Search

Monopile foundations contain welding residual stresses and are widely used in industry to support offshore wind turbines (OWTs). The monopiles are subjected to hammering loads during installation and cyclic loads during operation, therefore the influence of residual stress redistribution as a result of fatigue cycles must be evaluated in these structures. The existing empirical models to predict the residual stress redistribution in the presence of cyclic loading conditions are strongly dependent on the material, welding process and loading conditions. Hence, there is a need to predict the residual stress redistribution using finite element simulations. In this study numerical analyses have been conducted to predict the initial state of residual stress in a simplified weld geometry and examine the influence of subsequent cyclic loads on the relaxation behavior in residual stress profiles. The results have shown that fatigue cycles have a severe effect on residual stress relaxation with the greatest reduction in residual stress values observed in the first cycle. Moreover, the numerical prediction results have shown that the stress amplitude plays a key role in the extent of residual stress relaxation in welded structures.

Background Despite primary percutaneous coronary intervention (PPCI) is generally considered the best therapy in older frail adults with ST-segment elevation myocardial infarction (STEMI), the incidence of re-hospitalization for cardiovascular diseases remains significant in these patients. Aims We hypothesized that thrombus aspiration (TA) before PPCI could be a useful treatment for reducing mortality and rehospitalizations in frail patients undergoing PPCI for STEMI. Methods We conducted a study comparing PPCI alone vs TA + PPCI in frail STEMI patients. We examined a cohort of consecutive frail patients aged ≥ 65 years with first STEMI treated with PPCI between February 2008 and July 2015 at the Department of Cardiology of the “Cardarelli” Hospital in Naples, Italy. Results The study was completed by 389 patients (PPCI: 195, TA + PPCI: 194). At 1-month follow-up, the rate of death from any cause was 7.0% in patients treated with PPCI alone vs 3.0% in patients treated with TA + PPCI (p 0.036), whereas death from cardiovascular causes was 6.0% in the PPCI group vs 3.0% in the TA + PPCI group (p 0.028). Equally important, the rate of re-hospitalization due to heart failure was 7.5% in the PPCI group vs 4.0% in TA + PPCI group (p 0.025) and the rate of re-hospitalization due to acute coronary syndrome was 10.0% in the PPCI group vs 4.5% in the TA + PPCI group (p 0.016). Conclusion These results indicate the importance of TA in the treatment of STEMI in a group of high-risk patients such as elderly with frailty.

The aim of this study is to investigate the technical feasibility of an innovative vertical axis floating wind turbine concept with the main focus on the design and verification of the mooring system. The study is developed through iterative processes in order to identify the optimum design for the new floating wind turbine concept. The Ultimate Limit State (ULS) criteria have been considered to verify the integrity of the mooring system in the extreme environmental conditions with a 50-year return period. For this purpose, time domain dynamic analysis has been performed using the commercial software OrcaFlex [Orcina website, OrcaFlex software, https://www.orcina.com/ ]. Although the analysis is carried out for a specific site deemed suitable for the project, the results can be used as an input for any future application in other locations. The present study is intended to be a proof of concept with a proposed scientific framework for optimization of the mooring system which is considered to be a crucial part in the design of floating wind turbines due to their complex dynamic behavior.

In an age where sailing boats are losing their reputation of slow-moving vehicles, and where technologies are developing at explosive rhythm, the scantling criteria are deeply changing and naval ar...

Ship surveys are hazardous and expensive tasks as long as they are carried out by human surveyors to a large extent. The adoption of robotic means can enhance safety by replacing some human operations, filling the gap between the current approach and available robotic technologies, even from a regulatory point of view.The ROBINS project (ROBotics technology for INspection of Ships) is a collaborative project co-funded within the H2020 EU Research and Innovation programme call, aimed at addressing the possible advantages of using robotics technology for inspection of ships, facing the corresponding challenges. In such a framework, a Testing Facility (TF) is built up and protocols are developed to test and assess robotic capabilities in carrying out inspections at least at the same quality level of humans’ ones.

This paper deals with the fatigue assessment of three ship structural details. While local approaches, which are proposed in relevant literature and which nowadays are also widely applied i...

The anti-ballistic properties of a new advanced composite armor system have been investigated with the aim to minimize the armor system total weight per unit area. The innovative protection, made of a silicon carbide ceramic outer layer and an inner composite back-packing layer formed by ultra-high molecular weight polyethylene (UHMWPE) fibers, namely $$\hbox {Dyneema}^\circledR $$ Hard Ballistic 26, was realized and then tested performing dedicated ballistic impact tests. In order to investigate its permanent deformation, ceramic cracking, dimension of the rupture, and extension of the impact damage, nondestructive and destructive tests were conducted on the tested panels. The experimental results were used to develop and validate a transient nonlinear dynamic simulation model of the high-velocity impact of a 7.62 AP bullet on the tested armor system. After an accurate setting of the parameters involved in the description of the material constitutive models and of the involved physical phenomena, a complex numerical model was developed in the $$\hbox {ANSYS-Autodyn}^\circledR $$ environment using both mesh and meshless approaches at the same time. The comparison reveals a good agreement between experimental and computational results in terms of ballistic properties, deformations, fragmentation, and fracture of the ballistic armor system. Hence, a new numerical model for the design and the optimization of the ballistic efficiency of composite armor systems was developed and can be now used in current practice.

This paper describes the large-scale testing and the finite element simulations of the collapse of a steel-composite joint, both bolted and bonded. The joined structures are typical ones of shipbuilding and namely of naval ships. Composite superstructures, beside a valuable weight reduction, may improve the signature features of the ship by embedding installed electronic devices into a composite mast. In the frame of a broader research project, including the electromagnetic characterization of the composite structures, also the structural design and its optimization were exploited, embracing, among other issues, the joining solutions between the steel deck structures to the composite ones of the superstructure side shell. A large-scale specimen of the joint was conceived and collapse tested while, in parallel, design simulations were carried out at different levels of detail. Eventually, a complete description of the collapse of the joint, including the nonlinear simulation by finite element analysis of the progressive failure of the composite laminates of the side shell was obtained and test results were used to validate the numerical models. Depending on the design stage, various scantling procedures, from a very simplified one to a rather complex and time-consuming numerical analysis, can now be applied to verify the structural behavior of these steel to composite joints as well as to select the most cost-effective solution among several options.

A Fluid-Structure Interaction (FSI) conventional case study is proposed to be used as a benchmark for numerical analyses. Experimental tests were carried out to provide targets for comparisons; in particular, the study regarded the estimate of the deformed configuration ("flying shape" in the sailing field) of a square sail under a uniform flow regime in a wind tunnel facility. Several tests have been carried out at different wind velocities. The sailcloth has been characterized by means of mono-axial tensile tests obtaining Young's and shear moduli as well as Poisson's coefficients, which have then been used as input parameters for numerical analyses. Test results are considered a benchmark target deserving challenging aspects for numerical simulations in spite of the selected simple test geometry and conditions. Numerical tests have been carried out by means of a commercial software (ADINA™). Analyses used a strongly coupled partitioned approach between a Finite Volume Method (FVM) based on Reynolds Averaged Navier Stokes (RANS) equations, whereas a Finite Element Method (FEM) has been adopted for the structural field. A comparison has been eventually carried out assessing different numerical models. A good overall agreement between experimental and numerical results has been obtained by suitably setting FSI simulation algorithms.

In this paper, we report our study on a numerical fluid-structure interaction problem originally presented by Mok et al. (2001) in two dimensions and later studied in three dimensions by Valdes Vazquez (2007), Lombardi (2012), and Trimarchi (2012). We focus on a 3D test case in which we evaluated the sensitivity of several input parameters on the fluid and structural results. In particular, this analysis provides a starting point from which we can look deeper into specific aspects of these simulations and analyze more realistic cases, e.g., in sails design. In this study, using the commercial software ADINA™, we addressed a well-known unsteadiness problem comprising a square box representing the fluid domain with a flexible bottom modeled with structural shell elements. We compared data from previously published work whose authors used the same numerical approach, i.e., a partitioned approach coupling a finite volume solver (for the fluid domain) and a finite element solver (for the solid domain). Specifically, we established several benchmarks and made comparisons with respect to fluid and solid meshes, structural element types, and structural damping, as well as solution algorithms. Moreover, we compared our method with a monolithic finite element solution method. Our comparisons of new and old results provide an outline of best practices for such simulations.

The interest in floating offshore wind turbines (FOWT) has been growing substantially over the last decade and, after a number of prototypes deployed [1], the first offshore floating wind farms have been approved and are being developed. While a number of international research activities have been conducted on the dynamics of offshore floating HAWT systems (e.g. OC3-Phase IV2, OC4-Phase II3), relatively few studies have been conducted on floating VAWT systems, despite their potential advantages [2]. Due to the substantial differences between HAWT and VAWT aerodynamics, the analyses on floating HAWT cannot be extended to floating VAWT systems. The main aim of the present work is to compare the dynamic response of the FOWT system adopting two different mooring dynamics approaches. Two version of the in-house aero-hydro-mooring coupled model of dynamics for VAWT “FloVAWT” [3] are used: one which adopts a mooring quasi-static model, and solves the equations using an energetic approach [4], and a modified version of FloVAWT, which uses instead the lumped-mass mooring line model “MoorDyn” [5]. The floating VAWT system considered is based on a 5MW Darrieus type rotor supported by the OC4-Phase II3 semi-submersible. The results for the considered metocean conditions show that MoorDyn approach estimate larger translational displacements of the platform, compared to the quasi-static rigid approach previously implemented in FloVAWT. As expected, the magnitudes of the forces along the lines are lower, being part of the energy employed for the elastic deformation of the cables. A systematic comparison of the differences between the two approaches is presented.

Traditionally, propeller design has been focused on all activities necessary to obtain a propeller featuring a high efficiency, avoiding erosive cavitation for given operating conditions and having adequate structural strength. In recent years, more and more challenging requirements have been imposed, such as the reduction of radiated noise and pressures pulses, requiring more precise analyses and methods in the optimization of the propeller performance. On the other hand, the evaluation of the propeller strength still relies on simplified methods, which basically consider the blade as a cantilever beam subjected to characteristic static forces. Since the loads acting on a blade are variable in the blade revolution and in different operating conditions throughout the ship life, a procedure to account for the influence of fatigue phenomena is proposed. The fatigue assessment could reduce the safety factor in the propeller scantling rules and allow improving the quality of propeller design (e.g. obtaining higher efficiency, margin on cavitation phenomena, less noise).

During the fabrication of two different structures (a ship and a bridge), made by mild construction steel, some unacceptable anomalies were detected; the structures were almost completely fabricated and a repair of the defected structural details was impractical due to the extent of the defected zones. A fitness-for-service assessment has therefore been carried out, in both cases, by performing fatigue tests on representative samples, cut off from the structure and by evaluating the fatigue resistance curve. A re-assessment of the structural details in question was undertaken, on the basis of the experimental S-N curve, evaluating the fitness for service of the “defected details”. The experimental tests showed that the detected anomalies had no influence on the fatigue strength of the welded joints and that the examined details (a butt joint and a cruciform joint) behave in accordance with the relevant FAT classes. The experimental program has also given the opportunity to compare different methodologies for fatigue assessment: the Effective Notch Stress Method, the Fracture Mechanics Method and the Peak Stress Method. The different procedures have been applied to the tested specimens, and the expected fatigue life was compared with the experimental one.

The aim of this paper is to study the concept of shear lag effective breadth of plating, widely applied in the scantling assessments of metallic ship structures, for the special case of composite hull stiffened plating. Indeed, geometries and material behaviour are rather different and the definition of the effective breadth is worthy of investigation. A broad literature survey highlighted that the case of composites is almost not covered by previous studies and that only simplified empirical formulations are proposed for effective breadth evaluations in the rules of classification societies. Thus, suitable finite element models were created and validated to investigate the behaviour of the effective breadth of stiffened laminates when varying geometrical and other typical parameters of composite made ship structures. It was found useful to switch from stresses to strains in the effective breadth definition, considering the anisotropy of the material. An extensive sensitivity analysis allowed assessing th...

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...

This paper deals with an experimental/numerical comparison of the interlaminar shear stress in typical marine composite laminates manufactured according to two different fabrication processes, namely vacuum infusion and pre-impregnated lay-up. Experimental tests were carried out at the Marine Structures Testing Lab of the University of Genova. Actually, among widely applied empirical formulations for the characterization of composites suggested by Classification Societies rules, the ones for the interlaminar shear strength appear the most scattered because of the complexity in assessing failure phenomena. Composite manufacturers generally carry out rather extensive tests for the complete characterization of the laminates. Due to non-linearities involved in the captioned study, the support of nonlinear numerical models was required. The aim of the comprehensive use of numerical approaches is the reduction of time-consuming and expensive experimental campaigns. Three different FE modeling strategies are proposed in order to verify the reliability of the numerical results in comparison with experimental targets. The merits and shortcomings of each are discussed, also comparing different types of finite element formulations and mesh refinement sensitivity.

This paper deals with the buckling behavior of composite sandwich columns under compressive loading. Namely, finite element (FE) modeling strategies are discussed with the aim to test a suitable and cost effective solution for assessing the buckling behavior of delaminated sandwich laminates. Indeed, pleasure craft industry is now facing the challenge of thinner and thinner skin laminates. Buckling, that in past years was not a governing limit state because of rather high thicknesses and of limited spans of structural elements, should be now assessed possibly accounting for actual defects, i.e. delaminations, and applying straightforward but cost-effective approaches, easy to implement in the everyday practice of composite hull structural design. A suitable test case, available in open literature, was selected and results of the proposed modeling strategy are compared with experimental ones as well as with other numerical estimates, showing its capabilities and addressing hints for FE application.

Ducted propellers, in decelerating duct configuration, may represent a possible solution for the designer to reduce cavitation and its side effects, that is, induced pressures and radiated noise; however, their design still presents challenges, due to the complex evaluation of the decelerating duct effects and to the limited amount of available experimental information. In the present paper, a hybrid design approach, adopting a coupled lifting line/panel method solver and a successive refinement with panel solver and optimization techniques, is presented. In order to validate this procedure and provide information about these propulsors, experimental results at towing tank and cavitation tunnel are compared with numerical predictions. Moreover, additional results obtained by means of a commercial RANS solver, not directly adopted in the design loop, are also presented, allowing to stress the relative merits and shortcomings of the different numerical approaches.

This paper deals with the buckling strength of typical ship stiffened panels built in fibreglass composite laminates. The results obtained applying analytical formulations based on equilibrium and potential energy equations are compared with the ones obtained by linearised eigenvalue analyses of rather detailed finite-element models. Analytical formulations consider an elementary panel only, accounting for the boundary effects of stiffeners surrounding its edges, while FE models fully describe the interactions among plate and stiffeners as a whole. A sensitivity analysis to highlight the most influencing parameters in the problem is also presented. So far no systematic scantling assessment of buckling behaviour of hull shell and deck panels seems to be recommended by classification societies’ rules for pleasure crafts made in composite materials. Thus, this paper aims at illustrating the application limits of analytical methods, natural candidates to become the basis of rule requirements. Difficulties in ...

A sensitivity analysis is applied to a reliability model for fatigue life calculations of typical welded joints based on fracture mechanics. The aim is to select the most influencing parameters, before and after inspection updating. A literature survey allowed to provide an overview of the input parameter values, looking at reducing as far as possible the complexity of the numerical model and at identifying the most influencing ones.

Ship structures are likely to be subject to age-related deterioration such as corrosion wastage, cracking or mechanical damage. It has reportedly been recognised that such age-related deterioration is almost always involved in the catastrophic failures of ship structures including total losses. While such accidents typically cause concern to the public, maintenance and repair of aged structures is quite costly and complex. It is thus of great importance to develop advanced technologies allowing for proper management and control of such age-related deterioration. This paper summarises the report of the ISSC 2006 Committee V.6 presenting current practices, recent advances and future trends on condition assessment of aged ships. This includes assessment of the structural condition in view of the serviceability and safety, methods for repair, quantification of strength of deteriorated and repaired ships (as well as criteria for acceptable damage), with due account of the uncertainties involved. Consi...