Desired Velocity Field Research Articles

Analysis of local density during football stadium access: Integrating pedestrian flow simulations and empirical data

This study analyzes numerically the access of football fans to a typical football stadium through pedestrian flow simulations. With this aim, we introduce a novel framework to address the difficulty of simulating pedestrian dynamics in highly complex geometries with multiple accesses. The framework consists of a combination of the Social Force Model (SFM) and Computational Fluid Dynamics tools to calculate multiple desired velocity maps. The introduction of this framework allows the predefinition of the desired velocity fields for the complex geometries in both the interior and surrounding area of the stadium. We validate the results of the proposed framework using actual entry-rate data from the turnstiles of three gates for 15 matches provided by the football club. Remarkably, the validation process allows us to describe the temporal evolution of the spatial distribution of pedestrians during their arrival with a single set of parameters valid for all the analyzed matches. Finally, we assess the potential fatality risk based on the local pedestrian density varying the total number of attendees and their arrival rate. The outcome evidences permanent clogs emerge at the entrance in the most extreme cases with high attendance or low standard deviation of the arrival rate, indicating the possibility of fatality occurrence.

Airflow and thermal comfort evaluation of a room with different outlet opening sizes and elevations ventilated by a two-sided wind catcher

Wind catchers as passive cooling systems contribute to the enhancement of air quality, thermal comfort, and reduction of energy consumption in the residential sector. In this paper, the indoor flow structure, crossflow ventilation characteristics, and thermal comfort of a room integrated with a two-sided wind catcher is numerically investigated. A mixed-climate condition and experimentally validated room dimensions are utilized to define the physics of the problem. 3D steady-state RANS CFD simulations, with different turbulence models for a reference case are simulated, and their performance is compared with the published literature. The following analyses are conducted based on a validated SST k-ω model and a fixed reference case dimensions with (1) five different room outlet elevations (top, reference case, middle, front of room inlet opening, and floor) and (2) four different outlet areas to the wall ratio (10%–40%). The results show that the room outlet mass flow rate increases up to 26% by decreasing the room outlet elevation from the top to the floor; the front and floor outlet elevations obtained the optimum thermal comfort metrics. At a specific room outlet opening elevation, increasing the room outlet area to wall ratio increases the mass flow rate; the 30% aspect ratio obtained the desired temperature stratification and velocity field. These results can be combined with architectural metrics towards improving user comfort in the buildings.

Field-Based Assist-as-Needed Control Schemes for Rehabilitation Robots

This article presents assistive control schemes for rehabilitation robots. The objective was to develop control strategies to follow a predefined path by maximizing the active participation of impaired subjects during training sessions. For this purpose, the path following task was defined in the velocity domain by constructing a desired velocity field around the path, and two different controllers were designed, which adjust the intervention of the robot according to the performance of the users, delivering an assist-as-needed (AAN) feature with adequate timing freedom. First, we developed an impedance controller for velocity tracking, which gains the AAN property by means of modulating the target impedance. Second, we designed a velocity tracking controller, which adjusts its contribution, in an AAN way, by monitoring the tracking error. Utilizing force sensors, the first method does not require a compliant robotic system, while the second approach does not need force sensors but provides its best AAN performance whenever the system is compliant. The controllers were featured by a force field component to avoid large position errors. The performance of the controllers was evaluated through experimental tests performed on a planar upper-limb training robot.

Adaptive anti control of chaos for robot manipulators with experimental evaluations

Roughly speaking, anti control of chaos consists in injecting a chaotic behavior to a system by means of a control scheme. This note introduces a new scheme to solve the anti control of chaos for robot manipulators. The proposed controller uses an adaption law to estimate the robot parameters on line. Thus, the controller does not require any knowledge of the physical parameters of the manipulator, such as masses, lengths of the links, moments of inertia, etc. The new scheme is based in the velocity field control paradigm, hence the specification of a chaotic system to define a desired velocity field is required. Experimental results in a two degrees-of-freedom direct-drive robot illustrate the practical feasibility of the introduced theory. In order to achieve anti control of chaos of our experimental system, two different chaotic attractors are used: the Genesio-Tesi system and a Jerk-type system. Results showed that the controller is able to inject the chaotic behavior to the robot while the robot parameters are estimated on line.

Two-parameter extremum problems of boundary control for stationary thermal convection equations

Two-parameter extremum problems of boundary control are formulated for the stationary thermal convection equations with Dirichlet boundary conditions for velocity and with mixed boundary conditions for temperature. The cost functional is defined as the root mean square integral deviation of the desired velocity (vorticity, or pressure) field from one given in some part of the flow region. Controls are the boundary functions involved in the Dirichlet condition for velocity on the boundary of the flow region and in the Neumann condition for temperature on part of the boundary. The uniqueness of the extremum problems is analyzed, and the stability of solutions with respect to certain perturbations in the cost functional and one of the functional parameters of the original model is estimated. Numerical results for a control problem associated with the minimization of the vorticity norm aimed at drag reduction are discussed.

Friction-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate

We show that small-amplitude periodic motion of a rigid plate causes point parts in frictional contact with the plate to move as if they are in a position-dependent velocity field. Further, we prove that every periodic plate motion maps to a unique velocity field. By allowing a plate to oscillate with six degrees of freedom, we can create a large family of programmable velocity fields. We examine in detail the class of plate motions described by sinusoidal linear and angular accelerations with a single frequency. We hypothesize that this simple class can generate all velocity fields that have constant and linear terms with respect to position, as well as some quadratic fields with respect to position. This set includes fields with isolated sinks and squeeze lines that can be used to perform tasks such as sensorless part orientation. Several of these fields have been verified on our programmable parts-feeding oscillatory device (PPOD). The PPOD is a parallel manipulator similar to a Stewart platform, but with flexures as joints. An iterative learning control algorithm is described that moves the platform with the six-degree-of-freedom periodic motion that creates the desired velocity field.

Generalized functions on Hilbert spaces, singular integral equations, and problems of aerodynamics and electrodynamics

External flow suction devices are used in aerodynamics to increase the lift of an airfoil in an ideal incompressible flow [1]. When solving this problem, the airfoil is modeled by a vortical layer [2], and the external flow suction device is modeled by a sink [3]. The desired velocity field around the profile should have the following property. In a neighborhood of the sink, the velocity field should have a sink-type singularity on the external side of the airfoil (where the sink lies), and it should be smooth on the opposite side. Naturally, if the airfoil satisfies the no-flow condition on the sink side, the sink point itself is excluded from this condition. The airfoil flow problem is thereby reduced to the solution of a singular integral equation on the profile contour with right-hand side undefined at the sink point. It follows from the analysis of tangential components of the velocity field in a neighborhood of the sink on the airfoil side where the velocity field is smooth that the solution of the resulting singular integral equation should be sought in the class of functions that have a singularity of the type of 1/x at the sink point [1]. In the numerical solution of this singular integral equation by the discrete vortex method, grid points are chosen so as to ensure that the sink point is one of them, and when replacing the singular integral equation by a system of linear algebraic equations, the equation corresponding to the sink point is omitted [1]. The omitted equation is replaced by another equation, which is derived from some physical considerations. This proves to be inconvenient, since, when using several external flow suction devices, one always has to decide how to fill in the missing equations. Hence it was suggested in [4] to satisfy the no-flow condition not on the side of the airfoil, where the sink lies, but on the opposite side, where the velocity field is smooth. This approach results in the appearance of a delta function supported at the sink point on the right-hand side of the corresponding singular integral equation. Now the singular integral equation should be treated as a pseudodifferential equation in the class of distributions. A version of such interpretation for a singular integral equation with a Hilbert kernel in the class of periodic distributions was presented in [5]. In this case, periodic distributions were treated as a subset of distributions on the entire real line. But this is inconvenient for singular integral equations on an interval in the class of distributions. However, it became simpler to use the discrete vortex method for the numerical solution of singular integral equations for the case in which the righthand side contains a delta function. The method acquired the same classical form [1] as for singular integral equations in the class of absolutely integrable functions, the delta function being replaced by the corresponding step function [6]. Note also that the solution of the problem on the computation of the input resistance of a thin wire antenna [7] powered by a current source leads to the analysis of a hypersingular integral equation on an interval, where the right-hand side contains a function with a singularity of the type of 1/x inside the solution domain. The solution of the corresponding characteristic equation was performed with the use of a spectral relation for a hypersingular integral operator on an interval, which provided a solution with a jump discontinuity at the point of the singularity of the right-hand side. In general, this solution should be considered in the class of distributions. This extension of the classical interpretation of singular and hypersingular integral equations and the corresponding

Object-transportation control of cooperative agv systems based on virtual-passivity decentralized control algorithm

Automatic guided vehicle in the factory has an important role to advance the flexible manufacturing system. In this paper, we propose a novel object-transportation control algorithm of cooperative AGV systems to apply decentralized control to multiple AGV systems. Each AGV system is under nonholonomic constraints and conveys a common object-transportation in a horizontal plain. Moreover it is shown that cooperative robot systems ensure stability and the velocities of augmented systems convergence to a scaled multiple of each desired velocity field for cooperative AGV systems. Finally, the application of proposed virtual passivity-based decentralized control algorithm via system augmentation is applied to trace a circle. Finally, the simulation and experimental results for the object-transportation by two AGV systems illustrates the validity of the proposed virtual-passivity decentralized control algorithm.

Adaptive Modular Vector Field Control for Robot Contact Tasks in Uncertain Environments

We propose adaptive modular vector field control (AMVFC) for a robot manipulator to interact with uncertain environmental geometric constraints. Starting from an uncertain geometric model of the environment, we first parameterize the desired velocity vector field of the robot using the weighted combination of a set of basis vector fields. Then, to overcome the influence of environmental model uncertainty, we add force feedback to adjust robot dynamics and the weight parameters of the desired velocity field for the robot to approach the real environment. Simulation of a robot interacting with uncertain circles and an ellipse demonstrates the effectiveness of our approach.

Adaptive Desired Velocity Field Control for Cooperative Mobile Robotic Systems with Decentralized PVFC

Passive velocity field control (PVFC) was previously developed for mechanical systems which have strong coordination and must interact with the physical environment. Moreover, In our previous researches, the extended PVFC algorithm for multiple manipulator systems is also introduced. The methodology of PVFC and extended PVFC encode tasks using time invariant desired velocity fields instead of the more traditional method of time trajectories and guarantees that the closed loop system behave passively with environment power as the supply rate. This paper addresses an adaptive generation method of the desired velocity field for cooperative mobile robots with decentralized PVFC. Of course, this paper is a method of decentralized control algorithm for cooperative mobile robot systems handling a common object in a coordinated way. The proposed control method for cooperative mobile robots in constructed based on the extended PVFC in this paper. Moreover the stability and the boundedness are ensured using projection algorithm. Finally the effectiveness of proposed control method is examined by numerical simulation for cooperation tasks with two 3-wheeled mobile robot systems to consider our previous research.

Shape Optimization Based on Traction Method Using voxel-FEM

Using a voxel finite element method that allows us to integrate modeling and analysis of a complicated three-dimensional structure, a new numerical method for shape optimization problem was proposed here based on the traction method. A minimization problem of stress nonuniformity in the domain was formulated for a three-dimensional linear elastic structure. In this method, a domain variation that was obtained as a velocity field from a shape gradient function was accomplished by removal and addition of the voxel elements on the domain surface. First, a case study for a plate with fillets under compression verified that the desired velocity field based on stress nonuniformity was successfully expressed by the discretized domain variation using voxel finite elements. Second, case studies for cantilevers subjected to a concentrated and uniformly distributed forces demonstrated that the minimization of the stress nonuniformity was achieved by changing the domain shape. In addition, a possibility of the topological change as well as shape change was suggested using the proposed method.

Passivity Based Control of Automated Driver Based on Velocity Field

The objectives of automated driver are to let vehicles track the desired trajectory in a natural way and to mantain good ride quality. In order to satisfy the above objective, this paper use the control technique based on velocity fields concepts and Passivity Based Control (PBC) method to derive the control law, such that longitudinal, lateral and yaw velocity converge asymtotically to a desired velocity field. Simulation results show the performance of the controller.

A robust velocity field control

This paper is devoted to velocity field control (VFC) of uncertain robotic manipulators. We propose a proportional-integral (PI)-type controller derived from modeling error compensation ideas and singular perturbation theory, that requires a minimum knowledge of the plant (i.e., constant estimate of the inertia matrix). It is shown that semiglobal practical stabilization is achieved; that is, given any compact set of initial velocity field errors, there exist PI control gains which guarantee that the robot tracks a desired velocity field with arbitrary accuracy. The proposed controller was experimentally evaluated on a two degrees-of-freedom arm.

Adaptive Desired Velocity Field Generation for Leader-Follower Type Cooperative Wheeled Mobile Robots with Decentralized Passive Velocity Field Control

Adaptive Desired Velocity Field Generation for Leader-Follower Type Cooperative Wheeled Mobile Robots with Decentralized Passive Velocity Field Control

Passive velocity field control (PVFC). Part I. Geometry and robustness

Passive velocity field control is a control methodology for fully actuated mechanical systems, in which the motion task is specified behaviorally in terms of a velocity field, and the closed-loop system is passive with respect to a supply rate given by the environment power input. The control law is derived geometrically and the geometric and robustness properties of the closed-loop system are analyzed. It is shown that the closed-loop unforced trajectories are geodesics of a closed-loop connection which is compatible with an inertia metric, and that the velocity of the system converges exponentially to a scaled multiple of the desired velocity field. The robustness property of the system exhibits some strong directional preference. In particular, disturbances that push in the direction of the desired momentum do not adversely affect the performance. Moreover, robustness property also improves with more energy in the system.

Passive velocity field control of mechanical manipulators

Two concepts are advocated for the task specification and control of mechanical manipulators: 1) coding tasks in terms of velocity fields; 2) designing controllers so that the manipulator when under feedback control, interacts in an energetically passive manner with its physical environment. Based on these two concepts, a new passive velocity field controller is proposed which mimics the behavior of a passive energy storage element, such as a flywheel or a spring. It stores and releases energy while interacting with the manipulator, but does not generate any. The controller has the interesting property that it stabilizes any multiple (positive or negative) of the desired velocity field, and exponentially stabilizes the particular multiple of the desired velocity field which is determined by the total kinetic energy of the manipulator control system.

Drop breakup in the flow through fixed beds via stochastic simulation in model Gaussian fields

Shaqfeh and Koch have shown that the flow through a dilute disordered fixed bed of fibers produces large polymer conformation change beyond a certain critical flow rate [J. Fluid Mech. 244, 17 (1992)]. We now examine the effect of this flow on the shape and breakup of viscous drops. Because the flow through a dilute fixed bed is equivalent to a certain anisotropic Gaussian flow field, we follow our previous paper and reproduce a model of the flow through a spectral expansion where the wave number vectors are chosen from statistical distributions which ensure that the desired velocity field will be realized [Phys. Fluids 9, 1222 (1997)]. We examine the dynamics of model drop shapes, averaged over the Gaussian statistics of the flow field, by synthesizing a large number of flow realizations. The drop surface is modeled using the first, second, and third order small deformation theories which can accurately predict critical conditions in classical strong flows. While the first order model yields a bounded average drop shape for all flow conditions, the second and third order models demonstrate that the flow through fixed beds is indeed “strong” since beyond a certain value of the pore-size capillary number, Ca∼0.15, large average drop deformation occurs and the average drop shape becomes unbounded (“drop breakup”). This critical condition is determined for various viscosity ratios and fixed bed particle volume fractions. Similar to a simple shear flow, we find that there is a critical viscosity ratio, χ∼2.5, beyond which breakup is not observed in the fixed bed for any Ca. In addition, the critical condition is shown to depend heavily on the transient nature of the flow in the bed since approximately half of the flow fields in which drop breakup occurs would not break an initially spherical drop at any Ca if they were steady. For supercritical capillary numbers, we define conditions under which the unbounded drop shapes fragment into smaller droplets and we examine the drop breakup rates as a percentage of the drop population.

Computations of Boundary Optimal Control Problems for an Electrically Conducting Fluid

We study four optimal control problems for an electrically conducting fluid. The control is the (normal) electrical current on the boundary of the flow domain. The objectives are to match a desired velocity field, or to match a desired electrical potential field, or to minimize the potential gradient, or to minimize the vorticity in the flow domain. We develop a systematic way to use the Lagrange multiplier rules to derive an optimality system of equations from which an optimal solution can be computed. Mixed finite element methods are used to find approximate solutions for the optimality systems of equations that characterize the optimal controls. A direct method and an iterative method are proposed for solving the discrete, nonlinear optimality systems of equations. Numerical results for several examples are presented.

Experiments on the Diffusion of Smoke in Isotropic Turbulent Flow

Detailed properties of the downstream evolution of smoke released in an isotropic turbulent flowfield are reported. Effects of turbulence on the mass-transfer characteristics of the flow, which in turn affect such things as the spread of pollution and the rate of chemical reactions, are studied. Smoke is released a short distance downstream of a uniform grid placed perpendicular to a uniform stream of air in a wind tunnel. A laser Doppler velocimeter is used to make the desired velocity field measurements, and a laser light-scatttering technique provides the instantaneous11 mass fraction c of smoke at the same point in the flowfield. One-point statistical properties of the velocity and concentration fields are obtained. The one-point cross correlations cu and cv are also reported.

Experimental Investigation of an Axisymmetric Jet in a Coflowing Airstream

The flow development of an axisymmetric jet exhausting into a moving airstream has been studied. The jet has a Reynolds number of 22,600, and the ratio of the jet velocity to the wind tunnel velocity is 5.1 to 1. The flow field of the axisymmetric jet was examined at locations varying from approximately zero to eight diameters downstream of the orifice. Of primary concern at each downstream location was the mapping of the one point statistical properties of the flow, including mean velocity, turbulent intensity, and intermittency. Autocorrelations and power spectral density curves were determined for both the fluctuating velocity field and the concentration signal at various distances from the jet's center line for different downstream locations. A laser Doppler velocimeter, using a phase locked loop processor, was used to make the desired velocity field measurements which were compared with hot wire anemometer and pressure probe data.