Circumferential Angle Research Articles

Twisted optical-fiber-based acousto-optic tunable filter controlled by the flexural acoustic polarization

The spectral characteristics of twisted fiber-based acousto-optic filters are theoretically investigated. The influences of three types of flexural acoustic polarization states — linear, circular, and elliptical polarizations — on filter spectra are studied under realistic experimental conditions: a fiber length of 5 – 20 cm and a circumferential fiber twist angle of 80 nm for a twist angle of 12π. We will describe how the transmission of each resonance peak can also be selectively tuned by adjusting the ellipticity of the input acoustic polarization from linear to circular. The results illustrate that our approach exploiting a combination of the fiber twist and acoustic polarization management offers an excellent route to the spectral shaping of all-fiber acousto-optic devices in that the transmission of multiple resonances, as well as their spectral positions, are readily and individually controllable in a single device configuration. In addition, we also propose a novel cosine apodization method to suppress the undesirable sidelobe spectra occurring between the dual resonance peaks. The technique is based on a cosine modulation of the AO coupling strength along the fiber, which is achieved by using a combination of the fiber’s circumferential twist and the linear acoustic polarization. The proposed scheme is useful to minimize the crosstalk occurring between adjacent resonance peaks. We highlight that our approach is directly applicable to matched filtering as robust, adaptable, stable, and versatile optical filters.

Registration of coronary arteries in computed tomography angiography images using Hidden Markov Model.

Computed tomography angiography (CTA) allows for not only diagnosis of coronary artery disease (CAD) with high spatial resolution but also monitoring the remodeling of vessel walls in the progression of CAD. Alignment of coronary arteries in CTA images acquired at different times (with a 3-7 years interval) is required to visualize and analyze the geometric and structural changes quantitatively. Previous work in image registration primarily focused on large anatomical structures and leads to suboptimal results when applying to registration of coronary arteries. In this paper, we develop a novel method to directly align the straightened coronary arteries in the cylindrical coordinate system guided by the extracted centerlines. By using a Hidden Markov Model (HMM), image intensity information from CTA and geometric information of extracted coronary arteries are combined to align coronary arteries. After registration, the pathological features in two straightened coronary arteries can be directly visualized side by side by synchronizing the corresponding cross-sectional slices and circumferential rotation angles. By evaluating with manually labeled landmarks, the average distance error is 1.6 mm.

Experimental study of jet impingement heat transfer on a variable-curvature concave surface in a wing leading edge

In this paper, extensive experimental investigation of the heat transfer characteristics of jet impingement on a variable-curvature concave surface in a wing leading edge was conducted for aircraft anti-icing applications. The experiments were carried out over a wide range of parameters: the jet Reynolds number, Rej, from 51,021 to 85,340, the relative tube-to-surface distance, H/d, from 1.736 to 19.76, and the circumferential angle of jet holes on the piccolo tube, θ, from −60° to 60°. In addition, jet impingements with single one, two and three rows of aligned jet holes were all investigated. Experimental results revealed the effects of various parameters on the performance and characteristics of jet impingement heat transfer in the specific structure adopted here, and our insufficient understanding on the corresponding physical mechanism was presented. It was found that the jet impingement heat transfer performance was enhanced with the increase of jet Reynolds number. For single one row of jet holes, an optimal H/d of 4.5 was determined under Rej=51,021 and d=2mm, for which the jet impingement achieved the best heat transfer performance. For two and three rows of aligned jet holes, the Nux curves in the chordwise direction exhibited much different shapes due to different intensity of the interference between adjacent air jets. This work contributes to a better understanding of the jet impingement heat transfer on a concave surface in a wing leading edge, which can lead to optimal design of the aircraft anti-icing system.

On the collapse resistance of multilayer cemented casing in directional well under anisotropic formation

In this paper, the mechanical characteristics of a multilayer cemented casing system in directional well under anisotropic formation have been presented to investigate the collapse resistance of casing under non-uniform in-situ stress. The model has considered the deviation angle, azimuth angle and the formation transverse anisotropy simultaneously. During analysis, the original in-situ stress tensor has been transformed into three stress tensors through the conversion of coordinate and stress decomposition based on the elastic mechanics. The formation mechanical parameters (Young's modulus and Poisson's ratio) have been taken as a function of wellbore circumferential angle during analysis procedure. In addition, a simplified model has been analyzed to verify the correctness of the method proposed in this paper. Subsequently, the stress distributions of the system have been obtained through solving the governing equations. On this basis, the influences of geometric parameters and mechanical parameters on the casing collapse resistance have been discussed to acquire a comprehensive understanding of this problem. Finally, some significant conclusions have been drawn based on the discussion mentioned above.

Distinguishable circumferential inclined direction tilt sensor based on fiber Bragg grating with wide measuring range and high accuracy

One novel distinguishable circumferential inclined direction tilt sensor is demonstrated by incorporating two strain sensitivity fiber Bragg gratings (FBGs) with two orthogonal triangular cantilever beam and using one fiber Bragg grating (FBG) as temperature compensation element. According to spatial vector and space geometry, theory calculation model of the proposed FBG tilt sensor which can be used to obtain the azimuth and tile angle of the inclined direction is established. To obtain its measuring characteristics, calibration experiment on one prototype of the proposed FBG tilt sensor is carried out. After temperature sensitivity experiment data analysis, the proposed FBG tilt sensor exhibits excellent temperature compensation characteristics. In 2-D tilt angle experiment, tilt measurement sensitivities of these two strain sensitivity FBGs are 140.85°/nm and 101.01°/nm over a wide range of 60º. Further, azimuth and tile angle of the inclined direction can be obtained by the proposed FBG tilt sensor which is verified in circumferential angle experiment. Experiment data show that relative errors of azimuth are 0.55% (positive direction) and 1.14% (negative direction), respectively, and relative errors of tilt angle are all less than 3%. Experiment results confirm that the proposed distinguishable circumferential inclined direction tilt sensor based on FBG can achieve azimuth and tile angle measurement with wide measuring range and high accuracy.

A CNC grinding method and envelope residual model for face gear

This paper proposes a grinding method for face gears with CNC machines. Interpolation formulas of CNC linkage are deduced based on a five-coordinate machine tool. An analytical model for predicting envelope residual when grinding face gears based on grinding disc wheel is developed. The generating laws of envelope residual for the envelope manner are investigated. The influence of tool feed magnitude on surface envelope residuals is analyzed in circumferential angle direction. The maximum envelope residual increases nonlinearly with incremental angle. A grinding experiment is performed on a CNC grinding machine. The tooth surface deviation indicates that the CNC grinding method is efficient. The variation trends of different feed magnitudes along circumferential angle direction coincide with the simulation results. Finally, the values of envelope residuals are verified by an envelope simulation with software AutoCAD. The study provides an effective approach for parameter selection of highly precise and efficient grinding of face gear.

Numerical investigation of performance of a fast gas–solid separator

In this study, the performance of a fast gas–solid separator was simulated based on the commercial software Fluent 6.2. The tangential velocity dominated the three-dimensional gas velocity, and decreased with the increase of the circumferential angle and radial position. In the separator housing, the swirling gas flow is similar to a modified or quasi free vortex. In the gas outlet tube, gas swirls with a rotation direction reverse to that in the separator housing. The ratio of circulation gas flow rate over the inlet gas flow rate changed only slightly with the increase of the inlet gas velocity, remaining at approximately 0.49. There was a stagnant particle layer on the separator base, inducing particle re-entrainment by circulation gas. In the present study, the separation efficiency of fine particles decreased with increasing inlet gas velocity, approximately remaining a constant as the particle diameter is greater than 12.5μm.

Modal expansion analysis of nonlinear circumferential guided wave propagation in a circular tube

Within the second-order perturbation approximation, the nonlinear effect of primary circumferential guided wave propagation in a circular tube is investigated using modal expansion analysis for waveguide excitation. The nonlinearity of the wave equation governing the wave propagation ensures the second-harmonic generation accompanying primary circumferential guided wave propagation. This nonlinearity may be treated as a second-order perturbation of the linear elastic response. The fields of the second harmonics of primary circumferential guided wave propagation are considered as superpositions of the fields of a series of double frequency circumferential guided wave (DFCGW) modes. Based on the momentum theorem and mathematical formulae of nonlinear stress tensor and its divergence under the cylindrical coordinate system, the mathematical expressions of the corresponding double frequency traction stress tensors and bulk driving forces are deduced for a certain primary circumferential guided wave mode. Subsequently, the equation governing the DFCGW mode expansion coefficient is established. Finally, the mathematical expression of second-harmonic field of the primary circumferential guided wave mode in a tube is derived. The results of the theoretical analyses and numerical calculations indicate that the degree of cumulative growth of the DFCGW mode with circumferential angle is obviously influenced by that of phase velocity matching between the primary and double frequency wave modes. It is found that the amplitude of the DFCGW mode can grow with circumferential angle when its phase velocity matches with that of the primary circumferential guided wave, and that the amplitude of the DFCGW mode will show a beat effect with circumferential angle when its phase velocity is not equal to that of the primary wave mode. The DFCGW mode, whose phase velocity matches with that of the primary wave mode, plays a dominant role in the field of second harmonic generated by the primary wave mode propagation, and the contribution of the other DFCGW modes to the said second-harmonic field is negligible after the primary wave mode has propagated some circumferential angle.

Soft Sensor for Oxide Scales on the Steam Side of Superheater Tubes under Uneven Circumferential Load

A soft sensor for oxide scales on the steam side of superheater tubes of utility boiler under uneven circumferential loading is proposed for the first time. First finite volume method is employed to simulate oxide scales growth temperature on the steam side of superheater tube. Then appropriate time and spatial intervals are selected to calculate oxide scales thickness along the circumferential direction. On the basis of the oxide scale thickness, the stress of oxide scales is calculated by the finite element method. At last, the oxide scale thickness and stress sensors are established on support vector machine (SMV) optimized by particle swarm optimization (PSO) with time and circumferential angles as inputs and oxide scale thickness and stress as outputs. Temperature and stress calculation methods are validated by the operation data and experimental data, respectively. The soft sensor is applied to the superheater tubes of some power plant. Results show that the soft sensor can give enough accurate results for oxide scale thickness and stress in reasonable time. The forecasting model provides a convenient way for the research of the oxide scale failure.

周方向表面欠陥を有する管の欠陥評価に用いる安全率

In order to prevent failure of piping, limitation on flaw depth according to the circumferential flaw angle is prescribed in the Fitness-For-Service Codes (FFS Codes) of the Japan Society of Mechanical Engineers (JSME). First, the applicability of the limit load assessment method was examined when the flaw angle was large. Then, the influence of the crack growth estimation and flaw sizing errors on the reliability of the flaw evaluation was examined. Since the limit load assessment method can predict plastic collapse strength of a flawed pipe appropriately irrespective of a flaw angle, it is applicable to flaw evaluation even if a flaw angle becomes large. However, precision of flaw evaluation much depends on the variation of the material strength (flow stress) and the flaw size measurement error. Probabilistic analyses considering these variations were performed and influence on failure probability of a pipe was evaluated quantitatively. As a result, the simplified method for evaluating the safety factors according to those variations and satisfying target reliability was proposed. The proposed methods give the flaw evaluation result which has equivalent reliability irrespective of a flaw angle.

Fluid–Structure Interaction of an Elastically Mounted Slender Body at High Incidence

A numerical study of the fluid–structure interaction of an inclined tangent ogive-cylinder rigid body, mounted on torsion springs that can rotate in the pitching, yawing, and rolling directions, is conducted. The body is subjected to three-dimensional compressible laminar flow at a Reynolds number of 30,000 and a Mach number of 0.2. A second-order implicit finite difference scheme is employed for the flow equations, adapted to a curvilinear coordinate system, whereas the coupled structural equations, written using an Euler angle notation, are solved by a fourth-order Runge–Kutta method. A detailed investigation of two angles of attack, and , is described. For a fixed body at , the yaw moment changed smoothly with the location of the circumferential disturbance, whereas at the yaw moment was characterized by an almost square-wave variation behavior with bifurcation points at disturbance circumferential roll angles , , and . For an elastically mounted body, the response at for all disturbance locations resulted in large-amplitude periodic yawing and pitching moments. The response at resulted in large-amplitude moments, which occurred only for disturbance locations that coincided with the bifurcation points of the fixed body. The response at the bifurcation points was found to be quasi-periodic for , periodic for , and nonstationary for .

Numerical investigation on characteristics of falling film in horizontal-tube falling film evaporator

Horizontal-tube falling film technology is widely used in multi-effect desalination plant. The film characteristics of falling water film outside the tubes in horizontal-tube falling film evaporator were simulated. The numerical result was compared with the experimental result and they were proven with good agreement. The film thickness distribution at different Reynolds number and different circular angle had been investigated. Also, the effects of liquid flow rate and tube diameter on the film thickness distribution were discussed in detail. Numerical simulation result shows that, with the increase in Reynolds number, the falling film thickness at a certain circumferential angle increases with almost linear growth rate, and the thinnest film at the surface of the tube appears at the angle of about 120°. The result also indicates that the local dry out spot on the surface of the tube would occur when the fluid flow rate decreases to a certain value. In addition, the film thickness decreases with the increase in the tube diameter at a fixed fluid flow rate.

Effects of age on the physiological and mechanical characteristics of human femoropopliteal arteries

Surgical and interventional therapies for peripheral artery disease (PAD) are notorious for high rates of failure. Interactions between the artery and repair materials play an important role, but comprehensive data describing the physiological and mechanical characteristics of human femoropopliteal arteries are not available. Fresh femoropopliteal arteries were obtained from 70 human subjects (13–79years old), and in situ vs. excised arterial lengths were measured. Circumferential and longitudinal opening angles were determined for proximal superficial femoral, proximal popliteal and distal popliteal arteries. Mechanical properties were assessed by multi-ratio planar biaxial extension, and experimental data were used to calculate physiological stresses and stretches, in situ axial force and anisotropy. Verhoeff–Van Gieson-stained axial and transverse arterial sections were used for histological analysis. Most specimens demonstrated nonlinear deformations and were more compliant longitudinally than circumferentially. In situ axial pre-stretch decreased 0.088 per decade of life. In situ axial force and axial stress also decreased with age, but circumferential physiological stress remained constant. Physiological circumferential stretch decreased 55–75% after 45years of age. Histology demonstrated a thickened external elastic lamina with longitudinally oriented elastin that was denser in smaller, younger arteries. Axial elastin likely regulates axial pre-stretch to help accommodate the complex deformations required of the artery wall during locomotion. Degradation and fragmentation of elastin as a consequence of age, cyclic mechanical stress and atherosclerotic arterial disease may contribute to decreased in situ axial pre-stretch, predisposing to more severe kinking of the artery during limb flexion and loss of energy-efficient arterial function.

Analysis of the Temperature Evolution during Lined Pipe Welding

A numerical analysis of thermal phenomena occurring during lined-pipe welding is presented in this paper. Numerical models of surfaces and volumetric heat sources were used to predict the time evolution of the temperature field both in a corrosion-resistance-alloy (CRA) liner, made of SUS304 stainless steel (SS), and for the single-pass girth welding of a carbon-manganese (C-Mn) steel pipe. Using the finite-element code ABAQUS, three-dimensional non-liner heat-transfer analyses was carried out to simulate the gas-tungsten-arc (GTA) welding process used in liner welding and the metal-inert-gas (MIG) welding process consumed in C-Mn steel backing welding. FORTRAN user subroutines were coded to implement the movable welding heat source and heat transfer coefficient models. The thermal history was numerically computed at locations where circumferential angles from the welding start/atop position are 90°, 180° and 270° with respect to axial distances from the weld centerline (WC). Keywords: Finite element analysis FEA, CRA Liner, C-Mn steel backing, Heat source, Thermal history.

Investigation on the placement effect of UHF sensor and propagation characteristics of PD-induced electromagnetic wave in GIS based on FDTD method

Using ultra-high-frequency (UHF) method in practical partial discharge (PD) detection can be affected by the positioning and placement of the UHF sensor. This in turn can affect the PD diagnosis. To ensure optimal performance of the sensor and understand the propagation process of electromagnetic (EM) wave, there is a need to fully analyze how the sensor's placement affects the output signal and the attenuation of EM wave in various positions and directions. As the previous researches are mainly concentrating on the radial component of the UHF signal, the propagation of the signal components in axial and radial directions and that perpendicular to the radial direction of the GIS tank are investigated in detail in this paper. Firstly, the attenuation of UHF signals at different radial positions of a GIS model is analyzed using the finite difference time domain (FDTD) method. Then, secondly, the coupled signals in the three directions are calculated respectively. By comparing the signal received for different directions and circumferential angles, the peak to peak value (Vpp) and cumulative energy of the coupled voltage in each case are considered both in the time and frequency domain. As well, the attenuation characteristics and rules are summarized, based on which a new method for circumferential and axial location is proposed. The investigation on the propagation and the detection mechanism of EM wave in GIS provides a significant understanding of the application of UHF sensor and actual PD detection.

Three-dimensional finite element welding residual stress analysis of penetration nozzles: I – Sensitivity of analysis variables

This paper investigates effects of variables related to 3-D finite element welding residual stress analyses of penetration nozzles on residual stresses. Five variables are considered; (i) number of elements in the circumferential direction, (ii) number of beads in the circumferential direction, (iii) kinematic boundary conditions, (iv) circumferential modelling angle in 3-D finite element models and (v) detailed weld shape. Based on sensitivity analysis results, guidelines for 3-D finite element welding residual stress analyses of penetration nozzles are provided.

Analysis of pressure fluctuations induced by multi‐horizontal submerged jets in the novel jet tank

AbstractBy means of detrending moving average and rescaled range analysis, the multifractal characteristics of the pressure fluctuation rate series (PFRS) derived from instantaneous fluctuations signals (PFS) in circulating jet tank (CJT) were investigated and the criteria of different scales were established. The central parts of the probability density functions of PFRS were exponentially distributed, and the positive part decayed slower than the negative part. The existence of multifractal characteristics of PFRS under different circumferential angles had been confirmed by both the strong q‐dependence of generalised Hurst exponents and continuous wavelet decompositions. The high frequency Hurst exponents based on rescaled range analysis were all >0.66 with the changing Re, which presented that PFRS had the long‐range dependence and aperiodicity. The local fractal dimensions declined with the increasing scales and presented the same trend at different dimensionless radial positions r/R0. The decomposed fluctuation components at scale a = 1–4 had different local fractal dimensions which revealed that the fluid flow was more complicated. The fluctuation energy profiles of PFRS indicated that the instantaneous pressure fluctuations were dominated by the interaction between macro‐scale vortexes and liquid phase.

Experimental and numerical investigations on slot air jet impingement cooling of a heated cylindrical concave surface

Experimental and numerical studies have been carried out for slot air jet impingement on a heated concave surface of a partially opened-top horizontal cylinder of length L = 20 cm. The slot jet is situated at the symmetry line of the partially opened-top cylinder along the gravity vector and impinges to the bottom of the cylinder which is designated as θ = 0°. The width of the opening at the top of the horizontal cylinder is W = 3 cm which corresponds to a circumferential angle Δθ = 50.8°. The experiments are performed by a Mach–Zehnder interferometer which enables to measure the local convection heat transfer coefficient. Also, a finite volume method based on the SIMPLE algorithm and non-orthogonal grid discretization scheme is used to solve the continuity, momentum, and energy equations. The Poisson equations are solved for (x, y) to find the grid points which are distributed in a non-uniform manner with higher concentration close to the solid regions. The effects of jet Reynolds number (Rej) in the range from 190 to 1,600 and the ratio of spacing between nozzle and cylinder surface to the jet width from H = 1.5 to H = 10.7 on the local and average Nusselt numbers are examined. It is observed that maximum Nusselt number occurs at the stagnation point at (θ = 0°) and the local heat transfer coefficient decreases on the circumferential surface of the cylinder with increase of θ as a result of thermal boundary layer thickness growth. Also results show that the local and average heat transfer coefficients are raised by increasing the jet Reynolds number and by decreasing the nozzle-to-surface spacing.

Three-dimensional circular various weave patterns in woven preform structures

The aim of this study was to develop three-dimensional (3D) fully interlaced representative circular woven preform structures and to understand the effects of weave pattern and number of layers on 3D circular woven structures. Various 3D circular woven preforms were developed. Data generated from these structures included yarn-to-yarn space, density, yarn angle, yarn length and crimp. It was shown that the weave patterns affected the 3D circular woven preform structures. The yarn-to-yarn spaces in the 3D fully interlaced circular structures were high compared to the traditional 3D orthogonal circular woven structures in fabric circumference (fabric outside surface) due to the interlacement of the yarn sets. The 3D plain, twill and satin structures resulted in axial angle (θ a) in fabric length; circumferential angle (θ c), and interlaced radial angle (θ ri) in fabric circumference and fabric diameter due to the axial-circumferential and axial-radial interlacements. The weave patterns slightly affected the yarn angles. On the other hand, it was observed that the number of layers considerably affected the radial arc length and the radial length in wall thickness in the 3D circular woven structure. The interlacement on 3D plain, twill and satin circular woven structures resulted in axial crimp, circumferential crimp and radial crimp. The crimps in the 3D fully interlaced circular woven structures slightly depended on the types of weave pattern and the number of layers.

Pressure of Newtonian fluid flow through curved pipes and elbows

Under conditions of high temperature and high pressure, the non-uniformity of pressure loads has intensified the stress concentration which impacts the safety of curved pipes and elbows. This paper focuses on the pressure distribution and flow characteristic in a curved 90° bend pipe with circular cross-sections, which are widely used in industrial applications. These flow and pressure characteristics in curved bend pipes have been researched by employing numerical simulation and theoretical analysis. Based on the dimensionless analysis method a formula for the pressure of Newtonian fluid flow through the elbow pipes is deduced. Also the pressure distributions of several elbows with different curvature ratio R/D are obtained by numerical methods. The influence of these non-dimensional parameters such as non-dimensional curvature ratio, Reynolds number and non-dimensional axial angle α and circumferential angle β on the pressure distribution in elbow pipes is discussed in detail. A number of important results have been achieved. This paper provides theoretical and numerical methods to understand the mechanical property of fluid flow in elbow pipes, to analyze the stress and to design the wall thickness of elbow pipes.