panels. This has the effect of coupling in-plane bending and torsional motions within the frame. This paper discusses the transmission behavior through frame junctions that accounts for the in-plane constraint in idealized form by assuming that the attached skin panels completely prohibit inplane motion in the frames. Also, transverse shear deformation is accounted for in describing the relatively deep web frame constructions common in aircraft structures. Longitudinal motion in the frames is not included in the model. Transmission coefficient predictions again show the importance of out-of-plane bending deformation to the transmission of vibratory energy in an aircraft structure. Comparisons are shown with measured vibration transmission data along the framing in the overhead of a helicopter airframe, with good agreement. The frame junction description has been implemented within a general purpose statistical energy analysis (SEA) computer code in modeling the entire airframe structure including skin panels.

A Simplified Racking Analysis of a Car Carrier by Using Symbolic Calculations

In this paper a simplified analysis is proposed for the selection of structural systems of a car carrier, whose transverse structural system has wise variations such as a partial bulkhead system and a strong web frame system depending on the relevant design philosophies. Introducing a simple beam model, which can be solved by a symbolic manipulation procedure, one can observe that the racking deformation of the transverse section is mainly influenced by the non-dimensional shearing rigidity defined in the present analysis. Comparing the partial bulkhead and strong web frame systems, the shearing rigidities at the bulkhead sections having the latter system is considerably small, and correspondingly is racking deformation obtained by the simplified analysis is several times larger than that of the former system. In order to predict the racking deformation of actual ships having various transverse rigidities, an effective method is proposed, where the simple beam analysis using symbolic calculations is combined with the numerical data obtained by precise three-dimensional structural analyses of ships having similar principal dimensions. The validity of the proposed method is confirmed by comparing the predicted values with the precise numerical results.

THE “NO FRAME” CONCEPT —IT'S IMPACT ON SHIPYARD COST

ABSTRACTA proposed cost effective alternative to current U.S. Navy structurally configured hulls is presented in this paper. This proposed design for producibility concept involves the elimination of structural stanchions and transverse web frames. The potential impact of this “no frame” concept on structural design, weight and construction and material costs for naval surface frigates and destroyers is reflected in 1) reduced costs for the installation of distributive systems and 2) a reduced number and complexity of structural details providing a more reliable and less costly structure.This study was performed in three parts: 1) Determine the most feasible length between bulkheads without frames; 2) Using this length perform detail weight studies and construction and material costs analysis comparison on a 72‐foot long hull module, with and without frames, for a FFG‐7, and 3) Estimate the saving in man hours of labor on the installation of distributive systems and shipfitting for an FFG‐7.For the feasible length studies on the “no frame” structural configuration, thirty‐seven strength, weight and vertical center of gravity studies were performed on two ship classes; twenty‐two on the FFG‐7 class and fifteen on the DD‐963 class. The detailed weight studies and construction and material cost analyses were conducted for FFG‐7 “no frame” and “as built” modules. Results indicating the “no frame” concept module was 6.8% heavier and 14.8% less costly than the “as built” module.For the impact of an FFG‐7 “no frame” structurally configured hull on the cost of labor required for the installation of distributive systems and for other functional work such as ship fitting, welding, and electrical, this study indicated a reduction of 169,206 labor hours per ship, representing 7.12% of the total required man hours to fabricate an FFG‐7 class ship.With the employment of the “no frame” concept, certain areas of significant concern and potential risk were addressed. These include: 1) the actual impact on structural weight and cost, 2) the actual impact on the installation of distributive systems and on other functional systems, 3) effects on a typical opening in a “no frame” structurally configured deck, 4) secondary (hydrostatic) load induced bending moments and shear forces at longitudinal beam and transverse bulkhead intersections, and 5) the vibrational response of a “no frame” structurally configured deck.