Improving a strongly coupled method for FSI by a simple approximation of the pressure tangent matrix

La interacción de los fluidos con las estructuras de su entorno es un desafío clásico para las técnicas numéricas. El objetivo de este trabajo es doble: en primer lugar se proporciona una explicación teórica simple de los principales problemas que se deben superar cuando se trata con un fluido incompresible. A continuación se introduce y justifica un nuevo procedimiento para la solución de problemas complejos de interacción fluido-estructura. Dicha estrategia se basa en la introducción de un «laplaciano de interfase» en el contorno común entre ambos medios. La idea es considerar la dependencia entre la presión del fluido y la velocidad de la estructura como un problema no lineal, que se va a resolver mediante un esquema cuasi-Newton. Se demuestra que el término de interfase resultante es una aproximación de la matriz tangente de dicho problema no lineal, usando exclusivamente álgebra lineal discreta. Finalmente, se verifica la validez de la técnica propuesta mediante su aplicación a algunos ejemplos.The interaction of fluids with surrounding structures constitutes a classical challenge for the different numerical techniques. The aim of current work is twofold: first we provide a simple theoretical explanation of the problems to be faced in incompressible FSI. Then we introduce and justify a new procedure for the solution of complex fluid-structure interaction problems. Such a new strategy is based on the introduction of an «interface Laplacian» at the coupling boundary. The idea is to consider the dependence between fluid pressure and structural velocity as a non linear problem for which a Quasi-Newton scheme is sought. The new interface term is then proved to be an approximation of the tangent matrix for such non-linear problem. In the derivation of this result we make use exclusively of discrete linear algebra. Finally, we prove the efficiency of the new approach showing its ability to tackle standard benchmark problems.Peer Reviewe

Understanding Mechanical Response of Elastomeric Graphene Networks

Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls

Validation and Generalizability of Preoperative PROMIS Scores to Predict Postoperative Success in Foot and Ankle Patients

Background: A recent publication reported preoperative Patient-Reported Outcomes Measurement Instrumentation System (PROMIS) scores to be highly predictive in identifying patients who would and would not benefit from foot and ankle surgery. Their applicability to other patient populations is unknown. The aim of this study was to assess the validation and generalizability of previously published preoperative PROMIS physical function (PF) and pain interference (PI) threshold t scores as predictors of postoperative clinically meaningful improvement in foot and ankle patients from a geographically unique patient population. Methods: Prospective PROMIS PF and PI scores of consecutive patient visits to a tertiary foot and ankle clinic were obtained between January 2014 and November 2016. Patients undergoing elective foot and ankle surgery were identified and PROMIS values obtained at initial and follow-up visits (average, 7.9 months). Analysis of variance was used to assess differences in PROMIS scores before and after surgery. The distributive method was used to estimate a minimal clinically important difference (MCID). Receiver operating characteristic curve analysis was used to determine thresholds for achieving and failing to achieve MCID. To assess the validity and generalizability of these threshold values, they were compared with previously published threshold values for accuracy using likelihood ratios and pre- and posttest probabilities, and the percentages of patients identified as achieving and failing to achieve MCID were evaluated using χ2 analysis. Results: There were significant improvements in PF (P \u3c .001) and PI (P \u3c .001) after surgery. The area under the curve for PF (0.77) was significant (P \u3c .01), and the thresholds for achieving MCID and not achieving MCID were similar to those in the prior study. A significant proportion of patients (88.9%) identified as not likely to achieve MCID failed to achieve MCID (P = .03). A significant proportion of patients (84.2%) identified as likely to achieve MCID did achieve MCID (P \u3c .01). The area under the curve for PROMIS PI was not significant. Conclusions: PROMIS PF threshold scores from published data were successful in classifying patients from a different patient and geographic population who would improve with surgery. If functional improvement is the goal, these thresholds could be used to help identify patients who will benefit from surgery and, most important, those who will not, adding value to foot and ankle health care. Level of evidence: Level II, Prospective Comparative Stud

Printing in three dimensions with graphene

Responsive graphene oxide sheets form non‐covalent networks with optimum rheological properties for 3D printing. These networks have shear thinning behavior and sufficiently high elastic shear modulus (G′) to build self‐supporting 3D structures by direct write assembly. Drying and thermal reduction leads to ultra‐light graphene‐only structures with restored conductivity and elastomeric behavior

Validación del empleo de aleaciones superelásticas en distracción mandibular

Peer Reviewe