Amplitude Angle Research Articles

Finite obstacle effect on the aerodynamic performance of a hovering wing

The finite obstacle effect on the aerodynamic performance of a normal hovering wing is studied using the immersed boundary method. Phenomena of a two-dimensional wing hovering above, under, or on the side of a circular obstacle are presented. Parameters including obstacle size, distance, location, and flapping angle are investigated to study how the aerodynamic force and flow field are affected. The diameter of the obstacle ranges from 0.5c to 12c and the distance between the centroid of the wing and obstacle surface from 0.5c to 6c (c is the wing chord length). Previous observations of ground effects including force enhancement, reduction, and recovery occur similarly when the wing hovers above the obstacle of diameter greater than 2c. However, finite obstacles affect the aerodynamic performance differently when the size shrinks to a critical value. Force drops when the wing moves close and rises when moving away, opposite to the ground effect. As flapping angle amplitude increases, the force change tends to be consistent for different-sized obstacles. The top or side effect shows a different influence on the force change. Force monotonically increases as the distance decreases when the wing hovers under the obstacle. The side effect places a less important factor on the aerodynamic performance. All force changes under such circumstance are less than 13% referring to nonobstacle result. The gap between the leading or trailing edge of the wing and obstacle surface plays a significant role in the leading and trailing edge vortices generating, shedding, and pairing, which greatly affects the force change.

Overview of High Energy String Scattering Amplitudes and Symmetries of String Theory

In this paper, we studied symmetries of string scattering amplitudes in the high energy limits of both the fixed angle or Gross regime (GR) and the fixed momentum transfer or Regge regime (RR). We calculated high energy string scattering amplitudes (SSA) at arbitrary mass levels for both regimes. We discovered the infinite linear relations among fixed angle string amplitudes and the ifinite recurrence relations among Regge string amplitudes. The linear relations we obtained in the GR corrected the saddle point calculations by Gross, Gross and Mende. In addition, for the high energy closed string scatterings, our results differ from theirs by an oscillating prefactor which was crucial to recover the KLT relation valid for all energies. We showed that all the high energy string amplitudes can be solved using the linear or recurrence relations, so that all the string amplitudes can be expressed in terms of a single string amplitude. We further found that, at each mass level, the ratios among the fixed angle amplitudes can be extracted from the Regge string scattering amplitudes. Finally, we reviewed the recent developments on the discovery of infinite number of recurrence relations valid for all energies among Lauricella SSA. The symmetries or relations among SSA at various limits obtained previously can be exactly reproduced. It leads us to argue that the known S L ( K + 3 , C ) dynamical symmetry of the Lauricella function may be crucial to probe spacetime symmetry of string theory.

Study on the influence of pumping system on the hydrodynamic performance of air tanker

The influence of the pumping system on the hydrodynamic performance of the air tanker were investigated in this paper. The hydrodynamic performance of the air tanker with different displacements under the different Froude numbers was studied by experimental method. RANS methods and overset mesh were used to compute the viscous flow field of an air tanker under three conditions at different Froude numbers. Numerical method adopted in this paper was verified and validated by comparing the experimental results with the simulation results. The experimental results showed that the total resistance and the heave amplitude of air tanker with different displacements increased, while the pitch angle decreased, as the speed increased. And the larger the displacement, the greater the total resistance, pitch angle and heave amplitude. The simulation results showed that the drainage efficiency, the load of the baler and the additional pitching moment showed non-linear growth with increasing speed. As the baler lowered, the total resistance and heave amplitude of the aircraft increased, but the pitch reduced. The effect on the hydrodynamic performance of air tanker was not obvious as the baler closed.

Multiaxial cyclic behaviour of extruded and forged AZ80 Mg alloy

The quasi-static and cyclic response of as-extruded and closed-die extruded-forged AZ80 Mg alloy forged at 250 °C and 20 mm/sec was investigated. Servo hydraulic, fully reversed, strain controlled uniaxial “push-pull”, pure torsion, and biaxial fatigue testing were also conducted on the closed-die forged alloy. Two uniaxial loading paths (pure axial and pure shear) and three different biaxial loading paths were investigated (proportional loading, and non-proportional loading at phase angles of 45° and 90°). After forging of the as-extruded billet, the yield stress in the axial direction increased by 46%, the failure elongation by 35% and the ultimate strength by 13%. The spatial variation in both the local texture, microstructure and superficial hardness throughout the cross section of the forging was investigated and discussed. The web region in the center of the forged billet exhibited a virtually fully recrystallized and refined microstructure with intense basal texture, whereas the rib regions on each side exhibited a partially recrystallized and coarser microstructure with less intense texture. The fatigue life of the forged material in the axial direction showed dramatic improvement relative to the as-extruded material at strain amplitudes which were less than 0.35%. However, at higher strain amplitudes, there are significantly higher cyclic stresses (and associated fatigue damage) in the forged material (relative to the as-extruded), resulting in a decrease in life under fully reversed strain controlled fatigue loading. For the pure axial strain path, the total amount of strain energy density (SED) observed in the stabilized response was a function of number of cycles only, and was insensitive to material condition (as-extruded or forged). However, for the forged material, of all the strain paths investigated, only the pure shear path demonstrated a significantly different relationship of total SED vs. life. Furthermore, the amount of total SED for a given number of cycles decreases when biaxial loading is introduced, though following the same general relationship as the pure axial strain path. The effect of a decrease in total SED for a given number of cycles occurred in all biaxial strain paths, with proportional being the least prominent, then 45° and 90° out of phase being progressively more pronounced respectively. Both the Smith Watson Topper (SWT) and Jahed-Varvani (JV) models were utilized to predict the fatigue life of the uniaxial and biaxial cyclic tests. Calibration of each models intrinsic parameters were done using both of the uniaxial loading paths individually, then these same parameters were used in combination with one another to predict the life in the biaxial cases. Both the SWT and JV models are capable of giving an acceptable prediction, however the JV model’s prediction is more reliable, especially when the cyclic response has pronounced asymmetry. The biaxial fatigue response is somewhat dominated by the axial component for two significant reasons; firstly, the shape of the hysteresis in the shear direction dramatically changes based on phase angle and axial strain amplitude, whereas the axial hysteresis loop remains somewhat invariant to the presence or modulation of the other loading axis. Secondly, the initial crack propagation mode is predominantly transverse to the axial direction in all strain paths except for pure shear (which exhibits longitudinal cracking). Tensile cracking dominating the biaxial failure mode provides qualitative justification of a modification factor to an existing energy based biaxial fatigue life prediction model, enabling it to predict the life of extruded and forged AZ80 Mg reliably for a variety of different biaxial strain paths.

A 2D model for analysis of rain-wind induced vibration of stay cables

Rain-wind induced vibration of stay cables (RWIV) in cable-stayed bridges is a special aerodynamic phenomenon as it is easy to be influenced by many factors, especially velocity and impact angle of wind. This paper proposes a new assumption of the impact angle of wind on the cable in analyzing cable vibration response subjected to wind and rain. This angle is considered as a harmonic oscillation function around the equilibrium position that is the initial angle of impact, and its angular frequency equals of the rivulet and the cable. The amplitude of impact angle of wind depends on wind velocity, initial position and that of rivulet. The assumption is verified by comparison with experimental results. The effects of rivulet oscillation components and aerodynamic forces are also discussed in this paper.
 Keywords: cable; rain-wind induced vibration; rivulet; analytical model; vibration.

Effect of Slat and Gap Width of Slatted Concrete Flooring on Sow Gait Using Kinematics Analysis.

Simple SummaryThe housing of gestating sows is currently moving from individual stalls to group housing in most Western countries. If the design of slatted concrete floors was well studied for smaller animals such as finishing pigs, less information is available for sows. Slatted concrete floors can have negative effects on sow health, especially in connection with lameness. The aim of this study was to determine the optimal slat and gap widths of slatted concrete floors for the ease of movement of sows. After testing several combinations of slat and gap widths and quantifying the gait of walking sows using kinematics analysis, we determined that the usual 25-mm gap/125-mm slat commonly used in North America may not be optimal to facilitate the ease of movement of sows. In particular, sows’ gait was less affected by smaller gap widths. Further research is now necessary to assess the impact of floor design on behavior, lameness occurrence, performances and longevity of sows.The housing of gestating sows in groups requires sound information about the adapted design of the pen floor. Slatted concrete floors are commonly used for effective drainage of manure but can cause feet injuries and lameness. In the present study, kinematics were used to characterize the gait of 12 gilts and 12 lame sows walking in a corridor on slatted concrete floors with different combinations of slat (85, 105 or 125 mm) and gap (19, 22 or 25 mm) widths. The nine experimental floors were tested with slats in the perpendicular and parallel orientation to the direction of animal walk, according to a duplicated lattice design. Gait parameters were quantified using spatial, temporal and angular kinematics for front and rear limbs. Some parameters were significantly affected by the treatments (p < 0.05), but the effects differed between gilts and lame sows and between slat orientations. Gap width had a significant effect on parameters such as back angle, stride length, foot height, and carpal and tarsal joint angle amplitudes. Slat width significantly affected parameters such as foot height, and carpal and tarsal joint angle amplitudes. Comparisons of the different combinations of slat and gap widths revealed that slats with a width of 105–125 mm and gap width of 19–22 mm had the least effect on the gait characteristics of the gilts and sows.

Energetics and mixing in buoyancy-driven near-bottom stratified flow

Turbulence and mixing in a near-bottom convectively driven flow are examined by numerical simulations of a model problem: a statically unstable disturbance at a slope with inclination $\unicode[STIX]{x1D6FD}$ in a stable background with buoyancy frequency $N$ . The influence of slope angle and initial disturbance amplitude are quantified in a parametric study. The flow evolution involves energy exchange between four energy reservoirs, namely the mean and turbulent components of kinetic energy (KE) and available potential energy (APE). In contrast to the zero-slope case where the mean flow is negligible, the presence of a slope leads to a current that oscillates with $\unicode[STIX]{x1D714}=N\sin \unicode[STIX]{x1D6FD}$ and qualitatively changes the subsequent evolution of the initial density disturbance. The frequency, $N\sin \unicode[STIX]{x1D6FD}$ , and the initial speed of the current are predicted using linear theory. The energy transfer in the sloping cases is dominated by an oscillatory exchange between mean APE and mean KE with a transfer to turbulence at specific phases. In all simulated cases, the positive buoyancy flux during episodes of convective instability at the zero-velocity phase is the dominant contributor to turbulent kinetic energy (TKE) although the shear production becomes increasingly important with increasing $\unicode[STIX]{x1D6FD}$ . Energy that initially resides wholly in mean available potential energy is lost through conversion to turbulence and the subsequent dissipation of TKE and turbulent available potential energy. A key result is that, in contrast to the explosive loss of energy during the initial convective instability in the non-sloping case, the sloping cases exhibit a more gradual energy loss that is sustained over a long time interval. The slope-parallel oscillation introduces a new flow time scale $T=2\unicode[STIX]{x03C0}/(N\sin \unicode[STIX]{x1D6FD})$ and, consequently, the fraction of initial APE that is converted to turbulence during convective instability progressively decreases with increasing $\unicode[STIX]{x1D6FD}$ . For moderate slopes with $\unicode[STIX]{x1D6FD}&lt;10^{\circ }$ , most of the net energy loss takes place during an initial, short ( $Nt\approx 20$ ) interval with periodic convective overturns. For steeper slopes, most of the energy loss takes place during a later, long ( $Nt&gt;100$ ) interval when both shear and convective instability occur, and the energy loss rate is approximately constant. The mixing efficiency during the initial period dominated by convectively driven turbulence is found to be substantially higher (exceeds 0.5) than the widely used value of 0.2. The mixing efficiency at long time in the present problem of a convective overturn at a boundary varies between 0.24 and 0.3.

BASELINE PLASMA THROMBOELASTOGRAPHY IN KEMP'S RIDLEY (LEPIDOCHELYS KEMPII), GREEN (CHELONIA MYDAS) AND LOGGERHEAD (CARETTA CARETTA) SEA TURTLES AND ITS USE TO DIAGNOSE COAGULOPATHIES IN COLD-STUNNED KEMP'S RIDLEY AND GREEN SEA TURTLES.

Cold-stunning in sea turtles is a frequent natural cause of mortality and is defined as a hypothermic state due to exposure to water temperatures <12°C. Derangements of biochemistry and hematology data by cold stunning have been well documented, although the effects on coagulation have not yet been investigated. The objectives of this study were to characterize the hemostatic state of non-cold-stunned sea turtles and to compare cold-stunned sea turtles at admission and after successful rehabilitation via a sea turtle-specific thromboelastography (TEG) protocol. TEG enables evaluation of the entire coagulation process, and the methodology has recently been established in sea turtles. Initially, 30 wild and apparently healthy sea turtles were sampled as controls: loggerhead sea turtles (Caretta caretta), n =17; Kemp's ridley sea turtles (Lepidochelys kempii), n = 8; and green turtles (Chelonia mydas), n = 5. In addition, paired TEG samples were performed on 32 Ch. mydas and 14 L. kempii at admission and prerelease after successful rehabilitation from cold stunning. Statistically significant differences in reaction time, kinetics, angle, and maximum amplitude parameters in L. kempii and Ch. mydas species demonstrated that the time taken for blood clot formation was prolonged and the strength of the clot formed was reduced by cold stunning. These findings indicate that cold stunning may cause disorders in hemostasis that can contribute to the severity of the condition. Early diagnosis of coagulopathies in the clinical assessment of a cold-stunned sea turtle may influence the treatment approach and clinical outcome of the case.

Air damping of high performance resonating micro-mirrors with angular vertical comb-drive actuators

The maximum scan angle amplitude of resonating micro-mirrors, intended for micro-projection display applications is limited by air damping. Three-dimensional transient Navier–Stokes (N–S) simulations are performed to analyse the fluid flow interactions with a high frequency scanning micro-mirror driven by angular vertical comb (AVC) actuators. The time-dependent damping moment contributions due to viscous shear and pressure drag are subsequently computed for both the mirror plate and comb-drive structures. A computational-efficient N–S model of the AVC structure, based on the sliding mesh technique available in ANSYS Fluent, is proposed. The effect of scan angle amplitude on the damping moment and the flow regime surrounding the oscillating micro-mirror plate is analysed in detail. It is shown that the simplified damping models applicable to resonant MEMS devices are not valid within the operating range of high performance micro-scanners. From dynamic mesh N–S simulations, the effect of the underlying mirror cavity wall on pressure drag damping is also evaluated. Good qualitative agreement in the overall quality factor is achieved between simulation and measurement results.

Thromboelastography Parameters Are Associated with Cirrhosis Severity.

Coagulopathy in cirrhosis represents complex coagulation derangements, and thromboelastography (TEG) measures these complex derangements. We sought to evaluate associations between TEG parameters and validated measures of cirrhosis severity, which have not been previously investigated. Adults with cirrhosis undergoing liver transplant (LT) were identified. Patients had TEG drawn immediately prior to LT. TEG parameters included reaction time (R), kinetic time (K), alpha angle (α), and maximum amplitude (MA). The validated measures of cirrhosis severity were MELD-Na and clinical stage of cirrhosis (classified using history of varices, variceal bleeding, or ascites). Multivariable linear and logistic regression analyses were conducted to evaluate the associations between TEG and stage of cirrhosis and MELD-Na. Among 164 patients with cirrhosis, advancing stage of cirrhosis was associated with more hypocoagulable TEG parameters including longer K-time (p = 0.05) and lower MA (p < 0.001). Similarly, with increasing MELD-Na quartiles, K-time was longer (p < 0.001), and both MA and α-angle decreased (p < 0.001, for both). Variceal bleeding within 6weeks prior to LT was associated with longer R-times (p = 0.02), longer K-times (p = 0.04), smaller α-angle (p = 0.03), and lower MA (p = 0.01). On multivariable analyses, decreasing MA remained statistically significantly associated with advancing stage of cirrhosis and increasing MELD-Na, after adjusting for multiple covariates including platelet count, (p = 0.02 and p < 0.0001, respectively). Hypocoagulable TEG measurements are associated with advancing stage of cirrhosis and increasing MELD-Na among patients with cirrhosis. These data indicate that TEG, as an informative measure of complex hemostatic function, may be a useful objective marker of liver disease severity in cirrhosis.

Practical Adaptation of a Low-Cost Voltage Transducer with an Open Feedback Loop for Precise Measurement of Distorted Voltages.

This paper presents the project proposal of a low-cost transducer with a Hall-effect sensor placed in a ferromagnetic core’s air gap, which enables the measurement of the distorted voltage instantaneous values without the feedback loop used for measurements in electrical machines. The presented transducer allows for electrical separation between the measured voltage and the voltage at the output. Moreover, the influences of frequency, additional resistance, and the reactance of the winding circuit on the voltage phase shift caused by winding inductance with ferrite core and amplitude are discussed. The result of simulating leakage inductance of measuring winding with ferrite core with an air gap is calculated using finite element analysis. Experimental investigations of the voltage phase shift angle and output voltage amplitude drop for the voltage transducers with an open feedback loop are carried out, taking into account the linear core magnetization characteristic.

Effect of sudden change in free stream velocity on the wind turbine airfoil performance based on boundary element method

In this study, the aerodynamic effects of sudden change in magnitude of incident velocity are investigated in detail for wind turbine airfoils. For this purpose, the unsteady panel method which is based on two-dimensional singularity approach has been developed. The model is first validated via using both the analytical functions and experimental data. The jump in free-stream velocity has been supposed to be applied in two different cases. The first is the airfoil at initially steady state and the second is the airfoil experiencing sinusoidal free-stream velocity. For both cases, the parametric study has been performed consequently investigating the effects of velocity difference magnitude, phase angle, airfoil characteristic and relative velocity oscillation amplitude. The response pattern of lift coefficient is shown to be a combination of three distinct behaviors: an initial jump, a secondary fall and a damped like envelope. The results showed that when the sudden velocity change is being applied on steady case, the time constant of recovery is finite and limited, while for the oscillatory case, the recovery time scale is considerably increased. Moreover, the local change in the normalized lift coefficient seems to be less than 0.3 for the steady case, while it can rise to 0.9 in dynamic oscillatory case. The magnitude of overshoot and undershoot has meaningful correlation with both relative velocity change and the initial phase in which the change occurs.

Comparison of immediate effects of sling-based manual therapy on specific spine levels in subjects with neck pain and forward head posture: a randomized clinical trial

Purpose: Forward head posture is identified as the flexion of the lower cervical spine along with the extension of the upper cervical spine, with an overall increase in the cervical curve. This study aimed to compare the immediate effect of upper-cervical level and cervicothoracic junction level manual therapy on head posture, cervical range of motion and muscle activity of the subjects with forward head posture.Methods: A total 22 subjects with chronic neck pain (numeric pain rating scale >3, forward head posture: cranio-vertebral angle <51°) participated in the study and were randomly allocated into the upper-cervical (n = 11) and cervicothoracic junction (n = 11) groups. Cranio-vertebral angle, cervical range of motion, and electromyography amplitude during performance of the craniocervical flexion test were measured before and immediately after the intervention.Results/findings: There were no significant main effects for the group by time outcome score of craniovertebral angle and electromyography amplitude. However, in the range of motion of the cervical area, the cervicothoracic junction group showed a significant increase in extension and right rotation than the upper-cervical group (p < 0.05). Moreover, in both groups, the electromyography amplitude of the sternocleidomastoid muscle was significantly reduced after intervention. The electromyography amplitude of the anterior scalene muscle in only the cervicothoracic junction group was significantly reduced after intervention (p < 0.05).Conclusion: Cervicothoracic junction manual therapy improved cervical alignment, cervical mobility (extension, rotation), and muscle recruitment ability in subjects with forward head posture. These observations may partially explain the efficacy of this manual therapy in rehabilitation of individuals with mechanical neck disorder (with forward head posture).Implications for rehabilitationForward head posture is identified as the flexion of the lower cervical spine along with the extension of the upper cervical spine, with an overall increase in the cervical curve.Cervicothoracic area manual therapy in subjects with neck pain and forward head posture better improved the muscle recruitment ability than upper cervical area manual therapy during motor tasks.

Trauma Resuscitation Consideration: Sex Matters

Sex dimorphisms in coagulation have been recognized, but whole blood assessment of these dimorphisms and their relationship to outcomes in trauma have not been investigated. This study characterizes the viscoelastic hemostatic profile of severely injured patients by sex, and examines how sex-specific coagulation differences affect clinical outcomes, specifically, massive transfusion (MT) and death. We hypothesized that severely injured females are more hypercoagulable and therefore, have lower rates of MT and mortality. Hemostatic profiles and clinical outcomes from all trauma activation patients from 2 level I trauma centers were examined, with sex as an experimental variable. As part of a prospective study, whole blood was collected and thrombelastography (TEG) was performed. Coagulation profiles were compared between sexes, and association with MT and mortality were examined. Poisson regression with robust standard errors was performed. Overall, 464 patients (23% female) were included. By TEG, females had a more hypercoagulable profile, with a higher angle (clot propagation) and maximum amplitude (MA, clot strength). Females were less likely to present with hyperfibrinolysis or prolonged activating clotting time than males. In the setting of depressed clot strength (abnormal MA), female sex conferred a survival benefit, and hyperfibrinolysis was associated with higher case-fatality rate in males. Severely injured females have a more hypercoagulable profile than males. This hypercoagulable status conferred a protective effect against mortality in the setting of diminished clot strength. The mechanism behind these dimorphisms needs to be elucidated and may have treatment implications for sex-specific trauma resuscitation.

Impact of Marine Exposure on Hemostatic Gauzes Using Thromboelastography.

Military forces render emergency care in marine environments, where care for exsanguination is challenging. However, the effect of saltwater on the functionality of hemostatic agents is unknown. In this study, we used thromboelastography (TEG) to quantify the effect of saltwater on the efficacy of five gauze products. Blood from 24 healthy adult men was diluted by 30% with hetastarch to mimic hemodilution. Dry and saltwater-soaked Kerlix™, ChitoGauze®, Combat Gauze®, NuStat™, and WoundClot™ were contrasted in terms of the TEG parameters of speed of clot initiation (R), clot amplification (K), α angle (i.e., clot formation rate), and maximum amplitude of clot (MA), using repeated-measures analysis of variance at the p < .05 statistical significance threshold. Compared with untreated dilute blood, R was significantly faster when any dry or wet gauze was added, with the fastest R values recorded for Combat Gauze. K and α angle findings were mixed. MA was greater than diluted blood for dry hemostatic gauze, but in the wet condition, only the MA for Combat Gauze was significantly greater than that of diluted blood. Gauze products, wet or dry, improved clotting compared to diluted blood without gauze. Saltwater exposure did not significantly detract from this benefit. Our findings suggest that Combat Gauze may be the choice hemostatic gauze for maritime environments.

Retrieval strategy for failed satellite on tether optimal balance swing angle

A retrieval control strategy for failed satellite, which is connected to a servicing spacecraft by a tether, is studied. The Lagrange analytical mechanics based dynamics modeling for the system composed of a servicing spacecraft, a tether and a failed satellite, is presented under the earth center inertia coordinate system, then model simplification is conducted under the assumption that the failed satellite's mass is far smaller than the servicing spacecraft's, meanwhile the tether's length is far smaller than the size of the servicing spacecraft's orbit. Analysis shows that the retrieval process is intrinsically unstable as the Coriolis force functions is a negative damping. A retrieval strategy based on only the tether's tension is designed, resulting in the fastest retrieval speed. In the proposed strategy, firstly, the tether's swing angle amplitude is adjusted to 45° by deploying/retrieving the tether; then the tether swings freely with fixed length until it reaches negative maximum angle -45°; finally, the tether is retrieved by the pre-assigned exponential law. For simplicity, only the coplanar situation, that the tether swings in the plane of the servicing spacecraft's orbit, is studied. Numerical simulation verifies the effectiveness of the strategy proposed.

New method for edges detection of magnetic sources using logistic function

The tilt angle of the analytic signal amplitude (TA) is defined as the arctangent of the ratio of the first vertical derivative to the total horizontal derivative of the analytic signal amplitude. It is commonly used as a useful tool to estimate edges of magnetic sources because its value is slightly dependence on the direction of magnetization vector, and it is more effective in estimating the edges of the bodies than the analytic signal amplitude and the standard tilt angle. Based on logistic function (L) that has the same shape with the shape of arctangent function, and the derivatives of the analytic signal amplitude, we introduce some new filters which also can reduce the effect of the magnetization direction. Other notable features of these filters are that they produce amplitude maxima over the edges of sources and that they balance anomalies from shallow and deep sources. The feasibility of the proposed filters is demonstrated on noise-free and noisy synthetic magnetic data from two 3D models where the obtained results coincide well with the actual edges. The effectiveness of the filters is also evaluated by comparing it with other edge detection methods. The results also show that our filters are less sensitive to variations in the depth of the source bodies and that a modified logistic function (Lk) can achieve better edge detection results than the analytic signal amplitude (AS), the analytic signal amplitude of the tilt angle (AT), the TA and L filters. The filters are also applied to real magnetic data from an area in south-central Vietnam, and the results demonstrate that the proposed filters is a useful tool for the qualitative interpretation of magnetic data.

Influences of secondary arc-based grading capacitor of multi-break circuit breaker on the transient stability of power system

The grading capacitor (GC) of circuit breaker (CB) is one of the most cost-effective methods to suppress secondary arc. Taking the double-break CB as an example, its topology is briefly introduced. The electric circuit for power system with GC is then established. From the perspective of minimizing secondary arc current, the formula for the capacitance of GC is deduced according to the Kirchhoff's voltage law. Based on the equal-area criterion, the transient process of power angle and speed of generator in the event of fault is investigated, and the role of GC in the transient stability is quantitatively investigated. Meanwhile, the expressions for the accelerating and decelerating areas are computed through the numerical calculus, and the impact of GC capacitance on the critical clearing time (CCT) is discussed. Furthermore, to verify the aforementioned analysis, a model is established in the environment of MATLAB/Simulink, and two cases are considered, i.e., a single machine infinite bus (SMIB) power system and a multi-machine power system. Both the theoretical analysis and the simulation results demonstrate that the use of GC can strength the electrical connection between two remote power sources, undermines the oscillating amplitude of power angle, and shorten the attenuation duration. As a result, the CCT and transient margin would be increased. In other words, we can prong the dead time and guarantee the successfulness for autoreclosure scheme. The GC of CB is much superior to the existing four-legged shunt reactor and high speed grounding switch in addressing the secondary arc issue.

Analysis of surface texturing in radial ultrasonic vibration-assisted turning

Surface texturing has become a potential way to achieve good friction performance or suitable wettability for different mechanical product surfaces. For fabricating micro-textured surface efficiently and cost-effectively, a texturing method of radial ultrasonic vibration-assisted turning (RUVT) was proposed. The theoretical model of texturing generation was established, which can describe the arrangement and geometry of micro-textures. Based on the theoretical model, a surface topography simulation was further used to characterize the influence of processing parameters on micro-dimpled patterns. This experimental process was performed on a CNC lathe and copper 1100 was chosen as the workpiece material. The simulated and experimental results show that surfaces covered with evenly distributed micro-dimples can be fabricated, which basically confirms the validity of theoretical model. The processing parameters, including clearance angle, spindle speed, feed rate and vibration amplitude, play important influence on the arrangement and geometry of micro-dimples. It is demonstrated that the method of RUVT is an efficient and cost-effective way for fast generation of cylindrical micro-textured surface.

A transient hydrodynamic lubrication comparative analysis for misaligned micro-grooved bearing considering axial reciprocating movement of shaft

Abstract A transient hydrodynamic lubrication model is proposed to investigate the lubrication performance of micro-grooved journal bearings, considering the axial flow caused by the axial reciprocating movement of the shaft. The lubrication performance of the bearing engineered with three different microgroove distributions, i.e. straight groove, spiral groove, and herringbone groove are compared systematically, including the load capacity and friction coefficient. The results suggest that the herringbone-grooved bearing exhibits the maximum load capacity in the positive axial movement, followed by straight-grooved bearing, and finally spiral-grooved bearing. The spiral-grooved bearing produces the minimum fluctuation amplitude of load capacity and attitude angle in one reciprocating period. The increased frequency of the axial movement can increase the value of load capacity for three micro-grooved bearings during the positive movement of the shaft; however, it does not affect the distribution trends of load capacity among the three micro-grooved bearings. Moreover, the effects of groove angle (β), degree of misalignment (Dm), and misalignment direction angle (α) on the lubrication performance of the micro-grooved bearing are investigated. The results indicate that the herringbone-grooved bearing exhibits better lubrication performance than the spiral-grooved bearing in the positive axial movement at any β. The present study also indicates that the load capacity of considering axial movement is more sensitive to Dm than that of not considering axial movement. The misalignment direction angle will result in the decreased load capacity of the micro-grooved bearing.