Shape Curvature Research Articles

Effect of damage on the vibration modal of a novel three-dimensional and four-directional braided composite T-beam

The effect of damage on the modal properties of a three-dimensional (3Dim) and four-directional (4Dir) braided composite T-beam was investigated by means of modal experiments and finite element analysis (FEA). The experimental tests on these damaged T-beams showed alteration of the vibration mode response. The damage obviously changed the mode shape curvatures. The influence of the damage upon the modal shape curvatures of the T-beam could be used to detect and localize the damage. Finite element modeling (FEM) of the damaged T-beam revealed that the damage affected the natural frequency of the T-beam but did not affect its modal shape.

Descrição de cultivares locais de feijão-caupi coletados na microrregião Cruzeiro do Sul, Acre, Brasil

A distribuição de sementes comerciais ameaça erodir o germoplasma local em regiões tradicionais de plantio de feijões-caupi (Vigna unguiculata). O objetivo deste trabalho foi descrever as cultivares locais de feijão-caupi da Resex Alto Juruá e da microrregião Cruzeiro do Sul - AC. Foram conduzidos dois experimentos nos anos de 2011 e 2012, em sistema convencional e, em sistema de plantio em aleias, respectivamente. O delineamento experimental adotado nos experimentos foi de blocos ao acaso com nove tratamentos (cultivares), três repetições por tratamento, parcelas de 12 m2 e espaçamento de 0,45 m entre plantas e linhas. Foram observados vinte caracteres qualitativos e 21 quantitativos. A análise de variância conjunta dos experimentos apresentou significativo para genótipo, sistema de plantio e interação genótipo/sistema de plantio. A característica qualitativa com maior variação entre os genótipos foi subclasse comercial, seguida da cor do grão, pigmentação da vagem imatura, forma do folíolo apical, cor das folhas e curvatura da vagem. O hábito da planta, tendência a enrolar-se ao tutor, fixação da vagem ao pedúnculo e espessura de parede da vagem não apresentam diferenças. Dos caracteres quantitativos apenas número de dias até 50% das plantas em florescimento e número de lóculos/vagem não diferiram estatisticamente entre cultivares. Os valores médios para comprimento de vagem, comprimento do pedúnculo, número de vagens por pedúnculo e número de vagens por planta foram baixos, entretanto, o germoplasma coletado apresentou características valorizadas como ciclo precoce, arquitetura adequada da planta além da adaptação ao plantio em várzeas.

Análisis y Comparación del Descriptor Cone Curvature frente al Reconocimiento de Expresiones Faciales

Se presenta el resultado de analizar el comportamiento del descriptor de forma Cone Curvature (CC) en la tarea de reconocimiento de expresiones faciales en imágenes 3D. El descriptor CC es una representación del modelo 3D que se calcula a partir de un conjunto de ondas de modelado para cada vértice de una malla poligonal. Se empleó la base de datos de rostros 3D (BU-3DFE), la cual contiene imágenes con 6 expresiones faciales. Con el uso del descriptor CC, las expresiones fueron reconocidas en un porcentaje promedio del 76.67% con una red neuronal, y del 78.88% con un clasificador bayesiano. Al realizar una combinación del descriptor CC con otros descriptores como DESIRE y Spherical Spin Image, se logr´o un porcentaje promedio de reconocimiento de gestos del 90.27% y del 97.2 %, usando los mismos clasificadores mencionados previamente.

Damage Detection in Laminated Composite Beams, Plates and Shells Using Dynamic Analysis

Vibration-based technique to detect damage in laminated composite beams, rectangular plates and cylindrical shells is presented in this paper.A parameter called damage indicator calculated based on mode shape curvature isused in this studyto detect the location and size of small damages accurately in laminated composite structures. Through numerical analysis of laminated compositecantilevered beam, plate and cylindrical shell models with edge crack as damage, the absolute change inthe damage indicator is localized in the region of damage. Thechange in damage indicatorincreases withincreasing size of damage. Thisinformationis obtained by considering two cases of damage sizes (case-1 and case-2)in the structures. Finite element methodbased commercial analysis package ANSYSis used to obtain thenormalized displacement mode shapesof the three models both for intact and damaged states and then the damage indicator is calculated from the mode shapes data.The numerical analysis to detect damage is followed by validation by experimental modal testing.

Modal parametric changes in a steel bridge with retrofitting

This paper presents the status improvement of an old damaged deck type rural road steel truss bridge through the modal parametric study after partial retrofitting. The dynamic and static tests on bridge were carried out as in damaged state and after partial retrofitting. The dynamic testing on the steel bridge was carried out using accelerometers under similar environmental conditions with same speed of the moving vehicle. The comparison of the modal parameters i.e., frequency, mode shape mode shape curvature, modal strain energy, along with the deflection parameter are studied with respect to structural analytical model parameters. The status up gradation for the upper and downstream truss obtained was different due to differential level of damage in the bridge. Also after retrofitting the structural elemental behavior obtained was not same as desired. The damage level obtained through static tests carried out using total station indicated further retrofitting requirement.

Application of higher order finite differences to damage localization in laminated composite plates

The localization of damage in composite plates and other structures is often performed based on mode shape curvatures. These curvatures are usually computed using finite differences. However, finite differences spread and amplify numerical and experimental errors. A technique based on the Ritz method allows to choose an optimal spatial sampling in order to minimize this problem. In the present work we apply this technique, along with the second and fourth order finite differences to compute the mode shape curvatures. To evaluate the successfulness of the damage localizations a quality evaluator is proposed in this paper. The need for the optimal spatial sampling is verified by analyzing two locations of a wide range of damage severities. Damage localizations obtained with second and fourth order finite differences were compared and it was found out that the results are better when one uses the highest order finite difference.

Peptide Self-Assemblies for Drug Delivery.

Peptide amphiphiles (PAs) are novel engineered biomaterials able to self-assemble into supramolecular systems that have shown significant promise in drug delivery across the cell membane and across challenging biological barriers showing promise in the field of brain diseases, regenerative medicine and cancer. PAs are amino-acid block co-polymers, with a peptide backbone composed usually of 8-30 amino acids, a hydrophilic block formed by polar amino acids, a hydrophobic block which usually entails either non-polar or aromatic amino acids and alkyl, acyl or aryl lipidic tails and in some cases a spacer or a conjugated targeting moiety. Finely tuning the balance between the hydrophilic and hydrophobic blocks results in a range of supramolecular structures that are usually stabilised by hydrophobic, electrostatic, β-sheet hydrogen bonds and π-π stacking interactions. In an aqueous environment, the final size, shape and interfacial curvature of the PA is a result of the complex interplay of all these interactions. Lanreotide is the first PA to be licensed for the treatment of acromegaly and neuroendocrine tumours as a hydrogel administered subcutaneously, while a number of other PAs are undergoing preclinical development. This review discusses PAs architecture fundamentals that govern their self-assembly into supramolecular systems for applications in drug delivery.

Clavicular curvature and locomotion in anthropoid primates: A 3D geometric morphometric analysis.

As a component of the primate shoulder, the clavicle is expected to reflect locomotor adaptations. Whereas previous work has generally focused on clavicular length and torsion, the shape of clavicular curvature may better distinguish taxa and provide additional information about upper limb use in locomotion. This study uses three-dimensional geometric morphometrics to analyze shape differences in the curvatures of the clavicle in different locomotor groups of anthropoid primates. Sliding semi-landmarks were placed on clavicles of 10 Anthropoid primate species (total n = 85) that display a range of locomotor behaviors. Landmarks (k = 39) were chosen to capture the overall curvature of the clavicle in three dimensions. The degree of ventral curvature in the clavicle represents a gradient from most-curved in suspensory genera (e.g., Ateles, Hylobates, and Pongo) to least-curved in genera that are rarely suspensory (e.g., Papio and Gorilla). This curvature may allow an increased range of craniodorsal movement without the clavicle impinging on the thoracic outlet. An inferior curvature of the medial clavicle is found in hominoids and brachiators. This curvature could help stabilize the shoulder and prevent superior dislocation of the clavicle in suspension. Finally, a superior curvature in the lateral part of the clavicle, most pronounced in quadrupedal monkeys, may be related to the relative position of the scapula and sternum. Patterns of clavicular curvature in anthropoid primates reflect locomotor behavior and successfully distinguished among taxonomic and locomotor groups. In the future, this method could be used to assess locomotor behavior in fossil primates. Am J Phys Anthropol 158:257-268, 2015. © 2015 Wiley Periodicals, Inc.

Why neutron guides may end up breaking down? Some results on the macroscopic behaviour of alkali-borosilicate glass support plates under neutron irradiation

In this paper we report on a first part of a study on the mechanisms leading to brittle fracture in neutron guides made of glass as structural element. Such devices are widely used to deliver thermal and cold neutron beams to experimental lines in most large neutron research facilities. We present results on macroscopic properties of samples of guide glass substrates which are subjected to neutron irradiation at relatively large fluences. The results show a striking dependence of some of the macroscopic properties such as density, shape or surface curvature upon the specific chemical composition of a given glass. The relevance of the present findings for the installation of either replacement guides at the existing facilities or for the deployment of instruments for ongoing projects such as the European Spallation Source is briefly discussed.

Natural frequency changes due to damage in composite beams

Transversal cracks in structures affect their stiffness as well as the natural frequency values. This paper presents a research performed to find the way how frequencies of sandwich beams change by the occurrence of damage. The influence of the locally stored energy, for ten transverse vibration modes, on the frequency shifts is derived from a study regarding the effect of stiffness decrease, realized by means of the finite element analysis. The relation between the local value of the bending moment and the frequency drop is exemplified by a concrete case. It is demonstrated that a reference curve representing the damage severity exists whence any frequency shift is derivable in respect to damage depth and location. This curve is obtained, for isotropic and multi-layer beams as well, from the stored energy (i.e. stiffness decrease), and is similar to that attained using the stress intensity factor in fracture mechanics. Also, it is proved that, for a given crack, irrespective to its depth, the frequency drop ratio of any two transverse modes is similar. This permitted separating the effect of damage location from that of its severity and to define a Damage Location Indicator as a sequence of squared of the normalized mode shape curvatures.

Numerical investigation on Coanda flow over a logarithmic surface

The Coanda effect has been introduced into lift generation designs. In this paper, a logarithmic spiral surface is introduced as a curvature shape to evaluate the development of jet flow along the Coanda curvature. Moreover, 2D computational fluid dynamics numerical simulation is adopted to measure velocity profile, jet width growth, maximum velocity decay, and surface static pressure along the curvature surface. A parametric study on the effect of varying exit jet heights on the Coanda effect is also presented. Results show that jet width grows proportionally along the curved surface, and the proportional decay of maximum velocity and surface pressure is lower than the atmospheric pressure. A wider exit jet height produces lower static pressure on the unmanned aerial vehicle surface and a slower maximum velocity decay. Overall parametric analysis of varying exit jet heights shows that the effective range of d/R is 0.1 to 0.14.

Laser-assisted morphing of complex three dimensional objects.

Morphing refers to the smooth transition from a specific shape into another one, in which the initial and final shapes can be significantly different. A typical illustration is to turn a cube into a sphere by continuous change of shape curvatures. Here, we demonstrate a process of laser-induced morphing, driven by surface tension and thermally-controlled viscosity. As a proof-of-concept, we turn 3D glass structures fabricated by a femtosecond laser into other shapes by locally heating up the structure with a feedback-controlled CO2 laser. We further show that this laser morphing process can be accurately modelled and predicted.

A unified approach for nonlinear vibration analysis of curved structures using non-uniform rational B-spline representation

A novel procedure for the nonlinear vibration analysis of curved beam is presented. The Non-Uniform Rational B-Spline (NURBS) is combined with the Euler−Bernoulli beam theory to define the curvature of the structure. The governing equation of motion and the general frequency formula, using the NURBS variables, is applicable for any type of curvatures, is developed. The Galerkin procedure is implemented to obtain the nonlinear ordinary differential equation of curved system and the multiple time scales method is utilized to find the corresponding frequency responses. As a case study, the nonlinear vibration of carbon nanotubes with different shapes of curvature is investigated. The effect of oscillation amplitude and the waviness on the natural frequency of the curved nanotube is evaluated and the primary resonance case of system with respect to the variations of different parameters is discussed. For the sake of comparison of the results obtained with those from the molecular dynamic simulation, the natural frequencies evaluated from the proposed approach are compared with those reported in literature for few types of carbon nanotube simulation.

An experimental evaluation of the reliability of a damage localization algorithm based on FRF interpolation

In this paper two methods for damage localization, the IDDM (Interpolation Damage Detecting Method), and the Modal Shape Curvature Method (MSCM) are applied to the same experimental case of a cantilever aluminum beam for which several different damage scenarios have been artificially reproduced in laboratory. IDDM is a new method recently proposed in literature which is on the definition of a damage-sensitive feature in terms of the accuracy of a spline function interpolating the Operational Displacement Shapes of the structure. This paper will present a comparison between the two methods on experimental data from a laboratory bench structure. Results show that, due to the small changes of the damage features induced by damage, both methods require a high-quality data set to provide a reliable damage localization even if the number of false alarms is slightly lower if the IDDM is applied.

Impact damage identification in composite skin-stiffener structures based on modal curvatures

The feasibility of a vibration-based damage identification approach for impact damage in two advanced composite skin-stiffener structures is investigated in this paper. Mode shape curvatures combined with the modal strain energy damage index (MSE-DI) algorithm are utilized to identify the damage. Special attention is paid to the effective application of this vibration-based methodology by investigating the relation between the damage location, the structural design, and the dynamic behavior. The performance of a 1D and 2D formulation of the MSE-DI algorithm is compared for several damage scenarios. Experiments demonstrated the capabilities of the MSE-DI algorithm to detect, localize, and roughly quantify the size of barely visible impact damage in advanced composite structures. It is concluded that the method is particularly effective for health monitoring of skin-stiffener connections. The most effective results were obtained by considering the 1D formulation in the direction of the stiffeners for the stiffener mid-section and perpendicular to the stiffeners for the stiffener run-out. The method remained inconclusive in the case of pure skin-related damage. The results obtained in this study contribute to the development of guidelines for vibration-based structural health monitoring of advanced composite skin-stiffener structures. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of asymmetrical backpack load on spinal curvature in school children.

Carrying a backpack is common among schoolchildren. The effect of backpack load on spine pain and posture defects in children is often raised in the literature. According to scientific research, the maximum backpack load that is safe for children must not exceed 10-15% of their body mass. There is a lack of scientific reports related to the effect of frequently wearing a backpack on one shoulder among children and young adults and its influence on the shape of the anterior-posterior curvatures of spine. The aim of this study is to evaluate body posture parameters in the sagittal plane for an asymmetrical backpack load equal to 10% of a child's body mass. The study was conducted using 162 primary schoolchildren aged 11-13 years. Each participant underwent three tests that examined postural parameters, including habitual posture, with the backpack on the participant's right and left shoulder. Posture was measured with the CQ Elektronik; which uses photogrammetry to make anthropometric calculations based on an image of the examined surface. The asymmetrical backpack load resulted in a significant reduction of thoracic kyphosis (GKP: p=0.040). The angle of thoracic kyphosis increased between the measurements. The difference (GAMMA=0.054) revealed that the results were approaching significance. Considering the gravity of the problem, children should be educated on ergonomics by teachers, physiotherapist or nurses, including instructions on carrying a backpack and the effects of disregarding the basic rules on body posture, as part of their school curriculum. The acceptable backpack load, which is now believed to be 10% of the child's body mass, should be carefully considered by scientists. Our own results show that even a load of 10% of the body mass may induce negative changes in spinal posture.

Intraoperative passive knee kinematics during total knee arthroplasty surgery.

Surgical navigation systems for total knee arthroplasty (TKA) surgery are capable of capturing passive three-dimensional (3D) angular joint movement patterns intraoperatively. Improved understanding of patient-specific knee kinematic changes between pre and post-implant states and their relationship with post-operative function may be important in optimizing TKA outcomes. However, a comprehensive characterization of the variability among patients has yet to be investigated. The objective of this study was to characterize the variability within frontal plane joint movement patterns intraoperatively during a passive knee flexion exercise. Three hundred and forty patients with severe knee osteoarthritis (OA) received a primary TKA using a navigation system. Passive kinematics were captured prior to (pre-implant), and after prosthesis insertion (post-implant). Principal component analysis (PCA) was used to capture characteristic patterns of knee angle kinematics among patients, to identify potential patient subgroups based on these patterns, and to examine the subgroup-specific changes in these patterns between pre- and post-implant states. The first four extracted patterns explained 99.9% of the diversity within the frontal plane angle patterns among the patients. Post-implant, the magnitude of the frontal plane angle shifted toward a neutral mechanical axis in all phenotypes, yet subtle pattern (shape of curvature) features of the pre-implant state persisted.

The shape of the oceanic nitracline

Abstract. In most regions of the ocean, nitrate is depleted near the surface by phytoplankton consumption and increases with depth, exhibiting a strong vertical gradient in the pycnocline (here referred to as the nitracline). The vertical supply of nutrients to the surface euphotic zone is influenced by the vertical gradient (slope) of the nitracline and by the vertical separation (depth) of the nitracline from the sunlit surface layer. Hence it is important to understand the shape (slope and curvature) and depth of the oceanic nitracline. By using density coordinates to analyze nitrate profiles from autonomous Autonomous Profiling EXplorer floats with In-Situ Ultraviolet Spectrophotometers (APEX-ISUS) and ship-based platforms (World Ocean Atlas – WOA09; Hawaii Ocean Time-series – HOT; Bermuda Atlantic Time-series Study – BATS; and California Cooperative Oceanic Fisheries Investigations – CalCOFI), we are able to eliminate much of the spatial and temporal variability in the profiles and derive robust relationships between nitrate and density. This allows us to characterize the depth, slope and curvature of the nitracline in different regions of the world's oceans. The analysis reveals distinguishing patterns in the nitracline between subtropical gyres, upwelling regions and subpolar gyres. We propose a one-dimensional, mechanistic model that relates the shape of the nitracline to the relative depths of the surface mixed layer and euphotic layer. Though heuristic, the model accounts for some of the seasonal patterns and regional differences in the nitrate–density relationships seen in the data.

Comparative study of performance of neutral axis tracking based damage detection

This paper presents a comparative study of a novel SHM technique for damage isolation. The performance of the Neutral Axis (NA) tracking based damage detection strategy is compared to other popularly used vibration based damage detection methods viz. ECOMAC, Mode Shape Curvature Method and Strain Flexibility Index Method. The sensitivity of the novel method is compared under changing ambient temperature conditions and in the presence of measurement noise. Finite Element Analysis (FEA) of the DTU 10 MW Wind Turbine was conducted to compare the local damage identification capability of each method and the results are presented. Under the conditions examined, the proposed method was found to be robust to ambient condition changes and measurement noise. The damage identification in some is either at par with the methods mentioned in the literature or better under the investigated damage scenarios.

PENINGKATAN HASIL BELAJAR SISWA KELAS IX DENGAN PEMBELAJARAN STAD PADA BANGUN RUANG SISI LENGKUNG TABUNG DI MTs. SA MIFTAHUL HUDA

This study investigated how STAD strategy could be implemented to enhance the students’ mathematics achievement on the concept of the shape of thecylinder curvature facefor the first semester students in grade IX,MTs. SA Miftahul Huda Mayangan, in the academic year 2014/2015. The research design adopted for this study is classroom action research (CAR)consisted two cycles. The data collection for this action research study took many forms; observation, interview, test, and documentation. The result of data analysis on cycle 1 showed that the students’ score after altering into percentage gained only 76%. It was very small percentage to fulfill the criterion of minimum completeness (KKM) 75%. Based on the result on the first cycle, it was necessary for the researcher to conduct the next cyclical procedure. In cycle 2,the percentage of the students’ score was significantly increased. It was derived 88%.Accordingly, it proved that the target of CAR success could finally be achieved. Therefore, the next action could be stopped.Keywords: STAD, area of shape, students’ achievement.