Enthalpy

It's getting clearer. - Something indeed happened in the world of electric motors when I was looking in an other direction. - Most "pictures" at Abb's doc are edited, more or less heavily (one is completely botched, intentionally I'd say). Do not rely on them to infer dimensions. - Explanations that look convincing, but available in German only: http://de.wikipedia.org/wiki/Synchron-Reluktanzmotor - Have a look at Vagati's patent too. http://www.google.com/patents/US5818140 It really is a reluctance motor. To my understanding, it has the properties and performances of any reluctance motor, BUT Alfredo Vagati managed to let it run smoothly by subdividing the pole shoes and the gaps. The division shall have no simple ratio with the stator's teeth. Interestingly, the divided gaps are now narrow, but they nearly add up to define the maximum reluctance of the rotor, so this maximum reluctance isn't lost when subdividing the pole shoes and gaps. Check with your stamping workers what minimum metal width they want. Abb's "pictures" lie there, it's nearly certain. Beware, at the rotor's rim, this has consequences on the motor's performance. "Flux barriers" must be wording of the patent, but that's misleading. Alas, we don't have barriers against the induction - a basic difficulty of magnetic design, especially harmful at reluctance motors. Varied approaches can evaluate the torque. I suggest again to compute the flux variation, multiply by the current around the best positions - and as usual, the number of poles, an equivalent value for the non-uniform induction, AND not forget how currents add in a three-phase stator, not confound peak, mean and rms currents, and so on. The less simple part is that the stator's induction is phased (tilted) with respect to the rotor. This needs magnetic leaks small enough, which is possible on a small machine. Now that a reluctance motor can run smoothly, its advantage at moderate power machines is that the rotor losses are small. Then, at identical losses, it can be smaller than a squirrel cage machine. Not smaller than a permanent magnets machine, but cheaper. And for MW-GW machines, I don't see it compete, because the leaks prevent the reluctance machine work, at least if reasonably sized.

Seen it. I'll give it a thought.

JC told "resistance", why look elsewhere?

As a fundamental force, it can't be explained in terms of other things. Like in mathematics, axioms do not result from theorems. Nor can you explain the taste of salt - but you can tell that seawater or oysters taste salty. What we know is how it behaves, how to make and use it. Magnetism is created by a flow of charged particles - except for the less comfortable case of the magnetic dipole resulting from the spin of elementary particles, especially the electron. People happily observe that this magnetic dipole appears at charged particles - nice that the neutron was observed to be composed of several charged particles. Though, the particle's spin is not a geometric rotation, and the relationship between the particle's mass, mechanic moment and magnetic moment (so-called Landé factor) differs from a big rotating object. Electric potentials are relative to an other. We can't tell the electric potential of the Earth, the Galaxy... only if it differs from an other object and by how much. In that sense, absolutely no limit. The potential differences are not limited, to my knowledge. Only the distance limits them. Sparks limit to 10kV/mm in the air and 50kV/mm in good plastics (the voltage isn't proportional to the distance); vacuum itself has a limited insulation capability - unless the electrodes are the reason, this domain isn't well known presently. At the scale of atoms and particles, you can get potential differences of 1MV over 100pm, a huge field far above our macroscopic capabilities - and then the creation of virtual electron+positron pairs limits the field. Humans can make over 10MV for some duration, and achieve a huge field (not potential) at a short and concentrated laser pulse. http://en.wikipedia.org/wiki/Femtosecond_laser http://www.rp-photonics.com/titanium_sapphire_lasers.html ---------- No theoretical limit to the magnetic field, to my knowledge. Magnetic fields resulting from ferromagnetic materials are limited by the dipole of electrons and the density of these active electrons in the solid, almost one per atom. This result in 2.3T in the Fe-Co alloy, very close to the computed limit. Superconducting coils are limited by the superconductors to 10T or little more presently. But copper coils powered by short current pulses achieve >200T... a few times before they're destroyed. Some laser pulses, short and concentrated, achieve a bigger magnetic field - an alternating one, and of short duration. ---------- Every material contains electrons and reacts to man-made magnetic fields. The effect on the electrons can be significant but only if some electrons are not paired and only with a big external field - the material's reaction isn't so remarkable: para- and dia-magnetism. Electrons in living matter, plastics... tend to be paired, and their reaction to the external field is opposite and cancels out. Some molecules like O2 have unpaired electrons and show a less weak magnetism. Only ferromagnetism is strong, that is, a small external action results in a big effect. This is because the material's electrons have already arranged among themselves, and the external action (man-made if you wish) just influences this order. Ferromagnetic materials rely on electrons in two (or more?) different conditions that make magnetic dipoles of different strengths and are strongly coupled with an other. Now, imagine that the dipole strengths alternate in the material, like white and black on a chessboard. Neighbour dipoles adopt opposite orientations spontaneously just like big magnets do, but if the stronger and weaker dipoles alternate regularly, you get all the stronger in one direction and the weaker in the other, and the result is not zero. This is essentially a ferromagnetic material, present but not common in Nature. This order holds within "Weiss domains", typically few µm big, which are spontaneously completely magnetized. These domains tend to orient themselves opposed to their neighbours, again like big magnets do. Though, two possibilites permit a global field: - If the limits between the Weiss domains, called Bloch walls, move easily. This is a soft ferromagnetic material like transformer steel: an external field influences the dipoles at the walls (which get conflicting influences from both domains hence are sensitive to other actions) to flip in the favourable direction. Now, a limited external influence gets parts of the strong spontaneous magnetization in its favour, and the effect is strong. - Or if the Bloch walls are hard to move but the previous history of the material put them out of the neutral position. This is a hard ferromagnetic material, or a permanent magnet, once it has been made. Ferromagnetic materials often contain certain atoms like Fe, Ni, Co, Gd... but not necessarily: CrO2 is a permanent magnet but neither Cr nor O2 are, so it's molecular property. The opposite example are austenitic stainless steel which contain mainly iron but aren't ferromagnetic. Even some ferromagnetic plastics have been made.

CasualKilla, the puzzles you submit here correspond to what every electronics student must know - not to what electromagnetics experts may ignore. If you're willing to test the knowledge of forum members, add 40dB difficulty.

Please provide a link to a technical description by ABB - not to videos of unknown origin. Until I see that, I consider the picture as a fake. It was a picture of a squirrel cage motor, where someone has pasted some bizarre drawing. Sorry, but either you try to pull my leg, or someone pulled yours. I won't invest any time in that without a serious reference.

A toroid of material density rho used at tensile stress sigma attains the azimutal speed U and stores in its volume V the kinetic energy A disk leads to the same conclusions and even the same figures as a toroid within few per-cents: Unless the speed or the mass are constrained, only the strength and the cost per volume unit count. Steel is as strong as carbon fibre and much cheaper at identical volume. Ballast (concrete, water...) added to the strong material stores the same energy at a lower speed. Running water, balls, rolls in a racetrack stores the energy defined again by the track's strength and volume. A steady water track could be easier than a rotating toroid and might even use the ground's strength, but I haven't found a convincing setup.

I don't understand the benefit of such a design. I'm still convinced that simple teeth at the rotor, the rest plain steel, is at least as good. I can't even understand the picture, which seems edited. Do you have a link to ABB's document?

Hey CasualKilla, if you really want to test this forum's members, you need something more difficult. I mean, seriously more difficult.

Transporting a flywheel limits its size. Forging and turning it in situ needs huge tools that would serve for few parts. Alternately, we could transport steel coils and wind the band in situ as bigger toroids. A assembled shape can define the toroid's inner diameter and be removed after winding. Below few mm, the band is light enough that the glue between the turns (hot glue, epoxy...) holds the external turn of the spiral. The toroid holds the centrifugal force by themselves; a few tilted bands hold the much smaller toroid's weight only. They cross the azimutal bands many times, for instance where these end, and are nearly radial, overlapping an other around the shaft. Cold work can harden some steels (duplex, austenitic stainless, and more) to 2000MPa and keep them resilient. This permits 419m/s with 20% speed margin but rolling mills seem to limit the bands' width to h=0.7m; then e=1m and R=9m (the size of Itaipú's alternators, just faster) store 3h*2.5MW, that is, a 1000MW power plant could use 120 flywheels to absorb 300MW at night and restore them during peak consumption. Heat treatment achieves only 1500MPa hence 364m/s for cheap resilient alloys, but hot rolling permits h=1.5m and possibly more. Then e=2m and R=24m store 3h*22MW in 3550t, so just 14 flywheels smoothen out the 1000MW consumption. Can we increase h (and then e)? Maybe if the bands make helices rather than a spiral, but the ends' behaviour isn't clear; leading the bands there towards the shaft may improve. I prefer some narrower bands so the edges at successive turns don't overlap, here sketched with one single narrower width and without the tilted bands. Now a 3550t toroid doesn't take R=24m any more, but just R=6m h=5.2m e=2.3m. Other proportions may enable a horizontal shaft. One shaft can also carry several toroids with separate tilted bands; I doubt one can interleave the tilted bands. Magnetic levitation may save the tilted bands altogether. Marc Schaefer, aka Enthalpy

The spinning rate of 67P decreases with time, as reported by the Beeb: http://www.bbc.com/news/science-environment-31965458 by one second a day from presently 12.4 hour period. This makes a strong change over 100 years spent near the Sun - very quick at astronomical time-scale: the orbital period is 6 years. You can also appreciate visually on Esa's nice picture (click to see the motion, visible on the Bbc's paper too) that 67P has its rotation axis oriented at the biggest moment of inertia: This latter supports the idea that damping mechanisms are efficient enough to tumble the rotation axis. Which does not imply that the neck of 67P was previously in the ecliptic plane hence evaporated more quickly - but that a necessary condition, the ability to tumble, is met.

There you have a standard design of a reluctance motor http://en.wikipedia.org/wiki/Reluctance_motor variants exist, especially micro-stepper which have several teeth per pole, but these teeth join a bit farther from the gap. My opinion is that, for any significant power and torque, the "flux barriers" don't bring an advantage. Unless I miss something. See the drawing a Wiki? There are wiiiiiide gaps between the poles, and one good reason is that the flux shall not cross them. TIny "Flux barriers" won't do that job. I had thought at superconductor time ago but the type I get overriden by a tiny induction already, and type II don't reject the flux. Normal conductors can block only a varying flux, which isn't the normal operation of a reluctance motor. Anyway, I got disappointed by the reluctance motor because it's not faster than a permanent magnet motor. At identical rotor diameter it would, but at identical torque the permanent magnet motor can have a smaller diameter, and then it runs as quickly and is smaller, more efficient, silent and so on.

The pre-catastrophy data shows very little difference between Japan in general and Osaka (and far less difference between the countries than expected). This gives me confidence that it applies to Fukuhima as well - unless, of course, the power plant had already polluted the prefecture before. The partial overlap of the samples is not a concern, because both samples begin at 0 years and end at 18 years. In the village example, you get the same proportion whether you iterate the study 2 years, 10 years or 50 years later. Well, here we have discrepancies of 15 standard deviations between the pre-catastrophy and the 2014 studies - nothing to fine-tune with subtle arguments.

Toroids are to spin quickly to store energy, but shall please stay dynamically stable. That is, if some locations move slightly outwards and others inwards, the centrifugal force tends to exaggerate this, but the stiffness must suffice to prevent a runaway. The stability conditions must be known, but not having my books here, I've recomputed it. The toroids here a mean radius R and a rectangular section of height h and radial thickness e. Just as in Euler's theory, I fourierize the arbitrary deformation and observe that higher harmonics are less critical as they need more elastic energy, so I keep only the second one since the first is meaningless: U*sin(2*alpha), where alpha is the geometric angle. For this small arbitrary amplitude U, I evaluate and compare the elastic and centrifugal energies. The stiffness would increase a bit if e<<h. The bending is per length unit R*d(alpha). The kinetic energy is a difference with U=0. Then I introduce the longitudinal sound velocity and get a simple expression. Flexural sound speed gives the same result. From EI*k4 = µ*w2 where I is the bending moment, k*2pi*R makes two phase turns, µ is the mass per length unit, and w is 2pi*F, I obtain that the toroid must rotate slower than the lowest bending mode propagates - quite similar to the dynamic stability of shafts. For steel, 5140m/s and 400m/s +20% margin demand e/R>0,081. Marc Schaefer, aka Enthalpy

Once the reluctance motor runs synchronously with the mains, the added conductors don't prevent flux from passing the "barriers". Conductors only hinder the flux variations over time. By the way, you can suppress the sketched "induction barriers". What you need are plain pole shoes with a big spacing between them, since distance is the only way to reduce the leaked flux. A look at existing designs maybe? The torque comes from the reluctance that varies with the rotor's orientation in the stator's induction. You can compute it through the flux that the rotor's orientation permits; one numerical way is to check how many V*s at the stator's coils an angle variation of the rotor induces (either the gap defines the induction, or the saturation of the magnetic material); combined with the amps*turns at the stator, you get an energy per angle unit, which is a torque. The whole difficulty is to evaluate the flux as a function of the angle, because the flux passes much through the air. This is a fundamental limit of the reluctance machine, which can't use big currents hence isn't very strong at a given size. At an induction machine, stator and rotor currents define where the induction starts and stops. These can be - and are, at big machines - many times stronger than the current that would create the same induction over the gap or over a limited air distance. In addition, induction machines use inductions between -1T and +1T for instance, not just +0.5T and +1.5T for instance at a reluctance machine. All this combined makes the induction machine much more powerful.

In addition to radiation pressure, light "attracts" matter, as any energy does, yes. (Relativity people wouldn't formulate it "attract"). Though, that won't by far suffice to replace dark matter.

A true reluctance machine runs only when synchronous. It needs electronics that provides current at each instant to the proper coils so a permanent torque results. This means that the current's phase and frequency are made as a function of the rotor's angle, and it begins at zero frequency to start the motor. Though, many reluctance machines provide some path to induced currents, and then they achieve some torque despite the current's frequency doesn't match the mechanical frequency, just like in an asynchronous machine. These motors can start with a current at fixed frequency like 50Hz. Many centrifuges (for blood separation and so on) work that way. Flux barriers would be so nice to have.... How do you achieve a good one? Magnetic leakage is a strong limit to every magnetic machine, and especially the reluctance machine is a poor answer to this, which limits the torque and power as compared with an induction machine. Type I superconductors are flux barriers but only against a very small induction, bringing nothing better than air.

Ions in vacuum are rare on Earth, because they demand several eV energy to create, which makes them extremely reactive - more so than atoms or molecules. This case would be rather clear. Though, ions can be created with little energy in a solvent, and this is how chemists usually understand "ion". Then, the comparison with neutral molecules isn't clear at all, since the solvent stabilizes an ion much.

Your blunder about prevalence claimed to always increase shows you don't understand statistics. Suggesting that you do and I don't can only worsen the impression you make on readers. May I politely suggest that you use a more modest language? Yes, it is one of the studies I checked, and its opinion radically differs. But on the other hand, the number of thyroid cancers among children around Fukushima does increase quickly and is way above the pre-catastrophy figure in Japan, and way above the figures in other countries. So which one is right? Statistical noise can't explain the differences. At least, are all studies of good faith? The YBq at Hiroshima include all radioelements, especially those with extremely short half-life which, as they act only very near the explosion center, add no damage to people. It is something that the late director of the plant lindered, as his decisions delayed the explosion of the reactors, so the sub-second to day-lived radioelements had already disappeared. If comparing the radiocaesiums, Fukushima has released 100 to 5,000 times (the lower figure convincing me better) more radioactivity than Hiroshima. Logically enough, since few kg uranium react in a bomb, while a reactor accumulates products from 100s kg uranium.

The standard design with a few radial booms grants more mass to each boom and eases its conception... I too eventually grasped that, and here's a seemingly manageable boom design at rugby stadium scale, with five 85m long booms for 1.72hm2 sail area, plus a fore and an aft half-booms. Each boom consists of fourteen segments, 6.1m long plus overlap, which are concentric tubes that extend after separation from the launcher. The length fits in Falcon, Zenit, Soyuz fairings, Vega with some adaptation, and more. The angles between the extended booms result from shrouds whose nonparallel directions prevent collective buckling at the segments' joints. The tubes have inner and outer faces of 110g/m2 carbon fibre reinforced polymer (almost a papersheet, exists for hobbyists) on a 2mm core of 100kg/m3 balsa. Polymer foam would degas less. Could balsa be pyrolyzed and densified by a carburizing gas? That would achieve clean and possibly refractory sandwiches, not only for solar sails. Central segments have D=0.30m, decreasing in 4.6mm radius steps to D=0.18m for the far segments. This leaves only 2.4mm radius clearance for tolerances, guidance and drive, for which cables and punched belts look possible. Segments weigh 2.1kg mean, 5+2/2 booms 180kg. Taking for the Cfrp 1550kg/m3, longitudinal 98GPa and transverse 47GPa, the D=0.30m segment buckles at 48kN (oval) but 32kN (Euler) and the D=0.18m segment at 7kN. When testing one sector on Earth, the static compressive force is 1kN at D=0.30m. Look how nicely megalomaniac: A 7.5µm film adds 200kg (including some fibres to stop tears), 25km shrouds 40kg, so the sail weighs 420kg or 24g/m2. 480kg bus and payload get 61µm/s2 when towing with 45° at Earth's distance from the Sun: reach Mercury in 5 years, take 5 more to bring samples back or to achieve a polar solar orbit. Marc Schaefer, aka Enthalpy

Maye a simpler example will explain you better why a prevalence doesn't increase over time in an equilibrium situation. Let's take a village of constant population over generations. Someone makes studies over the group of inhabitants aged 18 or less. His study topic is just the proportion of people over 10 in this group. Obviously, someone attaining 10 will not regress under 10 - just like someone diagnosed with thyroid cancer will not improve spontaneously. Nevertheless, apart from fluctuations, the study made 5 years later, or 20 years later, or 100 years later, will find the same proportion of young people above 10 in the 0-18 group: approximately 8/18. This is because people near 18 leave the study group just like around Fukushima, and new people enter the group, and this compensates the evolution that lets individuals pass from the <10 subgroup to the >10 one. Whether the successive study groups overlap at few years distance, or not at two generations distance, doesn't change the result. Exactly the same way, the proportion of people under 18 affected by a thyroid cancer does not increase naturaly over time. This does need a new cause: the radioiodine pollution by the nuclear catastrophy at Fukushima dai-ichi. I hope this is now clear enough to everybody. --------------------------------------------------------- Thyroid cancer isn't a nice thing neither. It is generally well cured, but by removing the thyroid altogether, which implies a treatment for the rest of the life. Also, that study finds that more aggressive cancers result from the same exposition: http://www.ucsf.edu/news/2014/10/120011/radiation-exposure-linked-aggressive-thyroid-cancers --------------------------------------------------------- "No additional thyroid cancers observed in the first 4 years around Chernobyl" is a lie. The numbers did increase - they were just too small to be convincing, 2/yr becoming 4/yr and 5/yr. While such small numbers do not prove a definite increase, they can even less exclude an increase. The experience of Chernobyl certainly cannot serve to dismiss a relationship between the early increase around Fukushima and the radioactive pollution. --------------------------------------------------------- "No statistics in Japan before the catastrophy" was an other lie. It was surprising enough, and here comes the answer, paper there citing IARC itself: http://www.scielo.br/scielo.php?pid=s0004-27302007000500012&script=sci_arttext http://www.scielo.br/img/revistas/abem/v51n5/a11tab1f.gif Parkin DM, Kramárová E, Draper GJ, Masuyer E, Michaelis J, Neglia J, et al. (eds). International incidence of childhood cancer. IARC Scientific Publication No 144. Lyon: IARCPress, 1999. Click to magnify It gives incidences (new cases per year) for varied countries including Japan, where it is rather low at 1.1ppm/year between 10-14yr and 0.1ppm/yr <10yr. Differences aren't huge between the countries neither, so we could extrapolate to 14-18yr using detailed data from an other country if any necessary. Converting the incidences in a prevalence, assuming an equal distribution of people among the ages 0-18: 1.1ppm*(1+2+3+4+5+6+7+8+9)+0.1ppm*(10+11+12+13+14+15+16+17+18+19)=64ppm so the pre-catastrophy statistics would predict 19 cases among 298,577 children around Fukushima, not the observed 86.

It is a population limited to 18 years in both samples. So without the consequences of a disaster, samples taken at two different times would show the same proportion - whether some people pertain to both samples or not. This is not a matter of same population or not. In the healthy situation, that is the steady state, sick people attaining 18 exit the sample, healthy younger people enter the sample, and the observation is constant up to the statisctical fluctuations. Here we see a big increase that is statistically extremely significant. It does not need an unaffected population as reference to see an increase.

As both groups limit the age to 18, the number of detection would not increase over time in a stable situation. The probability of being affected increases over age, but the older individuals exit the observed group at 18 and young unaffected children enter the group. The observed group is huge: hundreds of thousands, and the number of cancers is big as well, almost hundred, enough for rock-solid statistics. Because there was no study before the catastrophy, I don't compare the situations before and after. Just the two studies after the catastrophy show an obvious, quick and alarming rise in the number of cancers. That they are already visible can only mean that the peak will be worse. Around Chernobyl the statistics for thyroid cancer are clear. They show a direct correlation with the radioiodine dosis, and the number of cases made it obvious rather quickly.

I have some protection software but it's tuned to tell me each time it refuses data. It did so when an alleged infection was detected here. What I believed to have seen is that the older page addresses on Scienceforums were different, so I imagined that Google and here the thread lists pointed to a mismatched address. My end of the Internet is in old Europe, where censorship does exist. The excuse is terrorisme / child pornography / illegal drugs, but censorship is known to exceed this field in a manner hard to justify nor even grasp. Then the Internet also relies on computers and software, which do need reasons to malfunction - but not clear reasons. I don't want to make a hastily opinion on the present case.

The stator current flowing in the slit creates an induction across the air gap (and serves other purposes too). This induction varies quickly, just from one side of the slit to the other, and stays essentially constant between two slits (from the stator or the rotor), since induction has a circulation only around a current.. This differs strongly from the model of a rotating induction created by the stator: the induction should vary over time and position as a sine, very smothly. The brutal variation creates cogging at the motor, steps at the electric voltage hence current, and losses since quick induction variations result in stronger eddy currents. Tilting the slits, or the rotor's bars in a squirrel cage, spreads over time the transition of a rotor pole versus a stator pole. The other precaution is to split the coils over several slits, so the induction step spreads over several slits as well. The smart placing of the phases' coils contribute a lot as well. The result is great. A three-phase machine runs very smoothly despite slits would have let it cog brutally like a small DC motor does. Close to a 1400MW generator (=20,000 engines of 95hp) you can talk almost normally. All this is achieved with coils and slits all identical, just by placing them properly. An engineering achievement.