Sloshing and slamming testing

Moving liquids can exert enormous pressure on structures inside and outside ships and on offshore installations such as oil and gas platforms or wind turbines. Reliable measurements of sloshing (LNG movements and cavitation) and slamming (wave impacts) phenomena require application-specific pressure sensors and dynamometers.

Sloshing: testing and assessment solutions for LNG tankers

Natural gas serves as an alternative energy source and is transported by special LNG (Liquefied Natural Gas) tankers around the world. Their tank structures have to withstand movements of LNG – the so-called sloshing – even in heavy swells. Kistler provides research laboratories worldwide with application-specific pressure sensors – including IEPE and very compact solutions – for sloshing testing and assessment.

Natural gas can only be transported efficiently in liquefied form. Cooling the gas to –162°C (–260°F) makes its volume 600 times smaller, so it can be transported by LNG tankers. Wind and waves can cause movements of the LNG in partially filled ship tanks. These movements – known as sloshing – can affect ship stability and may expose the internal tank membranes to heavy loads.

Many research laboratories throughout the world study the sloshing-induced dynamic loads on the tank structures of LNG tankers. Sloshing testing and assessment procedures usually involve a rectangular 2D model of an LNG tank on a hexapod; small-scale 3D models are also used. The pressure sensors are usually deployed in cluster configurations on the tank model wall, at various locations where severe impacts are most likely.

Small size

A small front diameter is one of the key requirements for the sensors in this application. Thanks to this configuration, the sensors can be installed as close to one another as possible so as to optimize spatial resolution.

Fast rise time

Impact pressures are largely dependent on induced motion. They can range from 50 mbar to 7 bar, with fast rise times of between 1 and 10 ms. These conditions require pressure sensors with fast rise times and/or high natural frequencies.

IEPE (voltage)

This application requires a considerable number of sensors, so a cost-effective measuring chain solution is essential. Thanks to IEPE technology, the pressure sensors can be connected directly to the DAQ system with no need for costly charge amplifiers.

Low thermal shock

Measured impact pressures may be affected by a pressure sensor's thermal shock behavior. The design of Kistler's 601C series features very low sensitivity to thermal shock, so these sensors are highly suitable for measuring impact pressures due to sloshing.

Marine slamming: precise testing of motions and loads caused by waves

Ocean engineering tanks are used as a seakeeping and maneuvering basin to not only verify the performance and safety of a ship but also offshore structures like oil and gas platforms or wind turbines. Dedicated solutions from Kistler for this application range from different pressure sensors to dynamometers for studying the coupling of aerodynamics and hydrodynamics.

Applications for the wave basins described here include testing of moored or fixed objects (such as oil and gas platforms or offshore wind turbines) to determine motions and loads caused by waves and wind. For offshore wind turbine testing, the wind and waves that act simultaneously on the turbine can be measured by a set of 3-component dynamometers positioned at the base of the mast between the anchorage and the unit under test. This marine slamming testing provides high-quality benchmark data to validate methods of simulating the coupling between aerodynamic and hydrodynamic behaviors. Test measurements for oil and gas platforms (or even ships) typically require the pressure sensors to be flush-mounted on the wall of the structure or the ship's hull.

High sensitivity

Expected pressure of less than 1 bar should be measured with the correct accuracy; thanks to IEPE technology, the pressure sensors can be connected directly to the DAQ system with no need for costly charge amplifiers.

Low thermal shock

Fast rise time

Common impact pressures are below 1 bar with fast rise times of roughly 1 ms. These conditions require pressure sensors with fast rise times and/or high natural frequencies.

Rangeability

Piezoelectric technology can handle heavy structures while focusing on the smallest dynamic variations thanks to the right choice of charge amplifier settings.

Waterproof force sensors

Force sensors from Kistler are hermetically sealed with a welded design to ensure that they are watertight. Cables are fitted with seals specifically designed for underwater use. Further water tightness can be achieved by welding a 1698A cable on a triaxial force sensor.