Applied Mechanics and Materials Vols. 592-594

Abstract: The research work addresses question on dynamic characteristic of structure which exhibit periodicity at nanoscale viz. single layer graphene sheet using multiscale analysis approach. The carbon-carbon bond of graphene sheet is modeled as space frame element whereas the carbon atom is modeled as 3D-mass element without rotary inertia. Molecular structural mechanics (MSM) model has been used to find the equivalent geometric and elastic properties of space frame element to represent carbon-carbon bond. In molecular structural mechanics model, force field is expressed in the form of steric potential energy by omitting the electrostatic interaction. Sectional stiffness parameters are linked with the force field constants to derive the equivalent elastic and geometric properties of space frame element. This approach is used here to investigate the dynamic behavior of single layer graphene sheet. Simulations have been carried out with different values of aspect ratio to know the effect of variation in length and width on the natural frequencies of graphene structure. Molecular dynamic simulation has also been carried out on the same structure of graphene sheet to validate the results of proposed molecular structural mechanics model.

Abstract: In this paper numerical simulation is carried out using commercially available tool Fluent® to predict the performance of a Wells turbine in an oscillating water column wave energy convertor. A wells turbine is the turbo machinery that rotates in same direction as the air flow through the turbine in either axial direction. The main aim of this investigation is to predict complex flow mechanism like separation and recirculation around the turbine blades and subsequently reduction in torque coefficient at higher flow rate. Numerical simulations have been executed by solving the RANS equations together with k-w SST turbulence model. Then a detailed description of flow and overall performance analysis at different flow rate is presented in this paper.

Abstract: Generally, vehicle safety is a vital issue in the field of automobile industry. Ensuring the safety of passengers is one of the prime challenges for vehicle design engineers. Automobile safety can be determined from the ability of vehicle structure and its internal support systems to protect the occupants from injuries during an accident. In the present work an attempt has been made to determine the dynamic crash characteristics of hollow aluminum tubes for various impact velocities using numerical technique. Aluminum tubes with diagonal ribs were modeled with and without considering the presence of cracks. Surface cut outs were introduced to verify their influence on energy absorption. One of the important crash parameter peak force experienced by the tubes with rib is compared with tubes without rib. Reduced peak force was observed for the tubes with ribs compared to the ones without ribs, which indicates higher energy absorbing capacity of the tube with the presence of ribs. Significant increase in initial peak force (R_F) was noticed with increase of impact velocity. Higher impact energy absorption was noted for a structure with the presence of slit. Experiments were conducted on ribbed hollow tubes and specimens with through hole at the center of the specimen. Results indicate that, ribbed specimens provide significant reduction of peak force compared to bare specimen.

Abstract: In this paper the numerical analysis for an unstructured polyhedral 3bladed un-skewed propeller in steady and transient analysis is discussed and the results are compared with the experimental data. A moving reference frame method is adopted by creating an interface between the propeller and the domain for the rotation of the propeller. The hydrodynamic coefficients such as Thrust coefficient (K_t), Torque coefficient (K_q), circumferentially averaged axial, radial and tangential velocity are compared with the experimental data. The computational time for each simulation is compared and concluded that marine propellers consume less computational time in the steady analysis when compared with the unsteady analysis.

Abstract: Parametric study of satellite reflectors mainly involves selection, creation of geometry of antenna dish and stiffeners, material selection for antenna dish and stiffeners and analysis. Creation of geometry is done by standard modeling software, conversion of solid model into a Finite Element (FE) model and analysis of the same by using a standard Finite Element Method (FEM) tool.

Abstract: Synchro drive uses chain sprocket mechanism to drive three wheels at vertex of triangular chaises and has limited load bearing capacities due to asymmetry. The driving and steering motors fixed near to the vertex of the triangular chassis and wear in chains over a period of time results in increased dead reckoning. The concept of simple pivot based mobile platform using two drives overcasts a conventional synchro drive omnidirectional mobile platform in many aspects .This mobile platform has symmetric chassis with six wheels that makes platform stable irrespective of any configuration. Gear trains to steer the four corner wheels in tandem with pivot wheel adds omnidirectional feature along with increased load bearing capacities and reduced dead reckoning. This paper highlights the concept of pivot steer based omnidirectional mobile platform.

Abstract: A finite element analysis procedure is developed for progressive failure analysis of laminated composite plates under in plane tensile loading. A finite element model is based on higher order shear deformation theory (HSDT) with seven degrees of freedom. The degradation technique used for degradation of material properties of a failed ply is a ply discounting approach. The mode dependant Hashin and Lee failure criterion is used for the progressive failure analysis. The results of first ply failure load and last ply failure load are obtained for different stacking sequence of composite plate. The results shows that a considerable amount of strength remains un utilized in composite laminates after first ply failure of laminates.

Abstract: Steering knuckle is one of the critical components for a four wheel vehicle which links suspension, steering system, wheel hub and brake to the chassis. While undergoing varying loads subjected to different conditions, it doesn’t affect vehicle steering performance and other desired vehicle characteristics. The static strength test for steering knuckle is necessary to validate the component according to the application. Here, the steering arm static analysis of steering knuckle was done by using finite element analysis (FEA software) and experimental testing by using hydraulic actuators and fixtures. The result from the virtual Analysis and Experimental analysis has been compared and validated for the SG Iron Steering knuckle.

Abstract: The life expectancy or failure of aerospace pressure vessels is evaluated by the critical stress intensity determined by the crack growth resistance curve of a material. Load versus crack mouth opening displacement data is generated from the Compact Tension specimens made from the weld joints of maraging steel rocket motor segments. The steps involved to generate critical stress intensity factor is explained. A power law is adopted to model the crack extension in terms of stress intensity factor and determine the maximum failure load of weld specimens. Maximum failure loads of CT specimens obtained by test and analysis are presented.

Abstract: The present work is focused on the graph theory which is used for structural analysis of kinematic chain and identification of degree of freedom. A method based on graph theory is proposed in this paper to solve structural problems by using a suitable example of fourteen links kinematic chain. Purpose of this paper is to give an easy and reliable method for structural analysis of fourteen links kinematic chain. Here, a simple incidence matrix is used to represent the kinematic chain. The proposed method is applied for determining the characteristic polynomial equation of fourteen links kinematic chain. An algebraic test based on graph theory is also used for identifying degree of freedom of kinematic chain whether it is total, partial or fractionated degree of freedom.