Silvertip Design
This is the first slide in a presentation to demonstrate how the
simulation works and hopefully how we can learn from it. The left
mouse button (LMB) moves forward to the next slide; RMB moves
back one slide; the MMB opens a side menu showing all of the
slides. With the presentation displayed in a separate window the
slides should still be accessible from the main simulation's bullet links.
The main option buttons:
- 'Pause'/'Resume' the simulation
- 'Mean' (toggles) the current average (yellow) bar and a reference
average (green) bar.
The road traffic properties are controlled by the sliders below:
- 'Density' [vehicles/km/lane] - the calculations use decimal values to
more accurately represent larger systems.
- 'Truck Fraction' as a percentage [%] - the simulation can only add
or remove single vehicles and the road is about 0.75 kilometers long.
- 'Timewarp' speeds up the simulation, but not the vehicles, so that
flow patterns can develop more quickly after changes are made.
The vehicle properties are controlled by additional sliders.
Max Accel (a) - maximum acceleration
Conf. Decel (b) - comfortable deceleration (braking)
Max Speed (v) - maximum speed
Time Gap (T) - miniumum gap between vehicles in seconds [s]
Min Gap (s) - miniumum distance between vehicles [m]
Two sliders control the introduction and removal of BladeRunner vehicles.
'BR Cars' sets the average number of cars carried by a BladeRunner
platform with a carBus body.
BR Usage [%] defines the percentage of the cars on the road (density
minus the fraction that are trucks) that will be transported.
A carBus can carry up to twelve cityCars but with the load length split
to also carry freight pods, or a freight unit, there is no lower limit to
viability. Clicking in the middle of the BR Usage slider will introduce
enough carBuses to remove half of the cars from the road and provide
the power to charge the cityCars directly while on the move
(plug-in en-route).
As a first approximation the average power [kW] of each vehicle type
multiplied by the number of vehicles of that type per kilometer [v/km]
together gives a total power per kilometer for the highway.
( 37kW x 58 cars ) + ( 112kW x 2 trucks ) = 2,370 [kW/km]
Enabling the mean (or average) option shows a 'yellow' moving bar.
Disable and re-enable it also shows a green bar. This logs all of the
calculated average values for all plots for the current vehicle type(s) and
drag components (hill, drive-line, tyres ..) selected.
The total number of vehicles 'on the road' per kilometer multiplied by the
average speed of the highway is the current vph. The logged values are
the current values stored when 'Mean' is re-enabled.
Eg. swapping 50% of the heavy and expensive 'self-charging' hybrid cars
to small and affordable pure electric city cars (BR Usage). The energy
consumed per km reduces to just 1672kW a saving of nearly 30%.
(37kW x 29 cars) + (112kW x 2 trucks) + (75kW x 5 carBuses)
Actual throughput increases by 28% while traffic density drops by 40%
The traffic flow simulation can be adjusted by using the slider panel
(below). Changes are made progressively with each time step of the
simulation. Vehicles appearing or disappearing in an instant is not
normal behaviour and as manoeuvres require the agents (vehicles) to
know where other vehicles are in relation to themselves - some panic.
These occasional and short lived outbursts are listed in the console.
If you would like to reuse the new settings they can be exported as a
javascript object or JSON file. The parameters and their values form a
single line of text. Word-wrap in a text editor helps visualise the
settings but 'sublimetext', for example, has an html/css/JS prettify
extension that reformats the object as an indented list making it easy to
see and to edit.
'Reload', restarts the simulation with the page's default settings. Or
'Browse' for an earlier saved JSON file and then 'Import' those settings to
overwrite the default values. This process of saving and reloading using
alternative settings requires that cookies are enabled in the browser. This
also goes for the changing of the number of lanes in the highway.
Tabs (0..3) are the four vehicle types. Clicking on an extended tab
returns to the simulation. The coloured variables in the mathematical
expression are explained in the legend (below). The top level expression is
'State of charge'. Clicking on any variable digs into the expression and
exposes other variables used in the calculations.
By clicking on the variable to the left of the '=' sign takes you back. The
value of the variable for each vehicle is plotted in the graph above. The
points are coloured by vehicle type and move from top to bottom based
on their position on the road. The ring road is about 0.75km long and
starts on the right (at 3 O'clock).
The hill climb and decent energy (power and force) is split between energy
used (Eu) to provide tractive power and energy in from brake power
(Ei). But the total brake power 'Pb' is then only stored or discarded
based on a vehicle's ability to recover brake energy 'Rb' [%] or not.
The inertia force 'Fa' does not include the rotational inertias of the wheels,
motor/engine or drive chain due to their significance in motorway driving.
They act like flywheels storing and releasing energy. In terms of vehicle
dynamics, they tend to hold you back when you want to go faster and
push you forward when you need to slow down.
The standard deviation (sigma) and the 'mean' value (greek letter mu) are
calculated for all of the vehicles of the selected type, and the distribution
curve is shown. Clicking in the graph area allows the distribution curve
to be moved to points of interest. A second click releases the action.
The 'tick' and the 'cross' icons at the top of the plot allow the
parameter values to be recalculated for all but the 'ego' vehicle of the
selected type (tab); if the Sankey diagram is active behind the plot only
the ego vehicle will be affected. The 'tick' has to be selected twice to
activate edit as there is no undo. The 'cross' then writes any changes to
the default settings. Switching tabs only avoids updating the settings.
The speeds of the vehicles are plotted against road position with the
darker coloured bars representing the inside (left lane). Other plots
include the Frequency distribution of the speed, the Energy split with
several unit options and the 'State of Charge'.
The plots only show the vehicle type(s) and the drag properties selected.
Auto-scaling is active only when there is a single vehicle type active and
while the 'Mean' is disabled. When two or more vehicle types are active
the Y-axis scale can be changed by toggling the vehicle type on and off for
the scale you would like to use.
All calculations are done in SI units - kgs, metres, seconds. But the unit
of energy typically used for batteries and household bills is [kWh].
Conversions are also made for energy intensity and fuel consumption and
vehicle power is expressed as energy/time or [kW].
Tab (4) opens the calculation sheets 0 to 6. The blue values can be
edited directly or changed incrementally by the mouse wheel.
Different browsers respond differently to these inputs. The values are
identified by a letter (a) to (z). Hovering over the letter with the
mouse will show the expression. Numbers after the letter indicate
the calculation sheet the value is on (typically the current sheet).
By pausing the simulation and reducing the 'Max Speed' to a very low
value the drag components for individual vehicle types can be plotted
separately. By then increasing the 'Max speed' when the simulation is
resumed a 'V-axis' sweep plot will be produced. A total of the selected
parameters is also plotted. The plot is cleared by toggling the V-axis
button and only creates plots for the vehicle types selected.
The Sankey diagram shows the energy flow for one of the vehicles. The
drag force components [N] x the distance travelled [m] is the work
done [Nm]. The rate of doing the work is power [W] and the time
it takes [s]. Energy in [Nm] or [Ws] or Joules[J]. Dimensional
analysis is great. A force [N] x a velocity [m/s] = Power [Nm/s] or
Energy [Ws] expended per second [W]. Larger amounts of energy are
in kW and hours [kWh] or 3.6[MJ].
Selecting 'Sankey' when the simulation is running allows you to pick a
vehicle. The simulation pauses and the pause button changes to '-ego-'
and will turn the pointer to a '+' when pressed. Picking a vehicle adds a
black dot on its roof and restarts the simulation. The 'ego' vehicle also
shows up in the other plots as a black dot or bar. A second 'pause /
resume' button at the top of the page can cancel the sequence.
Once an 'ego' vehicle is selected its current values are dispayed in the
diagram on the left. The force and power reflect the drag components
selected. But the total work done, the state of charge and the driveline
losses do not change. The drag 'bars' scale with force (or power/speed in
the case of aircon.) and the 'Regen' potential includes the downhill brake
forces. The simulation is driven by the traffic model.
The heat rejected on the right assumes that the vehicle has an engine and
that its thermal efficiency is say 45% (0.45). The amount of
mechanical energy required by the vehicle - which we know - divided by
0.45 is the fuel energy needed. The fuel energy minus the Work energy is
the Thermal energy.
As thermal energy is termed 'rejected' or 'wasted' we can change the sign.
Similarly the processing and distribution of the fuel consumes energy and
yields the total input ('well to wheel'). Electric vehicles reduce the local
heat wasted and the distribution losses significantly but not totally and the
need for cabin heating or air-conditioning consumes (or wastes) energy.
With an 'ego' vehicle selected the current values can also be logged to
produce a 'History' plot. The yellow 'mean' bar has been replaced
with a white bar showing the current total value for the ego vehicle.
The white band is the average for the other vehicles of the same type,
plus and minus one standard deviation (68% of the vehicles).
The units can be changed and the plot will be auto-scaled. The
simulation time scrolls along the X-axis. Increasing the timewarp
value compresses the time axis. With the 'History' plot active the log
buffer can be exported to a spreadsheet in csv format using the 'Export'
button. At the same time the ego vehicle parameters can be saved in
JSON format. Both files have a default date_time name convention.
The SOC history (above) shows the charge remaining in the battery (or
fuel in the tank) and would typically drop over time until the driver
decides to pull into a services and fill up. The BladeRunner vehicle
selected shows the opposite with all (six + one) charge levels increasing
over time when driving in the GPT lane. With twelve cityCars all
charging the carBus would have to run off its own batteries initially.
When in the GPT lane the rolling resistance for the vehicle swaps
between (Rt) rubber tyres and (Rw) steel wheels. And if the
charging power (Pin) is above 1kW the vehicle will also draw power
from the panels between the tracks. The charging rate (Ri) defines
how much of the available power the vehicle actually draws and in the
case of a carBus, priority is given to charging the cars onboard.
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Slide One
Buttons
Vehicle properties
BladeRunner
First approximation
Vehicles per hour
Enable mean bars
BladeRunner usage
Slider panel
Reuse settings
Browse and Import
Speeds plot
Energy plot
SI units
Vehicle types
Vehicle parameter plot
Hill climb force 'Fhx'
Inertia force 'Fa'
Standard deviation
'tick' and 'cross'
Calculation sheets 0..6
Calculation sheet 4
V-Axis
Sweep plot
Sankey diagram
Ego vehicle
Work done
Thermal efficiency
Rejected heat
Energy history
Current total value
Export logged data
SOC history
Guided power transfer (GPT)