I wonder if there could be enough amplified energy to rupture something unfortunate, ie the COPV, or something very close to it, a connector perhaps.
Quote from: JamesH65 on 10/06/2016 12:38 pmI wonder if there could be enough amplified energy to rupture something unfortunate, ie the COPV, or something very close to it, a connector perhaps.My guess would be the connector between the COPV and the rest of the helium system, I have no inside knowledge, but it seems to me that that is where the maximum stress from any vibration would be.
Quote from: MikeAtkinson on 10/06/2016 12:44 pmQuote from: JamesH65 on 10/06/2016 12:38 pmI wonder if there could be enough amplified energy to rupture something unfortunate, ie the COPV, or something very close to it, a connector perhaps.My guess would be the connector between the COPV and the rest of the helium system, I have no inside knowledge, but it seems to me that that is where the maximum stress from any vibration would be.And also likely the weakest point of the COPV since they had to drill through it (most likely) to attache the connector.
There is a temperature gradient as well as a pressure gradient in these COPV. The bottom of the COPV is cold when immersed in LOX and area near the fill port is warm from expanded helium. Modeling this gets complicated when combined with stresses from pressure gradients and differential thermal contraction of the metal liner and the composite overwrap.
Quote from: Mike_1179 on 10/06/2016 03:37 pmThere is a temperature gradient as well as a pressure gradient in these COPV. The bottom of the COPV is cold when immersed in LOX and area near the fill port is warm from expanded helium. Modeling this gets complicated when combined with stresses from pressure gradients and differential thermal contraction of the metal liner and the composite overwrap.I don't think it's safe to assume the COPVs were immersed or even touching the LOX at that point in the sequence, unless there was a major change in the timeline. The S2 LOX tank wasn't due to finish filling for several more minutes according to the FT sequence someone posted in the first thread.
Early on, a reddit commenter quoted a SpaceX source as saying they had observed some "weird harmonics" in a COPV during tanking, and this could also be consistent with some operational irregularity causing unexpected phenomena.
Quote from: Kabloona on 10/06/2016 02:54 amEarly on, a reddit commenter quoted a SpaceX source as saying they had observed some "weird harmonics" in a COPV during tanking, and this could also be consistent with some operational irregularity causing unexpected phenomena.The mention of weird harmonics has made me wonder if they have managed to unwittingly make a thermoacoustic heat engine. This could generate sound waves in the helium, powered by the temperature difference between the LOX and the ambient air. These sound waves can have very large amplitudes and could potentially damage the COPV. The COPV would be acting as a resonator with the valves, connectors and piping between the the stage and the GSE acting as a regenerator. The heat input would come from the warm helium being loaded, with the heat sink being the LOX. Obviously this is just speculation at the moment, and I don't think we don't have enough information about the details of the helium system to say anything definitive, but perhaps it will give someone at SpaceX something else to think about.
Quote from: Kabloona on 10/06/2016 02:54 amEarly on, a reddit commenter quoted a SpaceX source as saying they had observed some "weird harmonics" in a COPV during tanking, and this could also be consistent with some operational irregularity causing unexpected phenomena.The mention of weird harmonics has made me wonder if they have managed to unwittingly make a thermoacoustic heat engine. This could generate sound waves in the helium, powered by the temperature difference between the LOX and the ambient air. These sound waves can have very large amplitudes and could potentially damage the COPV. The COPV would be acting as a resonator with the valves, connectors and piping between the the stage and the GSE acting as a regenerator. The heat input would come from the warm helium being loaded, with the heat sink being the LOX.
Assuming an operation error (no defects or installation errors). 1. COPV being filled to operational pressure before being completely immersed.
Quote from: Kabloona on 10/06/2016 02:54 amEarly on, a reddit commenter quoted a SpaceX source as saying they had observed some "weird harmonics" in a COPV during tanking, and this could also be consistent with some operational irregularity causing unexpected phenomena.The mention of weird harmonics has made me wonder if they have managed to unwittingly make a thermoacoustic heat engine. This could generate sound waves in the helium, powered by the temperature difference between the LOX and the ambient air. These sound waves can have very large amplitudes and could potentially damage the COPV.
What you just described is known as "Helium Hammer" and was observed, with near catastrophic effects in early spaceflight projects dealing with cooling systems using liquid helium.
Quote from: woods170 on 10/07/2016 09:34 amWhat you just described is known as "Helium Hammer" and was observed, with near catastrophic effects in early spaceflight projects dealing with cooling systems using liquid helium. The helium used in F9 is not a liquid though. Would you get this same effect through simply heating then re-cooling gaseous helium?
Quote from: Mike_1179 on 10/07/2016 01:09 pmQuote from: woods170 on 10/07/2016 09:34 amWhat you just described is known as "Helium Hammer" and was observed, with near catastrophic effects in early spaceflight projects dealing with cooling systems using liquid helium. The helium used in F9 is not a liquid though. Would you get this same effect through simply heating then re-cooling gaseous helium?No, but the thermoacoustic heat engine effect can happen with a purely gaseous medium, so it could have occurred here.