DREsden Sodium facility for DYNamo and thermohydraulic studies
| Project: | DRESDYN |
| Contact: | Dipl.-Ing. Stephan Beisitzer |
| Objective target: | Assessment of the static and fatigue strength of a precession driven dynamo for the investigation of the development of the earth’s magnetic field within the project DRESDYN |
It is supposed that the rotation and the precession movement of the earth are responsible for the evolution of the earth’s magnetic field as they induce special flows of the liquid metals existing in the outer core of the earth. For this reason the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) was initiated at the Helmholtz-Zentrum Dresden-Rossendorf. Thereby the previously mentioned correlation shall be proved experimentally for the first time without using propellers or guidings for the formation of the intended flows as in preceding experiments. Within this project the Chair of Dynamics and Mechanism Design is responsible for the durable dimensioning of the test facility.
The construction of the experimental plant consists of a pressure vessel with an interior diameter of two meters and a length of about four and a half meters which itself has a weight of nearly 23 tons. The vessel rotates with up to 10 Hz around its longitudinal axis and the whole platform is able to turn around a second axis with up to 1 Hz. The vessel is filled with more than eight tons of liquid sodium. Unfortunately, sodium inflames when being in contact with air. Consequently, high safety requirements are essential and any failure during operation has to be avoided. So a detailed analysis using the finite element method is necessary considering the various mechanical and thermal loads.
<>
A reliable computation of stresses requires the consideration of all relevant loads. On the one hand there are the mechanical loads resulting from the rotation about two axes. In addition to the centrifugal forces these rotations lead to a gyroscopic moment of up to eight million Nm. Both effects cause an oscillating pressure load with a maximum of more than 20 bar on the inner walls of the pressure tank. With increasing angular velocity of the platform a rising level of turbulence can be observed in the fluid resulting in a complex pressure distribution. Besides the gravity force and the loads according to the radial and axial imbalance are taken into account. On the other hand there are the thermal loads. As the sodium has to remain liquid, temperatures up to 250 °C can occur during operation and the friction induced by the turbulences within the fluid causes a heat generation reaching a maximum of 650 kW at the highest angular velocity of precession. As a result, convection and radiation are crucial for the computation of the temperature distribution and the thermal induced stresses. Altogether, several tens of thousands load cases have to be taken into account.
| Current status: | An algorithm was developed to effectively identify the relevant load cases in accordance to FKM guideline for the static and fatigue strength assessment considering all possible load case combinations for every node. So the computation of the utilization ratio is possible within an acceptable amount of time on the whole surface to ensure a durable design of the vessel and the welded joints. |
| Duration: | since 01/2013 |
| Funding/partner: | HELMHOLTZ-ZENTRUM DRESDEN-ROSSENDORF SBS BÜHNENTECHNIK GMBH |
Publications:
- Stephan Beisitzer, Michael Scheffler, Michael Beitelschmidt: Assessment of the static and fatigue strength of a precession driven dynamo under thermomechanical loads, PAMM 12/2014; 14(1)