Scantling Design Research Articles

A rational approach for the scantling design of GRP pleasure crafts

In various fields of industrial engineering, including naval architecture, structural design is considered one of the most challenging steps by designers as it shall accommodate all other design aspects, likely already defined in earlier steps. Moreover, structures need to comply with specific requirements, i.e. limit states, while also performing in accordance with user's demands in terms of mission profile. In a goal-based design perspective, limit state criteria have to be defined accounting for both, structural robustness, functional and operational demands. Construction feasibility is an issue as well, further constraining the scantling design. Balancing construction needs, ship performances and structural aspects is not always an easy task.The environment in which a ship operates is indeed complex and verification of safety and robustness is usually carried out in accordance with classification societies and other rules, possibly applying direct calculations whenever applicable rules do not provide suitable solutions. At the same time, the asset needs to fulfill various attributes specified by the owner. As a matter of facts, the scantling design is mathematically a multivariate and over-constrained problem whose feasible solutions are in fact rather few. In the case of composite pleasure craft hull structures, while the number of design variables increases, feasibility constraints also largely reduce the design space.To address these challenges, designers may nowadays exploit new procedures able to reduce structural weight, though ensuring that the asset performs safely and adequately meeting client's requirements. To achieve this, designers may combine a more rational design philosophy with currently available numerical problem-solving applications to obtain a rational trade-off among all actually feasible solutions, which are relatively few.Thus, the objective of this study is to present a dependable numerical method for determining the scantling while reducing the weight of hull composite structures of pleasure crafts. This method aims to provide the most suitable, high-performing, and safe layout in the quickest and easiest possible manner. It turns out that counterintuitive, yet feasible and fit-for-purpose, structural lay-outs can be obtained.

Ship weight reduction by parametric design of hull scantling

In this paper, a semi-automatic design procedure for concept and preliminary phases of hull structural design is described. It allows investigating the design of ship structures, consisting of a series of stiffened panels surrounded by primary members, assembled to form the hull girder. The optimal configuration of the structural lay-out and the best scantling of each structural component (i.e. platings, ordinary stiffeners and primary elements) is provided, accounting for interactions among all structural components as well as integration of primary, secondary and tertiary responses. The proposed method allows the minimization of the overall weight of hull blocks intended as the sum of stiffened panels’ weight (shell and stiffeners) plus that of the surrounding primary members. A dedicated application in VBA language (Visual Basic for Applications) has been developed in which scantling checks have been implemented by applying a few rules formulations after a comprehensive analysis of involved variables defining the state of the hull structural system. The proposed scantling design approach is very practical, it follows well-known hull structural design principles and it takes advantage of the nowadays widely available computation means to update the traditional sequence of the scantling checks in a more rational way and to select the optimal lay-out scantling solutions among truly feasible ones.

A design approach to reduce hull weight of naval ships

ABSTRACT Hull weight is a design parameter affecting the whole performances of a ship, being related to building costs, operational costs, maintenance and durability, and not least to satisfaction of functional requirements. Naval ships are no exception and impact of hull weight is crucial to fulfil mission requirements. In the light of the above, weight reduction is one of the main design drivers and it should be duly accounted for since the concept design phase. In this paper, a design approach intended for pre-contractual design phases is presented. It takes advantage of recent developments and trends of construction rules as well as of nowadays-available computation potential to update and improve the traditional scantling design approach, applied since decades by designers. The complexity and computational burden is kept to a minimum to provide a user-friendly procedure applicable in everyday working practice. Designers’ experience and judgment continue to drive the whole process. A Visual Basic support software has been developed with worksheet interfaces to implement the proposed scantling design procedure. Test cases showed significant weight reductions with respect to as-built ships and to scantling obtained by applying traditional design procedures.

Analysis and Design of Steel a Floating Pontoon Jetty for Use in the Coastal Waters of Nigeria

Floating pontoons are semi-permanently moored structures on a water body to provide boarding access to commuters. The decision to develop such structures was informed by the need to provide berthing access to river crafts that operate on the coastal waters of Bayelsa State, Nigeria. In this project, a floating pontoon, a gangway, and other supporting structures like scantlings and spud pillars, were designed to meet the needs and environmental requirements of the area. Standards consulted are the DNV Rules for the classification of ships; DNV Rules for the classification of Floating Docks; ABS Rules for Building and Classing Steel Barges; and other relevant Nigeria and Imo standards. The pontoon designed has dimensions: 13 x 12 x 4.8 m; gross tonnage of 15 tonnes; 2nos. of dry tanks of capacity 17.2 m³ and 6nos. of manholes of 450 x 550 mm. The strength of materials analysis was limited to the floating pontoon for limitations of space for this paper. The pontoon and scantling design has been done based on the worst condition of design pressure which is for the maximum submersion draft. Normal grade steel of yield strength 235 MPa is chosen for all members except the pontoon girders, frames and pillars. This is to reduce the material scantlings and to ensure higher strength with lesser scantlings. Longitudinal framing is adopted in the pontoons as the pontoon structure needs more strength in the longitudinal direction.

Analysis and Design of Steel a Floating Pontoon Jetty for Use in the Coastal Waters of Nigeria

Floating pontoons are semi-permanently moored structures on a water body to provide boarding access to commuters. The decision to develop such structures was informed by the need to provide berthing access to river crafts that operate on the coastal waters of Bayelsa State, Nigeria. In this project, a floating pontoon, a gangway, and other supporting structures like scantlings and spud pillars, were designed to meet the needs and environmental requirements of the area. Standards consulted are the DNV Rules for the classification of ships; DNV Rules for the classification of Floating Docks; ABS Rules for Building and Classing Steel Barges; and other relevant Nigeria and Imo standards. The pontoon designed has dimensions: 13 x 12 x 4.8 m; gross tonnage of 15 tonnes; 2nos. of dry tanks of capacity 17.2 m³ and 6nos. of manholes of 450 x 550 mm. The strength of materials analysis was limited to the floating pontoon for limitations of space for this paper. The pontoon and scantling design has been done based on the worst condition of design pressure which is for the maximum submersion draft. Normal grade steel of yield strength 235 MPa is chosen for all members except the pontoon girders, frames and pillars. This is to reduce the material scantlings and to ensure higher strength with lesser scantlings. Longitudinal framing is adopted in the pontoons as the pontoon structure needs more strength in the longitudinal direction.

3D Topology Optimization of Fixed Offshore Structure and Experimental Validation

In this study, we performed a three-dimensional (3D) topology optimization of a fixed offshore structure to enhance its structural stiffness. The proposed topology optimization is based on the solid isotropic material with penalization (SIMP) method, where a volume constraint is applied to utilize an equivalent amount of material as that used for the rule-based scantling design. To investigate the effects of the main legs of the fixed offshore structure on its structural stiffness, the leg region is selectively considered in the design domain of the topology optimization problem. The obtained optimal designs and the rule-based scantling design of the structure are manufactured by 3D metal printing technology to experimentally validate the topology optimization. The behaviors under compressive loading of the obtained optimal designs are compared with those of the rule-based scantling design using a universal testing machine (UTM). Based on the structural experiments, we concluded that by employing the topology optimization method, the structural stiffness of the structure was enhanced compared to that of the rule-based scantling design for an equal amount of the fabrication material. Furthermore, by effectively combining the topology optimization and rule-based scantling methods, we succeeded in enhancing the structural stiffness and improving the breaking load of the fixed offshore structure.

Development of design factor predicting the ultimate strength for wide spacing in container curved bilge structures

The aim of the present study is to develop a curvature factor to estimate the ultimate strength and the progressive collapse behaviour of a stiffened curved plate under combined in-plane compression and lateral pressure. Stiffened curved plates are used in various parts of ship and offshore structures, such as bilge structures, columns and the inside structures of offshore semisubmersible rigs. The curvature of a cylindrically curved plate is found to increase the buckling strength and ultimate strength compared with a plate without curvature. Based on the numerical results of a series of nonlinear finite element calculations for all edges with symmetric curved plating with varying parameters such as slenderness ratio, stiffener size, flank angle and amplitude of lateral pressure, an empirical design factor is derived to predict the curvature influence for a fundamental scantling design by rule guidance. The outcomes can be widely referred to in basic designs to decide the required bilge thickness during local scantling.

Dynamic buckling of masts of large sail ships

The design of sail systems is a fascinating topic that naval architects have been facing since many centuries and nowadays is revived because of the increasing size of modern pleasure and racing yachts. It is hence surprising that empiricism largely drives mast and rigging design even at the present time. Actually, while structural dynamics is explicitly considered in current scantling design of hull structures, this is not usually the case for mast and rigging. However, numerical simulations can now be successfully applied to assess effects of load variations in time. Considering the governing limit states and the typical behaviour of a pre-tensioned slender structure, the dynamic buckling of the bottom panel of a typical large mast is evaluated in this paper, showing significant differences from the widely applied quasi-static approach. The obtained results provide a new perspective for the scantling assessment of sail systems, overcoming the current empirical and prescriptive approach proposed by rules of classification societies and international standards.

Scantling multi-objective optimisation of a LNG carrier

Numerous real-world problems related to ship design can be solved by various alternatives. However, the scantling design has conflicting objectives such as minimum production cost, minimum weight and maximum moment of inertia (stiffness). Therefore a multi-purpose solution had to be settled in order to meet all these requirements at once. Ship design is a complex endeavour requiring successful coordination of many different disciplines, both technical and non-technical. Basic design is the least defined stage of the ship design process and seeks to define the optimal amidships section structure. For that purpose, recent improvements have been made to a numerical tool in order to optimise the scantling of ship sections by considering production cost, weight and moment of inertia in the optimisation objective function. A multi-criteria optimisation of a LNG carrier is conducted in this paper to illustrate the analysis process. Pareto frontiers are obtained and results have been validated by the Bureau Veritas rules. The methodology presented in this paper has demonstrated its effectiveness in optimising scantling of ships at a very early design stage thanks to a management of critical problems usually studied at a later stage of the design.

The lengthening of a small chemical tanker: a comparison of class scantling rules

The classification societies' rules have been updated and improved dramatically in the last years, crossing from empirically-based and prescriptive rules to more rational rules based on reliability analyses and recommending design criteria rather than codifying design scantlings. However, the complexity of the new rules needs to be faced by computer software issued by the class societies themselves. This article presents the results of some preliminary structural design calculations, carried out according to five different classification societies' rules (BV, DnV, GL, LR and RINA) and using the associated softwares, on a small double hull tanker built in the nineties. In view of the possible lengthening of the ship, the scantling design has been carried out on the midship section, aiming to compare the different rules, requirements and criteria before and after lengthening. An analysis of general check formulations has been firstly carried out, highlighting similarities and differences in the scantling criteria. Then, results of the exercise have been compared to evaluate the best solution for lengthening, and rules requirements have been commented on in the light of the methods and criteria previously reported with the aim to contribute to the rules harmonization process.