The purpose of the Reliability-Based Design Optimization (RBDO) is to find the best compromise between safety and cost. Therefore, several methods, such as the Hybrid Method (HM) and the Optimum Safety Factor (OSF) method, are developed to achieve this purpose. However, these methods have been applied only on static cases and some special dynamic ones. But, in real mechanical applications, structures are subject to random vibrations and these vibrations can cause a fatigue damage. So, in this paper, we propose an extension of these methods in the case of structures under random vibrations and then demonstrate their efficiency. Also, a Robust Hybrid Method (RHM) is then developed to overcome the difficulties of the classical one. A numerical application is then used to present the advantages of the modified hybrid method for treating problem of structures subject to random vibration considering fatigue damage.

Constitutive equations, based on continuum mechanics and representing behavior of a mixture of two elastic solids, can be used for modeling of materials such as particulate composites. In this study, the behavior of continuum of a mixture occupying half-space under axisymmetric loads is calculated using Fourier and Hankel transform methods. For this purpose, Love's strain functions are used and the general solution of problem under proper boundary conditions is presented. By applying the results obtained to the sinusoidal distributed vertical load and Boussinesq problems that require the use of Cartesian and cylindrical coordinate systems, displacement vectors, diffusive force vector and components of stress tensors are calculated. At the end of the study, the experimental results of a special particulate composite are used to check the accuracy of the solutions obtained.

A numerical coupled thermoplasticity multiscale procedure for small strain analysis is developed in the finite element environment. It is suitable for simulation of thermo-mechanical behavior and overall response of metallic materials, using standard approximation method based on the concept of representative volume element (RVE). The local level isothermal analysis that models the micro-scale, is fully coupled to the global level non-isothermal analysis. The global macro-scale tangent stiffness operator is obtained using numerical differentiation procedure using the forward difference scheme. The numerical procedure is developed for two-dimensional problems, using Abaqus user-defined subroutines. Applicability of the proposed framework is presented on several representative examples.

The autofocusing (AF) performance of cell phone cameras is critically dependent on the design of the voice-coil motor (VCM) used to drive the lens module. Also, the metal springs in the AF module should combine high stiffness with a good actuation response and a light weight. The present study utilizes a reverse engineering approach to construct three-dimensional finite element models of the top and bottom springs in the VCM mechanism. Simulations are then performed to investigate the von Mises stress distribution and stiffness characteristics of the two springs given horizontal and vertical orientations of the AF module, respectively. In performing the simulations, the actuation force is computed using two different analysis methods, namely a simplify structure method and a coupled electromagnetic-structural method. It is shown that the simplify structure method has the advantages of a lower computational complexity and a more comprehensive modeling capability. A further series of simulations is thus to examine the effects of the spring shape parameters on the reaction force developed by the spring stiffness. The results show that the spring stiffness increases with an increasing thickness and a decreasing rib length. The simulation results obtained for different spring shape parameter settings are summarized in the form of a parameter design chart for predicting the reaction force given known values of the spring rib length and spring thickness.

A model of Twin-cell Composite Box Beam (TCCBB), which is composed of concrete plate and thin-walled steel box beam with twin-cell, is proposed in this paper. Combined with structural features, longitudinal interfacial slip mode (LISM) and related shear hysteresis functions (SHFS) of this TCCBB model are defined respectively; analytical formulation describing combination effect between interfacial slip and shear lag is launched for this TCCBB model under even load. Based on established governing differential equations and its relative boundary conditions (calculated with compatible mechanism of interfacial slip and shear lag effect), closed form solutions of normal stress and shear stress are derived for this TCCBB model, as well as effective shear-lag coefficient and effective coupled behavior coefficient. To obtain more accurate computational results of specific coupled mechanism of this TCCBB model, numerical example is carried out to analyze and predict coupled mechanism of interfacial slip and shear lag effect for this type of composite structures.

The problem of a circular elastic inclusion perfectly bonded to a matrix of infinite extent and subjected to arbitrarily thermal loading has been solved explicitly in terms of the corresponding homogeneous problem based on the inversion and Kelvin's transformation. It is to be noted that the relations established in this paper between the stress functions are algebraic and do not involve integration or solution of some other equations. Furthermore, the transformation leading from the solution for the homogeneous problem to that for the heterogeneous one is very simple, algebraic and universal in the sense of being independent of loading considered. The case of two bonded half-planes is obtained as a limiting case.

In this study, a micromechanics model has been proposed for predicting the effects of particle size and aggregation on elastic properties of nanocomposites, and the interphase between the particle and matrix is also taken into account. Inherent characteristics of nanoparticle, such as small size and high surface area ratio, make nanoparticle in a state of unstable energy and easy to agglomerate in matrix. The analytical expressions for the effective elastic modulus of nanocomposites are derived, which can consider the effect of particle agglomeration. The dispersion state or degree of agglomeration of nanoparticle and the thickness and stiffness of interphase are known to have a significant influence on nanocomposites. The results show that the increase of particle radius and agglomeration volume fractions reduces the elastic stiffness of nanocomposites. Moreover, the composite reinforcement can be improved by increases of interphase thickness and stiffness.

The effective lifetimes of electronic packages are affected by various thermos-mechanical deformations. Creep is considered the most salient mechanism in the failure of solder joints. Many researchers have conducted reasonable studies to portray the behavior of creep deformation using numerical models and further extended their research scope to forecast the lifetimes of packages with the results obtained from creep models. Many studies have identified particular creep and lifetime models to be nominal based on experimental data.

In this study, the characteristics of familiar creep models were examined in detail, and their significance was made known. Lifetime prediction models that seem prominent among researchers were discussed in detail. Finite element analysis of a wafer level chip-scale package (WLCSP) used to figure out the engagement of different creep models and their capability of materializing creep deformation was investigated via simulation. The results from the simulation were applied to different lifetime prediction models, and their predictions were examined carefully. After considering the various factors that affected the reliability study of the solders, the Garofalo-Arrhenius creep model and modified strain energy density model seemed to be convincingly productive for studying the reliability of various electronic packages.

It has demonstrated to exploit various layout effects of advanced strained engineering to enhanced the performance of nano-scaled transistors. In actual fabrications, the gate framework usually protrudes out to the channel area even over the spuriously diffused active region, over the soft shallow trench isolation region. The foregoing device feature is interesting and critical when enhancing and managing mobility gain are taken into account by used mechanics and induced strained silicon technology in narrow scale channel widths devices. Thus, a silicon-based 22 nm p-type MOSFET combined stressors of a source/drain Si75Ge25 alloy and a -2 GPa compressive contact etch stop layer with different protrudent gate widths to investigate this issue. The fabricated oriented stress simulation extracted stress component within the device channel to estimate and analyze the performance of mobility gain and stress contours for the concerned nanoscale device.

A simple numerical method is proposed in the paper for fluid flow around a moving boundary of irregular shape. The unsteady term is discretized with the implicit scheme such that large time step is allowed. All of the computations are performed on non-staggered Cartesian grid system. Fine Cartesian patch grid system covering the moving object is employed to resolve the solution around the solid body. A closed curve defined by connecting the solid grid points adjacent to the solid-liquid interface is referred to as virtual boundary. The narrow irregular strip of solid between the virtual boundary and the actual solid-fluid interface is called pseudo-fluid. The general fluid region consisting of both fluid and pseudo-fluid is a regular domain that can be efficiently solved with conventional numerical method. In this connection, external force is imposed at each fluid grid point adjacent to the solid-fluid interface to compensate for the numerical error arising from the assumption of pseudo-fluid. The solution procedure is iterated until the required external force converges. Accuracy of the new numerical method is validated through three test problems. The numerical method then is used to investigate the flow induced by the flapping wings of a tethered dragonfly in literature. The corresponding CFL numbers of the four examples are infinity, 20, 100, and 3.29.

Nano-nozzles are an essential part of the nano electromechanical systems (NEMS). Cross-sectional geometry of nano-nozzles has a significant role on the fluid flow inside them. So, main purpose of the present study is related to the effects of different symmetrical cross-sections on the fluid flow behavior inside of nano-nozzles. To this accomplishment, five different cross-sectional geometries (equilateral triangle, square, regular hexagon, elliptical and circular) are investigated by using molecular dynamics (MD) simulation. In addition, TIP4P is used for atomistic water model. In order to evaluate the fluid flow behavior, non-dimensional physical parameters such as Fanning friction factor, velocity profile and density number are analyzed. Obtained results are shown that the flow behavior characteristics appreciably depend on the geometry of nano-nozzle's cross-section. Velocity profile and density number for five different cross sections of nano-nozzle at three various measurement gauges are presented and discussed.

The increasing demands on renewable energy nowadays caused the development of marine current turbine industry. In order to improve the current design of marine current turbines, studies were conducted to analyse their hydrodynamic performances during operation. Since most of the time marine current turbines operate in arrays, it is important to understand the interactions between the turbines in order to design the optimum turbine farm. OpenFOAM® was used to simulate the turbine interactions of conventional and biomimetic marine current turbines in tandem configuration. The conventional marine current turbines were referred to Pinon et al. (2012) and Mycek et al. (2013) while the biomimetic marine current turbine was adopted from Chu (2016). The numerical simulations were conducted with turbines in different inter-device distances, A/D. The percentage differences of ‘‘efficiency’’, η between the IFREMER-LOMC and the biomimetic turbine case of inter-device distances, A/D = 4, 6, 8 and 10 are 14.3%, 6.4%, 3% and 1.92% respectively. The results show that the power produced by the biomimetic turbines in tandem is comparable with the IFREMER-LOMC turbines when A/D > 4. The biomimetic marine current turbines can be a fair choice due to their potential to have alternative fabrication method of their sheet-like turbine blades.

In this study MHD flow around and through porous cylinder is numerically investigated. The governing equations are developed in polar coordinate arrangement in both porous and non-porous media on the basis of single-domain technique. The equations are solved numerically based on finite volume method over staggered grid structure. Nusselt number and drag coefficient are selected as two key parameters describing performance of this system. By applying response surface methodology the sensitivity of these parameters to main factors of the problem, including Stuart number, Darcy number and Reynolds number are quantified. RSM is also utilized to perform an optimization process to find the best condition in which the lowest drag force and highest heat transfer rate occur simultaneously. The CFD analysis is carried out for variant Reynolds numbers (10 ≤ Re ≤ 40), Darcy numbers (10-6 ≤ Da ≤ 10-2) and Stuart numbers (2 ≤ N ≤ 10). Streamlines and isotherms are presented to indicate the impacts of such parameters on heat and fluid flow. It can be seen that, Drag coefficient and Nusselt number increase by augmenting magnetic field strength. Beside, Darcy number and Reynolds numbers have a direct and inverse effect on Nuave and Cd, respectively. Results of optimization process show that Nuave and Cd are more sensitive to Reynolds and Stuart numbers, respectively, while they less sensitive to Darcy number. Moreover, it is revealed that the optimum condition occurs at Da = 10-2, Re = 38.1 and N = 4.49.

Based on the basic equations of electromagnetic elastic motion and the expression of electromagnetic force, the electromagnetic vibration equation of the rectangular thin plate in transverse magnetic field is obtained. For a rectangular plate with one side fixed and three other sides simply supported, its time variable and space variable are separated by the method of Galerkin, and the two-degree-of-freedom nonlinear Duffing vibration differential equations are proposed. The method of multiple scales is adopted to solve the model equations and obtain four first-order ordinary differential equations governing modulation of the amplitudes and phase angles involved via 1:1 or 1:3 internal resonances with different size ratios. With a numerical example, the time history response diagrams, phase portraits and 3-dimension responses of two order modal amplitudes are respectively captured. And the effects of initial values, thickness and magnetic field intensities on internal resonance characteristics are discussed respectively. The results also present obvious characteristics of typical nonlinear internal resonance in this paper.

Hemostasis, a process which causes bleeding to stop, can be enhanced using chitosan; but the detailed mechanism is unclear. Red blood cells (RBCs) adhere to chitosan because of their opposite charges, but the adhesion force is small, 3.83 pN as measured here using an optical tweezer, such that the direct adhesion cannot be the sole cause for hemostasis. However, it was observed in this study that layer structures of aggregated RBCs were formed next to chitosan objects in both static and flowing environments, but not formed next to cotton and rayon yarns. The layer structure is the clue for the initiation of hemostatsis. Through the supporting measurements of zeta potentials of RBCs and pH's using blood-chitosan mixtures, it is proposed here that the formation of the RBC layer structure next to chitosan objects is due to the reduction of repulsive electric double layer force between RBCs, because of the association of H+ deprotonated from chitosan with COO− on RBC membrane, under the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. The results are beneficial for designing effective chitosan-based wound dressings, and also for general biomedical applications.