Influence of hysteretic stress path behavior on seal integrity during gas storage operation in a depleted reservoir

In this study,we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir.Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County(California,USA),which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production.In our simulations,the geomechanical behavior of the sand reservoir is modeled using two models:(1)a linear elastic model(non-hysteretic stress path)that does not take into consideration irreversible deformation,and(2)a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction(hysteretic stress path).It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude.Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure.Moreover,this irreversible compaction may bring the nearby faults closer to reactivation.However,regardless of the two models applied,the geomechanical analysis shows that for the estimated stress conditions applied in this study,the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.

Least Squares Support Vector Machine Based Real-Time Fault Diagnosis Model for Gas Path Parameters of Aero Engines

Least squares support vector machine （LS-SVM） is applied in gas path fault diagnosis for aero engines. Firstly, the deviation data of engine cruise are analyzed. Then, model selection is conducted using pattern search method. Finally, by decoding aircraft communication addressing and reporting system （ACARS） report, a real-time cruise data set is acquired, and the diagnosis model is adopted to process data. In contrast to the radial basis function （RBF） neutral network, LS-SVM is more suitable for real-time diagnosis of gas turbine engine.

Extrapolation for Aeroengine Gas Path Faults with SVM Bases on Genetic Algorithm

Mining aeroengine operational data and developing fault diagnosis models for aeroengines are to avoid running aeroengines under undesired conditions.Because of the complexity of working environment and faults of aeroengines,it is unavoidable that the monitored parameters vary widely and possess larger noise levels.This paper reports the extrapolation of a diagnosis model for 20 gas path faults of a double-spool turbofan civil aeroengine.By applying support vector machine(SVM)algorithm together with genetic algorithm(GA),the fault diagnosis model is obtained from the training set that was based on the deviations of the monitored parameters superimposed with the noise level of 10%.The SVM model(C=24.7034;γ=179.835)was extrapolated for the samples whose noise levels were larger than 10%.The accuracies of extrapolation for samples with the noise levels of 20%and 30%are 97%and 94%,respectively.Compared with the models reported on the same faults,the extrapolation results of the GASVM model are accurate.

Gas Path Fault Tolerant Control of Aero-Engine Based on On-Board Model

A fault tolerant control method is proposed in this paper for a turbofan engine gas path degradation through the full flight envelope. A Quantum-behaved Particle Swarm Optimization(QPSO) algorithm is applied to obtain engine inputs adjustments, which contribute to construct off-line performance accommodation interpolation schedules. With a double closed-loop control system structure, command control is corrected based on real-time fault diagnostic results. Simulations indicate that fault tolerant control could reduce thrust and stall margin loss effectively in gas path faults.

Non-universal Fermi polaron in quasi two-dimensional quantum gases

We consider an impurity problem in a quasi-two-dimensional Fermi gas, where a spin-down impurity is immersed in a Fermi sea of N spin-up atoms. Using a variational approach and an effective two-channel model, we obtain the energy for a wide range of interaction strength and for various different mass ratios between the impurity and the background fermion in the context of heteronuclear mixture. We demonstrate that in a quasi-two-dimensional Fermi gas there exists a transition of the ground state from polaron in the weakly interacting region to molecule in the strongly interacting region.The critical interaction strength of the polaron–molecule transition is non-universal and depends on the particle density of the background Fermi sea. We also investigate the excited repulsive polaron state, and find similar non-universal behavior.

Knowledge and data jointly driven aeroengine gas path performance assessment method

Aeroengines,as the sole power source for aircraft,play a vital role in ensuring flight safety.The gas path,which represents the fundamental pathway for airflow within an aeroengine,directly impacts the aeroengine's performance,fuel efficiency,and safety.Therefore,timely and accurate evaluation of gas path performance is of paramount importance.This paper proposes a knowledge and data jointly driven aeroengine gas path performance assessment method,combining Fingerprint and gas path parameter deviation values.Firstly,Fingerprint is used to correct gas path parameter deviation values,eliminating parameter shifts caused by non-component performance degradation.Secondly,coarse errors are removed using the Romanovsky criterion for short-term data divided by an equal-length overlapping sliding window.Thirdly,an Ensemble Empirical Mode Decomposition and Non-Local Means(EEMD-NLM)filtering method is designed to“clean”data noise,completing the preprocessing for gas path parameter deviation values.Afterward,based on the characteristics of gas path parameter deviation values,a Dynamic Temporary Blended Network(DTBN)model is built to extract its temporal features,cascaded with Multi-Layer Perceptron(MLP),and combined with Fingerprint to construct a Dynamic Temporary Blended AutoEncoder(DTB-AutoEncoder).Eventually,by training this improved autoencoder,the aeroengine gas path multi-component performance assessment model is formed,which can sufficiently decouple the nonlinear mapping relationship between aeroengine gas path multi-component performance degradation and gas path parameter deviation values,thereby achieving the performance assessment of engine gas path components.Through practical application cases,the effectiveness of this model in assessing the aeroengine gas path multi-component performance is verified.

基于遗传-BP神经网络的航空发动机气路故障诊断研究（英文）

为提高BP神经网络诊断发动机气路故障的准确率,利用遗传算法对BP神经网络的初始连接权值和阀值在解空间内进化寻优,再将优化结果赋给网络以梯度下降算法进行二次训练,再对待检故障样本进行诊断。结果表明:GA-BP网络在输出精度、收敛速度及收敛曲线平滑性上明显优于普通BP网络,为航空发动机故障诊断领域的研究提出了新的思路和方法,具有一定研究价值。

Investigations into sensing characteristics of circular thin-plate electrostatic sensors for gas path monitoring

Circular thin-plate electrostatic sensors are promising in gas path monitoring due to their advantages of non-intrusiveness and easy installation. The spatial sensitivity and filtering effect are two important performance parameters. In this paper, an analytically mathematical model of induced charge on a circular thin-plate electrode is first derived. Then the spatial sensitivity and filtering effect of the circular electrostatic sensor are investigated by numerical calculations. Finally,experimental studies are performed to testify the theoretical results. Both theoretical and experimental results demonstrate that circular thin-plate electrostatic sensors act as a low-pass filter in the spatial frequency domain, and both the spatial filtering effect and the temporal frequency response characteristics depend strongly on the spatial position and velocity of the charged particle. These conclusions can provide guidelines for the optimal design of circular thin-plate electrostatic sensors.

Application of causality diagram in system safety analysis

Causality Diagram (CD) is a new graphical knowledge representation based on probability theory. The application of this methodology in the safety analysis of the gas explosion in collieries was discussed in this paper, and the Minimal Cut Set, the Minimal Path Set and the Importance were introduced to develop the methodology. These concepts are employed to analyze the influence each event has on the top event ? the gas explosion, so as to find out about the defects of the system and accordingly help to work out the emphasis of the precautionary work and some preventive measures as well. The results of the safety analysis are in accordance with the practical requirements; therefore the preventive measures are certain to work effectively. In brief, according to the research CD is so effective in the safety analysis and the safety assessment that it can be a qualitative and quantitative method to predict the accident as well as offer some effective measures for the investigation, the prevention and the control of the accident.

A mean free path approach to the micro/nanochannel gas flows

We investigate the gas flows near to solid surfaces in terms of the local spatial variation in the molecular mean free path(MFP).Molecular dynamics(MD)is the appropriate scientific tool for obtaining molecularly-accurate dynamic information in micro and nano-scale gas flows,and has been used to evaluate the molecular mean free path of gases.In the calibration procedure,the viscosity of a gas in the homogeneous case can be recovered in our MD simulations and reach good agreement with the theoretical prediction and data from NIST.In surface-bounded gas flows,if the collisions between gas molecules and walls are counted,a spatially-varying mean free path is presented,and for the first time we have observed that the distribution of the free paths deviates from the exponential one and spikes appear in their distributions at larger Kn,i.e.in the transition flow regime.Based on elementary kinetic theory,the effective viscosity of the gas derived from the mean free path has been incorporated into the framework of the continuum-fluid dynamics equations,and micro-Couette flows are performed to demonstrate this potential application.

On the Definition of State Variables for an Internal State Variable Constitutive Model Describing Metal Deformation

The quest for an internal state variable constitutive model describing metal deformation is reviewed. First, analogy is drawn between a deformation model and the Ideal Gas Law. The use of strain as a variable in deformation models is discussed, and whether strain serves as an internal state variable is considered. A simple experiment that demonstrated path dependence in copper is described. The importance of defining appropriate internal state variables for a constitutive law relates to the ability to accurately model temperature and strain-rate dependencies in deformation simulations.

Simulation and Training Package on Corex Process

The flow behaviors in a gas solid contactor with inclined perforated plates that form a zigzag path were experimentally studied. In this contactor solid particles slide down along the inclined perforated plates by the upflowing gas. This structure, called as 'z path moving bed', has some of the advantages of both moving and fluidized beds. The discharge rate of solid particles, inclination angle of the perforated plate, aperture ratio of the perforated plate, size of particles and gas velocity were chosen as parameters for experimental conditions. The stable operation conditions were certained for the particles and apparatus used. The pressure drop, bed height and residence time distribution of particles were measured versus gas velocity.

Hybrid Fault Diagnosis and Isolation for Component and Sensor of APU in a Distributed Control System

This paper addresses the gas path component and sensor fault diagnosis and isolation(FDI) for the auxiliary power unit(APU). A nonlinear dynamic model and a distributed state estimator are combined for the distributed control system. The distributed extended Kalman filter(DEKF)is served as a state estimator,which is utilized to estimate the gas path components’ flow capacity. The DEKF includes one main filter and five sub-filter groups related to five sensors of APU and each sub-filter yields local state flow capacity. The main filter collects and fuses the local state information,and then the state estimations are feedback to the sub-filters. The packet loss model is introduced in the DEKF algorithm in the APU distributed control architecture. FDI strategy with a performance index named weight sum of squared residuals(WSSR) is designed and used to identify the APU sensor fault by removing one sub-filter each time. The very sensor fault occurs as its performance index WSSR is different from the remaining sub-filter combinations. And the estimated value of the soft redundancy replaces the fault sensor measurement to isolate the fault measurement. It is worth noting that the proposed approach serves for not only the sensor failure but also the hybrid fault issue of APU gas path components and sensors. The simulation and comparison are systematically carried out by using the APU test data,and the superiority of the proposed methodology is verified.

Advances in multipass cell for absorption spectroscopy-based trace gas sensing technology[Invited]

In the field of absorption spectroscopy,the multipass cell[MPC]is one of the key elements.It has the advantages of simple structure,easy adjustment,and high spectral coverage,which is an effective way to improve the detection sensitivity of gas sensing systems such as tunable diode laser absorption spectroscopy.This invited paper summarizes the design theory and the research results of some mainstream types of MPCs based on two mirrors and more than two mirrors in recent years,and briefly introduces the application of some processed products.The design theory of modified ABCD matrix and vector reflection principle are explained in detail.Finally,trends in its development are predicted.

Rapid hydrocarbon accumulation mechanism in later period in Kelasu thrust belt in Kuqa depression

Based on the analyses of generation, migration and accumulation of oil and gas in the structures of Kela 1, Kela 2 and Kela 3 in Kasangtuokai anticlinal belt using a series of geological and geochemical evidence, this paper proposes that the rapid rate of hydrocarbon generation, main drain path for over-pressured fluid flow and converging conduit system are indispensable conditions for the rapid, late-stage gas accumulation in the Kelasu thrust belt in the Kuqa depression. Due to structural over-lapping and the resultant rapid burial, the maturity of the source rocks had been increased rapidly from 1.3 to 2.5% Ro within 2.3 Ma, with an average rate of Ro increase up to 0.539% Ro/Ma. The rapid matura-tion of the source rocks had provided sufficient gases for late-stage gas accumulation. The kelasu structural belt has a variety of faults, but only the fault that related with fault propagation fold and cut through the gypsiferous mudstone cap could act as the main path for overpressured fluid release and then for fast gas accumulation in low fluid potential area. All the evidence from surface structure map, seismic profile explanation, authigenic kaolinite and reservoir property demonstrates that the main drain path related with faults for overpressured fluid and the converging conduit system are the key point for the formation of the giant Kela 2 gas field. By contrast, the Kela 1 and Kela 3 structures lo-cated on both sides of Kela 2 structure, are not favourable for gas accumulation due to lacking con-verging conduit system.