M.P.L. Parente

Establishing the biomechanical properties of the pelvic soft tissues through an inverse finite element analysis using magnetic resonance imaging

The mechanical characteristics of the female pelvic floor are relevant when explaining pelvic dysfunction. The decreased elasticity of the tissue often causes inability to maintain urethral position, also leading to vaginal and rectal descend when coughing or defecating as a response to an increase in the internal abdominal pressure. These conditions can be associated with changes in the mechanical properties of the supportive structures—namely, the pelvic floor muscles—including impairment. In this work, we used an inverse finite element analysis to calculate the material constants for the passive mechanical behavior of the pelvic floor muscles. The numerical model of the pelvic floor muscles and bones was built from magnetic resonance axial images acquired at rest. Muscle deformation, simulating the Valsalva maneuver with a pressure of 4u2009KPa, was compared with the muscle displacement obtained through additional dynamic magnetic resonance imaging. The difference in displacement was of 0.15u2009mm in the antero-posterior direction and 3.69u2009mm in the supero-inferior direction, equating to a percentage error of 7.0% and 16.9%, respectively. We obtained the shortest difference in the displacements using an iterative process that reached the material constants for the Mooney–Rivlin constitutive model (c10=11.8u2009KPa and c20=5.53u2009E−02u2009KPa). For each iteration, the orthogonal distance between each node from the group of nodes which defined the puborectal muscle in the numerical model versus dynamic magnetic resonance imaging was computed. With the methodology used in this work, it was possible to obtain in vivo biomechanical properties of the pelvic floor muscles for a specific subject using input information acquired non-invasively.

Enhanced Assumed Strain Shell and Solid‐Shell Elements: Application in Sheet Metal Forming Processes

Reliable numerical analysis of sheet metal forming processes using commercial finite element programs involves a variety of fields within computational mechanics area. Material models, contact algorithms, robust and fast incremental and iterative solution techniques are among the key factors that a finite element package must rely upon. Nevertheless, the finite element formulation itself still represents a milestone of crucial importance in the overall quality of the final solution. As sheet metal forming processes present very strong test cases to the performance of finite elements, robust formulations are then desired. In this work, classes of finite elements involving only the Enhanced Assumed Strain (EAS) method are analyzed. Starting from an innovative approach to eliminate transverse shear locking in shell elements (S4E6P5 shell element) and going through a new approach for a volumetric and transverse shear locking‐free solid‐shell element with a low number of internal variables (HCiS12 solid‐shell ...

Chapter Twenty-One – Biomechanical Childbirth Simulations

Modeling the events that take place during childbirth requires an integration of morphological features, tissue characteristics, and prediction of the most probable fetal movements according to the inputs submitted to the computational model. The choice of the material properties and constitutive models affect the outputs, and the challenge still points out to how to mathematically describe the pelvic soft tissues if experimental proof is not possible. Several authors explored the modeling of vaginal delivery by focusing on different aspects: the maternal pelvic bones, the fetus position, and head molding, but most of them focused on the effects of vaginal delivery on the pelvic floor muscles. The present chapter reviews the events that occur during childbirth, to better illustrate the features described in a computational reproduction of labor. The focus is set on the results from different numerical simulation approaches, and on the biomechanical analysis of the pelvic floor muscles and fetal head passage.

Dynamic study of the middle ear

The human ear is a complex biomechanical system and is divided by three parts: outer, middle and inner ear.