Computational Fluid Dynamics

The use of Computational Fluid Dynamics (CFD) by practicing engineers and analysts has increased dramatically over the past few years. The increase is due to advances in computational methods together with the increase in performance and affordability of computers.

The increased use of CFD has established commercial CFD as credible design tools for solving practical industrial and environmental flow problems. These range from simple one-dimensional heat conduction problems to highly complex problems such as flow around the ship's hull.

Primary purpose ship based CFD codes is the minimization of wave making resistance. Visualization of the computed results gives a clear view of all features of the wave pattern, hull pressure distribution and streamline direction over the hull. Analysis and expert judgment then indicate which modifications of the hull form will reduce the wavemaking. In a few steps a hull form can thus be optimized efficiently and quickly. Additionally, the predicted pressure distribution may indicate possible improvements from the viscous resistance point of view (e.g. reduction of flow separation). The flow direction on the hull can be used for aligning bilge keels or knuckle lines with the local flow. Predicted far-field wave heights are relevant for wash.

The naval and commercial ship design communities have long needed a predictive capability to address the complex interaction between a ship's boundary layer, the nonlinear free-surface, and the propulsor. In commercial ship design, the prediction of near-field flows is central to the problems of unsteady propeller loads, cavitation, and propeller-induced hull vibrations. The solution to these problems requires detailed knowledge of the turbulent stern flow (including thick and perhaps separated boundary layers), bilge vorticity, and propeller/hull interaction. In naval ship design, near-field flow predications are needed to develop designs with reduced acoustic and non-acoustic signatures, particularly through the prediction of propeller acoustic output and the far field wakes observed by synthetic aperture radar.

As a result these are really high end codes and can be very important tools for a successful design work. They will be more widely used in near future. But high level of fluid dynamics knowledge and experience are required even to understand the results.

On the other hand hydrodynamic behaviors of the ships, cruising in wave conditions was a forgotten factor for the ship designers. But in last two decades this trend have begun to change. Hydrodynamic tank tests are expensive and time consuming work for the many design projects because of the budget and time limitations. Hand calculations are not practically possible to solve this problem. There is only one solution; computer simulations. Predicting the ships responses, accelerations and dynamic hull loading due to the waves in a variety of sea conditions can help for better optimizations. Of course hydrodynamic response codes have significant limitations but can be a valuable design tool for an experienced engineer.

Related pages;

  1. CFD codes for ship design.
  2. Hydrodynamic response analysis codes.
  3. General purpose CFD codes.
  4. Grid - Mesh generation software for pre-processing.
  5. Scientific data visualization software for post-processing.
  6. Also check the technical papers links for related issue

last update at 23-May-2007

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