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Search Results: 1 - 10 of 401339 matches for " Ramana M. Pidaparti "
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Investigation of the Effects of Emphysema and Influenza on Alveolar Sacs Closure through CFD Simulation  [PDF]
Parya Aghasafari, Israr B. M. Ibrahim, Ramana M. Pidaparti
Journal of Biomedical Science and Engineering (JBiSE) , 2016, DOI: 10.4236/jbise.2016.96022
Abstract: Emphysema and influenza directly affect alveolar sacs and cause problems in lung performance during the breathing cycle. In this study, the effects of Emphysema and Influenza on alveolar sac’s air flow characteristics are investigated through Computational Fluid Dynamics (CFD) simulation. Both normal and Emphysemic alveolar sac models with varying collapsed volumes resulting from influenza virus replication were developed. Maximum, area average pressure, and wall shear stress (WSS) in collapsed and open alveolar sacs models were compared. It was found that a collapse at half of the volume at the bottom of the alveolar sacs’ models would cause a decrease in average and maximum pressure values and yield higher WSS values for fluid flow during the breathing cycle. On the other hand, a quarter volume collapse at the bottom and side of the model resulted in higher values for average and maximum pressure and WSS. Additionally, results also showed that a combination of alveolar sacs closure and Emphysema would generally lead to an increase in fluid pressure and average WSS during breathing. Maximum WSS was observed during exhalation and maximum WSS decrease occurred during inhalation. Findings are in good agreement with previous studies and suggest that emphysema and influenza virus affect fluid flow and may contribute to alveolar sac closure. However, more realistic simulations should include the fluid-solid interaction studies.
Effect of off-axis cell orientation on mechanical properties in smooth muscle tissue  [PDF]
P. A. Sarma, Ramana M. Pidaparti, Richard A. Meiss
Journal of Biomedical Science and Engineering (JBiSE) , 2011, DOI: 10.4236/jbise.2011.41002
Abstract: The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical proper-ties. The off-axis cell orientation "θ” not only effects the shortening strain but also modifies the shear stress relationship significantly. Both experiments and finite element analysis were carried out on a tracheal smooth muscle strip to study how the cell alignment in smooth muscle affects the shear stiffness and shear stresses as well as deformation. A simple model for shear stiffness is derived using the data from experiments. Shear stiffness results obtained from the model indicate that the muscle shear stiff-ness values increase non-linearly with strain and with higher off-axis alignment of cells. Results of deforma-tion and shear stresses obtained from finite element analsysis indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% of strain are 2.5 times the corresponding values at 20% of strain for all three off-axis cell orientation values θ = 15?, 30? and 45?.
Analysis for stress environment in the alveolar sac model  [PDF]
Ramana M. Pidaparti, Matthew Burnette, Rebecca L. Heise, Angela Reynolds
Journal of Biomedical Science and Engineering (JBiSE) , 2013, DOI: 10.4236/jbise.2013.69110
Abstract: Better understanding of alveolar mechanics is very important in order to avoid lung injuries for patients undergoing mechanical ventilation for treatment of respiratory problems. The objective of this study was to investigate the alveolar mechanics for two different alveolar sac models, one based on actual geometry and the other an idealized spherical geometry using coupled fluid-solid computational analysis. Both the models were analyzed through coupled fluid-solid analysis to estimate the parameters such as pressures/ velocities and displacements/stresses under mechanical ventilation conditions. The results obtained from the fluid analysis indicate that both the alveolar geometries give similar results for pressures and velocities. However, the results obtained from coupled fluid-solid analysis indicate that the actual alveolar geometry results in smaller displacements in comparison to a spherical alveolar model. This trend is also true for stress/strain between the two models. The results presented indicate that alveolar geometry greatly affects the pressure/velocities as well as displacements and stresses/strains.
Inhalation Induced Stresses and Flow Characteristics in Human Airways through Fluid-Structure Interaction Analysis
Kittisak Koombua,Ramana M. Pidaparti
Modelling and Simulation in Engineering , 2008, DOI: 10.1155/2008/358748
Abstract: Better understanding of stresses and flow characteristics in the human airways is very important for many clinical applications such as aerosol drug therapy, inhalation toxicology, and airway remodeling process. The bifurcation geometry of airway generations 3 to 5 based on the ICRP tracheobronchial model was chosen to analyze the flow characteristics and stresses during inhalation. A computational model was developed to investigate the airway tissue flexibility effect on stresses and flow characteristics in the airways. The finite-element method with the fluid-structure interaction analysis was employed to investigate the transient responses of the flow characteristics and stresses in the airways during inhalation. The simulation results showed that tissue flexibility affected the maximum airflow velocity, airway pressure, and wall shear stress about 2%, 7%, and 6%, respectively. The simulation results also showed that the differences between the orthotropic and isotropic material models on the airway stresses were in the ranges of 25–52%. The results from the present study suggest that it is very important to incorporate the orthotropic tissue properties into a computational model for studying flow characteristics and stresses in the airways.
Breast Tumor Simulation and Parameters Estimation Using Evolutionary Algorithms
Manu Mital,Ramana M. Pidaparti
Modelling and Simulation in Engineering , 2008, DOI: 10.1155/2008/756436
Abstract: An estimation methodology is presented to determine the breast tumor parameters using the surface temperature profile that may be obtained by infrared thermography. The estimation methodology involves evolutionary algorithms using artificial neural network (ANN) and genetic algorithm (GA). The ANN is used to map the relationship of tumor parameters (depth, size, and heat generation) to the temperature profile over the idealized breast model. The relationship obtained from ANN is compared to that obtained by finite element software. Results from ANN training/testing were in good agreement with those obtained from finite element model. After ANN validation, GA is used to estimate tumor parameters by minimizing a fitness function involving comparing the temperature profiles from simulated or clinical data to those obtained by ANN. Results show that it is possible to determine the depth, diameter, and heat generation rate from the surface temperature data (with 5% random noise) with good accuracy for the 2D model. With 10% noise, the accuracy of estimation deteriorates for deep-seated tumors with low heat generation. In order to further develop this methodology for use in a clinical scenario, several aspects such as 3D breast geometry and the effects of nonuniform cooling should be considered in future investigations.
A Theoretical Model for Metal Corrosion Degradation
David V. Svintradze,Ramana M. Pidaparti
International Journal of Corrosion , 2010, DOI: 10.1155/2010/279540
Abstract: Many aluminum and stainless steel alloys contain thin oxide layers on the metal surface which greatly reduce the corrosion rate. Pitting corrosion, a result of localized breakdown of such films, results in accelerated dissolution of the underlying metal through pits. Many researchers have studied pitting corrosion for several decades and the exact governing equation for corrosion pit degradation has not been obtained. In this study, the governing equation for corrosion degradation due to pitting corrosion behavior was derived from solid-state physics and some solutions and simulations are presented and discussed. 1. Introduction Pitting corrosion is known to be one of the major damage mechanisms affecting the integrity of many materials and structures in civil, nuclear, and aerospace engineering. Corrosion pits generally initiate due to some chemical or physical heterogeneity at the surface, such as inclusions, second phase particles, flaws, mechanical damage, or dislocations. Pitting corrosion, a result of localized breakdown of such films, results in accelerated dissolution of the underlying metal. The corrosion mechanisms depend on the material composition, electrolyte and other environmental conditions [1–3]. The most corrosion models in literature are focused on the electrochemical reaction during the corrosion process [4–6]. Mathematical models are utilized to get a better understanding of the pitting corrosion process [1–3]. Models are included in a set of governing equations. Numerical modeling is especially important with the pitting corrosion because most governing equations do not have close form solutions to describe the process. Pitting corrosion is a very complex process and may involve many mechanisms. In general, the corrosion degradation modeling should involve not only physico-chemical and environmental factors. The pitting corrosion mechanisms may initiate at multiple levels starting from nano to micro and macrolevels. Zavadil et al. [7] investigated the contribution of voids and their shapes at nanoscale at the Al/oxide interface to pit initiation and propagation in passive metals. Interestingly, Renner et al. [8] observed the initial corrosion at the atomic scale in single crystal alloy in sulphuric acid solution. Martin et al. [9] conducted in situ AFM detection of pit onset location on stainless steel and concluded that pits were randomly distributed at the nanoscale and revealed that 70% of the pits initiated at strain hardened areas resulting from mechanical polishing. At microscale, the pit initiation and propagation mechanism
Evaluation of Corrosion Growth on SS304 Based on Textural and Color Features from Image Analysis
Ramana M. Pidaparti,Brian Hinderliter,Darshan Maskey
ISRN Corrosion , 2013, DOI: 10.1155/2013/376823
Abstract: Corrosion surface damage in the form of pitting and microcracks is observed in many systems and affects the integrity of steel structures in nuclear, civil, and industrial engineering. In order to gain a better understanding and develop nondestructive and automatic detection/assessment of corrosion damage and its growth, an image analysis based on texture using wavelet transforms and color features was carried out. Experiments were conducted on steel 304 panels under three different electrolyte solutions, and periodic scans were used to obtain the images for analysis over time. The results obtained from the image analysis are presented to illustrate the metrics which best characterize early stage corrosion damage growth behavior. The results obtained indicate that textural features in combination with color features are more effective and may be used for correlating service/failure conditions based on corrosion morphology. 1. Introduction Engineering components made from structural steel 304 metals are being used in many industries, commercial and domestic fields, because of their chemical durability, mechanical properties, weldability, good corrosion, and heat resistant properties. Corrosion of stainless steel in aggressive environmental conditions in particular is a fundamental concern to academia and industry due to the destructive nature of corrosion on mechanical properties of components. Ships, storage tanks, bridges, and pipelines commonly made from structural steel are not sufficiently resistant to corrosion in their operating environments which impacts corrosion costs associated with maintenance and also safety risks. Therefore, corrosion monitoring is an important issue in detecting corrosion damage and its growth before failures occur [1–3]. There are many different experimental and analysis methods used for corrosion inspection and monitoring purposes. These include mechanical measurements (weight loss), chemical analysis, and visual inspections. In visual inspections, the corrosion damage identification requires an expert who can clearly demarcate the corrosion based on experience as well as types of corrosion, with red rust as a common experience. Usually, the corrosion process produces rough surfaces, and image analysis based on textural features can be used for quantification and discriminate corrosion extent and type. Several authors investigated automatic corrosion detection using image processing techniques [4–7]. Computer image processing involves definition and development of techniques and algorithms for processing pictorial data
Design of an Implantable Device for Ocular Drug Delivery
Jae-Hwan Lee,Ramana M. Pidaparti,Gary M. Atkinson,Ramana S. Moorthy
Journal of Drug Delivery , 2012, DOI: 10.1155/2012/527516
Abstract: Ocular diseases, such as, glaucoma, age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa require drug management in order to prevent blindness and affecting million of adults in USA and worldwide. There is an increasing need to develop devices for drug delivery to address ocular diseases. This study focuses on the design, simulation, and development of an implantable ocular drug delivery device consisting of micro-/nanochannels embedded between top and bottom covers with a drug reservoir made from polydimethylsiloxane (PDMS) which is silicon-based organic and biodegradable polymer. Several simulations were carried out with six different micro-channel configurations in order to see the feasibility for ocular drug delivery applications. Based on the results obtained, channel design of osmotic I and osmotic II satisfied the diffusion rates required for ocular drug delivery. Finally, a prototype illustrating the three components of the drug delivery design is presented. In the future, the device will be tested for its functionality and diffusion characteristics.
Solution of Two-Dimensional Viscous Flow Driven by Motion of Flexible Walls
Ravi Bhadauria,Ramana M. Pidaparti,Mohamed Gad-el-Hak
CFD Letters , 2010,
Abstract: An exact solution of the Navier–Stokes equations for a flow driven by motion of flexible wall is developed. A simple two-dimensional channel with deforming walls is considered as domain. The governing equations are linearized for low Reynolds number and large Womersley number Newtonian flows. Appropriate boundary conditions for general deformation are decomposed into harmonic excitations in space by Fourier series decomposition. A model of harmonic boundary deformation is considered and results are compared with computational fluid dynamics predictions. The results of velocity profiles across the channel and the centerline velocities of the channel are in good agreement with CFD solution. The analytical model developed provides quantitative descriptions of the flow field for a wide spectrum of actuating frequnecy and boundary conditions. The presented model can be used as an effective framework for preliminary design and optimization of displacement micropumps and other miniature applications.
The Phenomenology of a Hidden Symmetry Breaking Sector at Electron-Positron Colliders
M. V. Ramana
Physics , 1993,
Abstract: We calculate the production rate of gauge-boson pairs at $e^+e^-$ colliders in a model with a ``hidden'' electroweak symmetry breaking sector - i.e. one in which there are a large number of particles in the symmetry breaking sector other than the $W^{\pm}$ \thinspace and the $Z^0$. In such a model, the elastic $W^{\pm}$ \thinspace and $Z^0$ scattering amplitudes are small and structureless, i.e. lacking any discernable resonances, at all energies. We show that two gauge boson fusion signal of electroweak symmetry breaking is swamped by the background. Therefore, we cannot rely on gauge boson pairs as a signal of the dynamics of symmetry breaking.
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