Maron A.,Canal de Experiencias Hidrodinamicas de El Pardo CEHIPAR
International Journal of Naval Architecture and Ocean Engineering | Year: 2014
Large size ships have a very flexible construction resulting in low resonance frequencies of the structural eigen-modes. This feature increases the dynamic response of the structure on short period waves (springing) and on impulsive wave loads (whipping). This dynamic response in its turn increases both the fatigue damage and the ultimate load on the structure; these aspects illustrate the importance of including the dynamic response into the design loads for these ship types. Experiments have been carried out using a segmented scaled model of a container ship in a Seakeeping Basin. This paper describes the development of the model for these experiments; the choice was made to divide the hull into six rigid segments connected with a flexible beam. In order to model the typical feature of the open structure of the containership that the shear center is well below the keel line of the vessel, the beam was built into the model as low as possible. The model was instrumented with accelerometers and rotation rate gyroscopes on each segment, relative wave height meters and pressure gauges in the bow area. The beam was instrumented with strain gauges to measure the internal loads at the position of each of the cuts. Experiments have been carried out in regular waves at different amplitudes for the same wave period and in long crested irregular waves for a matrix of wave heights and periods. The results of the experiments are compared to results of calculations with a linear model based on potential flow theory that includes the effects of the flexural modes. Some of the tests were repeated with additional links between the segments to increase the model rigidity by several orders of magnitude, in order to compare the loads between a rigid and a flexible model. © 2014, Society of Naval Architects of Korea. All rights reserved.
Haimov H.,Canal de Experiencias Hidrodinamicas de El Pardo CEHIPAR |
Gallego V.,Instituto Tecnologico La Maranosa ITM |
Molinelli E.,Canal de Experiencias Hidrodinamicas de El Pardo CEHIPAR |
Trujillo B.,Instituto Tecnologico La Maranosa ITM
Ocean Engineering | Year: 2015
The study describes the implementation of experimental procedure for measuring the hydrodynamic noise generated by model scale marine propellers in atmospheric towing tank. The study is limited to non-cavitating conditions of the propeller as the experimental tank is at atmospheric pressure. The towing carriage and conditions have not been altered admitting the existence of considerable background noise. The feasibility analysis included experimental and theoretical study of the background noise at the operating conditions. Some considerations about the uncertainty of the results are also presented. The experimental equipment, set up and procedure for measuring the acoustic pressure around model ship propeller and/or hull is also described. Simultaneous measurements with various differently positioned hydrophones at multiple hydrodynamic conditions permitted to evaluate the background and propeller/hull generated acoustic field at a range of frequencies. An appropriate treatment of the recorded time series characterised the background disturbances and permitted to obtain net results with sufficient signal to noise ratio, mostly from narrowband spectral analysis. Results for the impact of the hull presence on propeller acoustic field are presented and discussed. The extrapolated results are compared informatively with full scale measurements. The research presented in this paper is a result of the Collaboration agreement on underwater acoustics between CEHIPAR and ITM and is partially funded by the European Commission project AQUO (Achieve Quieter Oceans by Shipping Noise Footprint Reduction), Seventh Framework Programme, Grant number 314227, FP7-SST-2012.1.1-1. © 2015 Elsevier Ltd.