Nonlinear Observer-Based Feedback for Open-Channel Level Control

This paper is devoted to nonlinear observer and controller design for water level control of open-channel flow in irrigation canals or dam-river systems. A finite-dimensional model, previously developed by orthogonal collocation methods, based on Saint Venant equations and used for control design, is now further used for online flow rate and water infiltration estimation. This is done by a so-called state observer. In particular, the estimates obtained in this way can successfully be used in a controller previously proposed, resulting in a water level control law using only two level measurements along the canal (instead of the four measurements previously needed). The study is restricted to the case of a rectangular wetted section and subcritical flow. The results have been validated by simulations, on an implicit finite difference simulator based on a Preissmann scheme for various scenarios.     

LDV measurements and computation of a turbulent circular jet placed non-concentrically in a confining pipe

Quantitative and nonintrusive fluid velocity and turbulence measurements obtained using laser Doppler velocimetry (LDV) in a circular jet that is positioned nonconcentrically in a confining pipe are presented. The experimental findings are compared with the results obtained by the finite-element computational simulation of the flow. The measured and predicted contours of the time-averaged axial velocity reveal the presence of a three-dimensional (3-D) asymmetric reverse-flow region, with its radial and circumferential extent depending on the axial position and the eccentricity ratio. Due to the weakened radial mixing and spreading of the jet for the higher eccentricities, the transition to the fully developed state is delayed for the high eccentricity cases. Measured and predicted contours of the axial turbulence fluctuations exhibit the ringlike distribution, although it is observed in an offset position for a given eccentricity ratio. At the downstream stations, the ringlike distribution tends to become more symmetric. The basic phenomena of flow reversal, preferential mixing, and shear layer growth are recovered by the computational predictions based on the high-Reynolds-number turbulence model. The time-averaged velocity measurements compare well with the predictions, whereas only qualitative comparison can be observed between the measured and predicted turbulence fluctuations.     

Modeling Evapotranspiration Effects on Air Flowing in a Small Glass Roofed Tunnel

A preliminary investigation into the feasibility of erecting a solar chimney power plant requires a model incorporating all possible aspects of such a power plant and giving results on an hourly basis. Possible agricultural activities underneath the outer section of the solar collector would require a model predicting the changing state of the air due to evapotranspiration effects as it flows from the perimeter of the collector to the chimney in the center. The vegetation temperature and irrigation requirements need to be determined in order to ascertain how far inward crops may be planted without being subjected to heat stress. A small experimental glass roofed tunnel was constructed, planted with grass, and the changing state of the air, drawn over the grass by a fan, was determined using wet- and dry-bulb temperature measurements and the mass flow rate of the air. Starting off with a known air state inlet condition, conservation and the Penman-Monteith equations were applied to subsequent 1-m lengths of the tunnel and the state of the air at the outlet was predicted and compared with the measured state of the air. The predicted and measured values were found to be in agreement within experimental limits giving confidence in incorporating this model into the larger model of the solar chimney.     

Speed, size, and edge-rate information for the detection of collision events.

In the present study an alternative analysis to τ? was considered that was based on perceived speed and size and that assumed constant deceleration for the detection of collision events. Observers were presented with displays simulating a 3-D environment with obstacles in the path of observer motion. During the trial, observer motion decelerated at a constant rate and was followed by a blackout prior to the end of the display. Observers had to detect which trials resulted in a collision. The results indicate that collision detection varied as a function of the size of the obstacles, observer speed, and edge rate—findings not predicted by an analysis of τ?. The results suggest that observers use an analysis based on speed and size information. A model that assumes constant deceleration is proposed for braking control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social influence processes in group brainstorming.

A series of studies examined the role of social influence processes in group brainstorming. Two studies with pairs and 1 with groups of 4 revealed that the performance of participants in interactive groups is more similar than the performance of those in nominal groups. A 4th study demonstrated that performance levels in an initial group session predicted performance on a different problem 2 sessions later. In a 5th study it was found that the productivity gap between an interactive and nominal group could be eliminated by giving interactive group members a performance standard comparable with the typical performance of nominal groups. These studies indicate that performance levels in brainstorming groups are strongly affected by exposure to information about the performance of others. It is proposed that social matching of low performance levels by interactive group members may be an important factor in the productivity loss observed in group brainstorming. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fluid velocities in induction melting furnaces: Part I. Theory and laboratory experiments

Fluid flow in an induction furnace due to electromagnetic stirring forces is predicted theoretically from furnace design parameters by the simultaneous solution of the Maxwell and Navier Stokes equations. Streamline plots and velocity profiles are obtained and compared with surface velocities measured experimentally. The measurements were made on a mercury pool stirred inductively by a Tocco 30 kW 3 kHz induction melting unit. The agreement between the experimental measurements and theoretical predictions was good considering that no curve fitting by manipulation of adjustable parameters was involved. It is believed that such a model would be of value in the design and development of induction furnaces.     

Model Predictive Control of Structures under Earthquakes using Acceleration Feedback

This paper presents a general formulation of the model predictive control (MPC) scheme with special reference to acceleration feedback in structural control under earthquakes. The MPC scheme is based on a prediction model of the system response to obtain the control action by minimizing an objective function. Optimization objectives include minimization of the difference between the predicted and desired response trajectories, and of the control effort subject to certain constraints. The effectiveness of MPC has been demonstrated to be equivalent to the optimal control. In this study, the prediction model is formulated using a feedback loop containing acceleration measurements from various locations in the structure. The state observer utilizes the Kalman-Bucy filter to estimate the states of the system from the acceleration feedback. Examples of single-story and three-story buildings equipped with control devices are used to demonstrate the effectiveness of the MPC scheme based on acceleration feedback. Both buildings are analyzed using an active tendon control device and an active mass damper (AMD). A two-story building with an AMD is used to experimentally validate the numerical control scheme. The results demonstrate the effectiveness of the MPC scheme using acceleration feedback. The acceleration feedback framework developed in this paper should serve as a building block for future extensions of MPC in capturing and benefiting from the attractive features of MPC, i.e., computational expediency, real-time applications, intrinsic compensation for time delays, and treatment of constraints, for implementation in civil structures.     

Efficient Model Correction Method with Modal Measurement

An efficient model correction method is proposed by using the modal measurement from a structural system. The method corrects/updates the mass and stiffness matrix without imposing any parameterization. It considers the information from both the nominal finite-element model and the measurement of modal frequencies and mode shapes. The method is computationally very efficient and it does not require computation of the complete set of eigenvalues and eigenvectors of the nominal model. Instead, only the nominal eigenvalues and eigenvectors of the modes to be corrected are needed. The Gram-Schmidt orthogonalization process is used to construct a basis that satisfies the mass orthogonality condition. This basis is used to transform the eigenvectors of the nominal model so that the corrected model is compatible with the measurement. A thousand-degree-of-freedom chainlike system and a 1,440-degree-of-freedom structural frame are used to illustrate the proposed method.     

Searching imagined environments.

Subjects read narratives describing directions of objects around a standing or reclining observer, who was periodically reoriented. RTs were measured to identify which object was currently located beyond the observer's head, feet, front, back, right, and left. When the observer was standing, head/feet RTs were fastest, followed by front/back and then right/left. For the reclining observer, front/back RTs were fastest, followed by head/feet and then right/left. The data support the spatial framework model, according to which space is conceptualized in terms of three axes whose accessibility depends on body asymmetries and the relation of the body to the world. The data allow rejection of the equiavailability model, according to which RTs to all directions are equal, and the mental transformation model, according to which RTs increase with angular disparity from front. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Crystal Plasticity Model Validation Using Combined High-Energy Diffraction Microscopy Data for a Ti-7Al Specimen

High-Energy Diffraction Microscopy (HEDM) is a 3-d X-ray characterization method that is uniquely suited to measuring the evolving micro-mechanical state and microstructure of polycrystalline materials during in situ processing. The near-field and far-field configurations provide complementary information; orientation maps computed from the near-field measurements provide grain morphologies, while the high angular resolution of the far-field measurements provides intergranular strain tensors. The ability to measure these data during deformation in situ makes HEDM an ideal tool for validating micro-mechanical deformation models that make their predictions at the scale of individual grains. Crystal Plasticity Finite Element Models (CPFEM) are one such class of micro-mechanical models. While there have been extensive studies validating homogenized CPFEM response at a macroscopic level, a lack of detailed data measured at the level of the microstructure has hindered more stringent model validation efforts. We utilize an HEDM dataset from an alpha-titanium alloy (Ti-7Al), collected at the Advanced Photon Source, Argonne National Laboratory, under in situ tensile deformation. The initial microstructure of the central slab of the gage section, measured via near-field HEDM, is used to inform a CPFEM model. The predicted intergranular stresses for 39 internal grains are then directly compared to data from 4 far-field measurements taken between ~4 and ~80 pct of the macroscopic yield strength. The evolution of the elastic strain state from the CPFEM model and far-field HEDM measurements up to incipient yield are shown to be in good agreement, while residual stress at the individual grain level is found to influence the intergranular stress state even upon loading. Implications for application of such an integrated computational/experimental approach to phenomena such as fatigue are discussed.     

无速度传感器矢量控制系统设计与仿真

针对无速度传感器矢量控制系统中电压模型磁通观察器存在积分运算问题和低速运行时转速难以控制的问题,设计了利用电流模型修正电压模型的磁通观察器和PI自适应法速度观察器,建立了转速电流双闭环调速系统。仿真结果表明:低速下稳态精度比较好,估算速度毛刺较少,系统对转子参数有较强的鲁棒性。仿真证明了该方法的有效性。     

Stream Temperature Dynamics in Upland Agricultural Watersheds

A numerical model to compute the free-surface flow hydrodynamics and stream temperature dynamics by solving the depth-averaged, 1D unsteady flow and heat transport equations is presented. The hydrodynamics model considers the effects of arbitrary stream geometry, variable slopes, variable flow regimes, and unsteady boundary conditions. The thermal transport model accounts for the effects of solar radiation, air temperature, relative humidity, cloud cover, wind speed, heat conduction between water and streambed, subsurface flow, and shading by riparian vegetation. The model is verified with measurements in a stream in an upland agricultural watershed located in Indiana. Diurnal variations in the streamflow and stream temperatures are highly transient. The proposed model predicted well the streamflow and stream temperatures that were measured every 15 min over 25 days. The results of this study demonstrate that the solar (shortwave) radiation and subsurface inflow are the most significant contributors to the stream heat budget.     

New Method for Estimation of Discharge

A new technique for drawing isovel patterns in an open or closed channel is presented. It is assumed that the velocity at each arbitrary point in the conduit is affected by the hydraulic characteristics of the boundary. While any velocity profile can be applied to the model, a power-law formula is used here. In addition to the isovels patterns, the energy and momentum correction factors (α and β), the ratio of mean to maximum velocity (V/umax), and the position of the maximum velocity are calculated. To examine the results obtained, the model was applied to a pipe with a circular cross section. A comparison between the profiles of the proposed model and the available power-law profile indicated that the two profiles were coincident with each other over the majority of the cross section. Furthermore, the predicted isovels were compared with velocity measurements in the main flow direction obtained along the centerline and lateral direction of a rectangular flume. The estimated discharge, based on measured points on the upper half of the flow depth away from the boundaries was within ±7% of the measured and much better in comparison to the prediction of one- and two-point methods. The prediction of the depth-averaged velocity values for the River Severn in the United Kingdom shows a good agreement with the measured data and the best analytical results obtained by the depth-averaged Navier–Stokes equations.     

The prediction of total body water from bioelectrical impedance in patients with anorexia nervosa

A simple mathematical model is proposed that predicts the dynamics of chronic progressive renal disease. The model consists of coupled linear differential equations formed from three state variables, four control parameters, and three parameters related to initial conditions. All have straightforward physical interpretations. Applied to a population of nephrons, the model predicted the hypertrophic and sclerotic features of parenchyma progressing towards end-stage renal disease. Simulation results compared favorably with measurements obtained from the literature involving the subtotal nephrectomy rat model for renal disease. The time course of disease progression and treatment were considered. Also, the implications of the model for designing new diagnostic techniques using ultrasonic analysis are discussed.     

State Space Formulation for Linear Viscoelastic Dynamic Systems with Memory

A dynamic system with memory is a system for which knowledge of the equations of motion, together with the state at a given time instant t0 is insufficient to predict the evolution of the state at time instants t>t0. To calculate the response of systems with memory starting from an initial time instant t0, complete knowledge of the history of the system for t相似文献   

具有伸长率分配计算功能的轧制力预报智能模型研究

针对双机架平整机的特性,以基态弯辊力下带材出口板形最好为准则,提出具有双机架平整机伸长率分配系数计算功能的轧制力模型;在此基础上,为了改善传统轧制力模型的预报精度,提出了先通过神经网络利用在线测得的实际数据预测变形抗力和摩擦因数,再与轧制力机理模型自学习过程相结合的轧制力预报新方法;并将其应用于宝钢1220双机架平整机的生产实践,结果表明此模型可以高精度地预报轧制压力.     

DSC Model for Soil and Interface Including Liquefaction and Prediction of Centrifuge Test

Realistic predictions of dynamic soil–structure interaction problems require appropriate constitutive models for the characterization of soils and interfaces. This paper presents a unified model based on the disturbed state concept (DSC). The parameters for the models for the Nevada sand, and sand–metal interface are obtained based on available triaxial test data on the sand and interfaces. The predicted stress–strain–pore water pressure behavior for the sand using the DSC model is compared with the test data. In addition, a finite element procedure with the DSC model, based on the generalized Biot’s theory, is used to predict the measured responses for a pile (aluminum) sand foundation problem obtained by using the centrifuge test. The predictions compared very well with measured pore water pressures. The DSC model is used to identify microstructural instability leading to liquefaction. A procedure is proposed to apply the proposed method for analysis and design for dynamic response and liquefaction.     

Analytical,numerical, and experimental analysis of inverse macrosegregation during upward unidirectional solidification of Al-Cu alloys

The present work focuses on the influence of alloy solute content, melt superheat, and metal/mold heat transfer on inverse segregation during upward solidification of Al-Cu alloys. The experimental segregation profiles of Al 4.5 wt pct Cu, 6.2 wt pct Cu, and 8.1 wt pct Cu alloys are compared with theoretical predictions furnished by analytical and numerical models, with transient h _i profiles being determined in each experiment. The analytical model is based on an analytical heat-transfer model coupled with the classical local solute redistribution equation proposed by Flemings and Nereo. The numerical model is that proposed by Voller, with some changes introduced to take into account different thermophysical properties for the liquid and solid phases, time variable metal/mold interface heat-transfer coefficient, and a variable space grid to assure the accuracy of results without raising the number of nodes. It was observed that the numerical predictions generally conform with the experimental segregation measurements and that the predicted analytical segregation, despite its simplicity, also compares favorably with the experimental scatter except for high melt superheat.     

Damage Detection in Composite Materials Using Identification Techniques

The present paper describes an approach for damage detection in composite structures that has its basis in methods of system identification. Response of a damaged structure differs from predictions obtained from a mathematical model of the original structure, where such a model is typically a finite‐element representation of the structure. In the present work dealing with composite materials, two distinct analytical models, one using two‐dimensional (2D) elements in conjunction with the classical lamination theory and another using three‐dimensional (3D) elements were considered. The output error approach of system identification was employed to determine changes in the analytical model necessary to minimize differences between the measured and predicted response. The proposed method is an extension of the stiffness‐reduction approach for damage detection to realistic structures. Numerical simulation of measurements of static deflections, strains, and vibration modes were used in the identification procedure. The methodology was implemented for representative composite structures. Principal shortcomings in the proposed approach and possible methods to circumvent these problems are discussed in the paper.