Nominal Point Research Articles

Dynamic parsimonious model and experimental validation of a gas microturbine at part-load conditions

The aim of this work is to present an analytical parsimonious model, developed with Matlab Simulink®, which, with computational simplicity and with only a few technical data as input, obtained easily from technical datasheets, is able to predict both the dynamic and steady state performances of a natural gas microturbine, at nominal point and at part-load conditions. Scaling techniques have been applied to the main components of the model, in order to allow a large range of plant sizes (20–200 kWel) to be simulated. The validation of the simulation code has been carried out by means of experimental data obtained from a commercial 100 kWel mGT installed at the Politecnico di Torino, whose experimental characterization was carried out by the Authors. The agreement of the simulated results with the experimental figures has resulted to be very good, considering the computational simplicity of the model. The main results of the study are presented in the paper.

Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation

Nowadays, the lack of confidence in the prediction of combustor-turbine interactions and more specifically our ability to predict the migration of hot spots through this interface leads to the application of extra safety margins, which are detrimental to an optimized turbine design and efficiency. To understand the physics and flow at this interface, a full 360 deg nonreactive combustor simulator (CS) representative of a recent lean burn chamber together with a 1.5 turbine stage is instrumented at DLR in Gottingen (Germany) within the European project FACTOR. The chamber operates with axial swirlers especially designed to reproduce engine-realistic velocity and temperature distortion profiles, allowing the investigation of the hot streaks transport through the high pressure (HP) stage. First, a true scale three injector annular sector of the CS without turbine is assembled and tested at the University of Florence. To generate the hot steaks, the swirlers are fed by an air flow at 531 K, while the liners are cooled by an effusion system fed with air at ambient temperature. In addition to static pressure taps and thermocouples, the test rig will be equipped with an automatic traverse system which allows detailed measurements at the combustor exit by means of a 5-hole probe, a thermocouple, and hot wire anemometers. This paper presents the design process and instrumentation of the trisector CS, with a special focus on large Eddy simulations (LES) which were widely used to validate the design choices. It was indeed decided to take advantage of the ability and maturity of LES to properly capture turbulence and mixing within combustion chambers, despite an increased computational cost as compared to usual Reynolds averaged Navier Stokes (RANS) approaches. For preliminary design, simulations of a single periodic sector (representative of the DLR full annular rig) are compared to simulations of the trisector test rig, showing no difference on the central swirler predictions, comforting the choice for the trisector. In parallel, to allow hot wire anemometry (HWA) measurements, the selection of an isothermal operating point, representative of the nominal point, is assessed and validated by use of LES.

Construction algorithm for computing tooth thickness in the normal section in nominal contact point cylindrical transmission Novikova

Construction algorithm for computing tooth thickness in the normal section in nominal contact point cylindrical transmission Novikova

Comparison of Air Temperature Calibrations

European national metrology institutes use calibration systems of various types for calibrating thermometers in air. These were compared to each other for the first time in a project organized by the European Association of National Metrology Institutes (EURAMET). This EURAMET P1061 comparison project had two main objectives: (1) to study the equivalence of calibrations performed by different laboratories and (2) to investigate correlations between calibration methods and achievable uncertainties. The comparison was realized using a pair of 100 $$\Omega $$ platinum resistance thermometer probes connected to a digital thermometer bridge as the transfer standard. The probes had different dimensions and surface properties. The measurements covered the temperature range between $$-40\,^{\circ }\mathrm{{C}}$$ and $$+150\,^{\circ }\mathrm{{C}}$$ , but each laboratory chose a subrange most relevant to its scope and performed measurements at five nominal temperature points covering the subrange. To enable comparison between the laboratories, comparison reference functions were determined using weighted least-squares fitting. Various effects related to variations in heat transfer conditions were demonstrated but clear correlations to specific characteristics of calibration system were not identified. Calibrations in air and liquid agreed typically within $$\pm 0.05\,^{\circ }\mathrm{{C}}$$ at $$+10\,^{\circ }\mathrm{{C}}$$ and $$+80\,^{\circ }\mathrm{{C}}$$ . Expanded uncertainties determined by the participants ranged from $$0.02\,^{\circ }\mathrm{{C}}$$ to $$0.4\,^{\circ }\mathrm{{C}}$$ and they were shown to be realistic in most cases.

Design of a multivariable neural controller for control of a nonlinear MIMO plant

Abstract The paper presents the training problem of a set of neural nets to obtain a (gain-scheduling, adaptive) multivariable neural controller for control of a nonlinear MIMO dynamic process represented by a mathematical model of Low-Frequency (LF) motions of a drillship over the drilling point at the sea bottom. The designed neural controller contains a set of neural nets that determine values of its parameters chosen on the basis of two measured auxiliary signals. These are the ship’s current forward speed measured with respect to water and the systematically calculated difference between the course angle and the sea current (yaw angle). Four different methods for synthesis of multivariable modal controllers are used to obtain source data for training the neural controller with parameters reproduced by neural networks. Neural networks are designed on the basis of 3650 modal controllers obtained with the use of the pole placement technique after having linearized the model of LF motions made by the vessel at its nominal operating points in steady states that are dependent on the specified yaw angle and the sea current velocity. The final part of the paper includes simulation results of system operation with a neural controller along with conclusions and final remarks.

ADAPTACYJNY REGULATOR LQR W UKŁADZIE STEROWANIA KĄTEM KURSOWYM I PRĘDKOŚCIĄ STATKU OPISANEGO NIELINIOWYM MODELEM DYNAMICZNYM MIMO

In the paper an adaptive control system for the nonlinear 4-DoF model of a container vessel is presented. The considered model of the ship includes input signals saturations and dynamics of actuators. Main goal of the presented control system is control of the course angle and speed of the ship relative to water. The system synthesis is carried out by means of LQ-optimal control method. Sets of controller parameters are designed using linearization of the considered model in the nominal steady-state operating points of the ship. The final part of the paper includes simulation results of control system operation with full nonlinear MIMO model of the container vessel.

Improved Self-optimizing Control Method Based on Piece-wise Linearization

The existing self-optimizing control (SOC) methods are all based on the linearized model around the nominal point, which may cause big objective function loss due to linearization error when the process is highly nonlinear. This paper presents an improved SOC method based on piece-wise linearization. Piece-wise linearized models are obtained at different operation points, then the linear SOC method is applied and the controlled variables are synthesized finally. The new method minimizes the average loss in a wider range hence the self-optimizing performance is better. A numerical case and an exothermic reactor are studied to demonstrate the usage of the proposed method.

Evaluation Of Different Probing Systems Used In Articulated Arm Coordinate Measuring Machines

Abstract This paper presents a comparison of different techniques to capture nominal data for its use in later verification and kinematic parameter identification procedures for articulated arm coordinate measuring machines (AACMM). By using four different probing systems (passive spherical probe, active spherical probe, self-centering passive probe and self-centering active probe) the accuracy and repeatability of captured points has been evaluated by comparing these points to nominal points materialized by a ball-bar gauge distributed in several positions of the measurement volume. Then, by comparing these systems it is possible to characterize the influence of the force over the final results for each of the gauge and probing system configurations. The results with each of the systems studied show the advantages and original accuracy obtained by active probes, and thus their suitability in verification (active probes) and kinematic parameter identification (self-centering active probes) procedures.

Complex Field Fault Modeling-Based Optimal Frequency Selection in Linear Analog Circuit Fault Diagnosis

Owing to the lack of feasible fault modeling method, hard (open and short) faults, and discretized parametric faults are still the mostly used fault models. These models cannot characterize all soft (parameter shifting) faults because that the parameter of analog element be of continuity character. To address this concern, a complex field fault modeling method is presented first. If fault happens to passive element xi in linear analog circuit, the real (Ur) and imaginary (Uj) parts of faulty voltage phasor U°(U°=Ur+j Uj) must satisfy binary quadratic function Fi(Ur,Uj)=0, which is independent from the value of element xi and uniquely determined by its location and the nominal circuit under test. Hence, the binary quadratic function can model any continuous parameter shifting (soft) or hard fault. Second, to avoid calculating the explicit expression of binary quadratic function, a simulation-based method is given to obtain the locus of the change in the function Fz in the complex plane. Besides, the nominal (fault-free) point, the loci determined by the binary quadratic functions might intersect with each other. It is referred to as aliasing problem in this paper. This problem can be solved by adjusting the frequency of the input signal. Therefore, a constraint optimization method is proposed to select optimal test frequencies. The proposed test generation and compression methods, when combined with the complex field modeling method, can pinpoint much more fault components with less test points and frequencies when compared with the other methods.

Impact of measurement procedure when error mapping and compensating a small CNC machine using a multilateration laser interferometer

This paper deals with the accuracy of compensation of machine tools using a tracking interferometer using the multilateration method. The measurement strategy and thermal drift compensation of the measurements are studied. It shows that most effects of temperature are accurately compensated by the laser tracking interferometer software. However, thermal drifts of accessories are not taken into account, and are therefore not corrected. To validate the robustness of procedures, the geometrical errors of the same machine tool were measured by five measurement strategies using the same equipment. Each strategy is devised and carried out independently by a different person from several institutions. For each strategy, the geometrical compensations were applied to a set of nominal tool path points. The difference, between the nominal points and the compensated or uncompensated points was calculated. This criterion was used to discuss the procedures employed by the participants.

Design Optimization of a Loudspeaker Utilizing Sampling-Based Sensitivity Information of a Hyperspherical Local Window

This paper proposes an efficient optimization method that can deal with electromagnetic design problems with high-dimensional design variables. To achieve this, the universal Kriging method is combined with a new-type local window, called the hypersphere, and the truncated Gaussian sampling. At the center of a nominal design point, accurate surrogate models for performance functions of interest are generated in a relatively small hyperspherical local window. The first-order design sensitivity values are extracted from Jacobian matrices of the locally approximated models. Such optimization scheme considerably reduces sampling points and iterative designs, and also facilitates deriving the design sensitivity with high precision. The proposed method is tested with two design models having more than 10 design variables. Its efficiency and accuracy is thoroughly investigated by comparing it with existing methods.

Multivariable Adaptive Controller for the Nonlinear MIMO Model of a Container Ship

The paper presents an adaptive multivariable control system for a Multi-Input, Multi-Output (MIMO) nonlinear dynamic process. The problems under study are exemplified by a synthesis of a course angle and forward speed control system for the nonlinear four-Degrees-of-Freedom (4-DoF) mathematical model of a single-screw, high-speed container ship. The paper presents the complexity of the assumed model to be analyzed and a synthesis method for the multivariable adaptive modal controller. Due to a strongly nonlinear nature of the ship movements equations a multivariable adaptive controller is tuned in relation to changeable hydrodynamic operating conditions of the ship. In accordance with the given operating conditions controller parameters are chosen on the basis of four measured auxiliary signals. The system synthesis is carried out by linearization of the nonlinear model of the ship at its nominal operating points in the steady-state and by means of a pole placement control method. The final part of the paper includes results of simulation tests of the proposed control system carried out in the MATLAB/Simulink environment along with conclusions and final remarks.

Efficiency Optimization of Six-phase Induction Motors by Fuzzy Controller

In this paper efficiency improvement of a Six-phase Induction Machine (6PIM) with fuzzy Anfis method is presented. Six phase induction machine is supplied by SPWM (Sine Pulse Width Modulation). The motor efficiency in low speed or low load conditions (under nominal point) is low. The purpose of this paper is to reduce core losses of six phase induction motor in these conditions. Fuzzy flux search controller is a simple technique and robust against parameter changes that can be easily implemented. Loss minimum point of six phase induction motor is related to stator current, thus by decreasing of current the loss is decreased. Results are presented in the paper to verify the effectiveness of the proposed approach. DOI: http://dx.doi.org/10.5755/j01.eee.19.10.5895

Residual amplitude modulation in interferometric gravitational wave detectors

The effects of residual amplitude modulation (RAM) in laser interferometers using heterodyne sensing can be substantial and difficult to mitigate. In this work, we analyze the effects of RAM on a complex laser interferometer used for gravitational wave detection. The RAM introduces unwanted offsets in the cavity length signals and thereby shifts the operating point of the optical cavities from the nominal point via feedback control. This shift causes variations in the sensing matrix, and leads to degradation in the performance of the precision noise subtraction scheme of the multiple-degree-of-freedom control system. In addition, such detuned optical cavities produce an optomechanical spring, which also perturbs the sensing matrix. We use our simulations to derive requirements on RAM for the Advanced LIGO (aLIGO) detectors, and show that the RAM expected in aLIGO will not limit its sensitivity.

Impact point model predictive control of a spin-stabilized projectile with instability protection

Most smart projectile control systems generate lateral control forces to guide the round to a target. Experience has shown that under the right combination of body orientation, translational velocity, and angular velocity, relatively low lateral control force inputs can induce instability of the round. To solve this problem, an additional control logic layer is appended to a nominal impact point flight control law to protect it from instability in these infrequent, but consequential situations. To highlight the newly developed control logic, a smart 155 mm spin-stabilized projectile equipped with a rotating paddle control mechanism is considered. For this example configuration, cross range maneuvering occasionally induces instability. Simulation results, using both rigid and multi-body nonlinear flight dynamics models, indicate that the addition of the instability protection layer in the control logic prevents projectile instability while not substantially altering target impact statistics. The nature of this protector design lends itself well to the use of a GPU to perform the calculations, greatly decreasing the computation time needed.

Using LMIs to optimize robustness of observer‐based state‐feedback for a synchrotron

SUMMARYIn this article, a synthesis method for linear systems subject to uncertain time‐varying parameters is proposed. Starting with the given values for the nominal parameters, the first objective is to find a constant state feedback such that the controlled system is stabilized and given dynamic specifications, such as a minimal decay rate, are met. In a second step, the constant feedback is then locally optimized such that the uncertain system parameters are allowed to vary around their nominal point as much as possible, whereas stabilization and dynamic specifications still hold. In addition, the procedure is extended toward observer‐based state feedback. Finally, this approach is applied to a synchrotron example, where the particle beam in longitudinal direction is to be stabilized and the coherent synchrotron frequency as well as the damping rate are uncertain. Copyright © 2013 John Wiley & Sons, Ltd.

Simulation of near surge instabilities onset in a turbocharger compressor

This study focuses on numerical simulations of a small automotive turbocharger compressor stage. Two medium speed characteristics were reproduced from nominal operating points to surge and were compared with experimental measurements. The aim of this study is to analyze the flow unsteadiness occurring near the surge line. The complete geometry of the impeller is meshed; hence, no spatio-temporal hypothesis is done during simulations. The main flow patterns are investigated to identify structures that might be responsible of surge inception. Results show that both impeller and diffuser are affected by stall. Blade channels are affected by a complete shroud recirculation extending from upstream of the impeller inlet to the diffuser inlet. Three radial recirculation zones are detected on the vaneless diffuser walls, strongly influenced by the two-pike asymmetric pressure field induced by the volute tongue. Its influence is observed at the inlet of the compressor, increasing the inter-blade flow unsteadiness.

POINT CLOUD METRICS FOR SEPARATING STANDING ARCHAEOLOGICAL REMAINS AND LOW VEGETATION IN ALS DATA

Abstract. The integration of Airborne Laser Scanning survey into archaeological research and cultural heritage management has substantially added to our knowledge of archaeological remains in forested areas, and is changing our understanding of how these landscapes functioned in the past. While many types of archaeological remains manifest as micro-topography, several important classes of features commonly appear as standing remains. The identification of these remains is important for archaeological prospection surveys based on ALS data, and typically represent structures from the Roman, Medieval and early Modern periods. Standing structures in mixed scenes with vegetation are not well addressed by standard classification approaches developed to identify bare earth (terrain), individual trees or plot characteristics, or buildings (roofed structures). In this paper we propose an approach to the identification of these structures in the point cloud based on multi-scale measures of local density, roughness, and normal orientation. We demonstrate this approach using discrete-return ALS data collected in the Franche-Comte region of France at a nominal point density of 8 pts/m2, a resolution which, in coming years, will become increasingly available to archaeologists through government supported mapping schemes.

What price quitting? The price of cigarettes at which smokers say they would seriously consider trying to quit

BackgroundDeciding on an appropriate level for taxes on tobacco products is a critical issue in tobacco control. The aim of the present study was to describe the critical price points for packs for smokers of each pack size, to calculate what this would equate to in terms of price per stick, and to ascertain whether price points varied by age, socio-economic status and heaviness of smoking.MethodsIn November 2011, 586 Victorian smokers of factory-made cigarettes were asked during a telephone survey about their usual brand, including the size and cost of their usual pack. They were also asked about use of illicit tobacco. Smokers estimated what price their preferred pack would need to reach before they would seriously consider quitting.ResultsThree-quarters of regular smokers of manufactured cigarettes could envisage their usual brand reaching a price at which they would seriously consider quitting. Analyses revealed that answers clustered around whole numbers, (AUD$15, $20, $25 and $30), with a median nominated price point of AUD$20 per pack. The median price point at which regular smokers would consider quitting was calculated to be 80 cents per stick, compared to the current median reported stick price of 60 cents.Of the smokers who nominated a price point, 60.1% indicated they would seriously consider quitting if the cost of their usual brand equated to 80 cents per stick or less; 87.5% would seriously consider quitting if sticks reached one dollar each.ConclusionsThese results do suggest a potentially useful approach to setting taxes in Australia. If taxes can be set high enough to ensure that the cost of the smokers’ preferred packs exceeds critical price points, then it seems likely that more people would seriously attempt to quit than if the price increased to a level even slightly below the price points. Our study suggests that a tax increase large enough to ensure that a typical pack of 25 cigarettes in Australia cost at least AUD$20 would prompt more than 60% of smokers able to nominate a price point to seriously think about quitting, with particularly strong effects among low-SES smokers.

Spatially explicit competition in a mixed planting of Araucaria cunninghamii and Flindersia brayleyana

A 20-year-old Nelder wheel planted with hoop pine (Araucaria cunninghamii Aiton ex D.Don) and Queensland maple (Flindersia brayleyana F.Muell.) in 18 spokes and 8 rings represents nominal point densities of 3,580, 2,150, 1,140, 595, 305, 158, 82, and 42 stems/ha and offers an opportunity to examine competition and spatial interaction between these two species. This study aimed to evaluate the intraspecific and interspecific competition between two contrasting tree species and to determine the distance over which competition can be observed. Competition was estimated using Hegyi’s index, implemented using the Simile visual modeling environment, and calibrated using nonlinear least squares with PEST. Interactions were detected between pairs of stems closer than D ij < 40(d i + d j ) where D is distance (in centimeters) and d is stem diameter (in centimeters diameter at breast height). F. brayleyana trees surrounded by A. cunninghamii trees experience negligible competition, whereas A. cunninghamii surrounded by F. brayleyana trees suffer strong competition. Forty times diameter offers a useful guide to the extent of competition in even-aged stands planted with these species. Competition can be observed empirically when pairs of trees are closer than 40 times the sum of their diameters, but the intensity of the competition may vary considerably with species.