bluuebunny/crossref_metadata_2025 huggingface dataset:
Content and Language Integration in K–12 Contexts: Student Outcomes, Teacher Practices, and Stakeholder Perspectives
Authors: Tedick Diane J. , Cammarata Laurent
Published: May 2012

This literature review, which examines the research on integrating the teaching of content and language at the pre‐K–12 level, provides a synthesis of research conducted over the past 10 years in a wide array of educational contexts, ranging from content‐driven, high time‐intensive to language‐driven, low time‐intensive program models. Organized into three major thematic strands, this review examines research on student outcomes, on classroom interaction studies that emphasize teacher practice, and on stakeholder perspectives in contexts where approaches aiming at integrating content and language in instruction are being implemented. The review concludes with a discussion highlighting key issues that remain to be addressed and outlines directions for future research.
In Search of Innovation: Research on Effective Models of Foreign Language Teacher Preparation
Authors: Huhn Christina
Published: May 2012

Today's teachers must be more than transmitters of knowledge who orchestrate repetitive practice of decontextualized language forms with students: They need to infuse language instruction with meaning and purpose, design opportunities for interaction within and beyond the classroom, and provide responsive and useful assistance throughout the learning process. This review reveals a paucity of empirical research that provides evidence for models of foreign language teacher preparation with the potential to prepare teachers for this role. Despite this lack of research, this review illustrates how the ACTFL/NCATE Program Standards for the Preparation of Foreign Language Teachers (ACTFL, 2002) may be invoked as a viable framework for identifying the components of effective and innovative foreign language teacher preparation programs, presenting current programs that exemplify those components, and suggesting continued application of the standards and future research to further define features of model teacher preparation.
Distorted‐distance models for directional dispersal: a general framework with application to a wind‐dispersed tree
Authors: van Putten Bram , Visser Marco D. , Muller‐Landau Helene C. , Jansen Patrick A.
Published: May 2012

1. Seed and pollen dispersal is often directionally biased, because of the inherent directionality of wind and many other dispersal vectors. Nevertheless, the vast majority of studies of seed and pollen dispersal fit isotropic dispersal kernels to data, implicitly assuming that dispersal is equally likely in all directions.

2. Here, we offer a flexible method for stochastic modelling of directional dispersal data. We show how anisotropic models can be constructed by combining standard dispersal functions with ‘distorted‐distance functions’ that transform the circular contour lines of any isotropic dispersal kernel into non‐circular shapes. Many existing anisotropic phenomenological models of seed and pollen dispersal are special cases of our framework.

3. We present functional forms for the specific case of elliptic distorted‐distance functions, under which contour lines of the seed shadow become non‐concentric, nested ellipses, and show how models using these functions can be constructed and parameterized. R‐code is provided.

4. We applied the elliptic anisotropic models to characterize seed dispersal in the wind‐dispersed Neotropical treeLuehea seemannii(Malvaceae) on Barro Colorado Island, Panama. We used inverse modelling to fit alternative models to data of seed rain into seed traps, the locations of seed traps and adult trees, and tree size.

5. Our anisotropic model performed considerably better than commonly applied isotropic models, revealing that seed dispersal ofL. seemanniiwas strongly directional. The best‐fitting model combined a 3‐parameter elliptic distorted‐distance function that captured the strong directional biases with a 1‐parameter exponential dispersal kernel, a 1‐parameter negative binomial probability distribution describing the clumping of seed rain and a 1‐parameter function relating tree fecundity to tree diameter.

6. The framework presented in this paper enables more flexible and accurate modelling of directional dispersal data. It is applicable not only to studies of seed dispersal, but also to a wide range of other problems in which large numbers of particles disperse from one or more point sources.
Large Eddy Simulation of the Unsteady Flow in a Radial Compressor Operating Near Surge
Authors: Hellstrom Fredrik , Gutmark Ephraim , Fuchs Laszlo
Published: May 2012

The flow in a centrifugal compressor has been computed using large eddy simulation (LES). The investigated geometry is that of a ported shroud compressor with a 10 blade impeller with an exducer diameter of 88 mm. The computational data compares favorably with measured data for the same compressor and operational point. For the considered operational point near surge, the flow field in the entire compressor stage is unsteady. Back-flow occurs in the diffuser, wheel, and the ported shroud channels resulting in back-flow at the walls in the inlet region of the compressor. In the diffuser and volute, the flow is highly unsteady with perturbations that are convected around the volute, affecting the flow field in most of the entire compressor. The mechanism driving this unsteadiness is assessed by flow visualizations, frequency analysis, and correlations of pressure and velocity data in order to gain a more comprehensive understanding of the mechanism leading to stall and surge.
Effects of an Upstream Cavity on the Secondary Flow in a Transonic Turbine Cascade
Authors: Abo El Ella H. M. , Sjolander S. A. , Praisner T. J.
Published: May 2012

This paper examines experimentally the effects of an upstream cavity on the flow structures and secondary losses in a transonic linear turbine cascade. The cavity approximates the endwall geometry resulting from the platform overlap at the interface between stationary and rotating turbine blade rows. Previous investigations of the effects of upstream cavity geometries have been conducted mainly at low-speed conditions. The present work aims to extend such research into the transonic regime with a more engine representative upstream platform geometry. The investigations were carried out in a blow-down type wind tunnel. The cavity is located at 30 % of axial chord from the leading edge, extends 17 % of axial-chord in depth, and is followed by a smooth ramp to return the endwall to its nominal height. Two cascades are examined for the same blade geometry: the baseline cascade with a flat endwall and the cascade with the cavity endwall. Measurements were made at the design incidence and the outlet design Mach number of 0.80. At this condition, the Reynolds number based on outlet velocity is about 600,000. Off-design outlet Mach numbers of 0.69, and 0.89 were also investigated. Flowfield measurements were carried out at 40 % axial-chord downstream of the trailing edge, using a seven-hole pressure probe, to quantify losses and identify the flow structures. Additionally, surface flow visualization using an ultra-violet reactive dye was employed at the design Mach number, on the endwall and blade surfaces, to help in the interpretation of the flow physics. The experimental results also include blade-loading distributions, and the probe measurements were processed to obtain total-pressure loss coefficients, and streamwise vorticity distributions. It was found that the presence of the upstream cavity noticeably altered the structure and the strength of the secondary flow. Some effect on the secondary losses was also evident, with the cavity having a larger effect at the higher Mach number.
A New Reduced Order Modeling for Stability and Forced Response Analysis of Aero-Coupled Blades Considering Various Mode Families
Authors: Mayorca María A. , Vogt Damian M. , Fransson Torsten H. , Mårtensson Hans
Published: May 2012

This paper presents the description and application of a new method for stability and forced response analyses of aerodynamically coupled blades considering the interaction of various mode families. The method, here referred as multimode least square, considers the unsteady forces due to the blade motion at different modes shape families and calculates the aerodynamic matrixes by means of a least square (L2) approximations. This approach permits the prediction of mode families’ interaction with capabilities of structural, aerodynamic and force mistuning. A projection technique is implemented in order to reduce the computational domain. Application of the method on tuned and structural mistuned forced response and stability analyses is presented on a highly loaded transonic compressor blade. When considering structural mistuning the forced response amplitude magnification is highly affected by the change in aerodynamic damping due to mistuning. Analyses of structural mistuning without aerodynamic coupling might result in over-estimated or under-estimated response when the source of damping is mainly aerodynamic. The frequency split due to mistuning can cause that mode families’ interact due to reducing their frequencies separation. The advantage of the present method is that the effect of mode family interaction on aerodynamic damping and forced response is captured not being restricted to single mode families.
A Study of Fan-Distortion Interaction Within the NASA Rotor 67 Transonic Stage
Authors: Fidalgo V. Jerez , Hall C. A. , Colin Y.
Published: May 2012

The performance of a transonic fan operating within nonuniform inlet flow remains a key concern for the design and operability of a turbofan engine. This paper applies computational methods to improve the understanding of the interaction between a transonic fan and an inlet total pressure distortion. The test case studied is the NASA rotor 67 stage operating with a total pressure distortion covering a 120-deg sector of the inlet flow field. Full-annulus, unsteady, three-dimensional CFD has been used to simulate the test rig installation and the full fan assembly operating with inlet distortion. Novel post-processing methods have been applied to extract the fan performance and features of the interaction between the fan and the nonuniform inflow. The results of the unsteady computations agree well with the measurement data. The local operating condition of the fan at different positions around the annulus has been tracked and analyzed, and this is shown to be highly dependent on the swirl and mass flow redistribution that the rotor induces ahead of it due to the incoming distortion. The upstream flow effects lead to a variation in work input that determines the distortion pattern seen downstream of the fan stage. In addition, the unsteady computations also reveal more complex flow features downstream of the fan stage, which arise due to the three dimensionality of the flow and unsteadiness.
Optimal Parameter Estimation for Long-Term Prediction in the Presence of Model Mismatch
Authors: Lee Ryan Sangjun , Buzzard Gregery T. , Meckl Peter H.
Published: May 2012

For nonlinear multi-input multi-output (MIMO) systems such as multilink robotic manipulators, finding a correct, physically derived model structure is almost impossible, so that significant model mismatch is nearly inevitable. Moreover, in the presence of model mismatch, the use of least-squares minimization of the one-step-ahead prediction error (residual error) to estimate unknown parameters in a given model structure often leads to model predictions that are extremely inaccurate beyond a short time interval. In this paper, we develop a method for optimal parameter estimation for accurate long-term prediction models in the presence of significant model mismatch in practice. For many practical cases, where a correct model and the correct number of degrees of freedom for a given model structure are unknown, we combine the use of long-term prediction error with frequency-based regularization to produce more accurate long-term prediction models for actual MIMO nonlinear systems.
Forced Convection Heat Transfer in Spray Formed Copper and Nickel Foam Heat Exchanger Tubes
Authors: Tsolas Nicholas , Chandra Sanjeev
Published: May 2012

A thermal spray coating process was used to deposit dense 2 mm thick metal skins on the surfaces of square cross-section channels (300 mm × 20 mm × 20 mm) of nickel and copper foams with 10 and 40 PPI (pores per inch) pore densities. A heater was wrapped around the channels to apply surface heat-fluxes varying from 427 to 6846 W/m2. Compressed air was blown through the channels at flow rates of 5–80 l/min. Foam and fluid temperature distributions along the length of the channel and the pressure drop across it were measured. The foam was modeled as a porous medium and properties such as permeability K and inertial coefficient CF were determined from the experimental data. Local and average convective heat transfer coefficients were calculated from air and foam temperature measurements. Nusselt numbers were calculated and correlated in terms of the Reynolds, Prandtl, and Darcy numbers. Heat transfer to air flowing through a 10 PPI foam channel was shown to have increased nearly seven times compared to that of hollow tube with the same dimensions.
Numerical Simulation of Wind Distributions for Resource Assessment in Southeastern Eritrea, East Africa
Authors: Lebassi-Habtezion B. , Van Buskirk R.
Published: May 2012

We present the results of a simulation study of the wind energy resources of southeastern Eritrea. In this study, we simulate the three dimensional wind fields during typical, steady conditions of the Southern Red Sea southeast monsoon season. The simulations verify the existence of a low level jet (LLJ) contained within the highly stratified marine layer over the Southern Red Sea. The LLJ is caused by the channeling and the acceleration of marine layer flow as it passes through the strait of Bab el Mandeb on its way from the Indian Ocean to the Eastern Sahara. The LLJ extends from 12.5 deg to 14.5 deg N latitude in the Southern Red Sea and has peak velocities at 300–600 m elevation above the sea. Sea-land breezes advect the high speeds of the LLJ onshore along a 200 km stretch of southeastern Eritrean coastline, producing an excellent wind energy resource that peaks daily at 3 p.m. LST. This resource is currently under development for both grid-connected and decentralized village wind energy applications.
Understanding Effect of Grain Boundaries in the Fracture Behavior of Polycrystalline Tungsten under Mode-I Loading
Authors: Lee Hongsuk , Tomar Vikas
Published: May 2012

Polycrystalline tungsten is considered as an important material in aerospace, automobile, and energy industries due to its excellent thermal and mechanical properties. While grain boundaries (GBs) are perceived to play a major role in polycrystalline tungsten failure resistance, experimental data are scarce on explicit contribution of GBs to tungsten failure resistance. The present work focuses on understanding the effect of GB property variation on fracture resistance of polycrystalline tungsten. The cohesive finite element method is used for the simulation of crack propagation in polycrystalline tungsten microstructures. The results show a significant effect of GB property variation on change of crack propagation patterns during tungsten fracture. A variation of 10% in GB fracture energy resulted in distinctly different crack patterns with different primary crack propagation direction and the microcrack density. Based on the observed microstructural fracture attributes, a relation between cohesive energy dissipation and microcrack density in polycrystalline tungsten microstructures is proposed.
Hemodialysis Graft Resistance Adjustment Device
Authors: Hopkins Brandon J. , Wu Huayin , Marks William H. , Quan Qimin , Kesner Samuel , Ozaki C. Keith , Walsh Conor
Published: May 2012

Up to eight percent of patients develop steal syndrome after prosthetic dialysis access graft placement, which is characterized by low blood flow to the hand. Steal syndrome results in a cold hand, pain, and in extreme cases, loss of function and tissue damage. A practical and easy way of adjusting the fluidic resistance in a graft to attenuate the risk of steal physiology would greatly benefit both surgeons and patients. This paper describes the design and development of a device that can be attached to a dialysis access graft at the time of surgical implantation to enable providers to externally adjust the resistance of the graft postoperatively. Bench level flow experiments and magnetic setups were used to establish design requirements and test prototypes. The Graft Resistance Adjustment Mechanism (GRAM) can be applied to a standard graft before or after it is implanted and a non-contact magnetic coupling enables actuation through the skin for graft compression. The device features a winch-driven system to provide translational movement for a graft compression unit. We expect such a device to enable noninvasive management of steal syndrome in a manner that does not change the existing graft and support technologies, thus reducing patient complications and reducing costs to hospitals.
Piecewise B-Spline Tool Paths With the Arc-Length Parameter and Their Application on High Feed, Accurate CNC Milling of Free-Form Profiles
Authors: Chen Zezhong C. , Khan Maqsood A.
Published: May 2012

To conduct B-spline curve machining, first, B-spline tool paths with feed rates are planned; and second, the B-spline interpolator generates tool trajectories in real-time based on the paths fed into the computer numerically controlled (CNC) controller. Currently, the paths are often planned geometrically with a nonarc-length parameter. Literally, the interpolator can process B-spline paths with the arc-length parameter well, while it sometimes is challenged to work with the nonarc-length parameterized B-spline paths. As a consequence, it is difficult to ensure high accuracy of the tool trajectories in B-spline machining in terms of their corresponding paths; especially, if the feed is very high, smooth tool kinematics cannot be well maintained. To root out these problems, a new type of tool path—piecewise B-spline tool paths with the arc-length parameter—is first proposed in this work. Given a B-spline path with a nonarc-length parameter, it is accurately converted into a B-spline path with an arc-length parameter before sending it into the CNC controller. Furthermore, if the prescribed feed rate is very high and the arc-length parameterized B-spline path is disqualified, it is split into pieces represented with distinct arc-length parameterized B-spline paths in different feed rates. The main advantage of these piecewise paths is that they can eliminate the problems encountered by the existing B-spline interpolator with input of nonarc-length parameterized B-spline paths. Therefore, the piecewise arc-length parameterized B-spline paths are a genuine solution to high feed-and-accuracy B-spline machining.
The Biomechanical Function of Arterial Elastin in Solutes
Authors: Zou Yu , Zhang Yanhang
Published: May 2012

Elastin is essential to accommodate physiological deformation and provide elastic support for blood vessels. As a long-lived extracellular matrix protein, elastin can suffer from cumulative effects of exposure to chemical damage, which greatly compromises the mechanical function of elastin. The mechanical properties of elastin are closely related to its microstructure and the external chemical environments. The purpose of this study is to investigate the changes in the macroscopic elastic and viscoelastic properties of isolated porcine aortic elastin under the effects of nonenzymatic mediated in vitro elastin–lipid interactions and glycation. Sodium dodecyl sulfate (SDS) was used for elastin–lipid interaction, while glucose was used for glycation of elastin. Elastin samples were incubated in SDS (20 mM) or glucose (2 M) solutions and were allowed to equilibrate for 48 h at room temperature. Control experiments were performed in 1  ×  Phosphate buffered saline (PBS). Biaxial tensile and stress relaxation experiments were performed to study the mechanical behavior of elastin with solute effects. Experimental results reveal that both the elastic and viscoelastic behaviors of elastin change in different biochemical solvents environments. The tangent stiffness of SDS treated elastin decreases to 63.57 ± 4.7% of the control condition in circumference and to 58.43 ± 2.65% in the longitude. Glucose treated elastin exhibits an increase in stiffness to 145.06 ± 1.48% of the control condition in the longitude but remains similar mechanical response in the circumferential direction. During stress relaxation experiments with a holding period of half an hour, elastin treated with SDS or glucose shows more prominent stress relaxation than the untreated ones.
A Mixed Frequency/Time-Domain Method to Evaluate the Performance of Semi-Active Steering Damper Control Strategies During Challenging Maneuvers
Authors: De Filippi Pierpaolo , Savaresi Sergio M.
Published: May 2012

This work presents the validation of control strategies for a semi-active steering damper aimed at improving the stability of two-wheeled vehicles by controlling the weave and wobble modes. A mixed frequency/time-domain method is introduced to evaluate the performance of the control strategies. The proposed cost functions allow one to evaluate the influence of the algorithms on the damping of the weave and wobble modes and also the overall performance in terms of stability of the steering assembly and of the chassis. The performance of the control algorithms is assessed on a multibody motorcycle simulator considering three challenging maneuvers that excite both the weave and wobble modes, such as kick-back and strong braking while cornering at high speed.
Classifications of Intentions for Controlling of a Multifunctional Knee-Ankle-Foot Orthosis
Authors: Wu Sai-Kit , Driver Tad , Shen Xiangrong
Published: May 2012

This paper describes motion intention classifiers which utilize reaction forces signals from heel and toe; and hip velocity information to predict subject’s intention. Those classifiers using Bayes method to predict (i) walk-to-stop, (ii) walking-speed-changing, and (iii) stop-to-motions. They are very accurate (most of them have accuracy rate higher than 90%) and a significant step in order to develop a multifunctional knee-ankle-foot orthosis.
Mixed H2/H∞ Observer-Based LPV Control of a Hydraulic Engine Cam Phasing Actuator
Authors: White Andrew , Ren Zhen , Zhu Guoming , Choi Jongeun
Published: May 2012

In this paper, a series of closed-loop system identification tests was performed for a variable valve timing cam phaser system on a test bench to obtain a family of linear models for an array of engine speeds and oil pressures. Using engine speed and oil pressure as the system parameters, the family of linear models was translated into a linear parameter varying (LPV) system. The engine speed and oil pressure can be measured in real-time by these sensors equipped on the engine, thus allowing their use as scheduling parameters. An observer-based gain-scheduling controller for the obtained LPV system is then designed based on the numerically efficient convex optimization or linear matrix inequality (LMI) technique. Test bench results show the effectiveness of the proposed scheme.
GPS-Free Terrain-Based Vehicle Tracking Performance as a Function of Inertial Sensor Characteristics
Authors: Jerath Kshitij , Brennan Sean N.
Published: May 2012

Prior experiments have confirmed that specific terrain-based localization algorithms, designed to work in GPS-free or degraded-GPS environments, achieve vehicle tracking with tactical-grade inertial sensors. However, the vehicle tracking performance of these algorithms using low-cost inertial sensors with inferior specifications has not been verified. The included work identifies, through simulations, the effect of inertial sensor characteristics on vehicle tracking accuracy when using a specific terrain-based tracking algorithm based on Unscented Kalman Filters. Results indicate that vehicle tracking is achievable even when low-cost inertial sensors with inferior specifications are used. However, the precision of vehicle tracking decreases approximately linearly as bias instability and angle random walk coefficients increase. The results also indicate that as sensor cost increases, the variance in vehicle tracking error asymptotically tends to zero. Put simply, as desired precision increases, increasingly larger and quantifiable investment is required to attain an improvement in vehicle tracking precision.
Modeling Peroxidase-Oxidase Interactions
Authors: Schaffer W. M. , Bronnikova T. V.
Published: May 2012

Reactive oxygen species (ROS) and peroxidase-oxidase (PO) reactions are Janus-faced contributors to cellular metabolism. At low concentrations, reactive oxygen species serve as signaling molecules; at high concentrations, as destroyers of proteins, lipids and DNA. Correspondingly, PO reactions are both sources and consumers of ROS. In the present paper, we study a well-tested model of the PO reaction based on horseradish peroxidase chemistry. Our principal predictions are these: 1. Under hypoxia, the PO reaction can emit pulses of hydrogen peroxide at apparently arbitrarily long intervals. 2. For a wide range of input rates, continuing infusions of ROS are transduced into bounded dynamics. 3. The response to ROS input is hysteretic. 4. With sufficient input, regulatory capacity is exceeded and hydrogen peroxide, but not superoxide, accumulates. These results are discussed with regard to the episodic nature of neurodevelopmental and neurodegenerative diseases that have been linked to oxidative stress and to downstream interactions that may result in positive feedback and pathology of increasing severity.
Optimal Nominal Pressurization Generation: A Novel Idea for a Discrete Logic Control Using an Independent Metering Valve Configuration
Authors: Meyer Christian , Weiler Daniel , Murrenhoff Hubertus
Published: May 2012

When using an independent metering valve configuration with a multivariable control concept the position and the rod side pressure level and therefore the pressurization level of the cylinder drive can be controlled. By controlling the rod side pressure and the position separately the operating area of the cylinder drive changes dependent on the actual nominal rod-side pressure. In order to reach every operation point with optimal stiffness a nominal pressure generation dependent on the actual operating point is needed. In this article a novel idea how to realize such a logic control for the optimal nominal pressurization level generation is presented. The main focus in this paper is the principal structure of such a logic control. The functionality is shown by simulation and measurement results of a differential cylinder drive.
Adaptive H∞ Vibration Control
Authors: O’Brien Richard T. , Watkins R. Joseph
Published: May 2012

This paper presents a procedure for designing an adaptive H∞ controller to reject sinusoidal disturbances with unknown constant frequencies. The proposed adaptive controller identifies the tonal frequencies in the disturbance and updates the controller to attenuate these frequencies. The controller design builds upon a closed-form solution for a simplified single-frequency attenuation problem. An application to optical beam jitter control illustrates the design procedure and its properties.
Energy-Based Modeling of Alternative Energy Storage Systems for Hybrid Vehicles
Authors: McDonough J. , Jebakumar K. , Chiara F. , Canova M. , Koprubasi K.
Published: May 2012

Alternative energy storage systems (AESS) are receiving considerable interest today for low-cost mild-hybrid vehicles where the electrical system is substituted with mechanical or hydraulic energy storage. As these technologies are being explored, simulation tools become helpful to predict the behavior of the energy storage system during vehicle use, as well as to conduct comparative studies evaluating the energy and power density, fuel economy improvement, system weight and costs. This paper presents an energy-based modeling approach to characterize the low-frequency dynamic behavior of alternative energy storage systems for hybrid vehicle applications, with the ability to predict the energy flows and sources of energy loss during driving operations. The model aims at evaluating the potential, in terms of efficiency and fuel economy improvement, offered by non-electrified energy storage systems, such as mechanical (flywheels) or hydraulic (accumulators). The modeling tool developed is able to provide a characterization of the performance of each of the two systems starting from a characterization of the components energy conversion behavior. The paper includes a simulation study where the performance of a mechanical and hydraulic energy storage system are compared on a forward-oriented hybrid vehicle simulator, with the objective of characterizing and comparing the energy recuperation process and the energy efficiency of the two systems.
Analysis of Antagonist Stiffness for Nested Compliant Mechanisms in Agonist-Antagonist Arrangements
Authors: Schultz Joshua A. , Ueda Jun
Published: May 2012

Members of the animal kingdom produce motion by muscle contraction. Biological muscle can be viewed as a unidirectional actuator. To achieve bidirectional motion, each muscle has a corresponding antagonist muscle whose contraction produces motion in the opposite direction. This gives biological systems the unique ability to modulate the stiffness of a joint, which is important when interacting with the environment. Certain bio-inspired robotic systems incorporate antagonistic pairs in an attempt to produce similar desirable properties. The cellular actuator employs nested compliant mechanisms to produce human-scale motion from piezoelectric stack actuators, which on their own have a small displacement. The expression for the stiffness of the actuator composed of these mechanisms takes the form of a continued fraction, which results from the nested structure. In this way, the stiffness can be easily approximated to a desired degree of accuracy by considering only the outermost mechanisms.
A Servo-Pneumatic Positioning System Driven by Fast Switching On/Off Valves
Authors: Locateli Cristiano Cardoso , De Negri Victor Juliano , De Pieri Edson Roberto
Published: May 2012

This paper discusses the theoretical and experimental results of a position control system using a pneumatic actuator driven by fast switching on/off valves. To begin with, there is a brief introduction about servo-pneumatic systems driven by fast switching valves. Subsequently, the mathematical model of the servo-pneumatic system is discussed involving directional fast switching on/off valves and the flow control valves, modeled according to the mass flow equation based on ISO 6358 and the actuator modeled by Newton’s second law and the continuity equation. The system control is performed through the pulse width modulation (PWM) technique used with a proportional-integrative-derivative (PID) controller. The system performance is analyzed in relation to its application for power control of wind turbines. The simulations of the servo-pneumatic system were carried out by Matlab/Simulink with the experimental results obtained through a test bench.
A Reduced-Order Model for Dynamic Vacuum Arc Remelting Pool Depth Estimation and Control
Authors: Lopez Luis Felipe , Beaman Joseph J. , Williamson Rodney L.
Published: May 2012

Vacuum arc remelting (VAR) is an industrial metallurgical process widely used throughout the specialty metals industry to cast large alloy ingots. A reduced-order model of the growing and solidifying ingot was developed specifically for dynamic control and estimation of the depth of molten liquid pool atop the ingot in a VAR process. This model accounts only for the thermal aspects of the system ignoring high-fidelity physics such as fluid flow and electromagnetic effects. Spectral methods were used to obtain a set of nonlinear dynamic equations which capture the transient characteristics of liquid pool shape variations around a quasi-steady operating condition. These nonlinear equations are then linearized about this operating condition and further simplified by suppressing fast modes. The resulting system can be described by only six state variables. The reduced order model compares favorably to pool depth changes predicted by an accurate finite-volume model. A first approach to use this model in the design of a dynamic VAR pool depth estimator and controller is also proposed.
Integrated Plant and Controller Design of a Combine Harvester System
Authors: Xie Yangmin , Alleyne Andrew
Published: May 2012

This article proposes a plant and controller design method based on performance analysis of a header height control problem on a combine harvester. The achievable bandwidth was found to be limited by the under-actuated and non-collocated features of the mechanical structure, and a parameter optimization is then applied to solve this problem by improving the property of open loop zeros and poles. H∞ controller design is used to achieve the best performance with the considerations of tracking bandwidth, disturbance rejection and control energy. The simulation results show that this approach can obtain relatively high closed loop bandwidth which surpasses the bandwidth limitation of the original plant. The simulation of tracking comparison also shows that the integrated plant and controller design generate a superior system response.
A Higher-Order Method for Dynamic Optimization of Controllable LTI Systems
Authors: Zanotto Damiano , Agrawal Sunil K. , Rosati Giulio
Published: May 2012

This work describes a new procedure for dynamic optimization of controllable Linear time-invariant (LTI) systems. Unlike the traditional approach, which results in 2n first order differential equations, the method proposed here yields a set of m differential equations, whose highest order is twice the controllability index of the system p. This paper generalizes the approach presented in a previous work [1] to any controllable LTI system.
Model Predictive Control of an Electro-Hydraulic Powertrain With Energy Storage
Authors: Deppen Timothy O. , Alleyne Andrew G. , Stelson Kim A. , Meyer Jonathan J.
Published: May 2012

This paper presents a model predictive control approach to solving the energy management problem within a series hydraulic hybrid powertrain. The hydraulic hybrid utilizes a high pressure accumulator for energy storage which has superior power density than conventional battery technology. This makes fluid power attractive for urban driving applications in which there are frequent starts and stops and large startup power demands. Model predictive control was chosen for control design because this technique requires no information about the future drive cycle, which can be highly uncertain in urban settings. The proposed control strategy was validated experimentally using an electro-hydraulic powertrain testbed which includes energy storage. The experimental study demonstrates the controller’s ability to track a reference trajectory while achieving efficient engine operation.
Model-Based Flow Property Estimation Using an Ionic Polymer-Metal Composite Beam
Authors: Chen Xuefei , Zhu Guoming , Yang Xiaojian , Tan Xiaobo
Published: May 2012

Ionic Polymer-Metal Composite (IPMC) material is capable of producing electrical current signal closely correlated to its mechanical movement due to redistribution of the free ions inside the IPMC material. Motivated by the potential applications of this intrinsic characteristic of IPMC beams to automotive engines for flow property measurements, such as fuel flow viscosity, this paper presents a finite-element dynamic model of an IPMC beam and uses it to estimate the fluid properties based upon the measured IPMC signal using the least squares minimization approach. The results show that with the distinct output signals of the IPMC beam under different fluid media, the identified flow properties (such as drag coefficient) have a good agreement with the actual fluid properties. This is very important for automotive applications when the characteristics of the fuel blend (such as gasoline and ethanol) need to be identified.
Spool Valve With Arbitrary Area-Schedule and Application to a Camless Engine Valve Actuator
Authors: Gillella Pradeep , Sun Zongxuan
Published: May 2012

This paper presents the design of a flow control valve in which the area-schedule i.e., the relationship between the spool position and the metering orifice area, can be chosen arbitrarily. The motivation for such a flow controller comes from a novel hydraulic actuator intended for camless valve actuation in internal combustion engines. The proposed actuator has a unique internal feedback system in which the motion of the flow regulator’s spool is hydro-mechanically coupled to the motion of the actuator. Lack of direct control over the spool position necessitates the appropriate modification of the area-schedule in order to control the variation of the orifice area. The design modifications required to realize the area-schedules are first discussed. A systematic procedure which combines CFD analysis and geometry based analysis is then developed to characterize the variation of the effective orifice area for various spool designs. The proposed analysis procedure is validated with experimental data from a prototype spool valve. The fast turn around time of the proposed analysis technique is used to develop an automated procedure to design the 3D features on the spool required to realize a specified area-schedule.
Diesel Engine Intake Condition Control-Oriented Models for Active Fuel Injection Profile Control
Authors: Yan Fengjun , Wang Junmin
Published: May 2012

Fueling control in Diesel engines is not only of significance to the combustion process in one particular cycle, but also influences the subsequent dynamics of air-path loop and combustion events, particularly when exhaust gas recirculation (EGR) is employed. To better reveal such inherently interactive relations, this paper presents a physics-based, control-oriented model describing the dynamics of the intake conditions with fuel injection profile being its input for Diesel engines equipped with EGR and turbocharging systems. The effectiveness of this model is validated by comparing the predictive results with those produced by a high-fidelity 1-D computational GT-Power engine model.
Design of Energy-Saving PZT Drive Amplifiers for Mobile and Wearable Physical Assists
Authors: Barraga´n Patrick R. , Tsukahara Shinichiro , Asada H. Harry
Published: May 2012

An energy-efficient circuit for driving PZT actuators using a charge recovery technique is explored in this paper. Mobile and wearable devices for physical assists requiring extended battery life and/or minimal battery weight will benefit from this technology. PZT is a capacitive transducer and can produce constant force for extended periods with little power consumption. Furthermore, energy can be saved by moving charge from one PZT stack to another instead of draining to ground. This paper describes an efficient charge-recovery circuit that can capture 40∼65% of the energy in one PZT unit by transferring it to another PZT unit. The battery then must only supply the remaining charge thereby increasing battery life. First, the basic principle of the charge-recovery technique is described. The idealized circuit architecture and possible implementation are presented. Then, the electrical circuit behavior is analyzed. PZT hysteresis is discussed, and results are presented.
Integrated Powertrain Control to Meet Low CO2 Emissions for a Hybrid Distribution Truck With SCR-DeNOx System
Authors: Willems Frank , Spronkmans Stefan , Kessels John
Published: May 2012

This article presents a cost-based optimization strategy that explicitly deals with the requirements for fuel consumption and emissions. Based on the Integrated Powertrain Control (IPC) approach, the overall powertrain performance is optimized by integrated energy and emission management. The potential of this strategy is demonstrated for a parallel hybrid diesel truck with a Selective Catalytic Reduction (SCR) de-NOx system. New results are presented for a challenging city cycle; although the average power demand is low, IPC is able to keep the SCR catalyst temperature relatively high. With this IPC approach, the CO2-NOx trade-off is optimized in a systematic way. It is demonstrated that CO2 emissions and related operating costs are reduced by 3.5% or 24.9% NOx emission reduction is achieved, depending on the applied IPC calibration.
Predictive Cruise Control With Probabilistic Constraints for Eco Driving
Authors: Zhang Chen , Vahidi Ardalan
Published: May 2012

In predictive adaptive cruise control systems, a major challenge is estimating the future driving pattern of the lead car. This paper proposes an adaptive cruise control system that acts more smoothly and fuel efficiently by utilizing probabilistic information of velocity transition of the front car. The car following problem is formulated in a chance constrained model predictive control framework in which the inter-vehicle gap constraints are enforced probabilistically. The probability distribution of the position of the front car is estimated through a Markov Chain Monte Carlo (MCMC) simulation. The position probability distribution is then utilized to convert the chance constrained MPC problem to a deterministic linear MPC problem. Two case studies with two real driving cycle profiles are presented to show the potential improvement in fuel economy.
Stability Analysis of a Hydraulic Free Piston Engine With HCCI Combustion
Authors: Li Ke , Sun Zongxuan
Published: May 2012

This paper analyzes the stability of the dynamic coupling among the homogeneous charge compression ignition (HCCI) combustion, gas exchange dynamics and the piston dynamics in a hydraulic free piston engine. The intrinsic feedback nature of the system makes the stability of the engine operation difficult to predict. Specifically, output from the gas exchange process of the previous cycle affects the combustion timing of the current cycle. The combustion force and hydraulic loading together determine how far the piston can travel (dead center positions) and provide input for the current cycle gas exchange process. A discrete cycle-to-cycle based model that captures this dynamic coupling is described in the paper. Linearization of the model gives us the insight of the engine stability under any given operation conditions. The stability analysis is validated with Matlab numerical simulation results of a high-order nonlinear model under a specified set of operation conditions. The proposed methodology can be transformed and applied to analyze stability of systems with similar dynamics couplings.
Spherical Modeling and Nonlinear Model Predictive Control of Electroporation
Authors: Yi Jingang , Li Jianbo , Lin Hao
Published: May 2012

Electroporation is an effective means to deliver molecules into the cellular cytoplasm, and has been widely applied in both biological research and clinical applications. The process however suffers from low viability and efficiency. In this work, we present a multi-pulse feedback control scheme for enhancing viability and efficiency of electroporation process. We first present a spherical model for cell transmembrane potential (TMP) dynamics to describe the spatial distribution of electric potential on cell membrane. Then we analyze the models and discuss the bifurcation property of the system. Based on the dynamic models, we design a nonlinear model predictive controller (NMPC) to track pore size profiles in electroporation. We demonstrate that by using NMPC, the pore size can be precisely regulated to targeted values for drug delivery applications. The control design is illustrated through simulation examples.
An Online Adaptive Fast Control Approach Based on Local Linearization and Its Application to a Large Inertia System
Authors: Xie Jia , Zhao Shengdun , Sha Zhenghui , Liang Jintao
Published: May 2012

In this paper, an online adaptive fast control approach (OAFC) based on local linearization is proposed. This engineering approach has two distinctive features: a) it can realize stable steady-state control; and b) it can make the transition control process fast and smooth. It applies a hybrid structure system and uses the local linearization in a small range of the error to solve the control problem caused by the nonlinear, time-varying, and time-delay large inertia system involved in this paper. Firstly, by timely decoupling the transition process and the steady state, the time of the transition process is reduced. Then, OAFC is realized by proposed OAFC algorithm and an online adaptive fast parameters calculation method. Finally, OAFC is applied to a large inertia system — wet raw material mill in a cement plant. The practical application and the control results demonstrate the effectiveness and implementability of the proposed approach.
Waveform Analysis of an Electro-Hydraulic Vibrator
Authors: Ren Y. , Ruan J. , Burton R. T.
Published: May 2012

The frequency bandwidth of conventional electro-hydraulic vibrator is always limited to a rather narrow range. This restriction is attributed not only to the limited response capability of the servo valve but also to the electro-hydraulic servo system itself the bandwidth of which is unable to be extended. Thus, the parallel design of a two-dimensional valve (here within defined as a 2D valve) and a servo valve is adopted to control an electro-hydraulic vibrator in half-close-loop mode so that the frequency bandwidth is greatly extended and the precision control of the vibration characteristic variables such as waveform shape is preserved. The analysis and experimental results demonstrate that the waveform distortion is less than 10%, up to 2000 Hz. It was concluded that the feasibility of the half closed loop design is established for the realization of the high frequency vibration.
Accurate Motion Control of Linear Motors With Adaptive Robust Compensation of Nonlinear Electromagnetic Field Effect
Authors: Chen Zheng , Yao Bin , Wang Qingfeng
Published: May 2012

Iron-core linear motors have been widely used in high-speed/high-accuracy positioning systems due to the elimination of mechanical transmissions. Many control methodologies have been developed for linear motor motion control, such as H∞ control, adaptive control and sliding mode control. Compensations of various nonlinearities such as frictions and cogging forces have also been carried out to obtain better tracking performance. However, the relationship between the driving current and the resulting motor force has been assumed to be linear, which is invalid for high driving coil currents due to the saturating electromagnetic field effect. This paper focuses on the effective compensation of nonlinear electromagnetic field effect so that the system can be operated at even higher acceleration or heavier load without losing achievable control performance. Specifically, cubic polynomials with unknown weights are used for an effective approximation of the unknown nonlinearity between the electromagnetic force and the driving current. The effectiveness of such an approximation is verified by off-line identification experiments. An adaptive robust control (ARC) algorithm with online tuning of the unknown weights and other system parameters is then developed to account for various uncertainties. Theoretically, the proposed ARC algorithm achieves a guaranteed transient and steady-state performance for position tracking, as well as zero steady-state tracking error when subjected to parametric uncertainties only. Comparative experiments of ARC with and without compensation of electromagnetic nonlinearity done on a linear-motor-driven industrial gantry will be shown. The results show that the proposed ARC algorithm achieves better tracking performance than existing ones, validating the effectiveness of the proposed approach in practical applications.