Computer Modeling in Engineering & Sciences

Multiscale isogeometric topology optimization with unified structural skeleton

2020-05-11T02:00:53+08:00

This paper proposes a multiscale isogeometric topology optimization (ITO) method where the configuration and layout of microstructures are optimized simultaneously. At micro scale, a shape deformation method is presented to transform a prototype microstructure (PM) for obtaining a series of graded microstructures (GMs), where microstructural skeleton based on the level set framework is applied to retain more topology features and improve the connectability. For the macro scale calculation, the effective mechanical properties can be estimated by means of the numerical homogenization method. By adopting identical non-uniform rational basis splines (NURBS) as basis functions for both parameterized level set model and isogeometric calculation model, the isogeometric analysis (IGA) is integrated into the level set method, which benefits to higher accuracy and efficiency. Numerical examples demonstrate that, the proposed method is effective in improving the performance and manufacturability.

Multiresolution isogeometric topology optimisation using moving morphable voids

2020-05-11T02:00:58+08:00

A general and new explicit isogeometric topology optimisation approach with moving morphable voids (MMV) is proposed. In this approach, a novel multiresolution scheme with two distinct discretization levels is developed to obtain high-resolution designs with a relatively low computational cost. Ersatz material model based on NURBS interpolation is utilised to represent both the Young’s modulus of the material and the density field, and Greville abscissae collocation scheme is adopted to recognise the geometry. Two benchmark examples are tested to illustrate the effectiveness of the proposed method. Numerical results show that high-resolution designs can be obtained with relatively low computational cost, and the optimisation can be significantly improved without introducing additional DOFs.

Numerical Analysis on Multi-Field Characteristics and Synergy in a Large-Size Annular Combustion Chamber with Double Swirlers

2020-05-11T02:00:53+08:00

Dimensionless variation of seepage in porous media with cracks stimulated by low-frequency vibration

2020-05-11T02:00:57+08:00

Wave propagating theory and seepage mechanics for fractured porous media had usually been studied independently. The variation of wave-induced flow as well as channeling flow between fracture and rock matrix was mainly investigated, respectively. When external low frequency vibration was loaded in developing reservoir with natural cracks, a study coupling wave-induced flow and initial flow in dual porous media should be involved in. Thereby, a combination of wave propagating theory for porous media with cracks (the effective stiffness matrix, the inertia effect of wave-induced flow) and dual porous media seepage mechanics (the continuity equation, state equation as well as definite solution conditions) was done. The model about seepage in porous media with cracks under low-frequency vibration excitation was built. Then, a matrix which was expressed by dimensionless fluid and solid displacements and used to solve the mathematical model was given. The physical properties and the seepage field were simulated to check the applicability of external low frequency vibration load on dual porous media. A parametric study about different vibration parameters was also done to discover the mechanism, finally. The results showed that the different improvement in the flow velocities of fluid inner crack and rock matrix was got by low-frequency vibration stimulation. Compared with that in single porous media, the stimulation effect on fluid inner matrix of dual porous media was weakened relatively. When the object of external low frequency vibration was toward to increasing the channeling flow between the crack and rock matrix or to increasing the flow velocity in rock matrix, different optimal vibration parameters were needed. The theoretical study was hoped to help analysis on wave coupled seepage field in fractured porous media and provide suggestion for the application of low frequency wave related techniques.

Numerical study on rock breaking mechanism of supercritical CO2 jet based on smoothed particle hydrodynamics

2020-05-11T02:00:56+08:00

Supercritical carbon dioxide (SC-CO₂) jet rock breaking is a nonlinear impact dynamics problem involving many factors. Considering that the complexity of the physical properties of the SC-CO₂ jet in the rock breaking process and the mesh distortion problem in dealing with large deformation problems using the finite element method, the smoothed particle hydrodynamics (SPH) method is used to simulate and analyze the rock breaking process by SC-CO₂ jet, which is based on the derivation of the jet velocity-density evolution mathematical model. The results indicate that there is an optimal rock breaking temperature by SC-CO₂. The volume and length of the rock fracture increases with the rising of the jet temperature, but falls when the jet temperature exceeds 340K. The SC-CO₂ jet can achieve rock breaking more effectively than the water jet, with more complicated perforation shapes and larger fracture volumes. The stress analysis shows that the SC-CO₂ rock fracturing process could be obviously divided into the fracture accumulation stage, the rapid failure stage, and the breaking stabilization stage. The high diffusivity of SC-CO₂ is the primary cause of the stress fluctuation and W-shaped fracture morphology. The simulated and calculated results are generally in conformity with the published experimental data. This study provides a theoretical guidance for further study on SC-CO₂ fracturing mechanism and rock breaking efficiency.

A lane detection method based on semantic segmentation

2020-05-11T02:00:55+08:00

This paper proposes a novel method of lane detection, which adopts VGG16 as the basis of convolutional neural network to extract lane line features by cavity convolution, wherein the lane lines are divided into dotted lines and solid lines. Expanding the field of experience through hollow convolution, the full connection layer of the network is discarded, the last largest pooling layer of the VGG16 network is removed, and the processing of the last three convolution layers is replaced by hole convolution. At the same time, CNN adopts the encoder and decoder structure mode, and uses the index function of the maximum pooling layer in the decoder part to upsample the encoder in a counter-pooling manner, realizing semantic segmentation. And combined with the instance segmentation, and finally through the fitting to achieve the detection of the lane line. In addition, the currently disclosed lane line data sets are relatively small, and there is no distinction between lane solid lines and dashed lines. To this end, our work made a lane line data set for the lane virtual and real identification, and based on the proposed algorithm effective verification of the data set achieved by the increased segmentation. The final test shows that the proposed method has a good balance between lane detection speed and accuracy, which has good robustness.

A Numerical Algorithm Based on Quadratic Finite Element for Two-Dimensional Nonlinear Time Fractional Thermal Diffusion Model

2020-05-11T02:00:55+08:00

In this article, a high-order scheme, which is formulated by combining the quadratic finite element method in space and second-order time discrete scheme, is developed for looking for the numerical solution of two-dimensional nonlinear time fractional thermal diffusion model. The time Caputo fractional derivative is approximated by using the $L2$-1$_\sigma$ formula, the first-order derivative and nonlinear term is discretized by some second-order approximation formulas, and the quadratic finite element is used to approximate the spatial direction. The error accuracy $O(h^3+\Delta t^2)$ is obtained, which is verified by the numerical results.

Integral Transform Method for a Porous Slider with Magnetic Field and Velocity Slip

2020-05-11T02:00:58+08:00

Current research is about the injection of a viscous fluid in the presence of a transverse uniform magnetic field to reduce the sliding drag. There is a slip-on both the slider and the ground in the two cases, for example, a long porous slider (LPS) and a circular porous slider (CPS). By utilizing similarity transformation Navier-Stokes equations are converted into coupled equations which are tackled by Integral Transform Method (ITM). Solutions are obtained for different values of Reynolds numbers, velocity slip, and magnetic field. We found that surface slip and Reynolds number has a substantial influence on the lift and drag of long and circular sliders, whereas the magnetic effect is also noticeable.

Application of Two-Stage Stochastic Programming for Water Resources Management Problem in Pentagonal Fuzzy Neutrosophic Environment

2021-10-28T10:36:59+08:00

Water resources management (WRM) model aims to utilize the availability of water resources so as to meet the demand of many users as possible as can. In this paper, a two-stage stochastic programming for optimizing WRM problem is introduced in pentagonal fuzzy neutrosophic environment. The problem is considered by incorporating probabilistic seasonal flow and pentagonal fuzzy neutrosophic numbers for all water-allocation target, net benefit, net benefit reduction, and seasonal flow. Based on the score function, the problem under consideration becomes deterministic one and with any linear programming techniques, we obtain the solution. For illustration, an example is given for the sake of the paper.

Analysis of Naval Ship Evacuation Using Stochastic Simulation Models and Experimental Data Sets

2020-05-11T02:00:54+08:00

The study of emergency evacuation in public spaces, buildings and large ships may present parallel characteristic in terms of complexity of the layout but there are also significant differences that can hindering passengers to reach muster stations or the lifeboats. There are many hazards on a ship that can cause an emergency evacuation, the most severe result in loss of lives. Providing safe and effective evacuation of passengers from ships in an emergency situation becomes critical. Recently, computer simulation has become an indispensable technology in various fields, among them, the evacuation models that recently evolved incorporating human behavioral factors.
In this work, an analysis of evacuation in a Landing Helicopter Dock (LHD) ship was conducted. Escape routes specified by the ship’s procedures were introduced in the model and the six emergency scenarios of the Naval Ship Code were simulated. The crew and embarked troops were introduced with their different evacuation behavior, in addition, walking speeds were extracted from data set collected in experiments conducted at other warships. From the results of the simulations, the longest time was chosen and confidence intervals constructed to determine the total evacuation time. Finally, results show that evacuation time meets regulatory requirements and the usefulness and low cost of the evacuation simulation for testing and refining possible ships’ layouts and emergency scenarios.

Multi-Scale Damage Model for Quasi-Brittle Composite Materials

2020-05-11T02:00:57+08:00

In the present paper, a hierarchical multi-scale method is developed for the nonlinear analysis of composite materials undergoing heterogenity and damage. Starting from the homogenization theory, the energy equivalence between scales is developed. Then accompanied with the energy based damage model, the multi-scale damage evolutions are resolved by homogenizing the energy scalar over the meso-cell. The macroscopic behaviors described by the multi-scale damage evolutions represent the mesoscopic heterogeneity and damage of the composites. A rather simple structure made from particle reinforced composite materials is developed as an numerical example. The agreement between the full-scale simulating results and the multi-scale simulating results demonstrates the capacity of the proposed model to simulate nonlinear behaviors of quasi-brittle composite materials within the multi-scale framework.

An equivalent strain based multi-scale damage model of concrete

2020-05-11T02:00:59+08:00

A multi-scale damage model of concrete is proposed based on the concept of energy equivalent strain for generic two- or three-dimensional applications. Continuum damage mechanics (CDM) serves as the framework to describe the basic damage variables, namely the tensile and compressive damage. The homogenized Helmholtz free energy is introduced as the bridge to link the micro-cell and macroscopic material. The crack propagation in micro-cells is modeled, and the Helmholtz free energy in the cracked micro-structure is calculated and employed to extract the damage evolution functions in the macroscopic material. Based on the damage energy release rates (DERRs) and damage consistent condition, the energy equivalent strain is used to expand the uniaxial damage model to the multi-dimensional damage model. Agreements with existing experimental data that include uniaxial tensile and compressive tests, biaxial compression and biaxial peak stress envelop demonstrate the capacity of the multi-scale damage model in reproducing the typical nonlinear performances of concrete specimens. The simulation of precast laminated concrete slab further demonstrates its application to concrete structures.

Real-Time Thermomechanical Modeling of PV Cell Fabrication via a POD-Trained RBF Interpolation Network

2020-05-11T02:00:52+08:00

This paper presents a numerical reduced order model framework to simulate the physics of the thermomechanical processes that occur during c-Si photovoltaic (PV) cell fabrication. A real-time response surface based on a Radial-basis function (RBF) interpolation network trained by a Proper Orthogonal Decomposition (POD) of the solution fields is developed for the calculation of thermal loading conditions on PV cells during the fabrication processes. The outcome is a stand-alone computational tool that provides, in real time, the quantitative and qualitative thermomechanical response as a function of user-controlled input parameters for fabrication processes with the precision of 3D finite element analysis (FEA). This tool provides an effective avenue for design and optimization as well as for failure prediction of PV cells

Application of Smooth Particle Hydrodynamics Method for Modelling Blood flow with Thrombus Formation

2020-05-11T02:00:56+08:00

Thrombosis plays a crucial role in atherosclerosis or in haemostasis when a blood vessel is injured. This article focuses on using a meshless particle-based Lagrangian numerical technique, the smoothed particles hydrodynamic (SPH) method, to study the flow behaviour of blood and to explore the flow parameters that induce formation of a thrombus in a blood vessel. Due to its simplicity and effectiveness, the SPH method is employed here to simulate the process of thrombogenesis and to study the effect of various blood flow parameters. In the present SPH simulation, blood is modelled by two sets of particles that have the characteristics of plasma and of platelets, respectively. To simulate coagulation of platelets which leads to a thrombus, the so-called adhesion and aggregation mechanisms of the platelets during this process are modelled by an inter-particle force model. The transport of platelets in the flowing blood, platelet adhesion and aggregation processes are coupled with viscous blood flow for various low Reynolds number scenarios. The numerical results are compared with the experimental observations and a good agreement is found between the simulated and experimental results.

A Implementation of PSOANN optimized PI control algorithm for Shunt active filter

2020-05-11T02:00:59+08:00

This paper proposes the optimum controller for shunt active filter(SAF) to mitigate the harmonics and maintain the power quality in the distribution system. It consists of shunt active filter, Voltage Source Inverter (VSI), series inductor and DC bus and non-linear load. The proposed hybrid approach is a combination of Particle Swarm Optimization (PSO) and Artificial Neural Network (ANN) termed as PSOANN. The PI controller gain parameters of k_pand k_i are optimized with the help of PSOANN. The PSOANN improves the accuracy of tuning the gain parameters under steady and dynamic load conditions; thereby it reduces the values of THD within the prescribed limits of IEEE 519. The PSO optimizes the dataset of terminal voltage and DC voltage present in shunt active filter for different load conditions. The optimized dataset acts as the input for the controller to predict the optimal gain with minimal error and to generate the optimized control signal for the SAF. The proposed methodology is modeled and simulated with the help of MATLAB/Simulink platform and illustrated the few test cases considered for exhibiting the performance of the proposed hybrid controller. The experimental results are measured with developed laboratory prototype and compared with the simulation results to validate the effectiveness of the proposed control methodology.

Impact dynamics of the dragonfly wings

2020-05-11T02:01:00+08:00

The lift force was reported not to be high enough to support the dragonfly’s weight during flight in some conventional investigations, and higher lift force is required for its takeoff. In this study, by employing a thin plate model, impact effect is explored for the wing deformation in flapping during dragonfly's takeoff. The static displacement is formulated to compare with the dynamical displacement caused by impact. The governing equation of motion for the impact dynamics of the dragonfly wings is derived based on Newton's second law. Separation of variables technique and assumed modes method are introduced to solve the resulting equations. Further, lift force is presented for the cases of considering and without considering the impact on the wing flapping which indicates that the impact has prominent effects for the dragonfly’s aerodynamic performance. Numerical simulations demonstrate that considering the impact effect on the wing flapping can increase the wing deformation, which results in the rise of the lift force. The enhanced lift force is of critical importance for the dragonfly's takeoff.

Complex dynamics of a discrete predator-prey model with functional response of Holling type III

2020-05-11T02:01:00+08:00

In this paper, we propose a discrete Lotka-Volterra predator-prey model with the functional response of Holling type III. We investigate the stability of the fixed points
of this model. Also, we studied the effects of changing each control parameter on the long-time behavior of the model. This model contains a lot of complex dynamics behavior
ranging from a stable fixed point to chaotic attractors. We use the maximum Lyapunov exponent to confirm the chaotic dynamical behaviors of the system. Finally, we illustrated
the analytical results by some numerical emulations.

On the simulation of fragmentation during the process of ceramic tile impacted by blunt projectile with SPH method

2020-05-11T02:01:01+08:00

Ceramics are extensively used in protective structures which are often subjected to projectile impacts. During an impact process of a ceramic target by a projectile, fragmentation occurs in both the target and the projectile. It is challenging to simulate such events and predict residual mass and velocity of the projectile. In this work, we attempt to use smoothed particle hydrodynamics (SPH) to reproduce fragmentation of the target and the projectile and predict residual mass and velocity of the projectile during a projectile impact of a ceramic target. SPH models for an alumina ceramic tile impacted by a blunt tungsten heavy alloy projectile are established. SPH simulation results of residual mass and velocity of the projectile as well as ejecta and bulge movements of the ceramic tile are obtained and compared with experimental data and simulation results of other numerical approaches. It is found that SPH simulation can properly reproduce the impact fragmentation of the target and the projectile, and shows advantages over existing numerical approaches in the prediction accuracy of residual mass and velocity. Moreover, effects of some numerical aspects of SPH, including particle spacing, contact treatment and parameters in artificial viscosity and smoothing length, on simulation results are identified. A simple approach using identical smoothing length and balanced artificial viscosity is proposed to reduce particle spacing sensitivity. The observed parametric effects and the proposed approach will provide guidance to set appropriate parameters values for SPH simulation of impact fragmentation.

A unified non-dimensional parameter for finite element mesh for beams resting on elastic foundation

2020-05-11T02:01:01+08:00

A structure discretising into elements is a key step in the finite element analysis. The discretised geometry used to formulate a finite element model can greatly affect the accuracy and validity. This paper presents a unified non-dimensional parameter to generate cubic finite element mesh for beams resting on elastic foundation. A uniform beam resting on elastic foundation with various values of flexural stiffness and elastic supporting coefficients subject to static load and moving load are used to illustrate the application of the proposed parameter. The numerical results show that (a) even if the values of the flexural stiffness of the beam and elastic supporting coefficient of the elastic foundation are different, the same parameter "s" can ensure the same accuracy of the FEM solution, but the accuracy is different for the same element length; therefore, the proposed non-dimensional parameter "s" can indeed be used as a unified index to generate element mesh for a beam resting on elastic foundation, whereas the use of the same element length as a criterion may be misleading; (b) the errors between FEM and exact solutions for the maximum vertical displacement, shear force and bending moment of the beam increase with the increases of the non-dimensional parameter "s"; and (c) for the given allowable errors calculating vertical displacement, shear force and bending moment of the beam under static load and moving load, the corresponding values of the proposed parameter are provided and used to guide the finite element mesh.