COMPUTATIONAL FLUID DYNAMICS
Computational fluid dynamics (CFD) is a tool used by naval architects among others to predict the performance of e.g. a ship. It is best described as a virtual sea trial where the ship's behavior is investigated long before the ship is even built.
We offer in-house CFD services through state-of-the-art software. Long experience in CFD combined with an unrivalled knowledge of ship design enables us to offer not only a result, but a solution and a recommendation based on the results received.
A sample of what we are able to offer is listed below, the simulations are just as accurate for planning hulls which is helpful to determine for example the hump.
- Calm water resistance
- Calm water trim
- Cavitation analysis
- Appendage performance
- Aerodynamic behavior of air flow
- Aerodynamic behavior of exhaust gases
- Sea keeping in head waves
- Roll decay
The outcome of a CFD simulation is highly dependent on the end user. It is important to treat the numerics correctly and we are therefore verifying all of our simulations to similar vessels or model tests, if available. The figure below shows the difference between turbulence models for two different cases. Note that the model which is good for Vessel A is underpredicting the results rather severe for Vessel B. However, note the accuracy for the chosen models.
numerical sea trials
We evaluate hulls in numerical sea trials by utilizing modified CFD-methods. It is an efficient method to predict resistance, trim angle and hydrodynamic properties of a hull design. Compared to model tests, the simulations are carried out in full scale and problems with scale effects are thereby effectively removed. Propeller thrust and various appendages can be included in the simulations to get information about cavitation risks, wake fields and lift/drag from appendages.
If you want to make a quick evaluation of several hull designs, a model test is probably too expensive or too time consuming to be realistic. In such situations, a numerical sea trial is a good option. The analysis will provide you with the desired results without use of an expensive model. If you provide us with a 3D model and some basic ship parameters such as center of gravity and displacement, we are able to execute the analysis. The result can be presented in a rendered view to look more realistic in your marketing material.
We work hard trying to propel the development of CFD usage in ship building. The video above visualizes a 19m vessel being simulated with self-propulsion. We are thus coming closer to reality and are able to, in an accurate way, describe the performance and characteristics of the hull long before it is built. These simulations reduce the risk to build a ship that does not fulfill the requirements and thereby reduce the overall building cost.
CFD is an efficient tool for problem solving. It has been used in several projects to localize the root of a problem or to simply understand the physics behind a phenomenon.
The above film visualizes the solution of a problem a client experienced where a sonar, mounted on the bottom of the hull, was disturbed by bubbles in the flow. We simulated the flow and designed a low resistance solution that reduced the bubbles in the sonar area.
numerical sea keeping and motion analysis
Sea keeping and motion analysis is a costly operation at a model test facility. We have developed a cost-efficient method where a combination of CFD and strip theory is used to predict the vessel's motions. The result is presented in operation curves where the operability is shown for a predefined speed and sea state.
By using linear strip theory software, we can assess the seakeeping performance of ships by simulate wave induced motions. Using basic hull data as input, important aspect of ship safety can be predicted such as roll and pitch angle, accelerations and probability of slamming and green water. It is also possible to evaluate the effect of various active and passive appendages such as roll stabilizing fins, bilge keels or interceptors.