måndag 27 januari 2020

Boeing 737 Max: Perspective and Questions

The BNP of Sweden is about 500 billion USD, and that of the US 18 000 billion USD, about 40 times as big reflecting a population of 10 million in Sweden and 300 million in the US.

Today nearly 1000 Boeing Max are grounded each one selling for 100 million USD with a total of 100 billion USD grounded, about 20% of the BNP in Sweden and 0.5% of the BNP of the US.

The yearly revenue of Boeing is about 100 billion and the total stock value 200 billion USD.

  • Will the Max ever fly again? What happens with Boeing if not? If half of the total value is lost? 
  • Why did the Boeing engineers design an airplane which showed to have a tendency to stall? 
  • Was it because they used standard CFD (computational fluid dynamics) software which could not predict stall?
  • What new CFD software will be required to get the Max in the air?
PS Boeing 797/NMA Is Going Back To The Drawing Boards:
  • Boeing has shelved all of its plans for the ‘797 NMA’ and has been asked to return to the drawing board by its new CEO.
Will the 737 Max also be returned to the drawing board?  Compare with this post.

tisdag 21 januari 2020

The True Total Greenhouse Effect is +9 C, not +33 C

Misconception: Without greenhouse gasses the Earth would be a frozen snowball at  -18 C.
What is the warming effect of the radiative action of the Earth atmosphere on the temperature of the surface of the Earth, the so-called greenhouse effect? 

What would thus the temperature be if the atmosphere was fully transparent without the so-called greenhouse gasses water vapour and CO2, thus without effects of (infrared) radiation? This would be like an Earth with no atmosphere.

And the other way around: What would the temperature be if the atmosphere was fully opaque?

These questions connect to earlier posts such as this, and these if you want to browse. For a revelation of the mystery of black body radiation, see the web site Computational Black Body Radiation.

The standard answer propagated by global warming alarmism is that the greenhouse effect is +33 C. It is claimed that with a fully transparent (or no) atmosphere, the Earth would be a frozen ball at -18 C instead of the observed +15 C with a difference of 33 C. 

The presence of greenhouse gasses is thus what makes the Earth livable. The message is that the greenhouse effect is big = 33 C and as such will lead to dangerous global warming of 3 C upon a small increase of CO2 as the "best estimate" of IPCC, as 1/10 of an estimated big greenhouse effect.

This is the very basis of climate alarmism demanding a stop to emission of CO2 to prevent the Earth + atmosphere passing a tipping point into a run-away greenhouse effect approaching the surface temperature of Venus with its atmosphere filled with CO2, that is a roaring Hell at 462 C.

This is the apocalypse waiting unless we cut down CO2 emissions from human activity to zero and form a fossil free world following the lead of Sweden now transforming into the first fossil free welfare state as required by the New Swedish Climate Law.

To check the alarm signal of 33 C let us recall Stephan-Boltzmanns radiation law for a grey body:
  • $Q = \epsilon\sigma T^4$
connecting radiance $Q$ at temperature $T$ in Kelvin K into a background at 0 K, through Stephan Boltzmann's constant $\sigma$ with $0\le\epsilon\le 1$ a coefficient of emissivity with a black body characterised by $\epsilon =1$.

Assuming absorptivity=emissivity (according to Kirchhoff's law), we can use the SB-law to compute the temperature $T$ of a grey body at a certain distance $D$ from the Sun knowing that the temperature $T_S$ at the emitting surface of the Sun (acting like a black body) is 5778 Kelvin K. What is needed is the ratio $q=R/D$ with $R$ the radius of the Sun, with $q^2$ the dilution effect depending on distance/area. All grey bodies at the same distance from the Sun would then have the same surface temperature (compare with discussion here).  

For the Earth $q =0.00465047$ which gives the surface temperature $T_E$ through the following formula resulting from the above SB-law:
  • $T_E = (0.25*q^2)^{0.25}*5778 = 279$ K
with the first factor $0.25$ the ratio between projected surface to total surface of a sphere. The temperature of the Earth as a grey body with fully transparent (or no)  atmosphere, would thus be 279 K or +6 C.

For Mars with a very thin almost transparent atmosphere and with a distance to the Sun equal to 1.524 astronomical units, the formula gives 225 K, to be compared with observed about 228 K (-60 C), with then a small 3 C greenhouse effect. The two small moons Phobos and Deimos of Mars are reported to have about the same temperature of 233 K.  

For Mercury essentially without atmosphere with a distance to the Sun of 0.4 au, the formula gives 440 K, just as observed with zero greenhouse effect.

The mean value of max and min temperatures of Ganymede, the largest of Jupiter's moons with a very thin atmosphere of Oxygen, is -125 C, which fits well with the formula with a distance of 5.2 au, again with zero greenhouse effect.

For Titan the largest moon of Saturn at a distance of 9.6 au the formula gives 90 K to be compared with an observed surface temperature of 94 K, thus with a very modest greenhouse effect of 4 K from an atmosphere somewhat denser than that of the Earth consisting mainly of nitrogen.  

For Pluto with average au = 40 the formula gives 44 K = - 229 C in agreement with observed temperature varying between - 223 and - 233 C.

For the Moon (without atmosphere) rotating once every month, it is more natural to use the formula with the factor 0.25 replaced by 1 representing maximal (instead of mean) temperature to get +121 C fitting fairly well with observed maximal temperature  +127 C.

We thus see that the formula works (surprisingly or not) very well for Mercury, Mars, Ganymede, Pluto and the Moon essentially without atmospheres, and so we may expect it to serve also for an Earth without atmosphere: 

The recorded mean temperature on the Earth surface is 288 C with gives a total atmosphere effect of +9 C, from fully transparent (or no) 279 K to observed 288 K with greenhouses gasses present into a semi-opaque atmosphere.

The total greenhouse effect is thus at most 9 C, instead of the 33 C as the corner stone of global warming alarmism.

The observed greenhouse effect of 9 C would then represent an observation of the total effect of the atmosphere on surface temperature, including both radiation and thermodynamics with gravitational lapse rate. Observation and not speculation.

Of course, the assumption that for the Earth without atmosphere emissivity=absorptivity, can be debated, since absorption and emission occurs at vastly different light frequencies, but yet may serve to get a rough estimate of the greenhouse effect (with Mercury, Mars, Ganymede, Pluto and the Moon essentially without atmospheres as observational support of the formula).

The temperature 255 K (-18 C) behind 33 C comes from an application of the SB-law assuming absorptivity = 0.7 and emissivity = 1 with questionable logic.

We can go one step further and predict what the temperature $T_E$ would be with a fully opaque
atmosphere by extrapolation from the present observed situation with the "infrared atmospheric window" acting as fully transparent atmosphere letting through 1/6 of the total emitted (infrared) radiation from the Earth surface directly into outer space. Closing the window from 5/6 to fully shut into a fully opaque atmosphere could then have an effect of $9/5$ C, less than 2 C. This is the observed variation of temperature after the last ice age. 

The ultimate effect of endless emission of CO2 into the atmosphere (without changing total density much) would thus be less than 2 C and so from any possible level (like doubling or quadrupling) the effect would be less than 1 C. 

This argument thus supports an idea that climate sensitivity as the temperature increase upon doubling of CO2 from preindustrial level is less than 1 C. This is based on observation of temperature 288 K (15 C) and atmospheric window 5/6 shut combined with the SB-law. Pretty basic and undisputable.

One can argue that the observations used in the argument include "feed-back" (from convection and evaporation). This is  to be compared with another common argument based on (invented) "radiative forcing without feed-back" as 1 C, which is inflated to 3 C by free invention of thermodynamic feed-back. 

We can see the reduction of the basic greenhouse effect from 33 C to 9 C with a factor of 3-4, as a
reduction of the "best prediction" of climate sensitivity by IPCC of alarming 3 C into non-alarming 1 C. It may be as simple as that, to give the hope back to the people of the world. 

PS1 In recent work by Nikolov and Zeller (referring to work by Volokin and ReLlez) the greenhouse effect is claimed to be whopping +90 C. A coming post will explain the origin of this utterly alarming  (misleading) number. Nikolov and Zeller do not start out very promising: Thermal enhancement of 90 K creates a logical conundrum...appears inexplicable..Stay tuned...

PS2 The infrared atmospheric window is indicated in blue in the following picture:   

PS3 The thick CO2 atmosphere of Venus is fully shut, while the very high surface temperature of +462 C is a thermodynamic effect of high pressure from gravitation and not any "greenhouse effect" from CO2.  For a Venus without atmosphere the grey body formula gives +60 C. 

söndag 12 januari 2020

On Real Simulation

The painter, the painting and the nude physical origin.
Icarus Digital Math will be launched under the banner:
  • automated real simulation. 
Here "real" signifies that the simulation can serve as true prediction of reality and "automated" that the key elements of the simulation
  1. mathematical modeling in terms of differential equations
  2. discretisation in terms of algebraic equations
  3. computational solution of algebraic equations, 
are carried out in the form of computational software, such as FEniCS. 

The term "real simulation" may seem like an oxymoron with an apparent contradiction between reality as ”what is” and simulation as ”what is computed/imagined”. But the relation between reality as god-given physical origin and simulation as man-made mathematical model or picture, is in fact very complex and as such an important aspect of both science and arts. 

The postmodernist philosopher Baudrillard coined the concept of ”hyperreality” with the image filling the empty place of a non-existing origin, as true reality with Disneyland as example. 

The computer scientist Dijkstra similarly elevated the model as the "abstract machine" more true than the "physical machine": 
  • Originally I viewed it as the function of the abstract machine to provide a truthful picture of the physical reality. Later, however, I learned to consider the abstract machine as the true one, because that is the only one we can think ; it is the physical machine's purpose to supply a working model, a (hopefully) sufficiently accurate physical simulation of the true, abstract machine.
It also comes to full expression in the Copenhagen Interpretation of Quantum Mechanics with the observer intimately coupled with the observed reality, in particular deciding the fate of Schrödinger's cat in the process of observation. 

In arts, the relation between the painter, the picture and the model is also filled with deep meaning, connecting to Plato's allegory of the cave with shadows forming the reality. 

onsdag 8 januari 2020

Boeing Flight Simulator?

The Guardian reports:
  • Boeing now recommends 737 Max flight simulator training for pilots.
  • Decision is a reversal of company’s long-held position that computer-based training alone was adequate.
In order for a flight simulator to correctly prepare pilots to handle real flight, the simulator must represent reality, which requires CFD (computational fluid dynamics) software capable of predicting the real reaction of the airplane upon control input from the pilot, including the critical phenomenon of stall which must be avoided. Standard CFD does not have this capability since it is based on prescriptive modeling.

Without CFD the action of an airplane, beyond simply guessing, will have to be discovered from extensive experience in real flight, where extreme situations such as stall are hazardous to test and thus must be avoided.     

DFS Direct Finite Element Simulation is new CFD software based on first principle physics without prescriptive modeling, which has shown to be truly predictive of complex flight dynamics including stall, beyond the capability of standard CFD.    

The design debacle behind the two 737 Max crashes can be connected to the use of standard CFD without stall prediction.

The question is now if Boeing is going to use DFS to design the intended upgrade of the automatic stall prevention system MCAS and the flight simulator preparing pilots to handle 737 Max with MCAS. Or if Boeing will continue to rely on standard software without stall prediction.

See also: Boeing employees’ frightening internal messages released in 737 Max investigation:
  • Would you put your family on a Max simulator trained aircraft? I wouldn’t.
  • This airplane is designed by clowns who in turn are supervised by monkeys.

lördag 4 januari 2020

Automated Flight Based on Predictive Flight Simulation

WSJ reports:
  • MAX Crashes Strengthen Resolve of Boeing to Automate Flight. 
  • Boeing, Airbus and industry experts for long have planned more technology to prevent pilot error.
  • Boeing Co. is increasingly committed to transferring more control of aircraft from pilots to computers after two crashes exposed flaws in an automated system on its 737 MAX that overpowered aviators in the disasters. 
  • Executives at Boeing and other makers of planes and cockpit-automation systems for some time have believed more-sophisticated systems are necessary to serve as backstops for pilots, help them assimilate information and, in some cases, provide immediate responses to imminent hazards...
Jetliners have auto-pilot systems relieving pilots from routine flight control when cruising, while a fighter jet like the JAS Gripen requires automatic control to handle the built-in instability allowing quick turns. 

An auto-pilot is like a cruise-control on a car set to maintain a given speed as an option for steady cruising, without true capability to replace the pilot under variable conditions. Not so sophisticated. 

The forward canard of JAS Gripen is used to automatically stabilise the flight, which is too delicate for manual pilot control. The interaction between the pilot and the control system carries the danger of PIO pilot induced oscillations, which caused two early JAS crashes before the software was tamed to slower turns. 

The two Boeing 737 Max crashes were caused by the MCAS control system installed to help the pilot  stay away from stall in climb at full throttle after start by automatically pointing the nose down upon input from a single angle of attack sensor. But the sensor failed and MCAS forced the plane into the ground. Not so sophisticated.

So, Boeing is now searching for "more-sophisticated systems to respond to imminent hazards" in different forms of automated flight.     

Development of automated flight would be greatly helped if predictive computational simulation of the dynamic action of an airplane from controls including throttle, rudder, elevators, slats, flaps and spoilers, was possible, since it could replace difficult time-consuming real flight testing. 

Standard software for CFD Computational Fluid Dynamics is not truly predictive, since it hinges on wall and turbulence models, which are prescriptive rather than predictive, and thus do not well serve this purpose. 

But there is light in the tunnel (for Boeing): DFS Direct Finite Element Simulation is new unique CFD software offered by Icarus Digital Math allowing prediction of the full dynamic flight characteristics of an airplane from first principle physics, without wall and turbulence models. 

DFS thus opens the possibility to construct a flight simulator based on first principle physics, which is truly predictive and as such can contribute to the development of (safe) automated flight.   

fredag 20 december 2019

Can FAA Authorise an Airliner for Passenger Transportation with Negative Longitudinal Stability?

The new Boeing 737 Max came out from a hastened design process, where an existing airframe dating back to 1967 was equipped with larger more fuel efficient engines mounted further forward and higher on the wings to satisfy requirements on ground clearance. The Max showed a tendency to stall in climb and turn as an effect of the new engines apparently giving extra lift thus moving the centre of lift CL ahead of the center of gravity CG into possibly negative longitudinal stability. To compensate the software MCAS was installed with the objective to automatically pitch the nose down upon input from an angle of attack sensor. For details, see Boeing 737 Max Groundings.

It appears that the idea was to hide the MCAS to not distract the pilot, but with a malfunctioning sensor that led to the fatal crashes.

But a civil airplane for passenger transportation is required to have positive longitudinal stability (see also FAA 1962 4b.150) with then CL behind CG, which pitches the nose down on increasing angle of attack and thus, without software or pilot control, maintains stable flight without stall.

Apparently, Boeing did not have the capacity to predict the tendency to stall of the new design using Computational Fluid Dynamics CFD, and so make a redesign into airplane with better stall characteristics. DFS is CFD software with the unique capability of predicting stall.

How could then FAA authorise the Max, when it was clear from the presence of MCAS that the Max design did not fully meet a requirement of longitudinal stability?  Or was the MCAS hidden also to FAA? And how will it be possible for FAA to reauthorise the Max if the basic design is kept and only the software is updated? Is it possible to guarantee that the MCAS will always work as intended, if the flight characteristics cannot be fully explored in real life testing and neither in CFD simulation? The new DFS Flight Simulator under construction can answer this question.

The Swedish military jet fighter JAS-Gripen was designed to have negative longitudinal stability to allow quick turns, which required stabilising software. After two crashes the software was modified into slower turns, which was ok since the plane was not used for combat.

First crash:

Second crash (2.23):

torsdag 19 december 2019

Non-Scientific Speculations by 2019 Nobel Laureates

Stone Age scientists raising alarm about global cooling.
The traditional discussion on Swedish State Television with the 2019 Nobel Laureates has taken place under the usual title "Geniuses Speculate" as a gift to the Swedish people and to humanity.

The main theme was of course climate where all Laureates except one expressed their firm conviction  that science is settled on a rock-solid prediction of catastrophic global warming due to emission of CO2 from burning of fossil,  which must be stopped by all means and at any cost: By 2050 the World must be fossil free, and this is possible since people are willing to sacrifice.

The exception was Physics Laureate James Peebles who dared to say that science cannot tell if the globe is warming or cooling, in particular not because of a small change of the trace gas CO2 in the atmosphere, recalling Yogi Berra: Prediction is difficult, in particular about the future. Peebles also questioned the willingness of people to sacrifice the pleasures offered by the present fossil society.   

Peebles was then declared to be a "heretic" with the important role of giving additional support to the belief of the believers, as expressed by Medicin Laureate William G. Kaelin Jr: Since a heretic (by definition) is wrong, it helps to show what is right and therefore the heretic must be given the right to expression.

So Peebles as Laureate was allowed to express his skepticism to CO2 climate alarmism in Swedish State Television, as a unique exception from Swedish State controlled climate alarmism policy towards the goal of Sweden as the first fossil free society, since the Stone Age.

The view expressed by Laureate Kaelin can be seen as a misinterpretation of the proverb "the exception confirms the rule" attributed to Cicero in the form:
  • exceptio probat regulam in casibus non exceptis
which is to be interpreted as saying that an exception requires the existence of rule as background, not that a counterexample to a scientific theory proves that the theory is correct. Laureates... 

onsdag 18 december 2019

Boeing Halts Production of 737 Max vs DFS

Boeing will halt production of troubled 737 Max airplane. It’s unclear how long the suspension will last.

Compare with CFD State-of-the-Art/NASA 2030 Vision vs DFS recalling that Boeing and its competitors are very conservative companies and penetration of CFD is gradual.

Yes, Boeing indeed took a very conservative approach when launching the new 737 Max by equipping a design from 1967 by new larger supposedly more fuel efficient engines, which had to mounted farther forward and higher to clear ground. 

The result showed to be an airplane with a tendency to stall in low-speed climb and turn, which must have come as a surprise, because the standard software for CFD Computational Fluid Dynamics used by Boeing does not have the capability to predict the complex flow dynamics of stall. 

But the design was kept by Boeing, in line with its conservative company strategy, and to fix the instability the MCAS software was installed with the objective to automatically pitch the nose down on input from an angle of attack sensor. But the system malfunctioned with catastrophic consequences. 

The idea has then, since the the 737 Max fleet was grounded in March 2019, been to improve the software to make it safe, but reauthorisation by FAA is dragging and may never come. So now the production is halted and may never be resumed. 

DFS Direct Finite Element Simulation from Icarus Digital Math  is new software for CFD with the capability if predicting full flight characteristics of an airplane including stability and tendency to stall, as a realisation already today of NASA CFD Vision 2030.  DFS comes with new mathematical theory explaining for the first time The Secret of Flight.             

DFS as new computation/theory is now being presented to Boeing towards evaluation of the new predictive capabilities of DFS and possible incorporate into the designs process. Big values are at stake.

The catch for Boeing is that if the Max requires stabilising software, then it will be very hard to demonstrate that the software always will operate as intended and thus for FAA to re-authorise. The other possibility is that in fact the software is not needed, but that requires predictive computational simulation capability at Boeing trusted by FAA, since real flight testing of extreme situations is hazardous. In both cases, both Boeing and FAA have a problem, for which the only real solution may well be to put an end to the whole story of 737 Max.

How long time would it take for Boeing to make a whole new design (for the new engine or better) meeting todays expectations, using a tool like DFS and then start production?  Two years?      

tisdag 17 december 2019

The True Explanation of the Coanda Effect

A common description of the generation of lift of a wing is through the Coanda effect as the "tendency of a fluid jet to stay attached to a convex surface" typically demonstrated by a teaspoon in the water jet from a faucet subject to a lift force:

The same argument is then used to explain the generation of lift of a wing or airfoil:

But why does a fluid have a "tendency to stay attached to a convex surface"? The standard answer going back to Prandtl's boundary layer theory, is that it is an effect of viscosity which gives a fluid a "stickiness" which makes it "stick" to a surface with zero relative velocity as a no-slip boundary condition.

The new theory of flight exposed on The Secret of Flight gives a different explanation of the generation of lift as instead an effect a slip boundary condition allowing the fluid to slide along the surface with vanishingly small skin friction and then stay attached without separation because of the following property of 2d potential flow (stationary incompressible flow without rotational motion in two dimensions as in the airfoil picture):
  • Potential flow can only separate a stagnation where the flow velocity is zero.  
The reason is that the boundary of the 2d airfoil section with a slip boundary is a streamline followed by fluid particles sliding along the boundary. This means that a nearby streamline in the fluid will stay close to the boundary as long as the flow velocity is positive. The nature of flow separating at stagnation can be seen in the potential flow over the half-plane $y\ge 0$ in a $(x,y)$ 2d coordinate system with boundary $y=0$ with velocity $(v_x,v_y)$ given by
  • $v_x=-x$ and $v_y=y$ with stagnation at $(0,0)$.      
We see that the flow is incompressible and is directed towards $x=0$ with $y=0$ serving as a streamline and that the flow velocity $v_y=y$ away from the boundary is small for $y$ small thus preventing separation in finite time and allowing separation only after long time as the flow approaches $x=0$ with very small velocity $v_x=-x$. We see stagnation in the separated flow at stall  in the airfoil picture above.

Summary:  Incompressible flow can stay attached to a convex surface without separation and thus generate lift of wing,
  • because it satisfies a slip boundary condition,
  • not because it sticks to the boundary with a no-slip.      
The consequences are far-reaching as concerns both computational simulation and understanding of slightly viscous incompressible fluid flow including flight aerodynamics.

In fact, in laminar flow with no-slip the pressure gradient vanishes close to the boundary and so the flow cannot stay attached to a convex boundary. 

måndag 16 december 2019

Prescription vs Prediction in CFD

Recent posts compare the standard methods of CFD based on turbulence and wall models (RANS, LES and DES as a combination), with DFS Direct Finite Element Simulation without turbulence and wall models as best possible solution of Euler's equations.

DFS has shown to accurately predict complex aerodynamics such as the stall of an airplane by capturing both turbulence and flow separation from first principle physics. DFS thus predicts the full flight characteristics of an airplane with the only input being the shape of the airplane. DFS not only predicts flow separation but also makes it understandable as 3d rotational slip separation with point or line stagnation.

This is a stunning example of the ideal according to Einstein of a mathematical model capable of predicting true physics without input of physical parameters. It is like predicting the circumference of a circle with radius 1 to be $2\pi$, just much more complicated and surprising.

With the standard methods of RANS-LES prediction is replaced by prescription mediated through the turbulence and wall models containing many parameters.  As a result RANS-LES cannot truly predict flow separation since that has to be built into the wall model, by either prescribing the flow to stay attached to a smooth solid wall and separate at a corner, or separate under influence of an "adverse pressure gradient".

The main novelty of DFS is thus the possibility of true prediction, which is not possible with RANS-LES which include prescription.  This connects to Bohr's comment to Einstein's claim that God does not trow dice, in the form:
  • Einstein, stop telling God what to do!
RANS-LES tells physics what to do. DFS predicts what physics does.

DFS prediction of stall of a jumbojet with flow separation on top of the
inner part of the wing, in close agreement with observation.