HyperLoopDesign
HIGH-SPEED TRANSPORTATION INTO THE FUTURE
HyperLoopDesign is a resource for Hyperloop engineers, looking at the design challenges and solutions for final designs or sub-systems.
Hyperloop Alpha, August 2013.
Elon Musk's original proposed Hyperloop Alpha, which runs in a 2.23m (7ft4") diameter tube, at an absolute pressure of 100 Pa ( 1/1000 atmosphere). It used air bearing skis, with an air compressor to provide air. Acceleration thrust is from linear motors on limited sections of the track.
Slow progress so far
It is now nearly 6 years since Hyperloop Alpha, and progress has been disappointing. The most important decision has been the choice of levitation:- air skis, maglev or wheels. But designers seem to be attracted to technology which is "new" or "futuristic" rather than a logical and balanced decision of the alternatives.
Wheels are the best option for high speeds, metal rims have been used at 1,200 km/h (1997) and pneumatic tires at 1,000 km/h (1970), in speed record cars on unprepared surfaces. In contrast, maglev, with $billions of investment, has only achieved 603 km/h (2015), only slightly faster than a high-speed-rail test train.
Hyperloop's initial focus was on air skis, designers taking a year or two to realise that it is impossible to generate enough lift under the skis when the compressor is drawing air from a near-vacuum.
Now all the development focus is on maglev. Maglev has been unsuccessful due to the extreme cost of the track, lined with continuous copper coils. After 70 years of research, only one 30km system is in service. A maglev Hyperloop is not likely to be built, due to the high maglev cost added to the cost of the vacuum tube.
Hyperloop Cheetah
Cheetah is a design variation released by Richard Macfarlane in January 2014, with a number of changes to simplify and solve problems.
Wheels are used which provide traction. Steam from the cooling system is ejected into the tube, increasing the speed of sound, and reducing aerodynamic drag.
The pod is 3 seats wide, and the tube is now 2.6 - 2.8m diameter. The seats are in 3 seating modules which roll out at the station.
Designers should study all the alternatives ... including wheels!
Designers should be more open-minded about the levitation alternatives. Study the history, do the calculations, and choose the technology that is most likely to achieve the required performance.
Running inside the curved tube is ideal, for fast cornering and safety. There is a wide range of alternatives of wheel types and running surfaces. Pneumatic tires are possible, with their excellent bump absorption and good grip. Metal-rimmed wheels on a resilient surface in the tube is a more durable option. With modern materials, the centrifugal loads on wheels at 1,200 km/h are quiet moderate.
Future Hyperloop research should be focussed on high speed, and how best to achieve it. The commercial companies should avoid getting trapped into endless maglev research. And the student teams have already seen that the fastest entries in the Pod Competitions are simple wheeled designs with a good power/weight ratio.
Cheetah links :-
VacuuDuct - shorter pods that can combine into a train
Competition Pod - for the 2016 Pod Competition.
Wheels - the simpler and more achieveable option.
Elon Musk spoke at the 2016 Pod Competition, and recommended wheels.
Wheels have been proved at higher speeds than any other levitation
Pneumatic tires are the preferred option if achievable
Steel rim wheels on a resilient surface are a good alternative
Continuous traction is a great advantage
Wheel forces are analysed here
Maglev and air bearing skis
Hyperloop Alpha originally proposed air ski bearings for levitation. But there may be insufficient airflow in the near-vacuum. See air skis here.
The tube in the 2016 Pod Competition has an aluminium plate for maglev, but any plate maglev will suffer high drag. See passive maglev plate here. See Arx Pax here.
Maglev using copper coils along the whole route would be the ideal levitation system, except for the extreme expense. See maglev coils here.
Wheel research and development
A considerable budget is available for wheel research, as $billions can be saved in the cost of a simple tube without rails, linear motors etc.
Rolling road test rig can be used for initial research.
Full speed pod testing would need a test track at least 45km long.
A CFD study is important to study aerodynamic drag.
Station layouts, airlocks and passenger loading
A Hyperloop station needs to be different from a train station, because of the vacuum and the structural requirements of the pressure hull.
Side doors on the pod, why they are not feasible
Mobile seating modules that travel to the passengers
Cooling using steam
Cooling is very efficient by boiling water, and ejecting the steam into the tube
Steam has a higher speed of sound, reducing the Mach no. of the pod, reducing aerodynamic drag and shock waves
Steam in the tube reduces vacuum energy cost
Vacuum pumping energy is greatly reduced, because the steam only needs to be pumped to a low-pressure condenser
The Natural Steam Vacuum is a very low energy solution for 3kPa pressure
Vacuum pumps and initial evacuation. Choosing suitable vacuum pumps, and calculating the energy cost of the initial tube evauation, and airlock pumping
Kantrowitz - there is no limit
Hyperloop Alpha proposed that there is a definite limit to speeds inside a tube, depending on the tube/pod area ratio, but this falsely used incompressible flow theory at high speeds. External compression is a much lower energy solution, than the complex compressor of Alpha.
The vacuum tube is the heart of Hyperloop.
It is by far the biggest expense, and the quality of it affects the experience for the passengers.
Hyperloop’s greatest challenge is to provide smooth bump-free travel at high speeds.
It is likely that the maximum speed is limited by the achievable accuracy of the tube.
A resilient suspension system is important
