Analysis of mechanical behavior and hysteresis heat generating mechanism of PDM motor

Positive displacement motor (PDM), which is prone to high temperature fatigue failure, can be weakened in its application in deep and superdeep well. In order to study the forced state, deformation regularity and thermal hysteresis of PDM motor, the paper established the three-dimensional thermal-mechanical coupled Finite element model (FEM). Based on the theoretical research, experimental study and numerical simulation, the study found that the displacement of stator lining shows a sinusoidal variation under internal pressure, when adapting the general form of sine function to fitting inner contour line deformation function. Then the paper analyzed the hysteresis heat generating mechanism of the motor, learning that hysteresis thermogenous of stator lining occurs due to the viscoelastic of rubber material and cyclic loading of stator lining. A heartburn happens gradually in the center of the thickest part of the stator lining as temperature increases, which means work efficiency and service life of PDM will be decreased when used in deep or superdeep well. In this paper, we established a theory equation for the choice of interference fit and motor linetype optimization design, showing hysteresis heat generating analyzing model and method are reasonable enough to significantly improve PDM’s structure and help better use PDM in deep and surdeep well.     

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation.     

Stiffness and damping coefficients for journal bearing using the 3D transient flow calculation

The dynamic coefficients of journal bearing are necessary components in the analysis of linear stability and response of rotating dynamic systems. We propose a new method for the numerical identification of bearing support force coefficients in flexible rotor-bearing systems based on the 3D transient flow calculation. The CFD commercial software FLUENT is mainly used in this simulation, which employs a finite volume method for the discretization of the Navier-Stokes equations. To determine the dynamic coefficients, a new mesh movement approach is presented to update the volume mesh when the journal moves during the 3D transient flow calculation of a journal bearing. Existing dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. Measurements and identification are performed on a test rotor supported on a pair of identical two-lobe fluid film bearings, and the results obtained from the CFD methods agree well with experimental results. The results indicate that the methods proposed in this paper can predict the dynamic coefficients of the journal bearing in a rotor-bearing system effectively, and provide a further tool for stability analysis.     

Investigation of the correlation between noise & vibration characteristics and unsteady flow in a circulator pump

Circulator pumps have wide engineering applications but the acoustics, vibration and unsteady flow structures of the circulator pump are still not fully understood. We investigated the noise and vibration characteristics and unsteady flow structures in a circulator pump at different flow rates. Three-dimensional, unsteady RANS equations were solved on high-quality structured meshes with SST k-ω turbulence model numerically. Measurements were made in a semi-anechoic chamber to get an overview of noise and vibration level of a pump at different flow rates. The 1/3 octave-band filter technique was applied to obtain the explicit frequency spectra of sound, pressure fluctuations and vibration signals and their principal frequencies were identified successfully. The air-borne noise level of the designed condition is lower than that of the off-design conditions, and the highest sound pressure level is found at part-load condition. The acoustic emission from the pump is mainly caused by unsteady flow structures and pressure fluctuations. In addition, both the link between airborne noise and pressure fluctuation, and the correlation between vibration and unsteady hydrodynamic forces, were quantitatively examined and verified. This work offers good data to understand noise and vibration characteristics of circulator pumps and the relationships among the noise, vibration and unsteady flow structures.     

New encapsulation method using low-melting-point alloy for sealing micro heat pipes

This study proposed a method using Low-melting-point alloy (LMPA) to seal Micro heat pipes (MHPs), which were made of Si substrates and glass covers. Corresponding MHP structures with charging and sealing channels were designed. Three different auxiliary structures were investigated to study the sealability of MHPs with LMPA. One structure is rectangular and the others are triangular with corner angles of 30° and 45°, respectively. Each auxiliary channel for LMPA is 0.5 mm wide and 135 μm deep. LMPA was heated to molten state, injected to channels, and then cooled to room temperature. According to the material characteristic of LMPA, the alloy should swell in the following 12 hours to form strong interaction force between LMPA and Si walls. Experimental results show that the flow speed of liquid LMPA in channels plays an important role in sealing MHPs, and the sealing performance of triangular structures is always better than that of rectangular structure. Therefore, triangular structures are more suitable in sealing MHPs than rectangular ones. LMPA sealing is a plane packaging method that can be applied in the thermal management of high-power IC device and LEDs. Meanwhile, implanting in commercialized fabrication of MHP is easy.     

A study of flow patterns for staggered cylinders at low Reynolds number by spectral element method

This study investigates the pattern of flow past two staggered array cylinders using the spectral element method by varying the distance between the cylinders and the angle of incidence (α) at low Reynolds numbers (Re = 100-800). Six flow patterns are identified as Shear layer reattachment (SLR), Induced separation (IS), Vortex impingement (VI), Synchronized vortex shedding (SVS), Vortex pairing and enveloping (VPE), and Vortex pairing splitting and enveloping (VPSE). These flow patterns can be transformed from one to another by changing the distance between the cylinders, the angle of incidence, or Re. SLR, IS and VI flow patterns appear in regimes with small angles of incidence (i.e., α ≤ 30° ) and hold only a single von Karman vortex shedding in a wake with one shedding frequency. SVS, VPE and VPSE flow patterns appear in regimes with large angles of incidence (i.e., 30° ≤ α ≤ 50° ) and present two synchronized von Karman vortices. Quantitative analyses and physical interpretation are also conducted to determine the generation mechanisms of the said flow patterns.     

Acoustic radiation from modal vibration of automotive brake drum

The vibro-acoustic characteristics of an automotive brake drum is studied by applying a hybrid approach, which combines a numerical vibration analysis with an analytical acoustic solution. Specifically, structural vibration of a drum is investigated with the numerical finite element analysis, and vibratory displacements of the outer surface of the drum is approximated by simple mathematical expressions. Then, radiation of sound from the drum vibration is calculated using well-known theoretical solutions based on the simplified modal displacements. Finally, the calculation results are compared with those obtained by full numerical analyses. The results show that the numerical-analytical hybrid method allows relatively accurate calculation of vibro-acoustic properties of a brake drum under realistic boundary conditions.     

Experimental and numerical study of a modified ASTM C633 adhesion test for strongly-bonded coatings

When coatings are strongly bonded to their substrates it is often difficult to measure the adhesion values. The proposed method, which is suggested naming “silver print test”, consists in covering the central part of the samples with a thin layer of silver paint, before coating. The process used for testing this new method was the Air plasma spraying (APS), and the materials used were alumina coatings on C35 steel substrates, previously pre-oxidized in CO₂. The silver painted area was composed of small grains that did not oxidize but that significantly sintered during the APS process. The silver layer reduced the surface where the coating was linked to the substrate, which allowed its debonding, using the classical adhesion test ASTM C633-13, while the direct use of this test (without silver painting) led to ruptures inside the glue used in this test. The numerical modelling, based on the finite element method with the ABAQUS software, provided results in good agreement with the experimental measurements. This concordance validated the used method and allowed accessing to the values of adherence when the experimental test ASTM C633-13 failed, because of ruptures in the glue. After standardization, the “silver print test” might be used for other kinds of deposition methods, such as PVD, CVD, PECVD.     

Deformation temperature and material constitutive model of cupronickel B10

Cupronickel B10—an important material used in aircraft carriers—exhibits excellent electrochemical and mechanical properties, such as high corrosion resistance and weldability. The Split-Hopkinson pressure bar (SHPB) test is a classical method to obtain the dynamic mechanical properties of solid materials. However, the deformation temperature has long been ignored in SHPB studies, which results in low accuracy of the material constitutive model. Thus, in this study, a new method for obtained the deformation temperature was proposed and the modified material equation was validated using experimental data. Quasi-static compression and SHPB experiments were conducted with a thermocouple. The results revealed that the deformation temperature of the quasi-static tests was nearly zero, whereas that of the SHPB experiments ranged from 40 to 90 °C. Therefore, the method developed to describe the deformation temperature can be used to improve the precision of SHPB experiments, as demonstrated for the case of cupronickel B10.     

Application of the ultrasonic propagation imaging system to an immersed metallic structure with a crack under a randomly oscillating water surface

Ultrasound is widely used and studied to satisfy the increased demands of the Non-destructive evaluation (NDE) and testing of underwater structures. However, because of the large size and mass of underwater structures, such as submarines, ship hulls, or nuclear reactor pipe lines, it is difficult to inspect the structures during operation. This underwater NDE technology is challenging but could be highly beneficial because the time and cost of maintenance will be effectively reduced. We propose an NDE method for immersed structures using an ultrasonic propagation imaging system with a piezoelectric sensor. The underwater sensing capability of a piezoelectric sensor is experimentally demonstrated using an aluminum plate specimen. A piezoelectric sensor can compensate for the decreased signal amplitudes due to leaky waves that are generated on interfaces between structures and water, since water transmits signals better than air. Additionally, a piezoelectric sensor can be applied even if the water surface is oscillating. Using these properties, the laser induced guided Ultrasonic propagation imager (UPI) inspected a T-shaped steel structure with a 2-mm crack on the weld zone. The inspection was implemented in three cases: a specimen without water, a specimen immersed in water and a specimen immersed in water with a randomly oscillating surface. The crack was visualized and measured using the ultrasonic wave propagation imaging algorithm, the adjacent wave subtraction algorithm, and the variable time window amplitude mapping algorithm. In the case with a randomly oscillating water surface, the laser pulse was refracted randomly based on Snell’s law. This phenomenon may cause degradation of the inspecting results. However, a repeated scanning process and outlier elimination led to an improved signal-to-noise ratio such that it was able to detect the crack. These results demonstrate the possibility to apply the laser UPI to submerged structures even if the water surface is randomly oscillating.