Numerous Control Methods Research Articles

Application of numerical transition control method to enhance turbulence in a natural convection boundary layer over a vertical heated plate

The present paper describes the application of local perturbations in Large Eddy Simulation to enhance transition to turbulence applied on the heated wall of a natural convection boundary layer. Simulations are carried out with a Prandtl number Pr=0.71 and a maximum Grashof number of Gr=4.1×1011. The purpose of this work is to accelerate the transition process in the numerical domain, reducing the needed simulation effort to reach the turbulent regime in a natural convection boundary layer flow. A parametric study has been performed to identify the fastest transition to turbulence in the proposed technique. The obtained results are compared with experimental, empirical and other numerical reference data to assess the method’s performance. The analysis of the transition method contemplates its effect in the mean flow field, as well as in the resolved Reynolds stresses and turbulent heat fluxes.

G-band Rectangular Beam Extended Interaction Klystron Based on Bi-Periodic Structure

A rectangular beam G-band extended interaction klystron (EIK) based on planar bi-periodic slow wave structure (SWS) is proposed. Such structure has the advantages of uniform and strong electric field, as well as the large frequency spacing, which implies that EIK adopting such structure will have strong beam–wave interaction and will be easy to avoid the mode competition. Furthermore, the planar structure is compatible to the microfabrication technology, thus reducing the fabrication difficulty of THz vacuum electron devices with small sizes. Compared with the sheet beam and large beam current, the rectangular beam with small aspect ratio and the decreased current is easy to realize the beam focusing and high power in engineering. Under the voltage of 16.5 kV, current of 0.3 A, and beam size of 0.30 mm × 0.13 mm, particle in cell simulations show a considerable output power of 390 W, with gain of 38.9 dB, efficiency of 7.9%, and relatively wide bandwidth of 800 MHz. The high-frequency structure has been fabricated by computer numerical control method, and the measurement results are close to the simulations. The proposed planar bi-periodic SWS shows certain superiorities in the performance improvement of millimeter-wave and terahertz EIK.

Spiral Bevel Gears Face Roughness Prediction Produced by CNC End Milling Centers.

The emergence of multitasking machines in the machine tool sector presents new opportunities for the machining of large size gears and short production series in these machines. However, the possibility of using standard tools in conventional machines for gears machining represents a technological challenge from the point of view of workpiece quality. Machining conditions in order to achieve both dimensional and surface quality requirements need to be determined. With these considerations in mind, computer numerical control (CNC) methods to provide useful tools for gear processing are studied. Thus, a model for the prediction of surface roughness obtained on the teeth surface of a machined spiral bevel gear in a multiprocess machine is presented. Machining strategies and optimal machining parameters were studied, and the roughness model is validated for 3 + 2 axes and 5 continuous axes machining strategies.

Horned lark damage to pre-emerged canola seedlings

Winter canola (Brassica napus L.) is considered the most promising domestically-produced oilseed feedstock for biodiesel production and for diversifying wheat (Triticum aestivum L.)-based cropping systems in the Inland Pacific Northwest, USA. Winter canola field experiments conducted in east-central Washington were completely destroyed, and commercial fields were damaged or destroyed, over several years by large flocks of horned larks (Eremophilia alperestis L.) that ate the cotyledon leaves of pre-emerged and newly-emerged seedlings. Numerous control methods were attempted in field experiments, including laying bird netting over the entire experiment, placement of a life-size predator decoy in a field experiment, loud propane-powered cannon blasts, and mixing garlic with canola seed before planting followed by spraying garlic water on the soil surface. None of the attempted control methods were successful. This is the first report in the literature of horned lark damage to pre-emerged and newly-emerged canola seedlings. We discuss questions relevant to our novel account as well as potential abatement using falcons and non-toxic chemical repellents for the protection of industrial canola crops associated with horned lark depredation.

A Novel Adaptive Wide Area PSS Based on Output-Only Modal Analysis

Usage of wide area PSSs (WAPSS) in actual power systems is limited because of their restricted adaptability to different operating conditions. Numerous adaptive control methods have been proposed to solve this problem, but they are limited due to strict prerequisites, such as the necessity of consistent excitations or large disturbances. This paper, therefore, presents a novel adaptive wide area PSS (AWAPSS), which has the ability of tracking system operating condition without the need for meeting the above prerequisites. The inherent dead-band structure of a WAPSS enables a steady system to perform like in an open loop, thus allowing the parameters of a WAPSS to be tuned adaptively through output-only modal analysis. The effectiveness of the novel AWAPSS has been validated in a two-area four-machine system as well as in a large complex system, China Southern Grid.

Bed bugs (Cimex lectularius): Biology and their Role as Pests to Humans

Bed bugs (Cimex lectularius) are blood feeding ectoparasites that have evolved as human pests due to their unique biology and reproduction. Common side effects of bed bug bites include: skin lesions, localized inflammation, itchiness and anxiety. There are numerous control methods to reduce bed bug populations such as vacuuming, steaming, laundering, exposure to extreme temperatures and chemical eradication methods. Bed bugs have become resistant to pyrethroid insecticides and DDT, supporting the cosmopolitan reemergence of bed bugs in the last couple decades.

Virtual Formation Method for Precise Autonomous Absolute Orbit Control

This paper analyzes the problem of precise autonomous orbit control of a spacecraft in a low Earth orbit. Autonomous onboard orbit control means that the spacecraft maintains its ground track close to a reference trajectory, without operator intervention. The problem is formulated as a specific case of two spacecraft in formation in which one, the reference, is virtual and affected only by the Earth’s gravitational field. A new parametrization, the relative Earth-fixed elements, is introduced to describe the relative motion of the two spacecraft’s subsatellite points on the Earth surface. These relative elements enable the translation of absolute-into-relative orbit-control requirements and the straightforward use of modern control-theory techniques for orbit control. As a demonstration, linear and quadratic optimum regulators are designed and compared, by means of numerical simulations, with an analytical autonomous orbit-control algorithm that has been validated in flight. The differences of the numerical and analytical control methods are identified and discussed.

PCIM: Project Control and Inhibiting-Factors Management Model

In construction projects, the aim of project control is to ensure projects finish on time, within budget, and achieve other project objectives. During the last few decades, numerous project control methods have been developed and adopted by project managers in practice. However, many existing methods focus on describing what the processes and tasks of project control are; not on how these tasks should be conducted. There is also a potential gap between principles that underly these methods and project control practice. As a result, time and cost overruns are still common in construction projects, partly attributable to deficiencies of existing project control methods and difficulties in implementing them. This paper describes a new project cost and time control model, the project control and inhibiting factors management (PCIM) model, developed through a study involving extensive interaction with construction practitioners in the UK, which better reflects the real needs of project managers. A set of good practice checklist is also developed to facilitate implementation of the model.

Symplectic Transformation Based Analytical and Numerical Methods for Linear Quadratic Control with Hard Terminal Constraints

Feedback gain and feedforward input of conventional linear quadratic (LQ) hard terminal controllers tend to infinity at terminal time, so that the conventional controllers have to go open-loop for a short interval before the final time. This short interval is called blind time. To avoid the terminal infinite feedback control gain and feedforward input, new optimal control laws are proposed for hard terminal control of linear time-varying systems. Furthermore, a structure-preserving numerical method is also presented to evaluate the time-varying optimal feedback and feedforward control gains and corresponding optimal trajectory. The analytical and numerical methods being developed here are based on the application of symplectic (canonical) transformation and generating functions of Hamiltonian systems. Different from the existing generating function method for optimal control, the first type of generating function plays a key role in solving the associated Hamiltonian two-point boundary-value problem (TPBVP), while the second generating function is employed to recover the first type. This note uses the second and third types of generating functions to find novel optimal control laws by solving the Hamiltonian TPBVP, which eliminates the infinite control gains of conventional optimal control laws near terminal time. Since the optimal trajectory of the closed-loop system is a solution of the Hamiltonian TPBVP, by using symplecticity of the solution operator of the linear Hamiltonian system, this paper also derives a structure-preserving matrix recursive algorithm for the computation of time-varying optimal control gains and the systems optimal trajectories. Numerical simulations show that this structure-preserving algorithm gives accurate results for relative large discrete steps and keeps geometric properties of the solutions.

Finding the Most Likely Trajectories of Optimally-Controlled Stochastic Systems

AbstractOptimal trajectories of deterministic systems satisfy Pontryagin's maximum principle and can be computed efficiently. Related results for stochastic systems exist but they lack the simplicity and computational efficiency of the deterministic case. Here we show that a certain class of both discrete-time and continuous-time nonlinear stochastic control problems obey a classic maximum principle, in the sense that the most likely trajectory of the optimally-controlled stochastic system is the solution to a deterministic optimal control problem. Apart from their theoretical significance, our results yield new numerical methods for stochastic control.

An Investigation on the Ship Rudder with Different Control System

In this study, it has been searched that how control changes with different controls by discussing technical properties of a chemical tanker. Nowadays numerous control methods have been developed on this purpose. In this study, controlling of drift and roll motions of chemical tankers has been done by using proportional, integral, derivative and fuzzy logic methods. In performed simulations, second order Nomoto model has been used for drift motion that has one degree of freedom.

Numerical simulation of temperature rise within hydrogen vehicle cylinder during refueling

Basing on the Spallart-Allmaras turbulence model and the real gas equation of state, a numerical model is proposed in this paper to study the mechanism of temperature rise within hydrogen vehicle cylinder during refueling. The model is validated by comparing calculated results with experimental data. With the validated model, the effect of mass filling rate, initial pressure within cylinder and ambient temperature on the maximum temperature rise during refueling are investigated. The study shows that the maximum temperature rise increases with the growth in mass filling rate and ambient temperature, while it descends as the initial pressure increases. Finally, an empirical formula is obtained by fitting numerical results and effective methods for temperature control is given.

Numerical study and control method of interaction of nucleation and boundary layer separation in condensing flow

The spontaneous nucleation flow in turbine cascade was numerically studied. The model was implemented within a full Navier-Stokes viscous flow solution procedure and the process of condensation was calculated by the quadrature method of moments that shows good accuracy with very broad size distributions. Results were presented for viscous and inviscous flow, showing the influence of boundary layer separation and wake vortices on spontaneous nucleation. The results show that the degree of flow separation in wet steam flow is greater than that in superheated steam flow due to condensation shock and that the loss cannot be neglected. Furthermore, the impact of boundary layer separation and wake vortices on velocity profiles and its implications for profile loss were considered. The calculations showed that layer separation and wake vortices influence nucleation rate, leading to different droplet distributions. A method for controlling homogeneous nucleation and for reducing degree of flow separation in high-speed transonic wet steam flow was presented. The liquid phase parameter distribution is sensitive to the suction side profile of turbine cascade, which impacts the nucleation rate distribution leading to different droplet distributions and affects the degree of flow separation. The numerical study provides a practical design method for turbine blade to reduce wetness losses.

A discrete model of the plate heat exchanger

A discrete model of the plate heat exchanger Developing numerical control methods requires precise models of technical machines. The article presents a discrete model of a plate heat exchanger. The model was worked out based on differential equations to secure high accuracy. Correctness of the model was verified using the data for the M10 - MFM cooler produced by Alfa-Laval.

Energy controlled shunt active power filters

PurposeShunt active power filters are used to decrease or almost eliminate non‐active currents flowing through the supply source. Numerous control methods of active filters have been proposed in many papers. The aim of this paper is to demonstrate a simple but very effective method of obtaining the compensated load active current.Design/methodology/approachThe method allows one to control the shunt active power filter only by monitoring energy stored in the filter. Based on the introduced generic structure of the filter the changes of filter energy are examined in order to obtain the reference current for the filter compensation action.FindingsThis presented method can be implemented to nearly all structures of active filters. It is suitable not only for the single‐phase but also for the three‐phase circuit. Such energy‐controlled filters may be built on the basis of voltage‐ and current‐source inverters as well.Originality/valueThis paper provides an alternative approach to address the problem of the shunt active filter control method. The paper shows that monitoring the filter's energy suffices for proper control of the filter compensation action.

Numerical solution methods for singular control with multiple state dependent forms

We use several recently developed techniques along with two established optimal control softwares to solve a variation of a widely studied singular optimal control problem. The problem displays some interesting features from both the analytical and numerical point of view. In particular, we show that, during singular arcs, the optimal control takes on one of two distinct state dependent forms. We also demonstrate how the numerical solution methods can easily get trapped in what may appear to be local optima when applied to this problem.

Computational dynamics: theory and applications of multibody systems

Multibody system dynamics is an essential part of computational dynamics a topic more generally dealing with kinematics and dynamics of rigid and flexible systems, finite elements methods, and numerical methods for synthesis, optimization and control including nonlinear dynamics approaches. The theoretical background of multibody dynamics is presented, the efficiency of recursive algorithms is shown, methods for dynamical analysis are summarized, and applications to vehicle dynamics and biomechanics are reported. In particular, the wear of railway wheels of high-speed trains and the metabolical cost of human locomotion is analyzed using multibody system methods.

Microencapsulated BioBullets for the Control of Biofouling Zebra Mussels

The widespread invasion of freshwaters by the zebra mussel, Dreissena polymorpha, during the last 2 decades has made it one of the world's most economically and ecologically important pests. Since arriving in the North American Great Lakes in the 1980s, zebra mussels have become a major biofouler, blocking the raw water cooling systems of power stations and water treatment works and costing U.S. dollars 1-5 billion per year. Despite the development of numerous control methods, chlorination remains the only widespread and licensed technique. Zebra mussels are able to sense chlorine and othertoxins in their surrounding environment and respond by closing their valves, thus enabling them to avoid toxic effects for up to 3 weeks. Furthermore, prolonged dosing of chlorine in raw water produces ecotoxic trihalomethanes (THMs) by reaction with organic material in the water. We have developed a novel, environmentally safe, and effective method for controlling the zebra mussel: the BioBullet. Our method uses the encapsulation of an active ingredient (KCI) in microscopic particles of edible material. The mussels' natural filtering ability then removes and concentrates the particles from the water, without stimulating the valve-closing response. By using the mussels' filtering behavior to concentrate BioBullets the absolute quantity of active ingredient added to the water can be reduced substantially. Our approach allows us to engineer the particles to break up and dissolve completely within a few hours, thus eliminating the risk of polluting the wider ecosystem. We demonstrate that the effectiveness of a toxin in the control of biofouling filter-feeders can be enhanced greatly by using our technique. This paves the way for a new approach to the control of some of the world's most important economic pests.

A comparison of algorithms for control constrained optimal control of the Burgers equation

A comparison of three different but related numerical methods for control constrained optimal control of the Burgers equation is carried out. We develop the principal ideas of the different strategies considered and present detailed numerical examples. Lastly, conclusions about the behavior of the approaches are obtained.

Validated numerical methods for systems and control engineering

The aim of this research is to investigate the development of numerical methods for systems and control which have a guarantee on accuracy. An end-product of such research is an algorithm which could be described as "infallible" in the following sense: the user would specify a priori a tolerance as small as desired, and the computer would provide an answer which was guaranteed to be accurate to the specified tolerance. Though this is an established subject within Computer Science [5], as well as a few application areas in science and engineering (see [1, Part III]), the direction appears to be quite new in the control systems area. A characteristic feature of previous work is the application of computer algebra tools and the avoidance of floating-point arithmetic.