River transport by Barges : Resistance and Directional Stability Problems

River transport of bulk goods and liquids is mostly carried out by barges, especially on long distances, and it can be pushed or towed. The transport by pushed barges is safer and generates less resistance, but in some cases the transport with towed barges is required. In the latter case it must be ensured a good route-keeping to the barges, in order to be easily controlled and sure from getting out of the planned route and to be stranded on a shore. In general the route keeping is guaranteed by couples of stern skegs, which must be designed according to the barge typology. In a river navigation also the effects due to shallow water and the river currents must be taken into account. In this paper the mentioned problems will be explained in detail and some results obtained with experiments with model barges in an experimental tank will be presented

L'utilizzo dell'aria quale elemento ausiliario per la riduzione della resistenza all'avanzamento delle carene

Air is often used as a lifting element, to support and sustain a high speed craft, by generating an aircushion at high pressures. The air can be used also as a lubrication system on a faired bottom of a fast or slow boat, by generating artificial cavities, which reduce the boat viscous resistance. Russian researchers, at Krylov Institute of St. Petersburg, studied these phenomena since the sixties and allowed the development of such typology of ships, both fast and slow. After a short explanation of the basic principles which define the supercavitation on a hull bottom, and after having defined the most important physical variables which influence the cavity growth, a series of results obtained on three ACS (Air Cavity Ship) models, tested at DINMA facilities, are shown. The results obtained are discussed and a series of considerations regarding the recent development of these hulls are made

Transporte fluvial por barcazas: resistencia y problemas de estabilidad direccional

River transport of bulk goods and liquids is mostly carried out by barges, especially on long distances, and it can be pushed or towed. The transport by pushed barges is safer and generates less resistance, but in some cases the transport with towed barges is required. In the latter case it must be ensured a good route-keeping to the barges, in order to be easily controlled and sure from getting out of the planned route and to be stranded on a shore. In general the route keeping is guaranteed by couples of stern skegs, which must be designed according to the barge typology. In a river navigation also the effects due to shallow water and the river currents must be taken into account. In this paper the mentioned problems will be explained in detail and some results obtained with experiments with model barges in an experimental tank will be presented.El transporte fluvial de carga seca y cargas voluminosas se hace principalmente por medio de barcazas, especialmente para largas distancias, que pueden ser remolcadas o empujadas. El transporte por barcazas de empuje es más seguro y genera menos resistencia, pero en algunos casos el transporte con barcazas remolcadas es necesario. En el segundo de los casos se debe garantizar una buena manutención de ruta a las barcazas, para que puedan ser controladas fácilmente y evitar que salgan de su ruta planeada y terminen en las orillas. Generalmente la estabilidad de ruta se garantiza con skegs en la popa, que deben ser diseñados de acuerdo a la tipología de barcaza. Además, en la navegación fluvial deben tomarse en cuenta los efectos debidos a las bajas profundidades y la corriente de los ríos. En esta exposición los mencionados problemas se explicarán en detalle y algunos resultados obtenidos con pruebas con modelos de barcazas probados en un tanque de pruebas serán presentados y discutidos

Improvement in Resistance Performance on High Block Coefficient Hulls with Air Lubrication

Artificial air cavities are proposed for their use on high block coefficient hulls, navigating at low speeds, to reduce their resistance. The air lubrication reduces the friction resistance and, consequently, the ship total resistance. This result will be demonstrated through a series of experiments carried out by many researchers and by the author too [1]. The hull models of a tanker and of a dredger have been modified, by creating artificial cavities on the bottom. The models have been tested at the DINMA laboratories of the University of Trieste and the physical phenomena arising from the cavities generation and their development have been investigated by using submerged cameras. From these measures and the images reproducing the cavity growth, it is possible to search the appropriate geometrical solution to reduce the ship resistance. The results obtained are encouraging, but require new tests for the hull optimization

Evoluzioni e tendenze nello sviluppo idrodinamico delle moderne carene veloci

La tendenza che accompagna l'evoluzione delle linee delle carene veloci ha evidenziato degli aspetti che riguardano sia le linee di carena, intese nell'aspetto globale, sia l'applicazione di appendici atte a modificare gli assetti ed a ridurre la resistenza all'avanzamento, nonch\ue9 i moti nave delle stesse. Tra le forme di carena maggiormente studiate ci sono certamente quelle dei trimarani, ottenuti modificando la tradizionale geometria degli scafi. Le monocarene sono sempre pi\uf9 oggetto di varianti che coinvol-gono modifiche locali che comportano l'applicazione di appendici (flap poppieri, interceptors o forme BLB) per ridurre gli assetti in corsa e la resistenza all'avanzamento. L'applicazione di foils portanti, su monocarene e catamarani, introduce poi ulteriori elementi di sviluppo, che portano a miglior tenuta al mare ed a evidenti riduzioni della resistenza al moto. Nel lavoro saranno presentate alcune recenti soluzioni provate alla vasca navale dell'Universit\ue0 di Trieste

STUDY AND EXPERIMENTS ON THE HULL RESISTANCE REDUCTION BY AIR VENTILATION IN CALM WATER FOR SEMI-DISPLACEMENT HULLS

One of the most interesting viscous drag reduction techniques for a boat hull is the so called air lubrication. Although this method has been known for many years, it is scarcely applied in the shipbuilding industry, because it requires to re-design the hull bottom, to define and generate the artificial cavities where the air bubbles can be generated and supplied by using an airflow. It has been demonstrated that the drug reduction is more consistent on full form and slow hulls, where the viscous resistance component is the prevailing one. Recently, as found in (Sverchkov, 2010), it has been demonstrated that the drag reduction can be obtained also for planing hulls. But information regarding applications for semi-displacement hulls characterized by FN 650.45 and FN 64 0.65, which are navigation conditions in which many boat hulls used for recreational activities operate, is more scarce. A series of tests have been carried out on some models, navigating in semi-displacement condition at the towing tank of the University of Trieste and the results will be presented and discussed (Pugnetti and Zotti, 2005

Experimental and Numerical Evaluation of an innovative Planing hull

In this paper the static and dynamic behaviour of an innovative hull is studied. The hull, called Y-Hull, consists of an hybrid structure between a catamaran and a mono hull; it was tested in the towing tank at the laboratories of the University of Trieste. The most distinctive feature is the presence of a central tunnel that affects the back part of the hull. In its foeward part, the hull has a geometry similar to conventional hulls with a very marked V shape. This allows to have good directional characteristics and a good seakeeping in rough sea conditions. The aft part has the typical form of multihull with the hige difference that the area affected by the presence of the tunnel lies Always below the water plane. This work shows the interresting results of the tests performed in the tank and a series of numerical tests performed with the aim to develop future enhancements. Numerical simulations were carried out in order to understand the distribution of pressure on the bottom. In this way it was possible to perform appropriate shape optimizations

Comparison between RANS Simulations with low number of Cells and BEM Analysis for a high Speed Trimaran Hull

The use of RANS viscous CFD simulations to evaluate the resistance of ships is well established. These methods, however, often require a high number of calculation cells with consequent substantial hardware requirements. BEM analysis can be performed in a short time and with modest hardware resources, but returned more qualitative results without the viscous part, even if proven and reliable. The objective is to achieve good RANS simulations in a short time so as to make them competitive with panel methods especially in the evaluation phase of different design alternatives. The aim of this work is to study and standardize the operating modes to do viscous simulations with low number of cells, for carrying out more rapidly the calculations, without any necessity of super-computers. The foregoing methods are applied to study high speed trimaran hulls. For the RANS method a system of localized mesh-sizing of the computational grid is evaluated to get a good simulation in the shortest time possible. Results for resistance and trim from RANS 3-DOF simulations are compared with experimental towing tank tests and with BEM analysis also using transverse and longitudinal wave-cuts. 1