A Deep Learning Simulation Framework for Building Digital Twins of
Wind Farms: Concepts and Roadmap
Subodh M. Joshi
a
, Thivin Anandh
b
and Sashikumaar Ganesan
c
Department of Computational and Data Sciences, Indian Institute of Science, Bangalore, 560012, India
Keywords:
Digital Twins, Physics Informed Neural Networks, Dynamic Mode Decomposition, Wind Engineering,
Physics-AI Hybrid Modeling.
Abstract:
Simulation-based Digital Twins are often limited by the difficulties encountered in the real-time simulation
of continuous physical systems, for example, fluid flow simulations in complex domains. Classical methods
used to simulate such systems, such as the mesh-based methods, typically require state-of-the-art computing
infrastructure to get a rapid estimation of the trajectory of the system dynamics if the problem size is large.
We propose a simulation framework comprising of a Physics Informed Neural Network (PINN) and a model
order reduction strategy based on the Dynamic Mode Decomposition (DMD) technique for rapid simulation of
fluid flows, such as air, in complex domains. This framework is primarily targeted at realizing a Digital Twin
of a wind farm in terms of the aerodynamics aspects. However, the framework will be flexible and capable
of creating simulation-based Digital Twins of other systems involving continuous physics. The reduced order
model aims to make this framework lightweight, such that a trained model will be able to run even on compact
edge devices. In this paper, we present the building blocks of this framework, a few key concepts, and a
roadmap for completing the framework. We illustrate our approach with the help of an example in transient
heat transfer.
1 INTRODUCTION
‘Digital Twins’ technology is set to transform main-
stream scientific computing thanks to a significant rise
in computing power and the development of innova-
tive algorithms. Digital Twins are becoming ubiqui-
tous because they help in improved efficiency, safety,
and reliability of engineering systems. A Digital Twin
refers to a digital representation of any physical sys-
tem, such that it closely follows the physical system
and serves as its virtual counterpart. A Digital Twin
typically consists of a physical system, its virtual (dig-
ital) model, and a two-way flow of data between the
two. Development of a Digital Twin in turn necessi-
tates the development of: (a) ‘faster than real-time’
simulation of the physical system on a computer (b) a
mechanism to incorporate real-time data from multi-
ple sensors into the simulation, and dynamically adapt
the simulation in response to these data, and (c) real-
time analytics predicting a future trajectory of the sys-
tem dynamics, which in turn helps in decision mak-
a
https://orcid.org/0000-0002-9239-8866
b
https://orcid.org/0000-0003-4969-3242
c
https://orcid.org/0000-0003-1858-3972
ing. Further, a Digital Twin necessarily involves a
two-way transfer of the information between the vir-
tual and the physical models, unlike a Digital Shadow,
which typically involves the flow of information from
the physical system to its digital counterpart alone.
We refer to (Fuller et al., 2020) for a detailed discus-
sion on the engineering aspects of Digital Twins. Al-
though this technology has come a long way in the
last decade, it still needs to overcome a few hurdles to
fully mature. One such challenge faced by researchers
today is that of achieving a faster than real-time sim-
ulation of complex fluid flows encountered in many
physical systems (Molinaro et al., 2021).
In this paper, we propose a simulation framework
for real-time simulation of fluid flows, possibly in-
volving a domain with a complex shape. The key re-
quirement of such a framework would be to capture
all the essential aspects of the flow physics while also
being computationally lightweight to achieve a near
real-time simulation. A few other desirable proper-
ties of the framework include:
1. Easy to use and easy to include new flow physics.
2. Suitable for large and computationally challeng-
ing problems.
356
Joshi, S., Anandh, T. and Ganesan, S.
A Deep Learning Simulation Framework for Building Digital Twins of Wind Farms: Concepts and Roadmap.
DOI: 10.5220/0011319500003274
In Proceedings of the 12th International Conference on Simulation and Modeling Methodologies, Technologies and Applications (SIMULTECH 2022), pages 356-363
ISBN: 978-989-758-578-4; ISSN: 2184-2841
Copyright
c
2022 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
3. Amenable for parallelization for added accelera-
tion and lightweight to port even on edge devices
if required.
4. Flexible and easy to use with other libraries used
for data analysis, visualization, and computing.
The traditional methods for simulation of con-
tinuous physical systems, such as the mesh-based
methods, are often computationally expensive and
require state-of-the-art computing infrastructure for
simulations of large systems. In recent times, a
new class of numerical methods is gaining pop-
ularity for simulation of continuous physical sys-
tems, namely the Physics Informed Machine Learn-
ing methods (Karniadakis et al., 2021). Physics In-
formed Neural Networks (PINNs) is a revolutionary
method which solves constrained Partial Differential
Equations (PDEs) with the help of a Deep Learning
model (Raissi et al., 2019). This method has accrued
significant attention since its inception thanks to its
strengths, viz. a) an elegant formulation b) compara-
ble accuracy to the classical methods at a marginal
computing cost c) availability of powerful libraries
for Machine / Deep Learning d) ability to exploit
Graphics Processing Units (GPUs) or hybrid com-
puting hardware platforms for parallel computing etc.
There have been several variations proposed inspired
from the original PINNs method. We present a short
literature review of Deep Learning-based simulation
methods in the next section. Due to the strengths of
the PINNs method, we choose it as the core physics
simulator for our framework. As a Proof-of-Concept
(PoC), we incorporate the original form of the PINNs
method into our framework. However, we subse-
quently plan to explore other improved techniques,
such as the variational PINNs (VPINNs).
The second essential component of our framework
includes a Reduced Order Model (ROM) based on
the Dynamic Mode Decomposition (DMD) strategy
(Schmid, 2010) on top of the PINNs model. DMD is
a technique for model order reduction where the sys-
tem dynamics is approximated to be linear in space-
time. DMD, also known as the Koopman mode anal-
ysis, gives a spectral decomposition of the spatio-
temporal data (Kutz et al., 2016). Depending on the
required level of the model fidelity, only a few modes
of this spectral decomposition can be re-combined to
generate a reasonably accurate reconstruction of the
original spatio-temporal data. Unlike Proper Orthog-
onal Decomposition (POD), the DMD modes need
not be orthogonal and are accompanied by the time
dynamics. This is a very powerful technique to de-
rive a model-agnostic data-driven ROM of the phys-
ical/computational system. There exist a few vari-
ations of this method, suitable for different applica-
tions. We present further details of this technique and
a short literature survey in the next section. In the pro-
posed technique, the Koopman mode analysis is per-
formed to get the dynamic modes of the data-matrix
created from the output of the PINNs model. Only a
small number of dynamic modes, enough to capture
the maximum variance of the system is required to re-
construct the system-dynamics. The DMD ROM will
not only reduce the computing time for short-term
predictions, but also make our model lightweight in
order to port it even on an edge device. The trained
neural network or/and the DMD model can be de-
ployed on an edge device for short-term predictions,
which can then be re-trained periodically. The de-
tailed procedure to deploy a DMD ROM in synchro-
nization with the PINNs model is described in the
subsequent sections.
In this paper, we present the key concepts and
ideas behind the proposed framework, its building
blocks and the road-map for its implementation. The
rest of the paper is organized as follows: section
2 presents a detailed review of Physics Informed
Machine Learning and model order reduction using
DMD. Section 3 presents the proposed framework, its
building blocks, and the key concepts behind its op-
eration. We present one motivating example in tran-
sient heat transfer to demonstrate the working of our
framework in section 4. The road-map for its imple-
mentation is presented in section 5. Lastly, we present
the conclusions in section 6.
2 LITERATURE REVIEW
In the recent times, Machine Learning, and in par-
ticular Neural Networks are gaining popularity for
scientific computing (Aimone et al., 2017; Karni-
adakis et al., 2021) including fluid dynamics simu-
lations (Brunton et al., 2020). A key strength of this
approach lies in the superior computational speedups
possible in contrast to the classical techniques for the
same level of numerical accuracy. In particular, the
Physics Informed Neural Networks (PINNs) intro-
duced by Raissi et al. (Raissi et al., 2019) have caught
the attention of the scientific community since intro-
duced in 2019. In PINNs, the loss function for the
neural network optimization includes the residual of
the governing PDEs in addition to the losses associ-
ated with the initial and the boundary conditions. The
derivatives of the conserved variables with respect to
the spatio-temporal variables required for constitut-
ing this loss function (i.e., inputs to the network) are
found through forward-mode Automatic Differentia-
tion (Raissi et al., 2019; G
¨
une et al., 2018). PINNs
A Deep Learning Simulation Framework for Building Digital Twins of Wind Farms: Concepts and Roadmap
357
have been used in a wide range of applications, in-
cluding Navier-Stokes equations for modeling fluid
flows (Jin et al., 2021), earth system modeling (Ir-
rgang et al., 2021), high-speed flows (Mao et al.,
2020), hyperbolic transport problems (Eduardo and
Florindo, 2021) etc. We refer to a recent pre-print
by Cuomo et. al. (Cuomo et al., 2022) for a de-
tailed survey of the PINNs method, a few of its vari-
ants and various applications are solved using it. As
a Proof-of-Concept (PoC), we have implemented the
original PINNs method of Raissi et al. in the current
(experimental) version of the framework. However,
we plan to incorporate the latest ML-based methods
in the proposed framework in the future.
The next important component of our framework
is the model order reduction scheme using Dynamic
Mode Decomposition (DMD). DMD was first intro-
duced by Schmid for spectral analysis of the nu-
merical and experimental data for fluid dynamics
(Schmid, 2010). Since its inception, several vari-
ants of this technique have been developed by various
researchers. (Schmid et al., 2011) presents a com-
prehensive review of applications of DMD in scien-
tific computing. In DMD, the spatio-temporal data is
decomposed in spectral modes (also called Dynamic
modes) and the associated time dynamics. The de-
tailed algorithm for DMD, its variations, a few ap-
plications and its connections with the Koopman-
mode analysis have been presented in (Kutz et al.,
2016). Additionally, we refer to the recent review of
the DMD method and its variants given in (Schmid,
2021). In our framework, we implement the DMD
ROM in PyDMD, an open-source Python library for
dynamic mode decomposition (Demo et al., 2018).
Further details regarding the implementation and the
working of our framework are presented in the next
section.
3 PINNs-DMD SIMULATION
FRAMEWORK FOR DIGITAL
TWINS
In this framework, we use a Physics Informed Neural
Network in its original (differential) form for carrying
out the fluid flow simulations. In the current version
of the software, we have implemented the original
PINN method from Raissi et. al. (Raissi et al., 2019).
However, we plan to explore other methods and de-
velop novel methods targeted for this application in
future. In the PoC version of our framework, we use
the Python-based library DeepXDE (Lu et al., 2021)
for the implementation of the PINN-based Navier-
Stokes equations solver. The output of the PINNs
model is used to create a spatio-temporal data ma-
trix which is in turn used for creating a reduced order
model (ROM). We use the classical DMD method for
the creation of this ROM. In the future, we plan to ex-
plore a more efficient and accurate variant of DMD,
such as higher-order DMD or multi-resolution DMD
for this application. For the DMD implementation,
we use the open-source library PyDMD (Demo et al.,
2018). Since DeepXDE and PyDMD are both imple-
mented in Python, the integration of the two models
becomes easy. Further, Python offers a rich suite of
software libraries for analysis, computing and visu-
alization, which help in making the framework more
useful and versatile.
3.1 How the Proposed Framework
Works
The framework works as follows:
1. A Physics Informed Neural Network (PINN) acts
as a data-driven physics-aware solver. The PINN
model estimates the flow conditions inside the do-
main, for example, a wind farm, respecting the
boundary conditions, the initial conditions, and
the flow physics.
2. Once the boundary data become stable, the PINN
starts training a Dynamic Mode Decomposition
(DMD) reduced order model (ROM). This mainly
consists of creating the data-matrix containing the
spatio-temporal data corresponding to the flow
variables such as velocity and pressure, followed
by spectral decomposition of this data to get Dy-
namic modes and the associated time dynamics.
3. The DMD ROM will be responsible for the real-
time prediction of flow conditions on the domain.
We consider only a few prominent modes (cumu-
latively containing at least 90% energy) resulting
in reduced storage and processing power require-
ments. This in turn also allows us to run the ROM
model on a low-power computer such as an edge
device.
4. An analytics module keeps monitoring the time-
dependent boundary conditions. As soon as any
changes in the boundary conditions beyond a
threshold value are detected, the PINN model un-
dergoes an online training to accommodate the
changing boundary conditions.
5. When the changes stabilize, the PINN model re-
trains the DMD ROM to economically yield the
real-time flow predictions.
SIMULTECH 2022 - 12th International Conference on Simulation and Modeling Methodologies, Technologies and Applications
358
6. The PINN model will be trained on a high-
performance computing hardware such as a clus-
ter equipped with GPUs. However, once trained,
the model can be ported on an edge device such as
NVIDIA Jetson Nano. Alternately, the ROM can
be ported on the edge device, and the PINN can
be trained and deployed on a cluster computer.
7. The framework also contains some auxiliary code.
The auxiliary modules will be responsible for data
visualization, file handling and tools for analytics
such as anomaly detection, error monitoring, cre-
ating a meta-model, automated testing, etc.
Figure 1: A schematic illustrating the proposed framework.
Figure 1 shows a ‘Digital Shadow’ or the
simulation-based Digital Twin framework. In the cur-
rent work, we focus on the digital representation of
the physical system, and not on the feedback and the
control module. However, these components will be
considered for implementation in the future.
3.2 Strengths of This Approach
1. The use of PINNs as a physics solver offers three
main advantages:
(a) PINNs fundamentally perform a nonlinear re-
gression and are naturally suited for solving
coupled nonlinear PDEs. This makes the
framework versatile and allows the integration
of other physics to the framework as required
with relative ease.
(b) PINNs technology is based on Artificial Neu-
ral Networks (ANNs) and the backpropagation
algorithm. There are many powerful libraries
available for this purpose. Thus, the proposed
framework benefits from these libraries.
(c) Compared to the traditional (mesh-based)
methods for solving PDEs, the PINNs method
is relatively more amenable for parallel imple-
mentation using GPU devices. This imparts su-
perior speedups required for near real-time sim-
ulations.
2. The main advantage that this framework offers
compared to the traditional methods is that it fa-
cilitates continuous (online) training of the PINNs
model while the DMD ROM yields short-term
predictions.
3. The DMD based ROM makes the framework even
faster. DMD is a model-agnostic means to derive
a ROM model. Further, it is a very simple tech-
nique to implement. Once built, the deployment
of a DMD ROM requires very little computational
power and therefore is ideal for deployment on an
edge computing platform.
4. The entire framework is planned and developed
in Python, a general purpose programming lan-
guage. Many powerful libraries exist for Deep
Learning, data analysis, visualization, and file
handling in Python. The framework will greatly
benefit from these libraries.
5. The framework is flexible. The framework allows
the integration of different (and more powerful)
techniques for the physics simulation, as well as
the model order reduction. Thus, methods bet-
ter suited for different applications and hardware
platforms can be incorporated as required.
4 NUMERICAL EXAMPLE
4.1 Problem Description
We consider the 2D time-dependent diffusion equa-
tion (Ganesan and Tobiska, 2017) as follows,
u
t
α∇
2
u = 0, in = [0, 1]
2
(1)
α = 1
We consider a unit square as the computational do-
main. Initially, the entire domain has a uniform tem-
perature (u(t = 0) = u
0
) value of zero. The Bound-
ary conditions imposed on the problem are graphi-
cally illustrated in Figure 2. As the time advances,
the heat dissipates in the domain, affecting the tem-
perature (u(t)) at every point on the domain.
4.2 Numerical Solution
We simulate this system till time t = 0.15s. Fig-
ure 3 shows the temperature variation at the location
(x, y) := (0.5, 0.625). We also indicate the solutions
obtained using a Finite Element Method (FEM) in
A Deep Learning Simulation Framework for Building Digital Twins of Wind Farms: Concepts and Roadmap
359
Figure 2: Computational domain (unit square) along with
the boundary conditions.
0.0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Time(s)
0.02
0.00
0.02
0.04
u(t)
Solution at x = 0.5 y = 0.625
PINNs
DMD ROM
FEM
Figure 3: Time Series Solution at at y = 0.625.
the same figure. We refer to (Ganesan and Tobiska,
2017) for the theory and the implementation details
of FEM. It can be seen that the PINNs-based solution
follows a similar general trend of time evolution as
the FEM-based solution. The sparse sampling of data
used for training the PINNs model, which helps in
rapid training of the PINNs model, leads to the rel-
ative difference between the FEM solution and the
PINNs solution. However, the focus of this paper is
not on the comparison between the mesh-based meth-
ods (e.g., Finite Volume or Element methods) and the
PINNs method. Instead, we wish to emphasize on the
performance of the DMD ROM meta-model in com-
parison to the PINNs based physics solver, which is
the key idea behind this framework. It can be seen
from Figure 3 that the ROM solution obtained using
the DMD modes closely follows the PINNs solution.
These results show promise, and the proposed frame-
work can be developed further for more complex ap-
plications. In this PoC version of the framework, we
have deployed a rather crude PINNs model facilitates
rapid prototyping by reducing training time. There is
scope to improve the accuracy of the PINNs solver
with respect to the mesh-based numerical methods.
As listed in the roadmap of our framework in subse-
quent sections, we have accounted for these optimiza-
tions in our development plan.
Figure 4: Solution comparison - PINNs vs DMD ROM.
Figure 5: First Two DMD modes of the System.
1.0 0.5
0.0 0.5 1.0
Real p ar t
1.0
0.5
0.0
0.5
1.0
Imaginary par t
Figure 6: Eigenvalues in the complex plane.
Figure 4 shows the distribution of the solution
on the domain computed using the PINNs method
and the DMD ROM method derived from the PINNs
method. It can be seen that the reduced order model
produces an identical solution as the PINNs method.
Figure 5 shows the first two eigenmodes obtained us-
ing the dynamic mode decomposition. These modes
SIMULTECH 2022 - 12th International Conference on Simulation and Modeling Methodologies, Technologies and Applications
360
show a visual representation of the spectral decompo-
sition using the DMD method. Figure 6 shows the
eigenvalues obtained during the dynamic mode de-
composition. It can be seen that all of the eigenval-
ues have the value of the real part less than 1, i.e.,
contained within the unit circle (also shown in the fig-
ure). This shows that the DMD ROM model is sta-
ble in time and produces reliable results. Thus, the
PINNs model coupled with the DMD ROM produces
identical results as the PINNs model alone. The sig-
nificance of this observation is that, once the bound-
ary data stabilizes, the DMD ROM alone can be used
for near-term predictions, and the cost associated with
the PINNs forward propagation is saved. Further,
the PINNs can undergo online training independently
to accommodate the changing boundary conditions
while the DMD ROM continues to produce the near-
term predictions. For large networks and complex
physical systems, this would result in considerable
savings in computing time.
5 ROADMAP FOR
IMPLEMENTATION
In this section, we discuss the roadmap for building
the proposed framework. The following points will
be considered during the development:
1. Core libraries for physics simulation:
We plan to implement the original PINN method
of Raissi et. al. (Raissi et al., 2019) to simulate
the wind flow around the wind turbines in the first
version of the framework. Once the proof of con-
cept (PoC) is built, the framework would be im-
proved by incorporating other state-of-the-art AI
solvers. In the PoC version, we plan to implement
the PINNs method using the DeepXDE library
(Lu et al., 2021). However, we will also explore
other, more powerful libraries such as NVIDIA
Modulus for large-scale problems in the future.
2. Reduced order model
In the current PoC framework, we have deployed
the classical DMD algorithm for model order re-
duction using the PyDMD library. In the fu-
ture, we plan to incorporate other advanced DMD-
based schemes (e.g. multi-resolution DMD,
Higher-order DMD etc.). Further, we plan to de-
ploy the DMD ROM on an edge device such as
NVIDIA Jetson Nano.
3. High performance computing
The challenge we foresee in developing a Digital
Twin of the entire wind farm, is the scaling of the
Deep Learning model on parallel hardware plat-
forms. We plan to develop a hardware-aware im-
plementation of the PINNs and the DMD models
to complete the online training rapidly.
4. Uncertainty quantification
We plan to incorporate an inbuilt mechanism for
uncertainty quantification, taking into account pa-
rameter uncertainties. Further, the initial and
boundary conditions can be considered as statis-
tical distributions rather than fixed values, and ac-
cordingly, a statistical description of the flow field
can be sought (Yang and Perdikaris, 2019; Yang
et al., 2021).
5. Computing on edge devices
We plan to port the reduced order model on an
edge device. The purpose of this development is
twofold.
(a) It shows the capability of our approach to pre-
dict near-term physics, while being lightweight
in order to work even on an edge device.
(b) It serves the purpose of flow prediction where
the HPC facilities are not readily available.
We will experiment with deploying the ROM as
well as the trained PINNs model on an edge de-
vice such as NVIDIA Jetson Nano.
6. Analytics
We can use the rich ecosystem of libraries and
softwares for data analytics, visualization, and file
handling that Python offers. The framework will
contain auxiliary code catering to data analysis
(for example, anomaly detection), visualization
of the physical data as well as time-series infor-
mation pertaining to the important flow parame-
ters, displaying and monitoring error metrics etc.
Lastly, we plan to include code to export the raw
data in various file formats to facilitate scientific
visualization using third-party libraries.
7. Optimization
Finally, we plan to perform studies to derive the
best performing network architectures and hyper-
parameters for the PINNs model. This will en-
sure optimal performance from our PINNs and
DMD ROM models. Further, we plan to exper-
iment with the training process of PINNs itself.
In this regard, the important question to address
is whether we can train the PINNs on a range of
boundary values instead of a fixed value in order
to minimize re-training of the PINNs, which can
be costly. We plan to validate our approach first on
academic test cases (e.g., simple test cases in heat
transfer, incompressible fluid dynamics, etc.) fol-
lowed by simulations of a single wind turbine, and
lastly, simulation of a wind farm. At each level of
A Deep Learning Simulation Framework for Building Digital Twins of Wind Farms: Concepts and Roadmap
361
testing, different aspects of the framework, such
as numerical accuracy, efficiency, hardware scal-
ing etc., will be tested, validated, and improved.
6 CONCLUSION
We propose a Python-based framework for
simulation-based Digital Twin of continuous
physical systems. The primary target application
for this framework is the simulation of a wind farm
from the aerodynamics point of view. However,
the framework can be easily adapted for use in
other fluid flow applications and other continuous
physical phenomena. We use PINNs as the main
physics simulator and a DMD-based ROM for further
accelerating the simulations. The novelty of this
approach lies in online training of the DMD ROM by
the PINNs model for rapid flow prediction. Further,
the framework aims to provide an-inbuilt uncertainty
quantification of the flow variables and yield a
real-time simulation of the continuous systems via
online training. The training of the PINNs model
will take place in a cluster computer, whereas the
trained PINNs model, along with the DMD based
ROM, will be ported on an edge device. In this paper,
we have demonstrated our approach with the help of
an example in transient heat transfer. In the future,
we plan to develop this framework further to enable
real-time simulation of complex physical phenomena,
including aerodynamics simulations of a large wind
farm. Lastly, we also present a roadmap for the
implementation of the proposed framework, where
we identify a few challenges we may encounter and
steps for their mitigation.
ACKNOWLEDGEMENTS
The authors would like to thank Dr. Abhineet Gupta
and Dr. Suranjan Sarkar (Shell, Bangalore) for their
feedback and discussions. The authors would like to
thank the anonymous reviewers for their detailed re-
views.
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