Steady Calculations Research Articles

Integer-N PLLs Verification Methodology: Large Signal Steady State and Noise Analysis

The need for accurate and fast verification of the phase locked loop (PLL) circuits is a designers' important concern before the chip tape-out. This paper covers two major PLL characteristics for circuit verification: steady-state response and phase noise. A new simulation methodology is proposed and comprehensively described. It is general purpose and can be implemented within the framework of all commercial radio frequency integrated circuit (RFIC) simulation tools. By using the new algorithm, we succeed in predicting integer-N PLL's characteristics with the same precision as the conventional brute-force transistor-level simulation while spending much less time and computer memory. It is composed of two stages, a hierarchical analysis algorithm for the steady state response calculation and a bottom-up behavioral modeling strategy for the phase noise analysis that accurately accounts for the non-idealities in all PLL blocks.

Numerical Evaluation of Dynamic Transfer Matrix and Unsteady Cavitation Characteristics of an Inducer

The transfer matrix and unsteady cavitation characteristics, cavitation compliance and mass flow gain factor, of cavitating inducer were evaluated by CFD using commercial software. Quasi-steady values of cavitation compliance and mass flow gain factor were obtained first by using steady calculations at various flow rate and inlet cavitation number. Then unsteady calculations were made to determine the transfer matrix and the cavitation characteristics. The results are compared with experiments to show the validity of calculations.

Energy Equation Derivation of the Oil-Gas Flow in Pipelines

In the simulation of oil-gas pipeline multiphase flow, thermodynamic computation is an important process interacting with the hydraulic calculation and it influences the convergence of the program and the accuracy of the results. The form of the energy equation is the key to the thermodynamic computation. Based on the energy equation of oil-gas flow in pipeline, the Explicit Temperature Drop Formula (ETDF) is derived for oilgas steady state temperature calculation. This new energy equation has considered many factors, such as Joule-Thomson effect, pressure work, friction work and impact of terrain undulation and heat transfer Oil & Gas Science and Technology – Rev. IFP Energies nouvelles with the surroundings along the line. So it is an overall form of energy equation, which could describe the actual fact of multiphase pipeline accurately. Therefore, some standpoints in literatures on the temperature calculation of oil-gas two-phase flow in pipelines are reviewed. Elimination of temperature iteration loop and integration of the explicit temperature equation, instead of enthalpy energy equation, into the conjugated hydraulic and thermal computation have been found to improve the efficiency of algorithm. The calculation applied to both the component model, also applied to the black-oil model. This model is incorporated into the component model and black-oil model, respectively, and two simulations are carried out with two practical pipeline Yingmai-Yaha and Lufeng multiphase pipeline and the temperature results are compared with the simulation calculated by the OLGA and the measured. It is shown that this model has simulated the temperature distribution very well. Finally, we analyzed the influence of the specific heat capacity of oil and gas on the temperature of the mixture of fluids and the influence of the Joule-Thomson effect on the temperature distribution on the pipeline. It is shown that the Joule-Thomson coefficient is a key factor to well describe the oil-gas two-phase flow.

Calculation of Steady and Periodic Unsteady Blade Surface Heat Transfer in Separated Transitional Flow

In this work, aerothermal investigations of a highly loaded HP turbine blade are presented. The purpose of such investigations is to improve the physical understanding of the heat transfer in separated flow regions, with the final goal of optimizing cooling configurations for aerodynamically highly loaded turbine designs. The analysis is focused on the T120 cascade, that was recently tested experimentally in the framework of the European project AITEB-2 (Aero-thermal Investigation of Turbine Endwalls and Blades). Such a cascade has a relatively low solidity that is responsible for the formation of a laminar separation bubble on the suction side of the blade. Separated-flow transition and transonic conditions downstream of the throat result in a flow configuration that is very challenging for traditional RANS solvers. Moreover, the separated flow transition pattern was found to have a strong impact on both the aerodynamic and thermal aspects. The study was carried out using a novel three-equation, transition-sensitive, turbulence model. It is based on the coupling of an additional transport equation for the laminar kinetic energy to the Wilcox k - ω model. Such an approach allows one to take into account the increase of the nonturbulent fluctuations in the pretransitional and transitional region. Comprehensive aerodynamic and heat transfer measurements were available for comparison purposes. In particular, heat transfer measurements cover different Mach and Reynolds numbers, in both steady and periodic unsteady inflow conditions. A detailed comparison between measurements and computations is presented, and the impact of transition-related aspects on the surface heat transfer is discussed.

Effects of graphite surface roughness on bypass flow computations for an HTGR

Bypass flow in a prismatic high temperature gas reactor (HTGR) occurs between graphite blocks as they sit side by side in the core. Bypass flow is not intentionally designed to occur in the reactor, but is present because of tolerances in manufacture, imperfect installation and expansion and shrinkage of the blocks from heating and irradiation. It is desired to increase the knowledge of the effects of such flow; it has been suggested that it may be as much as 20% of the total helium coolant flow [INL Report 2007, INL/EXT-07-13289]. Computational fluid dynamic (CFD) simulations can provide estimates of the scale and impacts of bypass flow. Previous CFD calculations have examined the effects of bypass gap width, level and distribution of heat generation and effects of shrinkage. The present contribution examines the effects of graphite surface roughness on the bypass flow for different relative roughness factors for three gap widths. Such calculations should be validated using specific bypass flow measurements. While such experiments are currently underway for the specific reference prismatic HTGR design for the next generation nuclear plant (NGNP) program of the U.S. Dept. of Energy, the data are not yet available. To enhance confidence in the present calculations, wall shear stress and heat transfer results for several turbulence models and their associated wall treatments are first compared for steady flow in a single tube that is representative of a coolant channel in the prismatic HTGR core. The results are compared to published correlations for wall shear stress and Nusselt number in turbulent pipe flow. Turbulence models that perform well are then used to make steady bypass flow calculations in a symmetric one-twelfth sector of a prismatic block that includes bypass flow. The comparison of shear stress and Nusselt number results with published correlations constitutes a partial validation of the CFD model. Results indicate that increasing surface roughness increases the maximum fuel and helium temperatures as do increases in gap width. However, maximum coolant temperature variation due to increased gap width is not changed by surface roughness.

A New Model for Keyhole Mode Laser Welding Using FLUENT

Evolution of the free surface at gas–liquid interface during keyhole mode welding is complex and its calculation is computationally expensive. Similarly, models based on only heat conduction without considering vapour cavity and liquid convection around it, are computationally efficient but are not effective in defining the weld pool shape especially for low conducting material like steel. In the present study a useful yet computationally efficient model has been presented for keyhole mode laser welding using commercial software FLUENT. Here instead of evolving the free surface of keyhole in a rigorous way, various possible steady keyhole shapes are assumed partially based on literature evidence and subsequently their dimensions are calculated by an overall heat balance. The estimated keyhole profile is then mapped into the thermo-fluid framework of FLUENT and steady computational fluid dynamics calculations is carried out around the keyhole that is considered rigid wall at boiling temperature. Next, an optimized keyhole shape is identified by comparing the predicted fusion lines with the experimental weld fusion lines reported in literature. Finally, using this optimized keyhole shape independent predictions are made for two materials of widely different thermal conductivities, like steel and aluminum, under different operating conditions. In all cases the results of the present simulation is found to in close agreement with experimental data and even better than the model predictions reported in literature. The present model emerges as a simple yet effective model for predicting the weld bead profile encompassing wide range of materials under different operating conditions.

Performance comparison of zeroth order nodal expansion methods in 3D rectangular geometry

This work presents a study on the performance comparison of zeroth order nodal expansion methods, NEM. A computer code based on zeroth order nodal expansion methods, ZONEM-3D, is developed for the steady state diffusion equation calculation using nodal expansion family methods including average current, average flux, point current and point flux in 3D cubic geometry. The aim of this work is to determine the relative merits of four variants in terms of accuracy per computing time expended. To speed up the solution schemes, we implemented the fission source weighting in the power method procedure. The influence and capability of the accelerating technique are investigated by considering the execution time through solving some test cases. Four popular test problems, BIBLIS-2D, ZION-2D PWR reactor benchmark, LMW LWR-3D and IAEA-3D benchmark, are used to assess the performance comparison of the methods. Overall, numerical results demonstrate although the accuracies of all methods are adequate but point methods are the most accurate of four variants on considered problems and have relatively higher accuracy than average methods by using coarse meshes. In contrast, execution time of average methods is less than point methods because of having less computational efforts. Also we find current methods have less execution time relative to flux methods. For surveying the influence of considered acceleration method, several fission source weightings are considered and investigated.

The 15N natural abundance of the N lost from an N‐saturated subtropical forest in southern China

The 15N‐enrichment of plants and soils is believed to indicate characteristics of the open nitrogen (N) cycle in terrestrial ecosystems because N lost from an ecosystem is presumably 15N‐depleted through isotopic fractionation. However, because of a lack of an appropriate analytical methodology to confirm that supposition, the δ15N value for total dissolved nitrogen (TDN, the sum of ammonium, nitrate, and dissolved organic N) in stream water from forests has been measured only rarely. This report describes the δ15N values for TDN, ammonium, and nitrate in precipitation and stream water, together with those for soil‐emitted nitrous oxide (N2O; measured once) in an N‐saturated subtropical forest in southern China. Concentration‐weighted δ15N values of TDN were −0.7‰ in precipitation and +1.2‰ in stream water. The difference in δ15N between soil (+3.9‰) and TDN in the stream water was 2.7‰. In contrast, soil‐emitted N2O was strongly 15N‐depleted (−14.3‰): 18‰ lower than that of the soil. Our results demonstrate that the discharged N loss is 15N‐depleted only slightly compared with soil N, and gaseous N losses can be a strong driver for raising the terrestrial ecosystem δ15N. Our findings suggest that the relation between ecosystem δ15N and the open N cycle can be interpreted better by considering the net discrimination against 15N determined by the balance between gaseous and discharge N losses. Steady state 15N budget calculations proposed by Houlton and Bai (2009) can provide important information about the gaseous N fluxes, which are difficult to measure directly. The steady state calculation for the relationships among gaseous N loss, apparent isotopic fractionation during gaseous N loss, and isotopic signature of N inputs suggests that precise measurements of unmeasured components (e.g., dry deposition, NO and N2 emission) are quite important for better estimation of gaseous N losses from the ecosystem.

Evaluation of various non-linear k–ɛ models for predicting wind flow around an isolated high-rise building within the surface boundary layer

This paper evaluates the performance of various non-linear k–ɛ models for predicting wind flow around an isolated high-rise building at a 1:1:2 (length: width: height) scale and within the turbulent boundary layer. Two cubic models, proposed by Ehrhard et al. and Craft et al., and one quadratic model proposed by Shih et al., are examined by comparing their simulation results with the experimental data. In this study, the three non-linear models can reproduce the vortex shedding behind building during unsteady calculations. However, these non-linear models cannot achieve a convergent solution in steady calculations. For the Shih model and the Ehrhard model, the magnitudes of the lateral velocity fluctuations normalized by the inlet wind speed at the height of building are only approximately 0.022, and for the Craft model, this dimensionless magnitude increases to approximately 0.11. These three non-linear models can reproduce the reverse flow on building roof. The Craft model slightly overpredicts the reattachment length on building roof. The other two non-linear models produce large roof re-circulation vortexes, which extend over the entire roof without attachment. Among the RANS models studied here, the Craft model shows the best agreement with the experimental data. The Craft model predicts the shortest reattachment length behind building among the revised k–ɛ models, while the other two non-linear models greatly overestimate the reattachment length behind building. The good performance of the Craft non-linear model in the wake region can be interpreted from the magnitude of the total kinetic energy after considering the solved wind fluctuations.

Development of Calculation Software of Steady State Parameters for HVDC Transmission

As the ± 800kV Xiangjiaba-Shanghai UHVDC pilot demonstration project has been completion production in China, an UHV AC and DC power era is coming in State Gird. A large number of calculations of main circuit steady state parameters for HVDC system are necessary for both HVDC transmission planning and design and checking DC projects in operation. Therefore, this paper firstly discusses the steady state parameters. Then considering the comprehensiveness of types of HVDC transmission, through digesting design features of foreign similar software, the steady state parameters calculation software for HVDC transmission is developed independently. It has features such as user-friendly interface, real-time calculation and calculation of comprehensive, rapid and accurate, using the mixed programming of Visual C++ (VC++) and MATLAB. Finally, take the ± 800kV Xiangjiaba-Shanghai UHVDC transmission project for example to calculate steady state parameters. The calculation results are accurate to meet the engineering requirements.

Simulation Research About Air Conditioning Load Calculation

Theory analysis method is adopted in this paper to review the development history of air-conditioning loads calculation, point out that the air-conditioning loads calculation went through from steady calculation to periodic unsteady calculation and then to new period of dynamic load calculation. Simulation calculation of air-conditioning cooling load have been developed deeply, and many software can be used to calculate the hourly cooling load about building. At last, The application of neutral network for prediction of cooling load in air conditioning systems have been introduced.

自由蛇行の発達に関する数値解析

In this study, the numerical flow and sediment-transport model including sub-models for bank erosion considering slump block, landing process and cut-offs, is confirmed that it can indicates that the effect of discharge variation and the formation of channel cutoffs are very important factor for the natural process of river meandering. In the steady flow calculation, the shape of meandering is transmitted from upstream to downstream. The wave height and wave length which transmit depend on the discharge. But in steady flow, the meandering shape which can be seen in a natural river cannot create. In the unsteady flow calculation, in which periodic discharge variation is set, the result shows the complicated meandering process which can be seen in a natural river. The results also indicate that the numerical model which includes the bank erosion considering slump blocks, landing process and cut-offs are reasonable.

On the Significance of Turbulence Models and Unsteady Effect on the Flow Prediction through A High Pressure Turbine Cascade

Unsteady flow simulations through a transonic turbine vane were carried out for an isentropic Mach number of 1.02 and a Reynolds number of 106. The main objective of the study is to investigate the effect of unsteadiness due to vortex shedding on the flow in transonic regime. The steady and the time-averaged unsteady results by employing three different turbulence models: shear stress transport (SST), k-ω, and ω Reynolds stress models were compared. The comparisons were emphasized on the isentropic Mach number along the blade and total pressure loss at the cascade exit. The results showed that both steady and unsteady calculations have good agreement with experimental data along the blade surface. However, at cascade exit, the unsteady calculations have much better agreement with experimental data than steady calculations. Based on these, we conclude that the unsteady flow calculations are essential for these types of problems.

Detailed comparisons of airborne formaldehyde measurements with box models during the 2006 INTEX-B and MILAGRO campaigns: potential evidence for significant impacts of unmeasured and multi-generation volatile organic carbon compounds

Abstract. Detailed comparisons of airborne CH2O measurements acquired by tunable diode laser absorption spectroscopy with steady state box model calculations were carried out using data from the 2006 INTEX-B and MILARGO campaign in order to improve our understanding of hydrocarbon oxidation processing. This study includes comparisons over Mexico (including Mexico City), the Gulf of Mexico, parts of the continental United States near the Gulf coast, as well as the more remote Pacific Ocean, and focuses on comparisons in the boundary layer. Select previous comparisons in other campaigns have highlighted some locations in the boundary layer where steady state box models have tended to underpredict CH2O, suggesting that standard steady state modeling assumptions might be unsuitable under these conditions, and pointing to a possible role for unmeasured hydrocarbons and/or additional primary emission sources of CH2O. Employing an improved instrument, more detailed measurement-model comparisons with better temporal overlap, up-to-date measurement and model precision estimates, up-to-date rate constants, and additional modeling tools based on both Lagrangian and Master Chemical Mechanism (MCM) runs, we have explained much of the disagreement between observed and predicted CH2O as resulting from non-steady-state atmospheric conditions in the vicinity of large pollution sources, and have quantified the disagreement as a function of plume lifetime (processing time). We show that in the near field (within ~4 to 6 h of the source), steady-state models can either over-or-underestimate observations, depending on the predominant non-steady-state influence. In addition, we show that even far field processes (10–40 h) can be influenced by non-steady-state conditions which can be responsible for CH2O model underestimations by ~20%. At the longer processing times in the 10 to 40 h range during Mexico City outflow events, MCM model calculations, using assumptions about initial amounts of high-order NMHCs, further indicate the potential importance of CH2O produced from unmeasured and multi-generation hydrocarbon oxidation compounds, particularly methylglyoxal, 3-hydroxypropanal, and butan-3-one-al.

Effect of Climate Change on MV Underground Network Operations in the Future Smart Grid Environment

In this paper, the steady state current rating calculations for 3-phase XLPE distribution power cables are performed using an analytical set of thermal equations. The analysis is made for different installation configurations (direct burial and tube installations) under various possible extreme Finnish environmental conditions. This study will enable electric power utilities to revise allowable current ratings to avoid damage to their power cables as well ensure safe and reliable distribution of power to the customers in the future smart grid environment. Ill. 6, bibl. 9, tabl. 5 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.115.9.743

Calculations of in-snow NO2and OH radical photochemical production and photolysis rates: A field and radiative-transfer study of the optical properties of Arctic (Ny-Ålesund, Svalbard) snow

[1] Depth-integrated production rates of OH radicals and NO2 molecules from snowpacks in Ny-Alesund, Svalbard, are calculated from fieldwork investigating the light penetration depth (e-folding depth) and nadir reflectivity of snowpacks during the unusually warm spring of 2006. Light penetration depths of 8.1, 11.3, 5.1, and 8.2 cm were measured for fresh, old, marine-influenced, and glacial snowpacks, respectively (wavelength 400 nm). Radiative-transfer calculations of the light penetration depths with reflectivity measurements produced scattering cross sections of 5.3, 9.5, 20, and 25.5 m2 kg−1 and absorption cross sections of 7.7, 1.4, 3.4, and 0.5 cm2 kg−1 for the fresh, old, marine-influenced, and glacial snowpacks, respectively (wavelength 400 nm). Photolysis rate coefficients, J, are presented as a function of snow depth and solar zenith angle for the four snowpacks for the photolysis of H2O2 and NO3−. Depth-integrated production rates of hydroxyl radicals are 1270, 2130, 950, and 1850 nmol m−2 h−1 (solar zenith angle of 60°) for fresh, old, marine-influenced, and glacial snowpacks, respectively. Depth-integrated production rates of NO2 are 32, 56, 11, and 22 nmol m−2 h−1 (solar zenith angle of 60°) for the fresh, old, marine-influenced, and glacial snowpacks, respectively. The uncertainty of repeated light penetration depth measurement was determined to be ∼20%, which propagates into a 20% error in depth-integrated production rates. A very simple steady state hydroxyl radical calculation demonstrates that a pseudo first-order loss rate of OH radicals of ∼102–104 s−1 is required in snowpack. The snowpacks around Ny-Alesund are thick enough to be considered optically infinite.

Analysis of CFD for the Vortex Rope in the Draft Tube Urged by the Long and Short Blades Runner

The RNG turbulence model is used to carry out the 3D steady turbulent calculation on the runner and draft tube of the Francis turbine. And the prototype of the Francis turbine is HLA351. Under 8 typical operating conditions, numerical simulation on how the runner outlet urge the vortex rope in draft tube are accomplished in this paper, and the calculation models are long blade model and mixed blade model. The results show that the runner outlet of the mixed model can lead the vortex rope location to the downstream relatively, reduce the circumfluence and cushion area and the probability of the second-vortex. What’s more, the flow pattern in mixed model is superior to the long model and that benefits the operation stability and economy of the unit.

Modelling and simulation methodology of channel cooling using hydrocarbon fuel as coolant under supercritical pressures

A one-dimensional cooling channel model is proposed using unsteady partial differential equations (PDEs) and taking into account the strong dependencies of hydrocarbon fuel properties on temperature and pressure. The model can be used to evaluate the performance of channel cooling using hydrocarbon fuel as coolant under supercritical pressures, and to guide the design of a thermal protection system for aerospace application. Meanwhile, a graphical simulation method is developed to directly solve the proposed model using Simulink by converting the PDE to a set of ordinary differential equations without any need to write program codes. The graphical method can reduce the substantive work resulting from program codes writing and debugging and bring about interactions with users through its graphical user interface. In order to show the usability of the proposed model and the developed graphical method, n-pentane, a typical hydrocarbon fuel, is taken as an example to run two simulations for steady and transient calculations. The developed graphical simulator for channel cooling is verified by comparing the calculation results with the experimental data of an electrical heating tube. It is believed that this investigation will pave the way for implementation of the graphical simulation of the whole cooled propulsion system used for supersonic or hypersonic flights.

Finite Element Analysis on Thermal Characteristic of the Headstock of NC Machine Tool

The final manufacturing performances of the machine tools will be influenced by its thermal characteristics seriously and accurately predict thermal characteristic is helpful to improve the machine design level. Based on the analysis on factors that influence machine thermal characteristic, finite element analysis model of the headstock has been constructed, and the steady temperature field distribution and thermal equilibrium time calculation of the headstock are calculated, and then the temperature field and thermal deformation of the headstock under the action of heat and structure load have been calculated, and analysis to identify the trend of the spindle assembly and headstock heat distortion are also been done. The analysis reveals the machine processing performance influence will be influenced by the hot asymmetric, the study give priority to spindle assembly of optimization design, thermal error compensation.

Numerical Investigations of the Efficiency of Circulation Control in a Compressor Stator

Airfoil active flow control has been attempted in the past in order to increase the permissible loading of boundary layers in gas turbine components. The present paper presents a stator with active flow control for a high-speed compressor using a Coanda surface near the trailing edge in order to inhibit boundary layer separation. The design intent is to reduce the number of vanes while—in order to ensure a good matching with the downstream rotor—the flow turning angle is kept constant. In a first step, numerical simulations of a linear compressor cascade with circulation control are conducted. The Coanda surface is located behind an injection slot on the airfoil suction side. Small blowing rates lead to a gain in efficiency associated with a rise in static pressure. In a second step, this result is transferred to a four-stage high-speed research compressor, where the circulation control is applied in the first stator. The design method and the first results are based on steady numerical calculations. The analysis of these results shows performance benefits of the concept. For both the cascade and the research compressor, the pressure gain and efficiency are shown as a function of blowing rate and jet power ratio. The comparison is performed based on a dimensionless efficiency, which takes into account the change in power loss.