A CFD Numerical Study to Evaluate the Effect of Deck Roughness and Length on Shipping Water Loading

Shipping water events that propagate over the decks of marine structures can generate significant loads on them. As the configuration of the structure may affect the loading behaviour, investigation of shipping water loads in different structural conditions is required. This paper presents a numerical investigation of the effect of deck roughness and deck length on vertical and horizontal loads caused by shipping water on a fixed structure. Systematic analyses were carried out of isolated shipping water events generated with the wet dam-break method and simulated with OpenFoam Computational Fluid Dynamics toolbox. The numerical approach was validated and then the shipping water loads were examined. It was found that, as roughness increased, the maximum vertical and horizontal loads showed a delay. As the deck length reduced, the vertical backflow loads tended to increase. These results suggest it may be worthwhile examining the behaviour of shipping water as it propagates over rough surfaces caused by fouling, corrosion, or those with small structural elements distributed on them. Moreover, the effect of deck length is important in understanding the order of magnitude of loads on structures with variable deck lengths, and those which have forward and backflow loading stages.

Experimental and Numerical Investigation of Green Water Occurrence for KRISO Container Ship

The occurrence of green water on the deck of Korea Research Institute of Ships & Ocean Engineering (KRISO) container ship is investigated using model test experiments and a fully coupled impulse response function (IRF)-computational fluid dynamics (CFD)-based numerical approach. In the experimental study, green water pressure over the deck and superstructure is investigated for different regular head wave conditions (wavelength/ship length ratio: .8-1.5) and vessel speeds (Froude number: .055-.166). The impact pressure on the deck is found to be highest at a wavelength/ship length ratio of 1.2 and increases drastically with the increase in Froude number. The variation of green water pressure with wave steepness is linear for points on the forward deck and quadratic for the superstructure. In the second part, a coupled IRF-CFD-based numerical method is developed in which the global hydrodynamic forces such as radiation-diffraction and Froude-Krylov force are computed using a potential flow solver, whereas the local pressure due to the shipping water impact is computed using CFD and added as an external force. Comparisons of vessel motions and green water pressures with experiments indicate that the coupled IRF-CFD method can be a robust and efficient tool to predict shipping water loads on ships.

COMPORTAMIENTO DINÁMICO DE UNA EMBARCACIÓN PESQUERA EN EL MAR PERUANO

El presente trabajo describe la metodología utilizada para predecir el comportamiento presentado por una embarcación de desplazamiento cuando ésta navega en determinada condición de mar. Es importante que el ingeniero naval determine este comportamiento en la fase de proyecto de la embarcación, porque de esta forma puede evaluar los efectos perjudiciales para su desempeño, como por ejemplo la emersión del propulsor, embarque de agua en la cubierta, slamming y excesivas aceleraciones verticales. Los efectos perjudiciales descritos anteriormente son predichos a través de los espectros de respuesta de la embarcación para una determinada condición de mar y para un determinado movimiento. El procedimiento utilizado para la obtención de los Espectros de Respuesta consiste en la superposición del Operador de Respuesta Unitaria en olas regulares de la embarcación para un determinado movimiento (RAO) y el Espectro de Energía de Pierson-Moskowitz, utilizado para representar el mar en una determinada condición. El Operador de Respuesta Unitaria de la embarcación fue determinado utilizando un programa de Dinámica de Navíos basado en la Teoría de las Rebanadas (Strip Theory) y; las diversas condiciones de mar consideradas, fueron caracterizadas utilizando datos metereológicos como la altura significativa (Hs) y periodo medio (Tm) de las olas, siendo estos datos importantes en la generación del Espectro de Energía para determinado estado de mar. Así mismo, se muestran los resultados del comportamiento de una embarcación pesquera operando en diversas condiciones típicas del litoral peruano. Los efectos perjudiciales fueron determinados y se evaluó su severidad en el desempeño de la embarcación a través de criterios de diseño. Palabras clave.- Emersión del propulsor, Operador de respuesta unitaria, Espectro de energía de Pierson-Moskowitz. ABSTRACTThis paper describes the methodology used to predict the behavior presented by a displacement boat when it sails in certain sea conditions. It is important that the naval engineer determines this behavior in the design phase of the boat, because this way you can evaluate the adverse performance, such as the rise of the propellant, shipping water on deck, slamming and excessive accelerations vertical. The harmful effects described above are predicted by the response spectra of the vessel for a given sea condition and for a given movement. The procedure used for obtaining Response Spectra consists of overlapping Unitary Operator Response in regular waves for a given vessel movement (RAO) and the energy spectrum of Pierson-Moskowitz, used to represent the sea in a certain condition. The operator of the boat united response was determined using a Dynamic Vessel program based on the Theory of slices (Strip Theory) and, the various sea conditions considered, were characterized using meteorological data as significant height (Hs) and mean period (Tm) of the waves, these data being important in the generation of the energy spectrum for a given sea state. It also shows the results of the behavior of a fishing vessel operating in various conditions typical of the Peruvian coast. Adverse effects were determined and assessed for severity in the performance of the boat through design. Keywords.- Emersion propeller, Unitary operator response, Energy spectrum Pierson-Moskowitz.

Hydrological and Morphological Changes of the Lower Danube Near Mohács, Hungary

Various direct human impacts changed the hydro-morphology of the Danube during the last centuries. The aims of the present study are (1) to analyze the water regime of the Danube River using the data of Mohács gauging station (1900-2013), and (2) to study the channel development (1952-2014) in connection with water regime changes and human impacts at a section near Bogyiszló (upstream of Mohács). According to the results the height of low water stages decreased by approx. 136 cm (1.2 cm/year), and new, high record flood stages were measured too. The discharge values appertaining to the same low water stages doubled, thus nowadays almost twice as much water flows through the cross-section of the channel at a given stage as at the beginning of the studied period. As the duration of low stages increased, the sandbar development intensified, thus the channel became narrower (by 48% at some places) and deeper thalweg evolved. Therefore, a smaller cross-section for flood-waves evolved, affecting the height of flood. These changes affect shipping, as due to riverbed incision and decrease of low water stages, the lowest shipping water level has to be set repeatedly at lower stages. Besides water extraction from the channel will have difficulties, thus irrigation and industrial cooling water supply will be limited in the future.