Enthalpy

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About Enthalpy

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  1. Enthalpy

    Fire in Notre Dame in Paris

    This is already complex technology, prone to failure and exposed to sabotage. ---------- As an old engineer, I've a gut feeling that Sprinklers that open when heat melts a valve and let water flow by gravity have decent chances to do more good than harm. But actively controlled hoses would go crazy and make damages more often than they mitigate a fire. Compare with the automatic anti-stalling piece of software. Not very complicated neither: check few sensors, pull the stick. But it went crazy on two flights recently. Or compare with the electronic smoke detectors we have in the houses presently. Good that they don't inundate the rooms every time they sound the alarm without a reason. This gives a sense of what complexity engineers can reliably master: it's very, very little. We need to fail several times, preferably at the beginning of the career on less important projects, to get this modesty. Automated or remotely controlled fire hoses would also need electricity, cameras and so on. In a degraded and stressful situation like a fire, you typically lose these resources when you need them. Firefighters do rely on technology, but the resources are brought from a place away from the fire, they are maintained daily, and are used regularly by people who train for it and have close control over the machines. Quite different from a remotely controlled device supposed to idle for thirty years and work when needed. ---------- How usual sabotage is, we can only guess. How far sabotage goes, we have examples. At the very Notre-Dame de Paris, dozens of statues were beheaded two decades ago, shortly after a similar sabotage happened in an other European country, friend and ally of France. Imagine: there are hundreds of cops, in uniform or not, in and around the cathedral. The group could enter the site, break the heads bang bang bang, and get away unnoticed. Or Ariane flight 36. The public learnt about a cloth in a propellant pipe, but there was also a leak in an other engine, a fire in a third, pogo oscillations in a fourth. This flight was "doomed", as they say. Few months later, the same happened at a US launcher, despite they probably expected it. With that in mind, the usual sprinkler has some resilience. Saboteurs need physical access to a limited location. Melting the valves needs some serious means, cutting the unexposed pipes too. My proposal with the tank on the ground is already less resilient. More locations can be attacked, and they're easier to access. It needs pressure in the tank or pumps and electricity. If controlled from the ground, sabotage is easier. Whether the net balance is still favourable as for passive sprinklers under a pool? A remotely-controlled jet, with cameras, transmissions, electricity+electronics+software, is quite vulnerable. Easier to hamper before starting a fire, easier to misuse to make damage without a fire.
  2. An example of a seaglider, Jura from the Scottish Marine Robotics Facility, meant for maximum efficiency to operate for months: sams.ac.uk and explanatory video Lhp368-NMFo Elegant laminar shape at 0:51, resembling my sketch but in true life Jan 26, 2013 in this thread It uses a bladder to control the buoyancy. No details provided, so a motor powered by a battery supposedly transfers the liquid between the bladder and the pressure vessel. The Oceanic temperature gradient would save this energy, but the equipment needs some electricity anyway, and months of autonomy are already a lot. Cute piece of engineering!
  3. Enthalpy

    Fire in Notre Dame in Paris

    Thinking more at the firefighter helicopter resulted in a hexacopter to improve the pointing freedom of the jet. Description of one sized to fit in a lorry, there: https://www.scienceforums.net/topic/75102-electric-helicopter/?do=findComment&comment=1102008 I'd say it's the same interrogation for non-historical buildings, whose answer is "yes" to sprinklers despite they may spurt without reason. But that is a good argument for fully passive sprinklers opened by heat rather that electronics, or worse, software. In the particular case of Notre-Dame's roof, there was nothing more apparently. A stone ceiling isolates it below, which avoided more fire damages. But I understand that water damage would be a concern in different buildings.
  4. Enthalpy

    Electric helicopter

    This quadcopter or, for redundancy, hexacopter shall extinguish fires, optionally in cities too. The multirotor is simpler and cheaper than a helicopter, and easier to (help) pilot by software. Its rotors are easier to surround by protective stators. It adds advantages specific to firefighters: The pipe and jet can aim up and down between the rotors, if no frame element interrupts the movement there, to tackle the braze from the side instead of fanning it. This lets tank in flight from a river, a fountain... with a reversible pump or two pumps. The tank is accessible from the top and the bottom. The jet creates a smaller torque and the rotors compensate it better. Mass estimate: -------------- 6*5kg Rotors with electric motors 30kg Gas turbine and generator, 70kW 3kg Empty tank 10kg Frame 10kg Pump 8kg Pipe 2kg Electronics 7kg Undetailed 200kg Water -------------- 100kg Empty 300kg Full Six D=1m rotors accelerate together 131kg/s air from 0 to 23m/s to hover. At 70% efficiency, this needs 50kW, but climbing at 7m/s takes 70kW, and hovering with a defect rotor needs power too. Batteries don't suffice here, a piston engine would reduce the payload. A fuel cell does the job but hydrogen may awake superstitions. A gas turbine is light, possibly from a small APU. Get inspiration there http://www.scienceforums.net/topic/73798-quick-electric-machines/?do=findComment&comment=737931 for the gearless light generator and for the geared motors. The pump isn't easy. 60% efficiency need 3.3kW for 2 bar and 200L in 20s. A centrifugal design is compact and the motor too, but it sucks water badly when air is in the pipe. Maybe a fast screw pump https://www.scienceforums.net/topic/73571-rocket-engine-with-electric-pumps/?do=findComment&comment=734835 or a second centrifugal pump at the lower end of an optionally separate pipe. Have floats under the frame? The pipe is preferably of graphite composite, possibly a sandwich. Metal would need intricate reinforcements. Software would usefully stabilize it against the frame's pitch. The sketches and figures let the copter fit in a lorry. 2-4 people carry it empty. It can still manoeuvre in Parisian streets, and possibly arrive by flight from the fire station. Scaling up and down is possible. Marc Schaefer, aka Enthalpy
  5. Enthalpy

    Fire in Notre Dame in Paris

    Used elsewhere too. A medium-sized helicopter can transport 1-2t, essentially water in this case. They often carry the water bag under a long line, to fly well above the flames. The Seine is less than 100m away from Notre-Dame and half a dozen heliports exist around Paris. If several helicopters and pilots can operate the water bag, then the helicopters might perhaps be commercial ones - or not. The difficulties I imagine: - It was not planned. This can't be improvised. - Overflying Paris is forbidden. - What targets? Monuments don't burn every year. Whether a chopper is good for bureaus and houses? An idle helicopter costs more over 800 years than a roof (yes, I know - but you got the idea). The beams burnt between the stone ceiling and the lead roofing. The roofing melted quickly away, leaving the beams exposed to falling water. When only 100t wood were burning, 10t water would have extinguished them with limited overweight on the building. This would have saved the spire and the stone ceiling below. Maybe a helicopter to fight fires in buildings could have a water jet if the recoil is moderate. The bag opened at once is meant against forest fires, where a strong impact is desired. Then you have the drawback of fanning the flames; could it be alleviated by flying higher and downwind? Sound reasonable to put the sprinklers targeting the wooden structure rather than the stones. I see no reason why they should only douse downwards. I understand the oldest ones have an opening that melts under heat and operate at low pressure from a tank above, whose weight may have been excessive for the old building. But presently the system could be more active and detect flames from a distance or smoke to spurt water upwards from a tank on the ground. Or the firefighters could have trucks whose jet reaches tall buildings. Rather not a free jet as it fans apart, but a long articulated stiff pipe similar to concrete pumps. It needs no-one at the top, only cameras and a remote control. The long arm must be strong and the truck stable.
  6. Enthalpy

    Fire in Notre Dame in Paris

    Thanks JC! And, yes, rebuilding as it was has excellent arguments in its favour, which I'm sensitive to. It's more that NDDP was ugly to my taste, and the dark grey roof contributed much to that, so I'd catch the opportunity to build something more pretty, with a roof of nice colour, and spires on the towers at last. ========== Trying to estimate the lead concentration sent in the air by the fire... Smelter workers had (in some places, have) harmful amounts of lead in the body due to lead's vapour pressure. If melting pure lead at 601K, the (equilibrium!) vapour pressure is 10-11atm. If bronze molten at 1210K contains 10%Pb, the lead vapour pressure is 10-4atm. wikipedia In Notre-Dame's fire, the lead roofing melted around 600K, but the drops that landed on the burning oak beams didn't leave the flames. At 1400K, lead vapour pressure is 10-2atm. In addition, liquid or gaseous lead in the flames made oxides that went in the atmosphere as fumes, in amounts not limited by the vapour pressure. To my opinion, this is probably the yellow smoke that I never saw over a wood fire. Or what would have been in big amount in the roof? The firefighters may have inhaled noxious amounts, especially those who climbed in the towers. The nearby inhabitants downwind too. Inhabitants farther downwind and by-passers maybe; the smoke didn't fall down immediately, according to the pictures. I consider prudent that all people who smelled the smoke clean the clothes they wore, and clean with a vacuum cleaner all surfaces of rooms whose window was open. Some study mapping the amounts would be urgently needed, diagnosis in the firefighters' blood more so. Treatments to lead poisoning exist wikipedia
  7. Enthalpy

    Magnetic Induction: How to...

    Some plastics can be welded by capacitive heating, not by inductive heating. It's known but uncommon because the process applies only to lossy plastics like PVC, not no PE, PP, PS, PETP and so on. An advantage is that the parts get hot at depth quickly.
  8. Enthalpy

    Fire in Notre Dame in Paris

    The answers I heard to some questions above about fighting the fire, in no special order: Paris' firefighters are highly regarded professionals who use(d) to be quick and efficient. But recently they took very long to extinguish a building fire that seemed banal to my untrained eye. The explanation I heard from the media, that the building was in second position from the street and this prevented using the normal equipment, was ludicrous, as about every street in Paris has two rows of buildings. Hydrants, trucks... are abundant and in good state. Driving in Paris is an odyssey for normal people but the mean delay there for firefighters in France is 13 min from call to operation, less in Paris. They have the keys and tools to remove all obstacles. The streets around Notre-Dame aren't by far the most crammed in Paris. I too heard that water bombers would destroy the old walls. I'm not fully convinced, because dropping the water from higher altitude reduces the impact force, and helicopters could do it more gently. Tanking is possible at an airport. But there is one other reason: the water bombers are based in Gardanne and would have taken roughly four hours to arrive in Paris. Plus some risk of being shot down if someone is unaware, since overflying Paris is forbidden. The firefighters' water jets couldn't reach the roof, this is BAD. They had 400 people quickly at the site, that must be >50 trucks, and I saw ONE water jet at a time and quite late. Essentially everything that could burn, did. The wood structure continued to burn for about 1.5h after the firefighters arrived, until the complete roof was lost. They couldn't do much more than taking artefacts out of the cathedral. It must be a very bad feeling for the professionals. The media commented "the towers were endangered, the firefighters saved them" and I vaguely suppose this is communication: the towers were not at risk, but the politicians had to report some sort of victory. Most buildings in Paris are 7 storeys tall by law, because this is how high the fire brigade reaches. Notre-Dame's roof is much higher. Taller buildings have their own means to extinguish fires, the cathedral didn't. In that sense, the fight was lost before it began, yes. And it was fool. I heard that an automatic extinguishing equipment would be too heavy for the old walls. My limited understanding is that skyscrapers have water reserves at the top, which may be difficult to add to a cathedral, but it should be possible to feed sprinklers from a tank on the ground, with a good pump or a pressure vessel. A first detector raised an alarm an hour before but people didn't find any fire. No more details. After the second alarm, reacting with extinguishers and buckets wasn't allegedly possible any more. I don't quite grasp how a fire might remain silent for an hour among old dust and dry oak wood, nor how it propagated among oak over >50m in two hours, but I have no experience for fires of that size. 900M€ presently, or 1G$. This is 16* the amount donated after the cyclone Idai in Mozambique and around plataformamedia.com
  9. Enthalpy

    Fire in Notre Dame in Paris

    The architect Jean-Michel Wilmotte too suggested to use titanium instead of lead for the roofing, earlier than I did : francetvinfo.fr - bfmtv.com - (both in French) He also proposes a metallic structure instead of oak. I stopped short of writing it because the raw data of oak tells it outperforms the alloys of aluminium or iron that resist corrosion and are easy to weld. Though, assemblies of metal beams lose less strength than with wood. He even proposes a titanium structure, which I consider difficult. I would not dare to weld titanium in the wild, as it demands an extreme protection against the atmosphere. Assembly by other means like bolts often waste much strength. But this depends on ingenuous ideas and practices, like welding complete arches in the workshop. He also describes as an advantage that titanium can look like the original, but I find the lead roofing horrible, and prefer to have a nice bright colour made possible by aluminium or titanium.
  10. Enthalpy

    Fire in Notre Dame in Paris

    What is the yellow smoke on the pictures of the fire? Here is a reduction from commons.wikimedia.org other pictures show the yellow smoke clearly too: forbes.com – news.sky.com – vox.com – ndtv.com The colour resembles lead oxide PbO en.wiki – fr.wiki and Notre-Dame's roofing was made of lead. What do you think? Thanks!
  11. Enthalpy

    Fire in Notre Dame in Paris

    As the roof of Notre-Dame of Paris shall be rebuilt, the usual interrogation is: identical to the previous version, or modernized? The previous roofing did resist corrosion for long, but its dark grey lead was horrible. Sorry, but yuk. We have better choices now than in the 19th century. A first hypothesis would be anodised aluminium alloy: 1050A, 6060, few more. These resist corrosion nicely, and anodisation improves further. Window frames of anodised 6060 show no corrosion in cities after 40 years, so I hope careful anodisation, possibly on alloy 1080 or 1099, would last for centuries. As needed for fastening, welding must be made before heat treatment, and folding before anodisation. The alumina layer can include nice pigments like deep gold colour, that seem to stay for centuries. All this needs to be checked. Titanium, alloyed or not, resists corrosion. It can be anodised, and while including pigments isn't done up to now, just the chosen oxide thickness gives nice colours, including gold, or blue and red for Paris. I trust this interference colour to be eternal. Aluminium and titanium would make a lighter roofing than lead. The wind drag stays the same. Stainless steel, for instance duplex, would definitely resist corrosion, but colour by anodisation is said not to last. I feel bare stainless steel isn't nice enough. At the price of a cathedral, even exotic metals are affordable if not cheap. 2mm sheets over 100m*50m weigh 100-160t, so even tantalum would cost only ~60M€ and be eternal, while niobium is cheaper and less hard. Zirconium and hafnium are dark. Supposedly, coloured anodisation isn't done for them up to now, but I wouldn't like bare metal, even if brilliant. Marc Schaefer, aka Enthalpy
  12. Enthalpy

    Woodwind Materials

    Tone holes let a woodwind body vibrate as they break the symmetry, so are there vibrations at the mouthpiece of a single-reed instrument? Let E=2.5GPa and rho=1400kg/m3 for ebonite. The dimensions are from a soprano clarinet. ========== Where the bore meets the reed, the mouthpiece section is open hence more flexible, and the sides may vibrate laterally. For hand computation, I model the U shape as a flat part hold at the middle, 4mm thick, 2*13mm wide. Per metre length, EI=13 and µ=5.6. The first flexural resonance, with k*13mm~pi/2, occurs around 3.6kHz. The fundamental of a soprano clarinet doesn't reach this frequency. Amateurs are expected to reach written G an octave above treble clef, so the resonance would be the H3 of a high note. For professionals who reach higher notes, it could also be H2. Resonance would affect the emission of a note and its timbre, as we hear these frequencies well. How much? Static 1Pa would deform the tips by 0.27nm, creating a displacement of 9*10-15m3. For comparison, a D=14.6mm L=0.4m air column (*0.5, the mean value of cos2) contains 33cm3, which 1Pa compress by 2.4*10-10m3, so the mouthpiece's lateral deformation is 26000* smaller. Now, ebonite may resonate with Q=40, so the deformation is 650* smaller and its phase dissipative. Accounting ideal bore friction, conduction and radiation for a clarinet at 3.6kHz, but not the losses at the tone holes, Q~50, which the /650 deformation reduces to 46. The effect is small. But if ebonite had been half as thick, the effect 8* worse and at a note's fundamental would have been annoying. Once again, existing designs are good but don't take huge margins. Metal puts stronger resonances at higher frequencies, which should make no difference here. It's more a matter of accurate manufacturing, thermal comfort, condensation. Polyketone with E=1.3GPa would need a bit more thickness, while liquid crystal polymer with E=9GPa could accept less. Ease of manufacturing can decide. ========== Pressure oscillations act vertically on the mouthpiece, stronger than at tone holes, and the opposite force on the reed acts only at the ligature, but the mouthpiece's tip vibrates little thanks to its stiffness. I make a very coarse model with thickness constant over the length. The first resonance is then around 7kHz and the displaced volume 5* smaller than for the sides lateral vibrations. Nothing to worry about. ========== The reed and mouthpiece end transmit strong vibrations downstream, possibly to the instrument's body. The big area at a pressure antinode has more potential than the closed tone holes effect described here on Nov 13 and 26, 2017. If the musician didn't apply his teeth and lip, the opposite pressure forces on the mouthpiece and reed would compensate at the ligature, because the reed resonates at a frequency exceeding much the sound, so its inertia is negligible and the reed transmits all the force over the ligature. The stiff teeth and skull reduce the mouthpiece's force, the softer lip at the reed's strong movement too. How much of each remains is impossible to evaluate from my armchair, sorry for that, but they won't compensate an other. The skilled musician reduces the reed's vibration amplitude with his lip consistency to obtain a mellow sound, so much of the force is absorbed. The cork isolates strongly the barrel or bocal from the mouthpiece's vibrations. A tenon of absorbing material like silver would be stiffer and damp the resonances too. Some mouthpieces have a softer insert for the teeth. It limits the transmission to the skull and internal ears, but may also damp the mouthpiece's movements. This, together with the mouthpiece's mass, could make a difference to the listener, more so at low instruments. Marc Schaefer, aka Enthalpy
  13. Enthalpy

    Hear a Luthéal

    As deduced from pictures of pianos and cimbaloms, this isn't very accurate... Piano strings propagate the sound 1.3* faster than air but cimbalom strings 0.7*, for those that not limited by the instrument's size and are not overspun. This must contribute to the typical cimbalom sound that lisps a bit. Wider instruments and strings more stressed would have a clearer voice, but would they be accepted as authentic cimbaloms? They would also be harder to move and demand a stronger frame. While a piano played with mallets resembles a cimbalom, its voice is a bit neater. So a grand piano may better imitate a cimbalom for Tzigane by detuning it a lot, up to an octave lower. This applies both if played with mallets or with harder hammer heads on the piano action. Marc Schaefer, aka Enthalpy
  14. Enthalpy

    Hear a Celesta

    The cymbalum, or cimbalom and so on, is common in Romania, Hungary and more Central and Eastern European countries, but elsewhere it's not so usual en.wiki and fr.wiki Fortunately there are records on the Web. EflpsFjkzxU traditional role and music. By the way, Victor Kopatchinsky is the father of Patricia, well known too, as a violinist 6aoL0wp6RjE away from folklore. Music 0:18 OUr20-jDN5o different country IPKIhnnhuTk jazz WyWPdG2hSuY called a (small) cimbalom too, while the santoor, yangqin and other hammered dulcimers are not.
  15. Enthalpy

    Hear a Luthéal

    The line at fourth minute of Tzigane would obviously be played on a cymbalum in a gypsy orchestra and is clearly meant to imitate one. Ravel's orchestral score gives it to a harp, I suppose because the cymbalum plays too faintly and is too rare, hence my proposal to play Tzigane with hammers on a grand piano, illustration: As usual, the percussionists shall experiment with mallet materials and mass. The cymbalum mallets are rather hard, and the piano strings need heavier ones. Two musicians access all strings from both sides of the grand piano with removed lid... at least on my sketch. Things look less easy on a real instrument. Here a Vienna model, picture gratefully pinched at Bösendorfer's website: The bass strings pass over others which are barely accessible. Where the piano's hammers strike, near the dampers, the strings are clear, but so near to the end the sound there may be dryer than the original. Some older pianos gave a better access, here a Pleyel with crossed strings, and parallel strings would be best, a Pleyel too: A recent grand piano with parallel strings exists at Chris Maene, possible option chrismaene.be ========== Alternative The complete action (from keys to hammers) of a grand piano is easily removed and replaced. An additional piano action could be prepared to imitate the cymbalum sound with much harder hammer heads. That makes an agile and loud instrument that plays the score easily. The additional action can belong to several orchestras or to a piano manufacturer. This applies to the violin and piano version too if two pianos are available. Marc Schaefer, aka Enthalpy