Direct Immersogeometric Fluid Flow and Heat Transfer Analysis of Objects Represented by Point Clouds

Immersogeometric analysis (IMGA) is a geometrically flexible method that enables one to perform multiphysics analysis directly using complex computer-aided design (CAD) models. In this paper, we develop a novel IMGA approach for simulating incompressible and compressible flows around complex geometries represented by point clouds. The point cloud object's geometry is represented using a set of unstructured points in the Euclidean space with (possible) orientation information in the form of surface normals. Due to the absence of topological information in the point cloud model, there are no guarantees for the geometric representation to be watertight or 2-manifold or to have consistent normals. To perform IMGA directly using point cloud geometries, we first develop a method for estimating the inside-outside information and the surface normals directly from the point cloud. We also propose a method to compute the Jacobian determinant for the surface integration (over the point cloud) necessary for the weak enforcement of Dirichlet boundary conditions. We validate these geometric estimation methods by comparing the geometric quantities computed from the point cloud with those obtained from analytical geometry and tessellated CAD models. In this work, we also develop thermal IMGA to simulate heat transfer in the presence of flow over complex geometries. The proposed framework is tested for a wide range of Reynolds and Mach numbers on benchmark problems of geometries represented by point clouds, showing the robustness and accuracy of the method. Finally, we demonstrate the applicability of our approach by performing IMGA on large industrial-scale construction machinery represented using a point cloud of more than 12 million points.Comment: 30 pages + references; Accepted in Computer Methods in Applied Mechanics and Engineerin

Optimizing Gas-Turbine Operation using Finite-Element CFD Modeling

Gas turbine engines are generally optimized to operate at nearly a fixed speed with fixed blade geometries for the design operating condition. The performance of gas turbine reduces when operated at different operating condition. In this work, we present a parametric study to optimize gas-turbine performance under off-design conditions by articulating the rotor blades in both clockwise and counterclockwise directions. Articulating the pitch angle of turbine blades in coordination with adjustable nozzle vanes can improve performance by maintaining flow incidence angles within the optimum range at certain off-design conditions. To observe the effect of rotor pitching on the performance of the gas turbine, a computational fluid dynamics (CFD) study is performed using the finite element formulation for compressible flows with moving domain. Results obtained from the CFD simulation for different rotor pitch angles are presented in this paper

Thinner biological tissues induce leaflet flutter in aortic heart valve replacements

Valvular heart disease has recently become an increasing public health concern due to the high prevalence of valve degeneration in aging populations. For patients with severely impacted aortic valves that require replacement, catheter-based bioprosthetic valve deployment offers a minimally invasive treatment option that eliminates many of the risks associated with surgical valve replacement. Although recent percutaneous device advancements have incorporated thinner, more flexible biological tissues to streamline safer deployment through catheters, the impact of such tissues in the complex, mechanically demanding, and highly dynamic valvular system remains poorly understood. The present work utilized a validated computational fluid–structure interaction approach to isolate the behavior of thinner, more compliant aortic valve tissues in a physiologically realistic system. This computational study identified and quantified significant leaflet flutter induced by the use of thinner tissues that initiated blood flow disturbances and oscillatory leaflet strains. The aortic flow and valvular dynamics associated with these thinner valvular tissues have not been previously identified and provide essential information that can significantly advance fundamental knowledge about the cardiac system and support future medical device innovation. Considering the risks associated with such observed flutter phenomena, including blood damage and accelerated leaflet deterioration, this study demonstrates the potentially serious impact of introducing thinner, more flexible tissues into the cardiac system

Sensor-based precision nutrient and irrigation management enhances the physiological performance, water productivity, and yield of soybean under system of crop intensification

Sensor-based decision tools provide a quick assessment of nutritional and physiological health status of crop, thereby enhancing the crop productivity. Therefore, a 2-year field study was undertaken with precision nutrient and irrigation management under system of crop intensification (SCI) to understand the applicability of sensor-based decision tools in improving the physiological performance, water productivity, and seed yield of soybean crop. The experiment consisted of three irrigation regimes [I1: standard flood irrigation at 50% depletion of available soil moisture (DASM) (FI), I2: sprinkler irrigation at 80% ETC (crop evapo-transpiration) (Spr 80% ETC), and I3: sprinkler irrigation at 60% ETC (Spr 60% ETC)] assigned in main plots, with five precision nutrient management (PNM) practices{PNM1-[SCI protocol], PNM2-[RDF, recommended dose of fertilizer: basal dose incorporated (50% N, full dose of P and K)], PNM3-[RDF: basal dose point placement (BDP) (50% N, full dose of P and K)], PNM4-[75% RDF: BDP (50% N, full dose of P and K)] and PNM5-[50% RDF: BDP (50% N, full P and K)]} assigned in sub-plots using a split-plot design with three replications. The remaining 50% N was top-dressed through SPAD assistance for all the PNM practices. Results showed that the adoption of Spr 80% ETC resulted in an increment of 25.6%, 17.6%, 35.4%, and 17.5% in net-photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and intercellular CO2 concentration (Ci), respectively, over FI. Among PNM plots, adoption of PNM3 resulted in a significant (p=0.05) improvement in photosynthetic characters like Pn (15.69 µ mol CO2 m−2 s−1), Tr (7.03 m mol H2O m−2 s−1), Gs (0.175 µmol CO2 mol−1 year−1), and Ci (271.7 mol H2O m2 s−1). Enhancement in SPAD (27% and 30%) and normalized difference vegetation index (NDVI) (42% and 52%) values were observed with nitrogen (N) top dressing through SPAD-guided nutrient management, helped enhance crop growth indices, coupled with better dry matter partitioning and interception of sunlight. Canopy temperature depression (CTD) in soybean reduced by 3.09–4.66°C due to adoption of sprinkler irrigation. Likewise, Spr 60% ETc recorded highest irrigation water productivity (1.08 kg ha−1 m−3). However, economic water productivity (27.5 INR ha−1 m−3) and water-use efficiency (7.6 kg ha−1 mm−1 day−1) of soybean got enhanced under Spr 80% ETc over conventional cultivation. Multiple correlation and PCA showed a positive correlation between physiological, growth, and yield parameters of soybean. Concurrently, the adoption of Spr 80% ETC with PNM3 recorded significantly higher grain yield (2.63 t ha−1) and biological yield (8.37 t ha−1) over other combinations. Thus, the performance of SCI protocols under sprinkler irrigation was found to be superior over conventional practices. Hence, integrating SCI with sensor-based precision nutrient and irrigation management could be a viable option for enhancing the crop productivity and enhance the resource-use efficiency in soybean under similar agro-ecological regions

Fluid–structure interaction modeling for compressible flow applications

In many aerospace applications, fluid–structure interaction (FSI) analysis is performed using standalone computational fluid dynamics (CFD) solvers and computational structural mechanics (CSM) solvers that typically exchange solution information over specific times or in a one-way manner to obtain final equilibrium solutions and configurations. However, this approach often suffers from convergence issues and may be less accurate in capturing the nonlinear forces acting at the fluid–structure interface in complex cases, such as aircraft tail buffeting problems. Computational modeling of aircraft tail buffeting has always been challenging due to high aerodynamic nonlinearities. With the increase in computing powers, strongly-coupled FSI simulations provide a timely and accurate alternative to wind tunnel and real flight testing. To model these complex aeroelasticity problems, this research work presents a high-fidelity strongly-coupled compressible flow computational FSI framework based on augmented Lagrangian approach. The FSI methodology is developed to handle the different nonmatching discretizations at the fluid–structure interface. Finite element based Navier–Stokes equation of compressible flow and the isogeometric analysis (IGA) based rotation-free Kirchhoff–Love shell structural formulation are considered to model the fluid and structural physics, respectively. The combined use of finite element for fluids and IGA for structures provides a good balance between speed, robustness, and accuracy for FSI simulations. The accuracy of the finite element-based Navier–Stokes equation of compressible flows for the aircraft aerodynamics problems, and the developed FSI methodology have been validated using several 2D and 3D benchmark problems in this work. The real-world application of the presented high-fidelity FSI methodology is demonstrated by performing the aircraft pitching maneuver using arbitrary Lagrangian–Eulerian (ALE) approach to simulate time-dependent angle of attack simulation, and study the effects of unsteady buffeting loads acting on the horizontal stabilizer of the aircraft

Effects of membrane and flexural stiffnesses on aortic valve dynamics: identifying the mechanics of leaflet flutter in thinner biological tissues

Valvular pathologies that induce deterioration in the aortic valve are a common cause of heart disease among aging populations. Although there are numerous available technologies to treat valvular conditions and replicate normal aortic function by replacing the diseased valve with a bioprosthetic implant, many of these devices face challenges in terms of long-term durability. One such phenomenon that may exacerbate valve deterioration and induce undesirable hemodynamic effects in the aorta is leaflet flutter, which is characterized by oscillatory motion in the biological tissues. While this behavior has been observed for thinner bioprosthetic valves, the specific underlying mechanics that lead to leaflet flutter have not previously been identified. This work proposes a computational approach to isolate the fundamental mechanics that induce leaflet flutter in thinner biological tissues during the cardiac cycle. The simulations in this work identify reduced flexural stiffness as the primary factor that contributes to increased leaflet flutter in thinner biological tissues, while decreased membrane stiffness and mass of the thinner tissues do not directly induce flutter in these valves. The results of this study provide an improved understanding of the mechanical tissue properties that contribute to flutter and offer significant insights into possible developments in the design of bioprosthetic tissues to account for and reduce the incidence of flutter.This is a manuscript an article published as Johnson, Emily L., Manoj R. Rajanna, Cheng-Hau Yang, and Ming-Chen Hsu. "Effects of membrane and flexural stiffnesses on aortic valve dynamics: identifying the mechanics of leaflet flutter in thinner biological tissues." Forces in Mechanics (2021): 100053. DOI: 10.1016/j.finmec.2021.100053. © 2021 The Authors. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission

Immersogeometric fluid–structure interaction modeling and simulation of transcatheter aortic valve replacement

The transcatheter aortic valve replacement (TAVR) has emerged as a minimally invasive alternative to surgical treatments of valvular heart disease. TAVR offers many advantages, however, the safe anchoring of the transcatheter heart valve (THV) in the patient’s anatomy is key to a successful procedure. In this paper, we develop and apply a novel immersogeometric fluid–structure interaction (FSI) framework for the modeling and simulation of the TAVR procedure to study the anchoring ability of the THV. To account for physiological realism, methods are proposed to model and couple the main components of the system, including the arterial wall, blood flow, valve leaflets, skirt, and frame. The THV is first crimped and deployed into an idealized ascending aorta. During the FSI simulation, the radial outward force and friction force between the aortic wall and the THV frame are examined over the entire cardiac cycle. The ratio between these two forces is computed and compared with the experimentally estimated coefficient of friction to study the likelihood of valve migration.This is a manuscript of an article published as Wu, Michael C.H., Heather M. Muchowski, Emily L. Johnson, Manoj R. Rajanna, and Ming-Chen Hsu. "Immersogeometric fluid–structure interaction modeling and simulation of transcatheter aortic valve replacement." Computer Methods in Applied Mechanics and Engineering 357 (2019): 112556. DOI: 10.1016/j.cma.2019.07.025. Posted with permission.</p

Immersogeometric fluid–structure interaction modeling and simulation of transcatheter aortic valve replacement

The transcatheter aortic valve replacement (TAVR) has emerged as a minimally invasive alternative to surgical treatments of valvular heart disease. TAVR offers many advantages, however, the safe anchoring of the transcatheter heart valve (THV) in the patient’s anatomy is key to a successful procedure. In this paper, we develop and apply a novel immersogeometric fluid–structure interaction (FSI) framework for the modeling and simulation of the TAVR procedure to study the anchoring ability of the THV. To account for physiological realism, methods are proposed to model and couple the main components of the system, including the arterial wall, blood flow, valve leaflets, skirt, and frame. The THV is first crimped and deployed into an idealized ascending aorta. During the FSI simulation, the radial outward force and friction force between the aortic wall and the THV frame are examined over the entire cardiac cycle. The ratio between these two forces is computed and compared with the experimentally estimated coefficient of friction to study the likelihood of valve migration

Buffet-Induced Structural Response Prediction of Aircraft Horizontal Stabilizers Based on Immersogeometric Analysis and an Isogeometric Blended Shell Approach

Aircraft horizontal stabilizers are prone to fatigue damage induced by the flow separation from aircraft wings and the subsequent impingement on the stabilizer structure in its wake, which is known as the buffet event. In this work, a hybrid immersogeometric and boundary-fitted CFD analysis with a high angle of attack (AOA) is carried out to accurately compute the aerodynamic loads on the stabilizer structure. Specifically, the entire aircraft except for the wing and stabilizers is immersed into a non-boundary-fitted fluid domain based on the immersogeometric analysis (IMGA) concept for computational savings, whereas the mesh surrounding the aircraft wing and stabilizers is boundary-fitted to accurately compute the aerodynamic loads on the stabilizer. The obtained time histories of the loads are then applied to structural analysis of the horizontal stabilizer and obtain high-fidelity stress response for subsequent fatigue assessment. In order to achieve computational efficiency, an isogeometric blended shell approach is developed that models the critical structural components of the stabilizer using continuum shells to obtain high-fidelity 3D stresses, whereas the non-critical components are modeled using computationally efficient Kirchhoff–Love thin shells. A simple frequency-domain fatigue analysis is then carried out to evaluate the buffet-induced fatigue damage of the stabilizer. The results from both the static and dynamic nonlinear blended shell analyses of a representative horizontal stabilizer demonstrate the numerical accuracy and computational efficiency of the proposed approach.This article is published as Liu, Ning, Jim Lua, Manoj Reddy Rajanna, Emily Johnson, Ming-Chen Hsu, and Nam D. Phan. "Buffet-Induced Structural Response Prediction of Aircraft Horizontal Stabilizers Based on Immersogeometric Analysis and an Isogeometric Blended Shell Approach." In AIAA SCITECH 2022 Forum, p. 0852. 2022. DOI: 10.2514/6.2022-0852. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted