Numerical investigation of the turbulent energy budget in the wake of freely oscillating elastically mounted cylinder at low reduced velocities

We present a numerical study of the turbulent kinetic energy budget in the wake of cylinders undergoing Vortex-Induced Vibration (VIV). We show three-dimensional Large Eddy Simulations (LES) of an elastically mounted circular cylinder in the synchronization regime at Reynolds number of Re=8000. The Immersed Boundary Method (IBM) is used to account for the presence of the cylinder. The flow field in the wake is decomposed using the triple decomposition splitting the flow variables in mean, coherent and stochastic components. The energy transfer between these scales of motions are then studied and the results of the free oscillation are compared to those of a forced oscillation. The turbulent kinetic energy budget shows that the maximum amplitude of VIV is defined by the ability of the mean flow to feed energy to the coherent structures in the wake. At amplitudes above this maximum amplitude, the energy of the coherent structures needs to be fed additionally by small scale, stochastic energy in form of backscatter to sustain its motion. Furthermore, we demonstrate that the maximum amplitude of the VIV is defined by the integral length scale of the turbulence in the wake

Effects of approach velocity and foot-target characteristics on the visual regulation of step length

Two questions emerge from the literature concerning the perceptual-motor processes underlying the visual regulation of step length. The first concerns the effects of velocity on the onset of visual control (VCO), when visual regulation of step length begins during goal-directed locomotion. The second concerns the effects of different obstacles such as a target or raised surface on step length regulation. In two separate experiments, participants (Experiment 1 & 2: n=12, 6 female, 6 male) walked, jogged, or sprinted towards an obstacle along a 10 m walkway, consisting of two marker-strips with alternating black and white 0.50 m markings. Each experiment consisted of three targeting or obstacle tasks with the requirement to both negotiate and continue moving (run-through) through the target. Five trials were conducted for each task and approach speed, with trials block randomised between the six participants of each gender. One 50 Hz video camera panned and filmed each trial from an elevated position, adjacent to the walkway. Video footage was digitized to deduce the gait characteristics. Results for the targeting tasks indicate a linear relationship between approach velocity and accuracy of final foot placement (r=0.89). When foot placement was highly constrained by the obstacle step length shortened during the entire approach. VCO was found to occur at an earlier tau-margin for lower approach velocities for both experiments, indicating that the optical variable ‘tau' is affected by approach velocity. A three-phase kinematic profile was found for all tasks, except for the take-off board condition when sprinting. Further research is needed to determine whether this velocity affect on VCO is due to ‘whole-body' approach velocity or whether it is a function of the differences between gait modes.

Growth of highly versus moderately trained competitive female artistic gymnasts

Purpose: To investigate whether growth was adversely affected in 137 young competitive female artistic gymnasts involved in different training volumes.

Methods: This was a 2-yr prospective cohort study in which height, sitting height, leg length, weight, skinfolds, and pubertal status were measured in competitive advanced (20–27 h·wk-1) and intermediate (7.5–22 h·wk-1) training level female gymnasts every 6–12 months. Biological parameters of the adolescent growth curve were estimated using the Preece–Baines growth model. Growth rates were estimated for both groups from the mixed-longitudinal data.

Results: Estimated ages at peak height velocity (PHV) (13–13.5 yr) and mean PHV (6.2–6.4 cm·yr-1) for the advanced- and intermediate-level gymnasts suggest that these gymnasts were later maturing and experienced a blunting of the growth spurt relative to reference values for U.S. youth. Comparison of growth velocities by pubertal status revealed that height velocity was lower in the advanced- versus the intermediate-level peripubertal gymnasts, which was due to a significant reduction in sitting height velocity (2.3 vs 3.1 cm·yr-1, P. < 0.05). No marked acceleration in height or sitting height velocity was detected in the advanced-level gymnasts from pre- to peripuberty. Inspection of individual growth rates revealed that over 35% of the pre- and peripubertal gymnasts experienced growth faltering (height velocity less than 4.5 cm·yr-1) during follow-up.

Conclusion: Advanced–and intermediate–training level competitive female gymnasts tend to exhibit an adolescent growth spurt that is similar in timing and tempo to short, normal, slowly maturing girls, but the high frequency of growth faltering suggests that training may alter the tempo of growth and maturation in some, but not all, female gymnasts.

Speed control and policing in a cellular mobile network: speedNet

In this paper, we describe SpeedNet, a GSM network variant which resembles an ad hoc wireless mobile network where base stations keep track of the velocities of mobile users (cars). SpeedNet is intended to track mobile users and their speed passively for both speed policing and control of traffic. The speed of the vehicle is controlled in a speed critical zone by means of an electro-mechanical control system, suitably referred to as VVLS (Vehicular Velocity Limiting System). VVLS is mounted on the vehicle and responds to the command signals generated by the base station. It also determines the next base station to handoff, in order to improve the connection reliability and bandwidth efficiency of the underlying network. Robust Extended Kalman Filter (REKF) is used as a passive velocity estimator of the mobile user with the widely used proportional and integral controller speed control. We demonstrate through simulation and analysis that our prediction algorithm can successfully estimate the mobile user’s velocity with low system complexity as it requires two closest mobile base station measurements and also it is robust against system uncertainties due to the inherent deterministic nature in the mobility model.

Development of low cost motion-sensing system

Micro-electro-mechanical system (MEMS) technology offers sensors with lower cost, smaller size, lower power consumption. In this paper, a kind of low cost motion-sensing system based MEMS sensors is developed. The objective of the design is low cost, small volume and light weight in order to be used in many fields. The constituting principle of the system is described. Algorithms and hardware of the system are researched. And the definition of coordinate, calculation of pose angle, transform of acceleration and calculation of the velocities and displacement of the moving object are presented with corresponding mathematics model and algorithms. The experiments are carried out in principle and results are given. It is proved that the low cost motion-sensing system is effective and correct.

Kinematic and dynamic modeling of a robotic head with linear motors

Our present research focuses on kinematic and dynamic modeling of a 3-DOF robotic cutting head for the next generation of CNC machines. The robotic cutting head is one kind of parallel manipulator of 3-PUU type, which has a high flexibility of motion in three-dimensional space. The parallel manipulator consists of three linear servomotors, which drive three connecting rods independently according to the cutting strategy. Being a parallel manipulator, the robotic cutting head has higher stiffness and position accuracy; consequently, higher velocities and accelerations can be achieved. A very suitable application of this mechanism is as a cutting head of a precision machine tool for three-dimensional cutting problems.

Speed control and policing in a cellular mobile network: SpeedNet

In this paper, we describe SpeedNet, a GSM network variant which resembles an ad hoc wireless mobile network where base stations (possibly other vehicles in the network) keep track of the velocities of mobile users (cars). SpeedNet is intended to track mobile users and their speed passively for both speed policing and control of traffic. The speed of the vehicle is controlled in a speed critical zone by means of an electro-mechanical control system, suitably referred to as VVLS (vehicular velocity limiting system). VVLS is mounted in the vehicle and responds to the command signals generated by the base station. It also determines the next basestation to handoff, in order to improve the connection reliability and bandwidth efficiency of the underlying network. Robust extended Kalman filter (REKF) is used as a passive velocity estimator of the mobile user with the widely used proportional and integral controller speed control. We demonstrate through simulation and analysis that our prediction algorithm can successfully estimate the mobile users velocity with low system complexity as it requires two closet mobile-base station measurement and also it is robust against system uncertainties due to the inherent deterministic nature in the mobility model.

Robust terminal attitude navigation for autonomous vehicles

Here we define the terminal attitude of the pursuer with respect to a target and present a LQR and H¿ control approach to solving the problem of pursuer achieving a desired terminal attack/approach angle. The intercept or engagement criteria is defined in terms of both minimizing the miss distance and controlling the pursuer's body attitude with respect to the target at the terminal point. This approach in comparison to previous approaches consider the relativistic approach of the pursuer with respect to the target as opposed the absolute velocities of the two dynamic bodies, and have possible applications ranging from autonomous vehicle entry in to a mother craft to nossle engagements in on-flight refuelling or even in precision missile guidance. Here we also suitably formulate the H¿ control ideas directly applicable to the underlying problem and presents both state feedback and output feed back results for the case of finite horizon and non-zero initial conditions together with a optimal parameter value to achieve a desired terminal characteristic in terms of the original weighting parameters.

Multi equal channel angular pressing with rotational dies

The recent successful development of the equal channel angular pressing (ECAP) process in metals provides a feasible solution to produce ultra-fine or nano-grained bulk: materials with tailored material properties. However, ECAP is difficult to scale up commercially due to excessive load requirements. In this paper, a new Multi-ECAP process with die rotation is considered to obtain ultra-fine grain structured materials under a moderate deformation force. It is shown that an addition of torsion results in a reduction in the pressing force and an increase in severity of plastic deformation. An analysis using the upper bound method is found to be useful in predicting the pressing load and flow pattern of ECAP with and without rotational dies. Solutions are obtained for different inclined channel angles under different angular velocities of dies. Relative pressures are presented and some computed solutions are compared with those found by FEM simulation. The theoretical predictions of the pressing load are in good agreement with the simulation results. The amount of plastic deformation is determined by the inclined angle between the two intersecting channels, and the velocity ratio between the angular velocity of dies and the normal component of the punch velocity.

Time-to-Collision (TTC) judgements with offsize objects show that Tau needs to be intergrated with familiar size to explain TTC performance

Observers judged TTC with computer-generated displays simulating an approaching object in three familiar-size conditions:

(i) Real-size (smaller, larger objects depicted as tennis, soccer balls respectively).
(ii) Off-size (smaller, larger objects depicted as soccer, tennis balls respectively).
(iii) Ambiguous-size (smaller, larger objects depicted as texture-less black balls of different size).

Displays simulated objects approaching observersí viewpoint from 24.96 m, and disappearing at 5.76 m. Manipulation of approach velocities (4.8-19.2 msec-1) produced viewing times from 1.0 to 4.0 sec, and delays between object disappearance and tau-based TTC ranging from 0.3 to 1.2 sec. Motion characteristics of smaller and larger objects in the three familiar-size conditions simulated those of approaching real-sized tennis and soccer balls respectively; that is, for each approach velocity, tau‚-based TTC was the same across the three conditions for smaller and larger objects.

Results showed that, consistent with the proposition of tau-determined TTC, TTC estimates in the real-size condition were uninfluenced by object size. This is contrary to previous reports that TTC for larger objects is underestimated relative to TTC for smaller objects. However, such size-dependent TTC differences were found in the ambiguous-size condition, with even larger differences in the off-size condition; TTCs for the ëlargerí tennis ball were much less than TTCs to the ësmallerí soccer ball compared to corresponding TTCs in the ambiguous-size condition. These results are problematic for the proposition that tau solely determines TTC. We discuss the role of perceptual learning in resolving this problem.

Application of radial return mapping algorithm for finite strain elastoplasticity in a hybrid finite element and particle-in-cell model

The radial return mapping algorithm within the computational context of a hybrid Finite Element and Particle-In-Cell (FE/PIC) method is constructed to allow a fluid flow FE/PIC code to be applied solid mechanic problems with large displacements and large deformations. The FE/PIC method retains the robustness of an Eulerian mesh and enables tracking of material deformation by a set of Lagrangian particles or material points. In the FE/PIC approach the particle velocities are interpolated from nodal velocities and then the particle position is updated using a suitable integration scheme, such as the 4th order Runge-Kutta scheme[1]. The strain increments are obtained from gradients of the nodal velocities at the material point positions, which are then used to evaluate the stress increment and update history variables. To obtain the stress increment from the strain increment, the nonlinear constitutive equations are solved in an incremental iterative integration scheme based on a radial return mapping algorithm[2]. A plane stress extension of a rectangular shape J2 elastoplastic material with isotropic, kinematic and combined hardening is performed as an example and for validation of the enhanced FE/PIC method. It is shown that the method is suitable for analysis of problems in crystal plasticity and metal forming. The method is specifically suitable for simulation of neighbouring microstructural phases with different constitutive equations in a multiscale material modelling framework.

New techniques and issues in assessing walking behavior and its contexts

In the first section of this article, we discuss the metabolic responses to walking by describing the economy of walking during different locomotion velocities. Gender, weight status, and growth effects on metabolic responses to walking are reviewed. In the second section, we examine the use of technology to assess walking patterns and behavior in the community. We use an engineering approach for understanding how to measure objects that move, and these methods are used to assess walking used in transportation. In the third part of the paper, we summarize self-report methods that have been used to assess walking behavior and highlight the strengths and weaknesses of these methods. We illustrate how self-report methods are used to quantify walking behavior in the surveillance systems that are now widely used to ascertain walking prevalence and temporal changes in different populations. In the final section, we discuss ways of measuring the walkability of neighborhoods and the community to understand the influence of the built environment on walking behavior.

3D virtual haptic cone for intuitive vehicle motion control

Haptic technology provides the ability for a system to recreate the sense of touch to a human operator, and as such offers wide reaching advantages. The ability to interact with the human's tactual modality introduces haptic human-machine interaction to replace or augment existing mediums such as visual and audible information. A distinct advantage of haptic human-machine interaction is the intrinsic bilateral nature, where information can be communicated in both directions simultaneously. This paper investigates the bilateral nature of the haptic interface in controlling the motion of a remote (or virtual) vehicle and presents the ability to provide an additional dimension of haptic information to the user over existing approaches [1-4]. The 3D virtual haptic cone offers the ability to not only provide the user with relevant haptic augmentation pertaining to the task at hand, as do existing approaches, however, to also simultaneously provide an intuitive indication of the current velocities being commanded.

Passive flow through an unstalked intertidal ascidian: Orientation and morphology enhance suspension feeding in Pyura stolonifera

Passive flow is believed to increase the gains and reduce the costs of active suspension feeding. We used a mixture of field and laboratory experiments to evaluate whether the unstalked intertidal ascidian Pyura stolonifera exploits passive flow. We predicted that its orientation to prevailing currents and the arrangement of its siphons would induce passive flow due to dynamic pressure at the inhalant siphon, as well as by the Bernoulli effect or viscous entrainment associated with different fluid velocities at each siphon, or by both mechanisms. The orientation of P. stolonifera at several locations along the Sydney-Illawarra coast (Australia) covering a wide range of wave exposures was nonrandom and revealed that the ascidians were con- sistently oriented with their inhalant siphons directed into the waves or backwash. Flume experiments using wax mod- els demonstrated that the arrangement of the siphons could induce passive flow and that passive flow was greatest when the inhalant siphon was oriented into the flow. Field exper- iments using transplanted animals confirmed that such an orientation resulted in ascidians gaining food at greater rates, as measured by fecal production, than when oriented perpendicular to the wave direction. We conclude that P. stolonifera enhances suspension feeding by inducing pas- sive flow and is, therefore, a facultatively active suspension feeder. Furthermore, we argue that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecolog- ically relevant results.

Enhancement of natural ventilation in high-rise residential buildings using stack system

This paper describes the feasibility study on the application of passive and active stack systems to enhance natural ventilation in public housing in Singapore. About 86% of the population is staying in high-rise public housing, known as Housing and Development Board (HDB) flats, which is designed for natural ventilation. The primary objective of this work is to assess the status of natural ventilation in a typical four-room HDB flat using scaled model in the wind tunnel, and to develop an effective passive or active stack system to enhance natural ventilation in the flat. Four numbers of stacks with different sizes were tested at two locations in the flat. The study shows that the passive stack, incorporating the principle of airflow due to buoyancy, does not enhance air velocity in the flat. However, the active stack which operates based on the suction effect induced by a fan fixed at the top of the stack leads to substantial increase in the air velocity at the room and thus meeting the human’s thermal comfort condition. It was noted that the velocities increase along with the increase in the stack size.