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Critical Transitions in Complex Systems

Critical transitions, Complex systems, Complex networks, Dynamical Systems, Thermoacoustics Instability, Oscillatory instability, Early warning signals (EWS), Smart passive control, Climate networks, Cloud microphysics.

IRIS Webinar

Many complex systems such as turbulent thermo-fluid systems, climate systems, financial markets, power grids, infectious diseases exhibit critical transitions where the system shifts abruptly from one state to another. Such critical transitions can have undesirable or even catastrophic consequences including failure of space missions, power blackouts, extreme weather, extinction of species in ecosystems and sudden crash of financial markets. The central objective of this proposal is to establish a world class center to study critical transitions and extreme events in flow and energy systems in engineering and nature. The center will strive to unravel the science behind these transitions in diverse systems and develop trained manpower and translational technologies.

  • We will develop technologies to anticipate critical transitions and extreme events, and mitigate the effect of these transitions through smart control actions.

  • We will translate the understanding obtained from the application of complexity science to such transitions into technology through product development and start-up incubation.

  • We will develop an online international education and technology dissemination program accessible to diverse audience across the globe through webinars, short term courses, workshops, and an international master’s program.

Critical Transitions in Complex Systems

R.I. Sujith

Principal Investigator

People

R. I. Sujith

Area of Interest

R. I. Sujith

Principal Investigator

Aerospace Engineering

Website Google Scholar
sujith@iitm.ac.in
Complex Systems Theory, Dynamical Systems Theory, Thermoacoustic Instability, Oscillatory Instabilities in Turbulent Flows, Climate Networks, Droplet Dynamics in Turbulent Flows and their Implications for Cloud Formation

Project

Diverse complex systems often exhibit common dynamical features during critical transitions, despite independent details of the physical problems. Apparently dissimilar phenomena such as thermoacoustic instability and climate systems are driven by the flow of fluid and energy and their interactions. In thermoacoustic systems, flow, flame, and acoustic dynamics interact through feedback loops giving rise to oscillatory instabilities. In climate systems, extreme rainfall is associated with spatiotemporally organized weather patterns, while floods are related to large scale atmospheric circulation anomalies.

Establish a worldclass center to study critical transitions and extreme events in flow & energy systems

However, all these complex phenomena occur due to interaction between various subsystems and display similar spatio-temporal patterns during critical transition in the system. It is of utmost importance to analyze, predict and possibly mitigate the occurrence of such catastrophic extreme events. A well-suited approach to study such highly interconnected systems is that of complex networks theory.

The temporal dynamics of such complex systems display intermittency prior to critical transition of the dynamics. Also, the spatio-temporal patterns observed prior to critical transitions in such systems have fractal characteristics. Such features may be analysed by constructing complex networks based on either physical or abstract interconnections in the complex system. We intend to use complex networks to identify critical regions, clusters and communities in the flow dynamics and their effect on critical transitions. The various subsystems portray interaction through various physical phenomena and such interactions occur at multiple scales.

Visualizing a thermoacoustic systems

We propose to study such multi-physics and multi-scale problems through multilayer network analysis which allows to treat each component as a layer of a larger and more complex network. Using complex networks approach, we not only aim to develop an understanding of the physical phenomena that lead to critical transitions in complex systems, but also develop early warning signals to predict the occurrence of such transitions.

  • The behavior of complex systems is often independent of the details of the problem. We need to investigate the common features of critical transitions, for different classes of systems. In particular, we need to identify their scaling laws, and the origin of the scaling. This understanding will help us to anticipate their occurrence, to predict their magnitude and to mitigate them.

  • Apparently dissimilar phenomena such as thermoacoustic instability and climate are driven by the flow of fluid and energy and their interactions. In thermoacoustic systems, the flow (vortical and acoustic) and the heat release from the flame are interacting through feedback loops. In climate systems, the flow (wind and ocean currents) and heat release rate (condensation of water vapor during precipitation) are interacting. Thus, methods and insights developed for one system can be applied to the other, with rich returns.

  • The tools developed by the complex systems community are often tested on synthetic data. Thermo-fluid systems offer a platform for development, application and refinement of these tools.

  • Floods are related to large scale atmospheric circulation anomalies. Extreme rainfall does not occur as isolated events, but associated with spatiotemporally organized weather patterns. Better understanding of such extreme events using complex systems approach will help us to anticipate their occurrence and to provide precursors.

  • Complex systems are highly interconnected. These connections can be physical (e.g., a power grid) or abstract as in the case of thermo-fluid systems. These connections are multi-physics, multiscale and multilayer. In thermoacoustics, there are vortical and heat release rate networks interacting between each other and through the acoustic field. In climate networks, we have multiple layers comprising wind velocity, temperature, precipitation and cloud cover with interaction across layers. Further, there are river networks, vegetation networks, land subsidence. We need to unravel the connections between these layers and find the origin of extreme events and precursors to these extreme events.

  • The temporal dynamics of complex systems display intermittency en route to critical transition; e.g., bursts of periodic oscillations amidst epochs of low amplitude chaos presage the onset of oscillatory instabilities such as thermoacoustic or aeroacoustic instabilities in turbulent flow. During the transition, the spatio-temporal dynamics shows the emergence of communities; e.g., the emergence of large vortices in thermo-fluid systems and the emergence of droplet clusters in clouds before the formation of rain drops. We need to unravel how such communities arise and their effect on critical transitions. Complex networks are ideally suited for this purpose.

  • Currently, the networks are formed primarily as correlation networks. We need to construct physics-inspired-networks with meaningful fluid dynamics.

  • The spatio-temporal dynamics of events leading up to a critical transition as diverse as thermoacoustic instability and spread of infectious diseases are highly heterogeneous. Ignoring this heterogeneity can lead to grossly wrong predictions.

  • The critical, but often ignored dependence of critical transitions in complex systems on the rate of change of parameter (R-tipping) needs to be investigated, to be able to successfully anticipate and mitigate these transitions (Ashwin et al. 2012). Further, practical situations may be complicated by the interaction of R-tipping and N-tipping (noise induced tipping), which will complicate control strategies.

  • We need to obtain early warning signals and have strategies to mitigate these transitions. Mitigation strategies in thermoacoustics include amplitude death, open loop forcing and various passive control strategies. Implementing these in highly turbulent real-world situations will be a challenge. Extreme climatic events such as synchronous floods have to be managed through the management of dams.

The central objective is to establish a world class centre to study critical transitions and extreme events in flow and energy systems in engineering and nature. The center will strive to unravel the science behind these transitions in diverse systems and develop trained manpower and translational technologies. The specific objectives are:
  • Develop tools for early warning of critical transitions and extreme events
  • Mitigating such transitions and their effects through smart control actions in engineering systems and suggesting better management of the effects of critical transitions and extreme events for natural systems.
  • Translating the understanding obtained from the application of complexity science to transitions into technology through product development and start-up incubation.
  • Develop an online international education and technology dissemination program accessible to diverse audience across the globe through webinars, short term courses, workshops and Master’s program.

Current status

Publications in research journals

  • A. Krishnan, R. I. Sujith, N. Marwan & Jürgen Kurths (2021) “Suppression of thermoacoustic instability by targeting the hubs of the turbulent networks in a bluff-body stabilized combustor”, Journal of Fluid Mechanics link.

  • S. Singh, A. Roy, K. V. Reeja, A. Nair, S. Chaudhury & R. I. Sujith (2021) “Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling”, Journal of Engineering for Gas Turbines and Power link.

  • T. Braun, V. Unni, R. I. Sujith, J. Kurths & N. Marwan (2021) “Detection of dynamical regime transitions with lacunarity as a multiscale recurrence quantification measure”, Nonlinear Dynamics link.

  • S. Tandon & R. I. Sujith (2021) “Condensation in the phase space and network topology during transition from chaos to order in turbulent thermoacoustic systems”, Chaos link.

  • A. Sahay, A. Roy, S. Pawar & R. I. Sujith (2021) “Dynamics of Coupled Thermoacoustic Oscillators Under Asymmetric Forcing”, Physical Review Applied link.

  • A. Roy & R. I. Sujith (2021) “Fractal dimension of premixed flames in intermittent turbulence”, Combustion and Flame link.

  • A. Roy, C. P. Premchand, M. Raghunathan, A. Krishnan, V. Nair & R. I. Sujith (2021) “Critical region in the spatiotemporal dynamics of a turbulent thermoacoustic system and smart passive control”, Combustion and Flame link.

  • A. Varghese, A. Chechkin, R. Metzler & R. I. Sujith (2021) “Capturing multifractality of pressure fluctuations in thermoacoustic systems using fractional-order derivatives”, Chaos link.

  • K. Manoj, S. A. Pawar & R. I. Sujith (2021) “Experimental investigation on the susceptibility of minimal networks to a change in topology and number of oscillators”, Physical Review E link.

  • I. Pavithran & R. I. Sujith (2021) “Effect of rate of change of parameter on early warning signals for critical transitions”, Chaos link.

  • T. M. Bury, R. I. Sujith, I. Pavithran, M. Scheffer, T. M. Lenton, M. Anand & C. T. Bauch (2021) “Deep learning for early warning signals of regime shifts”, bioRxiv link.

  • D. Premraj, K. Manoj, S. Pawar & R. I. Sujith (2021) “Effect of amplitude and frequency of limit cycle oscillators on their coupled and forced dynamics”, Nonlinear Dynamics link.

  • R. I. Sujith & V. R. Unni (2021) “Dynamical systems and complex systems theory to study unsteady combustion”, Invited Topical Review, Proceedings of the Combustion Institute link.

  • A. Roy, S. Singh, K. V. Reeja, A. Nair, S. Chaudhury & R. I. Sujith (2021) “Flame dynamics during intermittency and secondary bifurcation to longitudinal thermoacoustic instability in a swirl-stabilized annular combustor”, Proceedings of the Combustion Institute link.

  • S. A. Pawar, R. Raghunathan, K. V. Reeja, P. R. Midhun & R. I. Sujith (2021) “Effect of preheating on the transition to thermoacoustic instability in a bluff-body combustor”, Proceedings of the Combustion Institute link.

  • Induja Pavithran, Vishnu R. Unni, Alan J. Varghese, R. I. Sujith, Abhishek Saha, Norbert Marwan, and Juergen Kurths (2021) Predicting the Amplitude of Thermoacoustic Instability Using Universal Scaling Behaviour, Accepted for publication in Journal of Engineering for Gas Turbine Engines and Power.

  • Abhishek Kushwaha, Praveen Kasturi, Samadhan Pawar, R. I. Sujith, Ianko Chterev, and Isaac Boxx (2021) Dynamical characterization of thermoacoustic oscillations in a hydrogen-enriched partially premixed swirl-stabilized methane/air combustor, Accepted for publication in Journal of Engineering for Gas Turbine Engines and Power.

Review Papers
  • Sujith, R. I., & Unni, V. R. (2020). Complex system approach to investigate and mitigate thermoacoustic instability in turbulent combustors. Physics of Fluids, 32(6), 061401.
  • Sujith, R. I., & Unni, V. R. (2021). Dynamical systems and complex systems theory to study unsteady combustion. Proceedings of the Combustion Institute, 38(3), 3445-3462.
  • Juniper, M. P., & Sujith, R. I. (2018) Sensitivity and nonlinearity of thermoacoustic oscillations. Annual Review of Fluid Mechanics, 50, 661-689.
Invited Talks, Keynote address

  • R. I. Sujith “Spatiotemporal Dynamics of Thermoacoustic Instability”, International Indo-US online workshop on Application of Machine Learning and Dynamical Systems Approach for Early Detection and Control of Combustion Instabilities on January 5 - 7, 2021

  • “Dynamical systems and complex systems theory to study unsteady combustion”, Invited Topical Review, International Symposium on Combustion, Adelaide 2021 January 25-29.

  • R. I. Sujith “Complex system approach to investigate and mitigate thermoacoustic instability in turbulent combustors”, Georgia Tech Combustion Webinar, June 5, 2021

Patents:
  • SYSTEM AND METHOD FOR OPTIMIZING PASSIVE CONTROL OF OSCILLATORY INSTABILITIES IN TURBULENT FLOWS Patent No.: US 10,895,382 B2 (45) Date of Patent: Jan. 19, 2021; Inventors: Vishnu R. Unni Sujith Ramanpillai Indusekharan Nair, Abin Krishnan (IIT Madras) Norbert Marwan and Jürgen Kurths (Potsdam Institute for Climate Impact Research, Germany)

Collaborations

International Collaborations

National Collaborations

The Central Library Initiative

Prof Raman I Sujith

Current International Network Projects

POLKA (Pollution Know-How and Abatement): 2019-2023

Societal impact

Short term (<2 years)

The primary impact of the project in the short term will be in the areas of energy security, aviation and space. In the development of combustors for rockets, gas turbines for aero engines and electricity production, the occurrence of various thermo-fluid instabilities has been a plaguing problem. Our current research will enable us to predict, avoid or mitigate these instabilities.

Medium term (<5 years)

Extreme weather and climate-related events affect the society by causing death, injury, illness and socioeconomic impacts. With the help of complex network analysis, we will analyze interactions among different layers of satellite and ground-based data (wind, temperature, precipitation, land use, land topography etc.), providing insights regarding changing weather patterns and precursors for extreme events. Also, understanding cloud dynamics will have a strong social impact on safeguarding our agricultural fields and habitats of many living creatures during the time of the extreme events.

Long term (greater than 5 years, but less than 10 years)

We will provide guidelines for sustainable development accounting for the increased variability in weather patterns due to global warming. We will generate transdisciplinary insights and provide society and government with sound information for decision making. The startups we incubate will develop employment opportunities.

Sustenance statement

The basis of the center is a well thought out vision, refined over the years, and sustained passionate action based on this vision. The center will function as an agile and nimble unit, with ability to respond rapidly to opportunities and challenges. Students and post-docs come and go; however, we have systems in place to keep the knowledge and skills in the center. We will maintain long-term collaboration with students, maintain existing collaborations (both international and national) and identify new potentially fruitful collaborations. The team members will participate in workshops, both in person and online. We will have a system in place for maintaining our equipment. We will have annual maintenance contracts for the important equipment and will have dedicated maintenance schedule. The lab personnel will be responsible for the equipment to be operated in a sanitized dust-free and clean environment to prolong the life cycles of the components. The team will be well trained to operate the lasers, high speed cameras and other optical diagnostic equipment. There will be regular internal and external safety audits for the lab and lab equipment. Our projects and support from the industry and grants from funding agencies will ensure adequate funds for maintenance and for procuring additional equipment.

Media Outreach

  • IIT Madras: candle flame oscillators shine light on combustor stability, The Hindu February 08, 2020 Using stacks of candles tied together, and studying pairs, and quartets, of such candles, Dr. Sujith and his team has come up with interesting inputs that will help in building combustors in rockets. The research has been published in reputed journals Scientific Reports and Physical Review E. link

  • Research by IIT Madras is among the top papers cited by Chief Advisor to UK PM, The Times of India January 9, 2020 .A research paper by Prof. Sujith and his team was among the papers cited by Dominic Cummings, chief special adviser to the UK Prime Minister, Boris Johnson, to revamp decision-making strategies. Published in Scientific Reports by Nature, the research paper titled “Early warning signals for critical transitions in a thermoacoustic system” looks at early warning systems in physics that could be applied to other areas like finance to epidemics. link

    • Interview in Nature on this news: link

  • This IIT-Madras team has a way to kill the hum in gas engines, The Hindu BusinessLine November 26, 2019 Globally, the gas turbine industry loses as much as $1 billion annually due to downtime for turbine inspection and replacement of damaged parts due to such thermo-acoustic oscillations which occur in the combustors. A team led by Prof. Sujith came up with a simple and cost-effective solution for quenching thermoacoustic oscillations developed in multiple combustion systems, where the knowledge for the control of such oscillations remains limited. The research has been published in Chaos journal. link

  • IIT-M and GE tie up for precursor technology, The Times of India February 9, 2019 IIT Madras and General Electric (GE) are collaborating on the development of “precursor technology”, where early signal systems warning of engine malfunctions will be developed and applied in real-world situations in GE’s gas turbine component testing facility. According to Prof. Sujith, with its early warning feature, the technology can help GE save substantial money and time in testing their components. link

  • Decoding flame behaviour and how it helps jet engine design, The Economic Times March 3, 2019 link

  • Brennende Fragen zu singenden Flammen (Burning questions about singing flames) An article about Prof. Sujith’s research from a German research magazine TUM Campus: link

  • Emergence of order from chaos in turbulent systems and Bose-Einstein condensation, The Hindu, 5th June 2021. In a combination of theory and experiment, Prof. Sujith and his student Shruti Tandon have come up with an understanding of the emergence of order in chaotic systems by drawing an analogy with a phenomenon widely studied in quantum statistical physics – Bose-Einstein condensation (BEC). The research has been published in the reputed journal Chaos. link

  • Smothering the flames of instability, IIT Madras Shaastra May-June 2021. Combustion instability affects gas turbines and jets and rocket engines, and Sujith’s team work used a complex network approach to address it. link

Bluff-body stabilized turbulent combustor

Turbulent combustor in the presence of preheater

Swirl-stabilized annular turbulent combustor

Turbulence chamber for studying droplet clustering

Photos of Prof. Sujith with Virginie Maillard from Siemens (Head of Technology Field Simulation and Digital Twin, Siemens, Princeton, USA), taken at Sujith’s lab at IIT Madras.

Contact Us

If you wish to contact us reach out to us at:

Department of Aerospace Engineering,

IIT Madras, Chennai - 600036

India

sujith@iitm.ac.in