An immersed methodology for fluid-structure interaction using NURBS and T-splines: theory, algorithms, validation, and application to blood flow at small scales

[Abstract] Mesh-based immersed approaches shine in a variety of fluid-structure interaction (FSI) applications such as, e.g., simulations where the solid undergoes large displacements or rotations, particulate flow problems, and scenarios where the topology of the region occupied by the fluid varies in time. In this thesis, a new mesh-based immersed approach is proposed which is based on the use of di erent types of splines as basis functions. This approach is put forth for modeling and simulating di erent types of biological cells in blood flow at small scales. The specific contributions of this thesis are outlined as follows. Firstly, a hybrid variational-collocation immersed technique using nonuniform rational B-splines (NURBS) is presented. Newtonian viscous incompressible fluids and nonlinear hyperelastic incompressible solids are considered. Our formulation boils down to three coupled equations which are the linear momentum balance equation, the mass conservation equation, and the kinematic equation that relates the Lagrangian displacement with the Eulerian velocity. The latter is discretized in strong form using isogeometric collocation and the other two equations are discretized using the variational multiscale (VMS) paradigm. As usual in immersed FSI approaches, we define a background mesh on the whole computational domain and a Lagrangian mesh tailored to the region occupied by each solid. Besides of using NURBS for creating these meshes, the data transfer between the background mesh and the Lagrangian meshes is carried out using NURBS functions in such a way that no interpolation or projection is needed, thus avoiding the errors associated with these procedures. Regarding the time discretization, the generalized- method is used which leads to a fully-implicit and second-order accurate method. The methodology is validated in two- and three-dimensional settings comparing the terminal velocity of free-falling bulky solids obtained in our simulations with its theoretical value. Secondly, we extend our algorithms in order to use analysis-suitable T-splines (ASTS) as basis functions instead of NURBS. This required to develop isogeometric collocation methods for ASTS which was an open problem. The data transfer between meshes changes significantly from NURBS to ASTS due to the fact that their geometrical mappings are local to patches and elements, respectively. ASTS possess two main advantages with respect to NURBS: (1) ASTS support local h-refinement and (2) ASTS are unstructured. The ASTSbased method is validated solving again the aforementioned benchmark problems and showing the potential of ASTS to decrease the amount of elements needed, thus enhancing the e ciency of the method. Thirdly, capsules, modeled as solid-shell NURBS elements, are proposed as numerical proxies for representing red blood cells (RBCs). The dynamics of capsules are able to reproduce the main motions and shapes observed in experiments with RBCs in both shear and parabolic flows. Hemorheological properties as the Fåhræus and Fåhræus-Lindqvist e ects are captured in our simulations. In order to obtain the aforementioned results, it is essential to adequately satisfy the incompressibility constraint close to the fluid-solid interface, which is an arduous task in immersed approaches for fluid-structure interaction. Finally, compound capsules are presented as numerical proxies for cells with nucleus such as, e.g., white blood cells (WBCs) and circulating tumor cells (CTCs). The dynamics of hyperelastic compound capsules in shear flow are studied in both two- and three-dimensional settings. Moreover, we simulate how CTCs manage to pass through channel narrowings, which is an interesting characteristic of CTCs since it is used in experiments to sort CTCs from blood samples

Kirchhoff-Love shell representation and analysis using triangle configuration B-splines

This paper presents the application of triangle configuration B-splines (TCB-splines) for representing and analyzing the Kirchhoff-Love shell in the context of isogeometric analysis (IGA). The Kirchhoff-Love shell formulation requires global $C^1$-continuous basis functions. The nonuniform rational B-spline (NURBS)-based IGA has been extensively used for developing Kirchhoff-Love shell elements. However, shells with complex geometries inevitably need multiple patches and trimming techniques, where stitching patches with high continuity is a challenge. On the other hand, due to their unstructured nature, TCB-splines can accommodate general polygonal domains, have local refinement, and are flexible to model complex geometries with $C^1$ continuity, which naturally fit into the Kirchhoff-Love shell formulation with complex geometries. Therefore, we propose to use TCB-splines as basis functions for geometric representation and solution approximation. We apply our method to both linear and nonlinear benchmark shell problems, where the accuracy and robustness are validated. The applicability of the proposed approach to shell analysis is further exemplified by performing geometrically nonlinear Kirchhoff-Love shell simulations of a pipe junction and a front bumper represented by a single patch of TCB-splines

Grado de adherencia y conocimiento previo a la conciliación terapéutica en pacientes en diálisis peritoneal

Producción CientíficaEl empleo de medicamentos implica a pacientes y profesionales sanitarios, y puede dar lugar a errores con importantes repercusiones clínicas. A estos errores contribuyen la pluripatologìa, la polimedicaciòn, la fragmentación del sistema de salud (con múltiples médicos prescriptores sin registro único de salud), así como al desconocimiento del tratamiento por parte del paciente, familiares o cuidadores. Para disminuir estos errores de medicación se han propuesto varios procesos entre los que se incluyen la conciliación de la medicación (crear lista de medicación exacta que recoja todos los fármacos que el paciente toma), revisión del tratamiento (evaluar la lista para adecuación, efectividad, seguridad y conveniencia en conjunción con el estado de salud del paciente) y manejo individualizado de la terapia (comprobando adherencia, conocimiento de fármacos y lista de medicación «en la cartera»

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

The divergence-conforming immersed boundary method: Application to vesicle and capsule dynamics

We extend the recently introduced divergence-conforming immersed boundary (DCIB) method [1] to fluid-structure interaction (FSI) problems involving closed co-dimension one solids. We focus on capsules and vesicles, whose discretization is particularly challenging due to the higher-order derivatives that appear in their formulations. In two-dimensional settings, we employ cubic B-splines with periodic knot vectors to obtain discretizations of closed curves with C2 inter-element continuity. In three-dimensional settings, we use analysis-suitable bi-cubic T-splines to obtain discretizations of closed surfaces with at least C1 inter-element continuity. Large spurious changes of the fluid volume inside closed co-dimension one solids are a well-known issue for IB methods. The DCIB method results in volume changes orders of magnitude lower than conventional IB methods. This is a byproduct of discretizing the velocity-pressure pair with divergence-conforming B-splines, which lead to negligible incompressibility errors at the Eulerian level. The higher inter-element continuity of divergence-conforming B-splines is also crucial to avoid the quadrature/interpolation errors of IB methods becoming the dominant discretization error. Benchmark and application problems of vesicle and capsule dynamics are solved, including mesh-independence studies and comparisons with other numerical methods.</p

Seamless integration of design and Kirchhoff-Love shell analysis using analysis-suitable unstructured T-splines

Analysis-suitable T-splines (ASTS) including both extraordinary points and T-junctions are used to solve Kirchhoff-Love shell problems. Extraordinary points are required to represent surfaces with arbitrary topological genus. T-junctions enable local refinement of regions where increased resolution is needed. The benefits of using ASTS to define shell geometries are at least two-fold: (1) The manual and time-consuming task of building a new mesh from scratch using the CAD geometry as an input is avoided and (2) C-1 or higher inter-element continuity enables the discretization of shell formulations in primal form defined by fourth-order partial differential equations. A complete and state-of-the-art description of the development of ASTS, including extraordinary points and T-junctions, is presented. In particular, we improve the construction of C-1-continuous non-negative spline basis functions near extraordinary points to obtain optimal convergence rates with respect to the square root of the number of degrees of freedom when solving linear elliptic problems. The applicability of the proposed technology to shell analysis is exemplified by performing geometrically nonlinear Kirchhoff-Love shell simulations of a pinched hemisphere, an oil sump of a car, a pipe junction, and a B-pillar of a car with 15 holes. Building ASTS for these examples involves using T-junctions and extraordinary points with valences 3, 5, and 6, which often suffice for the design of free-form surfaces. Our analysis results are compared with data from the literature using either a seven-parameter shell formulation or Kirchhoff-Love shells. We have also imported both finite element meshes and ASTS meshes into the commercial software LS-DYNA, used Reissner-Mindlin shells, and compared the result with our Kirchhoff-Love shell results. Excellent agreement is found in all cases. The complexity of the shell geometries considered in this paper shows that ASTS are applicable to real-world industrial problems. (C) 2019 Elsevier B.V. All rights reserved

Radiation fog formation alerts using attenuated backscatter power from automatic lidars and ceilometers

International audienceRadiation fog occurs over many locations around the world in stable atmospheric conditions. Air traffic at busy airports can be significantly disrupted because low visibility at the ground makes it unsafe to take off, land and taxi on the ground. Current numerical weather prediction forecasts are able to predict general conditions favorable for fog formation, but not the exact time or location of fog occurrence. A selected set of observations available in near-real time at strategic locations could also be useful to track the evolution of key processes and key parameters that drive fog formation. Such observations could complement the information predicted by numerical weather prediction (NWP) models that is made available to airport forecasters in support of their fog forecast. This paper presents an experimental setup based on collocated automatic lidar and ceilometer measurements, relative humidity measurements and horizontal visibility measurements to study hygroscopic growth of fog condensation nuclei. This process can take several minutes to hours, and can be tracked using lidar- or ceilometer-attenuated backscatter profiles. Based on hygroscopic growth laws we derive a set of parameters that can be used to provide alerts minutes to hours prior to formation of radiation fog. We present an algorithm that uses the temporal evolution of attenuated backscatter measurements to derive pre-fog formation alerts. The performance of the algorithm is tested on 45 independent pre-fog situations at two locations (near Paris, France, and Brussels, Belgium). We find that an alert for pre-fog conditions predominantly occurs 10-50 min prior to fog formation at an altitude ranging 0 to 100 m above ground. In a few cases, alerts can occur up to 100 min prior to fog formation. Alert durations are found to be sensitive to the relative humidity conditions found a few hours prior to the fog