Search

An experimental campaign was conducted to study dynamic ice accretion on rotating aeroengine fan blades and evaluate the icing-induced performance degradation to the fan rotor. The experiments were performed in an icing research tunnel with a scaled spinner-fan model exposed to typical dry rime and wet glaze icing conditions. Although the accreted ice layers were found to conform well with the shapes of the fan blades under the rime icing condition, the performance of the fan rotor was found to degrade substantially due to the much rougher blade surfaces, causing up to 60% reduction in the pressure increment after 360 s of the rime icing experiment. More complicated, needlelike icicles were found to grow rapidly over the rotating spinner and fan blades under the glaze icing condition due to the combined effects of the aerodynamic forces and the centrifugal forces associated with the rotation motion. The irregular-shaped glaze ice structures were found to induce tremendous detrimental effects on the fan rotor, making the airflow depressurized, instead of pressurized, after passing the iced fan rotor. The iced spinner-fan model was always found to consume more power, regardless of rime or glaze ice structures accreted on the fan blades.

A room-temperature self-healing polyurethane elastomer synthesised via optimized hierarchical H-bonding interactions ultimately exhibited a synchronous self-healing efficiency of more than 83% with tensile strength, elongation, and toughness.

This article investigates modeling and control approaches to optimize the efficiency and power factor for discontinuous conduction mode boost power factor correction converters. First, with detailed consideration of parasitics and GaN HEMT transients, the input and output charges of the converter are exactly derived, where the rate forms the comprehensive charge rate (CCR) model. Second, based on the CCR model, the overall efficiency is derived. Since the overall efficiency is only related to the input voltage, output voltage, and switching on -time, an optimal on -time is calculated to achieve the maximum efficiency. Furthermore, with the optimal on -time, a maximum efficiency average current (MEAC) controller is proposed to regulate the input current while maintaining the maximum efficiency. With the predefined optimal on -time, a switching cycle modulation method is adopted to regulate the input current as sinusoid, which improves the power factor to unity. Finally, effectiveness of the MEAC control strategy is verified by simulations and experiments. Compared with conventional constant on -time control, it achieves an optimized efficiency and power factor over a large operation range.

This article reveals parasitics-induced current distortion (PCD) effect in discontinuous conduction mode boost power factor (PF) correction (PFC) converter. With consideration of parasitics, accurate inductor current is derived through total differential functions of line voltage, output voltage and duty cycle. Furthermore, the proposed current model is used to analyze PFC converter under conventional sensorless average current mode (SACM) control, which is achieved by a variable duty cycle. It is found that parasitics have considerable influence to the input current, and PCD leads to a degraded PF. In order to solve this issue, a current reshaping strategy is proposed to reduce the PCD phenomenon. Based on the damped current equations, a compensation gain is derived to reshape the input current, which reduces the current damping and distortion caused by parasitics. Both the PCD phenomenon and the current reshaping strategy are verified by simulations and experiments.

For switched mode power converters, boundary conduction mode (BCM) operation is an attractive alternative to improve the bandwidth, overall size, and efficiency. In this article, a sensorless ripple current mode (SRCM) controller is proposed to achieve inductor-deviation-tolerant BCM operation for boost converter. Compared to conventional approaches with current sensing or ZCD, the proposed controller relies on a digital algorithm to ensure consistent BCM operation. The algorithm calculates on / off durations of the main switch so that the inductor current valley value converges to zero. The convergence process is proved by a damped current model with considerations of parasitics and output voltage ripple. Since the convergence is not related to the inductor value, the SRCM controller achieves inductor-deviation-tolerant BCM operation. Furthermore, to improve the power efficiency, an optimal transition condition and a compensation time are adopted to achieve valley switching (VS). Finally, both consistent BCM operation and VS are achieved by the proposed control strategy. Simulations and experimental results prove that the controller effectively improves the closed-loop stability, the robustness to inductor deviation, and the power efficiency.

Valley-switching (VS) and zero-voltage switching (ZVS) improves overall efficiency in critical conduction mode (CRM) boost converters. To achieve VS/ZVS, off-time of the main switch is often extended to match the resonance period by circuit inductor and parasitic capacitors of switching components. In this article, a piecewise equivalent model for parasitic capacitors is proposed to derive analytical solutions of the resonant process, by which the numerical solutions of VS/ZVS time is calculated. To precisely achieve VS/ZVS in a boost converter, corresponding extended off-time based on the numerical solutions is implemented with an extended off-time (EOT) controller. The EOT controller makes the inductor volt-second unbalance in continuous conduction mode (CCM) operation during one switching cycle, leading to the convergence to CRM operation. The analytical and experimental results correct the results derived by conventional equivalent model for parasitic capacitors, which leads to deviated VS/ZVS boundary and wrongly calculated off-time. The proposed model and controller are verified in a non-synchronous CRM boost converter based on GaN high electron mobility transistor (HEMT) and SiC diode. With the derived extended off-time, a peak efficiency of 99.15% is achieved at output power level of 200W.

The exploitation of shale gas has attracted extensive attention in industry and academia. Multi-scale gas transportation mechanisms in matrix and fractures have been well studied. However, due to the presence of water originating from both fracking fluids and connate water, shale gas production is also greatly affected by water imbibition and flowback, of which the processes have not been thoroughly analyzed. This paper aims at presenting a comprehensive multi-continuum multi-component model to characterize the complicated shale gas flow behaviors as well as the impact of non-Darcy water flow on shale gas production. A two-phase numerical simulator is built up with multi-continuum settings. Shale matrix is split into organic and inorganic matters while natural and hydraulic fractures are modeled using an embedded discrete fracture model (EDFM). Fracture closure and elongation are modeled using a dynamic gridding approach. Different transportation mechanisms are considered to describe gas flow in shale, including Knudsen diffusion, ab/desorption, and convection. The low-velocity non-Darcy flow of water is used in inorganic pores to analyze the effect of water flow. A pre-stage model based on pumping history is simulated firstly before production starts. This serves as an initialization step to model fracking fluid imbibition and early-stage water flowback. This pre-stage simulation gives out more precise pressure and saturation profiles than the conventional non-equilibrium initialization method, especially in enhanced pore volumes and fractures. Based upon simulation results from the production period, Langmuir isotherm absorption has shown a massive impact on gas flow in shale, and Knudsen diffusion weights highest among transport mechanisms. Water non-Darcy flow better benefits in simulating both early-stage water flowback and production process compared with Darcy flow, which gives us a new explanation on the low flowback efficiency in real shale gas operations. Studies on early-stage water flowback also show that the flowback affects saturation distribution, which has a strong relationship with gas production and shall not be ignored. This work establishes a novel method to simulate and analyze shale gas production. It considers multiple and complex flow mechanisms and gives out better estimates of water flux. It is also used to initialize a model for pumping water imbibition and early-stage flowback, which can be used as technical resources for analyzing and simulating unconventional plays.

Propofol, a widely used short-acting intravenous sedative agent, has gradually gained attention due to the tumour-suppressing role and non-anaesthetic effect. Dysfunction of metabolic reprogramming has been recognised as a well-documented factor for tumour progression. The aim of this study is to explore the effect of propofol on the polyol pathway in gastric cancer cells. In this study, we found that propofol treatment led to a significant downregulation of cell proliferation in BGC823 and GES-1 cells, which was attributed to the decreased AR-mediated polyol pathway. Both aldo-keto reductase family 1, member B1 (AKR1B1) and AKR1B10 were significantly reduced in BGC823 and GES-1 cells in response to propofol stimulation, leading to decreased AR activity and sorbitol level. Addition of sorbitol could reverse the inhibitory effect of propofol on cell proliferation. Mechanically, propofol treatment drastically inhibited phosphorylation and nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (NRF2), subsequently decreased the binding of NRF2 to AR promoter. Overexpression of NRF2 resulted in the recovery of AR expression in gastric cancer cell with propofol treatment. Taken together, these finding showed that propofol suppressed cell proliferation in BGC823 and GES-1 cell through NRF2-mediated polyol pathway, which would aid the selection of sedation for patients with gastric cancer.

For boost converter operating in the discontinuous conduction mode (DCM), feedback and feedforward compensators are widely used to improve the converter performance. However, it is relatively difficult to optimize load transient response (LoTR), line transient response (LiTR), and reference tracking speed (RTS) simultaneously, since the optimizations require different compensators that are incompatible. In order to solve the issue, a superposed compensation strategy is proposed in this paper, which consists of a feedback compensator and two feedforward compensators. Each compensator is tuned according to an objective transfer function, which optimizes LoTR, LiTR, and RTS. The outputs are summed as duty cycle according to the linear superposition principle. Compatibility of the compensators is improved by designing the feedforward compensators to adapt to the feedback compensator. Furthermore, based on the closed-loop model, design rules for the objective transfer functions are given to minimize the influences of the sample-and-hold effect and calculation delay, which are intrinsic in a digital controller. Finally, converter's LoTR, LiTR, and RTS are simultaneously optimized, which is proven by closed-loop magnitude–frequency plots, state trajectory analyses, and experimental results.

An experimental study was performed to investigate the effects of ice accretion on the aerodynamic performances and wake characteristics of a propeller model used for Unmanned-Aerial-System (UAS) under different icing conditions (i.e., rime vs. glaze). The experimental study was conducted in the unique Icing Research Tunnel available at Iowa State University (ISU-IRT). In addition to acquiring the important features of ice accretion on the rotating propeller blade using a “phase-locked” imaging technique, the wake characteristics of the rotating UAS propeller under the different icing conditions were also resolved by using the Particle Imaging Velocimetry (PIV) technique along with the time-resolved measurements of aerodynamic forces and power consumption of the UAS propeller model. Both “free-run” and “phase-locked” PIV measurements were performed on the propeller model at the different stages of the icing experiments (i.e., before, during and after the dynamic icing processes) to provide both the instantaneous flow characteristics and the ensemble-averaged flow statistics (e.g., mean velocity, vorticity, and turbulence kinetic energy) in the wake of the rotating propeller model. To the best knowledge of the authors, this is the first work of its kind to provide detailed, temporally-resolved wake flow field measurements of UAS propeller under real icing conditions. It is found that while the rime ice accretion could closely follow the original profiles of the propeller blades, the glaze ice usually forms into very irregular structures that can significantly disturb the wake flow field of the rotating propeller model, generating the much larger and more complex vortices. Such complex large-scale vortices are found to enhance the turbulent mixing in the propeller wake and produce an evident velocity deficit channel around the outer board of the propeller blades, providing direct evidences in elucidating the dramatic decrease in thrust generation and the significant increase in power consumption of the rotating propeller model in icing conditions. The findings derived from this study are believed to be essential and very helpful to elucidate the underlying mechanisms of the aerodynamic performance degradation of ice accreting UAS propellers.

An experimental investigation was conducted to quantify the dynamic ice accretion and the unsteady heat transfer process over the ice accreting surfaces of composite-based airframes widely used for light-weight, Unmanned-Aerial-Systems (UAS), in comparison to those over the surfaces of metal-based airframes used by conventional manned aircraft, in order to elucidate the underlying icing physics specifically pertinent to UAS inflight icing phenomena. Two airfoil/wing models with the same airfoil shape, but made of different materials (i.e., thermoplastic material with the thermal conductivity being only ∼0.2 W/m⋅K to represent typical UAS airframe substrates vs. Aluminum with the thermal conductivity being ∼200 W/m⋅K widely used for conventional manned aircraft). The two test models were mounted side-by-side inside an Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT) under the same wet glaze or dry rime icing condition. During the icing experiment, while a high-speed imaging system was used to record the dynamic ice accretion process over the surfaces of the test models, an infrared thermal imaging system was also used to map the corresponding surface temperature distributions over the ice accreting airfoil surfaces. It was found that, upon the impacting of the airborne, super-cooled water droplets in ISU-IRT, ice would start to accrete rapidly on the surfaces of the test models with a significant amount of the latent heat of fusion being released associated with the phase changing of the impacted super-cooled water mass over the airfoil surfaces. The thermal conductivity of the airframe substrate was found to affect the dynamic ice accretion and unsteady heat transfer processes over the ice accreting surfaces significantly. With the two test models being exposed under the same icing conditions, the released latent heat of fusion was found to be dissipated much slower over the surface of the thermoplastic model, due to the much lower thermal conductivity of the thermoplastic substrate. In comparison with those on the surface of the Aluminum model, the slower dissipation of the released latent heat of fusion on the surface of the thermoplastic model was found to cause higher surface temperatures and greater “heated” regions near the airfoil leading edge, more obvious surface water runback over the airfoil surface, and formation of more complex rivulet-shaped ice structures at further downstream locations beyond the direct impinging zone of the super-cooled water droplets.

Hydraulic fracturing is extensively used to increase a wellbore contact area by creating complex fracture networks in unconventional reservoirs. The characterization of in-situ fracture networks is a common challenge, which has great significance to hydrocarbon production prediction and fracturing stimulation optimization. Tracer tests are often used to estimate the transport properties of fracture networks. The understanding of characteristics of fracture networks is explored by tracer numerical experiments. An integrated simulation workflow is developed to simulate the process of tracer injection and flowback in an individual stage of fractured horizontal wells. An individual fracturing stage consists of a single hydraulic (primary) fracture and stochastically generated secondary fractures. Fracture density, length, orientation and conductivity of secondary fractures are systematically altered to investigate the impacts of fracture networks on tracer flowback profiles. The fracture intersections and percolation analysis of fracture networks are correlated with the skewness of tracer flowback profiles. A parameter called a conductivity weighted effective fracture density is proposed to describe the relationship between secondary fracture networks and the shapes of tracer flowback profiles, which is a combination of fracture density, length, orientation and conductivity. The conductivity weighted fracture intersections between hydraulic fractures and secondary fractures are used to account for the impact of a boundary on tracer flowback profiles through which a fluid flows into a well. These relationships are validated by new sets of fracture networks and provide a constraint for fracture network characterization.

Water can rapidly breakthrough in natural fractured reservoirs and can result in waterflooding, usually shown as high water cut and low oil production in oil field. It is of great significance to study the characteristics of waterflooding in fractured reservoirs to recognize the fracture in order to enhance oil recovery. A discrete fracture model was established; water cut and water cut derivative curves were used to study the characteristics of waterflooding with a single fracture in different fracture widths and locations. It is found that the water cut curve of fractured reservoirs behaves in a step-type characteristic for proper fracture width but will disappear if the fracture width is very small or too great. According to the characteristics of water cut derivative curve, the fracture width increases to a specified value, the peaks shown on the curve will change from single to double but will revert back to one peak if the fracture width is very high. In addition, the time interval of the two peaks is positively related to fracture width, and the differences of the two peaks will behave more obvious if smaller distance between the fracture and injection well is chosen. From this study, an initial diagnosis of the reservoir fracture development can be carried out according to the characteristics of water cut curve and water cut derivative curve.

This paper presents an optimized duty cycle control to reduce the reverse conduction loss of GaN HEMTs in very high frequency (VHF) class Φ2 inverter. VHF class Φ2 inverters are widely used in wireless power transfer systems and DC-DC power converters due to its high power density and fast dynamic response. However, the overall efficiency can be easily degraded by the reverse conduction loss of GaN HEMTs, which is high in conventional fixed duty cycle control. To address this issue, this paper proposes an optimized duty cycle control to reduce the reverse conduction time and loss. Firstly, current of the power switch is derived by resolving the analytical expression of inductor current. Secondly, by exploring the spectrum of switching current and the switching node impedance characteristics, the drain voltage under different load resistance is derived. Through the derived drain voltage, the optimized duty cycle under different load is calculated, which significantly reduces the reverse conduction time. Thirdly, the optimized duty cycle control is realized through an analog circuit. By measuring the average input current, the load resistance is estimated and the duty cycle is adjusted to the optimized value accordingly. Finally, a 27.12MHz class Φ 2 inverter prototype is built to verify the proposed control strategy. Experimental results show that the proposed strategy improves the power efficiency over the whole load range, and achieves a peak efficiency of 93.6% at full load.

Background De novo lipogenesis (DNL) has been reported to involve in a serial types of disease. A standard triple therapy, including a PPI, omeprazole, and antibiotics (clarithromycin and amoxicillin), is widely used as the first-line regimen for helicobacter pylori (H. pylori)-infectious treatment. The objective of this study is to explore the function of a standard triple therapy on DNL. Methods and results We collected the clinical sample from the patients diagnosed with or without H. pylori infection. Oil red staining, real-time PCR, western blotting (WB) and adipored experiment were performed to detect the effect of a standard triple therapy on DNL. The expression of relative key enzymes was assessed in gastric mucosa of clinical sample by IHC. Both 54 cases with H. pylori-negative and 37 cases with H. pylori-positive were enrolled in this study, and IHC assay showed that both fatty acid synthase (FASN) and ATP-citrate lyase (ACLY) expression, the critical enzymes involved in DNL, were increased in gastric mucosa of patients with H. pylori-positive compared with that with H. pylori-negative. Real-time PCR and WB analysis showed that neither clarithromycin nor amoxicillin inhibited FASN and ACLY expression, while treatment of BGC823 cells with omeprazole with 200 μM or 300 μM significantly abolished FASN and ACLY expression, leading to reduce lipid content. Conclusion These findings suggested that omeprazole suppressed DNL in gastric cells, implying that targeting DNL is an alternative strategy in improving the treatment of patients with H. pylori infection.

Complex fracture networks are created by hydraulic fracturing in shale gas reservoirs. The well performance is largely affected by the geometrical properties of fracture networks. It is difficult to estimate well performance because a large number of parameters are used for characterization of a fracture network. In this study, only two parameters are screened to estimate the shale gas recovery by the method of design of experiments. Synthetic fracture networks are generated based on the stochastic theory to represent the secondary fractures in the hydraulic fracture network. Two numerical experiments are designed to correlate the fracture network properties to gas recovery estimated by a commercial software. Various fracture network parameters derived from the analyses of fracture intersection, fractal and percolation are screened to correlate the gas recovery. In terms of the internal structure of a fracture network, a dimensionless parameter called the effective fracture density is proposed to estimate shale gas recovery. It is a combination of the number of fractures, fracture length and orientation. In terms of the boundary of a fracture network, the shale gas recovery is determined by the number of intersection points between the primary fractures and secondary fractures (NIPS). The shale gas recovery predicted by the two parameters (the NIPS and the dimensionless fracture density) is accurate compared with that calculated by the commercial software, which provides us a practical method to estimate the gas recovery by eliminating the number of parameters used for fracture network properties.

An experimental study was conducted to investigate the dynamic ice accretion process over the blade surfaces of a rotating propeller model for unmanned-aerial-system (UAS) applications. In addition...

An experimental study was conducted to evaluate the effects of surface wettability on the dynamic ice accretion process over the surface of a rotating Unmanned-Aerial-System (UAS) propeller model and the resultant aerodynamic performance degradation due to the ice accretion. A propeller model was installed in an Icing Research Tunnel at Iowa State University (i.e., ISU-IRT) with its surface wettability changed significantly (i.e., hydrophilic surface versus superhydrophobic surface). In addition to acquiring “phase-locked” images to reveal the dynamic ice accretion process over the rotating propeller surface, the thrust generation and the required power input to drive the propeller model to operate at a constant rotation speed were also measured during the ice accretion process. The dynamic ice accretion process over the rotating propeller surface was found to vary remarkably with changes to the propeller surface wettability. By making the propeller surface superhydrophobic, the detrimental effects of the ice accretion on the aerodynamic performance of the propeller model were found to be mitigated greatly with much less ice accretion over the propeller surface, significant reduction of the thrust loss and less demand for extra power consumption due to the ice accretion, in comparison with the case with the propeller surface being hydrophilic.

We introduce a coupled dipstick and microscopy device for analyzing urine samples. The device is capable of accurately assessing urine dipstick results while simultaneously imaging the microscopic contents within the sample. We introduce a long working distance, cellphone-based microscope in combination with an oblique illumination scheme to accurately visualize and quantify particles within the urine sample. To facilitate accurate quantification, we couple the imaging set-up with a power-free filtration system. The proposed device is reusable, low-cost, and requires very little power. We show that results obtained with the proposed device and custom-built app are consistent with those obtained with the standard clinical protocol, suggesting the potential clinical utility of the device.

Multistage hydraulic fracturing for horizontal wells is extensively applied in the exploitation of tight oil reservoirs. Complex fracture networks with different scales are created and hydrocarbon flowing in the matrix demonstrates a Pre-Darcy characteristic due to a strong interaction of rock and fluids in nanoscale pores. The modeling of complex fracture networks and a Pre-Darcy effect is required in numerical simulation of tight oil reservoirs. In this paper, stochastic fracture networks are employed to mimic actual fracturing networks according to the corresponding probability density functions (PDFs), and microseismic events are used to constrain the locations of fractures. The numerical simulation for tight oil reservoirs is developed by considering complex fracture networks and the Pre-Darcy effect based on an embedded discrete fracture model (EDFM) framework. Finally, the influences of fracture network properties including isolated fractures, connected fracture networks and the Pre-Darcy effect on well production are investigated via integrating the developed fracture network generation and tight oil numerical simulator. The results indicate that for isolated fractures with no direct connection with a wellbore, there is little influence on well performance. The influence becomes more obvious when isolated fractures connect to a wellbore, and an increase in fracture length and conductivity can enhance well performance especially when fractures lie off streamline lines. Similarly, for a connected fracture network, an increase in fracture network properties (number, length and conductivity) can promote well performance and fractures perpendicular to a horizontal wellbore can generate a maximal flow rate compared with other fracture orientations. The fracture network connectivity plays an important role in the fluid flow, and there are good relationships between well production and two proposed parameters, which can be treated as candidates to characterize the flow characteristics in fractured reservoirs.

The complexity and heterogeneity of pore structure greatly affect gas-liquid accumulation and transport, and the fractal theory has been proven to be an effective approach for studying nanoscale reservoirs in shale, coal, and tight sandstones. However, researches on fractal characteristics and control mechanisms for the lacustrine tight carbonate have received little attention. Lacustrine tight carbonate samples from the Jurassic Da’anzhai Member in the Sichuan Basin in China were systematically investigated focusing on the fractal characteristics and control mechanisms of storage spaces, minerals, diagenesis, and paleoenvironments. The fractal dimensions can be separated into two different and valid parts including D1 (2.515–2.785, average 2.652) and D2 (2.424–2.562, average 2.485), and the correlation between them is negative rather than positive. The average pore diameters exhibit a positive correlation with D1 and a negative correlation with D2, and the storage space is positively correlated with D2 a...

Although excellent dielectric, piezoelectric, and pyroelectric properties matched with or even surpassing those of ferroelectric ceramics have been recently discovered in molecular ferroelectrics, their successful applications in devices are scarce. The fracture proneness of molecular ferroelectrics under mechanical loading precludes their applications as flexible sensors in bulk crystalline form. Here, self-powered flexible mechanical sensors prepared from the facile deposition of molecular ferroelectric [C(NH2 )3 ]ClO4 onto a porous polyurethane (PU) matrix are reported. [C(NH2 )3 ]ClO4 -PU is capable of detecting pressure of 3 Pa and strain of 1% that are hardly accessible by the state-of-the-art piezoelectric, triboelectric, and piezoresistive sensors, and presents the ability of sensing multimodal mechanical forces including compression, stretching, bending, shearing, and twisting with high cyclic stability. This scaling analysis corroborated with computational modeling provides detailed insights into the electro-mechanical coupling and establishes rules of engineering design and optimization for the hybrid sponges. Demonstrative applications of the [C(NH2 )3 ]ClO4 -PU array suggest potential uses in interactive electronics and robotic systems.

Tight oil reservoirs are commonly developed by a combination of horizontal wells and multistage hydraulic fracturing techniques. The characterization of complex fracture networks after fracturing treatments is a common challenge for unconventional reservoirs. Tracer flowback profiles can reveal a fracture network at an individual stage. However, the numerical simulation of tracer transport in fractured reservoirs usually employs a dual-porosity continuum medium model or describes fractures by an enlarged fracture aperture in a regular grid system that is not capable of modeling a complex fracture network. Especially, the influences of the properties of fracturing fluid and variations in fracture permeability caused by pressure changes on tracer flowback profiles are not investigated. In this paper, a two-phase (water and oil), four-component (oil, water, fracturing fluid and tracer) numerical simulator is developed based on a discrete fracture model for modeling tracer injection and flowback in tight oil reservoirs. With respect to fracture network modeling, the simulator is capable of explicitly modeling an arbitrary distribution of fracture networks with a real fracture aperture by triangular grids. With respect to mechanism consideration, the simulator considers the influences of fracturing fluid and pressure-dependent fracture permeability on tracer flowback profiles. The properties of tracer dispersion and adsorption are also considered in both fractures and matrix. To validate the proposed model, a comparison is performed with the commercial software Eclipse. Sensitivity studies are performed to investigate the influences of parameters on tracer flowback profiles. The presented simulator is applied in the Changji oilfield to characterize individual stages using a stochastic method. Results show that the developed simulator is accurate as with Eclipse. The filed application indicates that the presented simulator can model tracer flowback and production performance. Sensitivity studies show that an increase in permeability modulus and the viscosity of fracturing fluid delays the peak arrival time. An increase in permeability modulus decreases the peak amplitude while an increase in the viscosity of the fracturing fluid increases the peak amplitude. An increase in a dead pore volume and a residual resistance factor has little impact on the peak position and lowers the tails of tracer flowback profiles. The sensitivity studies provide valuable information in characterization of a fracture network using tracer flowback data.

In a sensorless predictive current controlled boost converter, parameterizing the inductor plays an important role in controller performance. In this paper, a solution for inductor parameters online identification is investigated. A small-signal injection strategy is proposed to create a transient state, and convergence problem of inductance identification in steady state can be avoided. Then, a charge balance current observer (CBCO), derived from capacitor current charging balance concept, is adopted to estimate the inductor current for inductance identification. Since inductance is not used in CBCO, current estimation is not affected by inductance identification error. Because of rank-deficient problem, instead of identifying inductor parasitic resistance solely, the inductor equivalent parasitic resistance is derived. By applying it into the conventional current observer for current control loop, the accuracy of current estimation can still be guaranteed since more parasitic effects are included. To improve the accuracy of inductance identification, a load identification method is investigated. Furthermore, the effect of the equivalent series resistance of output capacitor on the proposed algorithm is analyzed. Finally, its effectiveness is verified by experimental results.

Yao W, Zhao T, Chen Y, Zhong Y, Fan H, Zhang W, Li L. 2017. Habitat evaluation model for ecologically successful lake restoration. Lake Reserv Manage. 00:1–13.Anthropogenic activities have severely affected the quality of Qianling Lake, China, causing mud and sediment deposition, poor water quality, and degraded fish habitat. In some regions of the lake, fish habitat that was formerly dominant has disappeared completely. A few areas of desirable habitat persist as a result of purposeful restoration actions, and these areas provide important conservation and restoration opportunities. In this study, the ecological conditions of Qianling Lake were assessed to identify hydrodynamic conditions, sediment deposition, and fish habitat suitability to recommend strategies for improving and restoring these areas. Two restoration strategies, “flood flush” and “add an artificial island,” were proposed and modeled to predict the restoration effects. Simulation results showed that the restoration scheme “add an...

A discrete fracture model for multi-scale flow in large-scale fractured tight oil reservoirs is proposed considering the compressibility of reservoir rock and fluid, and the non-linear flow in the tight matrix. Validation of the model is performed, followed by the field application of the model. The two-point flux-approximation scheme is adopted in the model to calculate conductivity, and small grids at the fracture intersections are eliminated by the “star-delta” transformation method to improve the computational stability. The fully implicit discretization scheme is performed on the temporal domain. Automatic differentiation technique which can improve model establishment efficiency and computational accuracy is applied in the model to solve the numerical model. The model is validated with the simulation results of Eclipse and the historical production data of a long fractured horizontal well in a tight oil reservoir in Xinjiang oilfield. Simulation results of a field-scale reservoir show that the model proposed can simulate reservoirs with large-scale complex fracture systems; well productivity is positively correlated with the scale of the stimulated reservoir volume, and the difference in planar fracture density and fracture connectivity are proved to be the key factors that lead to the heterogeneous distribution of remaining oil in tight oil reservoirs. Key words: tight oil reservoir, discrete fracture model, multi-scale coupling, fracture network, volume fracturing

LLC resonant converter can achieve zero voltage switching (ZVS) for primary side devices and zero current switching (ZCS) for secondary side rectifiers while operating in discontinuous conduction mode (DCM). However, the parasitic capacitance significantly affects the ZVS realization of primary side switches for high frequency GaN-based LLC converter. In order to reveal the influence, this paper analyses ZVS transition process with consideration of secondary parasitic capacitance in a high frequency GaN-based LLC resonant converter under DCM mode. Then, an accurate model during ZVS transition is derived. To verify the analysis and the derived model, a 250V rating input and 270V/6.6A rating output GaN-based LLC converter prototype operating at 500 kHz is built. The experimental results are consistent with the theoretical analysis.

For boost converter operating in the Critical Conduction Mode (CRM), linear compensation strategy is widely used to improve the control performance. However, conventional linear compensation is designed for limited input, since transfer functions for different input are often incompatible. In this paper, transient responses with respect to input/reference voltage and load variations are optimized simultaneously by a linear superposition compensation strategy. The objective closed-loop transfer functions for each kind of variations are investigated, which contribute to the overall compensation loop design. According to linear superposition principle, the compensation results are summed as reference current, based on which the switching on/off time is modulated. Although the summed results are convergence, separate compensation loop that includes integral terms can lead to divergence in calculation process. To eliminate the potential divergence, the overall compensation loop is re-designed so as to suit digital implementation. Experimental results show that the linear superposition compensation strategy achieves great transient performance to different kind of variations.

The applications of organotin halide perovskites are limited because of their chemical instability under ambient conditions. Upon air exposure, Sn2+ can be rapidly oxidized to Sn4+, causing a large variation in the electronic properties. Here, the role of organic cations in degradation is investigated by comparing methylammonium tin iodide (MASnI3) and formamidinium tin iodide (FASnI3). Through chemical analyses and theoretical calculations, it is found that the organic cation strongly influences the oxidation of Sn2+ and the binding of H2O molecules to the perovskite lattice. On the one hand, Sn2+ can be easily oxidized to Sn4+ in MASnI3, and replacing MA with FA reduces the extent of Sn oxidation; on the other hand, FA forms a stronger hydrogen bond with H2O than does MA, leading to partial expansion of the perovskite network. The two processes compete in determining the material's conductivity. It is noted that the oxidation is a difficult process to prevent, while the water effect can be largely suppressed by reducing the moisture level. As a result, FASnI3-based conductors and photovoltaic cells exhibit much better reproducibility as compared to MASnI3-based devices. This study sheds light on the development of stable Pb-free perovskite optoelectronic devices through new material design.

River ecosystems are closely linked to flow velocity, depth, water temperature, and river bed substrates, and the alteration of hydrological regime due to dam operation has significant impacts on the river ecosystem. It is critical for river managers to seek the optimal solution to balance the environmental discharge requirement with hydropower production. This study investigated links between hydropower plant generation and stream habitat conditions in the You-shui River, China, and developed an optimization model to obtain the most beneficial solution for both generating capacity and environmental discharge. The typical annual flow rates were determined, and Chinese sucker (Procypris rabaudi) was chosen as the target fish with 4 life stages to represent the habitat suitability situation under the environmental discharge. The optimal model was designed to be a function of the maximum value of the sum of the power generating function and the overall suitability index (OSI) function. The traditiona...

In the present study, a comprehensive experimental study was conducted to quantify the dynamic ice accretion process on aero-engine inlet guide vanes (IGVs) and to characterize a hot-air-based anti-/de-icing system in order to optimize the design paradigms to reduce the requirements of the bleed air for IGV icing protection, thereby, minimizing the performance penalties to the aero-engines. A hollowed IGV model embedded with U-shaped hot-air flowing conduit was designed/manufactured and mounted inside an Icing Research Tunnel for the experimental study. During the experiments, while a high-speed imaging system was used to record the dynamic ice accretion or anti-/de-icing process over the surface of the IGV model for the test cases without and with turning on the hot-air supply system, the corresponding surface temperature distributions on the IGV model were also measured quantitatively by using a row of embedded thermocouples. The unsteady heat transfer process over the surface of the IGV model was analyzed quantitatively, revealing that the convective heat transfer would dissipate over 85% of the thermal energy provided by the hot-air stream for the anti-/de-icing operation. A comprehensive parametric study was also conducted to evaluate the effects of the operation parameters of the hot-air-based system on its performance for IGV icing protection. It was demonstrated clearly that, with proper operation parameter settings (i.e., the temperature of the hot-air stream being greater than 30 °C and its flow rate is higher than 4.0 g/s), the hot-air-based system was able to effectively prevent ice formation/accretion over the entire IGV surface. The quantitative measurement results would not only be very helpful to elucidate the underlying physics of the important microphysical processes pertinent to IGV icing phenomena, but also can be used as valued database to validate/verify theoretical modeling and numerical simulations for the development of effective and robust anti-/de-icing systems to protect IGVs from harsh icing environment.