Immersogeometric analysis of moving objects in incompressible flows

We deploy the immersogeometric approach for tracking moving objects. The method immerses objects into non-boundary-fitted meshes and weakly enforces Dirichlet boundary conditions on the object boundaries. The object motion is driven by the integrated surface force and external body forces. A residual-based variational multiscale method is employed to stabilize the finite element formulation for incompressible flows. Adaptively refined quadrature rules are used to better capture the geometry of the immersed boundaries by accurately integrating the intersected background elements. Treatment for the freshly-cleared nodes (i.e. background mesh nodes that are inside the object at one time step, but are in the fluid domain at the next time step) is considered. We assess the accuracy of the method by analyzing object motion in different flow structures including objects freely dropping in viscous fluids and particle focusing in unobstructed and obstructed micro-channels. We show that key quantities of interest are in very good agreements with analytical, numerical and experimental solutions. We also show a much better computational efficiency of this framework than current commercial codes using adaptive boundary-fitted approaches. We anticipate deploying this framework for applications of particle inertial migration in microfluidic channels

An immersogeometric formulation for free-surface flows with application to marine engineering problems

An immersogeometric formulation is proposed to simulate free-surface flows around structures with complex geometry. The fluid–fluid interface (air–water interface) is handled by the level set method, while the fluid–structure interface is handled through an immersogeometric approach by immersing structures into non-boundary-fitted meshes and enforcing Dirichlet boundary conditions weakly. Residual-based variational multiscale method (RBVMS) is employed to stabilize the coupled Navier–Stokes equations of incompressible flows and level set convection equation. Other level set techniques, including re-distancing and mass balancing, are also incorporated into the immersed formulation. Adaptive quadrature rule is used to better capture the geometry of the immersed structure boundary by accurately integrating the intersected background elements. Generalized-α role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative; \u3eα method is adopted for time integration, which results in a two-stage predictor multi-corrector algorithm. GMRES solver preconditioned with block Jacobian matrices of individual fluid and level set subproblems is used for solving the coupled linear systems arising from the multi-corrector stage. The capability and accuracy of the proposed method are assessed by simulating three challenging marine engineering problems, which are a solitary wave impacting a stationary platform, dam break with an obstacle, and planing of a DTMB 5415 ship model. A refinement study is performed. The predictions of key quantities of interest by the proposed formulation are in good agreement with experimental results and boundary-fitted simulation results from others. The proposed formulation has great potential for wide applications in marine engineering problems

Industrial scale large eddy simulations (LES) with adaptive octree meshes using immersogeometric analysis

We present a variant of the immersed boundary method integrated with octree meshes for highly efficient and accurate Large-Eddy Simulations (LES) of flows around complex geometries. We demonstrate the scalability of the proposed method up to $\mathcal{O}(32K)$ processors. This is achieved by (a) rapid in-out tests; (b) adaptive quadrature for an accurate evaluation of forces; (c) tensorized evaluation during matrix assembly. We showcase this method on two non-trivial applications: accurately computing the drag coefficient of a sphere across Reynolds numbers $1-10^6$ encompassing the drag crisis regime; simulating flow features across a semi-truck for investigating the effect of platooning on efficiency.Comment: Accepted for publication at Computer and Mathematics with Application

Progress in the Application of Biomimetic Mineralization for Tooth Repair

The tooth, including enamel and dentin, is a prominent biomineral that is produced by the biomineralization of living organisms. Although the mechanical performance of the tooth is outstanding, caries easily develop in a complex oral environment. The analysis of the chemical composition and the relationship between the mechanical properties and the structure is of great importance in solving caries. In this review, the multilevel structure and mechanical properties of enamel and dentin are briefly introduced, along with caries formation and the limitations of clinical dental restoration. Furthermore, the progress of the application of a wide range of biomimetic strategies for tooth remineralization is highlighted, including the use of calcium phosphate ionic clusters to construct the mineralization front, ensuring the oriented epitaxial growth of enamel crystals and replicating the complex structure of the enamel. Moreover, compared with the current clinical treatment, in which the resin composite and glass ionomer cement are the main repair materials and the high incidence of secondary caries leads to imperfect restorations, the remineralization tactics could achieve excellent repair effectiveness in reconstructing the complicated structure, restoring mechanical strength and gaining permanent repair. A basic understanding of enamel and dentin, their potential for restoration, and hopeful prospects for tooth repair that can be applied in the clinical setting, not just in the laboratory, is provided by this review

Immersogeometric analysis of moving objects in incompressible flows

We deploy the immersogeometric approach for tracking moving objects. The method immerses objects into non-boundary-fitted meshes and weakly enforces Dirichlet boundary conditions on the object boundaries. The object motion is driven by the integrated surface force and external body forces. A residual-based variational multiscale method is employed to stabilize the finite element formulation for incompressible flows. Adaptively refined quadrature rules are used to better capture the geometry of the immersed boundaries by accurately integrating the intersected background elements. Treatment for the freshly-cleared nodes (i.e. background mesh nodes that are inside the object at one time step, but are in the fluid domain at the next time step) is considered. We assess the accuracy of the method by analyzing object motion in different flow structures including objects freely dropping in viscous fluids and particle focusing in unobstructed and obstructed micro-channels. We show that key quantities of interest are in very good agreements with analytical, numerical and experimental solutions. We also show a much better computational efficiency of this framework than current commercial codes using adaptive boundary-fitted approaches. We anticipate deploying this framework for applications of particle inertial migration in microfluidic channels.This is a manuscript of an article published as Xu, Songzhe, Fei Xu, Aditya Kommajosula, Ming-Chen Hsu, and Baskar Ganapathysubramanian. "Immersogeometric analysis of moving objects in incompressible flows." Computers & Fluids 189 (2019): 24-33. DOI: 10.1016/j.compfluid.2019.05.018. Posted with permission.</p

An immersogeometric formulation for free-surface flows with application to marine engineering problems

An immersogeometric formulation is proposed to simulate free-surface flows around structures with complex geometry. The fluid–fluid interface (air–water interface) is handled by the level set method, while the fluid–structure interface is handled through an immersogeometric approach by immersing structures into non-boundary-fitted meshes and enforcing Dirichlet boundary conditions weakly. Residual-based variational multiscale method (RBVMS) is employed to stabilize the coupled Navier–Stokes equations of incompressible flows and level set convection equation. Other level set techniques, including re-distancing and mass balancing, are also incorporated into the immersed formulation. Adaptive quadrature rule is used to better capture the geometry of the immersed structure boundary by accurately integrating the intersected background elements. Generalized-α" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">α method is adopted for time integration, which results in a two-stage predictor multi-corrector algorithm. GMRES solver preconditioned with block Jacobian matrices of individual fluid and level set subproblems is used for solving the coupled linear systems arising from the multi-corrector stage. The capability and accuracy of the proposed method are assessed by simulating three challenging marine engineering problems, which are a solitary wave impacting a stationary platform, dam break with an obstacle, and planing of a DTMB 5415 ship model. A refinement study is performed. The predictions of key quantities of interest by the proposed formulation are in good agreement with experimental results and boundary-fitted simulation results from others. The proposed formulation has great potential for wide applications in marine engineering problems.This is a manuscript of an article published as Zhu, Qiming, Fei Xu, Songzhe Xu, Ming-Chen Hsu, and Jinhui Yan. "An immersogeometric formulation for free-surface flows with application to marine engineering problems." Computer Methods in Applied Mechanics and Engineering (2019): 112748. DOI: 10.1016/j.cma.2019.112748. Posted with permission.</p

Antibiotic resistance pattern of Klebsiella pneumoniae and Enterobacter sakazakii isolates from powdered infant formula

Morbidity and mortality of infant infections caused by contaminated powdered infant formula (PIF) have been reported worldwide, and pathogens like Enterobacter sakazakii and Klebsiella pneumoniae are important causative agents. To evaluate the prevalence of antibiotic resistance in E. sakazakii and K. pneumoniae that caused PIF contamination in Chinese market, all the isolates from PIF were analyzed for detecting resistance to antibiotics. 30 PIF samples were randomly purchased in Chinese market in 2009 and 7 E. sakazakii and 6 K. pneumoniae isolates were obtained from 8 samples (26.7%), the isolates were evaluated for antibiotics susceptibility by disk diffusion technique as recommended by the Clinical Laboratory Standards Institute (CLSI). Susceptibility results showed that each isolate had different levels of resistance to beta-lactam antibiotics, while sensitive to fluoroquinolones and aminoglycosides. One K. pneumoniae and one E. sakazakii isolate almost resisted all Cephalosporins chosen; the double-disk synergy test (DDST) showed these two isolates producing extended spectrum beta-lactamase (ESBL). This is the first report of ESBL-produing in E. sakazakii from powdered infant formula in China

Prevalence of Antibiotic-Resistant Escherichia coli in Drinking Water Sources in Hangzhou City

This study investigated the distribution of antibiotic resistant Escherichia coli (E. coli) and examined the possible relationship between water quality parameters and antibiotic resistance from two different drinking water sources (the Qiantang River and the Dongtiao Stream) in Hangzhou city of China. E. coli isolates were tested for their susceptibility to 18 antibiotics. Most of the isolates were resistant to tetracycline (TE), followed by ampicillin (AM), piperacillin (PIP), trimethoprim/sulfamethoxazole (SXT), and chloramphenicol (C). The antibiotic resistance rate of E. coli isolates from two water sources was similar; For E. coli isolates from the Qiantang River, their antibiotic resistance rates decreased from up- to downstream. Seasonally, the dry and wet season had little impact on antibiotic resistance. Spearman's rank correlation revealed significant correlation between resistance to TE and phenicols or ciprofloxacin (CIP), as well as quinolones (ciprofloxacin and levofloxacin) and cephalosporins or gentamicin (GM). Pearson's chi-square tests found certain water parameters such as nutrient concentration were strongly associated with resistance to some of the antibiotics. In addition, tet genes were detected from all 82 TE-resistant E. coli isolates, and most of the isolates (81.87%) contained multiple tet genes, which displayed 14 different combinations. Collectively, this study provided baseline data on antibiotic resistance of drinking water sources in Hangzhou city, which indicates drinking water sources could be the reservoir of antibiotic resistance, potentially presenting a public health risk