Marcelo Greco

Non-invasive methods of computer vision in the posture evaluation of adolescent idiopathic scoliosis

PURPOSE Reviewing techniques for non-invasive postural evaluation of adolescent idiopathic scoliosis (AIS) based on information extraction from images based on computer methods. METHODS The Scopus, Web of Science, MEDLINE, ScieLo and PubMed databases were used, for the period 2011-2015. RESULTS 131 articles were found based on keyword of which 15 articles met the established eligibility criteria. Of these, 4 were based on photogrammetry, and 11 based on laser, structured light, ultrasound, and Moiré projection. In these studies, the methodological quality varied from low to high. CONCLUSIONS The findings indicated diversity in methodologies; 14/15 articles reviewed were limited to the evaluation of the topography of the posterior back. A study, using two-dimensional photogrammetry, presented a whole body postural evaluation. As the asymmetry in AIS can be extended to the whole body, more attention should be given to develop full body assessment techniques to provide important additional data to aid in treatment decisions.

Using mathematical methods for designing optimal mixtures for building bricks prepared by solid industrial waste

This study evaluates the use of solid industrial waste generated by a water treatment plant (WTP) at a pulp mill in Brazil for manufacturing building bricks. The sludge from the WTP was mixed with three different wastes generated by the same factory (dregs, grits, and lime mud) and other wastes generated from crushing and grinding granite rock (granite fines). Mathematical and statistical methods are proposed for designing mixtures that satisfy the material properties for ceramic processing and the mechanical properties for the end product. A method for solving a linear system of equations using fewer equations than variables was required, as the number of materials exceeded the number of reference grain size distributions. This type of system is generally compatible and indeterminate. To obtain feasible solutions, a combination-of-variables method is proposed to optimize the mixture design. The formulation of the mixtures was based on the grain size distribution of the residues and the proportions of calcium, sodium, and potassium oxides in the mixtures. The nonparametric Kruskal–Wallis test and the median test were applied for all mixtures, followed by a multiple comparison test of classes. The mechanical properties of the specimens were evaluated after drying (linear shrinkage and flexural strength) and firing (ignition loss, linear shrinkage, and flexural strength) according to the Brazilian Association of Technical Standards and Brazilian Standards for red ceramics.

Accuracy of photogrammetry for detecting adolescent idiopathic scoliosis progression

BACKGROUND The gold standard method of monitoring the evolution of scoliosis has been serial standing, posteroanterior, full-length spine radiographs with curvature measurements using the Cobb method. However, over the course of follow-up, patients can receive high radiation doses. Various studies have shown that repeated exposure to radiation in children and adolescents can be harmful to their health. PURPOSE To determine the accuracy of photogrammetry in evaluating the progression of adolescent idiopathic scoliosis in comparison with radiography. STUDY DESIGN Diagnostic study. PATIENT SAMPLE Ninety adolescents subjected to radiographic follow-up of idiopathic scoliosis. OUTCOME MEASURES The angle of scoliotic curvature was measured using the Cobb radiographic method and photogrammetry. An increase of 5° or more between two radiographic exams was considered a progression of the curvature and was defined as the standard for calculations of sensitivity, specificity, predictive value, and accuracy of the photogrammetric method for measuring scoliosis progression. METHODS Patients were subjected to radiographic and photogrammetric exams concomitantly and were reevaluated after an average of 8.6 months. The exams were analyzed separately and independently by two examiners for progression of scoliosis. RESULTS The measurements of the curves at the beginning of the study were 39.5±16.7° and 39.5±14.3° for radiographic and photogrammetric exams, respectively (p=1.0). At the end of the study, the measurements of the curves were 40.2±16.2° and 41.3±15.1° for the radiographic and photogrammetric exams, respectively (p=.310). The photogrammetric method had an accuracy of 89% (Confidence interval [CI] 95%=82.5-95.5) for the detection of scoliosis progression, with a sensitivity of 94.4% (CI 95%=89.6-99.2), a specificity of 86.7% (CI 95%=79.7-93.7), a positive predictive value of 75.5% (CI 95%=66.6-84.4), a negative predictive value of 97.2% (CI 95%=93.8-100), and a Kappa index of 0.75 (CI 95%=66.1-83.9). The interclass correlation coefficient between the two methods was 0.74 (CI 95%=0.65-0.81; p=0). CONCLUSIONS The photogrammetric method showed good performance for detecting the progression of adolescent idiopathic scoliosis in comparison with the radiographic exam method.

Dynamic Instability in Shallow Arches under Transversal Forces and Plane Frames with Semirigid Connections

Structural engineering demands increasingly lighter systems, which can cause instability problems and compromise performance. A high slenderness index of a structural element makes it susceptible to instability. It is important to understand the problem, the limits of stability, and its postcritical behavior. An example that can occur in collapsed arches under a cross load is the dynamic snap-through behavior, where the structure in a given equilibrium condition jumps to a new remote equilibrium setting, causing usually sudden curvature. The semirigid connections are a source of physical nonlinearity and can influence the overall stability of the structural system, in addition to the distribution of stresses in the same system. Conventional approaches make use of static considerations. However, instability problems are inherently evolutionary processes, so a transient analysis is necessary for a complete description of structural behavior. The present work evaluates the geometrically nonlinear dynamic behavior of collapsed arches subjected to transverse force and plane frames with semirigid connections. The time domain responses, via Newmarks Method and positional formulation of the Finite Element Method, were obtained in terms of displacements, velocities, acceleration, and phase diagrams.

Modeling the creep behavior of GRFP truss structures with Positional Finite Element Method

This paper presents the development of a formulation, based on Positional Finite Element Method, to describe the viscoelastic mechanical behavior of space trusses. The numerical method used was chosen due to its efficiency in the applications concerning nonlinear numerical analyses. The formulation describes the positional variation over time under constant stress state (creep). The objective is to provide a way to quantify the creep behavior for space truss structures and thus contribute to the encouragement of GFRP usage in such structural components. Time-dependent behavior of such materials is one the most important factors for their use in design of structures, demanding studies about the deformations expected within the operational life of the structural systems. To perform this study, the proposed methodology considers a standard solid rheological model to describe stress-strain time-dependent law. This model is implemented in the formulation for quantify the total strain energy. The effects of the model parameters in the mechanical response of the structure with accentuated geometric nonlinearity were presented. In this analysis, it was possible to identify the influence of the elastic and the viscous moduli on the creep response. Model calibration was performed using test data obtained from literature and a GFRP transmission line tower cross-arm was simulated to predict the evolution of displacements under real operational loads. From the results, it was possible to observe a fast evolution of displacements due to the creep effect in the first 7,500 h. This increase was close to 0.6% in relation to the displacement obtained in the elastic behavior. The presented methodology provided a simple and efficient way to quantify the creep phenomenon in viscoelastic GFRP composites truss structures, as can be seen in the developed analyses.

Three-dimensional geometric model of the middle segment of the thoracic spine based on graphical images for finite element analysis

Abstract Introduction : Biomedical studies involve complex anatomical structures, which require specific methodology to generate their geometric models. The middle segment of the thoracic spine (T5-T10) is the site of the highest incidence of vertebral deformity in adolescents. Traditionally, its geometries are derived from computed tomography or magnetic resonance imaging data. However, this approach may restrict certain studies. The study aimed to generate two 3D geometric model of the T5-T10 thoracic spine segment, obtained from graphical images, and to create mesh for finite element studies. Methods : A 3D geometric model of T5-T10 was generated using two anatomical images of T6 vertebra (side and top). The geometric model was created in Autodesk  Maya 3D 2013, and the mesh process in HiperMesh and MeshMixer (v11.0.544 Autodesk). Results : The T5-T10 thoracic segment model is presented with its passive components, bones, intervertebral discs and flavum, intertransverse and supraspinous ligaments, in different views, as well as the volumetric mesh.

A SIMPLE FEM FORMULATION APPLIED TO NONLINEAR PROBLEMS OF IMPACT WITH THERMOMECHANICAL COUPLING

THE THERMAL EFFECTS OF PROBLEMS INVOLVING DEFORMABLE STRUCTURES ARE ESSENTIAL TO DESCRIBE THE BEHAVIOR OF MATERIALS IN FEASIBLE TERMS. VERIFYING THE TRANSFORMATION OF MECHANICAL ENERGY INTO HEAT IT IS POSSIBLE TO PREDICT THE MODIFICATIONS OF MECHANICAL PROPERTIES OF MATERIALS DUE TO ITS TEMPERATURE CHANGES. THE CURRENT PAPER PRESENTS THE NUMERICAL DEVELOPMENT OF A FINITE ELEMENT METHOD SUITABLE FOR NONLINEAR STRUCTURES COUPLED WITH THERMOMECHANICAL BEHAVIOR; INCLUDING IMPACT PROBLEMS. A SIMPLE AND EFFECTIVE ALTERNATIVE FORMULATION IS PRESENTED, CALLED FEM POSITIONAL, TO DEAL WITH THE DYNAMIC NONLINEAR SYSTEMS. THE DEVELOPED NUMERICAL IS BASED ON THE MINIMUM POTENTIAL ENERGY WRITTEN IN TERMS OF NODAL POSITIONS INSTEAD OF DISPLACEMENTS. THE EFFECTS OF GEOMETRICAL, MATERIAL AND THERMAL NONLINEARITIES ARE CONSIDERED. THE THERMODYNAMICALLY CONSISTENT FORMULATION IS BASED ON THE LAWS OF THERMODYNAMICS AND THE HELMHOLTZ FREE-ENERGY, USED TO DESCRIBE THE THERMOELASTIC AND THE THERMOPLASTIC BEHAVIORS. THE COUPLED THERMOMECHANICAL MODEL CAN RESULT IN SECONDARY EFFECTS THAT CAUSE REDISTRIBUTIONS OF INTERNAL EFFORTS, DEPENDING ON THE HISTORY OF DEFORMATION AND MATERIAL PROPERTIES. THE NUMERICAL RESULTS OF THE PROPOSED FORMULATION ARE COMPARED WITH EXAMPLES FOUND IN THE LITERATURE.

Impact Response of Flying Objects Modeled by Positional Finite Element Method

This paper analyzes the dynamic response of space and plane trusses with geometrical and material nonlinear behaviors using different time integration algorithms, considering an alternative Finite Element Method (FEM) formulation called positional FEM. Each algorithm is distinguished from each other by its specific form of position, velocity, acceleration and equilibrium equation concerning the stability, consistency, accuracy and efficiency of solution. Particularly, the impact problems against rigid walls are analyzed considering Null-Penetration Condition. This formulation is based on the minimum potential energy theorem written according to the nodal positions, instead of the structural displacements. It has the advantage of simplicity when compared with the classical counterparts, since it does not necessarily reply on the corotational axes. Moreover, the performance of each temporal integration algorithm is evaluated by numerical simulations.

APLICAÇÃO DE UM MÉTODO DE OTIMIZAÇÃO TOPOLÓGICA EVOLUCIONÁRIA DESENVOLVIDO EM SCRIPT PYTHON

The use of computational algorithms for optimized solutions has been becoming an excellent alternative to necessary and exhaustive verifications regarding the best structural conception. With the evolution of the computational capability and the Finite Elements Method, several topological optimization methods have been developed. Among these methods, the method called Evolutionary Structural Optimization (ESO) has been used on the structural problems solutions, through the application of Heuristic procedures on the analyses. The present paper deals with the topological optimization using the ESO method developed in a programming platform available on the software for multiphysics analyses Abaqus®. The ESO method is applied for some problems found in literature, both for static problems and for dynamic problems. The obtained results prove the efficiency of the implemented method. The last numerical application presents the optimization of a metallic flange used to support the motor of an aeolian turbine, comparing the results among two different design conceptions. Keywords: Topological optimization, evolutionary optimization, finite elements method.

Desenvolvimento de software educacional de engenharia para dosagem de mistura de materiais

The paper deals with the development of a software for the mix design of granular materials based on the method of least squares. The software, developed in Java, has the possibility of using a weighted cost function in the mixtures, the specificity for the application, and the gratuity. The problem to be solved is the determination of the proportions of each component to be used in the material mixture, so that the mixture has the appropriate particle size distribution characteristics specified by the technical standards. The obtained solutions showed excellent results of adhesion of particle size distributions satisfying the optimal distributions.