Transition Position Research Articles

P-010. Short-term prediction of preeclampsia using the sFlt-1/PlGF ratio in pregnant women with suspected preeclampsia

Short-carbon-fiber-reinforced polyetherimide (SCF/PEI) composites have good mechanical properties and are expected to have wide applications including components serving under water lubrication conditions. However, no work has been reported on the tribological behaviors of SCF/PEI composites under water lubrication conditions. This work attempts to explore the practicality of the SCF/PEI composite from a tribological point of view under water lubrication conditions. SCFs are coated by polydopamine (PDA) to enhance the interfacial interaction between fibers and matrix. The tribological performances of SCF/PEI composite are systematically investigated by sliding wear tests under tap and sea water lubrication conditions. Experimental results show that the SCF/PEI composite has a better friction performance in water lubrications than that under dry sliding because of the separation effects formed by a water molecule film and a transfer film. However, no remarkable differences of wear resistance are found between water lubrication and dry contact conditions, and the magnitude of specific wear rate under these conditions is around 1 × 10−6 mm3/N·m. It is found that contact surface hardness of the SCF/PEI composite is reduced after a sliding test in water due to the plasticization phenomenon, especially sea water can accelerate the diffusion of water molecules into matrix, making the specific wear rate in sea water is ten times of that in tap water for highly-loaded conditions. Meanwhile, the abrasive wear is observed to be the dominated wear mode in boundary lubrication regime, and the adhesion wear occurs around the transition position from the boundary to mixed lubrication regime. It is also found that pressure has a significant effect on the temperature rise within the contact surface than the speed does. Finally, the tribological performance of the SCF/PEI composite under water is exhibited to be better than that of most of polymers and composites reported previously.

Stochastic periodic orbits in fast-slow systems with self-induced stochastic resonance

Noise is ubiquitous in various systems. In systems with multiple timescales, noise can induce various coherent behaviors. Self-induced stochastic resonance (SISR) is a typical noise-induced phenomenon identified in such systems, wherein noise acting on the fast subsystem causes stochastic resonancelike boundary crossings. In this paper, we analyze the stochastic periodic orbits caused by SISR in fast-slow systems. By introducing the notion of the mean first passage velocity toward the boundary, a distance matching condition is established, through which the critical transition position of boundary crossing can be calculated. The theoretical stochastic periodic orbit can be accordingly obtained via gluing the dynamics along the slow manifolds. It is shown that the theoretical predictions are in excellent agreement with the results of Monte Carlo simulations for a piecewise linear FitzHugh-Nagumo system even for large noise. Furthermore, the proposed method is extended to the original FitzHugh-Nagumo system and also found to exhibit consistent accuracy. These results provide insights into the mechanisms of coherent behaviors in fast-slow systems and will shed light on the coherent behaviors in more complex systems and large networks.

Modeling of Transonic Transitional Three-Dimensional Flows for Aerodynamic Applications

The paper describes a technology designed for computing three-dimensional transonic laminar–turbulent flows at various aerodynamic configurations with the use of the general-purpose computational fluid dynamics code ANSYS Fluent and an integrated special module of computing the laminar–turbulent transition position created on the basis of the autonomous software package LOTRAN 3, developed previously by the authors. Within the framework of this technology, computations with a prolate spheroid and engine nacelle are performed for different Mach numbers ( Reynolds numbers ), and angles of attack ( to ). New results are obtained on the position of the laminar–turbulent transition in boundary layers in transonic flow regimes, and the problem of the dominating transition mechanism is considered. The results obtained in the present study are demonstrated to be in good agreement with experimental data on the position of the laminar–turbulent transition available in the literature.

Measurement of boundary layer transition on oscillating airfoil using cntTSP in low-speed wind tunnel

cntTSP is a flow visualization technique that combines temperature-sensitive paint (TSP) and carbon nanotube (CNT). TSP is a sprayable temperature sensor, and CNT is used as a thin inner electric heater for the TSP. The cntTSP technique allows the visualization of the movement of the boundary layer transition on a moving airfoil. In this study, cntTSP was applied to a pitch-oscillating airfoil in a low-speed wind tunnel. Three methods were compared as methods for detecting the boundary layer transition position. The transition position was successfully evaluated using a heat transfer coefficient that was calculated by the surface temperature. Moreover, at a high-reduced frequency, the detected transition positions were different between the pitching-up and pitching-down procedure. Moreover, we observed a hysteresis loop of the transition position.

Equilibrium folding and unfolding dynamics to reveal detailed free energy landscape of src SH3 protein by magnetic tweezers* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874309 and 11474237) and the 111 Project (Grant No. B16029).

Src SH3 protein domain is a typical two-state protein which has been confirmed by research of denaturant-induced unfolding dynamics. Force spectroscopy experiments by optical tweezers and atomic force microscopy have measured the force-dependent unfolding rates with different kinds of pulling geometry. However, the equilibrium folding and unfolding dynamics at constant forces has not been reported. Here, using stable magnetic tweezers, we performed equilibrium folding and unfolding dynamic measurement and force-jump measurement of src SH3 domain with tethering points at its N- and C-termini. From the obtained force-dependent transition rates, a detailed two-state free energy landscape of src SH3 protein is constructed with quantitative information of folding free energy, transition state barrier height and position, which exemplifies the capability of magnetic tweezers to study protein folding and unfolding dynamics.

Investigation on the motion conditions and dynamic interaction of vehicle and turnout due to differential wheelset misalignment

Assembly deviations of wheelsets cause differential wheelset misalignments and change the wheel-rail contact relationship in railway turnouts. In this paper, the motion conditions of wheelsets under the same bogie are analysed with differential wheelset misalignment based on the mechanical equilibrium condition. A rigid-flexible coupling model of vehicle-turnout dynamic interaction that fully considering different misalignment conditions is established to evaluate the wheel and turnout rails dynamic interaction and vehicle dynamic characteristics. The results show that wheelset misalignment can change wheel load transition position and affect wheel-rail contact conditions, especially when the misalignment direction is toward the switch rail. The larger misalignment angle will increase flange contact range and keep the normal contact stress at a higher level. Both misalignment angle and form determine the wheel-rail vertical force. The lateral force is mainly affected by the superposition effect of the eccentric load and the lateral impact of the wheel load transition.

The 1S0 → 3P1 transition position shift of Bi3+ ion doped Ln2O3 (Ln = Lu, Gd, La) phosphors

A series of Bi3+ ion doped Ln2O3 (Ln = Lu, Gd, La) phosphors have been prepared through a simple urea-based precipitation method. The 1S0 → 3P1 transition position shift of Bi3+ ion has been investigated in Bi3+-doped Ln2O3 phosphors. This is caused by difference of covalency and coordination number. The 1S0 → 3P1 transition of Bi3+ ion in Gd2O3 crystal shifts to lower energy position than that in Lu2O3 crystal for the same site due to the larger radius of Gd3+ ion compared to Lu3+ ion. However, the 1S0 → 3P1 transition of Bi3+ ion shifts to higher energy position owing to the increase of coordination number from cubic phase Lu2O3 and Gd2O3 crystals to hexagonal phase La2O3 crystal. Our work provides a reference to achieve various photoluminesence performances of Bi3+ ion doped oxides.

Visualized experiments on phase-change heat transfer of a metal “endoscopic” two-phase closed thermosyphon

A novel metal “endoscopic” two-phase closed thermosyphon (METPCT) which could be used to intuitively investigate the phase-change heat transfer and two-phase flow characteristics were developed. The visualized experimental set-up was established by using a rigid borescope and a high-speed camera. The phase-change heat transfer characteristics of the internal working fluid inside the METPCT under various cooling water temperatures (10, 15, 20 °C) and input power (100 ~ 900 W) have been investigated. Different heat and mass transfer regimes, e.g. start-up, geyser boiling and steady-state, were analyzed. During the start-up, the heat transfer in the evaporator is mainly heat conduction, natural convection and surface evaporation. Meanwhile, the start-up time decreases as the increases with cooling water temperature. The geyser boiling includes the incubation and expulsion stage, and the wall temperature response shows slight fluctuation and sharp fluctuation during the expulsion stage. In the steady-state, from bottom to top of the liquid pool in the evaporator, the two-phase flow pattern evolves from bubbly flow to slug flow, churn flow and then dispersed flow, and its transition position is closer to the bottom with the increase of input power. In addition, the heat transfer modes at the condenser are the combination of droplet condensation, discontinuous film condensation, and uniform film condensation. This work provides a new visualized experimental method to investigate the phase-change and two-phase flow properties in a TPCT, which helps to understand the heat and mass transfer mechanism of the TPCT.

Experimental research on crossflow instability for a hypersonic 4∶1 elliptic cone

In this work, the cross-flow instability on the surface of a blunt elliptical cone with a long-short-axis ratio of 4∶1 is studied experimentally in the Mach 6 hypersonic quiet wind tunnel. Comprehensive use of temperature sensitive paint (TSP) technology, nano-tracer-based planar laser scattering (NPLS) technology and Kulite sensor pressure test to measure the temperature distribution in the cross-flow area on the surface of the model, boundary layer flow structure and model surface pressure are tested. The mechanism of boundary layer transition in the cross-flow control area on the surface of the elliptical cone is studied, and the influence law of incoming flow unit Reynolds number and angle of attack on boundary layer transition is obtained, and some conclusions are obtained below. In the wind tunnel noise mode, the transition of the boundary layer in the cross-flow area between the surface center line and the leading edge of the elliptical cone model with a length-to-short-axis ratio of 4∶1 is controlled by the traveling waves, and no footprint of the steady vortex is found. The characteristic frequency of the traveling wave is about 20 kHz. When the unit Reynolds number of the incoming flow increases, the transition position will be advanced, and the frequency and amplitude of the traveling wave will increase. Within a certain angle of attack, the transition position of the upwind boundary layer is delayed, and the characteristic frequency of the traveling wave does not change much but the energy is weakened. When the angle of attack continues to increase, the transition phenomenon disappears.

Performance optimization and investigation of flow phenomena on tidal turbine blade airfoil considering cavitation and roughness

Since the underwater impurity and cavitation could have a significant impact on the aerodynamic performance of tidal turbine blade airfoil, it is necessary to consider both roughness and cavitation in the process of optimization design. In the present study, a novel multi-objective evolution algorithm based on NSGA‐II is proposed for the design of tidal turbine blade airfoil, to overcome the adverse effects of cavitation and roughness. Non-uniform rational B-spline (NURBS) representation is adopted in the process of optimization; a new performance evaluation index of airfoil under rough condition is formed; multi-objective optimization was conducted for NACA2415 airfoil. The minimum pressure coefficient is the criterion used for the identification of cavitation on tidal turbine blade airfoil. The CFD and XFOIL are employed to calculate the lift drag coefficient and pressure coefficient of airfoil. The transition position of airfoil is predicted by the improved transition model. A comprehensive experimental study was conducted to evaluate the aerodynamic performance of optimized airfoil, revealing flow patterns such as flow separation over the initial airfoil and optimized airfoil through smoke flow experiment. In order to simulate the rough condition, sandpaper was pasted on the leading edge surface of airfoil and experiments indicated that location and formation of laminar separation bubble were affected . Numerical simulation and experimental results show that the optimized airfoil enjoys a better aerodynamic performance than the original ones under the roughness condition, in terms of cavitation inhibition. Within the range of design conditions, the lift drag ratio of optimized airfoils increased by an average of 20% and the minimum pressure coefficient peak decreased by about 17.2% on average. Thus,the proposed method can effectively guide the design and technical reserve of the tidal turbine.

Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation

Thermographic flow visualization enables a noninvasive detection of the laminar–turbulent flow transition and allows a measurement of the impact of surface erosion and contamination due to insects, rain, dust, or hail by quantifying the amount of laminar flow reduction. The state-of-the-art image processing is designed to localize the natural flow transition as occurring on an undisturbed blade surface by use of a one-dimensional gradient evaluation. However, the occurrence of premature flow transitions leads to a high measurement uncertainty of the localized transition line or to a completely missed flow transition detection. For this reason, regions with turbulent flow are incorrectly assigned to the laminar flow region, which leads to a systematic deviation in the subsequent quantification of the spatial distribution of the boundary layer flow regimes. Therefore, a novel image processing method for the localization of the laminar–turbulent flow transition is introduced, which provides a reduced measurement uncertainty for sections with premature flow transitions. By the use of a two-dimensional image evaluation, local maximal temperature gradients are identified in order to locate the flow transition with a reduced uncertainty compared to the state-of-the-art method. The transition position can be used to quantify the reduction of the laminar flow regime surface area due to occurrences of premature flow transitions in order to measure the influence of surface contamination on the boundary layer flow. The image processing is applied to the thermographic measurement on a wind turbine of the type GE 1.5 sl in operation. In 11 blade segments with occurring premature flow transitions and a high enough contrast of the developed turbulence wedge, the introduced evaluation was able to locate the flow transition line correctly. The laminar flow reduction based on the evaluated flow transition position located with a significantly reduced systematic deviation amounts to 22% for the given measurement and can be used to estimate the reduction of the aerodynamic lift. Therefore, the image processing method introduced allows a more accurate estimation of the effects of real environmental conditions on the efficiency of wind turbines in operation.

Feeling Machine for Process Monitoring of Turning Hybrid Solid Components

The realization of the increasing automation of production systems requires the guarantee of process security as well as the resulting workpiece quality. For this purpose, monitoring systems are used, which monitor the machining based on machine control signals and external sensors. These systems are challenged by innovative design concepts such as hybrid components made of different materials, which lead to new disturbance variables in the process. Therefore, it is important to obtain as much process information as possible in order to achieve a robust and sensitive evaluation of the machining. Feeling machines with force sensing capabilities represent a promising approach to assist the monitoring. This paper provides, for the first time, an overview of the suitability of the feeling machine for process monitoring during turning operations. The process faults tool breakage, tool wear, and the variation of the material transition position of hybrid shafts that were researched and compared with a force dynamometer. For the investigation, longitudinal turning processes with shafts made of EN AW-6082 and 20MnCr5 were carried out. The results show the feeling machine is sensitive to all kinds of examined errors and can compete with a force dynamometer, especially for roughing operations.

Hydrate slurry flow characteristics influenced by formation, agglomeration and deposition in a fully visual flow loop

Gas hydrates pose impeded flow risks and serious safety hazards in oil and gas transportation pipelines. This makes it imperative to look for appropriate hydrate control strategies. In this study, the hydrate slurry flow characteristics were investigated under multiphase flow conditions using a high-pressure fully visual flow loop. At different liquid loadings and mixture velocities, pressure drop variations were monitored from the initial hydrate formation to deposition and bedding, and the flow patterns were observed throughout the experiments. It was found that the hydrate slurry flow may involve four stages of hydrate formation, agglomeration, deposition and bedding prior to pipeline blockage. The effective volume and water conversion fractions were also obtained at different stages. The results showed that the lower liquid loading causes quicker and more severe hydrate blockage problem mainly due to more mass transfer of gas into water hence higher water conversion rate. Moreover, lower mixture velocity resulted in a higher hydrate bedding tendency. The results also confirmed further formation and deposition of gas hydrates due to a drastic temperature drop immediately after the liquid flow stopped in the system. In addition, the flow characteristics in sloped pipe sections (both upslope and downslope) were studied to investigate the effect of driving forces on the hydrate deposition. Slug flow was observed in the upslope while stratified flow in the downslope. Furthermore, hydrate accumulation tends to occur in the transition position between the horizontal pipes and the sloped pipes due to the effect of gravity.

Effects of inlet turbulence intensity on wall heat transfer in a turbine guide vane

Heat transfer is an important phenomenon that exists in many industrial applications, especially for gas turbines, aeronautical engines. In this work, two different turbulence models ([Formula: see text] and SAS model) are used to investigate the effects of inlet turbulence on wall heat transfer and the characteristics of flow field in a well-known turbine guide vane (LS89). In order to handle the transition, Menter’s [Formula: see text] transition model is used. The simulations show that the inlet turbulence has an apparent effect on the wall heat transfer of the vane. Not only the maximum wall heat transfer coefficient is increased, the distribution of wall heat flux at the suction side is also modified. The isentropic Mach number along the vane surface is insensitive to the variance of inlet turbulence intensity. Besides, a shock appears in the throat and a laminar-to-turbulence transition position moves forward after the main flow turbulence is enhanced. Moreover, the results indicate that SAS model is capable of capturing more flow structures such as reflecting pressure waves and shedding vortexes while the [Formula: see text] model misses them due to the dissipation.

Chaotic photon spheres in non-Euclidean billiard

Abstract With the advancement in understanding of the physics inside chaotic systems, chaos has been harnessed from a nuisance to a beneficial factor in optical devices. Light–matter interaction in chaotic systems has been utilised for improving broadband energy harvesting and momentum transformations, achieving light localization beyond diffraction limit and even stabilizing the dynamics of high power laser. While extensive study about wave chaos has been made in deformed microcavities, investigation of how chaos dynamics evolves in curved space manifold remains elusive. Here, we study the non-Euclidean billiard of a torus-like manifold, which is a closed 2D cavity system with effective periodic boundaries. The ray chaotic behaviours on the deformed toroidal surface are explored using the geodesic equation. By tuning the deformation parameter of the torus, we observe the transition of the billiard from the ordered phase state to mixed phase states and then complete ray chaos. The photon sphere of the torus is identified as the transition position from ordered states to chaotic states. Compared with other chaotic behaviours resulted from the random scattering inside deformed cavities, we demonstrate chaotic dynamics purely on a curved surface, which may shed light on the better understanding of chaos in optics.

Low-Computation GNSS Signal Acquisition Method Based on a Complex Signal Phase in the Presence of Sign Transitions

During signal acquisition in a global navigation satellite system acquisition stage, a method of signal parameters estimation with low computational complexity is needed. However, due to the influence of sign transitions, the correct peak corresponding to the signal parameters is difficult to detect. For the estimation of the code phase of the received signal in the presence of sign transitions with low computational complexity, an acquisition method based on a complex signal phase (AMCSP) is proposed. The problem of estimating the sign transition position and the code phase is transformed into a problem of solving for a complex signal phase. Special block matrixes are constructed to obtain the complex signal phase, and integration processing is utilized to improve the detection probability performance. Based on an analysis of undesirable cases, a final code phase estimation process is proposed. Furthermore, expressions for the detection performance and computational complexity of AMCSP are derived. Simulation results demonstrate that the computational cost of AMCSP is much lower than that of a fast Fourier transform-based method.

Variable slip window technology in transition detection on pitching airfoil

In the pitching motion, the unsteady transition and relaminarization position plays an important role in the dynamic characteristics of the airfoil. In order to facilitate the computer to automatically and accurately calculate the position of the transition and relaminarization, a Variable Slip Window Technology (VSWT) suitable for airfoil dynamic data processing was developed using the S809 airfoil experimental data in this paper and two calculation strategies, i.e., global strategy and single point strategy, were proposed: global strategy and single point strategy. The core of the VSWT is the selection of the window function h and the parameters setting in the h function. The effect of the VSWT was evaluated using the dimensionless pulse strength value (INB), which can be used to evaluate the signal characteristics, of the root mean square (RMS) value of the fluctuating pressure. It is found that: the h function characteristics have a significant influence on the VSWT. The suitable functions are Hn function constructed in this paper and step function. For the left boundary of the magnified area, the step function can obtain the largest INB value, but the robustness is not good. The H1 function (Gaussian-like function, n = 1) can show higher robustness while ensuring a large INB value. The two computing strategies, which are single point strategy and global strategy, have their own advantages and disadvantages. The former strategy, that is the single point strategy, can achieve a higher INB value, but the RMS magnification at the feature position needs to be known in advance. Although the INB value obtained by the latter strategy, that is the global strategy, is slightly smaller than the calculation results of the former strategy, it is not necessary to know the RMS magnification at the feature position in advance. So the global strategy has better robustness. The experimental data of NACA0012 airfoil was used to further validate the developed VSWT in this paper, and the results show that the VSWT developed in this paper can still double the INB value of the transition/relaminarization position. The VSWT developed in this paper has certain practicability, which is convenient for the computer to automatically determine the transition/relaminarization characteristics.

Method of the Description of the Laminar-Turbulent Transition Position on a Swept Wing in the Flow with an Enhanced Level of Free-Stream Turbulence

A new experimental method for panoramic contactless determination of the laminar-turbulent transition position in a three-dimensional boundary layer is described. It is demonstrated that this method allows accurate determination of the transition region boundaries at both low and enhanced levels of free-stream turbulence.

Application of hot-film anemometry to resolve the unsteady boundary layer transition of a laminar airfoil experiencing limit cycle oscillations

The unsteady boundary layer behavior of a supercritical laminar airfoil model, which undergoes limit cycle oscillations in pitch, is investigated by the application of hot-film anemometry. The data basis is a 2D flutter experiment under transonic flow conditions. The laminar airfoil model was elastically mounted with a single degree of freedom in pitch and performed self-excited limit cycle oscillations at a Mach number of {text {Ma}}=0.73 and a Reynolds number of {text {Re}}approx 2times 10^6. An analysis of the hot-film signals on the basis of the quasi-wall shear stress is carried out, with which the boundary layer state for steady and unsteady flow is resolved. An algorithm is presented which allows an automated detection of the transition position, so that a correlation between airfoil motion and transition location movement can be quantified. A sudden movement of the boundary layer transition is observed at the upper and lower reversal points of the limit cycle oscillation, while in parts of the up- and downstroke of the laminar airfoil a shock-induced transition occurs. During the limit cycle oscillation, a delayed response of the boundary layer occurs, resulting in a significant phase lag between the movement of the boundary layer transition and the motion of the laminar airfoil.

Experimental study on effect of transverse groove with/without discharge hole on hypersonic blunt flat-plate boundary layer transition

Experiments are carried out on the <i>Φ</i>2 m Shock Tunnel (FD-14A) at the China Aerodynamics Research and Development Center to study the effect of the transverse groove with/without discharge hole on the hypersonic blunt flat-plate boundary layer transition, and the preliminary computational and theoretical research are carried out. The inflow Mach number of the test is 6, the unit Reynolds number is 3.3 × 10<sup>7</sup>/m, the leading edge radius of the flat-plate is 1 mm, and the angle of attack is –4°. Three different sets of two-dimensional transverse grooves are arranged at 110 mm away from the leading edge of the flat-plate. The width and depth of the grooves are, respectively, 2.5 mm and 1 mm for groove 1, 3.75 mm and 1.5 mm for groove 2, and 5 mm and 2 mm for groove 3, at the same time, both ends of the groove 1 can open the discharge hole (the discharge hole has a size of 2.5 mm × 5.0 mm and a width the same as that of groove 1). The discharge hole is denoted as the groove 4, and the smooth flat-plate when the groove is not included is denoted as groove 5 or the flat. The <i>Φ</i>2-mm-diameter cylindrical heat flux sensor is used to measure the heat flux distributions of the center line of the flat-plate under different conditions, and thus we can judge the transition of the boundary layer. The measurement results show that the smooth plate starts to transit at <i>x</i> ≈ 340 mm, and the transition is nearly completed at <i>x</i> ≈ 425 mm. The groove causes the transition position of the boundary layer of the plate to advance, and as the width and depth of the groove increase, the promoting effect on the transition is enhanced, and the transition position moves upstream. After the groove 1 is added to the discharge hole (groove 4), the heat flux distribution and the transition position are substantially the same as those of the smooth plate. After the boundary layer flow completely transits into turbulent flow, the difference in heat flux for each case is small, which indicates that the grooves of different specifications affect only the heat flux distribution in the transition process, but have little effect on the heat flux of the turbulent wall after the transition. The computational fluid dynamic results show that the discharge holes cause passive suction, and the test results show that the suction effect of the discharge holes at both ends of the groove counteracts the effect of the groove on the transition of the center line boundary layer, but it may be just a coincidence, and further research is needed. The linear stability theory (LST) and the optimal perturbation method are used to analyze the flow instability mechanism of the smooth blunt plate. The LST results show that there is no first mode instability nor second mode instability in the blunt plate flow. The modal instability mechanism cannot explain the observed transition in the test. The optimal disturbance calculation shows that the blunt plate flow suffers strong non-modal instability, which can qualitatively explain the observed transition phenomenon.