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Computational Simulation of Lightning Interaction with Systems for Surge Protection Design
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Tim McDonald, [email protected] PES SPDC
2
EMA Simulation for Surge Protection Design
• Aircraft Lightning Phenomenology• Current Challenging in Simulation Technologies• Case-study: Rocket Lightning Protection Design using Simulation• Case-study: Wind Turbine Lightning Protection Design using Simulation• How to Model Complex Cable Harnesses on Real Platforms• The Importance of Measurements
4
Aircraft Lightning Phenomenology
EMA PROPRIETARY INFORMATION
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A Cockpit View of Lightning BetweenBeijing and Shanghai
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A View from the Cockpit:How Does Lightning Interact with this Aircraft?
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8EMA PROPRIETARY INFORMATION
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The First Lightning Crashes of Aircraft3rd September 1915 3rd September 1929
German Zeppelin LZ40 (L10)Destroyed by lightning off Neuwerk Island, Germany.
Ford AT-5 Tri-MotorCrash of first heavier-than-air aircraft destroyed by a
lightning strike. All eight occupants died when the airplane struck ground near Mt. Taylor, New Mexico.
Description
• Stepped leader starts at cloud and travels toward the earth
• At a distance of ~50 m from earth, upward going leader begins
• Upward going leader connects to stepped leader
• Return stroke with large current travels upward to cloud
• Process may repeat
Lightning Cloud to Ground Scenario
EMA PROPRIETARY INFORMATION
Separation of charge by aerodynamic forces and contact electrification
Peak Power ~1013 watts
C = Speed of Light
~100 Million Volts
Image Charge
Upward Leader
Stepped Leader• I ~1000A• Speed ~C/1000
Return Stroke• I ~1000A avg.,
200kA 1% level• Speed ~C/3
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Lightning Initiation by Cosmic Rays
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Source:Joseph R. Dwyer, “A Bolt out of the Blue, Scientific American”, May, 2005
EMA PROPRIETARY INFORMATION
14
Click slide to animate image
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One of the Few Photos of the Upward Going Leader
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Return stroke draining cloud charge
The Cloud is a Charge Reservoir
Not All Lightning Goes to Earth17
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Brightness (and current) decreases with altitude
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Top of bright return stroke traveling upward
EMA PROPRIETARY INFORMATION
Some Facts About Lightning• 1% Peak Current: 200,000 amperes (100 watt light bulb uses
about 1/2 ampere)
• Largest measured: ~450,000 amperes (Sea of Japan)
• Restrikes in one flash: Up to about 24
• Most (90%) airplanes: Create their own lightning strikes (the lightning would not exist without the presence of the aircraft)
20EMA PROPRIETARY INFORMATION
How Does Lightning Strike an Aircraft• Two fundamentally different lightning
strike scenarios for aircraft
– Naturally occurring strike
– Aircraft triggered strike
• Research programs have shown that about 90% of strikes to aircraft are triggered, and only 10% are naturally occurring
21EMA PROPRIETARY INFORMATION
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Two Fundamentally Different Lightning Strike Scenarios for Aircraft
ChargeRegion
OppositePolarityChargeRegion
Bi-directional junction leaders originate at airplane
Naturally occurringleader originates at
charge region
ChargeRegion
OppositePolarityChargeRegion
Bi-directional leaders originate at airplane
Naturally occurring strike (~10%) Aircraft Triggered strike (~90%)
NASA F-106 Lightning Research Program (1982-1989)
• Objective: Fly instrumented aircraft into thunderstorms to intercept lightning and collect data to understand it
• Experienced more than 700 strikes
• Most were aircraft triggered lightning
• EMA/R.Perala participated
23EMA PROPRIETARY INFORMATION
24 EMA PROPRIETARY INFORMATION
NASA F-106 Lightning Research Program
(1982-1989)
F-106 work Resulted in:
• Article in IEEE Spectrum Magazine July 1988
• Best Paper Award at NASA Langley Research Center
• Impacted SAE ARP 5412 lightning environments, especially waveform H
EMA PROPRIETARY INFORMATION 25
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Sweeping Strokes Were Indicated by Photography and Attachment Patterns
View Looking Aft From Side Mounted Camera
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View Looking Aft From Side Mounted Camera
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View Looking Aft From Side Mounted Camera
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View Looking Aft From Side Mounted Camera
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View Looking Aft From Side Mounted Camera
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View Looking Aft From Side Mounted Camera
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View Looking Aft From Side Mounted Camera
EMA PROPRIETARY INFORMATION 33
What Causes an Aircraft to Trigger Lightning?
Answer: The local electric field at an aircraft extremity becomes large enough to cause air breakdown
• Aircraft local E field, directly related to local charge density Q, has two components:– Aircraft net charge, caused by normal P-Static (precipitation static), including engine
charging
– Aircraft polarization charge, caused by the background thunderstorm electric fields
34EMA PROPRIETARY INFORMATION
P-Static Charging by Triboelectrification• Collision with atmospheric particles
• Snow, hail, graupel, dust, snow, ice crystals, rain, water droplets
• Charge transfer at contact, also called contact electrification
• Charging rates proportional to aircraft speed and frontal area (collision cross section)
35EMA PROPRIETARY INFORMATION
Engine Charging• Sodium impurities in exhaust
• Sodium ions transport charge away, leaving net charge behind
• Requires an ambient electric field (fair weather ~100 V/m; or thunderstorm field)
36EMA PROPRIETARY INFORMATION
Example: Net Charge Distribution+ + + +
+ + + + + + + + + + + + + + + + + + + +
+ + + +
QsC/m2
S∫Qsds = Qnet
distance
+ + + + + + + + + + + + + + + + + + + + + + + + +
+ +
+ ++ + + +
+ ++ + + ++ + + +
+ + + + + + + +
+ + + + + +
+ + + + + +
+ + +
+ + + + + +
+ + +
+ + +
37EMA PROPRIETARY INFORMATION
Thunderstorm Static Electric Field
QsC/m2
S∫Qsds = 0
- - - - - - - - - - -- - - - - - - - - - - - - + + + + + - - - - - - - - - - - - - - + + + + + - - - - - - - - - - - - - - + + + + + + + +
- - - - - - - - - + + + + + + + +
distance
+ ++ + + ++ + + +
+ +
- - - - - - - - - - - - -- - - - - - - - - -- - - - - - - - - -
- - - - - -
--- -
-- - - - - -
+ + + + + + + + + + + + + + + + + + + ++ + + + + + +
- - - - - - - - - - - - -- - - - - - - - - -- - - - - - - - - -
- - - - - -
+ + +
+ + + + + +
- -- - - -- - - -
- - - -- - - -- - - -
- - - -
Example: Polarization Charge Distribution
38EMA PROPRIETARY INFORMATION
39
Lightning protection strips
Example: Triggered Lightning Simulation on 265m long Airship
39EMA PROPRIETARY INFORMATION
.mkV10=axE
90 kV/m
Enhancement Factor = 9
Electric Field Enhancement FactorsAxial Background Electric Field
40EMA PROPRIETARY INFORMATION
Triggered Lightning ExampleIn-Flight Measured and Computed Surface B-dot Probes
• Comparison of in-flight measured and modeled (based on non-linear air chemistry) results for F-106 triggered lightning
• Axial ambient field 200kV/m
• Net aircraft charge 0.9mC
• The longitudinal B-dot probe is on the top of the F-106 fuselage
Interpretation• An initial breakdown at the nose• A later breakdown at the tail
EMA PROPRIETARY INFORMATION 41
Air Breakdown Model and Prediction of Triggered Currents
• Air conductivity nonlinear function of the total electric field
q is the electronic charge, 1.6 x10-19 coulombs,
ne is the number density of electrons [m-3],
n- is the number density of negative ions [m-3],
n+ is the number density of positive ions [m-3],
µe is the electron mobility [m2/volt-sec] and
µi is the ion mobility [m2/volt-sec].
𝜎𝜎 = 𝑞𝑞(𝑛𝑛𝑛𝑛 𝜇𝜇𝑛𝑛 + 𝑛𝑛 + 𝑛𝑛 𝜇𝜇𝑖𝑖) 𝑛𝑛 = ne + n-- +
EMA PROPRIETARY INFORMATION 42
Ionization Rate Equations for the Creation andLoss of the Three Species
ee
ee
eeeee
GntQnnnnvnt
n
nnnvnt
n
tQnGnvnt
n
+=++•∇+∂∂
=+•∇+∂∂
=−++•∇+∂∂
•
−+++++
−+−−−
•
+
)()(
)(
)(][)(
δβ
αδ
αβ
αe is the electron attachment rate (sec-1),G is the electron avalanche rate (sec-1),β is the electron-ion recombination coefficient (m3-sec-1),δ is the negative-positive ion recombination
EMA PROPRIETARY INFORMATION 43
Comparison of Measured and Computed Responses in-flight on F-106B Measured
Calculated
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Pulses Measured on F-106B for Typical Triggered
Lightning Strike
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(400 Hz to 100 kHz)
FIN CURRENT
BOOM CURRENT
FIN CURRENT (DC to 400 Hz)
D-DOT
LIGHT SENSOR
RECORDER TRIGGER DISCRETE
Temporal character of typical lightning strike.
100 MILLISECONDS
EMA PROPRIETARY INFORMATION 46
Pulses Measured on F-106B Vertical Fin Cap
for Typical Lightning Strike
Temporal character of typical lightning strike.
(dc-400 Hz)
0.1 s
80 A
80 A
80 A
Transient recordertrigger
EMA PROPRIETARY INFORMATION 47
Pulses Measured on F-106 Vertical Fin Cap with 40 ns Sampling Rate for Typical Triggered Lightning Strike
Time, 𝜇𝜇s
Vertical fin cap current corresponding to figure 3. (Recorded at 40-ns sample interval.
0 320 640 960 1280 1600 1920 2240 2560
18
12
6
0
-6
-12
-18
It, kA
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Peak Current Level Distributions for Aircraft Triggered
and Natural Lightning
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A View from the Cockpit:How Does Lightning Interact with this Aircraft?
Answer: Aircraft charging by P-Static and External Background E-fields creates arcs and streamers around
the aircraft. Some are swept over the windshield.
EMA Simulation for Surge Protection Design
• Aircraft Lightning Phenomenology• Current Challenging in Simulation Technologies• Case-study: Rocket Lightning Protection Design using Simulation• Case-study: Wind Turbine Lightning Protection Design using Simulation• How to Model Complex Cable Harnesses on Real Platforms• The Importance of Measurements
The Problem
• Design teams are expected to use 3D CAD information
• The design cycles are shorter• Teams must do more work in less
time!
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PLM and Electromagnetics
• Currently experiencing universal adoption of product lifecycle management (PLM) systems that require a high-level of interoperability and a focus on change management.
• EM engineers must learn to use 3D geometry in a practical way in their work progress without letting the complexity of handling the full CAD overwhelm their design cycles
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Challenges for EM• Though improvements in simulation speed and new
acceleration methods are always desired, they are not the limiting factor
• More than 90 % of the EM effort is dominated by non-solver issues:– CAD to CAE, cleaning and defeaturing– Interpretation of results and design modifications– Requirements trace, system engineering and test
specification• Remainder of this segment of the talk will focus on
these non-solver concerns
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Automating geometric manipulation tasks
• CAD to CAE dominates the simulation work cycle
• Current state-of-the-art technologies automate common tasks
• The trend of automation will continue to include machine-learning geometry operations
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Automated Simplification
• The problem is not lack of detail but too much detail.
• Current mechanical CAD is heavy and complex.
• New advances in automatic simplification allow a reduction in CAD size and complexity without sacrificing accuracy.
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Joining Objects to prepare for Simulation
• Shrink-wrap generators join bodies in contact, ignore small gaps and removes small holes to prepare for successful automatic meshing
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Machine Learning for CAD Simplification
• Frontier of this realm is machine learning that is trained by analyzing human processing steps
• Requires database of “before” and “after” geometry to train models
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EMA Simulation for Surge Protection Design
• Aircraft Lightning Phenomenology• Current Challenging in Simulation Technologies• Case-study: Rocket Lightning Protection Design using Simulation• Case-study: Wind Turbine Lightning Protection Design using Simulation• How to Model Complex Cable Harnesses on Real Platforms• The Importance of Measurements
Falcon Rocket – Margin
Issues
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Lightning Strike to
Catenary
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Integrated harness and full-wave software for the correct coupling
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Diode Sizing
• Candidate TVS load placed in series• Current through TVS calculated• Power dissipated is current time clamping voltage• Compare power to de-rated power dissipation limit
of selected part• Repeat if necessary
62
EMA Simulation for Surge Protection Design
• Aircraft Lightning Phenomenology• Current Challenging in Simulation Technologies• Case-study: Rocket Lightning Protection Design using Simulation• Case-study: Wind Turbine Lightning Protection Design using Simulation• How to Model Complex Cable Harnesses on Real Platforms• The Importance of Measurements
EMA3D CAD Import
Cable Routes
New Cables in EMA3D CAD
FDTD Mesh (50 mm)
Cable Cross Section
Cable 1 Cable 2 Cable 3
EMA3D Cable Cross Section Tool
• EMA3D has the unique capability of Co-simulating with a full-featured Transmission Line Solver
• Ability to quickly calculate the accurate capacitance and inductance matrix for cable cross-section
• Easy drag and drop cable cross section tool
Speed
• EMA3D full-wave simulation completed in minutes
• Built-in gradual permittivity scaling speeds up time-domain simulation by a factor or more than ten
• Built-in parallel simulation capabilities allow for speed up over 100 times on multi-core workstations and computational clusters
Magnetic Fields
• EMA3D can create color picture probes, slice probes, and animations of any fields or currents as necessary.
• The tools are easy to use and visualize the results
• The results are in ASCII and are readily exported to other packages with minimal manipulation
Magnetic Field Slice Probe
Waveform 1 Overall Cable Bundle Current
Waveform 1 Individual Pin Current
Waveform 1 Individual Pin Voltage
DC Simulation
EMA3D built-in gradual permittivity scaling allows for a time-domain calculation of a ramp up to DC as described.
01Simulation completed in a little over an hour
02Not practical with other time-domain solvers
03
Ramp to 800 A DC Simulation Results: Pin Currents
Material Library
EMA3D includes built-in sample properties for standard types of cables:• Diameter• Resistance• Transfer impedance parameters
EMA Simulation for Surge Protection Design
• Aircraft Lightning Phenomenology• Current Challenging in Simulation Technologies• Case-study: Rocket Lightning Protection Design using Simulation• Case-study: Wind Turbine Lightning Protection Design using Simulation• How to Model Complex Cable Harnesses on Real Platforms• The Importance of Measurements
Classic Cable Simulation Real World Cables
The Cable Conundrum
82
Certain Cable Complexity is Required to Get the Right Answer
83
CEM Model Details• Simplified bulk representations of
harnesses were initially used in the models
• The resulting answer diverged from a comparison to testing by 9 dB
Initial Bulk Cable Detailed Harness Model
Approximate diameter and resistance
84
Results from More Accurate HarnessMore accurate harness development in the model also permitted pin voltage calculation and comparison
0 1 2 3
x 10-4
-120
-100
-80
-60
-40
-20
0
20Vmax = 83t1 = 5.4e-05t2 = 1.9e-04
Time [s]
Vol
tage
[V]
Test 17LTATM Mod 4
85
RF Cable Branching Effect on Coupling to Cables
86
• The branched cable dissipates nearly all of its energy by 100 μs, ten times faster than the cable harness without branches
• The first vehicle resonance as well as the other modes below 30 MHz have been largely reduced
Cable TopologyMaximum
Current Level(mA per V/m)
Current Level Reduction
Straight Uniformly Packed Cable 500 Baseline
With Branching 30 24 dB
The Best Solution
• Automation of simplification for cables• Rapid specification of cable harness details based on the wiring
diagram• Transmission line modeling co-simulated with 3D simulation to
resolve branches, shields, and multiple conductors• Accelerated methods to speed up calculation
Cable Routing Simplification
88
• The CAD description of cables can be incredibly complex
• Hand simplification takes a long time
• Over simplification can give the wrong answer
How do we get the harness details into the model?
• Many details need to be defined for cables:– Types (twisted pair, coax, etc.)– Wire gauge– Termination impedances– Circuit loads– Shield properties transfer
impedance
89
Cable Wiring Diagram Simulation Model
Cable Harness Definition in
MHARNESS Wizard
EMA Simulation for Surge Protection Design
• Aircraft Lightning Phenomenology• Current Challenging in Simulation Technologies• Case-study: Rocket Lightning Protection Design using Simulation• Case-study: Wind Turbine Lightning Protection Design using Simulation• How to Model Complex Cable Harnesses on Real Platforms• The Importance of Measurements
Concentrate on Measurements that
can be Generalized to Entire Platform
• Current approach to EMP, Lx and other E3 environments is based on pass-fail characterization of the entire platform
• Targeted measurements of critical material properties is fast and low cost
• These measurements are more useful to analysis techniques across the entire frequency range
Large Platform Validation is Enabling Technology
Computational Simulation of Lightning Interaction with Systems for Surge Protection Design
94
Tim McDonald, [email protected] PES SPDC