نشریه مهندسی دریا
پیاپی 4 (تابستان 1385)

In this paper, the spreading of three-dimensional, turbulent and unsteady inclined turbidity currents has been investigated. The experimental results were normalized in the form of non-dimensional plots and then a theoretical model was developed. The current width, b, and the relative situation of the tip of the nose of turbidity current, x, are normalized with respect to the buoyancy length scale and related time t is normalized with respect to the buoyancy time scale. Results show that the non-dimensional current width vs non-dimensional distance and non-dimensional time,, two regimes and are distinguished. This indicates that in these two regimes, the amount and type of the balanced forces are different. In regime, the rate of lateral growth is less than regime, while the current width in and regimes, respectively are proportional to and. In the plots of the non-dimensional current length vs. non-dimensional time, three regimes, and are distinguished. In regime, the rate of longitudinal growth is more than other regimes while regime is less. The current length in and regimes, respectively are proportional to and, approximately in regime, is proportional to

Underwater explosion is a common phenomenon to be considered for marine and coastal structures. Although it is not wise to design such structures based on explosion loads, but having studied the explosion wave and its demotic effects, location and geometries of these structures can be improved. In this study after introducing underwater explosion mechanism a summary of the numerical methods used for propagation of explosion waves in water is introduced and finally a preferable method is proposed for modeling the phenomenon. Based on such considerations numerical results using multipurpose commercial codes are successfully compared with empirical relations.

When the body is running at fully immersed condition in viscous fluid, there are two components of resistance, i.e. frictional resistance and form drag. When it is near the free surface, the additional drag encountered to the body which is wave-making drag. This paper is presents the hydrodynamic performance of high-speed Unmanned Underwater Vehicle (UUV) in fully immersed condition. We did 1000000 (cells) fluid mesh around the body using Navier Stokes (N-S) equations and appropriate boundary conditions. The calculations of drag and lift have been obtained at various speeds and attack angle. The model is used to solve the N-S equations. We firstly calculated for the sphere and the results of pressure distributions and drag are very good and satisfactory with the experimental data. The calculations are extended to the UUV and the pressure distributions and drag are shown in good agreement with data.

The Urmia Lake has distinctive nature, hydrodynamic and environmental properties that single out that from the other lakes in the world. Construction of Shahid Kalantari causeway can cause significant effects on natural regime of the lake. It may affect on environmental biology, hydraulic, water circulation regime and …. This paper deals with hydrodynamics of the lake. Two-dimensional surface simulation has been done with MIKE21 program. Flow regime and relative effects of parameters influencing that has been investigated. Results from this model when simulating normal condition, has been found to present a good correlation with field data as level fluctuations and velocity range. For that it seems that using 2D model for hydrodynamic is suitable but calibration with field data is needed for its approval. This model shows that the wind input as the main environmental parameter influencing the flow regime in the Lake and for that it is important object for defining design parameters.

Floating offshore structures, particularly floating oil production, storage and offloading systems (FPSOs) are still in great demand, both in small and large reservoirs, for deployment in deep water. The prediction of such vessels’ responses to her environmental loading over her lifetime is now often undertaken using response-based design methodology, although the approach is still in its early stages of development. Determining the vessel’s responses to hydrodynamic loads induced by long term sea environments is essential for implementing this approach effectively. However, it is often not practical to perform a complete simulation for every 3-hour period of environmental data being considered. Therefore, an Artificial Neural Networks (ANN) modelling technique has been developed for the prediction of FPSO’s responses to arbitrary wind, wave and current loads that alleviates this problem. Comparison of results obtained from a conventional mathematical model with those of the ANN-based technique for the case of a 200,000 tdw tanker demonstrates that the approach can successfully predict the vessel’s responses due to arbitrary loads.

The present paper offers a numerical model which can be applied for the simulation of wave height distribution on a 2-D horizontal soft mud layer. The model is based on mild slope equations and it includes combined wave refraction, diffraction, reflection and breaking. The high energy dissipation of wave height due to the presence of fluid mud layer has also been simulated. Wave height attenuation is calculated from a multi-layered wave-mud interaction model considering the vertical distribution of water content ratio in fluid mud layer. The constitutive equations of visco-elastic-plastic model are assumed for the rheological behavior of fluid mud. An artificial neural network is used as a part of wave attenuation calculation to speed up the computation. Applying the model in the East Bay, Louisiana at the mouth of Mississippi River shows a reasonable agreement with the wave height measurements.