ProPulse

Empirical Prediction of Pressure Pulses

Magnitude of pressure pulse induced by a propeller is an important design criterion. This is causing both noise and vibration. Noise level is essential in case of naval and passenger vessels, whereas high vibration level impacts all types of ship structure. Therefore prediction of pressure pulse has been a point of interest for many decades. Worst cases occur usually in cavitating condition and are determined by type, size and frequency of cavitation. This means that theoretical prediction of pressure pulses requires an accurate prediction of unsteady cavitation, which is only possible with intensive modelling and calculation. This has led to costly commercial software, which are complicated to use and which require extensive amount of input information.

On the contrary Holden empirical method, which was based on a database of measurements carried out until 1978, is an easy to use method with minimum number of input information. This has been successfully used for prediction of pressure pulses in last two decades. New analysis methods and measurements carried out at MARINTEK since 1980 offered the excellent opportunity to develop a new empirical method for prediction of pressure pulses. A method, which is easy to use but provides predictions accurate enough at early design stage.

Main components of a feed forward recall network with a single hidden layer.

Artificial neural network is applied for analysis of the database. This method is successfully used in recent years in different scientific fields. Artificial neural networks are in case of noisy data more efficient than conventional statistical methods and offer the unique capability of easy adoption to new data, which makes developed method a quasi-dynamic model. That means with the access to new measurement data, developed networks can be upgraded with minimum amount of efforts. Networks are translated to DLLs that can be implemented easily to existing software.

ProPulse
The software for pressure pulse prediction

Skilful programming of the method and corresponding Windows interface has yield to a user-friendly software, which may be implemented as a daily prediction tool for design engineer. The software has also a module to calculate pressure pulse according to Holden empirical method. Holden method requires even less number of inputs. The software is called ProPulse, an abbreviation for propeller pressure pulse. ProPulse is a Windows NT software. The results can be presented non-dimensional or with dimensions.

User may calculate pressure pulse for up to 13 different positions at each run. Output results are:

• First harmonic pressure pulse for non-cavitating case
• First harmonic pressure pulse for cavitating case
• Second harmonic pressure pulse for cavitating case

Input parameters are:

• Number of propellers
• Propeller main geometry data
• Propeller thrust coefficient
• Propeller advance coefficient
• Propeller direction of rotation
• Tip clearance
• Cavitation number
• Nominal wake screen
• Transducer position

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