Experimental study on the confined flow over a circular cylinder with a splitter plate

An experimental study was carried out to investigate the effect of a splitter plate on wake flows downstream of a circular cylinder symmetrically placed in a confined channel. A particle image velocimetry (PIV) measurement was applied to visualize the flow structure and analyze changes in the vortex shedding process. The control elements of the splitter plate length, L/D (D is the cylinder diameter) was varied from 0 to 1.5 and Reynolds number, Re_D was considered at 2400 and 3000. The experimental results showed that the splitter plate had an influence on stabilization of wake turbulences in a confined channel. For shorter splitter plate length of L/D=0.5 and 0.75 cases, flow structures were significantly modified and the vortex shedding frequency decreased as compared with bare cylinder cases. For longer splitter plate length of L/D=1, 1.25 and 1.5 cases, the generation of a secondary vortex was observed based on the snapshot proper orthogonal decomposition (snapshot POD) analysis. In addition, turbulent characteristics corresponding to turbulent kinetic energy (TKE) and Reynolds shear stress correlations took the lowest values and the dominant vortex shedding frequency disappeared. There was an optimal value of the splitter plate length at L/D=1 on suppression of velocity fluctuations. Moreover, the stabilizing effect of a splitter plate was more obvious at Reynolds number of Re_D=3000 than that at Re_D=2400.     

Novel intelligent real-time position tracking system using FPGA and fuzzy logic

The main aim of this paper is to test if FPGAs are able to achieve better position tracking performance than software-based soft real-time platforms. For comparison purposes, the same controller design was implemented in these architectures. A Multi-state Fuzzy Logic controller (FLC) was implemented both in a Xilinx^®${\mathrm{Xilinx}}^{\circledR }$ Virtex-II FPGA (XC2v1000) and in a soft real-time platform NI CompactRIO^®-9002${\mathrm{CompactRIO}}^{\circledR }\mathrm{-}9002$. The same sampling time was used. The comparative tests were conducted using a servo-pneumatic actuation system. Steady-state errors lower than 4 μm were reached for an arbitrary vertical positioning of a 6.2 kg mass when the controller was embedded into the FPGA platform. Performance gains up to 16 times in the steady-state error, up to 27 times in the overshoot and up to 19.5 times in the settling time were achieved by using the FPGA-based controller over the software-based FLC controller.     

Passive control of circular cylinder wake in shallow flow

The control of vortex shedding of a circular cylinder in shallow water using a splitter plate located in the downstream of the circular cylinder was studied by employing particle image velocimetry (PIV) technique. Experiments were carried out in a water channel having a test section of 8000 mm × 1000 mm × 750 mm dimensions at a Reynolds number of 6250. The length of the splitter plate (L) was varied within the range of 0.5 ? L/D ? 2 with an increment of 0.5. The plate was submerged into water at different height ratios (h_p/h_w) such as 0.25, 0.5, 0.75 and 1.0. Mean velocity vector field, corresponding vorticity contours, streamline topologies and turbulent quantities were calculated using 300 instantaneous velocity vector field measured by PIV. As the ratio of h_p/h_w increases, the effect of the splitter plate on the suppression of the vortex shedding increases. Flow characteristics and examination of spectra indicate that Karman vortex shedding is attenuated pronouncedly for the cases of L/D ? 1 and h_p/h_w ? 0.75. The transverse Reynolds normal stress is more effective on the attenuation of turbulent kinetic energy than the streamwise Reynolds normal stress. The value of peak transverse Reynolds normal stress is reduced to 90% of that of the bare cylinder at most.     

Stabilization of an inverted pendulum-cart system by fractional PI-state feedback

This paper deals with pole placement PI-state feedback controller design to control an integer order system. The fractional aspect of the control law is introduced by a dynamic state feedback as u(t)=_Kpx(t)+_KIIα(x(t))$u\left(t\right)=K_{p}x\left(t\right)+K_I{\mathfrak{I}}_{\alpha }\left(x\right(t\left)\right)$. The closed loop characteristic polynomial is thus fractional for which the roots are complex to calculate. The proposed method allows us to decompose this polynomial into a first order fractional polynomial and an integer order polynomial of order n−1$n-1$ (n being the order of the integer system). This new stabilization control algorithm is applied for an inverted pendulum-cart test-bed, and the effectiveness and robustness of the proposed control are examined by experiments.     

Exchange of angular momentum in EMCD experiments

In energy loss magnetic chiral dichroism (EMCD) experiments a chiral electronic transition is induced that obeys the dipole selection rule for the magnetic quantum number Δm=±1$\mathrm{\Delta }m=\pm 1$ or Δ_Lz=±?$\mathrm{\Delta }{L}_z=\pm ?$. The incident plane electron wave is inelastically scattered and is detected in the diffraction plane, i.e. again in a plane wave state. Naïve reasoning suggests that the angular momentum _Lz$L_z$ of the probe electron has not changed in the interaction since plane waves have 〈_Lz〉=0$〈L_z〉=0$. This leads to the seeming contradiction that angular momentum is not conserved in the interaction. A closer inspection shows that the density matrix of the probe has indeed 〈_Lz〉=±?$〈L_z〉=\pm ?$ after a chiral interaction. However, 〈_Lz〉$〈L_z〉$ is not conserved when the probe electron propagates further to the exit surface of the specimen because the rigid lattice breaks rotational symmetry. Thus, the angular momentum of the photo electron that is created in a chiral electronic transition stems from both the probing electron and the crystal lattice.     

The calibration and error compensation techniques for an Articulated Arm CMM with two parallel rotational axes

The calibration and error compensation techniques for an Articulated Arm Coordinate Measuring Machine (AACMM) with two parallel rotational axes are proposed. An improved six-parameter D–H model is established. The reversal techniques are used to calibrate the parallelism errors, arm lengths and zero position of the AACMM. The effects of the bending and torsion deformations caused by the gravity of the arms are removed. The experiments prove that the calibration method is simple and the measurement expanded uncertainty (_2uc$2_{u_c}$) of the developed AACMM with a measuring range of (∅200–∅1000 mm) × 250 mm is less than 10 μm after error compensation.     

Energy-filtered transmission electron microscopy based on inner-shell ionization

We demonstrate that energy-filtered transmission electron microscopy (EFTEM) based on inner-shell ionization can contain atomic resolution information. We present a comparison between experimental data and simulation for the EFTEM image of the _N4,5${\mathrm{N}}_{4,5}$ edge (threshold energy 99 eV) of lanthanum in _LaB6${\mathrm{LaB}}_6$ in which direct interpretation of the location of the lanthanum columns is possible. Our first principles approach is based on calculating transition potentials for inelastic scattering. For our case study, the localization of the transition potentials is such that elastic contrast is only weakly preserved in the EFTEM image. This is not always the case, but we show how the approach based on calculating the elastic wave function and the transition potentials can provide insight about when direct interpretation may and may not be possible. In our test specimen, the direct interpretation fails for thicker specimens when the long tails of the transition potential from multiple adjacent sites leads to significant image features other than at the sites of the element of interest. We can thus anticipate instances where direct interpretation may be more reliable, such as looking for a single impurity in an otherwise well known sample.     

Image simulation of high resolution energy filtered TEM images

Inelastic image simulation software is presented, implementing the double channeling approximation which takes into account the combination of multiple elastic and single inelastic scattering in a crystal. The approach is described with a density matrix formalism. Two applications in high resolution energy filtered (EFTEM) transmission electron microscopy (TEM) images are presented: thickness-defocus maps for _SrTiO3${\mathrm{SrTiO}}_3$ and exit plane intensities for an (_LaAlO3)3(_SrTiO3)3$({\mathrm{LaAlO}}_3{)}_3({\mathrm{SrTiO}}_3{)}_3$ multilayer system. Both systems show a severe breakdown in direct interpretability which becomes worse for higher acceleration voltages, thicker samples and lower excitation edge energies. Since this effect already occurs in the exit plane intensity, it is a fundamental limit and image simulations in EFTEM are indispensable just as they are indispensable for elastic high resolution TEM images.     

Effect of the reinforcement (carbon or glass fibres) on friction and wear behaviour of the PEEK against steel surface at long dry sliding

PEEK (poly-ether-ether-ketone) is a high performance engineering semicrystalline thermoplastic. PEEK has excellent tribological behaviour, which is optimised in the specially formulated tribological composite grade.This paper presents a comparative study of wear and friction on PEEK, PEEK-CF30 (wt%) and PEEK-GF30 (wt%) against steel, at long dry sliding. A plan of experiments was performed on a pin-on-disc machine, under the following conditions $pv=2\text{MPa}\text{m/s}$ (p = 8 MPa and $v=0.25\text{m/s}$; p = 2.68 MPa and $v=0.75\text{m}\text{/}\text{s}$) at the ambient temperature for a sliding distance of 15 km.PEEK-CF30 presented the lesser friction coefficient followed by PEEK. PEEK-GF30 presented the higher friction coefficient throughout all sliding distance. Both PEEK-CF30 and PEEK-GF30 have presented an excellent wear resistance relatively to PEEK while PEEK-CF30 presented the best tribological behaviour.     

Effects of flexible plate attached to the rear of the cylinder on flow structure

In this experimental study, the flow structure in the wake flow region was investigated with the Particle image velocimetry technique (PIV) by attaching elastic plates at different lengths behind the cylinder. The flow structure occurred at the wake flow region altered depending on the length of the flexible matter. In this experiment, the strips with the lengths of 75, 90, 120, 135 and 180 mm were used to control instabilities. Diameter of the cylinder (D) is 60 mm and the water height (h _w ) is 600 mm. Reynolds number was kept constant as 5000 based on cylinder diameter. The images were captured at mid-height of the cylinder (h _m ) which is 250 mm. As a result of experimental studies, attached flexible strip suppressed vortex shedding occurred in the behind of the cylinder and it is observed that effect of the length flexible of the strip is pretty much. Maximum level of flow characteristics such as Reynolds stress, fluctuation velocities and turbulent kinetic energy were decreased with flexible splitter plate and shifted through the downstream region.     

Sputtered Si-containing low-friction carbon coatings for elevated temperatures

This work presents a tribological study on three sputtered amorphous carbon-based coatings containing Si and Cr (a-C, a-C:Cr and a-C:Si). Molecular dynamics simulations predict tetrahedral bonds between C and Si in the a-C matrix. Ball-on-disk-tests against Al₂O₃ carried out at room temperature revealed a coefficient of friction of 0.08–0.1 for all films. Between 250 and 325 °C, Si decreases the COF and wear rate to $<0.05$ and $<5\times {10}^{-17}{\mathrm{m}}^3/\mathrm{N}\times \mathrm{laps}$, respectively. The a-C reference shows a COF of 0.15±0.05 and a wear rate of $1\times {10}^{-16}{\mathrm{m}}^3/\mathrm{N}\times \mathrm{laps}$, whereas the a-C:Cr film failed. The improved tribological performance of a-C:Si expands its application temperature to 450 °C and is most probably related to formation of Si-compounds on the film surface, as evidenced by X-ray photoelectron spectroscopy.     

A three-point electrical potential difference method for in situ monitoring of propagating mixed-mode cracks at high temperature

In this paper an electrical potential difference method for the real-time assessment of both the length and the direction of Mode II cracks is presented. Three measuring electrodes are placed in selected positions over the gauge area of a specially designed shear specimen and their readings are associated with the actual position of the crack tip using Finite Element Analysis (FEA). This information can be processed in real-time to provide continuous monitoring of the crack as it propagates either in pure Mode II (in-plane shear) or mixed Mode I (tension) and Mode II if the inclination of the crack exceeds 20°. In fatigue testing it is possible to produce dα/dN-Δ_KII$d\alpha /\mathit{dN}-\mathrm{\Delta }{K}_{\text{II}}$ (in pure-shear) and dα/dN-Δ_KI$d\alpha /\mathit{dN}-\mathrm{\Delta }{K}_{\text{I}}$ (in mixed-mode) plots on-line as the test is in execution. The method has been calibrated with optical measurements using a long-distance observation microscope on the nickel-based superalloy CMSX4 at high temperature. The main finding was that the central two sensing electrodes were sensitive to the length of the crack and insensitive to the crack angle, whereas the readings from the third electrode were sensitive to the crack angle and thus the exact position of the crack tip could be traced in real-time. Special techniques were implemented to rule-out thermoelectric effects and thermal stresses on the specimen.