Moment Characteristics Research Articles

Numerical Study of Transition of an Annular Lift Fan Aircraft

The present study aimed at studying the transition of annular lift fan aircraft through computational fluid dynamics (CFD) simulations. The oscillations of lift and drag, the optimization for the figure of merit, and the characteristics of drag, yawing, rolling and pitching moments in transition are studied. The results show that a two-stage upper and lower fan lift system can generate oscillations of lift and drag in transition, while a single-stage inner and outer fan lift system can eliminate the oscillations. The characteristics of momentum drag of the single-stage fans in transition are similar to that of the two-stage fans, but with the peak of drag lowered from 0.63 to 0.4 of the aircraft weight. The strategy to start transition from a negative angle of attack −21° further reduces the peak of drag to 0.29 of the weight. The strategy also reduces the peak of pitching torque, which needs upward extra thrusts of 0.39 of the weight to eliminate. The peak of rolling moment in transition needs differential upward thrusts of 0.04 of the weight to eliminate. The requirements for extra thrusts in transition lead to a total thrust–weight ratio of 0.7, which makes the aircraft more efficient for high speed cruise flight (higher than 0.7 Ma).

Force and Moment Characteristics of a Rhombi Tessellated Non-Pneumatic Tire

ABSTRACTThere has been a recent spate of activities in the design of non-pneumatic tires (NPTs). The validation of a NPT's design is incomplete unless its performance is compared with an equivalent pneumatic tire. Apart from its static behavior, an evaluation of the tire's performance can be done by observing its force and moment (F&M) characteristics. In the present work, an NPT has been designed with an aperiodic rhombi tessellated spoke acting as the load bearing member, where the “unit cell” design is based on the vertical, circumferential, and lateral stiffness offered by the structure. A three-dimensional finite element model has been used to capture the mechanics of load distribution in the spoke, contact patch, and variation of contact pressure distribution when the tire is subjected to different operating conditions. SIMULIA/Abaqus has been used to conduct static loading, acceleration/braking, and cornering analyses. The F&M characteristics have been extracted from these simulations and compared with those of a 165/70R14 passenger car tire. The variation in the vertical and circumferential stiffness based on the spoke geometry has also been highlighted. The use of conventional pneumatic tire's belts to alter the NPT's lateral stiffness, despite the tire behaving like a “bottom loader,” adds uniqueness to the design. The NPT's capability to match the pneumatic tire's performance and the variability observed in the tire's F&M characteristics reiterate the freedom available in NPT design, thus providing the opportunity to have similar tires with varying performance characteristics.

The free moment in running and its relation to joint loading and injury risk

The purpose of this study was to explore the relationship between free moment (FM) characteristics, joint mechanics and injury risk, in order to evaluate the potential of the FM as a variable for runner classification into functional groups with similar footwear demands. Lower extremity joint mechanics, ground reaction forces and the FM of 222 male and female injury free runners were analysed using an optoelectric motion capture system and a force plate while running at 3.5 m/s. During a follow-up period of 6 months, runners were reporting any running-related injuries to an experienced orthopaedist. Different FM patterns could be extracted using functional principal component analysis (FPCA). The first two eigenfunctions derived from FPCA were able to predict about 87% of the variance in the data-set and could be related to the two main functions of FM application in straight running -- transversal plane whole body oscillation control and compensation of insufficient transversal moment cancellation. FM patterns differed with respect to lower extremity joint moments and joint kinematics, mostly in the transversal and frontal plane of motion. Runners suffering from patellofemoral pain syndrome showed FM patterns with distinct external rotation components and differed from their matching controls, even though the number of runners, who suffered from injuries were too low to allow valid inferences. In conclusion, it seems that the FM could be useful in the classification of runners into functional groups as it possesses a considerable inter-subject variability, a relationship to the mechanical demands put on lower extremity joints and potentially to injury risk, while being comparably easy to measure.

External Part of School Leaving Examination and its Statistical Analysis in Selected Region

Abstract School leaving exam represents one of possibilities how to finish upbringing and education at high schools. School leaving exam (including its external part) is a form of graduation at high school and presents the basis for further studies at universities. Quality of education determines the competitiveness of graduates from primary, secondary school and universities on domestic as well as foreign labor market. Paper focuses on statistical evaluation of External part of school leaving exam on the set of 112 high schools of Presov Region in 2015. We evaluate an average percentage of school in External part of school leaving examination, an average grade of Slovak language and a number of tested students. To identify a district's correlations and differences Moran's Index, Kruskal-Wallis test or Kendal coefficient were used. The differences between the individual results in districts and its comparison are described by a few statistical methods (box plot, maps, moment characteristics) too.

Теоретическое и экспериментальное исследование задержки в программно-конфигурируемых сетях

This work is concerned with determination of packet delays inserted by using OpenFlow protocol in virtual computing cluster performed over software defined network by OpenNebula system with installed Floodlight controller. We experimentally found moment characteristics of packet delays. Based on these values we theoretically determined packet delays in channels both with and without OpenFlow via traffic simulation in the kind of queuing system H2/M/1. According to results, packer delay under using OpenFlow protocol is more 1.5 times then under without it. This fact should be taken into account for heavy load software defined network, while we performed experimental research under light load channels.

Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study.

This pilot study investigated whether a 10-week running program (10wkRP), which reduced the oxygen cost of running, affected resultant ground reaction force (GRF), leg axis alignment, joint moment characteristics, and gear ratios. Ten novice, female runners completed a 10wkRP. Running kinematics and kinetics, in addition to oxygen consumption ( V ˙ O 2 ) during steady-state running, were recorded pre- and post-10wkRP. V ˙ O 2 decreased (8%) from pre-10wkRP to post-10wkRP. There was a better alignment of the resultant GRF and leg axis at peak propulsion post-10wkRP compared with pre-10wkRP (10.8 ± 4.9 vs 1.6 ± 1.2°), as the resultant GRF vector was applied 7 ± 0.6° (P = 0.008) more horizontally. There were shorter external ankle moment arms (24%) and smaller knee extensor moments (23%) at peak braking post-10wkRP. The change in V ˙ O 2 was associated with the change in alignment of the resultant GRF and leg axis (rs = 0.88, P = 0.003). As runners became more economical, they exhibited a more aligned resultant GRF vector and leg axis at peak propulsion. This appears to be a self-optimization strategy that may improve performance. Additionally, changes to external ankle moment arms indicated beneficial low gear ratios were achieved at the time of peak braking force.

Multitasking With Television Among Adolescents

Using Ecological Momentary Assessment, we explored predictors of adolescents' television (TV) multitasking behaviors. We investigated whether demographic characteristics (age, gender, race/ethnicity, and maternal education) predict adolescents' likelihood of multitasking with TV. We also explored whether characteristics of the TV-multitasking moment (affect, TV genre, attention to people, and media multitasking) predict adolescents' likelihood of paying primary versus secondary attention to TV. Demographic characteristics do not predict TV multitasking. In TV-multitasking moments, primary attention to TV was more likely if adolescents experienced negative affect, watched a drama, or attended to people; it was less likely if they used computers or video games.

Biomechanical comparison of frontal plane knee joint moment arms during normal and Tai Chi walking

[Purpose] Medial knee osteoarthritis, a degenerative joint disease, affects adults. The external knee adduction moment, a surrogate knee-loading measure, has clinical implications for knee osteoarthritis patients. Tai Chi is a promising intervention for pain alleviation in knee osteoarthritis; however, the characteristics of external knee adduction moment during Tai Chi have not been established. [Subjects and Methods] During normal and Tai Chi walking, a gait analysis was performed to compare the external knee adduction moment moment-arm characteristics and paired t-tests to compare moment-arm magnitudes. [Results] A significant difference was observed in the average lateral direction of moment-arm magnitude during Tai Chi walking (−0.0239 ± 0.011 m) compared to that during normal walking (−0.0057 ± 0.004 m). No significant difference was found between conditions in average medial direction of moment-arm magnitude (normal walking: 0.0143 ± 0.010 m; Tai Chi walking: 0.0098 ± 0.014 m). [Conclusion] Tai Chi walking produced a larger peak lateral moment-arm value than normal walking during the stance phase, whereas Tai Chi walking and normal walking peak medial moment-arm values were similar, suggesting that medial knee joint loading may be avoided during Tai Chi walking.

階段降段と平地歩行における外部膝関節内転モーメントの特徴

階段降段と平地歩行における外部膝関節内転モーメントの特徴

Conditionally Minimax Prediction in Nonlinear Stochastic Systems

This paper describes an approach of nonlinear prediction in discrete-time stochastic systems. The method consists of two steps: preliminary statistical estimation of second-order moment characteristics and minimax optimization of structural coeficients. The minimax prediction algorithms are based on semidefinite programming over several kinds of confidence regions for the uncertain mean and covariance matrix. The guaranteed level of the mean square error (MSE) is provided by the minimax theorem on normal correlation.

Aerodynamic Interference Caused by the Inboard Leading-Edge Flap on the Outboard Area of the Cranked Arrow Wing

Wind tunnel tests were conducted on a cranked arrow wing model to reveal the relationship between the inboard leading edge flaps and vortex behavior formed on the outboard wing area. Aerodynamic force measurements and flow visualizations on the upper surface of the wing were made. The pitching moment characteristics indicate that there are two non-linear changes and the flow patterns which caused those changes are observed. The flow patterns indicate that the non-linear changes are caused both by the flow separation on the outside of the inboard vortex and by the one on the outside of the merging position of the inboard and outboard vortices. It was found that the inboard leading edge flap decreases the angle of attack when recovery from the first change occurs. The inboard leading edge flap also causes an increase in the magnitude of the second change.

Event-Triggered Decision Propagation in Proximity Networks

This paper proposes a novel event-triggered formulation as an extension of the recently develo- ped generalized gossip algorithm for decision/awareness propagation in mobile sensor networks modeled as proximity networks. The key idea is to expend energy for communication (message transmission and reception) only when there is any event of interest in the region of surveillance. The idea is implemented by using an agent’s belief about presence of a hotspot as feedback to change its probability of (communication) activity. In the original formulation, the evolution of network topology and the dynamics of decision propagation were completely decoupled which is no longer the case as a consequence of this feedback policy. Analytical results and numeri- cal experiments are presented to show a significant gain in energy savings with no change in the first moment characteristics of decision propagation. However, numerical experiments show that the second moment characteristics may change and theoretical results are provided for upper and lower bounds for second moment characteristics. Effects of false alarms on network formation and communication activity are also investigated.

Spectral features and perceptual judgment of place of affricate in Putonghua-speaking pre-adolescents with normal and cleft palate

PurposeThe aim of the study was to examine the relationship between the spectral features and perceptual judgments of places of affricate in Putonghua (standard Mandarin Chinese), and to explore the possible contribution of different spectral moments on correct perception of place of articulation information by typical pre-adolescent speakers and those with cleft palate. MethodA total of 139 affricates produced by 10 normal pre-adolescent speakers and 14 speakers with repaired cleft palate (distorted articulation) were presented to 12 listeners tasked with making a judgment of the accuracy of place of articulation using a visual analog scale. ResultsStatistical analysis showed a significant relationship between the third spectral moment (L3) and listeners’ perceptual judgment of typical alveolar and retroflex affricates. For productions by pre-adolescents with cleft palate, the first spectral moment (M1) was significantly correlated with listener perceptual scaling of retroflex affricates, but not for the alveolar affricates. ConclusionSpectral features were associated with the perception of place of affricate in Putonghua. Different spectral moment characteristics might be used by listeners when perceiving speech from individuals with cleft palate.

Modeling of reentry space vehicle aerodynamics with control thruster plume — free-stream interaction

Changes in aerodynamic characteristics of a space vehicle model due to interaction of the control thruster plume with the incoming flow are numerically studied. Parameters of the plume escaping from the thruster nozzle and flight data (velocity and altitude) are taken to be the parameters of the Intermediate eXperimental Vehicle. Simulations are performed by the Direct Simulation Monte Carlo Method. A multizone approach is used for combined modeling of the dense plume and the rarefied incoming flow. If the control thruster plume is fairly close to the space vehicle surface, flow interference is possible, which may alter the force and moment characteristics. In the problem considered in this paper, the pitching moment changes approximately by 10 % at altitudes below 120 km due to this interference.

Daily wellbeing in families with children: A harmonious and a disharmonious week

What makes daily life in families with young children harmonious, and are there better and worse times? Applying a daily approach, the present study examined one week in dual-earner families with young children, with special focus on families that reported either a harmonious or a disharmonious week in their family interaction. Quantitative and qualitative diary data were collected with mobile phones and with paper and pencil from 45 families. Fourteen families representing either disharmonious or harmonious interaction were chosen for a detailed analysis of good and difficult moments in the spousal and parent–child relationship. What most clearly distinguished these weeks was not the characteristics of good and difficult moments, but the frequency of these moments.

Continuity and discontinuity in the human use of the north coast of Santa Cruz (Patagonia Argentina) through its radiocarbon record

In this paper, the analysis of a radiocarbon database of the North Coast of Santa Cruz (central Patagonia, Argentina), is presented. Dated archaeological samples were obtained from 56 different types of archaeological sites (open-air -residential sites and burials-, and also rock shelters). The objective of this paper is assessing the continuities and discontinuities in the chronological signal of the area and identifying tendencies along the Holocene. The database currently contains 75 radiocarbon dates falling between ca. 8000 and 300 BP. The radiocarbon data base provides information on the chronological, spatial and contextual variability of the archaeological record of North Coast of Santa Cruz. By means of different analysis of sum of probabilities, we present three different chronological moments of human use of the coast and intermediate zone can be identified. A first moment is represented by early evidence of settlement during Middle Holocene. A second moment corresponds to a hiatus between ca. 5800 and ca. 3900 BP without archaeological evidence. Finally, a third moment is where an increasing of chronological signal occurred, related to greater artifactual variability and an increase in the intensity of human settlement in the Patagonian region. The causes that could have influenced in the discontinuity of the chronological signal of the study area, and the characteristics of the different moments identified are discussed.

Three-dimensional ankle moments and nonlinear summation of rat triceps surae muscles.

The Achilles tendon and epimuscular connective tissues mechanically link the triceps surae muscles. These pathways may cause joint moments exerted by each muscle individually not to sum linearly, both in magnitude and direction. The aims were (i) to assess effects of sagittal plane ankle angle (varied between 150° and 70°) on isometric ankle moments, in both magnitude and direction, exerted by active rat triceps surae muscles, (ii) to assess ankle moment summation between those muscles for a range of ankle angles and (iii) to assess effects of sagittal plane ankle angle and muscle activation on Achilles tendon length. At each ankle angle, soleus (SO) and gastrocnemius (GA) muscles were first excited separately to assess ankle-angle moment characteristics and subsequently both muscles were excited simultaneously to investigate moment summation. The magnitude of ankle moment exerted by SO and GA, the SO direction in the transverse and sagittal planes, and the GA direction in the transverse plane were significantly affected by ankle angle. SO moment direction in the frontal and sagittal planes were significantly different from that of GA. Nonlinear magnitude summation varied between 0.6±2.9% and −3.6±2.9%, while the nonlinear direction summation varied between 0.3±0.4° and −0.4±0.7° in the transverse plane, between 0.5±0.4° and 0.1±0.4° in the frontal plane, and between 3.0±7.9° and 0.3±2.3° in the sagittal plane. Changes in tendon length caused by SO contraction were significantly lower than those during contraction of GA and GA+SO simultaneously. Thus, moments exerted by GA and SO sum nonlinearly both in the magnitude and direction. The limited degree of nonlinear summation may be explained by different mechanisms acting in opposite directions.

Tire Transient Lateral Force Generation: Characterization and Contribution to Vehicle Handling Performance

ABSTRACT Tire force generation is often described in terms of a steady-state force response, which is considered independent of time and a function of the kinematic roll conditions such as slip angle. In addition to the steady-state response, the tire also exhibits a time-dependent transient force response, which in the lateral direction is a delay in the buildup of the cornering force. This delay is often characterized by the so-called tire relaxation length (RL) (Ly), a tire performance characteristic often thought to have a strong effect on handling performance. The definition and mechanistic interpretation of tire lateral RL is discussed, and different methods for measuring and interpreting lateral RL are compared. The measurement methods include different types of flat belt as well as static stiffness measurements. Because of different levels of measurement uncertainty, the repeatability and benefits of the different measurement methods are demonstrated. To determine the effect of including tire transient response in tire/vehicle system models, a handling study was performed. The study included a series of CarSim handling simulations with tires of different transient force and moment characteristics as well as an analysis of outdoor subjective handling ratings. The results show the relatively small contribution of tire transient characteristics to vehicle handling performance compared with the tire steady-state force response.

The effects of vortex breakdown on the static rolling aerodynamics of finned slender body

The static rolling aerodynamics of a finned slender body is numerically studied in this paper. Simulation results show a nonlinear uprising of the rolling moment when the angle of attack is greater than 20° in subsonic flows. Asymmetric vortex break down phenomenon on the “horizontal” rudders is found to be responsible for this phenomenon. By introducing the geometric-equivalent angle of attack and geometric-equivalent sweep angle, the cause of the nonlinear rolling moment characteristics can be explained by the delta wing vortex breakdown analysis.

State-Space Model and Simulation for Dynamic Stall

Because of the complexity of the progress of dynamic stall, the characteristic of dynamic stall of airfoil is always the difficulty of aerodynamics. A time-domain model has been formulated to represent the unsteady lift and pitching moment characteristics of a two-dimensional airfoil undergoing attached-flow conditions in a compressible flow and dynamic stall. The model is given as a set of first order differential state equations. The Beddoes-Leishman model was presented through modeling the effects of attached flow, separated flow and dynamic stall in the paper. A modified method is presented which includes a new stall-onset criterion and improves the position and separation conditions of the leading edge vortex, so that the B-L model is adaptive for lower Mach numbers. Then, the normal force and pitching moment on NACA0012 airfoil was calculated and compared with available experimental data to validate the reliability of the model.