Hyperloop Alpha Intro
Figure 1. Energy cost per passenger for a journey between Los Angeles and San Francisco for
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- Figure 2. Hyperloop conceptual diagram.
- Figure 3. Hyperloop tube stretching from Los Angeles to San Francisco.
- Figure 4. Hyperloop passenger capsule subsystem notional locations (not to scale).
- Figure 5. Hyperloop passenger transport capsule conceptual design sketch.
- Figure 7. Streamlines for capsule traveling at high subsonic velocities inside Hyperloop.
- Figure 8. Hyperloop passenger capsule version with doors open at the station.
- Figure 10. Compressor schematic for passenger capsule.
- Figure 11. Compressor schematic for passenger plus vehicle capsule.
- Figure 12: Schematic of air bearing skis that support the capsule.
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Figure 1. Energy cost per passenger for a journey between Los Angeles and San Francisco for various modes of transport. 4. Hyperloop Transportation System Hyperloop (Figure 2 and Figure 3) is a proposed transportation system for traveling between Los Angeles, California, and San Francisco, California in 35 minutes. The Hyperloop consists of several distinct components, including: 1.
a.
Sealed capsules carrying 28 passengers each that travel along the interior of the tube depart on average every 2 minutes from Los Angeles or San Francisco (up to every 30 seconds during peak usage hours).
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b.
A larger system has also been sized that allows transport of 3 full size automobiles with passengers to travel in the capsule. c.
miles (37 km) on average during operation. d.
The capsules are supported via air bearings that operate using a compressed air reservoir and aerodynamic lift. 2.
a.
The tube is made of steel. Two tubes will be welded together in a side-by-side configuration to allow the capsules to travel both directions. b.
c.
Solar arrays will cover the top of the tubes in order to provide power to the system. 3.
Propulsion: a.
Linear accelerators are constructed along the length of the tube at various locations to accelerate the capsules. b.
capsules via the linear accelerators. 4.
Route: a.
There will be a station at Los Angeles and San Francisco. Several stations along the way will be possible with splits in the tube. b.
constructed in the median.
Los Angeles, CA
Francisco, CA
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In addition to these aspects of the Hyperloop, safety and cost will also be addressed in this study. The Hyperloop is sized to allow expansion as the network becomes increasingly popular. The capacity would be on average 840 passengers per hour which is more than sufficient to transport all of the 6 million passengers traveling between Los Angeles and San Francisco areas per year. In addition, this accounts for 70% of those travelers to use the Hyperloop during rush hour. The lower cost of traveling on Hyperloop is likely to result in increased demand, in which case the time between capsule departures could be significantly shortened. 4.1. Capsule Two versions of the Hyperloop capsules are being considered: a passenger only version and a passenger plus vehicle version.
Assuming an average departure time of 2 minutes between capsules, a minimum of 28 passengers per capsule are required to meet 840 passengers per hour. It is possible to further increase the Hyperloop capacity by reducing the time between departures. The current baseline requires up to 40 capsules in activity during rush hour, 6 of which are at the terminals for loading and unloading of the passengers in approximately 5 minutes.
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Hyperloop Passenger Plus Vehicle Capsule The passenger plus vehicle version of the Hyperloop will depart as often as the passenger only version, but will accommodate 3 vehicles in addition to the passengers. All subsystems discussed in the following sections are featured on both capsules.
For travel at high speeds, the greatest power requirement is normally to overcome air resistance. Aerodynamic drag increases with the square of speed, and thus the power requirement increases with the cube of speed. For example, to travel twice as fast a vehicle must overcome four times the aerodynamic resistance, and input eight times the power. Just as aircraft climb to high altitudes to travel through less dense air, Hyperloop encloses the capsules in a reduced pressure tube. The pressure of air in Hyperloop is about 1/6 the pressure of the atmosphere on Mars. This is an operating pressure of 100 Pascals, which reduces the drag force of the air by 1,000 times relative to sea level conditions and would be equivalent to flying above 150,000 feet altitude. A hard vacuum is avoided as vacuums are expensive and difficult to maintain compared with low pressure solutions. Despite the low pressure, aerodynamic challenges must still be addressed. These include managing the formation of shock waves when the speed of the capsule approaches the speed of sound, and the air resistance increases sharply. Close to the cities where more turns must be navigated, capsules travel at a lower speed. This reduces the accelerations felt by the passengers, and also reduces power requirements for the capsule. The capsules travel at 760 mph (1,220 kph, Mach 0.99 at 68 ºF or 20 ºC). The proposed capsule geometry houses several distinct systems to reside within the outer mold line (Figure 4).
Compressor motor
Seating (2 x 14) Batteries Compressor fan Inlet
Air storage Suspension
Firewall/ sound bulkhead
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4.1.1. Geometry In order to optimize the capsule speed and performance, the frontal area has been minimized for size while maintaining passenger comfort (Figure 5 and Figure 6).
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The vehicle is streamlined to reduce drag and features a compressor at the leading face to ingest oncoming air for levitation and to a lesser extent propulsion. Aerodynamic simulations have demonstrated the validity of this ‘compressor within a tube’ concept (Figure 7).
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Hyperloop Passenger Capsule The maximum width is 4.43 ft (1.35 m) and maximum height is 3.61 ft (1.10 m). With rounded corners, this is equivalent to a 15 ft 2 (1.4 m 2 ) frontal area, not including any propulsion or suspension components. The aerodynamic power requirements at 700 mph (1,130 kph) is around only 134 hp (100 kW) with a drag force of only 72 lb f (320 N), or about the same force as the weight of one oversized checked bag at the airport. The doors on each side will open in a gullwing (or possibly sliding) manner to allow easy access during loading and unloading. The luggage compartment will be at the front or rear of the capsule. The overall structure weight is expected to be near 6,800 lb (3,100 kg) including the luggage compartments and door mechanism. The overall cost of the structure including manufacturing is targeted to be no more than $245,000.
The passenger plus vehicle version of the Hyperloop capsule has an increased frontal area of 43 ft 2 (4.0 m 2 ), not including any propulsion or suspension components. This accounts for enough width to fit a vehicle as large as the Tesla Model X. The aerodynamic power requirement at 700 mph (1,130 kph) is around only 382 hp (285 kW) with a drag force of 205 lb f (910 N). The doors on each side will open in a gullwing (or possibly sliding) manner to accommodate loading of vehicles, passengers, or freight. The overall structure weight is expected to be near 7,700 lb (3,500 kg) including the luggage compartments and door mechanism. The overall cost of the structure including manufacturing is targeted to be no more than $275,000.
The interior of the capsule is specifically designed with passenger safety and comfort in mind. The seats conform well to the body to maintain comfort during the high speed accelerations experienced during travel. Beautiful landscape will be displayed in the cabin and each passenger will have access their own personal entertainment system. Hyperloop Passenger Capsule The Hyperloop passenger capsule (Figure 8 and Figure 9) overall interior weight is expected to be near 5,500 lb (2,500 kg) including the seats, restraint systems, interior and door panels, luggage compartments, and entertainment Page 16
displays. The overall cost of the interior components is targeted to be no more than $255,000.
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Hyperloop Passenger Plus Vehicle Capsule The Hyperloop passenger plus vehicle capsule overall interior weight is expected to be near 6,000 lb (2,700 kg) including the seats, restraint systems, interior and door panels, luggage compartments, and entertainment displays. The overall cost of the interior components is targeted to be no more than $185,000. Note this cost is lower than the passenger only capsule interior as vehicles do not require the same level of comfort as passengers.
One important feature of the capsule is the onboard compressor, which serves two purposes. This system allows the capsule to traverse the relatively narrow tube without choking flow that travels between the capsule and the tube walls (resulting in a build-up of air mass in front of the capsule and increasing the drag) by compressing air that is bypassed through the capsule. It also supplies air to air bearings that support the weight of the capsule throughout the journey. The air processing occurs as follows (Figure 10 and Figure 11) (note mass counting is tracked in Section 4.1.4): Hyperloop Passenger Capsule 1.
Tube air is compressed with a compression ratio of 20:1 via an axial compressor. 2.
a.
The air travels via a narrow tube near bottom of the capsule to the tail. b.
A nozzle at the tail expands the flow generating thrust to mitigate some of the small amounts of aerodynamic and bearing drag. 3.
5.2:1 for the passenger version with additional cooling afterward. a.
This air is stored in onboard composite overwrap pressure vessels. b.
The stored air is eventually consumed by the air bearings to maintain distance between the capsule and tube walls. 4.
a.
Water is pumped at 0.30 lb/s (0.14 kg/s) through two intercoolers (639 lb or 290 kg total mass of coolant). b.
The steam is stored onboard until reaching the station. c.
Water and steam tanks are changed automatically at each stop. 5.
The compressor is powered by a 436 hp (325 kW) onboard electric motor:
a.
The motor has an estimated mass of 372 lb (169 kg), which includes power electronics. Page 18
b.
An estimated 3,400 lb (1,500 kg) of batteries provides 45 minutes of onboard compressor power, which is more than sufficient for the travel time with added reserve backup power. c.
Onboard batteries are changed at each stop and charged at the stations.
1.
Tube air is compressed with a compression ratio of 20:1 via an axial compressor. 2.
a.
The air travels via a narrow tube near bottom of the capsule to the tail. b.
A nozzle at the tail expands the flow generating thrust to mitigate some of the small amounts of aerodynamic and bearing drag. 3.
6.2:1 for the passenger plus vehicle version with additional cooling afterward.
in ≈ 52 kW Air In p ≈ 99 Pa T ≈ 292 K ?????? ≈ 0.49 kg/s
in ≈ 276 kW Air Out p ≈ 2.1 kPa T ≈ 857 K
?????? ≈ 0.2 kg/s Nozzle expander Axial compressor Intercooler Intercooler Air Out
F thrust
≈ 170 N P thrust
≈ 58 kW
Water Reservoir p ≈ 101 kPa T ≈ 293 K ?????? ≈ 290 kg
Air Out
p ≈ 11 kPa T ≈ 557 K Air Cooled T 300 K Air
p ≈ 11 kPa T ≈ 400 K Steam Out Water In ??????
?????? 2 ?????? ℓ ≈ 0.14 kg/s Steam
?????? ≈ 0.29 kg/s
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a.
This air is stored in onboard composite overwrap pressure vessels. b.
The stored air is eventually consumed by the air bearings to maintain distance between the capsule and tube walls. 4.
a.
Water is pumped at 0.86 lb/s (0.39 kg/s) through two intercoolers (1,800 lb or 818 kg total mass of coolant). b.
The steam is stored onboard until reaching the station. c.
Water and steam tanks are changed automatically at each stop. 5.
The compressor is powered by a 1,160 hp (865 kW) onboard electric motor:
a.
The motor has an estimated mass of 606 lb (275 kg), which includes power electronics. b.
An estimated 8,900 lb (4,000 kg) of batteries provides 45 minutes of onboard compressor power, which is more than sufficient for the travel time with added reserve backup power. c.
Onboard batteries are changed at each stop and charged at the stations.
P in ≈ 60 kW Air In p ≈ 99 Pa T ≈ 292 K ?????? ≈ 1.43 kg/s
in ≈ 808 kW Air Out p ≈ 2.1 kPa T ≈ 857 K
?????? ≈ 0.2 kg/s Nozzle expander Axial compressor Intercooler Intercooler Air Out
F thrust
≈ 72 N P thrust
≈ 247 kW
Water Reservoir p ≈ 101 kPa T ≈ 293 K ?????? ≈ 818 kg
Air Out
p ≈ 13.4 kPa T ≈ 592 K Air Cooled T 300 K Air
p ≈ 13.4 kPa T ≈ 400 K Steam Out Water In ??????
?????? 2 ?????? ℓ ≈ 0.39 kg/s Steam
?????? ≈ 1.23 kg/s
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4.1.4. Suspension Suspending the capsule within the tube presents a substantial technical challenge due to transonic cruising velocities. Conventional wheel and axle systems become impractical at high speed due frictional losses and dynamic instability. A viable technical solution is magnetic levitation; however the cost associated with material and construction is prohibitive. An alternative to these conventional options is an air bearing suspension. Air bearings offer stability and extremely low drag at a feasible cost by exploiting the ambient atmosphere in the tube.
Figure 12: Schematic of air bearing skis that support the capsule. Externally pressurized and aerodynamic air bearings are well suited for the Hyperloop due to exceptionally high stiffness, which is required to maintain stability at high speeds. When the gap height between a ski and the tube wall is reduced, the flow field in the gap exhibits a highly non-linear reaction resulting in large restoring pressures. The increased pressure pushes the ski away from the wall, allowing it to return to its nominal ride height. While a stiff air bearing suspension is superb for reliability and safety, it could create considerable discomfort for passengers onboard. To account for this, each ski is integrated into an independent mechanical suspension, ensuring a smooth ride for passengers. The capsule may also include traditional deployable wheels similar to aircraft landing gear for ease of movement at speeds under 100 mph (160 kph) and as a component of the overall safety system.
Hyperloop capsules will float above the tube’s surface on an array of 28 air bearing skis that are geometrically conformed to the tube walls. The skis, each 4.9 ft (1.5 meters) in length and 3.0 ft (0.9 meters) in width, support the weight of the capsule by floating on a pressurized cushion of air 0.020 to 0.050 in. (0.5 to 1.3 mm) off the ground. Peak pressures beneath the skis need only reach 1.4 psi (9.4 kPa) to support the passenger capsule (9% of sea level atmospheric pressure). The skis depend on two mechanisms to pressurize the thin air film: external pressurization and aerodynamics. The aerodynamic method of generating pressure under the air bearings becomes appreciable at moderate to high capsule speeds. As the capsule
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accelerates up to cruising speed, the front tip of each ski is elevated relative to the back tip such that the ski rests at a slight angle of 0.05º. Viscous forces trap a thin film of air in the converging gap between the ski and the tube wall. The air beneath the ski becomes pressurized which alters the flow field to satisfy fundamental laws of mass, momentum, and energy conservation. The resultant elevated pressure beneath the ski relative to the ambient atmosphere provides a net lifting force that is sufficient to support a portion of the capsule’s weight. However, the pressure field generated by aerodynamics is not sufficient to support the entire weight of the vehicle. At lower speeds, very little lift can be generated by aerodynamic mechanisms. As the capsule speed increases and compressibility effects become important, the pressure rise in the air bearing (assuming isothermal flow) will reach a limiting value which depends on the geometry of the air bearing. Thus additional sources of lift will be required. Lift is supplemented by injecting highly pressurized air into the gap. By applying an externally supplied pressure, a favorable pressure distribution is established beneath the bearing and sufficient lift is generated to support the capsule. This system is known as an external pressure (EP) bearing and it is effective when the capsule is stationary or moving at very high speeds. At nominal weight and g-loading, a capsule on the Hyperloop will require air injection beneath the ski at a rate of 0.44 lb/s (0.2 kg/s) at 1.4 psi (9.4 kPa) for the passenger capsule. The air is introduced via a network of grooves in the bearing’s bottom surface and is sourced directly from the high pressure air reservoir onboard the capsule. The aerodynamically and externally pressurized film beneath the skis will generate a drag force on the capsule. The drag may be computed by recognizing that fluid velocity in the flow field is driven by both the motion of the tube wall relative to the ski and by a pressure gradient, which is typically referred to as a Couette-Poiseuille flow. Such flows are well understood, and the resultant drag can be computed analytically (as done in this alpha study) and improved and/or validated by computational methods. The predicted total drag generated by the 28 air bearings at a capsule speed of 760 mph (1,220 kph) is 31 lb f (140 N), resulting in a 64 hp (48 kW) power loss. The passenger capsule air bearing system weight is expected to be about 6,200 lb (2,800 kg) including the compressors, air tank, plumbing, suspension, and bearing surfaces. The overall cost of the air bearing components is targeted to be no more than $475,000. Hyperloop Passenger Plus Vehicle Capsule The passenger plus vehicle version of the Hyperloop capsule places more aggressive lifting requirements on the air bearings, but the expanded diameter of the tube provides a greater surface area for lift generation. For this version, Page 22
an extra 12 in. (30 cm) of width would be added to each bearing. The nominal air supply pressure would increase to 1.6 psi (11.2 kPa), but the flow rate required would remain 0.44 lb/s (0.2 kg/s) thanks to the increased area under the skis. Drag on the skis at 42 lb f (187 N), results in a power loss of 85 hp (63 kW). The passenger plus vehicle capsule air bearing system weight is expected to be about 8,400 lb (3,800 kg) including the compressors, air tank, plumbing, suspension, and bearing surfaces. The overall cost of the air bearing components is targeted to be no more than $565,000.
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