The effect of longitudinal rails on an air cavity stepped planing hull

The use of ventilated hulls is rapidly expanding. However, experimental and numerical analyses are still very limited, particularly for high-speed vessels and for stepped planing hulls. In this work, the authors present a comparison between towing tank tests and CFD analyses carried out on a single-stepped planing hull provided with forced ventilation on the bottom. The boat has identical geometries to those presented by the authors in other works, but with the addition of longitudinal rails. In particular, the study addresses the effect of the rails on the bottom of the hull, in terms of drag, and the wetted surface assessment. The computational methodology is based on URANS equation with multiphase models for high-resolution interface capture between air and water. The tests have been performed varying seven velocities and six airflow rates and the no-air injection condition. Compared to flat-bottomed hulls, a higher incidence of numerical ventilation and air–water mixing effects was observed. At the same time, no major differences were noted in terms of the ability to drag the flow aft at low speeds. Results in terms of drag reduction, wetted surface, and its shape are discussed

Assessment of Damage Evolution in Sandwich Composite Material Subjected to Repeated Impacts by Means Optical Measurements

Abstract In the last decade, sandwich composite materials have had an increasing use in design of racing boats. The main reasons are: higher strength-weight ratio, low density, excellent durability and versatility. The knowledge of impact response is very important to design racing boats. The aim of the present study is the investigation of absorbing impact energy ability of a sandwich composite material used for offshore vessels in UIM (Unione Internationale Motonautique) Championship. The material analysed in this study is a sandwich manufactured with hand lay-up technique. In the first phase, the damage assessment of single impact has been studied with an optical measurement technique. In a second phase, the damage evaluation due to repeated impacts has been analysed with the similar technique

A comparative life cycle assessment of utility poles manufactured with different materials and dimensions

In the production of utility poles, used for transmission, telephony, telecommunications or lighting support, for many years, the steel has almost entirely replaced wood. In recent years, however, new composite materials are a great alternative to steel. The questions are: is the production of composite better in terms of environmental impact? Is the lifecycle of composite pole more eco-sustainable than lifecycle of steel pole? Where is the peak of pollution inside the lifecycle of both of technologies? In the last years, in order to deal with new European polices in environmental field, a new approach for the impact assessment has been developed: the Life Cycle Assessment. It involves a cradle-to-grave consideration of all stages of a product system. Stages include the extraction of raw material, the provision of energy for transportation and process, material processing and fabrication, product manufacture and distribution, use, recycling and disposal of the wastes and the product itself. A great potentiality of the Life Cycle assessment approach is to compare two different technologies designed for the same purpose, with the same functional unit, for understanding which of these two is better in terms of environmental impact. In this study, the goal is to evaluate the difference in environmental terms between two different technologies used for the production of poles for illumination support

A preliminary method for the numerical prediction of the behavior of air bubbles in the design of air cavity ships

Air-cavity ships (ACS) are advanced marine vehicles that use air injection under hull to improve the vessel’s hydrodynamic characteristics. Although the concept of drag reduction by supplying gas under the ship’s bottom was proposed in the 19th century by Froude and Laval, at this time there are not many systematic studies on this subject. This paper is a preliminary work with the purpose of being a basic tool for the design of the ACS with computational fluid dynamic methods. The study aims to conduct a series of computational tests to compare the numerical models of bubble with experimental data. The first step of this study was to investigate the behavior of free bubble in water, considering as parameters the critical mass of air, the rising speed and aspect ratio of the bubble. Then it is evaluated the interaction bubble-flat plate in order to obtain a reliable prediction of the behavior of air bubbles under the hull

Sail Plan Parametric CAD Model for an A-Class Catamaran Numerical Optimization Procedure Using Open Source Tools

A geometric tool for a catamarans sail plan and appendages optimization procedure is descripted. The method integrates a parametric CAD model, an automatic computational domain generator and a Velocity Prediction Program (VPP) based on a combination of sail RANS computations and analytical models. The boat performance is obtained, in an iterative process, solving the forces and moment equilibrium system of equations. Hull and appendages forces are modelled by analytical formulations. The closure of the equilibrium system is provided by the CFD solution of the sail plan. The procedure permits to find the combination of appendages configuration, rudders setting, sail planfonn, shape and trim that maximize the VMG (Velocity Made Good). A significant effort was addressed to the selection and evaluation of open-source tools to be adopted in the implementation of the method. The geometric parametric model, which is the core of the procedure, was object of particular attention. The FreeCAD geometric modeller was selected for this task. The sail shapes candidates are automatically generated, within the optimization procedure, by Python scripts that drive FreeCAD to update the geometry according to the variables combination A very flexible model, able to offer a very wide space of variables, was implemented. This paper describes the implemented geometric model and the environment in which is included

Composite sandwich impact response: Experimental and numerical analysis

The use of composite materials allows to have a great flexibility in terms of mechanical and physical characteristics. One of the most used composite structure in naval field, is the sandwich, which is composed by a stacking sequence of different plies. The designer, in preliminary phase, must handle a great quantity of degree of freedom (types of materials, orientation of the fibres, position along the stack, thickness, etc.) in order to reach the best compromise between mechanical behaviour, environmental impacts and production costs. Finite Element analysis represents a useful tool in order to optimize all these parameters and to estimate the outcome of experimental tests at design stage. The main goal of this work is to develop and to validate a FE model for the simulation of a particular family of composites, widely used in naval field and, in particular, in High Speed Crafts and powerboats. The first part of the paper concerns the experimental tests on two different types of sandwich specimens. Two families of tests were conducted: four-point bending tests and impact drop tests. The second part of the paper focuses on the validation of a FE model for both experimental setups

Fluid-structure interaction of downwind sails: a new computational method

The spreading of high computational resources at very low costs led, over the years, to develop new numerical approaches to simulate the fluid surrounding a sail and to investigate the fluid\ue2\u80\u93structure interaction. Most methods have concentrated on upwind sails, due to the difficulty of implementing downwind sailing configurations that present, usually, the problem of massive flow separation and large displacements of the sail under wind load. For these reasons, the problem of simulating the fluid\ue2\u80\u93structure interaction (FSI) on downwind sails is still subject of intensive investigation. In this paper, a new weak coupled procedure between a RANS solver and a FEM one has been implemented to study the FSI problem in downwind sailing configurations. The proposed approach is based on the progressive increasing of the wind velocity until reaching the design speed. In this way, the structural load is also applied progressively, therefore, overcoming typical convergence difficulties due to the non-linearity of the problem. Simulations have been performed on an all-purpose fractional gennaker. The new proposed method has been also compared with a classic weak FSI approach. Comparable results have been obtained in terms of flying shape of the gennaker and fluid-dynamic loads. The most significant characteristic of the proposed procedure is the easiness to find a solution in a very robust way without convergence problem, and also the capability to reduce the simulation time with regard to the computational cost

Human face reconstruction in biomedical applications

3D virtual reconstruction of human body parts is nowadays a common practice in many research fields such as the medical one, the manufacturing of customized products or the creation of personal avatar for gaming purpose. The acquisition can be performed with the use of an active stereo system (i.e., laser scanner, structured light sensors) or with the use of a passive image-based approach. While the former represents a consolidated approach in human modeling, the second is still an active research field. Usually, the reconstruction of a body part through a scanning system is expensive and requests to project light on the patient’s body. On the other hand, the image-based approach could use multi-photo technique to reconstruct a real scene and provides some advantages: low equipment costs (only one camera) and rapid acquisition process of the photo set. In this work, the use of the photogrammetry approach for the reconstruction of humans’ face has been investigated as an alternative to active scanning systems. Two different photogrammetric approaches have been tested to verify their potentiality and their sensitivity to configuration parameters. An initial comparison among them has been performed, considering the overall number of points detected (sparse point cloud reconstruction, dense point cloud reconstruction). Besides, to evaluate the accuracy of the reconstruction, a set of measures used in the design of wearable head-related products has been assessed