Anti-plane moving crack in a functionally graded piezoelectric layer between two dissimilar piezoelectric strips

The dynamic propagation of a crack in a functionally graded piezoelectric material (FGPM) interface layer between two dissimilar piezoelectric layers under anti-plane shear is analyzed using integral transform approaches. The properties of the FGPM layers vary continuously along the thickness. The FGPM layer and two homogeneous piezoelectric layers are connected weak-discontinuously. A constant velocity Yoffe-type moving crack is considered. The Fourier transform is used to reduce the problem to two sets of dual integral equations, which are then expressed to the Fredholm integral equations of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGPM to show the effects on electric loading, gradient of the material properties, crack moving velocity, and thickness of the layers. The following are helpful to increase resistance to crack propagation in the FGPM interface layer: (a) certain direction and magnitude of the electric loading, (b) increasing the thickness of the FGPM interface layer, and (c) increasing the thickness of the homogeneous piezoelectric layer to have larger material properties than those of the crack plane in the FGPM interface layer. The DERR always increases with the increase of crack moving velocity and the gradient of the material properties.     

Output power measurement of a blood pump considering pulsating flows

A blood flow simulator is one of the most useful tools for investigating the dynamic properties of a cardiovascular system. The blood pump in a blood flow simulator generates pulsating flows by oscillating a membrane mechanically at different pulse rates. To evaluate the performance of the blood pump properly, the flow characteristics of the pulsating flows should be considered. In this paper, two basic indicators for evaluating the blood pump characteristics, the output power and the overall efficiency, were determined with consideration of the pulsating flows, based on a phase-averaged analysis. These indicators were obtained by integrating closed contours in a P − Q diagram. The measured output power was expected to be meaningful for understanding the dynamic effects caused by pulsating flows.     

A numerical simulation of train-induced unsteady airflow in a tunnel of Seoul subway

This study has been conducted to investigate numerically the characteristics of train-induced unsteady airflow in a subway tunnel. A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train is applied. The validation of the present study has been carried out against the experimental data obtained by Kim and Kim [1] in a model tunnel. After this, for the geometries of the tunnel and subway train which are very similar to those of the Seoul subway, a three-dimensional unsteady tunnel flow is simulated. The predicted distributions of pressure and air velocity in the tunnel as well as the time series of mass flow rate at natural ventilation ducts reveal that the maximum exhaust mass flow rate of air through the duct occurs just before the frontal face of a train reaches the ventilation duct, while the suction mass flow rate through the duct reaches the maximum value just after the rear face of a train passes the ventilation duct. The results of this study can be utilized as basic data for optimizing the design of tunnel ventilation systems.     

Improved dynamic equations for the generally configured Stewart platform manipulator

In this paper, a Newton-Euler approach is utilized to generate the improved dynamic equations of the generally configured Stewart platform. Using the kinematic model of the universal joint, the rotational degree of freedom of the pods around the axial direction is taken into account in the formulation. The justifiable direction of the reaction moment on each pod is specified and considered in deriving the dynamic equations. Considering the theorem of parallel axes, the inertia tensors for different elements of the manipulator are obtained in this study. From a theoretical point, the improved formulation is more accurate in comparison with previous ones, and the necessity of the improvement is clear evident from significant differences in the simulation results for the improved model and the model without improvement. In addition to more feasibility of the structure and higher accuracy, the model is highly compatible with computer arithmetic and suitable for online applications for loop control problems in hardware.     

Ultrasonic Velocity as a Tool for Physical and Mechanical Parameters Prediction within Geo-Materials: Application on Cement Mortar

This paper discusses the ability of ultrasonic wave velocity to evaluate some physical parameters within mortar. The behavior of ultrasonic pulse velocity within mortar subjected to incremetal stress was also studied. For experimentation, we carried out ultrasonic measurements on mortar samples before and during uniaxial compressive strength, perpendicularly to the stress direction. The water/cement ratios were varied in order to contribute certain specific characteristics. A set of expressions was obtained linking the initial velocities of longitudinal ultrasonic waves with compressive strength, density, porosity and load at elastic limit.The evolution of ultrasonic velocity through mortar samples under continuous incremental uniaxial stress were also investigated. The results illustrated the behavior of ultrasonic pulse velocity as a function of the applied stress. It was observed that velocity did not decrease under initial loading and until about 70% of the ultimate stress, where sudden decrease occurred, followed by the failure of the material.     

Full Curve Damage Process of Polypropylene Fiber Reinforced Mortars under Dynamic Tensile Loading Based on Acoustic Emission Technique

The study of the full curve damage process of polypropylene fiber reinforced mortars under medium strain rate (10^–6 s^–1–10^–4 s^–1) could enrich the understanding of the dynamic damage characteristics of polypropylene fiber reinforced structures. In order to explore the physical mechanisms of polypropylene fiber in the dynamic damage process of the polypropylene fiber reinforced mortars. The real-time dynamic acoustic emission (AE) technology was applied to monitor the damage process of polypropylene fiber reinforced mortars at different strain rates. The analysis of characteristics of AE wavelet energy spectrum and the average AE peak frequency of polypropylene fiber reinforced mortars with different polypropylene fiber content at different strain rates were conducted. The results show that with the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increases first and then decreases and the average AE peak frequency increases gradually. The AE wavelet energy spectrum in ca8 frequency band and the average AE peak frequency decreases gradually with the increase of the strain rate, but them increases first and then decreases with the increase of polypropylene fiber content. The above AE characteristics could provide important information for the identification of dynamic damage mechanism of polypropylene reinforced fiber mortars.     

IBPSO-Based MUSIC Algorithm for Broken Rotor Bars Fault Detection of Induction Motors

In spectrum analysis of induction motor current, the characteristic components of broken rotor bars (BRB) fault are often submerged by the fundamental component. Although many detection methods have been proposed for this problem, the frequency resolution and accuracy are not high enough so that the reliability of BRB fault detection is affected. Thus, a new multiple signal classification (MUSIC) algorithm based on particle swarm intelligence search is developed. Since spectrum peak search in MUSIC is a multimodal optimization problem, an improved bare-bones particle swarm optimization algorithm (IBPSO) is proposed first. In the IBPSO, a modified strategy of subpopulation determination is introduced into BPSO for realizing multimodal search. And then, the new MUSIC algorithm, called IBPSO-based MUSIC, is proposed by replacing the fixed-step traversal search with IBPSO. Meanwhile, a simulation signal is used to test the effectiveness of the proposed algorithm. The simulation results show that its frequency precision reaches 10^?5, and the computational cost is only comparable to that of traditional MUSIC with 0.1 search step. Finally, the IBPSO-based MUSIC is applied in BRB fault detection of an induction motor, and the effectiveness and superiority are proved again. The proposed research provides a modified MUSIC algorithm which has sufficient frequency precision to detect BRB fault in induction motors.     

Ultrasound Imaging of Pipeline Crack Based on Composite Transducer Array

Cracks, especially small cracks are difficult to be detected in oil and gas transportation pipelines buried underground or covered with layers of material by using the traditional ultrasonic inspection techniques. Therefore, a new composite ultrasonic transducer array with three acoustic beam incidence modes is developed. The space model of the array is also established to obtain the defect reflection point location. And the crack ultrasound image is thus formed through a series of small cubical elements expanded around the point locations by using the projection of binarization values extracted from the received ultrasonic echo signals. Laboratory experiments are performed on a pipeline sample with different types of cracks to verify the effectiveness and performance of the proposed technique. From the image, the presence of small cracks can be clearly observed, in addition to the sizes and orientations of the cracks. The proposed technique can not only inspect common flaws, but also detect cracks with various orientations, which is helpful for defect evaluation in pipeline testing.     

Effect of Micro-scale Y Addition on the Fracture Properties of Al–Cu–Mn Alloy

Rare earth (RE) elements have positive effects on Al alloy, while most research is focused on microstructure and mechanical properties. As important application indices, toughness and plasticity are properties that are sensitive to alloy fracture characteristics, and few research studies have characterized the fracture properties of Al–Cu–Mn alloy on RE elements. The effect of different contents of Y on the fracture properties of Al–Cu–Mn alloy is investigated. T6 heat treatment (solid solution and artificial aging treatment), optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) methods are applied to the alloy. Results showed that when Y element is present at 0.1%, the section of the as-cast alloy has smaller sized dimples and the fracture mode presents ductile features. Slight changes in hardness are also observed and maintained at about 60 HV. With increasing content of the RE element Y from 0.1 to 0.5%, the θ phase and Cu atoms in the matrix were reduced and most stopped at Grain boundaries (GBs). Micro-segregation and an enriched zone of Y near the GBs gradually increased. At the same time, the inter-metallic compound AlCuY is aggregated at grain junctions causing deterioration of the micro-structure and fracture properties of the alloy. After T6 treatment, the flatness of the fracture surface was lower than that of all the as-cast alloy showing lots of dimples and teared edges with a significant increase in hardness. When Y content was 0.1%, the strength and hardness of the alloy increased due to refinement of the grain strengthening effect. The content of Y elements segregated in the inter-dendritic zone and GBs is reduced. Plasticity and deformation compatibility also improved, making cracks difficult to form and merge with each other along adjacent grain junctions and providing an increased potential for ductile fracture. This paper proposes the addition of RE Y as an effective and prospective strategy to improve the fracture properties of the Al–Cu–Mn alloy and provide a meaningful reference in terms of improving overall performance.     

Numerical Analysis and Verification of the Gas Jet from Aircraft Engines Impacting a Jet Blast Deflector

The process of the gas jet from aircraft engines impacting a jet blast deflector is not only a complex fluid–solid coupling problem that is not easy to compute, but also a safety issue that seriously interferes with flight deck environment. The computational fluid dynamics (CFD) method is used to simulate numerically the impact effect of gas jet from aircraft engines on a jet blast deflector by using the Reynolds-averaged Navier-Stokes (RANS) equations and turbulence models. First of all, during the pre-processing of numerical computation, a sub-domains hybrid meshing scheme is adopted to reduce mesh number and improve mesh quality. Then, four different turbulence models including shear-stress transport (SST) k-w, standard k-w, standard k-ε and Reynolds stress model (RSM) are used to compare and verify the correctness of numerical methods for gas jet from a single aircraft engine. The predicted values are in good agreement with the experimental data, and the distribution and regularity of shock wave, velocity, pressure and temperature of a single aircraft engine are got. The results show that SST k-w turbulence model is more suitable for the numerical simulation of compressible viscous gas jet with high prediction accuracy. Finally, the impact effect of gas jet from two aircraft engines on a jet blast deflector is analyzed based on the above numerical method, not only the flow parameters of gas jet and the interaction regularity between gas jet and the jet blast deflector are got, but also the thermal shock properties and dynamic impact characteristics of gas jet impacting the jet blast deflector are got. So the dangerous activity area of crew and equipments on the flight deck can be predicted qualitatively and quantitatively. The proposed research explores out a correct numerical method for the fluid–solid interaction during the impact process of supersonic gas jet, which provides an effective technical support for design, thermal ablation and structural damage analysis of a new jet blast deflector.