Transient Test Research Articles

Structural optimization of an arch-structured epoxy/rubber composite vibration isolator using deep Q-value neural network reinforcement learning

Vibration isolators are used to reduce unexpected vibrations that can negatively affect the system performance. For high load-bearing applications, vibration isolators must have high vibration reduction capabilities and strong load-carrying capacities. However, most studies on vibration isolators have focused only on vibration reduction characteristics. In this study, we performed structural optimization of an arch-structured epoxy/rubber composite vibration isolator using deep Q-value neural network (DQN) reinforcement learning. Our optimization framework, based on DQN reinforcement learning, iterated through modeling and structural/vibration analysis. Consequently, an optimal model with a high load-carrying capacity and excellent vibration reduction performance was obtained. This optimal model had a high safety factor even under a high pre-load and an elastic wave transmissibility value of less than −20 dB in the target frequency range. To validate the optimization results, an arch-structured epoxy/rubber composite vibration isolator was fabricated and vibration experiments were conducted. The fabricated vibration isolator showed good agreement with the vibration analysis results and excellent vibration reduction characteristics in the target frequency range, as confirmed by the transient response tests. This optimization method has potential applications in various fields because it can derive an optimal model considering multiple objectives with an efficient computational cost.

Discrepancy in ductility improvement in repeated stress relaxation of AA7075

The stress relaxation test is a commonly used transient test to determine the deformation kinetics during plastic deformation. This study reports the time-dependent deformation behavior of AA7075 alloy under different temper conditions. The deformation parameters, such as the apparent and true activation volume were estimated using single and repeated stress relaxation tests respectively. The results indicate that dislocation–dislocation interaction plays a critical role in the deformation behavior of the solution-treated condition, whereas dislocation–precipitate interaction dominates in the aged specimens. Additionally, the study found that single stress relaxation enhances the ductility of the deforming specimen, regardless of the temper condition. The ductility during repeated relaxation however had negative effects in aged samples. The possible mechanisms responsible for this discrepancy are discussed, providing a comprehensive overview of the time-dependent deformation behavior of AA7075 alloy.

Failure analysis of nuclear transient-tested UN tristructural isotropic fuel particles in a 3D printed SiC matrix

Fully ceramic microencapsulated fuel elements containing UN tristructural isotropic (TRISO) fuel particles within a 3D printed SiC matrix were subjected to transient testing with varying energy depositions. Detailed post-irradiation examinations were performed, including leaching in hot HNO3 and post-leaching X-ray computed tomography, to quantify the percentage of failed TRISO particles and crack propagation within the particles and surrounding fuel matrix. In parallel, detailed finite element analyses were performed for comparison with experimental findings and to better evaluate transient failure modes. The lowest transient energy deposition—which still exceeded bounding values for high-temperature gas-cooled reactor applications—resulted in no detectable TRISO particle failures or matrix cracking, which was consistent with the simulations. Simulations of the higher-energy transients for which significant TRISO particle failure was expected were generally able to reproduce the transient temperatures and matrix cracking. Thus, the TRISO particle failures were explained based on the effects of local SiC matrix thickness and porosity. Results generally confirmed the high strength of the additively manufactured SiC matrix but also affirmed the need for a modified UN TRISO architecture to prevent SiC matrix cracks from propagating through TRISO layers. This unique failure mode has not historically been considered for TRISO fuels contained in weaker graphite matrices.

Models and Interpretation Methods for Single-Hole Flowmeter Experiments

Subsurface and groundwater flow characterization is of great importance for various environmental applications, such as the dispersion of contaminants and their remediation. For single-hole flowmeter measurements, key characteristics, such as wellbore storage, skin factor heterogeneities, and variable pumping and aquifer flow rates, have a strong impact on the system characterization, whereas they are not fully considered in existing models and interpretation methods. In this study, we develop a new semi-analytical solution that considers all these characteristics in a physics-based consistent manner. We also present two new interpretation methods, the Double Flowmeter Test with Transient Flow rate (DFTTF) and the Transient Flow rate Flowmeter Test (TFFT), for interpreting data collected during single and multiple pumping tests, respectively. These solution and methods are used as follows. (i) The impact of wellbore storage, transient pumping rate, and property heterogeneities on the interpretation of data collected during single pumping tests are studied over 49 two-aquifer cases. (ii) The effect of the skin factor heterogeneity on transmissivity and storativity estimates, as well as the variability range of the (non-unique) corresponding solutions, are analyzed for the interpretation of multiple-pumping experiments. The results presented in this work show the importance of the various properties and processes that are considered, and the need for the new models and methods that are provided.

Study on the Effect of Exhaust Gas Recirculation Coupled Variable Geometry Turbocharger and Fuel Quantity Control on Transient Performance of Turbocharged Diesel Engine

With increasingly stringent emissions regulations, there are growing demands for the transient performance of diesel engines. This study conducted a transient bench test on a two-stage turbocharged heavy-duty diesel engine to optimize its performance during a load increase (20% to 100% in 1 s) at a constant speed (1200 RPM) transient process. The results showed that the transient control scheme using the low-pressure EGR system resulted in a 42.1% reduction in the peak value of soot emission, a 24.8% decrease in the peak value of NOx emission, a 9.14% decrease in ISFC and a 30.6% increase in maximum IMEP achieved in 1 s, compared to the steady-state optimization control scheme without EGR. Transient control scheme using the high-pressure EGR system resulted in a 24.4% reduction in the peak value of soot emission, a 31.8% reduction in the peak value of NOx emission, a 9.52% reduction in ISFC, and a 31.7% increase in maximum IMEP achieved in 1 s. The comparison of high and low-pressure EGR systems revealed that the low-pressure EGR system produced lower compromising emissions, while alterations in control parameters for the diesel engine with a high-pressure EGR system had a more significant impact on the transient process performance.

Photoelectric characteristics of hydrogen-terminated polycrystalline diamond MESFETs.

In the field of diamond MESFETs, this work is what we believe to be the first to investigate the optoelectronic properties of hydrogen-terminated polycrystalline diamond MESFETs under visible and near-UV light irradiation. It is shown that the diamond MESFETs are well suited for weak light detection in the near-ultraviolet region around the wavelength of 368 nm, with a responsivity of 6.14 × 106 A/W and an external quantum efficiency of 2.1 × 107 when the incident light power at 368.7 nm is only 0.75 µW/cm2. For incident light at 275.1 nm, the device's sensitivity and EQE increase as the incident light power increases; at an incident light power of 175.32 µW/cm2 and a VGS of -1 V, the device's sensitivity is 2.9 × 105 A/W and the EQE is 1.3 × 106. For incident light in the wavelength range of 660 nm to 404 nm with an optical power of 70 µW/cm2, the device achieves an average responsivity of 1.21 × 105 A/W. This indicates that hydrogen-terminated polycrystalline diamond MESFETs are suitable for visible and near-UV light detection, especially for weak near-UV light detection. However, the transient response test of the device shows a long relaxation time of about 0.2 s, so it is not yet suitable for high-speed UV communication or detection.

PW11Co/Ag3PO4/WS2 ternary composites with enhanced photocatalytic performance for the degradation of organic pollutants under visible light

A new composite material PW11Co/Ag3PO4/WS2 was designed and synthesized using cobalt-substituted Keggin-type phosphotungstic acid (PW11Co), silver phosphate (Ag3PO4) and tungsten sulfide (WS2) as experimental raw materials. Under simulated visible light, PW11Co/Ag3PO4/WS2 can efficiently degrade various dye molecules, and the removal rate is above 90% during 1 h (50 mg catalyst, 100 mL 20 mg/L of dyes). Excellent photocatalytic performance is attributed to high separation efficiency of the photogenerated carriers, which was proved by PL spectroscopy, transient photocurrent tests and the Nyquist diagram of PW11Co/Ag3PO4/WS2. The free radical trapping experiment showed that the hole (h+) and superoxide radical (O2−) were the main active species in the photocatalytic reaction. Based on energy band theory, a reasonable Z-scheme heterojunction mechanism was proposed for the progress of photocatalytic degradation.

Theoretical Developments for the Interpretation of Cavity Flow Permeability Tests Conducted on Intact Lac du Bonnet Granite

The permeability of intact geologic media features prominently in many geo-environmental endeavours. The laboratory estimation of permeability is an important adjunct to the field estimation of bulk permeability values, which involves a great deal of supplementary in situ investigations to correctly interpret field data. Laboratory permeability estimation is also a viable method if core samples are recovered from in situ geological mapping of the region under study. The basic methodologies for permeability estimation rely on either steady-state or transient tests of the geologic material depending on the anticipated permeability value. This paper presents a steady flow test conducted on a partially drilled cavity located on the axis of a cylindrical specimen. Certain compact theoretical relationships are proposed for the estimation of steady flow from a cavity of finite dimensions located along the axis of a cylindrical specimen. The relationships are used to estimate the permeability of a cylinder of Lac du Bonnet granite obtained from the western flank of the Canadian Shield. The results from the cavity flow permeability experiments are compared with other estimates for the permeability of granitic rocks reported in the literature.

A non-fueled nuclear-heated rod for in-pile transient boiling studies

Separate-effects boiling experiments have recently been conducted in the Transient Reactor Test Facility at Idaho National Laboratory to investigate transient heating and irradiation effects on cladding-to-coolant heat transfer. Specifically, transient critical heat flux (CHF) remains an important area of research, and better understanding of this phenomenon has potential for improving predictive models related to operational and safety limits. Consequently, this knowledge is expected to improve efficiency of light-water reactor operations. A novel borated nuclear-heated rodlet (BNHR) was designed to enable observation of transient cladding-to-coolant heat transfer phenomena. The final BNHR design takes a surrogate approach, wherein nuclear heating is induced by 10B(n, α) reactions rather than derived from fissions in a fueled specimen. The structure of the BNHR consists of a hollowed out borated (Bnat ∼ 2.05 wt%) stainless steel tube with an hourglass-shaped outer surface, capped at both ends with non-borated stainless steel. This geometry allows for inner-rodlet instrumentation and generation of the highest nuclear heating rates near the center of the rodlet to ensure onset of boiling near instrumentation for real-time observation. A novel approach to measuring the nuclear energy deposition rate in the BNHR separate and apart from the influence of the coolant, termed the n-α thermometer, is also detailed in this paper. This device has demonstrated excellent repeatability, and measurements indicate predictive modeling results for energy deposition in the BNHR rod agree within a 10% margin of the experiment measurements. These results give confidence that the BNHR design has successfully met experiment objectives.

Characteristics of Hydrogen Distribution under Steam Condensation in an Enclosed Vessel: Steady-State and Transient Tests

Although hydrogen has been recognized as a promising material for global energy transportation, its inadvertent leakage or generation into enclosed spaces may pose a risk of an explosion hazard in engineering facilities, including nuclear power plants. To manage the associated risks, it is crucial to identify the characteristics of hydrogen dispersion in air and its stratification behavior. In this study, we conducted an experimental investigation on the distribution of hydrogen in an enclosed vessel under steam-condensing conditions by using helium as a substitute for hydrogen. A series of steady-state and transient tests were carried out in a cylindrical test vessel, in which the interacting effect with steam condensation was simulated by employing a vertical condenser tube to promote the mixing of the steam-air-helium mixture. During transient tests, the impact of the jet momentum created by helium injection into the enclosure and subsequent buoyancy-driven redistribution of helium in the postinjection phase was observed.

Resumption of water capsule reactivity-initiated accident testing at TREAT

A series of integral reactivity-initiated accident commissioning experiments were completed in a new static water capsule in the Transient Reactor Test Facility (i.e., TREAT), marking the first such tests in the United States in more than 40 years. The test campaign included a verification test followed by five tests in the Static Environment Rodlet Transient Test Apparatus capsule. The capsule’s initial conditions varied from room temperature and pressure up to 200 °C and 2.5 MPa, with energy depositions varying between ∼ 500–1,100 J/gUO2. The series of tests allowed for a number of instrumentation qualifications and demonstrations, including cladding thermometry, rodlet plenum pressure, cladding elongation, and an electro-impedance boiling detector. Post-transient examinations such as gamma emission spectroscopy, profilometry, and microscopy were performed to document the end state of the fuel rods. The results from the experiments show that the fuel rodlets behaved very similar to historical tests under similar energy depositions. This paper documents the design of the capsule and highlights some results from the commissioning tests and post-transient examination.

Post-irradiation examination of the Sirius-1 nuclear thermal propulsion fuel test

Nuclear Thermal Propulsion (NTP) systems hold promise in reducing transit times for exploration of the solar system by both crewed and uncrewed missions. NTP systems currently under investigation include a once-through high-temperature gas-cooled fission reactor to provide thermal energy to heat the coolant, which also serves as the propellant. The fuel system consists of angular UN fuel particles dispersed in a matrix of W/Re, creating a ceramic and metallic composite or cermet, which has been irradiated in Idaho National Laboratory's (INL) Transient Reactor Test Facility (TREAT). This enabled evaluation of these materials under representative nuclear heating rates (∼95 K/s) and peak surface temperatures (∼2527 K). These surface conditions were indicative of achievement of the target peak internal temperature of approximately 2850 K. These tests named Sirius-1 (UN–W/Re), have been irradiated and this paper will present post-irradiation examination results. The Sirius-1 test produced minor, stable cracks in the fuel specimen and spalling of surface material. Volatilized uranium ‘soot’ was found deposited on the inner wall of the irradiation capsule indicating loss of some fissile material from the fuel specimen. Spalling from the surfaces was also noted upon visual inspection. Uranium diffusion from the fuel particles resulted in the formation of U/Re phases and the production of a laminar microstructure on the edge of the fuel system. Overall, the specimen was stable and remained within a coolable geometry upon conclusion of multiple thermal cycles to prototypical operating temperatures.

Characterization of micro-burnup treat irradiated U-22.5 at.% Zr and U-52.8 at.% Zr foils by transmission electron microscopy and X-ray diffraction

The uranium-zirconium (U-Zr) fuel system has been studied for decades, yet there remains a data gap of micro-burnup (BU) studies where the microstructure undergoes an initial transformation from as-fabricated to the true starting microstructure present in reactor. This study focusses on two U-Zr specimens, U-(22.5 and 52.8) at.% Zr, irradiated to <0.001 at.% BU (∼4.33E+15 F/cc) at 660 °C in the Transient Reactor Test Facility (TREAT). The samples were rapidly gas quenched (4–5 °C/min) to maintain the in-pile structure for post irradiation characterization and modeling input. The bulk features of the U-22.5 at.% Zr specimen were retained, suggesting an impact (beyond crystallographic texture) of the as-fabricated system. It was also found that Zr solubility in α-U increases to ∼18 at.%Zr at 660 °C, and subsequently influences phase fractions and grain boundary density. The U-52.8 at.% Zr alloy fully transformed into an equiaxed granular microstructure immediately upon reactor insertion, implying single phase γ-U-Zr at 660 °C. This work also identifies the retention of a face-centered-cubic Zr rind on the surface of the sample, suggesting that the mechanism of Zr-rind decomposition is not a trivial phase transformation at temperature, but rather likely a diffusion-based process.

PEST and AEM Modeling for Data Acquisition Planning.

A well-planned field data collection program should be designed to (1) collect a sufficient set of data of the right types at the right locations, and (2) collect a parsimonious set of data to avoid unnecessary costs. Combining PEST and a simple analytic element method (AEM) groundwater flow model for the site of interest provides a relatively simple, low-cost method of developing such a program. AEM models are well suited to this approach because they are quick to develop yet hydraulically accurate, reducing impacts on project budgets at early data collection planning stages; and quick to run, solving rapidly for the many iterations that PEST requires to generate good parameter estimates. This article shows two examples of this method: one for a steady state watershed model, and one for a transient pumping test project to demonstrate that PEST coupled with a simple AEM model that sketches out the key features of a site conceptual model can be an efficient tool in planning key parts of a hydrogeologic site investigation.

A coupling prediction model of annular pressure build-up for deepwater oil and gas wells during transient-state testing

To accurately predict annular pressure build-up of deepwater high pressure-high temperature oil and gas wells during the transient-state testing, a coupling prediction model of trapped & untrapped annular pressure build-up is proposed. For the short-term process of gas well transient testing, a wellbore transient heat transfer model has been established. Then the improved coupling model of trapped & untrapped annular pressure build-up is established, which is not only novelly considering fluid thermodynamic properties (isobaric expansion coefficient and isothermal compression coefficient) under high pressure-high temperature conditions and annulus fluid mass changes of untrapped annulus, but also considering annulus volume changes. For precise coupling calculating the annular pressure build-up, the annulus is divided into infinitesimal grid cells along well depth. The impact of different considering factors, testing times, testing production rates, formation permeability and cement sheath sealing positions on the annular pressure build-up in the model is investigated. The results show that conventional models (high pressure-high temperature properties and mass changes of the fluid are not considered) will greatly overestimate the annular pressure build-up; as the testing time increases, the impact of untrapped annulus fluid mass changes on the annular pressure build-up will gradually take the dominant role; reasonably optimizing the setting of untrapped annulus open hole section in high permeability formations and increasing the distance between cement sheath and the upper casing shoe can effectively relieve the increasing annular pressure build-up. These findings can achieve accurate prediction of trapped and untrapped annular pressure build-up, and play an important role in guaranteeing the wellbore integrity and safety of deepwater oil and gas wells during transient-state testing.

Novel Bi2WO6/MWCNT nanohybrids synthesis for high-performance photocatalytic activity of ciprofloxacin degradation under simulated sunlight irradiation

In this research, novel Bi2WO6/MWCNT nanohybrids were synthesized via a cost-effective hydrothermal route. The photocatalytic performance of these specimens was tested through the photodegradation of Ciprofloxacin (CIP) under simulated sunlight. Various physicochemical techniques systematically characterized the prepared pure, Bi2WO6/MWCNT nanohybrid photocatalysts. The XRD and Raman spectra revealed the structural/phase properties of Bi2WO6/MWCNT nanohybrids. FESEM and TEM pictures revealed the attachment and distribution of plate-like Bi2WO6 nanoparticles along the nanotubes. The optical absorption and bandgap energy of Bi2WO6 was affected by the addition of MWCNT, which was analyzed by UV-DRS spectroscopy. The introduction of MWCNT reduces the bandgap value of Bi2WO6 from 2.76 to 2.46 eV. The BWM-10 nanohybrid showed superior photocatalytic activity for CIP photodegradation; 91.3% of CIP was degraded under sunlight irradiation. The PL and transient photocurrent test confirm that photoinduced charge separation efficiency is better in BWM-10 nanohybrids. The scavenger test indicates that h+ & •O2 have mainly contributed to the CIP degradation process. Furthermore, the BWM-10 catalyst demonstrated outstanding reusability and firmness in four successive cycles. It is anticipated that the Bi2WO6/MWCNT nanohybrids will be employed as photocatalysts for environmental remediation and energy conversion. This research presents a novel technique for developing an effective photocatalyst for pollutant degradation.

Intake pressure control based on improved super-twisting for altitude ground test facilities

This paper focuses on the problem of rapid tracking of engine transient pressure, an improved super twisting algorithm (STA) is adopted to control the intake pressure of the engine. The high altitude platform is analyzed systematically, the mathematical model is derived, and the system and control object model are established. It is improved on the basis of classical STA method and has better control effect than PID control methods and LADRC. Transient state tests of the engine under three different working conditions(acceleration/deceleration state of pushing/pulling accelerator lever, engine intake pressure changing from 50kPa to 60kPa, and engine intake pressure changing from 60kPa to 70kPa) are simulated and verified. The simulation results show that, compared with the traditional PID and active disturbance rejection control(LADRC)strategies, the method proposed in this paper can track the inlet pressure of the engine in transition state quickly, and can reach and stabilize the given set value accurately and quickly.

Universal Absolute Stability Criterion for Single-Phase Grid-Following Inverters Equipped With Orthogonal-Normalization-Based Grid Synchronizer

The stability problem of grid-following inverters has been widely investigated. Nevertheless, existing literature has not yet proposed a strict stability analysis method for the overall grid-following inverter system with nonlinear nature. Focusing on single-phase systems, by using frequency-domain nonlinear theory, this article proposes a universal absolute stability criterion for the single-phase grid-following inverters (SGFIs) equipped with orthogonal-normalization-based grid synchronizer. It will be shown that a SGFI will be absolutely stable under small- and large-disturbances if both the traditional impedance criterion and the synchronous nonlinear criterion are satisfied. The usefulness and applicability of the proposed new criterion is demonstrated by a case study of the conventional LCL-type SGFI system. Finally, the theoretical analysis is fully supported by a series of steady-state and transient experimental tests.

Real-Time Transient Simulation and Studies of Offshore Wind Turbines

The real-time models of offshore wind turbine generators complied with industry standards are presented in this paper. The developed models provide essential capabilities for future electromagnetic transient controls and testing offshore wind farms, such as low-voltage ride-through, active/reactive power support, transient current limiting. Furthermore, the proposed models provide an additional capability of controlling negative sequence current, which meets the future requirements for protecting wind farm systems. This paper presents average-value and detailed switching real-time models in the Opal-RT real-time simulator. The efficacy of the proposed real-time models in terms of computational efficiency is demonstrated by comparing them with the non-real-time models. Extensive case studies are performed to demonstrate the control functions of the proposed models, such as dynamic-wind condition, power curtailment, low-voltage and fault ride-through, negative sequence current control, etc. The wind turbine model validation against the generic model presented by the Western Electricity Coordinating Council (WECC) is conducted to show their compliance with industry standards utilized by WECC. A real-time model of a 450 MW offshore wind farm is developed to show the feasibility of large-scale wind farm modeling.

Modeling of a capacitive voltage transformer for evaluation of transient response in conformity with the IEC 61869-5 Standard

This paper presents the implementation of a nonlinear model of a Capacitive Voltage Transformer (CVT) to evaluate the transient response in conformity with the international standard IEC 61869-5. The work is divided into three main steps: electrical tests to measure the CVT parameters and frequency response; implementation of linear mathematical modeling and an optimization algorithm to estimate unmeasured parameters; and implementation of nonlinear modeling in a simulation program for electromagnetic transients. First, the requirements of the IEC standard about the transient response of CVT are presented. Then, some important aspects of CVT modeling are discussed. Afterward, a linear model of a CVT is used to estimate the parameter not measured in the laboratory. Then, a nonlinear model is implemented in ATP. The model is validated in the time domain by comparing the simulation results with some signals measured in the laboratory. Finally, simulations of the transient response tests are made following the IEC 61869-5. The results show that the model developed in this work is reliable and can be used for the simulation of ferroresonance and transient response tests following the IEC 61869-5 when no laboratory structure is available.