Sudhi Uppuluri, CSEG LLC
Andrew Hintz, Mentor Graphics
Automotive Transient Thermal Modeling Seminar
www.mentor.com© 2012 Mentor Graphics Corp. Company Confidential2
Why do we care?
Many Technologies being explored/implemented to meet CAFÉ standards. And they don’t always work well together!
Automotive Transient Thermal Modeling Seminar, 2013, 09, 12
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Integrated System Simulation is the only way!
Many Supplier offering fuel economy technologies!— Some may not work as well for your system
OEM’s have the responsibility as system integrators to evaluate and cherry pick the technologies based on benefit/price ratio!
Automotive Transient Thermal Modeling Seminar, 2013, 09, 12
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Why is Engine Thermal Management important?
Cold Engine = Bad Fuel Economy
— Incomplete combustion
— Increased thermal losses through the combustion chamber walls
— Increased friction losses with the increase of the lubricant oil viscosity.
Frictional losses reduce as engine warms up
Reference: 2000-01-0299
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Why Engine Thermal Management Modeling is hard!
Why Engine
Thermal Manageme
nt Modeling is hard!
Responsibility fragmented across the organization
Model is data
hungry
Data not readily
available
Majority of data
is steady-state
Experimental procedures
are for validating
designs, not models
Requires expertise
across multiple subjects
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Modeling Considerations
Drive Cycles
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Flow of Today’s Talk
Overall Engine Thermal Model— Engine Structure sub-system— Cooling System sub-system— Front-end cooling pack sub-system— Cabin Model— Engine Oil Sub-system— Trans Oil sub-system
Modeling and evaluating FE improvement technologies— BSG (Start-Stop Scenario)— Dual Use heater core technology
Integrating with Control System/Vehicle Models Simplifying models into a response
surface/equation
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Introductions
CSEG Premier Consulting
Company on System Simulation
Mentor Graphics Consulting partner for advanced system modeling
> 25 yrs combined experience modeling automotive systems
Wide variety of tools including Flowmaster, Matlab/Simulink, GT Power, FloEFD, and custom application development in .NET
Mentor Graphics Application Engineer 5 years experience in
variety of industries and applications
Primary automotive engineer for Mechanical Analysis Division, including vehicle thermal management, hybrid/electric, exhaust, airside, cabin comfort, and lubrication modeling.
Automotive Transient Thermal Modeling Seminar, 2013, 09, 12
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Flowmaster V7 is a System Level CFD Simulation Software Program, enabling analysts and engineers to perform System Simulation to the design, validate, optimise and maintain complex fluid systems
— Pressure, temperature, and flow predictions— Liquid, gas, steam/water systems— Steady state & transient— Heat transfer— Design of experiments & parametric studies— Component sizing & flow balancing— Simulation Data Management— Built-in Empirical Data
System Modeling Platform
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What is Flowmaster?
Project View Schematic View Network View
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Sub-systems: Engine
Component – Engine: Basic— Pressure loss
– Fixed Loss Coefficient– Pressure loss vs. velocity– Pressure loss vs. volumetric flow rate– Pressure loss vs. volumetric flow rate
and temperature– Loss Coefficient vs. Reynolds
number*— Thermal inertia
– Solid type & mass– Initial temperature
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Sub-systems: Engine
Component – Engine: Basic— Heat Generation
– Heat Flow Rate– Fixed value– Heat flow rate vs. time– Signal input
• Customizable heat flow rate dependency
— Heat Transfer Coefficient– Dittus Boelter coefficients– Fixed value– Heat transfer coefficient vs.
Reynolds number– Signal input– Nusselts number vs. Reynolds and
Prandtl #s
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Modeling Engine Structure
◦ Capturing every heat transfer path (more components = more data required)
Reference: SAE paper 910302, Kaplan and Heywood.
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◦ Capturing every heat transfer path (more components = more data required)
Reference: SAE paper 960073, Bohac, Baker and Assanis.
Modeling Engine Structure
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Modeling Engine Structure
Capturing minimum number of masses to predict warm-up
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Get Heat additions/removal correct
+Qcomb
+QFric
Heat Loss to the ambient (Conduction + Natural convection + Forced convection)
Heat Loss to the Coolant
Heat Loss to the Oil
Heat absorbed by the mass
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FMEP – Through analytical methods
Your Initials, Presentation Title, Month Year
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Sub-systems: Cooling System
Component – Pump: Water Pump— Suter Head Curve*
– Pressure rise vs. rotational speed and fluid flow rate
— Suter Torque Curve*– Power consumption vs. rotational
speed and fluid flow rate— Rated data
– Flow– Head– Speed– Power or Efficiency
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*Suter Curves
Normalized curves (with respect to pump’s rated condition) describing variation in head or torque over full range of operating conditions— Utilizes Homologous Pump Laws
Suter curve conversion tool available in Flowmaster
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Sub-systems: Cooling System
Component – Pump: Test Data Supplier data can be directly
input into the model
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Sub-systems: Cooling System
Component – Thermostat— Control amount of fluid routed to
Radiator– Lift vs. temperature
– Defines valve’s position as function of fluid’s temperature
– One for heating, one for cooling– Alternatively, define Hysteresis offset
and one Lift vs. temperature curve— Bypass opening vs. opening
– Defines opening to bypass as function of opening to Radiator
— Simplified pressure loss– Loss Coefficient vs. opening
— Time Constant– Transport delay between coolant and
wax
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Transient Considerations on TSTAT
Time Constant is the time it takes TSTAT to open to 63% opening on a step change of temperature
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Sub-systems: Cooling System
Component – Reservoir: Expansion Tank— Tank dimensions
– Height of top above base– Height of each inlet/outlet with
respect to base– Height of base above “sea level”– Volume
– Constant horizontal cross-sectional area
– Cross-sectional area vs. height– Volume vs. height
— Initial pressure, temperature, liquid level
— Pressure loss at each arm for inflow & outflow scenarios
— Hard pressure constraints– Mimic functionality of pressure relief
or vacuum relief valveAutomotive Transient Thermal Modeling Seminar, 2013, 09, 12
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Sub-systems: Cooling System
Component – Reservoir: Expansion Tank— Thermal capacity of tank
– Tank material– Mass of empty tank
— Heat transfer between tank and environment
– Heat transfer coefficient– External surface area– Environment temperature
— Tank expansion– Reference pressure and temperature,
and Poisson’s Ratio– Surface of volume change vs.
pressure change and temperature change
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Sub-systems: Cooling System
Component – Heat-Exchanger: Radiator— Independent pressure loss data for
hot side and cold side– Fixed Loss Coefficient– Pressure loss vs. flow rate– Pressure loss vs. velocity– Loss Coefficient vs. Reynolds
numbers
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Sub-systems: Cooling System
Component – Heat-Exchanger: Radiator— Thermal interaction between fluids
– Fixed thermal duty– Fixed hot or cold side temperature
change– Fixed thermal effectiveness– Effectiveness vs. hot side flow and
cold side flow– Heat transfer coefficient (q/ITD*area)
vs. hot side mass flow rate and cold side mass flux (mass flow/area)
– Fixed overall heat transfer coefficient + effectiveness vs. number of transfer units and specific heat ratio
– Nusselt number vs. hot side and cold side Reynolds numbers*
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Transient Modeling Considerations
Loss Coeff vs Re curve accounts for changes pressure drop changes at different temperatures.
This is critical when running at different drive cycles.
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Transient Modeling Considerations
Preferred Approach as NU extrapolates well
Effectiveness is held constant outside the test data. And we are always operating outside the test data.
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*Loss Coefficient vs. Reynolds number
Pressure loss vs. fluid flow valid for specific fluid property
As fluid properties change, pressure loss changes
Loss Coefficient vs. Reynolds number— Reynolds number is ratio of inertial forces to viscous
forces– “Flow condition” based on fluid’s properties and fluid flow
— “K” value in first equation now varies with fluid properties and flow rate
— Higher accuracy in pressure loss calculations
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*Loss Coefficient vs. Reynolds number
“Loss Curve” conversion tool available in Flowmaster— Convert pressure loss vs. flow curve to Loss Coefficient
vs. Reynolds number
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*Nu vs. Rehot & Recold
Flowmaster conversion tool for Nusselt surface more “free-form”— Define hot and cold flow
– Volumetric or mass flow– Mass flux
— Thermal performance – Heat duty– Effectiveness– q/ITD*area– Exit hot side temperature– Exit cold side temperature
— Additional data– Hot and cold fluid types– Inlet hot and cold temperatures and pressures
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Sub-systems: Front End Air Cooling
Freest
ream
Freest
ream
Un
derb
od
y/U
nd
erh
ood
Fan
Rad
iato
r
Con
den
ser/
EO
C
Ch
arg
e A
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oole
r
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Sub-systems: Front End Air Cooling
Your Initials, Presentation Title, Month Year
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Non-uniformity of flow
Reference: A Systems Engineering Approach to Engine Cooling Design, Kanefsky, Nelson and Ranger, SAE Lecture, SP-1541
There is non-uniformity in airflow and temperature in the cooling pack.
Segmentation is one way to capture the non-uniformity accurately (Need to collaborate with CFD to determine non-uniformity at different driving conditions)
Nusselts number is the recommended way when modeling segmented heat exchangers.
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Sub-systems: Front End Air Cooling
Airside Visualizer and Segmenter (AVS)— Model a cooling pack where airflow through each
component is not equal– Doesn’t easily lend itself to 1D modeling
— Segments model in such a way to align common flow paths
Fig 60 image Reference: A Systems Engineering Approach to Engine Cooling Design, Kanefsky, Nelson and Ranger, SAE Lecture, SP-1541
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Sub-systems: Front End Air Cooling
Arrange components in 1-D manner— Add visualizer and
segmenter data for components in airside path
– Defines spatial arrangement of components
— Profile parameter options– Non-uniform parameters
— Running visualizer provides 3-D representation
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Sub-systems: Front End Air Cooling
Component – Radiator Shutter— Dimensions
– Height and width— Shutter opening
– Fixed value– Signal input
— Visualizer and Segmenter data— Pressure loss
– D.S. Miller data
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Sub-systems: Front End Air Cooling
Segmenter divides cooling pack into 1-D segments— Define split planes
– Number of splits– Spacing of splits– Manually define split plane
— Overlay split planes
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Sub-systems: Front End Air Cooling
Segmented results
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Front-end Cooling Pack Calibration
Accurate CFD under hood airflow information
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Sub-systems: Charge Air
Component – Turbo Charger— Compressor performance data
– Pressure ratio vs. corrected mass flow and corrected rotational speed
– Efficiency vs. corrected mass flow and pressure ratio
— Turbine performance data– Corrected mass flow vs. pressure
ratio– Efficiency vs. corrected mass flow
and pressure ratio
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Transient Conditions – Determination of ACT
Inputs are Charge Air Mass flow rate and temperatures
Air Charge Temperature (ACT) determined for the engine drive cycle Co-simulated with the combustion program
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Sub-systems: Engine Oil
Component – Closed System Sump— Two-arm reservoir— Sump is within the system— Initial liquid level, pressure, and
temperature specifier— Define volume— Thermal capacity of tank
Component – Open System Sump— One-arm reservoir
– Open-system offers a bit more stability
— Sump modeled as boundary condition
— Liquid level, pressure, and temperature specifier
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Sub-systems: Engine Oil
Component – Oil Pump Strainer— Based off Orifice: Square
component— Full flow area and orifice flow area— Loss coefficient vs. area ratio
– Default D.S. Miller data
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Sub-systems: Engine Oil
Component – Pump: Oil Pump— Positive displacement pump— Rotational speed
– Fixed value– Signal controlled
— Volumetric displacement– Fixed value– Surface map
– Flow and power vs. pressure rise and rotational speed
– Requires reference viscosity– Signal controlled
– Total displacement– Displacement ratio
— Pump coefficients– Leakage, Coulomb friction, Viscous
friction
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Sub-systems: Engine Oil
Component – Pressure Regulator— Three-arm component
– Through branch– Relief branch
— Sets pressure limit as function of flow rate
— When limit is reached, relief valve opens
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Sub-systems: Engine Oil
Component – Oil Filter— Pressure loss component
– Specify fixed loss coefficient– Pressure loss vs. flow or velocity– Loss coefficient vs. Reynolds number
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Sub-systems: Engine Oil
Component – Journal Bearings— Geometry of bearing
– Groove, bore, pocket— Rotational speed
– Fixed value– Vs. time– Signal controlled
— Rotating or rocking— Average clearance bearing to
journal– Fixed value– Signal controlled
— Bearing force– DIN (cycle averaged)
– Fixed value– Vs. time– Signal controlled
– Booker-Martin (discrete cycle angles)
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Sub-systems: Engine Oil
Component – Passage: Rotating— Pipe component that accounts for
pressure fluctuations due to centrifugal forces
– Define position of end points in relation to shaft
– Define motion– Circular– Piston/Slider– Cam Follower
Component – Loss: Bearing Entrance— Using in conjunction with Passage:
Rotating– Models oil flow from groove, bore, or
pocket of bearing to rotating hole in journal
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Sub-systems: Cabin Comfort
Component – Cabin— Solar radiation definition
– Direct and diffuse radiation– Fixed value– Vs. time
– Ground reflectivity– Azimuth and altitude angle
– Fixed value– Vs. time
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Sub-systems: Cabin Comfort
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Sub-systems: Cabin Comfort
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Sub-systems: Cabin Comfort
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Sub-systems: Cabin Comfort
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Component – Cabin— Key results
– Mean cabin temperature– Temperatures of different locations
– Roof, screen, instrument panel, etc– Cabin comfort
– Predicted percentage dissatisfied– Predicted mean vote
Sub-systems: Cabin Comfort
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Modeling multi-zone passenger cabin
Your Initials, Presentation Title, Month Year
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Integrating Sub-systems
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Technology Evaluation – Belt Starter Generator
Enables turning off engine when idling
Efficient and high power generation
Transient Considerations – — BSG head load and thermal
inertia— Effect to engine thermal
performance— Temperature of BSG (safe
operating temperatures)
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Technology Evaluation – Belt Starter Generator
Thermal Load of BSG
Zero Flow Heat Transfer
in engine block
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Technology Evaluation – Belt Starter Generator
Warm-up is affected as engine turns off during engine idle
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What is Zero Flow Heat Transfer (ZFHT)?– ZFHT allows heat transfer analysis
where flow conditions are below Flowmaster’s minimum flow threshold
Background— Modern automotive cooling
strategies use ‘low’ or ‘zero’ coolant flow to achieve rapid engine warm-up for
– Reduced emissions– Increased fuel economy
Zero Flow Heat Transfer
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Suitable for any single phase network that is…— Wholly, or partially, subject to
‘zero flow’ at some point in its operating cycle
— and intended for Incompressible HT analysis
A standard feature of the ‘Heat Transfer’ Option
Currently focused on cooling system analysis but can be used for any liquid application where the user needs to predict— HT in one or more static circuit— Resulting temperature values
Key user defined BCs include convective HTCs which are typically from:• 3D CFD component/sub-assy
models• Experimental results (i.e.
thermal survey of engine cooling system)
• Experience of a similar system
Zero Flow HTSystem simulation• HT Steady State• HT Transient
Predicted results for system• Heat transfer
distribution• Temperature profile
Zero Flow HT is…
Zero Flow Heat Transfer
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Technology Evaluation – Dual use Heater Core
Dual Use Heater Core – Heater Core is used to provide supplemental engine cooling, without affecting cabin comfort.
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Technology Evaluation – Dual use Heater Core
The effect on AGS closure rate, and required fan size can be performed with supplemental Engine Cooling model
AGS open control
Fan Size
Heater core airflow
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Technology Evaluation – Dual use Heater Core
AGS CLOSE
D
AGS OPEN
AGS Closed for significant portion of the time
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Technology Evaluation – Dual use Heater Core
Stable control of engine oil temperature
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Technology Evaluation – Dual use Heater Cooler
X CFM through Heater Core leads to
1.5X CFM reduction in Front end airflow (when AC is OFF)
1.2X CFM reduction in Front end airflow (when AC in ON)
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FLOWMASTER FOR SIMULINK
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Flowmaster for Simulink
A Flowmaster library providing an interface between Simulink & Flowmaster comprising allowing co-simulation between Flowmaster & Simulink.
The link comprises — A graphical user interface to configure the link— A Simulink S-Function to interface between Flowmaster &
Simulink
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Simulink Library Browser
Flowmaster for Simulink
Analysis Process
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Flowmaster for Simulink
The Flowmaster for Simulink interface in Simulink
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Flowmaster for Simulink
Interface to more than one Flowmaster network during a Simulink simulation
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Flowmaster for Simulink
Configuring a Flowmaster Network— Data is passed into and out of Flowmaster using COM
Controller & Gauge Components– Data in via COM Controller– Data out via COM Gauge
COM GaugeCOM Controller
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Flowmaster for Simulink
Configuring Flowmaster Controllers & Gauges— Each Controller and Gauge being used to in the link must
have a unique ‘Title’ set on the component data form
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Flowmaster for Simulink
Configuring Simulink— Data is passed into the Flowmaster block using a “goto”
block– “goto” block tag visibility must be set to Global
— Data is passed from Flowmaster block using a “from” block
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RESPONSE SURFACE MODELING
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Experiments: Response Surfaces & Meta-Models
Features— A Meta-model contains
simulation results sets, all defined input parameters, a selected output parameter and a radial function
— A Response Surface is a 3D plot of two selected input and one output parameter with an applied radial function
What it does— Provides a visual
representation of a Flowmaster system Meta-model
— Provides a means of evaluating the Meta-model prior to export as C code or an S-Function
Deviation tools to assess quality of the meta model
Response Surface generated in V7.9.1
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FM Application v Response Surface Model
Inputs Outputs
Inputs Outputs
• Design and model• Infinitely variable• No guarantee of convergence• Not real time simulation
• Pre-defined system• Bounded simulation• Guarantee of convergence• Real time simulation
Flowmaster V7 Application
Response Surface Model
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Simple Cooling Circuit example
Heat Load
Radiator
Front-end airflow
Bypass valve position
Target TempPump Speed
m_bypass
m_total
m_rad
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Response Surface Generation
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Creating an Response Surface in Flowmaster
A Response Surface is created in the following steps
Select a Radial
Function
Select Results set
Select Input
Parameters
Select Output
Parameter
Click Display
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Creating a Response Surface
A radial function is selected
The radial functions available are— Gaussian— Duchon’s— Hardys— Inverse MultiQuadrics
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Radial Functions
The following radial basis functions (RBF) were selected from common usage— Gaussian
— Duchon’s
— Hardy’s
— Inverse MultiQuadric
*where Φ(r) is the radial function and r0 is a scale factor and r is the radial distance between points
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Creating a Response Surface
Two input parameters are selected for the plot and one output parameter Clicking ‘Display’ shows the 3D and two 2D plots
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Evaluating a Response Surface
The effective fit of the applied radial function can be evaluated from the available deviation plots
Percentage deviation is calculated as the percentage difference between a results point and an interpolated point derived from the fitted curve
The Response Surface can be refined by selecting an alternative radial function, or if available alternative results sets e.g. with more or fewer levels
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Evaluating a Response Surface
Deviation details (2D scatter chart)
Surface plot points
Deviation mean line
Plotted deviation points(lower is better)
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Evaluating a Response Surface
3D Deviation plot
Input parameters
Deviation points as surface plot
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Export Code Examples
C code or an S-Function can be exported from a saved Meta-model by clicking the export button
C code S-Function code
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Today’s Talk
Overall Engine Thermal Model— Engine Structure sub-system— Cooling System sub-system— Front-end cooling pack sub-system— Cabin Model— Engine Oil Sub-system— Trans Oil sub-system
Modeling and evaluating FE improvement technologies— BSG (Start-Stop Scenario)— Dual Use heater core technology
Integrating with Control System/Vehicle Models Simplifying models into a response
surface/equation
Automotive Transient Thermal Modeling Seminar, 2013, 09, 12