Sloshing and Slamming Testing

Moving fluids can exert tremendous pressure on structures inside and outside ships and offshore facilities such as oil and gas platforms or wind turbines. Reliable measurements of sloshing (LNG movements and cavitation) and swash (wave effects) require application-specific pressure sensors and dynamometers.

Sloshing testing is part of the testing and evaluation solutions for LNG tankers. Natural gas serves as an alternative energy source and is transported around the world by special LNG (liquefied natural gas) tankers. Tank structures must withstand the movements of LNG (sloshing), even in intense waves. Advanced laboratories provide application-specific pressure sensors, including very compact solutions for sloshing testing and evaluation.

Natural gas can only be transported efficiently in liquefied form. Cooling the gas to 162 degrees reduces its volume by a factor of 600, so it can be transported by LNG tankers. Wind and waves can cause LNG to move in partially filled ship tanks. These movements, known as sloshing, can affect the stability of the ship and subject the inner tank membranes to heavy loads.

Many research laboratories worldwide study the dynamic loads induced by sloshing on LNG tanker tank structures. Sloshing testing and evaluation procedures typically involve a rectangular 2D model of an LNG tank on a hexagonal foot (small-scale 3D models are also used). Pressure sensors are often placed in cluster configurations on the tank model wall at various locations where severe impacts are most likely.

Sea impact testing is a precision testing method for wave-induced movements and loads. Ocean engineering tanks are used not only to verify the performance and safety of a ship, but also as a sea holding and maneuvering basin for offshore structures such as oil and gas platforms or wind turbines. Specialized solutions offered by advanced laboratories range from discrete pressure sensors to dynamometers to study the coupling of aerodynamics and hydrodynamics.

Applications for the wave basins described here include testing anchored or fixed objects (such as oil and gas platforms or offshore wind turbines) to determine the motions and loads caused by waves and wind. For offshore wind turbine testing, the wind and waves acting simultaneously on the turbine can be measured by a series of three-component dynamometers placed at the base of the mast between the anchor and the unit under test. This offshore impact test provides high-quality benchmark data to validate methods for simulating the coupling between aerodynamic and hydrodynamic behavior. Test measurements for oil and gas platforms or vessels often require pressure sensors to be mounted embedded in the wall of the structure or the hull of the vessel.

Sloshing is a violent resonant free surface flow in a vessel. The vessel may be excited by harmonic motion or may move with a ship in waves. A nonlinear analytical based sloshing model is used in sloshing calculations. Damping of sloshing motion is an important parameter around resonance for the combined ship motion and sloshing system.

In the sloshing laboratory the motions of a ship are simulated. A plastic tank mounted on top of the motion device represents a cargo tank of the ship. For technical reasons, liquid cargo tanks are never completely filled. If the liquid cargo is forced to move due to tank movements, sloshing occurs. The degree of excitation depends on the tank movements and the frequency spectrum. Typically, spectra corresponding to those in natural seaways are used.

During operation, even on moderate sea routes, tanks can be subjected to high sloshing loads. In the laboratory, loads on the tank are measured and analyzed, focusing on cargo containment systems used on liquefied natural gas (LNG) carriers.

The sloshing laboratory also examines, among other things, the sloshing loads in LNG tanks on ships. These are designed for the transport of natural gas at temperatures of approximately minus 162 degrees. Other types of tanks, such as swimming pools on cruise ships or vehicle tanks, may also be the subject of laboratory examinations.

In recent years, the importance of numerical simulations in marine hydrodynamics has increased rapidly, and tools for determining ship motions and loads for specific geometries and structural problems for specific loads have been developed separately (slamming test). Nowadays, combined calculation of ship motions and loads and structural problems with finite volume and finite element methods (fluid-structure interaction) are implemented in various numerical codes.

In a slammimg facility, experimental tests are performed on objects to validate numerical simulations. The aim of the impact facility is to measure pressures and stresses at defined locations during water hammer, as well as force and acceleration for different impact velocities. The standard tests performed in this context are piezoresistive measurement of pressures, strain gauges and piezoelectric measurement of acceleration and force.

Impact pressures resulting from wave slamming have serious consequences for the safety of structures such as the superstructure of a piled pier, offshore oil platform and open pier deck.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides “Sloshing and slamming testing” services with its trained and expert staff and advanced technological equipment.