Instantaneous Condition Research Articles

Low Frequency Current Ripple Reduction Technique With Active Control in a Fuel Cell Power System With Inverter Load

A fuel cell power system that contains a single-phase dc-ac inverter tends to draw an ac ripple current at twice the output frequency. Such a ripple current may shorten fuel cell life span and worsen the fuel efficiency due to the hystersis effect. The most obvious impact is it tends to reduce the fuel cell output capacity because the fuel cell controller trips under instantaneous over-current condition. In this paper, the ripple current propagation path is analyzed, and its linearized ac model is derived. The equivalent circuit model and ripple current reduction with passive energy storage component are simulated and verified with experiments. An advanced active control technique is then proposed to incorporate a current control loop in the dc-dc converter for ripple reduction. The proposed active ripple reduction method has been verified with computer simulation and hardware experiment with a proton exchange membrane type fuel cell using a multiphase dc-dc converter along with a full-bridge dc-ac inverter. Test results with open loop, single voltage loop, and the proposed active current-loop control are provided for comparison.

Modelling and characterization of chi-phase grain boundary precipitation during aging of Fe–Cr–Ni–Mo stainless steel

High molybdenum stainless steels may contain the chi-phase precipitate ( χ, Fe 36Cr 12Mo 10) which may lead to undesirable effects on strength, toughness and corrosion resistance. In the present work, specimens of a 12Cr–9Ni–4Mo wt% steel are heat treated at different temperatures and times, and the average particle size and particle size distribution of chi-phase precipitate are studied quantitatively. A computer model based on the KWN framework has been developed to describe the evolution of chi-phase precipitation. The kinetic model takes advantage of the KWN model to describe the precipitate particle size distribution, and is coupled with the thermodynamic software ThermoCalc ® for calculating the instantaneous local thermodynamic equilibrium condition at the interface and the driving force for nucleation. A modified version of Zener's theory accounting for capillarity effects at early growth stages is implemented in this model. The prediction of the model for chi-phase precipitation at a grain boundary is compared to experimental results and both the average particle size and the particle size distribution are found to be in good agreement with experimental observations at late precipitation stages.

OS10-1-2 Determination of positioning error of feed axes due to thermal expansion by infrared thermography

This paper reports on the experimental technique, based on thermographic measurements, to calculate the thermally induced positioning errors of the ball screw feed drives in machine tools. To compensate a thermal expansion of the ball screw, its temperature must be known with respect to its position, since the local temperature depends on the traversing program. The temperature increases were measured using resistance thermometers at several points of the ball screw. However, to obtain full temperature profile of the ball screw, the field of temperature was measured by infrared camera. Image processing of obtained thermographic snapshots was carried out using software MATLAB. Program enables to calculate temperature and its coordinate along an arbitrarily selected line. Thus the instantaneous temperature profiles along the ball screw are determined. A closed loop FEA was accomplished together with measurement. The programmed loop consists of thermal analysis followed by structural analysis. So the induced axial force is computed. It enables updating of heat sources according to instantaneous structural condition, so the non-steady heat sources in bearings are taken into account.

Metabolomic profiling of heat stress: hardening and recovery of homeostasis in Drosophila

Frequent exposure of terrestrial insects to temperature variation has led to the evolution of protective biochemical and physiological mechanisms, such as the heat shock response, which markedly increases the tolerance to heat stress. Insight into such mechanisms has, so far, mainly relied on selective studies of specific compounds or characteristics or studies at the genomic or proteomic levels. In the present study, we have used untargeted NMR metabolomic profiling to examine the biological response to heat stress in Drosophila melanogaster. The metabolite profile was analyzed during recovery after exposure to different thermal stress treatments and compared with untreated controls. Both moderate and severe heat stress gave clear effects on the metabolite profiles. The profiles clearly demonstrated that hardening by moderate heat stress led to a faster reestablishment of metabolite homeostasis after subsequent heat stress. Several metabolites were identified as responsive to heat stress and could be related to known physiological and biochemical responses. The time course of the recovery of metabolite homeostasis mirrored general changes in gene expression, showing that recovery follows the same temporal pattern at these two biological levels. Finally, our data show that heat hardening permits a quicker return to homeostasis, rather than a reduction of the acute metabolic perturbation and that the reestablishment of homeostasis is important for obtaining maximal heat-hardening effect. The results display the power of NMR metabolomic profiling for characterization of the instantaneous physiological condition, enabling direct visualization of the perturbation of and return to homeostasis.

Ionization of Al recoiled and sputtered from Al(100)

The absolute ionization probability of energetic $(>500\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ particles recoiled from Al(100) by 2 and $5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ ${\mathrm{Xe}}^{+}$ bombardment was measured with time-of-flight spectroscopy. These values were then used to calibrate the energy and angular distributions of low-energy $(10--600\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ sputtered ions collected with an electrostatic analyzer. The independent-particle model of nonadiabatic surface-atom charge exchange, which is typically used to analyze single scattering events, was applied to the ion fractions of the recoiled and sputtered atoms. The model describes all the experimental data from a few eV to the keV range if a different surface electronic temperature is used for recoiling and sputtering. This suggests that the ionization process depends on the instantaneous surface condition at the time of ion emission.

Time-Domain Non-Linear Strip Theory For Ship Motions

A new implementation of strip theory is proposed based on the strip theory by Salvesen, et al. [1] and early work by Westlake and Wilson [2]. Compared with traditional strip theory, the main difference is that the calculation is carried out in the time domain. This makes it possible to cope with relatively large-amplitude motions and non-constant forward speed problems. At each time step, the exact underwater sections are extracted; the velocity potential is required to satisfythis instantaneous body boundary condition, therefore the added mass, damping coefficients and exciting forces are timevariant, which produce a non-linearity. The diffraction force is added to work ofWestlake and Wilson, and the results show the effect of diffraction force is significant.

Responses to temperature and salinity by White Mullet Mugil curema: Possible explanation for the population decrease in Baja California Sur

The white mullet Mugil curema is distributed along the Gulf of Mexico and Pacific coasts and constitutes an important food resource in Mexico. However, during recent years the capture of this mugilid has decreased considerably, especially in Bahía and Ensenada de La Paz, Baja California Sur, Mexico. The effects of different levels of temperature (22, 26, and 30°C) and salinity (15, 25, and 35) on the instantaneous growth rate, energy content, and condition factor of early juveniles of Mugil curema were evaluated. Fish showed a lower growth rate, lower body energy content, and a less condition factor when exposed to high salinity and temperature. On the basis to the results obtained and considering the unusual extreme temperatures and salinity registered in Ensenada de La Paz, it is expected low functional performance of juvenile mullets beyond the overfishing might contribute to the population decrease of this resource.

Discussion: “An Experimental and Numerical Invesitgation Into the Mechanism of Rotating Instability” (Maerz, J., Hah, C., and Neise, W., 2002, ASME J. Turbomachinery, 124)

There is a lot to admire in this paper and I congratulate the authors in using experiment and CFD to contribute to the understanding of a complicated phenomenon. Once a flow becomes nonuniform, as it does for the flow described here, there a many more degrees of freedom and the flow can establish itself in many different ways. In consequence, flow that is stalled (in the sense that this takes for rotating stall in compressors) can exhibit many different arrangements. I would like to suggest that the rotating disturbance found here is a particular type of rotating stall corresponding to the special circumstances of an isolated rotor with large tip clearance. The problem that I have with this paper and with others that have come from Germany over the last few years is the term “rotating instability.” One of the useful conclusions from the present paper, referred to in the section “What We Learned” is that the flow is actually very stable. In fact, a condition of instability is very hard to observe, since it is by its very nature transient: A pencil standing vertically on its point is in a condition of instability, but the moment it is microscopically perturbed it ceases to be in the state of instability but is falling toward its new stable condition. The compressor will similarly be unstable at the instant before it moves from being unstalled to being in rotating stall; similarly, for a compressor in rotating stall, there will be an instantaneous condition of instability as the throttle is opened and it moves from stalled to unstalled. The stalled condition, however, is normally very stable. I have been told that the term “rotating instability” is well established and it is implied by this that it should remain in circulation. The term gained currency in Germany a few years ago to describe the type of rotating disturbance described in this paper. It was an unfortunate choice then and remains unfortunate now. It is a widely recognized feature of the English language that words can be created, adapted, and re-used to suit needs. One of the most famous of English quotations is “What’s in a name? that which we call a rose by any other name would smell as sweet” (Romeo and Juliet: Shakespeare). While accepting the spirit of this quotation, it is also true that it would be confusing to refer to a rose using the word “thorn,” or even the word “garlic.” Put another way, if we want to choose a new use for a word, we should make sure that it does not have a prior meaning that could be confusing, by implying properties that do not apply. Such is the case for “rotating instability,” which strictly has no clear meaning, but which implies a special condition that is inconsistent with the stable behavior of the rotating stall flow pattern that is the subject of this paper.

Thermal characterization of the phosphorus-containing sulfone-modified epoxy resins by thermogravimetric analysis and direct pyrolysis-GC/MS measurement on the thermally degradative volatiles

Thermal degradations of sulfone-containing epoxy resins modified with a linear phenylphosphonate (P2-EBPS) or a tribranched phosphate (P3-EBPS) in the main chains were conducted by thermogravimetric analysis. Thermal degradative volatiles (TDVs) were analyzed by direct pyrolysis (DP)-GC/MS spectrometer in the instantaneous pyrolytic condition at 900°C. A detailed study on the formation of the degradative volatiles was conducted by stepwise pyrolysis. Individual TDVs were separated through the GC column and detected by the mass detector. Results indicate that the degradation of the phosphated epoxy matrix started from the crosslinked aliphatic diglycidyl ether segment and released the phenol and its derivatives as the main aromatic TDVs. The organophosphorus group of the modified epoxy specimens must first be transformed into inorganic phosphate near 450°C at 10°C/ms, before the shielding effect can be effective. The phosphated P3-EBPS has better thermal properties than the phenylphosphonated P2-EBPS copolymer.

Reaction of Fuel NOx Formation for Gas Turbine Conditions

Ammonia contained in coal-gasified fuel is converted to nitrogen oxides (NOx) in the combustion process of a gas turbine in integrated coal gasification combined cycle (IGCC) system. Research data on fuel-NOx formation are insufficient, and there still remains a wide explored domain. The present research aims at obtaining fundamental knowledge of fuel-NOx formation characteristics by applying reaction kinetics to gas turbine conditions. An instantaneous mixing condition was assumed in the cross section of a gas turbine combustor and both gradual mixing condition and instantaneous mixing condition were assumed at secondary air inlet section. The results may be summarized as follows: (1) in the primary combustion zone under fuel rich condition, HCN and other intermediate products are formed as ammonia contained in the fuel decomposes; (2) formation characteristics of fuel-NOx are affected by the condition of secondary air mixing; and (3) the conversion ratio from ammonia to NOx declines as the pressure inside the combustor rises under the condition of gradual mixing at the secondary air inlet. These results obtained agreed approximately with the experimentation.

Prediction of the steady and non-steady flow performance of a highly loaded mixed flow turbine

This paper describes a method for predicting the performance under both turbine inlet steady state and non-steady state flow conditions of a mixed flow turbine used for turbocharged internal combustion engines. The mixed flow turbine steady state performances computed with the steady state performance prediction method are in good agreement with the experimental results obtained in the Imperial College turbocompressor cold air test rig. The unsteady state performance is computed using a one-dimensional model based on the solution of the unsteady one-dimensional flow equations. These equations are solved in the volute by a finite difference method using a four-step explicit Runge—Kutta scheme. The instantaneous volute exit condition is provided by the steady state rotor performance prediction model with the assumption of a quasi-steady state flow in the rotor. The computed instantaneous performances are in reasonable agreement with published experimental data for the same mixed flow turbine. The unsteady flow model is also used to study the effects of the frequency and the amplitude of the pulse on the performances of the mixed flow turbine.

The effects of semi-purified diets on growth and condition of Sepia officinalis L. (Mollusca: Cephalopoda)

The effects of five different surimi diets (fish myofibrillar protein concentrate) on growth and condition of Sepia officinalis were evaluated in terms of individual growth using different morphometric and biochemical parameters. A casein supplemented surimi diet produced significant growth (instantaneous growth rate 0.4–0.8% body weight). The digestive gland-to-body weight ratio increased and the cuttlebone-to-body weight ratio decreased significantly in relation to instantaneous growth rate. The RNA content of mantle muscle increased significantly, while the DNA content of mantle muscle did not change in relation to instantaneous growth rate. Mantle muscle protein content was depleted in cuttlefish with instantaneous growth rate ⩽0. No compensatory food consumption, food conversion or growth was observed for cuttlefish fed surimi diets after refeeding them with a natural diet (thawed raw shrimp). Digestive gland and cuttlebone-to-body weight ratios, and RNA content in mantle muscle could be used as short-term indicators of instantaneous growth rate and condition of cuttlefish. Mantle muscle protein content could be used as a long-term indicator.

Grain-Boundary Enhanced Diffusion from Instantaneous Source in Small-Grain Deep-Penetration Condition

The grain-boundary diffusion equation, Eq. (1.11), was derived for the small-grain deep-penetration diffusion, and solved for the instantaneous source condition. The obtained solution, Eq. (2.9), consists of two terms, one is the simple diffusion solution for the grain-boundary diffusion only, and the other is the factor which expresses the effect of the flux from the grain boundary toward the interior of the grains.Equation (3.4), which gives the average concentration at given distance and time, should be useful for determination of the diffusion parameters for the grain boundary and the bulk by tracer technique, and also for the analysis of kinetics in the formation of a grain-boundary phase by preferential diffusion in dielectric ceramics.

On the momentum forcing of a large-scale sea-ice model

A large-scale sea-ice - oceanic mixed-layer model for the Southern Ocean is forced with daily atmospheric fields from operational numerical weather prediction analyses. The strength of the atmospheric forcing is modified considering atmospheric surface-layer physics, which is itself directly dependent on the instantaneous sea-ice condition provided by the sea-ice model. In earlier applications, the atmospheric drag on sea ice was computed from the local momentum transfer over ice. In the present study, this is replaced by a large-scale momentum flux, which is characterized by a large-scale stability function and a large-scale roughness length. The large-scale roughness length depends on the local skin drags and on the form drag, where the latter is given as a function of the ice-plus-snow freeboard and the ice concentration, both provided by the sea-ice model. The thermodynamic part of the calculation is given by the local fluxes, which depend on the local stability of the atmospheric surface layer. This, physically more reasonable, description of the largescale dynamic forcing generally leads to an increase of the momentum transfer via an increase of the roughness length and a decrease of the stability in the atmospheric surface layer. Finally, this yields improved model results, especially in terms of a more dynamic pattern of the ice-thickness distribution.

Body and breathing movements in near-term fetuses and newborn infants of type-1 diabetic women

The generation of body and breathing movements was studied in relation to behavioural states in near-term fetuses ( n = 12) and newborn infants ( n = 7) of women with well-controlled type-1 diabetes. Results obtained from low-risk fetuses ( n = 12) and neonates ( n = 14) were used for comparison. Before birth, 2-h recordings were made of fetal heart rate and of fetal body movements, breathing and eye movements; the neonates were studied polygraphically during 6 h for heart rate, body movements, respiration, eye movements and EEG-pattern. The generation of body movements was similar in the fetuses of the diabetic and control groups. After birth, the duration per burst was longer in the diabetic group, both in state 1 and state 2, resulting in increased incidences. The incidence of fetal breathing movements tended to be higher in the diabetic group, but differences with the control group did not reach statistical significance. Breathing rate was considerably slower in fetuses of diabetic women present before birth. Periodic breathing occurred more often in the infants of diabetic women, especially in state 2 ( P < 0.02). Behavioural state organization was poor in the diabetic group, both before and after birth and resembled that of more immature fetuses and infants. The continuity of the poor behavioural state regulation from prenatal into postnatal life indicates that this cannot be attributed to the instantaneous unfavourable condition before birth. type-1 diabetes mellitus; fetus and newborn infant; behavioural states; body movements; breathing movements than in control fetuses, both in C1F ( P < 0.001) and C2F ( P < 0.002). This indicates altered regulation of breathing movements in diabetic pregnancy. In the neonates, breathing rate was identical in both groups. In either group breathing was slower in state 1 than in state 2; such a difference was not

Isothermal Reaction Kinetics of Kraft Delignification of Douglas-Fir

Abstract Kraft delignification of Douglas-fir (Pseudotsuga menziesii) wood meal was carried out under an instantaneous isothermal condition with a liquor-to-wood ratio of 50 to investigate the effects of reaction temperature and chemical concentration on the rate of delignification. The temperatures studied were in the range of 120 to 175°C. Three levels of [HO−l] and three levels of [HS−l] concentrations were investigated. In each case an efficient mechanical agitation of the pulping liquor was maintained and the delignification was extended to reach its completion. Using a nonlinear regression analysis on the delignification results, a single kinetics equation was resolved to describe the effect of temperature and chemical concentration on the rates of delignification for the initial, bulk, and final phases. This equation also revealed that the amounts of lignin removed due to the chemical reactions in the initial, bulk, and final phases were 18.8, 71.4, and 3.8%, respectively. About 6% of the total lignin was dissolved into the pulping solution before any significant chemical reaction occurred to the lignin core. The activation energies of delignification reactions in the initial, bulk, and final phases were 85.8, 123.8, and 110.0 kJ/mole, respectively. The Ln(pre-exponential factors) were 22.5, 30.5, and 23.4 m−l1 for the initial, bulk, and final phases, respectively. The rate of delignification was strongly affected by the presence of [HO−l] in the bulk and final phases. Whereas, [HS−l] had a significant effect on the rate of delignification only in the bulk phase. These chemical effects were also quantified.

The effect of water on the time-dependent deformation and fracture of a granite

The effect of water on the deformation, fracture and strength of Lac du Bonnet granite has been investigated through a variety of experimental techniques: standard short-term tests for compressive strength and fracture toughness, and longer-term, time dependent experiments that measure creep, static fatigue and slow crack velocity. When specimens of this granite are tested while in direct contact with water, such conventional measures of the short-term strength as the uniaxial compressive strength and the fracture toughness decrease by about 5% from the levels measured at room temperature and humidity. Because short-term tests require a few minutes to complete, part or all of this decrease in strength may only be due to time-dependent processes. When results of other, longer-term tests are extrapolated to zero elapsed time, the indication is that at very rapid loading rates (instantaneous or dynamic loading condition), the effect of water on strength may be negligible. In all time-dependent tests for creep strain, static fatigue and slow crack velocity, the effect of water is substantial. The creep strain and slow crack velocity increase and the long-term strength decreases when water is introduced into the previously dry testing environment. The size of the change, however, depends on the stress level (applied stress relative to the instantaneous strength). It is small at high stress levels becoming more substantial as the stress level is decreased. For example, at a stress level of 65%, the steady state creep rate of the lateral strain increased by 300% when water was allowed to flood the previously dry environmental chamber.

Linear-Quadratic Programming and Optimal Control

A generalized approach is taken to linear and quadratic programming in which dual as well as primal variables may be subjected to bounds, and constraints may be represented through penalties. Corresponding problem models in optimal control related to continuous-time programming are then set up and theorems on duality and the existence of solutions are derived. Optimality conditions are obtained in the form of a global saddle point property which decomposes into an instantaneous saddle point condition on the primal and dual control vectors at each time, along with an endpoint condition.

A computational aspect of kinetic depth effect.

A method is proposed to determine the rigid structure as well as the three dimensional motion of an object from a sequence of orthographically projected images. It is assumed that the velocities as well as the positions of the points attached to the object are observable in the images. The "instantaneous rigidity condition" wich states that the relative position vector between any two points is orthogonal to the corresponding relative velocity vector is derived from the condition of rigidity. Assuming further that the rotational velocity component is constant throughout the period of observation, each of the projected relative velocity vectors is shown to move along one of the elliptical trajectories, all of which are similar to one another. The orientations of the longer axes are common to every trajectory. Then one can determine the equations of the ellipses by observing only two points in three views or three points in two views. The solution is obtained from a set of linear equations. The length of the longer axis enables one to determine the relative velocity. The instantaneous rigidity condition is then used to obtain the relative position. The special cases where the rotational axis is either perpendicular to or parallel with the image plane are discussed. The above results are discussed in relation to the relevant psychophysical observations as well as theoretical studies.

Flow-resonant sound interaction in a duct containing a plate, part I: Semi-circular leading edge

The interaction between flow and flow-induced acoustic resonances near rigid plates with semi-circular leading edges located in a hard-walled duct is described. These plates generate acoustic resonances over flow velocity ranges depending on thickness, chord and trailing edge geometry, together with rigidity, internal dimensions, length of the working section and shape of the terminations of the working section. A potential flow model for the plate with a smooth leading edge is developed, and the acoustic power generated by vortices growing and shedding from the trailing edge is calculated. The rate of growth of the vortices is determined by an instantaneous Kutta condition applied over part of the cycle. This technique simulates the influence of the sound field on vortex growth.