Debanjan Mukherjee

Computational Assessment of the Relation Between Embolism Source and Embolus Distribution to the Circle of Willis for Improved Understanding of Stroke Etiology

Stroke caused by an embolism accounts for about a third of all stroke cases. Understanding the source and cause of the embolism is critical for diagnosis and long-term treatment of such stroke cases. The complex nature of the transport of an embolus within large arteries is a primary hindrance to a clear understanding of embolic stroke etiology. Recent advances in medical image-based computational hemodynamics modeling have rendered increasing utility to such techniques as a probe into the complex flow and transport phenomena in large arteries. In this work, we present a novel, patient-specific, computational framework for understanding embolic stroke etiology, by combining image-based hemodynamics with discrete particle dynamics and a sampling-based analysis. The framework allows us to explore the important question of how embolism source manifests itself in embolus distribution across the various major cerebral arteries. Our investigations illustrate prominent numerical evidence regarding (i) the size/inertia-dependent trends in embolus distribution to the brain; (ii) the relative distribution of cardiogenic versus aortogenic emboli among the anterior, middle, and posterior cerebral arteries; (iii) the left versus right brain preference in cardio-emboli and aortic-emboli transport; and (iv) the source-destination relationship for embolisms affecting the brain.

Inertial particle dynamics in large artery flows – Implications for modeling arterial embolisms

The complexity of inertial particle dynamics through swirling chaotic flow structures characteristic of pulsatile large-artery hemodynamics renders significant challenges in predictive understanding of transport of such particles. This is specifically crucial for arterial embolisms, where knowledge of embolus transport to major vascular beds helps in disease diagnosis and surgical planning. Using a computational framework built upon image-based CFD and discrete particle dynamics modeling, a multi-parameter sampling-based study was conducted on embolic particle dynamics and transport. The results highlighted the strong influence of material properties, embolus size, release instance, and embolus source on embolus distribution to the cerebral, renal and mesenteric, and ilio-femoral vasculature beds. The study also isolated the importance of shear-gradient lift, and elastohydrodynamic contact, in affecting embolic particle transport. Near-wall particle re-suspension due to lift alters aortogenic embolic particle dynamics significantly as compared to cardiogenic. The observations collectively indicated the complex interplay of particle inertia, fluid-particle density ratio, and wall collisions, with chaotic flow structures, which render the overall motion of the particles to be non-trivially dispersive in nature.

A discrete element based simulation framework to investigate particulate spray deposition processes

This work presents a computer simulation framework based on discrete element method to analyze manufacturing processes that comprise a loosely flowing stream of particles in a carrier fluid being deposited on a target surface. The individual particulate dynamics under the combined action of particle collisions, fluid-particle interactions, particle-surface contact and adhesive interactions is simulated, and aggregated to obtain global system behavior. A model for deposition which incorporates the effect of surface energy, impact velocity and particle size, is developed. The fluid-particle interaction is modeled using appropriate spray nozzle gas velocity distributions and a one-way coupling between the phases. It is found that the particle response times and the release velocity distribution of particles have a combined effect on inter-particle collisions during the flow along the spray. It is also found that resolution of the particulate collisions close to the target surface plays an important role in characterizing the trends in the deposit pattern. Analysis of the deposit pattern using metrics defined from the particle distribution on the target surface is provided to characterize the deposition efficiency, deposit size, and scatter due to collisions.

Technical note: Electromagnetic control of charged particulate spray systems-Models for planning the spray-gun operations

Charged particulate spray systems are common in many industrial and manufacturing processes. Using externally applied electromagnetic fields-the dynamics of these particulate sprays can be altered to achieve improved functionality and access to spray-sites that are hard to reach. With such an alteration the spray-particulate dynamics can become non-intuitive-thereby motivating a physically based modeling strategy to plan the spray-gun operations and translate this into the actual spray deposition on the target surface. In this paper we use the dynamics of charged particles to construct a set of simple geometric arguments for the identification of the mapping between the spray-gun trajectory (on its plane of traversal) and the spray-deposit location (on the plane of the target-surface). The parametric dependence of the mapping on spray-gun operation parameters (comprising nozzle velocity and trajectory) and external magnetic fields (comprising field strength and the region of applied field) is discussed. The role of such arguments in constructing appropriate computer simulation frameworks is then illustrated through an example of a discrete element simulation. Sensitivity to process parameters like particulate size and spray-gas velocity are also characterized for a given applied field.

Investigation of Guided-Particle Transport for Noninvasive Healing of Damaged Piping Systems by Use of Electro-Magneto-Mechanical Methods

Virtually all engineering applications involve the use of piping, conduits, and channels. In the petroleum industry, piping systems are extensively used in upstream and downstream processes. These piping systems often carry fluids that are corrosive, which leads to wear, cavitation, and cracking. The replacement of damaged piping systems can be quite expensive, both in terms of capital costs and in operational downtime. This motivates the present research on noninvasive healing of cracked piping systems. In this investigation, we propose to develop computational models for characterizing noninvasive repair strategies involving electromagnetically guided particles. The objective is to heal industrial-piping systems noninvasively, from the exterior of the system, during operation, resulting in no downtime and minimal relative cost. The particle accumulation at a target location is controlled by external electromagnetic/ mechanical means. There are two primary effects that play a role for guiding the particles to the solid-fluid-interface/wall: mechanical shear caused by the fluid flow, and an electrical or magnetic force. In this work we develop and study a relationship that characterizes contributions of both, and ascertain how this relationship scales with characteristic physical parameters. Characteristic nondimensional parameters that describe system behavior are derived, and their role in design is illustrated. A detailed, fully 3D discreteelement-simulation framework is presented, and illustrated by use of a model problem of magnetically guided particles. The detailed particle behavior is considered to be regulated by three effects: the field strength, the mass-flow rate, and the wall interactions.

Preliminary Concept and Feasibility Studies on Ocean Energy Device Design From Used Ships

The process of decommissioning ships, usually followed by ship scraping, is associated not only with significant costs but also with many environmental and toxic hazards. Thus, re usability of such ships will offer more advantages than recycling its steel. This paper proposes reusing a post-service life vessel by converting it into an Ocean Wave Energy Device. A systematic study on the preliminary estimation of energy extraction levels from ocean waves is presented, with some discussion on the energy of a ship-shaped body in motion in irregular seas. Heave motion was found to be more favorable for such applications. Thereafter concept designs have been proposed for the device, and the designs have been analyzed in terms of the extent of relative motion and power that could be obtained from each of them. Numerical simulation techniques have been used to generate the results. Through this analysis, it has been established that the idea of constructing such a device is feasible. The relatively slower but high-force systems can use a hydraulic take-off unit instead of electrical inductance generators. The mooring system has also been identified as a separate design problem. Further design issues including optimizing the different parameters, cost analysis and fabrication issues have not been considered — this work is aimed to provide the starting point of the design exercise.Copyright

Modeling blood flow around a thrombus using a hybrid particle–continuum approach

A hybrid, multiscale, particle–continuum numerical method is developed for resolving the interaction of a realistic thrombus geometry with unsteady hemodynamics typically occurring within large arteries. The method is based on a discrete particle/element description of the thrombus, coupled to blood flow using a fictitious domain finite element method. The efficacy of the discrete element approach in representing thrombi with arbitrary aggregate morphology and microstructure is demonstrated. The various features of the method are illustrated using a series of numerical experiments with a model system consisting of an occlusion embedded in a channel. The results from these numerical experiments establish that this approach can resolve the complex macroscale flow structures emanating from unsteady hemodynamics interacting with a thrombus. Simultaneously, it can also resolve micromechanical features, and microscale intra-thrombus flow and perfusion. Using a staggering algorithm, the method can further capture hemodynamics around time-varying thrombus manifolds. This is established using a numerical simulation of lysis of an idealized clot. The hybrid particle–continuum description of thrombus–hemodynamics interaction mechanics, and the unified treatment of macroscale as well as microscale flow and transport, renders significant advantages to the proposed method in enabling further investigations of physiological interest in thrombosis within patient-specific settings.

The Role of Circle of Willis Anatomy Variations in Cardio-embolic Stroke: A Patient-Specific Simulation Based Study

We describe a patient-specific simulation based investigation on the role of Circle of Willis anatomy in cardioembolic stroke. Our simulation framework consists of medical image-driven modeling of patient anatomy including the Circle, 3D blood flow simulation through patient vasculature, embolus transport modeling using a discrete particle dynamics technique, and a sampling based approach to incorporate parametric variations. A total of 24 (four patients and six Circle anatomies including the complete Circle) models were considered, with cardiogenic emboli of varying sizes and compositions released virtually and tracked to compute distribution to the brain. The results establish that Circle anatomical variations significantly influence embolus distribution to the six major cerebral arteries. Embolus distribution to MCA territory is found to be least sensitive to the influence of anatomical variations. For varying Circle topologies, differences in flow through cervical vasculature are observed. This incoming flow is recruited differently across the communicating arteries of the Circle for varying anastomoses. Emboli interact with the routed flow, and can undergo significant traversal across the Circle arterial segments, depending upon their inertia and density ratio with respect to blood. This interaction drives the underlying biomechanics of embolus transport across the Circle, explaining how Circle anatomy influences embolism risk.

Computer Modeling and Simulation Framework for Particulate Spray Based Manufacturing Processes

Particulate media are ubiquitous in modern manufacturing processes. These include spray-forming, abrasive finishing, and sintering based processes amongst others. All of these processes involve a flowing stream of discrete, particulate media. For these processes, the aggregate behavior originating from the individual particle or grain dynamics is of critical importance from a process engineering perspective. The discrete nature of the media poses unique challenges in formulating direct continuum theories. This motivates investigating appropriate discrete computational techniques. In this paper, we present a computer simulation framework based on collision driven particle dynamics to investigate the engineering of such manufacturing processes. This is part of an ongoing work on developing a general-purpose computer simulation tool to analyze the dynamics of particulate and granular media in engineering applications. This paper presents the overall framework and the underlying physical models. In particular, our focus is on modeling individual particle-based phenomena (including collisions, heat-exchange, and energy loss) and deriving the aggregate response of the media from individual particle dynamics. The technique is demonstrated using a numerical example for a spray coating deposition process. This example tracks the particulate behavior from the nozzle opening downstream until impact with substrate. Such investigations are useful to understand the effect of process parameters on the engineered output — which in this case entails the properties of the surface coating. The simulation is found to be reasonable in performance time.Copyright