Optimization of parallel manipulator trajectory for obstacle and singularity avoidances based on neural network

This paper presents a novel method for singularity-free path planning and obstacle avoidance of parallel manipulators. A modified 3-4-5 interpolating polynomial is used to plan a trajectory for a planar 3-DOF parallel manipulator. The polynomial function which is smooth and continuous in displacement, velocity, and acceleration is used to find a smooth path avoiding the obstacles and singularities. An artificial neural network is implemented to solve forward kinematics of the manipulator to estimate the distance between gripper and singularity or obstacle. The simulating results demonstrate the efficiency of the proposed algorithm.     

On singularities of multi-degree-of-freedom spherical mechanisms

For spherical mechanisms, instantaneous poles are as the counterparts of instant centers in planar mechanisms. However, they are not fully exploited to study the kinematic behavior of spherical mechanisms as the instant centers are for planar ones. The main purpose of this paper is the singularity analysis of multi-degree-of-freedom (DOF) spherical mechanisms. After reviewing the concepts of spherical motion and instantaneous poles, a geometrical technique is presented to identify the singularities of the mechanisms using the properties of instantaneous poles. The method is fast and comprehensive that can be easily employed for all types of multi-DOF spherical mechanisms. Two illustrative examples are included to show the effectiveness of the presented method and the obtained singularities are verified analytically.     

Novel CuO/polymethylenedisulfide nanocomposite for high performance electrocatalytic determination of hydrochlorothiazide in real samples

Journal of Porous Materials - Surface of a carbon paste electrode was modified by using copper oxide nanoparticles/polymethylenedisulfide (CuO NPs/PMDS) nanocomposite. X-ray diffraction...     

An interface‐enriched generalized FEM for problems with discontinuous gradient fields

A new generalized FEM is introduced for solving problems with discontinuous gradient fields. The method relies on enrichment functions associated with generalized degrees of freedom at the nodes generated from the intersection of the phase interface with element edges. The proposed approach has several advantages over conventional generalized FEM formulations, such as a lower computational cost, easier implementation, and straightforward handling of Dirichlet boundary conditions. A detailed convergence study of the proposed method and a comparison with the standard FEM are presented for heat transfer problems. The method achieves the optimal rate of convergence using meshes that do not conform to the interfaces present in the domain while achieving a level of accuracy comparable to that of the standard FEM with conforming meshes. Various application problems are presented, including the conjugate heat transfer problem encountered in microvascular materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of SiC content on the processing, compaction behavior, and properties of Al6061/SiC/Gr hybrid composites

Aluminum matrix composites reinforced with SiC and graphite (Gr) particles are a unique class of advanced engineered materials that have been developed to use in tribological applications. The conventional techniques for producing these composites have some drawbacks. In this study, a new method, namely In situ Powder Metallurgy (IPM), is applied for the preparation of Al6061/SiC/Gr hybrid composites. In this method, the stir casting and the powder metallurgy synthesizing processes are combined into an integrated net shape forming process. 0?C40 vol.% of SiC particles with an average size of 19 ??m, along with 9 vol.% of uncoated Gr particles, were introduced to the molten 6061 aluminum alloy. Then, the slurries were stirred in a specified time?Ctemperature regime resulting in mixtures of the SiC, Gr, and aluminum powder particles. The powder mixtures were cold pressed in six different pressures (between 250 and 750 MPa) and sintered. Finally, the produced composites were heat treated and their hardness and wear properties were investigated. Homogenous distribution of the SiC and Gr particles within the powder mixtures and the hybrid composites is clear from the SEM images. The results also show that the SiC particles decrease the compressibility of the hybrid powders and improve the hardness of composites. The best wear resistance is achieved in the hybrid composite containing 20 vol.% SiC particles.     

The wall–frame and the steel–concrete interactions in composite shear walls

The nonlinear pushover analyses of 24 composite steel plate shear walls (CSPSWs), 24 corresponding steel plate shear walls (SPSWs), and 24 corresponding frames are conducted. CSPSWs have different aspect ratios and infill steel plate thicknesses. The study aims to understand the wall–frame and steel–concrete interactions. The infill steel plate thickness and aspect ratio of CSPSW are the main parameters of the study. In CSPSWs, the percentage of absorbed shear forces by the infill composite wall is always greater than the infill plate of its corresponding SPSW. The percentage of shear in the composite wall is constant at the initial stage of loading up to a drift of 0.15–0.2%. By increasing the drift, the shear yielding of steel plate leads to a reduction of the shear force absorption. The reduction continues until the bulk of shear stiffness of CSPSW is provided by the frame. At the beginning of lateral loading, steel–concrete interactions increase until shear yield of steel plate. Following this stage, a sudden decrease takes place in shear force absorption of reinforced concrete (RC) panel. The reason is that, at the lower drifts, the steel plate has a tendency for elastic buckling, which is prevented by the RC panel. Finally, the shear force absorption remains approximately constant in the RC panel.     

Validation of dynamic block displacement analysis and modification of edge-to-edge contact constraints in 3-D DDA

The validity of three-dimensional discontinuous deformation analysis (3-D DDA) is examined by comparing its solution for dynamic block displacement with an analytical solution. Displacement of a single block on inclined planes subjected to dynamic loadings is studied for analytical solutions derived with respect to the frictional resistance offered by the planes. 3-D DDA predicts accurately the analytical displacements, and the results were found sensitive to the maximum displacement ratio, and the size of the time step, which are defined by the user. Best results were achieved when the actual displacements were approximately equal to the assumed maximum displacements per time step. Furthermore, edge-to-edge contact constraints have been improved by using the augmented Lagrangian method instead of the penalty method. Using the augmented Lagrangian method to enforce contact restraints retains the simplicity of the penalty method, and reduces its disadvantages. The new formulation of edge-to-edge contact using the augmented Lagrangian method is implemented in 3-D DDA and has been programmed in VC++. Finally two illustrative examples are presented for demonstrating this new approach.     

Effect of oxygenates blending with gasoline to improve fuel properties

The purpose of this paper is to study the effect of oxygenate additives into gasoline for the improvement of physicochemical properties of blends.Methyl Tertiary Butyl Ether(MTBE),Methanol,Tertiary butyl alcohol(TBA),and Tertiary amyl alcohol(TAA) blend into unleaded gasoline with various blended rates of 2.5%,5%,7.5%,10%,15%,and 20%.Physicochemical properties of blends are analyzed by the standard American Society of Testing and Materials(ASTM) methods.Methanol,TBA,and TAA increase density of the mixtures,but MTBE decreases density.The addition of oxygenates lead to a distortion of the base gasoline’s distillation curves.The Reid vapor pressure(RVP) of gasoline is found to increase with the addition of the oxygenated compounds.All oxygenates improve both motor and research octane numbers.Among these four additives,TBA shows the best fuel properties.     

Steel–concrete composite shear walls using precast high performance fiber reinforced concrete panels

In this research, seismic performance of composite steel plate shear walls (CSPSWs) using high performance fiber reinforced concrete (HPFRC) panels is experimentally and numerically investigated. Three one‐story one‐bay CSPSW specimens using precast HPFRC panels were designed and fabricated for cyclic quasi‐static experiments. The HPFRC panels of composite shear wall specimens did not have any steel rebars. The main purpose of the study was to understand the effects of rigid and semirigid HPFRC panels on the seismic behavior of the system. Shear capacity, ultimate shear strength, lateral stiffness, energy dissipation, and ductility ratios of the specimens are evaluated. The experimental results demonstrate that specimens were able to resist lateral load up to at least interstory drift of 6%. Using HPFRC panels, CSPSW specimens becomes stiffer in the elastic region, and the yield displacement of the shear wall is decreased; therefore, the ductility ratio of the system is increased. It should be noted that ultimate shear strength, initial elastic stiffness, and energy absorption of specimens with an HPFRC panel on one side or both sides of the infill steel plate were approximately the same. However, using two HPFRC panels is not economical in comparison with CSPSW with an HPFRC panel on one side. Additionally, the second panel increases the seismic mass of the structure.