The water bomb: This balloon, filled with 1500 liters of water was dropped onto the test model from 38 m height.
Researchers of Hamburg-Harburg Technical University have simulated, in a spectacular test, the impact of a rogue wave hitting a cruise liner's window. HBM's Genesis HighSpeed system ensured reliable data acquisition during the test.
Transparent, light weight, bright and spacious, large-size windows are increasingly being installed on large cruise liners which adds an architectural value to the cruise line, however, raises many questions regarding the ship's design. Wave impact is a particularly critical issue: What are the requirements for the design of ship's windows to be met to enable them to withstand the impact of large masses of water? Would the windows presently installed be able to withstand a so-called "rogue wave"?
An encounter with a rogue wave - though extremely rare - is a conceivable scenario. Ship accidents and encounters with occasional large "rogue waves" have time and again been reported over the past decades: reality or sailor's yarn? Only since September 11, 1995, when a rogue wave hit cruise liner Queen Elizabeth 2, is this phenomenon considered scientifically validated and proven.
Research of the topic has just begun - covering various aspects of ship design as well. What are the design requirements for ship components, for example, windows, to enable them to withstand the enormous force of a rogue wave hitting the ship? Can a window withstand a rogue wave at all? There is an increasing need to answer these questions, now more than ever since large are increasingly being installed on modern ships.
A research project led by Professor Wolfgang Fricke of the Institute for Ship Structural Design and Analysis of Hamburg-Harburg Technical University investigates the questions arising from the use of increasingly large windows on ships - also considering wave impact and even an encounter with a giant rogue wave.
Questions are being investigated experimentally - for example, in a test simulating a wave hitting a window that also was shown on television.
Research engineers wanted to find out whether the window would be destroyed and, in addition, what exactly would happen at the moment of impact. Two drop tests were performed: For the first drop test, the height and amount of water were chosen such that the glass did not suffer damage. The intention of the second drop test during which 1500 liters of water in a balloon were dropped from 38 m height was - in contrast to the television report - to break the window pane with the water balloon at any rate. Numerical calculations had been made before to meet this requirement.
No conclusive statement can be made about the wave height to which the force of the impact corresponds. However, this test has the advantage that the load is clearly defined and can be simulated using the Finite Element method and correlated with hydro-dynamic calculations.
The aim is to enable sudden loads occurring, for example, in heavy seas and the response of the hull structure to be computed and to identify potential approaches for improving structural design. For this purpose, measured values are compared with calculation results. Four type PMS40 pressure measurement gauges from HBM were installed on the window. PMS40 pressure measurement gauges are the ideal solution for transient pressuremeasurements, for example explosions or shock waves - applications where the rise time of the pressure curve is very short and pressure peaks are high.
Hamburg-Harburg Technical University opted for HBM's GEN2i mobile data recorder from the "Genesis HighSpeed" series as the data acquisition system to be used. With good reason: The moment the rogue wave hits, a huge amount of measurement data is generated; all of them need to be read out at high resolution to provide detailed insights into the events that took place in these seconds. The GEN2i has been equipped with a bridge amplifier input board offering 1 MegaSample/s sampling rate to enable even the fastest pressure peaks to be detected.
Extreme requirements for the test and measurement equipment - since millions of data per second need to be reliably saved and quickly visualized. These high levels of data processing performance are standard with Genesis HighSpeed: Perception software enables live data to be visualized on-screen within seconds using patented StatStream technology. The user has access to raw data instead of modeled information. Furthermore, data security is top priority - given the fact that it would be difficult or very expensive to repeat tests like this one.
Excellent data security, maximum resolution, fast processing: Reliable test and measurement equipment is a prerequisite for analysis of extreme tests and provides significant results - eventually increasing safety far out at sea.