Forces in mechanics最新文献

Plenty of research papers are available on the static and free vibration analysis of single-layer FG shells, however, literature on the analysis of FGM sandwich shells of double curvature is limited. Especially, the authors have not found any paper on the analysis of hyperbolic and elliptical paraboloid FGM sandwich shells. Therefore, FGM sandwich shallow shells with double curvature are analyzed in this study for the static and free vibration conditions. Face sheets of sandwich shells are made up of functionally graded material whereas the core is made up of isotropic material. A functionally graded material considered herein is a combination of alumina and aluminum. Sandwich shallow shells on rectangular planform are modeled using various equivalent single-layer shell theories via unified formulation considering the effects of shear deformation and rotary inertia. Different shell theories recovered from the present unified formulation satisfy the transverse shear stress-free conditions on the lower and upper surfaces of the shell. Hamilton's principle is applied to the present unified formulation for establishing equations of motion. Solutions to free vibration and static problems of simply-supported sandwich shells are obtained using Navier's technique. The numerical results of frequencies, displacements, and stresses are obtained for various types of shells, different sandwich schemes, different values of the power-law factor, and radii of curvature. The results available in the literature are used for the comparison of the present results and found in good agreement with those. However, many new and useful results are also reported in this paper for the reference of readers.

DMR 249A is a micro-alloyed high strength low alloy (HSLA) steel particularly designed for shipbuilding structures due to its excellent strength-to-weight ratio. In this investigation, the rotating-beam fatigue test was performed on the flux-cored arc welded (FCAW) butt joints of DMR 249A steel. And the fatigue test results compared to mechanical properties and microstructural characteristics. The transverse tensile, microhardness, impact, and fatigue properties were evaluated from across the butt weld. The S-N curve was constructed from the experimental data for the stress ratio R = -1. The evaluated fatigue life of the FCAW joint and parent metal was 366 MPa and 394 MPa, respectively. The maximum achieved transverse tensile strength and impact energy absorption of the FCAW joint was 578 MPa &174 J. The weld region contains an acicular ferrite microstructure, which exhibited improved properties of strength, toughness, and fatigue crack resistance. From the results, the fatigue strength of FCAW is 92.8% that of the parent metal and 62.8% equal to the tensile strength of the FCAW joint.

Heat transfer in Carreau–Yasuda fluid with mixed convection, effect of Cattaneo–Christov model of heat flux past a vertical flat plate has been studied in this paper. Using appropriate transformations, governing PDEs are reduced to higher order non-linear non-dimensional ODEs and subsequently these are solved using “bvp4c” package of MATLAB. The Carreau–Yasuda fluid is used to explore the behaviour of fluids having shear-thinning and shear-thickening characters for several values of the parameter called power law exponent involved in the fluid model. The effects of different physical parameters, such as Weissenberg number(We), thermal relaxation parameter(α), Carreau–Yasuda fluid parameter(d), mixed convection parameter(λ) and Prandtl number(Pr) on velocity and temperature has been investigated and depicted through graphs. Results reveals that for lower value of Pr velocity of fluid enhances with higher value of λ and reverse effect is witnessed for larger Pr. Also, velocity rises for shear-thinning fluid(STNF) and decreases for shear-thickening fluid(STKF) with We and d. Temperature exhibits growing behaviour for Cattaneo–Christov model of heat flux near the plate in comparison with Fourier's model, whereas velocity exhibits growing behaviour with α. For larger We, temperature in Carreau–Yasuda model upsurges for STKF and falls for STNF. The surface drag-force displays higher values for both STNF and STKF with growth in $\lambda$. The cooling rate rises/declines with We for STNFs/STKFs.

This study aims to understand the behaviour of a base isolated l-shaped building under far field and near field earthquake ground motion. A ten-storey l-shaped building was considered for the study and modelled using SAP2000, which is finite-element-based software. At first, a non-isolated model was created, and the required data was generated in order to develop an isolated model. After that, a non-linear time history analysis was performed, and the results of storey displacement, torsional irregularity, and base shear have been discussed for the base isolated model and the non-isolated model. The fundamental time period of base isolated l-shaped building was found to be 2.56 s while the base model had fundamental time period of 0.88 s. It was found in this study that higher peak ground acceleration (PGA) and peak ground velocity (PGV) of the ground motion led to higher storey displacement, storey drift, and base shear but a lower torsional irregularity ratio under near field ground motion, while torsional irregularity ratio of base isolated building was found to be increased under far field ground motion.

This paper presents the bending analysis of functionally graded material (FGM) plates using sinusoidal shear and normal deformation theory. The in-plane displacements include sinusoidal functions in the thickness coordinate to consider the effect of transverse shear deformation, and transverse displacement includes the effect of transverse normal strain using the cosine function in thickness coordinate. The displacement field of the theory enforces to satisfy shear stress-free boundary conditions on the top and bottom surfaces of the plate with realistic variations across the thickness. Plate material properties vary across thickness directions according to a power law. The boundary value problem of the theory is derived using the principle of virtual work. Simply supported plate bending problems are solved using the Navier solution technique. Response of the plate is obtained with respect to the type of load, type of plate, aspect ratio, and power law index. The results of present theory are compared with those of quasi-3D discrete layer theory and semi-analytical solutions based on the theory of elasticity to ensure the accuracy of theory. The current theory showed excellent agreement with more exact theories in bending response.

We report the effects of an externally applied magnetic field on an electrically conducting fluid flow in a locally constricted channel. With the use of finite-difference discretization and the ADI (Alternating directions implicit) scheme, the non-linear coupled magnetohydrodynamic (MHD) equations in two dimensions were numerically solved. When the magnetic Reynolds number R_M >> 1, an induced magnetic field forms in the motion and significantly affects flow. The electromagnetic force (Lorentz force) is developed and acts as a damping force. It results the suppression of flow separation regions developed due to the channel constrictions. It delays the onset of flow separation and the flow become stable. By employing suitable value of magnetic field one can completely suppress the flow separation. The induced magnetic field and current density vectors are dense at the constriction site due to high velocity shear in the downstream of the constriction, resulting in the creation of high shear magnetic and electric fields.

This communication about the mathematical model of analysis of heat transfer system which as the Jeffery fluid of MHD flow with the addition of the porous-stretching sheet in the system which in the form of partial differential equation (PDE) converted into Ordinary differential equation (ODE) using Numerical methods of lie similarity and transformation technique and with shooting method. The results depict that altering the parameters of Jeffery fluid, heat source, porosity in stretching sheet and the physical properties of magnetic field in the system with increasing manner, and the changes are observed in the way of reducing the temperature in the heat convicting or transferring system and therefore, increased the convection rate in the heat transfer system. The application of the heat transfer system in industrial machines, mass cloud data storage compartments, electronic device refrigeration etc., which has necessity to improve the heating and cooling system

The road surface's roughness is the primary source of vehicle oscillations when in motion. An active suspension is employed to enhance road holding, ride comfort, and stability. This research studies a dynamics model with 5 state variables to simulate vehicle oscillations based on four excitation scenarios from the road surface. In each instance, four distinct circumstances were discovered. Besides, the complicated control solution for an active suspension was created by this research, and it is called SMPIDF (Sliding Mode – PID tuned by Fuzzy). This is an entirely innovative algorithm with several significant benefits. The system's ultimate control signal is synthesized from the signals of the linear controller PID (Proportional – Integral – Derivative) and the nonlinear controller SMC (Sliding Mode Control). The defined fuzzy rule will continually alter the controller's settings. The simulation findings indicate that the acceleration and displacement of a car body are drastically decreased when an active suspension is managed to utilize the SMPIDF algorithm. The displacement and acceleration values do not surpass twenty percent and eighty percent, respectively, when compared to a car using a standard passive suspension. In addition, the characteristic of "chattering" does not occur when the controllers are combined. The overall effectiveness of this algorithm is rather significant. This approach applies to increasingly complicated models.

Wood is the organic hygroscopic material for excellence. Due to its extremely easy handling, it has always been used in many applications, especially as building material for artefacts and works of art. However, it is highly climate-susceptible as it swells or shrinks by exchanging moisture with the surrounding environment when natural or artificial microclimatic fluctuations occur. The shrinkage/swelling of wood, if repeated over time, may cause the arising of deformations or damage that may lead to catastrophic failures. For this reason, in this work, a preliminary study about the effect that repeated microclimatic loads have on wooden samples is carried out. To do so, well-established fatigue approaches have been implemented, with few simplifying considerations. The case study is a slice of Scots pine which is assumed to be stored inside Ringebu stave church (Norway). Ringebu indoor microclimate is reconstructed, through a proper transfer function, starting from outdoor temperature data downloaded from web platforms. The reconstructed indoor temperature timeseries cover three periods: far past (1948–1977), recent past (1981–2010) and far future (2071–2100). The results obtained for the three periods made it possible to gain insights about the climate-induced fatigue of wood and to preliminary assess the impact of climate change. It has been observed that successive similar temperature fluctuations can be potentially treated as a block of constant amplitude and constant frequency fatigue-like load. Finally, introducing few simplifying considerations, it has been assessed that the simulated behavior is coherent with the theoretical one coming from exploiting well-established thermo-based methods.

In this study, the solution of the contact problem in a functionally graded (FG) layer resting on elastic two quarter planes was done using the finite element method (FEM). The contact problem consists of two rigid circular punches loaded FG and two elastic quarter planes. P and Q loads are transmitted to the FG layer by two rigid circular punches. All surfaces in the problem were considered as frictionless and the weight effect is also taken into account. The two-dimensional model of the contact problem was created with the ANSYS package program based on FEM and the stress analyzes were performed. All operations of quarter planes and circular punches are done with standard ANSYS menus. However, defining the material properties of the FG layer and dividing into meshes in finite elements cannot be done with standard menus. For this reason, a special macro was added to the program in order to define the material properties of the FG layer and to perform the mesh division, and the necessary parameters were applied to the layer by this macro. In the study, the effects of external load, stiffness parameter (βh), density parameter (γh) and contact stresses of distributed load change, normal stresses, and stresses along the depth were investigated.