Low-Velocity Impact on a Functionally Graded Circular Thin Plate

In this paper, an alternative analysis strategy based on a Wavelet-Galerkin scheme specially tailored to solve impact problems of functionally graded orthotropic thin plates subjected to low-velocity impact is presented. The plate considered to be circular, is assumed to be clamped on its lateral edge and has internal supports of rigid, elastic and viscoelastic types. The material properties of the plate are represented in the form of exponential functions of the thickness coordinate. A rigid spherical indenter impacts the plate. The study is based on the classical lamination plate theory (CLT). An advanced contact law of the Hertzian type is adopted. A nonlinear Volterra integral equation system is obtained in the following unknown functions: the impact force and the dynamic reaction forces at the rigid, elastic and viscoelastic internal point supports. Numerical simulations displaying the contact force, the transversal displacement and the penetration depth are graphically presented, and pertinent conclusions regarding the implications of incorporation of graded material systems are outlined.

Thermo-Elasto-Hydrodynamic Analysis of a Crankshaft Journal Bearing

This paper summarizes the essential parts of a numerical analysis activity in which the application of the Thermo-Elasto-Hydro-Dynamic (TEHD) lubrication theory to a crankshaft journal bearing is examined. The study is carried out through numerical computations performed by a commercial flexible-multibody code which simulates the lubricated contact between elastic bodies in large displacement motion. A multibody model has been created and its thermal behaviour has been validated by comparison with experimental temperatures. The validated model is used to perform two comparative analyses between the TEHD modelling and the Elasto-Hydro-Dynamic (EHD) modelling for max torque and max power conditions. A parametric analysis is also performed in which some functional parameters of the bearing (such as journal speed and bearing clearance) are varied and the influence of these variations on reliability (damage parameters) and performances (lost power) of the bearing is monitored.

Strength of Adhesive Joints Under Impact Stress Conditions

The paper reports an experimental study on the bonded joints, carried out by means of an instrumented impact pendulum, equipped to load overlap specimens in tensile shear. Such testing configuration is the most adequate and natural to study the possible modifications of the behavior of the joint, changing from static to dynamic loading condition, keeping the same specimen type. The specimens were steel strips bonded by an epoxy adhesive (Hysol 3425). Several values of lap length, adhesive and adherends thickness were adopted, to achieve rupture under different stress combinations. The stress state at rupture has been calculated by means of a structural solution. The results show that it is possible to represent the failure condition on a chart having as axes the peel and shear structural stress, in a way similar to that found for static cases. Furthermore, in spite of the concerns associated with the impact condition, the strength of the adhesive does not decrease with respect to the case of static loading.

A Novel Design and Modelling of a Micro Underwater Vehicle With Flapping Fins

Systems and mechanisms of motion and stability applied in underwater vehicles although various but almost all rely on a conventional structure and frame work. In this paper in pursue of development a new mechanism in term of motion and performance, mainly biomimeticly inspired from fish flapping and their movement principles particularly flatfish, a new Micro Underwater Vehicle (MUV) is designed and fabricated. In modelling phase using ADAMS we simulated the dynamic performance of the mechanism. On the other hand in order to take the flexibility of the fins into account, we used ANSYS as a meshing tool. Linking these two software packages the modelling stages were completed.

Flow Induced Vibrations of Pressure Let-Down Station in QATARGAS

The use of the pipes to transfer oil and gases from production to export places is a common application in oil and gas industries. The safety and stability of the pipelines are crucial to prevent human and equipment losses. One of the criteria that jeopardize safety and stability of the pipelines is the vibration, and especially flow-induced vibration. Flow induced vibration in pipes is affected by many factors such as fluid type, flow velocity, fluid and pipes densities and fluid pressure. This study considers the analysis and modification of an upstream gas pipeline in QATARGAS Company. The study proposes some solutions to the problem of flow-induced vibration in pipes and the platform supporting them.

Numerical Simulation of Wear in Railway Wheel Profiles

The work describes a method to predict the evolution of the wheel profile of a railway vehicle, depending on the load history acting on the wheelset. The method is based on the determination of the wear on the contact area, which is divided into finite elements according to the strip theory. For each element, in presence of slip, the amount of material loss is evaluated depending on the local value of tangential force and creepage (the meaning of creepage is assumed according to the definition given in [14], [15], [16] as the ratio between the sliding velocity and the tangential rolling velocity). The empirical relation is evaluated according to results of experimental test obtained from literature. The wear is calculated for the entire contact area superimposing the contribution of each element. The motion of the wheelset in lateral direction causes a motion of the contact patch along the profile. Sequentially, the contact area will acquire a different contact shape and stress distribution. The shape of the worn profile depends on both the load condition and the motion of the wheelset with respect to the track. This profile can be obtained from the new one by subtracting at each time step the material removed from the contact area. This procedure is simple, but requires variable profiles for each time step, and is not efficient in computational terms. The strategy proposed here by the authors, is to consider finite periods obtained superimposing several revolution of the wheelset. The worn profile is evaluated in a single step from the cumulative of damage of an entire period. The limitation of this method consists in the different behavior of a wheelset with worn profile respect to a wheelset with new ones, and therefore produces different wear. It is necessary to determine an optimal value for the period to be used to re-evaluate the profile shape, in order to minimize the difference in the predicted shape itself. The method is applied to a suspended wheelset, running on a simulated test track, with S1002/UIC60 profiles. Different periods of re-evaluation of the profiles are considered in order to demonstrate the influence of this parameter.

Design of Trajectories With Physical Constraints for Very Lightweight Single Link Flexible Arms

This communication deals with feedforward control of light, flexible robotic arms. In particular we develop a new, objective method to design a family of trajectories that can be used as modified inputs which cancel the tip vibrations during the robot manoeuvres. This method takes into account the constraints encountered in real actuators (motors), such as a maximum motor torque, and those due to the mechanical limits of the link, such as the maximum deflection before reaching the elastic limit of the link. Parameters of the internal control of the actuators are also derived from the design process, gaining the fastest performance without saturating the motor. Lastly, we show some experimental results which clearly demonstrate the benefits of the new trajectories by comparing them to a linear one.

Impact and Blast Pulse: Improving Energy Absorption of Fibre-Reinforced Composites Through Optimized Tailoring

This paper tries to conjugate an improvement of stiffness and delamination damage resistance. A number of published results allow us to guess the existence of fibre orientations that are a good compromise for an optimal absorption of the incoming energy and for maintaining of a high stiffness. Optimal absorption is herein intended as a way not involving weak properties, such as interlaminar strength. We seek for an optimal orientation of reinforcement fibres through definition of stationary conditions for bending and shear energy contributions under in-plane variation of plate stiffness coefficients. Our goal is to tune the energy absorption as desired. Two kinds of optimized layers are studied, that are compatible with current production technologies: type 1 reduces bending without substantially increasing the transverse shear stresses, type 2 reduces transverse shear stresses without substantially increasing deflections. Incorporation into the laminates of couples of these layers with opposite features and the same mean properties of those they substitute allows an energy transfer from an unwanted to a wanted mode, as shown by the numerical applications. In this way, the deflections and the stresses inducing delamination damage of laminates subjected to impact and blast pulse loads were reduced, while damping should not substantially change since the variation of the orientation of fibres lies in a range where mild variations of it are induced.

Simulation and Experimental Study in Position Control of Servo Hydraulic System With Flexible Load Using Adaptive Neural Network and Differential Evolution Strategy

Hydraulic position servos with an asymmetrical cylinder are commonly used in industry. These kinds of systems are nonlinear in nature and generally difficult to control. Because of parameters changing during extending and retracting, using constant gain will cause overshoot, poor performance or even loss of system stability. The highly nonlinear behaviour of these devices makes them ideal subjects for applying different types of sophisticated controllers. This paper is concerned with a second order adaptive model reference and an artificial neural network controller to position tracking of a servo hydraulic with a flexible load. In present study, a neural network with two outputs is presented. One of the outputs of neural network is used for system’s dynamic compensator and another one for gain scheduling controller. To avoid the local minimum problem, Differential Evolution Algorithm (DEA) is used to find the weights and biases of neural network. The proposed controller is verified with a common used p-controller. The simulation and experimental results suggest that if the neural network is chosen and trained well, it improves all performance evaluation criteria such as stability, fast response, and accurate reference model tracking in servo hydraulic systems.

A New Recognition Method for Damping Coefficients of Rod Pumping System of Directional Well

In this paper, a pattern recognition method is put forward to identify damping coefficients of rod pumping system of directional well by using characteristics space mapping. The 24-direction chain code is presented to encode the curve of dynamometer card. The parametric equation of the dynamometer card curve is transformed into Fourier series whose coefficients can be computed according to the curve’s chain codes. By means of those Fourier coefficients, shape characteristics of the curve are extracted. Euclidean distance is introduced as the measurement of similar degree between the shape characteristics of measured dynamometer card and that of simulated dynamometer card. Changing the value of viscous damping coefficient and Coulomb damping coefficient in the simulation program, different simulated dynamometer cards are obtained. Substituting their shape characteristics to the Euclidean distance, respectively, a series of distances are acquired. When the distance is little than the given error, the corresponding values of the damping coefficients in the simulation program are regarded as real damping coefficients of the rod pumping system of directional well. In the end, an example is provided to show the correctness and effectiveness of the presented method.