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An Introduction to Aerostatics

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To start, aerostatics is the study of gases that are not in motion. It is a bit different from aerodynamics, as that is the study of gases that are in motion. However, we won't be mentioning aerodynamics too much, as that will be in a different article. :) Another cousin to this field is the study of hydrostatics, which studies fluids that are not in motion.

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Aerostatics are used in a variety of different fields. Aerostatic scientists study air densities, atmospheric pressure, gas allocation, and the barometric formula. Some other topics they discuss cross sections of the atmosphere, composition of mountain air, gas diffusion in soil, and overall gas mixture behaviors. 

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Pneumatics are also heavily used in this field, as they are perfect for studying gases under different pressures. Pneumatics is a branch of engineering that uses compressed gases to operate machines or vehicles.

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The Aerostat Industry

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An aerostat can be described as an aircraft that follows this science. It uses buoyant gas to lift itself in the air and then either floats away by the lift from this gas, or from an attached engine. So this can be applied to any hot air balloon, zeppelin, or other powered airships.

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Aerostats were first developed in 1709, and this was also when the first hot air balloon was made. It wasn't that impressive, but it was made by Bartolomeu Lourenço de Gusmão. He was a Brazilian priest and naturalist. His balloon was able to rise 4 meters off the ground. However, in 1783 France, Joseph and Étienne Montgolfier took a shot at creating their own hot air balloons. Their balloons were able to float higher than 4 meters, and could get up to 2km in the air. Their first aerostats were unmanned, but in the same year as their maiden flight, Joseph and Étienne would start hosting manned adventures. In 1785,  Jean-Pierre Blanchard would use his own aerostat to cross the English channel. This would be a first in aircraft history.  

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France would also become incredibly proud of their airships. After Britain lost The American War of Independence, France would fly their airships over the Château of Versailles as a general: "Hahahaha, you lost the war. Look at our awesome airships!" 

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The most famous aerostat is the Hindenburg. In 1937, this airship would crash and kill over 30 people. The disaster would also kill the entire aerostat industry. The disaster was so horrific, because it was one of the first aircraft disasters caught on film. This, on top of the troubling 1930s, (pre World War 2 climate) made a lot of people lose their trust in German aircrafts, and aerostats overall. Plus, planes became a lot more popular in the air travel industry.

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However, even though the Hindenburg would deflate most of the aerostat industry, this wouldn't stop the development of the technology. Hybrid aerostats started to be developed. These aerostats use both buoyancy and dynamic air flows to travel the skies. The Allsopp Helikite is one of these hybrid vehicles. It is considered one of the most stable and cost efficient aerostats in the world. It is a combination of both a helium balloon and a kite-like structure. It can also operate in high winds.

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Lockheed Martin and The United States Military have also taken an interest in aerostats. Currently, they are developing them for low cost Intelligence, surveillance and reconnaissance. As well as further uses in travel, fire fighting, and oversee missions. Lockheed Martin on the other hand, is looking into developing them for delivering personal and heavy cargo to remote areas and countries. They have spent over 20 years developing aerostat vehicles. 

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Further Aerostatic Technology And Concepts

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So as we've mentioned before, the barometric formula is used in aerostatics. However, it plays a huge part in how this science is calculated and formulated. This formula is used to express how the pressure or density of air changes with altitudes.  It can also apply to temperature lapse rates, and when measuring  exponential atmospheres. (I think you could easily visualize this change in density and temperature with a few custom volume VOPs in Houdini for your creations, but that's just me.)

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Engineers and scientists have made several pieces of technology around this theory, and aerostatic bearings are one of them. These bearings are primarily used in machinery tools, and other tools that might need a high amount of precision to operate. Such as gyroscopes. They can also handle extreme load of pressure, and can carry heavy objects.

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They operate by using pressurized gas to push internal bearings outward, and create a boundary of air between joints in the bearings. This basically means that aerostatic bearings avoid wearing and aging of it's joints by using air to generate actions. Aerostatic bearings are used a lot, and many studies have been done to further improve how compressed gasses can affect the efficiency of bearings. As well as how they handle fluids as well.

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Modeling Aerostatic Simulations

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So what does it take to create a simulation of something that stays very still? A lot of things. Plus, you have to incorporate and consider where your static air is located in the simulation, and how the other objects around it are going to operate. A lot of aerostatic simulations are based around how aerostatic technology can be incorporated into other tools. So Let's take a look at some scientific models.

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Aerostatic bearings are always seeking to be improved, so there have been countless studies done about what type of air they can use, and other factors. Such as if they can be made from porous metals and other materials. This might not seem like a big deal, but any metal that has a liquid or a gas distributed throughout can be classified as a porous metal. Porous metals are also formed though their solidification process when they are melted or welded into a certain shape. During this process, the atomic structure forms certain lattice structures under heat, which in turn can be weakened by pressure from liquids or gases. So there have been many practical and 3D tests to further analyze this behavior. Most have been from The University of Electronic Science and Technology of China.

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On top of this, there have been many other publications of this technology's experimental behavior. Some spanning as far back as 1967. 

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Some problems that arise from aerostatic technology, is that it can't really control the movement of whatever object or load it is carrying. So if an object moves while an aerostatic bearing is carrying it, the technology might be placed under a lot of stress. Simply because the vibrations from the object are not only shaking the metal structure of the bearing, but also the compressed air inside of it. This can also be caused by atmospheric air changes around the bearing. So this is where engineering simulations come to the rescue. 

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Researchers at Doshisha University in Japan have spent a lot of time analyzing this issue. (HERE) They have used a combination of computational fluid analysis of the airflows around bearings, to see their stress points. As well as further visualization tools. By calculating and simulating unsteady airflows around an object, they can better predict how the internal mechanisms will operate under stress, and how long they will last. Doing this in a 3D environment is also way cheaper than repeatedly destroying the same machinery over and over again.

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The University of Southampton also has numerous studies on aerostatics, and aerostatic bearings. A lot of their studies and simulations stretch back to 1974. They also have numerous publications on the science as well. Some of their more interesting studies are about how aerostatic and hydrostatic technologies can be combined together. As well as the development of valve controlled aerostatic bearings. 

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VFX Development, and Scientific Visualization

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So I think it's easy to assume that because this is the study of non-moving volumes, the best way to simulate or create an aerostatic simulation would be by creating a static volume. Or just laying down a VOP to colorize where densities are piling up. I admit, that would be pretty darn funny if you were trolling. But we can create things in this science to be more complex than that. So let's talk about some 3D simulations that we can dive into.

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NASA, (Based on the amount of aerostatic studies they have done.) seem pretty excited about aerostatic simulations. They have done numerous in person and physical tests on aerostatic vehicles for The United States Government, and for space travel. Aerostatic sciences are important for space travel because you never want to over inflate an astronaut's helmet, or the interior of a space shuttle. Plus, everything behaves differently in a vacuum, so certain tools or humans might react differently based on their new environment.

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So what type of 3D visualization does NASA do regarding this study, and how do they move exactly?

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Controlling how vibrations or sound affects aerostatic vehicles plays a huge part in their development. So NASA does a lot of 3D testing on their designs before they even start building them. They have been known to use their own OVERFLOW tool to simulate how pressure on their aircrafts might behave. The OVERFLOW tool is a custom NASA computational fluid dynamics tool for lower Mach number subsonic, transonic, and supersonic flows. They primarily used this tool for The Space Shuttle development, and how it would operate in Earth's atmosphere. It also visualized heat build up around the aircraft quite well.

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But NASA also wants to know how aircraft wings could be actively reshaped during flight to changing conditions in the air. Considering this for spacecraft design is important, as future spacecrafts might need to handle different atmospheres, environments, and need to be more aerodynamic. So to simulate these wing designs, NASA uses a few different supercomputers at the Ames Research Center to get the job done.

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Aerodynamic shape simulations take a lot of computing power. Especially when you are using fluid dynamics to get your result. So NASA also has their own render farm to make that process even smoother. 

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Fun side note: I'm not sure if anyone remembers in the early 2000s there were some concepts for inflatable for space hotels. I'm not sure if they are still developing them, but if they were, there probably would have to be a lot of aerostatic studies done for them. 

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Another cool thing to note, Smoothed-particle hydrodynamics and fluid simulations in general were first developed for astrophysical visualization in 1977. So a lot of fluid dynamics in your favorite 3D software are based off of these old systems.

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NASA has also held a few awesome scientific visualization contests throughout the years. In 2017, one of the simulations that one won their contest was for The Visualization of Clouds and Atmospheric Air Flows. This simulation was pretty interesting as it showed the clouds in both static and dynamic states. It also showed the evolution and precipitation processes of clouds, as well as an algorithm for 3D cloud classification. 

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But where would you start as a Houdini/VFX artist if you wanted to incorporate these concepts? Well, you could make your own hot air balloon or zeppelin simulations. Or even visualize the air dynamics around them. But beyond that you might run out of ideas.

 

So as a Houdini artist some simple aerostatic simulation questions you could ask yourself are:

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- How does sound, and it's corresponding waves affect a static volume?

- How does a static volume behave with certain air patterns?

- How do surrounding velocities affect static volumes?

- How can I simulate atmospheric pressure in Houdini? Does this involve colorizing certain areas, or something else?

- Can I create an opposite aerodynamic momentum based on how volumes or densities in my simulation operate?

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Then just brainstorm simulations from there. :) Already you might see the possibility to add more than just VDBs and clouds to your setup. You could also generate some pretty abstract results from these ideas as well.

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References:

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Modelling and Simulation of Aerostatic Thrust Bearings: https://ieeexplore.ieee.org/document/9107219

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Modeling and Performance Analysis of Aerostatic Bearings for Lifting Heavy Payload: https://www.sciencedirect.com/science/article/pii/S1877705814029464

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Modelling and Simulation of Aerostatic Thrust Bearings: https://publications.aston.ac.uk/id/eprint/41570/1/09107219.pdf

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Air bearing: https://en.wikipedia.org/wiki/Air_bearing

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Numerical Simulation and Experimental Verification of the Stiffness and Stability of Thrust Pad Aerostatic Bearings: https://link.springer.com/article/10.1186/s10033-018-0228-3

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Numerical Simulation of the Turbulent Flow in Ultra-Precision Aerostatic Bearings: https://www.scientific.net/AMR.680.417

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Nonlinear analysis and simulation of active hybrid aerodynamic and aerostatic bearing system: https://journals.sagepub.com/doi/full/10.1177/1461348418792737

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Mathematical Modeling on Statics and Dynamics of Aerostatic Thrust Bearing with External Combined Throttling and Elastic Orifice Fluid Flow Regulation: https://www.mdpi.com/2075-4442/8/5/57

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Simulation Of The Fluid Structure Interaction For An Aerostatic Bearing And A Flexible Substrate: https://www.witpress.com/elibrary/wit-transactions-on-engineering-sciences/82/27279

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Numerical Simulation and Experimental Study on the Gas-Solid Coupling of the Aerostatic Thrust Bearing with Elastic Equalizing Pressure Groove: https://www.hindawi.com/journals/sv/2017/5091452/

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Multi-physical Simulation Of Aerostatic Bearings: https://www.comsol.com/conference2020/download-abstract/911

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Numerical Simulation of Aerostatic Force Coefficients of Bridge Decks Using Continuous Torsional Motion Technique: https://ascelibrary.org/doi/10.1061/%28ASCE%29AS.1943-5525.0000896

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Simulation of the fluid structure interaction for an aerostatic bearing and a flexible substrate: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.735.8897&rep=rep1&type=pdf

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Numerical Simulation of Aerostatic Bearing Stiffness, Damping and Critical Frequency Properties Using Linear Stability Analysis: https://ui.adsabs.harvard.edu/abs/2020JIEIC.101..571D/abstract

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Numerical simulations on the stiffness of aerostatic air bearings: https://fse.studenttheses.ub.rug.nl/16738/

 

Dynamic Modeling of Aerostatic Spindle With Shaft Tilt Deformation: https://asmedigitalcollection.asme.org/manufacturingscience/article-abstract/142/2/021006/1071475/Dynamic-Modeling-of-Aerostatic-Spindle-With-Shaft?redirectedFrom=fulltext

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Simulation of air gap vibration on aerostatic bearing under flow/structure coupled conditions: https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7133/71330F/Simulation-of-air-gap-vibration-on-aerostatic-bearing-under-flow/10.1117/12.807791.short?SSO=1

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Influence of micro-scale velocity slip on the dynamic characteristics of aerostatic slider: https://www.emerald.com/insight/content/doi/10.1108/ILT-02-2020-0059/full/html?skipTracking=true

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aerostatic: https://en.wiktionary.org/wiki/aerostatic

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Aerostatic bearings design and analysis with the application to precision engineering: State-of-the-art and future perspectives: https://www.researchgate.net/publication/331217731_Aerostatic_bearings_design_and_analysis_with_the_application_to_precision_engineering_State-of-the-art_and_future_perspectives

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Clarifications of the mechanism of nano-fluctuation of aerostatic thrust bearing with surface restriction: https://www.sciencedirect.com/science/article/abs/pii/S0301679X11001071

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Gravity-Independent Experimental Study on a High-Speed Rotor Supported by Aerostatic Bearings: https://www.x-mol.com/paper/1311352888638017536

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Aerostatics: https://en.wikipedia.org/wiki/Aerostatics

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Aerostat: https://en.wikipedia.org/wiki/Aerostat

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Research and Analysis of the Static Characteristics of Aerostatic Bearings with a Multihole Integrated Restrictor: https://www.hindawi.com/journals/sv/2020/7426928/

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EARLY LONDON GAS INDUSTRY: http://marysgasbook.blogspot.com/2009/08/aerostatic-academy.html

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Yesterday’s innovations: the aerostatic balloon and the paper bag: https://www.atriainnovation.com/en/yesterdays-innovations-the-aerostatic-balloon-and-the-paper-bag/

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Aerostatic bearings: https://www.sciencedirect.com/topics/engineering/aerostatic-bearing

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Visualization of Clouds and Atmospheric Air Flows (IEEE Scientific Visualization Contest 2017): https://www.youtube.com/watch?v=6Z6cWDSlOL8

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Sample records for aerostatics: https://www.science.gov/topicpages/a/aerostatics

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Sample records for aerostatics: https://worldwidescience.org/topicpages/a/aerostatics.html

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CFD Simulation and Visual Analysis of Complex Time-Dependent Flight Vehicle Flow Fields: https://www.researchgate.net/publication/235060712_CFD_Simulation_and_Visual_Analysis_of_Complex_Time-Dependent_Flight_Vehicle_Flow_Fields

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Aerostat Hybrid: https://www.sbir.gov/sbirsearch/detail/1605917

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