Table Look-up Procedure Research Articles

Static and Rotordynamic Characteristics for Two Types of Novel Hole-Pattern Seals Operating in Supercritical CO2 Turbomachinery

Abstract In this paper, two novel hole-pattern seals were assessed for applications at the balance piston in a 14 MW supercritical CO2 turbine, focusing on the improvement of the seal leakage and rotordynamic performances. These two novel hole-pattern seals were derived from the conventional straight-through hole-pattern seal (HPS) with the same sealing clearance, diameter, axial length, hole diameter and depth, including a stepped hole-pattern damper seal (SHPS) and a grooved hole-pattern damper seal (GHPS). To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake also was designed and employed at seal entrance for each type seal. A comprehensive assessment and comparison was conducted on the conventional HPS and the present two novel hole-pattern seals (SHPS and GHPS) with a static concentric rotor. The leakage flow rates, rotordynamic force coefficients, cavity pressure, and swirl velocity developments were analyzed for three hole-pattern seal designs with/without swirl brakes at two inlet preswirl ratios (0.1, 0.5), using a transient computational fluid dynamics (CFD)-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the National Institute of Standards and Technology (NIST) database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions. Results show that the present two novel hole-pattern seals have better sealing capability, especially for the GHPS seal which leaks less by a factor of 44%. In general, the GHPS seal possesses the lowest positive effective stiffness, highest effective damping, and the lowest crossover frequency of 60–70 Hz, especially at high inlet preswirl case. From a viewpoint of the rotor stability and unbalance sensitivity analysis, the GHPS seal without entrance swirl brake is a better seal design scheme for the balance piston seal in sCO2 turbine.

Tabular Interpolation Approach Based on Stable Random Projection for Estimating Empirical Entropy of High-Speed Network Traffic

The empirical entropy of the network flow attributes is an essential measure for identifying anomalous network traffic. However, computing the exact entropy values for high-speed networks in real-time is computationally expensive. Accordingly, the present study replaces the complex computations of existing stable random projection methods for entropy estimation with a simple table lookup procedure. Notably, the size of the lookup table is reduced through a piece-wise linear interpolation heuristic in order to facilitate the implementation of the proposed scheme in resource-constrained pipeline environments. The proposed architecture enables entropy estimation to be performed using both the Log-Mean Estimator (LME) method and the New Estimator of Compressed Counting (NECC) algorithm reported in the literature. The feasibility of the proposed approach is verified empirically using both real-world network traffic traces and synthetic data streams. Moreover, the practical applicability is demonstrated via stream-based implementation in the programmable data planes of the NetFPGA-Plus framework and a Tofino P4 switch, respectively. The results indicate that the proposed tabulation-based entropy estimation scheme allows minimum-sized Ethernet frames to be processed with a wire speed of up to several hundred gigabits per second.

Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals Operating in Supercritical CO2 Turbomachinery

Abstract The balance piston seal in multiple-stage centrifugal compressors and axial turbines sustains the largest pressure drop through the machines and therefore plays an important role in successful full load operation at high rotational speed. This is especially true for power dense turbomachines in supercritical CO2 power cycles that generate or expend higher fluid pressures (above the critical value 7.3 MPa) and density (close to water 1000 kg/m3), because the fluid forces generated by the balance piston seals are directly proportional to the fluid density and the pressure drop across the seal. This paper presents a comprehensive assessment and comparison on the leakage and rotordynamic performance of three types of annular gas seals for application in a 14 MW supercritical CO2 turbine. These three seals represent the main seal types used in high-speed rotating machines at the balance piston location in efforts to limit internal leakage flow and achieve rotordynamic stability, including a labyrinth seal (LABY), a fully partitioned pocket damper seal (FPDS), and a hole-pattern damper seal (HPS). These three seals were designed to have the same sealing clearance and similar axial lengths. To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake was also designed and employed at seal entrance for each type seal to reduce the seal inlet preswirl velocity. Numerical results of leakage flow rates, rotordynamic force coefficients, cavity dynamic pressure, and swirl velocity developments were analyzed and compared for three seal designs at high positive inlet preswirl (in the direction of shaft rotation), using a proposed transient computational fluid dynamic (CFD)-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the National Institute of Standards and Technology reference fluid properties database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions. Results show that the inlet swirl brake can significantly reduce the preswirl velocity at seal entrance, lowering the effective damping crossover frequency fco (or even fco = 0) to maximize the full operational frequency range of the machines. In stability analysis phase of a MW-scale supercritical CO2 turbine/compressor, the seal stiffness effects on the rotor mode shape must be evaluated carefully, where the seal stiffness is sufficiently large (comparable to the bearing stiffness). From a rotordynamic viewpoint, the HPS seal with entrance swirl brake is a better seal concept for the balance piston seal in supercritical CO2 turbomachinery, which possesses the largest positive effective damping throughout the entire subsynchronous frequency range.

An equilibrium wall model for reacting turbulent flows with heat transfer

A wall model for reacting turbulent flows for predicting heat transfer in rocket engine combustion chambers is presented. The wall model is developed based on boundary layer equations and includes the effects of chemical reactions and variable properties. Assuming an equilibrium state near the wall, a simple set of momentum and enthalpy equation is formulated. A table look-up procedure is employed to calculate the contributions of chemical effects and mixture properties. For turbulence modeling of the inner layer, a modified mixing length model based on semi-local scaling is applied. The proposed equilibrium wall model is validated in two hydrogen/oxygen reacting cases. In the first validation case of a reacting turbulent channel flow, the equilibrium wall model accurately predicts the near-wall velocity and temperature fields. In contrast, the wall model when assuming frozen chemistry shows a discrepancy in temperature gradient and mixture properties. The heat flux balance in the equilibrium wall model highlights the important contributions of chemical effects. The second test case of a rocket combustion chamber shows that the equilibrium wall model is superior to the frozen wall model and wall function models in predicting wall shear stress and heat flux.

Parabolized stability analysis of chemically reacting boundary-layer flows in equilibrium conditions

Stability of self-similar hypersonic flows over a flat plate in local thermodynamic equilibrium is studied by means of linear parabolized stability equations. A spectral collocation numerical method together with a finite-difference-based marching scheme are used to solve the equations, while the gas mixture and transport properties are computed with a table look-up procedure. High-temperature effects are found to destabilize the second-Mack-mode regardless of the adiabatic/isothermal wall condition considered. On the other hand, nonlocal effects show a Mach-dependence influence: stabilizing at lower Mach, while destabilizing at higher ones. Strong oscillations in the growth rate of perturbations in local thermodynamic equilibrium are found to be caused by damped supersonic modes.

Modeling Multiphase Effects in CO2 Compressors at Subcritical Inlet Conditions

An advanced numerical framework to model CO2 compressors over a wide range of subcritical conditions is presented in this paper. Thermodynamic and transport properties are obtained through a table look-up procedure with specialized features for subcritical conditions. Phase change is triggered by the difference between the local values of pressure and saturation pressure, and both vaporization and condensation can be modeled. Rigorous validation of the framework is presented for condensation in high pressure CO2 using test data in a De Laval nozzle. The comparisons between computations and test data include: condensation onset locations, Wilson line, and nozzle pressure profiles as a function of inlet pressures. The framework is applied to the Sandia compressor that has been modeled over broad range of conditions spanning the saturation dome including: near critical inlet conditions (305.4 K, and 7.843 MPa), pure liquid inlet conditions (at 295 K), pure vapor inlet conditions (at 302 K), and two-phase inlet conditions (at 290 K). Multiphase effects ranging from cavitation at the liquid line to condensation at the vapor line have been simulated. The role of real fluid effects in enhancing multiphase effects at elevated temperatures closer to the critical point has been identified. The performance of the compressor has been compared with test data; the computational fluid dynamics (CFD) results also show that the head-flow coefficient curve collapses with relatively minor scatter, similar to the test data, when the flow coefficient is defined on the impeller exit meridional velocity.

Nonlinear Formulation Based on an Equation-of-State Free Method for Compositional Flow Simulation

Summary Compositional simulation is necessary for modeling complex enhanced oil recovery (EOR) processes. For accurate simulation of compositional processes, we need to resolve the coupling of the nonlinear conservation laws, which describe multiphase flow and transport, with the equilibrium phase behavior constraints. The complexity of the problem requires extensive computations and consumes significant time. This paper presents a new framework for the general compositional problem associated with multicomponent multiphase flow in porous media. Here, adaptive construction and interpolation using the supporting tie lines are used to obtain the phase state and the phase compositions. For the parameterization of the full solution of a complex compositional problem, we need only a limited number of supporting tie lines in the compositional space. The parameterized tie lines are triangulated using Delaunay tessellation, and natural-neighbor interpolation is used inside the simplexes. Then, the computation of the phase behavior in the course of a simulation becomes an iteration-free, table look-up procedure. The treatment of nonlinearities associated with complex thermodynamic behavior of the fluid is based on the new set of unknowns—tie-line parameters that allow for efficient representation of the subcritical region. For the supercritical region, we use the standard compositional variable set based on the overall composition. The efficiency and accuracy of the method are demonstrated for several multidimensional compositional problems of practical interest. In terms of the computational cost of the thermodynamic calculations, the proposed method shows results comparable to those of state-of-the-art techniques. Moreover, the method shows better nonlinear convergence in the case of near-miscible gas-injection simulation.

Conductivity-depth imaging of helicopter-borne TEM data based on a pseudolayer half-space model

Helicopter-borne time-domain electromagnetic (HTEM) systems with a concentric horizontal coil configuration have been used increasingly in mineral exploration. Conductivity-depth imaging (CDI) is a useful tool for mapping the distribution of geologic conductivity and for identifying conductive targets. A CDI algorithm for HTEM systems with a concentric coil configuration is developed based on the pseudolayer half-space model. Primary advantages of this model are immunity to altimeter errors and better resolution of conductive layers than other half-space models. Effective depth is derived empirically from the diffusion depth and apparent thickness of the pseudolayer. A table lookup procedure is established based on the analytic solution of a half-space model to speed up processing. This efficiency makes generation of real-time conductivity-depth images possible. Tests on synthetic data demonstrate that the pseudolayer conductivity-depth-imaging algorithm maps a wider range of conduc-tivities and does a better job of resolving highly conductive layers, compared with that of the homogeneous half-space model. Effective depths are close to true depths in many circumstances. Field examples show stable and geologically meaningful conductivity-depth images.

A method for the quantification of benzodiazepine receptors by using 123I-iomazenil and SPECT with one scan and one blood sampling.

Iodine-123-iomazenil (Iomazenil) is a ligand of central type benzodiazepine receptors for single photon emission computed tomography (SPECT). Previously we reported a simple, table look-up method for quantification of its binding potential (BP) by using two SPECT scans and calibrated standard input function with one blood sampling. This method is based on a two-compartment model (K1: influx rate constant; k2: efflux rate constant; Vd (= K1/k2): the total distribution volume corresponding BP), and requires two SPECT scans for calculating both K1 and Vd values. If the K1 value in the two-compartment model can be assumed to be constant, the radioactivity of one SPECT scan at 180 min after injection can be considered to tabulate as a function of Vd for a given K1 value and a given input function, and a table look-up procedure provides the corresponding Vd value. The purpose of this study was to develop a simple, autoradiographic method for quantification of BP by using one SPECT scan and calibrated standard input function with one blood sampling. SPECT studies were performed on 14 patients. A dynamic SPECT scan was initiated following an intravenous bolus injection of Iomazenil. A static SPECT scan was performed at 180 min after the injection. Frequent blood sampling from the brachial artery was performed on all subjects to determine the arterial input function. Simulation studies revealed that errors in calculated Vd values were around +/-10-15% for varied K1 values. A good correlation was observed between total distribution volume values calculated by three-compartment model analysis and those calculated by the present method (r = 0.90), supporting the validity of this method. The present method is simple and applicable for clinical use, and will be able to provide images of BP.

A simple method for the quantification of benzodiazepine receptors using iodine-123 iomazenil and single-photon emission tomography

Iodine-123 iomazenil (Iomazenil) is a ligand for central type benzodiazepine receptors that is suitable for single-photon emission tomography (SPET). The purpose of this study was to develop a simple method for the quantification of its binding potential (BP). The method is based on a two-compartment model (K1, influx rate constant; k2', efflux rate constant; VT' (=K1/k2'), the total distribution volumes relative to the total arterial tracer concentration), and requires two SPET scans and one blood sampling. For a given input function, the radioactivity ratio of the early to delayed scans can be considered to tabulate as a function of k2', and a table look-up procedure provides the corresponding k2' value, from which K1 and VT' values are then calculated. The arterial input function is obtained by calibration of the standard input function by the single blood sampling. SPET studies were performed on 14 patients with cerebrovascular diseases, dementia or brain tumours (mean age+/-SD, 56.0+/-12.2). None of the patients had any heart, renal or liver disease. A dynamic SPET scan was performed following intravenous bolus injection of Iomazenil. A static SPET scan was performed at 180 min after injection. Frequent blood sampling from the brachial artery was performed on all subjects for determination of the arterial input function. Two-compartment model analysis was validated for calculation of the VT' value of Iomazenil. Good correlations were observed between VT' values calculated by three-compartment model analysis and those calculated by the present method, in which the scan time combinations (early scan/delayed scan) used were 15/180 min, 30/180 min or 45/180 min (all combinations: r=0.92), supporting the validity of this method. The present method is simple and applicable for clinical use.

Novel techniques in high speed modem implementation using programmable DSPs

We present the design and performance of a high speed MSK modem that incorporates digital heterodyne processing. A novel table look-up procedure for direct IF/RF modulation, based on a suitable maximal-length shift register sequence, is described. High performance, linear phase, low-complexity mixing and filtering in the receiver is achieved using multirate IFIR filters, where the shaping filter may possibly beM-th-band. The configuration of the IFIR filters is chosen based on the carrier frequency and the filtering requirements.

Computational and experimental investigation of a turbulent non-premixed methane flame

Mathematical modeling of turbulent combustion processes is a challenging task, mainly because of the problem of describing the coupling of the chemical kinetics with the turbulent flow. Existing models still have to be improved, which can only be achieved by comparison and validation with experimental results. We present experimental results and numerical simulations of a piloted non-premixed methane-airflame of semitechnical size (50 kW). The experimental data comprise measurements of velocities, temperature, and species concentrations. The model used for the simulation of the turbulent flame consists of a k-ε model for the turbulent flow field combined with a Monte Carlo method for the solution of the joint probability density function (PDF) of velocities and scalars that overcomes the closure problem for the chemical kinetics. Finite-rate chemistry is incorporated in the model using a two-step reduced chemistry model obtained by an automatic mechanism reduction procedure based on intrinsic low-dimensional manifolds, together with a table look-up procedure. Comparisons of experimental and computational results show that the model is able to predict the main characteristics of the flame well. Discrepancies can be mainly attributed to deficiencies of the micromixing model and inaccuracies in the description of the turbulent flow field by the k-ε model. However, it is clearly shown that finite chemistry effects play a major role in this flame.

Method of use of voice message coder/decoder

A code excited linear predictive coder and decoder well suited to speech recording, transmission and reproduction, especially in voice messaging systems, provides backward adaptive gain control of stored codevectors to be applied to a synthesis filter prior to being compared with sequences of input speech signals. Simplified linear predictive parameter quantization using efficient table lookup procedures, efficient codevector storage and search all contribute in an illustrative embodiment to high quality coding and decoding with reduced computational complexity.

Feedback control of quantized constrained systems with applications to neuromorphic controllers design

During the last few years there has been considerable interest in the use of trainable controllers based upon the use of neuron like elements, with the expectation being that these controllers can be trained, with relatively little effort, to achieve performance. Good performance, however, hinges on the ability of the neural net to generate a good control law even when the input does not belong to the training set, and it has been shown that neural nets do not necessarily generalize well. It has been proposed that this problem can be solved by essentially quantizing the state space and then using a neural net to implement a table lookup procedure. There is little information on the effect of this quantization upon the controllability properties of the system. In this paper The authors address this problem by extending the theory of control of constrained systems to the case where the controls and measured states are restricted to finite or countably infinite sets. These results provide the theoretical framework for previously suggested neuromorphic controllers, but they are also valuable for analyzing the controllability properties of computer-based control systems. >

Case Study: An Application of the Revised NIOSH Lift Guide to a Multiple Task Job

The newly revised NIOSH lifting guide offers a multiple task strategy for frequency weighting multiple lifting tasks performed in a series; in close proximity of time. This strategy allows calculation of a composite lifting index (CLI) during assessment of jobs for which lifting variables are changing throughout the task. While the approach is useful, the number of calculations and table look-up procedures required is much larger than a single task strategy requires, and the process becomes tedious and error prone if performed manually. Consequently, a computer program was developed by Continental Insurance Corporate Loss Control in FORTRAN to automate table look-ups and required calculations. A case-study applying the multi-task approach to an actual job is shown. The job involves manual lifting/lowering of boxes from a queuing turntable to a pallet stack. The results indicate that the job is unacceptably hazardous, which agrees with subjective responses of workers. Possible worksite retrofit changes are also evaluated in a “what-if” manner. These results show that changes would improve the risk level, but proposed improvements were not sufficient to attain an acceptable risk level. Mechanization of the job is therefore suggested. Details regarding the multi-task application are discussed.

An experimental approach to the calibration and use of triple hot-wire probes

A method of calibrating and extracting velocities from arbitrary geometry triple hot-wire probes has been developed and tested. The three-step procedure involves experimental determination of an accurate cooling law for each wire in the array, use of these models to develop a set of tables relating anemometer output to flow velocity input, and a table look-up procedure to extract the velocities. The functional form for the cooling law can be arbitrarily chosen and these equations are never directly inverted. Solutions are tabulated making use of special variable transformations that separate the dependence on flow angle and velocity magnitude. Errors in the table look-up procedure are commensurate with those in exact inversion techniques. Most of the error arises from accurate determination of the cooling laws. An application to turbulent boundary layer measurements is presented as an example of the use of the method.

Simulation of the turn-on transient behavior of amorphous-silicon thin-film transistors

The turn-on transient behavior of amorphous-silicon (a-Si:H) thin-film transistors (TFT) was measured. The source current decay, after the initial step, had a double exponential decay within the first 6 ms. The source-current decay rate did not depend on the drain voltage, gate voltage or geometry of the device. In this study a modeling methodology based on a table look-up procedure was used to simulate the turn-on transient behavior of the a-Si:H TFT. Based on experimental evidence, the original five look-up tables were simplified to two tables. The simplified set of two tables was used to simulate the long-term transient behavior and yielded good agreement with the experimental results.

Fault modeling of physical failures in CMOS VLSI circuits

The analog complex physical fault of a gate-to-drain short in VLSI CMOS circuits is studied. A relationship between the inverse voltage of an inverter and the faulty voltage output is obtained and is then used to study the propagation of the faulty signal through successive gates. General graphical rules are developed which describe techniques for obtaining the operating point of the circuit through table look-up procedures. The technique is simple and can easily be added to known fault-simulation algorithms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of manual lifting tasks: a qualitative alternative to the NIOSH work practices guide.

A new method for evaluating ergonomic stresses on lifting tasks has been developed. This method utilizes the general procedures and hazard classification categories described in the National Institute for Occupational Safety and Health's (NIOSH) Work Practices Guide for Manual Lifting. The quantitative measurements of workplace dimensions and computations used by the NIOSH method to classify a job as "acceptable," "administrative controls required," or "hazardous" have been eliminated in favor of a table look-up procedure. A computer simulation was performed to compare results generated by the new method to results generated by the NIOSH method. The results of this simulation found that the new method was unbiased and was reasonably precise for most lifting activities.

Analysis of Manual Lifting Tasks: A Qualitative Alternative to the NIOSH Work Practices Guide

A new method for evaluating ergonomic stresses on lifting tasks has been developed. This method utilizes the general procedures and hazard classification categories described in the National Institute for Occupational Safety and Health's (NIOSH) Work Practices Guide for Manual Lifting. The quantitative measurements of workplace dimensions and computations used by the NIOSH method to classify a job as “acceptable,” “administrative controls required,” or “hazardous” have been eliminated in favor of a table look-up procedure. A computer simulation was performed to compare results generated by the new method to results generated by the NIOSH method. The results of this simulation found that the new method was unbiased and was reasonably precise for most lifting activities.