Desired Point Research Articles

Role of thermal intensity on operational characteristics of ultra-low emission colorless distributed combustion

This paper examines the development of ultra-low emission colorless distributed combustion (CDC) for gas turbines, operating at thermal intensity in the range of 5–453MW/m3atm. Higher thermal intensity combustors are desirable for increased performance with minimal increase in hardware costs in terms of both weight and volume of gas turbine combustors. Most land based gas turbine combustors operate at thermal intensity of about 15MW/m3atm but operation at higher intensity can provide increased performance. Design of high thermal intensity CDC combustor requires control of critical parameters, such as gas recirculation, fuel/oxidizer mixing, air preheats, and residence time distribution characteristics via proper selection of different air and fuel injection configurations to achieve desirable combustion characteristics. Initially, various flow field configurations were investigated at a low thermal intensity of 5MW/m3atm. This effort was followed by investigations at higher thermal intensity ranges of 20–40MW/m3atm by reducing the combustor volume for a forward flow configuration under more favorable novel non-premixed conditions. Further investigations were performed for a simpler combustor having single injection ports for air and fuel with detailed investigation of various flow field configurations performed at a thermal intensity of 28MW/m3atm. Further reduction in combustion volume resulted in thermal intensity of 57MW/m3atm. For the flow configurations investigated, reverse cross-flow configuration was found to give more favorable results with air injected from exit end and fuel injected in a cross-flow direction to the air flow. This reverse cross-flow geometry was investigated in detail by further reducing the combustor volume. Air injection diameter was increased to reduce the pressure drop across the combustor. The combustor was investigated at thermal intensity in the range of 53–85MW/m3atm. This geometry resulted in 4ppm NO emission and CO emissions of about 27ppm under novel non-premixed flow conditions at thermal intensity of 53MW/m3atm. The pressure drop at this operational point was less than 5% to meet the conventional combustor requirements. Further reduction in combustor volume resulted in very high thermal intensity in the range of 156–198MW/m3atm and at the most desirable operational point NO and CO emissions were 8ppm and 82ppm, respectively under novel non-premixed mode at a thermal intensity of 170MW/m3atm. Even further reduction in combustor volume resulted in combustor operation at ultra-high thermal intensity of 283–453MW/m3atm and at the desirable operating point the NO and CO emissions were 4ppm and 115ppm respectively at a thermal intensity of 340MW/m3atm. The sequential efforts reveal the possibility of significantly increasing the thermal intensity while still achieving desirable emission levels.

An energy exchanging and dropping-based model-free output feedback crane control method

For the overhead crane control problem, velocity-related terms (corresponding to full-state feedback) are generally required in the designed control systems for damping injection to achieve (asymptotic) stability. However, it is known that velocity signals may be noisy or even unmeasurable. Also, most existing controllers require full or partial plant physical parameters like rope length or load mass. To resolve these issues, a model-free energy exchanging and dropping-based control law is proposed to achieve output (only position/swing-angle) feedback control for overhead cranes. We synthesize a total energy function, consisting of the (generalized) crane energy and the controller energy, to render it to achieve its (local) minimum at the desired equilibrium point. The proposed control law is dynamically generated by an artificial block-spring system, which exchanges energy with the crane dynamics and then drops the energy via an elegant dropping mechanism to gradually attenuate the total energy. The corresponding stability and convergence analysis is implemented using some Lyapunov-like analysis. Simulation and experimental results suggest the effectiveness and feasibility of the proposed method for crane control, in terms of rapid swing suppression, efficient trolley positioning, as well as increased robustness.

New technology adoption in a Cournot oligopoly with spillovers

In a two-stage Cournot oligopoly where a subset of firms first make a choice between two alternative production technologies independently and then all firms compete in quantity, the effect of information spillovers is analyzed when the outcome of R&D is uncertain. It is shown that the range of parameter values that support heterogeneous firms in equilibrium will diminish as information spillovers become larger. Particularly, when the spillover effect is so strong that the investment by one firm is beneficial to its R&D active rivals, all active firms will choose the same technology. A similar result can be derived from a socially desirable point of view except that the cut-off magnitude of spillovers is different. By introducing a positive success probability to characterize the uncertainty of the R&D outcome, it is found that when information spillovers are not too small, there will be underinvestment in equilibrium relative to the social optimum.

Dissipative Hamiltonian realisation and decentralised saturated control of multi‐machine multi‐load power systems

Using the energy-based Hamiltonian function method, this study investigates the decentralised saturated excitation control of multi-machine multi-load power systems based on the structure preserving dynamic model. First, a constructive procedure is proposed for the dissipative Hamiltonian realisation of non-linear differential algebraic systems and transform the power system to its equivalent dissipative Hamiltonian system. Constant feedforward control is proposed to adjust the system to the desired equilibrium point. Then, we put forward a decentralised saturated excitation controller using only the local information. Simulation results show that the proposed control scheme can effectively improve the transient stability of the power system.

SU‐E‐T‐186: Treatment Planning Dose Accuracy of Whole Breast Irradiation Using Field‐In‐Field Technique

Purpose: To evaluate the planned dose accuracy of whole breast irradiation using field‐in‐field technique by comparing with 2D array detector measurements and Monte Carlo simulations. Methods: The ion chamber based Octavius 2D‐array detector (PTW, Freiburg, Germany) was used to measure the absolute dose and dose distributions of tangential field‐in‐field breast irradiation. A commercially available treatment planning system (Eclipse V10.0, Varian, Palo Alto CA USA) was used to calculate the absolute dose and dose distributions. Phantom geometry was simplified for the measurements and for Monte Carlo simulations, but its size and shape were similar to typical breast. The dose accuracy of the treatment planning system was evaluated and the desirable points for monitor unit calculation were recommended based on the results of the study. Results: The discrepancy between measured and planned dose distribution depended on the location of the monitor unit calculation point. The differences were larger when monitor unit calculation point was closer to the irradiated edges of phantom. The doses calculated by the treatment planning system near the center of the irradiated field were about 2% higher than measured doses. There was good agreement between the measured doses and those predicted by Monte Carlo methods. Conclusion: Because of inadequate treatment of scatter in the irradiation of breast with tangential ports, the dose predictions by a treatment planning system do not always agree with the actual measurements. The treatment planning algorithm evaluated in this study over‐compensates for the loss of scatter in tangential ports glancing the sloping surface of a typical breast. The choice of the prescription point can have significant effect on the dose prediction and the actual dose delivered. Keeping the prescription point away from the field edges will help improve the agreement between the calculated and measured dose.

Energy-shaping and integral control of the three-tank liquid level system

A novel method of energy-shaping and integral control is proposed for the three-tank liquid level system. The mathematical model of the three-tank liquid level system is established based on port-controlled Hamiltonian (PCH) systems and mass balance principle. The three-tank liquid level system PCH controller is designed by means of interconnection assignment and damping injection and energy-shaping. The desired equilibrium point is also determined. The stability of the liquid level system is analyzed based on the passivity-based control theory. The integral control is added to eliminate the steady-state errors of the liquid level system. Moreover, simulation and experiment test are also carried out based on the laboratory experiment platform. The results prove that the proposed control method has good dynamic and steady state performances.

Differential Neuro-Fuzzy Controller for Uncertain Nonlinear Systems

In general, output-based controller design remains an important research area in control theory. Most of the existing solutions use a state estimation algorithm to reconstruct a plausible approximation of the real state. Then, one can apply a nonlinear controller, based on fuzzy logic, for example, to enforce the system trajectories to a desirable stable equilibrium point. Nevertheless, the aforementioned method may not be suitable for uncertain systems affected by external noises. State observers based on the system's structure cannot be applied in those cases. However, some sort of adaptive estimation may be developed. This paper deals with a fuzzy controller that was designed using the state observer solution when the dynamic model of a plant contains uncertainties or it is partially unknown. Differential neural network (DNN) approach is applied in this uninformative situation. A new learning law, containing an adaptive adjustment rate, is suggested to enforce the stability condition for the observer's free parameters. On the other hand, nominal weights are adjusted during the preliminary training process using the least mean square method. Lyapunov theory is used to obtain the upper bounds for the weight's dynamics. The proposed method seems to be a more advanced option to control uncertain systems when the state available information is reduced. Even when several options exist to control this class of nonlinear systems such as PID, the method introduced here uses the knowledge on the system behavior and enforces the reconstruction of the immeasurable states. This last issue is an extra advantage because it serves as a general software sensor. The well-known two-link manipulator is used to show the effectiveness of the proposed algorithm. A couple of cases are used here: the full actuated and the under-actuated systems. In both situations, the controller achieves a better performance than the well-known PID controllers and a fuzzy controller using the estimated states produced by a high-order sliding-mode observer. A practical example showing how the fuzzy controller based on the estimated states produced by the differential neural network observer is also presented. The system used to test the controller is the anaerobic digestion. In this case, the benefits of this output-based controller are also demonstrated.

Iterative learning control in optimal tracking problems with specified data points

In this paper, we present two iterative learning control (ILC) frameworks for tracking problems with specified data points that are desired points at certain time instants. To design ILC systems for such problems, unlike traditional ILC approaches, we first develop an algorithm in which not only the control signal but also the reference trajectory is updated at each trial. We investigate the relationship between the reference trajectory and ILC tracking control as it relates to the rate of convergence. Second, a new ILC scheme is proposed to produce output curves that pass close to the desired points. Here, the control signals are generated by solving an optimal ILC problem with respect to the desired sampling points. One of the key advantages of the proposed approaches is a significant reduction of the computational cost.

Predicting Pharmacokinetic Profiles Using in Silico Derived Parameters

Human pharmacokinetic (PK) predictions play a critical role in assessing the quality of potential clinical candidates where the accurate estimation of clearance, volume of distribution, bioavailability, and the plasma-concentration-time profiles are the desired end points. While many methods for conducting predictions utilize in vivo data, predictions can be conducted successfully from in vitro or in silico data, applying modeling and simulation techniques. This approach can be facilitated using commercially available prediction software such as GastroPlus which has been reported to accurately predict the oral PK profile of small drug-like molecules. Herein, case studies are described where GastroPlus modeling and simulation was employed using in silico or in vitro data to predict PK profiles in early discovery. The results obtained demonstrate the feasibility of adequately predicting plasma-concentration-time profiles with in silico derived as well as in vitro measured parameters and hence predicting PK profiles with minimal data. The applicability of this approach can provide key information enabling decisions on either dose selection, chemistry strategy to improve compounds, or clinical protocol design, thus demonstrating the value of modeling and simulation in both early discovery and exploratory development for predicting absorption and disposition profiles.

Continuous Finite-Time Terminal Sliding Mode IDA-PBC Design for PMSM with the Port-Controlled Hamiltonian Model

Finite-time control scheme for speed regulation of permanent magnet synchronous motor (PMSM) is investigated under the port-controlled Hamiltonian (PCH), terminal sliding mode (TSM), and fast TSM stabilization theories. The desired equilibrium is assigned to the PCH structure model of PMSM by maximum torque per ampere (MTPA) principle, and the desired Hamiltonian function of state error is constructed in the form of fractional power structure as TSM and fast TSM, respectively. Finite-time TSM and fast TSM controllers are designed via interconnection and damping assignment passivity-based control (IDA-PBC) methodology, respectively, and the finite-time stability of the desired equilibrium point is also achieved under the PCH framework. Simulation results validate the improved performance of the presented scheme.

A discontinuous exponential stabilization law for an underactuated X4-AUV

In this paper, stabilization of a class of second-order nonholonomic systems for an underactuated X4-AUV is investigated. We present a model of the underactuated X4-AUV with six degrees of freedom (DOF) and four control inputs. Then, the system is written in a control-affine form by applying a partial linearization technique, and a dynamic controller based on Astolfi's discontinuous control is derived to stabilize all states of the system to the desired equilibrium point exponentially. The present approach does not necessitate the conversion of the system model into a "chained form", and thus does not rely on any special transformation techniques to obtain a canonical form. A simulation is conducted to demonstrate the effectiveness of the proposed controller.

Application of Fixator-Norator Pairs in Designing Active Loads and Current Mirrors in Analog Integrated Circuits

Design of analog integrated circuits is discussed in this paper. The emphasis is on the biasing design of ICs using Fixator-norator pairs. Fixators are used to keep the driver transistors biased at the desirable operating points while the pairing norators are used to allocate and specify the bias-supporting components. A bias-supporting component is shown to be one of the two categories: 1) a DC voltage source or a DC current source/sink or 2) a power-conducting component. A power-conducting component is typically a resistor in lumped circuits but an active load or current mirror in an analog IC. Three types of active loads are introduced and their design is also discussed in this paper. Two examples, one in bipolar and one in CMOS technology, demonstrate the analog IC design procedure.

Fault-Tolerant Control of a Nonlinear Process with Input Constraints

A Fault-Tolerant Control (FTC) methodology has been presented for nonlinear processes being imposed by control input constraints. The proposed methodology uses a combination of Feedback Linearization and Model Predictive Control (FLMPC) schemes. The resulting constraints in the transformed process will be dependent on the actual evolving states, making their incorporation in the design context a non-trivial task. A feasible direction method has been integrated in the design procedure based on active set technique to resolve the challenging constraint–based FLMPC problem. The formulated FLMPC design method is utilized to develop a FTC scheme by providing a set of backup control configurations for a CSTR benchmark process. The successful performance of the proposed FTC methodology has been demonstrated via a category of common fault scenarios by exercising an arbitrary replacement of control configurations through a supervisor to maintain the CSTR operation at an unstable desired steady-state point.

Modeling Inefficiencies in Visual Search

We have previously shown that visual search performance is well predicted by peripheral discriminability between patches containing multiple distractors and those containing distractors plus a target (Rosenholtz et al, in submission), which in turn is well predicted by a model in which the representation in peripheral vision consists of a rich set of summary statistics (Rosenholtz et al, in submission, and VSS 2009). Furthermore, we have developed an Ideal Saccadic Targeter model (saccades are made to the most likely target given the observations) to quantitatively predict mean number of fixations to find a target (Rosenholtz et al, VSS 2010). In this study, we examine four possible sources of inefficiency in human searchers relative to the ideal observer. (1) Memory. We compared the performance of the model with memory of the past k fixations against that of a memoryless model. (2) Location Uncertainty. We introduced location uncertainty by removing direct information about item location, so the model has to infer possible target locations from observations. The model has found the target if it fixates within one degree of it. (3) Saccade Length. Because humans prefer to saccade smaller distances (Zelinsky, 2008), we tested three ways of imposing this inefficiency: (a) strictly limiting saccade length, (b) having the model make intermediate saccades to a desired fixation point beyond a saccade limit, and (c) imposing a cost which depends on saccade length. (4) Ideal Decision Rule. We investigated the difference in search efficiency when using the optimal (maximum-a-posteriori) target location as opposed to picking the location with the highest targetness observation. Whether and how much memory was required depended on how saccade limitations were imposed. In general, the interaction between inefficiencies are complex. We show how the model predictions varies with these inefficiencies, and what sets of parameters best match observed human subject performances. Meeting abstract presented at VSS 2012

An increased coupling-based control method for underactuated crane systems: theoretical design and experimental implementation

A novel increased coupling-based nonlinear control strategy is proposed for underactuated overhead crane systems, which guarantees both fast trolley positioning and sufficient payload swing elimination performance. The developed controller is applicable to both regulation control and trajectory tracking control. To artificially increase the trolley-translation/payload-swing internal coupling, a payload position-like composite variable is introduced and a corresponding elegant error signal is then constructed, based on which a novel control law is designed to transform the overhead crane system into an interconnected system consisting of two subsystems with respect to (w.r.t.) the constructed error signal and the payload swing angle, respectively. Both subsystems are proven to be input-to-state stable (ISS); by invoking the small gain theorem, we show that the overall interconnected system is also ISS. LaSalle’s invariance theorem further proves that the system states asymptotically converge to the desired equilibrium point. Experimental results are included to demonstrate the feasibility and effectiveness of the proposed method and also its superior control performance over some existing schemes.

Biomechanics of high tibial osteotomy

This paper is a review of the biomechanical principles that support limb realignment surgery via osteotomy around the knee, principally high (proximal) tibial osteotomy. The basic biomechanical principles have been described, and the related literature examined for evidence to support the recommendations made. The forces on the knee when walking are shown to lead to most of the load acting through the medial compartment, the most frequent site of degeneration of the knee, due to the adduction moment that acts during the weight-acceptance phase. Realignment of the limb to move the mechanical axis to a desired point within the knee is described, and the resulting joint contact pressures in the medial and lateral compartments are shown to be higher in the less-congruent lateral articulation when the load passes through the centre of the knee. At the same time, there can be changes of the posterior slope of the tibial plateau, and a slope of ten degrees can induce a shearing force, which stretches the ACL, of 0.5 body weight when the knee force is 3 times body weight. The options regarding tibial or femoral or even double osteotomies are discussed in relation to medial-lateral slope of the joint line. Secondary effects such as alteration of collateral ligament tension or of the height of the patella are described. Critical review of the publications supporting osteotomy surgery suggests that many of the accepted 'rules' have little scientific evidence to show that they represent the best practise for long-term preservation of the joint.

Successful Superior Thyroid Artery Embolisation Using Microporous Beads

During placement of a central catheter in the left internal jugular vein, an arterial puncture led to an expanding haematoma at the level of the thyroid gland due to an ongoing bleeding fed by the left superior thyroid artery, which was successfully treated by embolisation using beads. The micro-porous structure of these microspheres offered optimal attrition, rigidity, elasticity and durability. These beads provided a controlled, targeted embolisation with a better ability to select the desired end point through choice of size.

A Cartesian non‐uniform grid interpolation method for fast field evaluation on elongated domains

SUMMARYAn algorithm for performing a fast evaluation on time harmonic fields radiated by two‐dimensional source constellations with elongated geometry is introduced. The suggested scheme attains a linear computational complexity. At the core of the algorithm is the idea of phase and amplitude compensation facilitating the conversion of fields radiated by spatially confined sources into bandlimited functions of the suitable coordinates. Thus, the fields or potentials are represented by their samples on sparse left‐side and right‐side non‐uniform Cartesian grids. These grids are employed both for the representation of outgoing fields and as targets for accumulating the incoming fields. Integrating this approach with the divide‐and‐conquer strategy, the algorithm relies on a binary hierarchical decomposition of the computational domain. The total field is computed via a two‐way multilevel process, which passes through all of the left‐side and right‐side grids, while systematically aggregating all subdomains' contributions, ending with the field interpolation back to the desired observation points. Copyright © 2012 John Wiley & Sons, Ltd.

Computerized simulation of tooth contact and error sensitivity investigation for ease-off hourglass worm drives

In the present paper, the tooth contact characteristics and the error sensitivity of the ease-off dual-torus double-enveloping hourglass worm drive (the DTT worm drive) are considered. The ease-off hourglass worm drive is composed of a standard hourglass worm and a modified worm wheel. In order to determine the instantaneous contact point of the mismatched worm pair, the two-stage downhill secant method (the TSDS method) is proposed to be used for solving the nonlinear contact equations. Roughly speaking, the main merits of the TSDS method are lower sensitivity to the initial guess, without a request for computing the Jacobi matrix and no singularity near the genuine solution. After ascertaining the transient contact point, the momentary contact ellipse, the instantaneous transmission ratio and some other tooth contact features are worked out by means of an improved local synthesis approach, which is proposed for point contact gear drives in this article. The results of computerized simulation show that, the mismatched worm gear set is able to accomplish desirable point contact, and has respectable load carrying capacity. On the other hand, the mismatched worm gearing is insensitive to the alignment errors, and its property of the transmission error is advantageous to reduce the noise and vibration.

Quadrangle Downscaling of Global Climate Models and Application to Riyadh

AbstractClimate change impact reports by the Intergovernmental Panel on Climate Change (IPCC) are well established throughout the world. By now many local, regional, and central authorities are aware of these impacts and they try to take necessary precautions according to their environmental circumstances. Preliminary decisions cannot be taken unless there is a model for future climate change impacts, especially for rainfall occurrence, amount, and frequency estimations. The main purpose is to combine the general circulation (climate) model (GCM) outputs with the local meteorology station records by a suitable downscaling procedure. In this paper, a statistical quadrangle downscaling model (QDM) is developed for rainfall estimations up to 2100. This model helps to downscale the nearby four scenario rainfall amounts at GCM grids to a desired point. Two main steps in the model structure are the use of a regional dependence function (RDF) for transferring the GCM output data from the four nearest grid points...