Large Parameter Variations Research Articles

Coupled Reservoir Geomechanical Simulations For the SAGD Process

Abstract Conventional reservoir simulation may not fully characterize the recovery mechanism of the SAGD process in uncemented oil sands reservoirs. Uncemented oil sands exhibit significantly different geomechanical behaviour from that of their cemented counterpart. Therefore, to fully explore the SAGD recovery process, coupled reservoir geomechanical simulations are required. This simulation technique can characterize both the multiphase fluid flow and reservoir parameter variations based on certain stress-strain relationships of oil sands in the SAGD process. In this paper, sequentially coupled reservoir geomechanical simulations are conducted. It is based on both the reservoir simulator, EXOTHERM, developed by T.T. &Associates Inc. and the geotechnical simulator, FLAC, developed by Itasca Consulting Group Inc. This paper discusses the strategies and methodology of the coupled reservoir geomechanical simulations for the SAGD process based on these two simulators. Meanwhile, the results of the conventional reservoir simulations and the coupled reservoir geomechanical simulations are compared. These comparisons are conducted based on initial stress conditions of K0= 1.0. The simulation results show that differences exist between coupled reservoir geomechanical simulations and conventional reservoir simulations under certain SAGD operation conditions. Introduction Canada has huge oil sand resources. Development technologies of oil sand resources include world-class surface mining, SAGD, Vapex, and cold production. The SAGD process has proven to be a promising technology and will play a critical role in the development of oil sand resources. In addition to reliable reservoir characterization and production facilities, realistic predictions of production performance are an important component in the design of commercial-scale SAGD projects. The realistic predictions of SAGD performance by numerical simulation are an integral component in the design and management of a SAGD project. Conventional reservoir numerical simulation emphasizes multiphase flow in porous media but generally does not take the interactions between fluids and solids into account. Unfortunately, this treatment is not correct for oil sand material. Oil sands are locked sands(1), which have very high rates of dilation at failure. In Athabasca deposits, McMurray Formation oil sands display a high incidence of tangential contacts as well as common straight and interpenetrative contacts(2). Owing to the grain-to-grain contacts observed in locked oil sands, it shows the following characteristics: absence of cohesion, highly quartzose mineralogy, high strength, steeply curved failure envelopes, low porosities, lack of interstitial cement, brittle behaviour, and exceptionally large dilation rates at failure(3). These properties are the basis of large variations of reservoir parameters and processes in the SAGD process. In the SAGD process, continuous steam injection and fluid flow can change reservoir pore pressure and temperature, which can increase or decrease the effective stress in the reservoir. Thus, deformations can occur in some regions. Likewise, the deformations of the oil sand material (skeleton and pores) changes the fluid flow-related reservoir parameters(4). This is obviously a coupled problem. Therefore, coupled reservoir geomechanical simulations are required. In this paper, two existing well-established simulator codes, EXOTHERM and FLAC, are explicitly coupled to characterize both the fluid flow and geomechanical behaviors in the SAGD process.

Robustness aspects in the design of a vehicle state estimator

In a vehicle, many parameters, such as the sprung mass, are not fixed. Rather, they change in a specified range. Vehicle control has to be able to cope with these potentially large parameter variations in the system. This paper deals with an algorithm, used to control the body slip angle. An estimator, part of the control, is used to obtain non-measurable signals. Whereas the vehicle parameters are uncertain, the estimator comprises of a vehicle model with fixed parameters. The objective is to find these nominal parameters, that guarantee optimal performance and stability in the complete parameter space of the vehicle. This requirement is defined in mathematics as an optimisation task. Even considering only the simple linear case, the problem very soon reaches such a complexity that it demands computational support. Nonlinear influences such as the tyre characteristics and weighting functions make analytical solutions either impossible or too restrictive for the design engineer.

Structure, stability and ELM dynamics of the H-mode pedestal in DIII-D

Experiments are described that have increased our understanding of the transport and stability physics that set the H-mode edge pedestal width and height, determine the onset of Type-I edge localized modes (ELMs) and produce the nonlinear dynamics of the ELM perturbation in the pedestal and scrape-off layer (SOL). Models now exist for the ne pedestal profile and the pe height at the onset of Type-I ELMs, and progress has been made towards models of the Te pedestal width and nonlinear ELM evolution. Similarity experiments between DIII-D and JET suggested that neutral penetration physics plays an important role in the relationship between the width and height of the ne pedestal. Plasma physics appears to dominate in setting the Te pedestal width. Measured pedestal conditions including edge current at ELM onset agree with intermediate-n peeling–ballooning (P–B) stability predictions. Midplane ELM dynamics data show the predicted (P–B) structure at the ELM onset, large rapid variations of the SOL parameters and fast radial propagation in later phases, similar to features in nonlinear ELM simulations.

Robust Antiwindup for Manual Flight Control of an Unstable Aircraft

A result on robust-in-the-large antiwindup compensation obtained for the case of asymptotically stable systems is extended to deal with unstable plants with asymptotically null references. The use of a weakened formulation of the antiwindup problem is crucial in the achievement of robustness to large parameter variations. The proposed design approach results in an antiwindup compensator that works as an add-on for any a priori given, high-performance controller, synthesized without taking saturation or robustness issues into account. The technique is applied to a reduced, short-period dynamic model of a highly unstable fighter aircraft, a case in which the issues of control saturation during aggressive maneuvering and robustness with respect to large parameter variations are of paramount importance. Simulations in low- and high-speed regimes demonstrate that the weakened antiwindup compensator outperforms previous antiwindup techniques in providing robust stability to the closed-loop system while exploiting the available control power in all of the considered maneuvers.

Comparative study on the relationship between photoperiodic host-seeking behavioral patterns and the eye parameters of mosquitoes

Relationships between the ommatidial structure and photoperiodic behavior of several mosquito species were investigated. Host-seeking behavioral patterns of mosquitoes were classified into four main groups based on previously compiled reports on field or laboratory biting activity. These groups were pattern I and I′ (nocturnal), pattern II (crepuscular and nocturnal), pattern III (crepuscular and diurnal), and pattern IV (diurnal). Eye parameters (product of facet diameter and interommatidial angle) of mosquitoes that belong to the pattern I and I′ group were higher (2.7–4.2) than those of mosquitoes that belong to the pattern IV group (0.8–2.3). Eye parameters of the mosquitoes categorized in the pattern II and III groups were intermediate (2.3–2.6). These results suggest that the crepuscular behavior of mosquitoes undergoes a transition in the course of evolution from nocturnal behavior to diurnal behavior. Large variations in the eye parameters were observed even within the same genus depending on their photoperiodic behavior. Therefore, the ommatidial structure of mosquitoes appears to be determined, not taxonomically, but evolutionarily by the photoenvironment in which the mosquitoes are most active.

Effects of temperature, ionic strength and pH on the function of skeletal muscle myosin from a eurythermal fish, Fundulus heteroclitus

The mummichog, Fundulus heteroclitus, is an intertidal fish that exhibits little change in swimming ability despite large and rapid variations in environmental parameters. We therefore tested the hypothesis that this nearly constant function is due to Fundulus myosin being intrinsically insensitive to changes of temperature, ionic strength and pH. In vitro motility assays were used to quantify the speed of unregulated actin filaments on myosin purified from F. heteroclitus glycolytic skeletal muscle. Filament speed was 2.07+/-0.17 microm s(-1) at 26 degrees C, ionic strength (Gamma/2) of 0.08 M Gamma/2 and pH 7.4. Speed increased as temperature increased over the range of 5-36 degrees C with an activation energy (E (a)) of 94.0+/-7.0 kJ mol(-1)) and an enthalpy (DeltaH (double dagger)) of 91.5+/-7.0 kJ mol(-1) at 20 degrees C. A linear relationship between temperature and ATPase activity was also obtained with actin-activated myosin Mg(2+)-ATPase assays over the temperature range 5-35 degrees C with E (a=)59.9+/-2.4 kJ mol(-1) and DeltaH (double dagger)=57.4+/-2.4 kJ mol(-1) at 20 degrees C. There was little or no effect of ionic strength on filament speed over the range 0.19 M Gamma/2-0.54 M Gamma/2. Speed increased significantly at lower ionic strengths and was 7.9-fold higher at 0.08 M Gamma/2 than at 0.19 M Gamma/2. Speed increased with pH with a 16-fold increase between pH 6.7 and 7.4. These results indicate that changes in physiological parameters that include temperature, pH and ionic strength affect the function of unregulated F. heteroclitus myosin, and thus other factors must be responsible for the mummichog's swimming performance being comparatively insensitive to environmental variation.

Immunosuppression in Pediatric Liver and Intestinal Transplantation: A Closer Look at the Arsenal

Immunosuppression in Pediatric Liver and Intestinal Transplantation: A Closer Look at the Arsenal

Improved Design of VSS Controller for a Linear Belt-Driven Servomechanism

This paper proposes a new control algorithm for a linear belt-driven servomechanism. The elasticity of the belt and large nonlinear friction along with large variation of parameters limit the applicability of the belt driven servosystems. Design of simple control that can guarantee stable, vibration-free operation for large variation of load is needed to extend application of such a linear stage. The proposed control is based on the application of sliding mode methods combined with Lyapunov design so it guarantees the stability of the system. Due to the restriction of the system motion to specially selected sliding mode manifold the vibration free position tracking is achieved with very good disturbance rejection. Proposed algorithm is simple and practical for an implementation and the tuning procedure of the control parameters is simple. The experiments have shown that the proposed control scheme effectively suppresses vibrations and assures wide closed-loop bandwidth for position tracking control.

Age, gender and litter‐related variation in T‐lymphocyte cytokine production in young pigs

The capacity of farm animals to produce cytokines could be an important determinant of robustness and health. From research in rodents and humans it appears that the production and the balance of T helper 1 (Th1) and T helper 2 (Th2)-type cytokines influences susceptibility to autoimmune and infectious diseases. It is known that pigs show a large variation in many immune response parameters. So far the extent of individual variation in the production of Th1- and Th2-type cytokines in commercial outbred pigs has not been reported. In the current experiment we determined mRNA expression, as well as protein production of cytokines in 32 pigs from eight litters. From each litter two male and two female pigs were tested at 2, 5 and 8 weeks of age. Two Th1-type cytokines, interleukin (IL)-2 and interferon (IFN)-gamma, and two Th2-type cytokines, IL-4 and IL-10, were measured after phytohaemagglutinin (PHA)-stimulation of blood mononuclear cells. Cytokine production and the Th1/Th2-ratio were highly variable. The variation in cytokine protein production was moderately consistent across ages, i.e. pigs that produced high levels of cytokine at 2 weeks of age tended to do so as well at 5 and 8 weeks of age. Cytokine production tended to increase with age, and gilts and boars differed in their IL-2/IL-4 ratio. Unexpectedly, age, gender and litter effects often differed for mRNA and protein production data. We hypothesize that cytokine production is a consistent trait in pigs, especially at the protein production level. Future investigations in more animals and across a wider age range are necessary.

Critical Re-evaluation of the O−H Bond Dissociation Enthalpy in Phenol

The gas-phase O-H bond dissociation enthalpy, BDE, in phenol provides an essential benchmark for calibrating the O-H BDEs of other phenols, data which aids our understanding of the reactivities of phenols, such as their relevant antioxidant activities. In a recent review, the O-H BDE for phenol was presented as 90 +/- 3 kcal mol(-1) (Acc. Chem. Res. 2003, 36, 255-263). Due to the large margin of error, such a parameter cannot be used for dynamic interpretations nor can it be used as an anchor point in the development of more advanced computational models. We have reevaluated the existing experimental gas-phase data (thermolyses and ion chemistry). The large errors and variations in thermodynamic parameters associated with the gas-phase ion chemistry methods produce inconsistent results, but the thermolytic data has afforded a value of 87.0 +/- 0.5 kcal mol(-1). Next, the effect of solvent has been carefully scrutinized in four liquid-phase methods for measuring the O-H BDE in phenol: photoacoustic calorimetry, one-electron potential measurements, an electrochemical cycle, and radical equilibrium electron paramagnetic resonance (REqEPR). The enthalpic effect due to solvation, by, e.g., water, could be rigorously accounted for by means of an empirical model and the difference in hydrogen bond interactions of the solvent with phenol and the phenoxyl radical. For the REqEPR method, a second correction is required since the calibration standard, the O-H BDE in 2,4,6-tri-tert-butylphenol, had to be revised. From the gas-phase thermolysis data and three liquid-phase techniques (excluding the electrochemical cycle method), the present analysis yields a gas-phase BDE of 86.7 +/- 0.7 kcal mol(-1). The O-H BDE was also estimated by state-of-the-art computational approaches (G3, CBS-APNO, and CBS-QB3) providing a range from 86.4 to 87.7 kcal mol(-1). We therefore recommend that in the future, and until further refinement is possible, the gas-phase O-H BDE in phenol should be presented as 86.7 +/- 0.7 kcal mol(-1).

Application of Neural Networks and State-Space Averaging to DC/DC PWM Converters in Sliding-Mode Operation

A novel output feedback neural controller is presented in This work for the implementation of sliding-mode control of dc/dc converters. The controller, which consists of a multilayer perceptron, has been trained in order to be robust for large variations of system parameters and state variables. Fast dynamic behavior is the other main advantage of the proposed controller, which allows realization of all beneficial features of the sliding-mode control technique. Other advantages of the controller are simplicity and low cost. Computer simulations have been carried out to investigate the effectiveness of the controller in voltage regulation for a relatively complex dc/dc converter topology of the Cuk converter. Simulation results confirm the excellent performance of the control system in response to large signal variations. In order to verify the simulation results, a controller prototype has been designed and built using analog components. The controller is applied to regulate the output voltage of the Cuk converter. Experimental results confirm the analytical and simulation achievements.

EXPERIMENTAL FREQUENCY-DOMAIN METHOD FOR CONTROL DESIGN IN HEAVY-DUTY VEHICLES

The large parameter variations in heavy-duty trucks make it very difficult to find appropriate settings for fixed structure speed controllers. Satisfying the design specifications with experience-based trial-and-error methods for the control design is very time-consuming. This paper discusses the use of experimental frequency domain methods for the tuning of speed controllers. The focus is on the cruise control, but the method is also applicable to other speed controllers. Experimental results are given to validate the approach.

後発医薬品の生物学的同等性試験における試験間差

The equivalencies of generic drugs are assessed by biological equivalency tests. These tests are conducted on healthy subjects by the crossover method in comparison with the original product, which makes them a useful method for comparing bioequivalencies among generics. However, since a large variation in the results is sometimes observed, we decided to determine what causes this.We requested 28 companies to provide biological equivalency test results for pravastatin sodium tablet (23 products) and compared pharmacokinetic parameters among them. There was a large variation in pharmacokinetic parameters, especially in maximum serum drug concentration, area under the serum concentration to time curve and elimination half-life, though there were no differences between the original product and generic product in each test.On comparing individual parameters from two tests that were carried out according to nearly the same protocol, there was a marked difference in the distribution of data among subjects, indicating that this was a factor causing parameter differences between tests. Thus, when pharmacists are thinking of using a generic drug, it is important for them to notonly consider average parameter values but also the process by which these values have been obtained.

Prediction of Uplift Capacity for Shallow Foundations Using Genetic Programming

In most geotechnical problems, it is too difficult to predict soil and structural behavior accurately, because of the large variation in soil parameters and the assumptions of numerical solutions. But recently many geotechnical problems are solved using Artificial Intelligence (AI) techniques, by presenting new solutions or developing existing ones. Genetic Programming, (GP), is one of the most recently developed (AI) techniques based on Genetic Algorithm (GA) technique. In this research, GP technique is utilized to develop prediction criteria for uplift capacity of shallow foundations using collected historical records. The uplift capacity formula is developed using special software written by the authors in Visual C++ language. The accuracy of the developed formula was also compared with earlier prediction methods.

Nonlinear Instabilities in TCP-RED

This work develops a discrete-time dynamical feedback system model for a simplified TCP network with RED control and provides a nonlinear analysis that can help in understanding observed parametric sensitivities. The model describes network dynamics over large parameter variations. The dynamical model is used to analyze the TCP-RED operating point and its stability with respect to various RED controller and system parameters. Bifurcations are shown to occur as system parameters are varied. These bifurcations, which involve the emergence of oscillatory and/or chaotic behavior, shed light on the parametric sensitivity observed in practice. The bifurcations arise due to the presence of a nonlinearity in the TCP throughput characteristic as a function of drop probability at the gateway. Among the bifurcations observed in the system are period doubling and border collision bifurcations. The bifurcations are studied analytically, numerically, and experimentally.

A pilot, two-year longitudinal study of the interrelationship between trabecular bone and articular cartilage in the osteoarthritic knee

To examine the relationship between structural changes of trabecular bone and cartilage, in patients with varying degrees of osteoarthritis (OA) over 2 years, using magnetic resonance imaging. High-resolution, axial images were acquired for assessing trabecular bone structure, using a 3-D fast gradient-echo sequence. High-resolution, fat-suppressed, sagittal images were acquired for assessing cartilage structure, using a 3-D spoiled gradient-echo sequence. In a subset of the patients, sagittal images were acquired for measuring T(2) relaxation time, using a 2-D dual-echo spin echo sequence. A large variation in bone and cartilage parameters is evident among individual subjects in each group, however, group-specific means demonstrate decreasing trends (in bone and cartilage parameters) in osteoarthritic subjects (especially in mild OA subjects). The mean T(2) increased significantly (P<0.05) between the baseline and follow-up exams for all cartilage compartments except the lateral tibia. A positive relationship was established between cartilage changes and localized bone changes closest to the joint line, while a negative relationship was established between cartilage changes and global bone changes farthest from the joint line. This study quantifies the changes in bone and cartilage structural parameters over time, and demonstrates a longitudinal relationship between the morphological changes in bone and cartilage structure in patients with varying degrees of OA. Although a large variation of bone and cartilage changes is apparent among subjects, significant trends are evident in a relatively small sample size, with a short follow-up duration.

A Feasibility Robust Optimization Method Using Sensitivity Region Concept

We present a robust optimization method that ensures feasibility of an optimized design when there are uncontrollable variations in design parameters. This method is developed based on the notion of a sensitivity region, which is a measure of how far a feasible design is from the boundary of a feasible domain in the parameter variation space. In this method, as the design moves further inside the feasible domain, and thus becoming more feasibly robust, the sensitivity region becomes larger. Our method is not sampling based so it does not require a presumed probability distribution as input and is reasonably efficient in terms of function evaluations. In addition, our method does not use gradient approximation and thus is applicable to problems that have nondifferentiable constraint functions and large parameter variations. As a demonstration, we applied our method to an engineering example, the design of a control valve actuator linkage. In this example, we show that our method finds an optimum design which is feasibly robust.

Elimination rate constants of 46 polycyclic aromatic hydrocarbons in the unionid mussel, Elliptio complanata.

Elimination rate constants (k2), biological half-lives (t(1/2)), and the time required to reach 95% of steady-state (t95) are reported for 46 individual polycyclic aromatic hydrocarbons (PAHs) including both parent and alkyl homologues, for the freshwater unionid mussel, Elliptio complanata. Elimination rate constants generally follow first-order kinetics and range from 0.04/day (d) for perylene to 0.26/d for 2,6-dimethylnapthalene, half-lives range from 2.6 to 16.5 d, and t95 values range from 11.3 to 71.3 d. These values compare well with other k2, t(1/2), and t95 values reported in the literature for PAHs and other classes of hydrophobic organic contaminants. A linear regression of k2 versus log Kow demonstrates dependence of PAH elimination on hydrophobicity, as measured by an r2 value of 0.83, and produces the following regression equation: k2 = -0.06 (log Kow) + 0.44. This study provides evidence that mussels experiencing different forms of physiological stress (e.g., handling stress and fungal or bacterial growth) can exhibit large variation in toxicokinetic parameters. These results are particularly relevant to the extrapolation of laboratory results to field situations.

Multi-objective robust optimization using a sensitivity region concept

In multi-objective design optimization, it is quite desirable to obtain solutions that are “multi-objectively” optimum and insensitive to uncontrollable (noisy) parameter variations. We call such solutions robust Pareto solutions. In this paper we present a method to measure the multi-objective sensitivity of a design alternative, and an approach to use such a measure to obtain multi-objectively robust Pareto optimum solutions. Our sensitivity measure does not require a presumed probability distribution of uncontrollable parameters and does not utilize gradient information; therefore, it is applicable to multi-objective optimization problems that have non-differentiable and/or discontinuous objective functions, and also to problems with large parameter variations. As a demonstration, we apply our robust optimization method to an engineering example, the design of a vibrating platform. We show that the solutions obtained for this example are indeed robust.

Expression, purification and crystallization of two peroxisomal acyl-CoA oxidases from Arabidopsis thaliana.

Two members of the acyl-CoA oxidase family from Arabidopsis thaliana have been cloned, overexpressed, purified and crystallized. Long-chain-specific acyl-CoA oxidase 1 crystals are characterized by a large variation in diffraction quality and non-isomorphous unit-cell parameters. The best crystals diffract to 2.0 angstrom using synchrotron radiation, have unit-cell parameters a = 85.2, b = 117.0, c = 131.0 angstrom, alpha = beta = gamma = 90 degrees and show P2(1)2(1)2(1) symmetry. There are two polypeptide chains in the asymmetric unit. Short-chain-specific acyl-CoA oxidase 4 crystals are trigonal, space group P3(1)21/P3(2)21, with unit-cell parameters a = b = 198.7, c = 149.6 angstroms. The crystals are most likely to contain six polypeptide chains in the asymmetric unit. Freshly prepared acyl-CoA oxidase 4 crystals diffract to 3.9 angstroms at cryogenic temperature at beamline I711, Max-Lab, but the diffraction quality degenerates after storage for only a few days in the crystallization drop. A selenomethionine-substituted form of the protein was produced and two-wavelength MAD data were collected at beamline BW7A, EMBL Outstation, Hamburg.