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An Error Estimator for the Finite Element Approximation of Plane and Cylindrical AcousticWaves
Get PDFThis paper deals with a Finite Element Method (FEM) for the approximation of the Helmholtz equation for two dimensional problems. The acoustic boundary conditions are weakly posed and an auxiliary problem with homogeneous boundary conditions is defined. This auxiliary approach allows for the formulation of a general solution method. Second order finite elements are used along with a discretization parameter based on the fixed wave vector and the imposed error tolerance. An explicit formula is defined for the mesh size control parameter based on Padé approximant. A parametric analysis is conducted to validate the rectangular finite element approach and the mesh control parameter. The results of the examples show that the discrete dispersion relation (DDR) can be used for the rectangular finite element mesh refinement under predefined error tolerances. It is also shown that the numerical formulation is robust and can be extended to higher order finite element analyses
Elastodynamic Analysis of Thick Multilayer Composite Plates by The Boundary Element Method
Get PDFDynamic stress analysis of laminated composites plates represents a relevant task in designing of aerospace, shipbuilding and automotive components where impulsive loads can lead to sudden structural failure. The mechanical complexity inherent to these kind of components makes the numerical modeling an essential engineering analysis tool. This work deals with dynamic analysis of stresses and deformations in laminated composites thick plates using a new Boundary Element Method formulation. Composite laminated plates were modeled using the Reissner’s plate theory. We propose a direct time-domain formulation based on elastostatic fundamental solution for symmetrical laminated thick plates. Formulation takes into account the rotational inertia of the plate. Domain integrals related to distributed body forces and those related to inertial terms are evaluated using the Radial Integration Method. Contour integrals are numerically evaluated using quadratic approximation for displacements and generalized forces. Time integration is performed using the Houbolt Integration Method. Resulting shear forces and bending moments are calculated. The results obtained using this formulation show good agreement when compared with finite element solutions
Method for Detecting Macroscopic Irregularities in Gears Based on Template Matching and the Nonequivalence Operation
Get PDFThe detection of macroscopic irregularities is an essential procedure during the production of gears, and it helps to guarantee the quality of electromechanical transmission equipment. The working principles of template matching and the image nonequivalence operation are described in detail in this paper. Gray-level transformation, edge-preserving filtering, image segmentation, feature extraction, and pattern recognition were analyzed, leading to the design of a defect detection system based on template matching and the nonequivalence operation, followed by the development of a hardware platform and application software for the system. The experimental results indicate that the proposed detection system could perform fast detection and evaluation of the appearance quality of pinions. The system has good stability and high detection accuracy, and can effectively reduce both detection time and cost
Pseudo-Linear Kalman Filter-based GPS Active Aircraft Tracking Algorithm
Get PDFFor the sake of a higher accuracy of active aircraft GPS tracking, the tracking algorithm based on pseudo-linear Kalman filter is hereby proposed. This algorithm simplifies geometrical and algebraic relations to obtain a pseudo-linear model, then tracking the target by means of Kalman filter algorithm. Meanwhile, the tracking algorithm is studied to build a velocity & position tracking model and a velocity & acceleration tracking model. As shown by the experimental result, the tracking algorithm based on pseudo-linear Kalman filter can meet the requirement of active aircraft GPS tracking, but also attain a higher tracking accuracy in velocity & acceleration tracking model
A Probabilistic Approach to Hazard Mapping Based on Computer Simulations. An Example for Lava Flows at Mount Etna
Get PDFDetermining sectors that could be affected by lava flows in volcanic areas is essential for risk mitigation purposes. Traditionally, when adopting methods based on probabilistic numerical simulations, the hazard is assessed by analysing a huge set of simulations of hypothetical events, each characterized by a distinct probability of occurrence based on statistics of historical events. If lateral or eccentric eruptions are also taken into account, simulated lava flows usually start from the nodes of regular grids of potential vents, uniformly covering the study area. In this study, an alternative approach to evaluate flow-type hazard, based on a nonuniform grid of potential vents, is proposed. The method takes into account expected changes in the topographic context due to successive lava-flow bodies, and allows to obtain more detailed maps for the most exposed areas, besides significantly reducing the computational efforts. The approach has been tested to evaluate lava-flow hazard at Mt Etna (Eastern Sicily, Southern Italy), and a preliminary analysis has been performed to investigate the behaviour of the adopted technique with respect to the number of performed sets of simulations to better understanding its predictive capability
On Collision Local Time of Two Independent Subfractional Brownian Motions
Get PDFWe study the existence of collision local time of two independent subfractional Brownian motions with different coefficients in (-1/2,1/2) using an alternative expression. We prove that the collision local time is a Hida distribution based on the canonical framework of white noise analysis, and get chaos expansions. Finally, we show that the collision local time exists in (L2) under appropriate conditions
Mathematical Model for Skeletal Muscle to Simulate the Concentric and Eccentric Contraction
Get PDFSkeletal muscles are responsible for the relative motion of the bones at the joints and provide the required strength. They exhibit highly nonlinear mechanical behaviour and are described by nonlinear hyperelastic constitutive relations. It is distinct from other biological soft tissue. Its hyperelastic or viscoelastic behaviour is modelled by using CE, SEE, and PEE. Contractile element simulates the behaviour of skeletal muscle when it is subjected to eccentric and concentric contraction. This research aims to estimate the stress induced in skeletal muscle in eccentric and concentric contraction with respect to the predefined strain. With the use of mathematical model for contraction of skeletal muscle for eccentric and concentric contraction, the stress induced in the skeletal muscle is estimated in this research. Mathematical model is developed for the muscle using EMG signals and Force-velocity relationship calculated. With the use of force-velocity of contraction of muscle, mathematical model is developed. This can be useful to understand the mechanical behaviour of skeletal muscles in eccentric and concentric contraction with clinical relevance.
Authors are further working to develop the mathematical model with torsion force with proper activation function of muscle and experimentation for extraction of the anisotropic mechanical properties of skeletal muscle
Numerical Simulation of Droplet Breakup, Splitting and Sorting in a Microfluidic Device
Get PDFDroplet generation, splitting and sorting are investigated numerically in the framework of a VOF technique for interface tracking and a finite-volume numerical method using the commercial code FLUENT. Droplets of water-in-oil are produced by a flow focusing technique relying on the use of a microchannell equipped with an obstacle to split the droplets. The influence of several parameters potentially affecting this process is investigated parametrically towards the end of identifying "optimal" conditions for droplet breakup. Such parameters include surface tension, the capillary number and the main channel width. We show that the capillary number plays a crucial role in determining droplet properties and the efficiency of the related generation process. An obstacle configuration can be effectively used to split a droplet, with the droplets being naturally sorted at the end of the main channel. Larger values of the capillary number generally lead to an increase in the droplet frequency and a decrease in its typical size
Mechanical Analysis of the Coupled Gas-Solid-Thermal Model during Rock Damage
No full textGas fracturing technology is the key to the exploration for unconventional petroleum resources and other engineering industries, so the research on the coupled gas-solid-thermal model during rock damage has the important significance to the development of gas fracturing technology. By introducing rock damage variable, the coupled gas-solid-thermal model during rock damage is established in this paper, besides, the rock damage constitutive is written with MATLAB software, which is embedded in the multi-physics coupling software COMSOL in the process of numerical computation. Based on this, the damage rule of rock mass around drilling under high pressure gas is analyzed. The results show when the ratio between x direction local stress σx and y direction local stress σy is 1, the rock failure is dominated by shear damage due to the effect of gas; when the ratio between x direction local stress σx and y direction local stress σy is 1/10, pull damage appears on both sides of drilling in the direction of Y because of the effect of gas; with the passage of time, the pore pressure in the rock mass increases gradually, while the pressure gradient decreases gradually; the primary temperature of rock mass has little influence on the pore pressure
Development and Characterization of the Midrib of Coconut Palm Leaf Reinforced Polyester Composite
Get PDFIn this paper, midrib of coconut palm leaves (MCL) was investigated for the purpose of development of natural fiber reinforced polymer matrix composites. A new natural fiber composite as MCL/polyester is developed by the hand lay-up method, and the material and mechanical properties of the fiber, matrix and composite materials were evaluated. The effect of fiber content on the tensile, flexural, impact, compressive strength and heat distortion temperature (HDT) was investigated. It was found that the MCL fiber had the maximum tensile strength, tensile modulus flexural strength, flexural modulus and Izod impact strength of 177.5MPa, 14.85GPa, 316.04MPa and 23.54GPa, 8.23KJ/m2 respectively. Reinforcement of MCL enhanced the mechanical properties of pure polyester, including that of tensile strength (by 26%), tensile modulus (by 356%), flexural strength (by 41.81%), flexural modulus (by 169%) and Izod impact strength (by 23 times), but the compressive strength was adversely affected. HDT decreased due to fiber loading, but increased with weight fraction of fiber content. Moreover, the experimental results were compared with theoretical model (Rule of mixture) and other natural fiber /polyester composites