Cavity Stability Research Articles

Analyses on stability of subsurface cavity using discrete element method simulations

Analyses on stability of subsurface cavity using discrete element method simulations

Conceptual similarities between zeolites and artificial enzymes.

By using a Diels-Alder (DA) reaction as a base case, we show that a pure silica zeolite acting as an entropy-trapping scaffold can be synthesized with an organic structure directing agent (OSDA) analogue of the transition state (TS) of the DA reaction. A cavity stabilization of the TS is observed with the corresponding decrease in the activation energy of the reaction. A lower enthalpy of activation and a larger decrease in entropy are obtained with the zeolite synthesized with the analogue of the DA TS when compared with other zeolitic structures. Those differences are maintained, while catalytic activity is increased, when active sites are introduced in the zeolite. The catalytic zeolitic system synthesized with the OSDA analogue of the TS shows conceptual similarities with "de novo design" of an artificial enzyme to perform DA reactions, in where a suitable scaffold of existing proteins is chosen, and computationally designed active sites able to catalyze the cycloaddition reaction are introduced.

Innovative extracting of optimum operational diagrams for a CW sealed CO2 laser based on the evolutionary genetic algorithm

Views Some innovative diagram for the optimum parameters in operation of a sealed CW CO2 laser was extracted by using the evolutionary genetic algorithm. By picking up an optimum value for the cavity stability parameter, geometrical factor (g), the optimum value of other parameters such as tube diameter, tube length and the coupler transmission, are resulted by these optimum diagrams.

Geomechanical modelling of sinkhole development using distinct elements: model verification for a single void space and application to the Dead Sea area

Abstract. Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth ∕ diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth ∕ diameter values in each material type may partly reflect sinkhole growth trends.

Probabilistic performance-based approaches to the static and seismic assessment of rock cavities

This paper demonstrates the applicability of a probabilistic performance-based approach to assess the stability of rock cavities under gravity and seismic loads, with reference to the case study of a Neapolitan room and pillar cave, located inside a rocky hill. An advanced 3D model was generated, importing in the numerical code the data acquired during a laser scanning-based geometrical survey. The careful reproduction of the on-site geometry was found to improve the reliability of the results of static and dynamic analyses; because (i) the load eccentricity induced by the irregular shape of the hill reduces the stability of pillars, (ii) the localization of the roof crack depends on the shape of the ceiling, and, furthermore, (iii) the global dynamic behaviour of the hill is affected by topographic effects. The safety factors of rooms and pillars computed after the seismic analyses were compared to their values before earthquake to highlight earthquake-induced modifications of the static equilibrium under gravity loads. Some considerations on the resilience of the cavity are reported based on the latter comparison.

Optimal design of diamond-air microcavities for quantum networks using an analytical approach

Defect centres in diamond are promising building blocks for quantum networks thanks to a long-lived spin state and bright spin-photon interface. However, their low fraction of emission into a desired optical mode limits the entangling success probability. The key to overcoming this is through Purcell enhancement of the emission. Open Fabry–Perot cavities with an embedded diamond membrane allow for such enhancement while retaining good emitter properties. To guide the focus for design improvements it is essential to understand the influence of different types of losses and geometry choices. In particular, in the design of these cavities a high Purcell factor has to be weighed against cavity stability and efficient outcoupling. To be able to make these trade-offs we develop analytic descriptions of such hybrid diamond-and-air cavities as an extension to previous numeric methods. The insights provided by this analysis yield an effective tool to find the optimal design parameters for a diamond-air cavity.

Residual phase noise suppression for Pound-Drever-Hall cavity stabilization with an electro-optic modulator

We propose a simple method to suppress residual frequency/phase noise in Pound-Drever-Hall (PDH) cavity stabilization setups. This method makes use of the electro-optic modulator that is commonly used in PDH setups, and hence, only requires the addition of a simple electronic feedback circuit. Here, we apply this method to stabilize a commercially available continuous wave (cw) laser to a high-finesse cavity, and we demonstrate additional phase noise suppression of ~30 dB and more from DC to 100 kHz, compared to the use of a fast-piezo actuator alone. This method can be applied to almost all PDH systems to achieve feedback bandwidths in the multi-MHz range. Furthermore, this method does not require additional actuators, such as acousto-optic modulators, and it does not introduce parasitic amplitude modulation to the first order. The limitations and drawbacks of this approach are also discussed.

Review on In Situ Acoustic Emission Monitoring in the Context of Structural Health Monitoring in Mines

A major task in mines and even more in underground repositories for nuclear waste is to investigate crack formation for evaluation of rock mass integrity of the host rock. Therefore, in situ acoustic emission (AE) monitoring are carried out in mines as part of geomechanical investigations regarding the stability of underground cavities and the integrity of the rock mass. In this work, the capability of in situ AE monitoring in the context of structural health monitoring (SHM) in mines and in various geological settings will be reported. SHM pointed out, that the AE network is able to monitoring AE activity in rock with a volume up to 10 6 cubicmeter and distances up to 200 m (e.g., 100 m × 100 m × 100 m) in the frequency range of 1 kHz to 150 kHz. Very small AE events with source size in approximately centimeter to millimeter scale are detected. The results show that AE activity monitors rock deformation in geological boundaries due to convergence of the rock. In addition, high AE activity occurs in zones of dilatancy stress in homogenous rock. In conclusion in situ AE monitoring is a useful tool to observe instabilities in rock long before any damage becomes visible.

A methodological approach to assess the hazard of underground cavities subjected to environmental weathering

Soft highly porous carbonate rocks, such as calcarenites, and soluble sulphate rocks, such as gypsum, are very common in the Mediterranean region and, due to their microstructure and chemical composition, are prone to water induced weathering mechanisms. Cliffs, underground cavities and other morphological features in such formations are hence affected by intense erosion phenomena and weathering processes responsible for unexpected collapses and sinkholes. Just considering the Apulian region (Italy), 150 sinkholes have been recorded since 1925, with increasing frequency since 2000 (Fiore et al., 2018). The geosystem’s failure is often the short- or long-term result of a very complex hydro-chemo-mechanical process taking place at the micro-scale which can be detected and analysed by means of field and laboratory experimental test campaigns. Therefore, stability problems are often related to changes of the mechanical properties of the rock forming the cave caused by environmental weathering processes, despite the external boundary conditions are not changing with time. The paper deals with the assessment of hazard associated with the stability of abandoned underground caves, which is nowadays frequently required for land and urban planning activities. A methodological approach for hazard assessment based on a step-by-step procedure is proposed. This includes in-situ surveys, laboratory experimental studies, theoretical analyses and finally numerical investigations. The approach derives from the experience developed from several case studies analysed by the authors. In this work, two of these are presented. The first one concerns the stability of an anthropic cavity in a calcarenite formation which is affected by a water induced short-term and long-term debonding processes. The second one regards the stability of a three-level abandoned gypsum mine, the lowest level being partially flooded by water. The methodological procedure aims to evaluate the factors controlling the change of the mechanical properties of the rock so that efficient remediation measures can be designed in order to avoid any further decay of the rock mass stability with time.The proposed methodological approach, validated on real case studies, shows the convenience of performing advanced experimental, theoretical and numerical studies to properly assess the hazard in space and time and to better design the mitigation measures if they are required. The adoption of the proposed approach reduced the remediation costs of the second case study of one order of magnitude.

Invited Article: Tuning and stabilization of optomechanical crystal cavities through NEMS integration

Nanobeam optomechanical crystals, in which localized GHz frequency mechanical modes are coupled to wavelength-scale optical modes, are being employed in a variety of experiments across different material platforms. Here, we demonstrate the electrostatic tuning and stabilization of such devices, by integrating a Si3N4 slot-mode optomechanical crystal cavity with a nanoelectromechanical systems element, which controls the displacement of an additional “tuning” beam within the optical near-field of the optomechanical cavity. Under DC operation, tuning of the optical cavity wavelength across several optical linewidths with little degradation of the optical quality factor (Q ≈ 105) is observed. The AC response of the tuning mechanism is measured, revealing actuator resonance frequencies in the 10 MHz–20 MHz range, consistent with the predictions from simulations. Feedback control of the optical mode resonance frequency is demonstrated, and alternative actuator geometries are presented.

Experimental study on combustion characteristics of kerosene-fueled scramjet combustor

ABSTRACTKerosene-fueled ignition combustion test was carried out in a scramjet combustor under the condition of total temperature of 810 K, Mach number of 2.0 and different total pressures of 600, 700, 800 and 900 kPa. The combustor model was a dual-mode combustor with double cavity flameholder. Hydrogen was injected in the first cavity, and kerosene was injected in front of the first cavity. Hydrogen, being pilot flame, was the first to be ignited by the spark plug, and then kerosene was ignited by hydrogen. Kerosene was kept burning solely after hydrogen was stopped injecting. Combustion luminosity images were pictured in tests. The test results showed that all the combustion modes of kerosene and hydrogen were upstream cavity stabilization mode under different fueling conditions. Under the higher entrance pressure or the higher kerosene equivalence ratios, the kerosene combustions were upstream cavity stabilization mode. Under the lower entrance pressure or the lower kerosene equivalence ratios, the combustions were downstream cavity stabilization combustion mode. Under the middle entrance pressure or the kerosene equivalence ratios, oscillations of combustion mode occurred. The flameholding capacity of the kerosene-fueled combustor increases with the increase of the entrance total pressure.

Dual-Wavelength Good-Bad-Cavity Laser System for Cavity-Stabilized Active Optical Clock.

Active optical clocks (AOCs) have the intrinsic suppression of the influence of the cavity's noise on the output frequency, giving rise to the potentially ultranarrow linewidth. To break the cavity's thermal noise limitation by taking full advantage of the AOC's principle, as well as to achieve a long-term instability, we propose a scheme of cavity-stabilized active optical clock. The system consists of two key procedures. The dual-wavelength (DW) output signals share the same cavity and work in the good- and the bad-cavity regime, respectively. Then, the good-cavity signal is locked to a reference cavity by the Pound-Drever-Hall (PDH) technique to stabilize the main-cavity length. By doing this, the main-cavity's noise is expected to be reduced to the thermal noise floor of the reference cavity. Hence, the frequency stability of the bad-cavity signal will break this noise floor due to the suppression of the cavity-pulling effect. Experimentally, we realize the DW good-bad-cavity laser system by taking the Nd:YAG 1064 nm and Cs 1470 nm transitions as the good- and bad-cavity gain medium. The power and linewidth characteristics of the DW output are studied. Limitation factors of the clock frequency as well as the feasibility of the PDH cavity stabilization are analyzed.

Quasi-3-D Modeling of Higher Order Mode Instability in a Two-Gap Input Cavity of Broadband MBK

We present the results of our comprehensive study of the stability of a two-gap input cavity used in an experimental broadband multiple-beam klystron (MBK) with 18 beams and 7 cavities, which was designed for projected >500 kW maximum output power and ~13% bandwidth (so-called NRL MBK-3 design). The device was experimentally observed to be prone to self-excitation at all beam voltages below its designed operational value of ~42 kV. Postexperiment examination of the two-gap input cavity revealed traces of breakdown on its face. Detailed simulations performed using a 3-D computational electromagnetic code HFSS have shown presence of a few high-Q higher order modes (HOMs), which could explain self-excitation of the two-gap input cavity in a wide range of beam voltages. To explore HOM instability of the two-gap input cavity of the MBK in greater details, we applied the code TESLA-MB, which represents a parallel extension of the 2-D large-signal klystron code TESLA and which is suitable for an accurate modeling of multiple-beam devices with unique distributions of R/Qs over gaps in all its beam-tunnels.

Design and construction recommendations for connections arrangement in anchored veneers with continuous air cavity

DOI: 10.7764/RDLC.17.1.137 The optimization of connections arrangement to guarantee the anchored veneers with continuous air cavity stability is necessary, for better performance and durability of the facade. In this paper, different arrangements for the anchors to structure and different kinds of inner leaf are proposed, with the aim of selecting the best for the behavior of the facade against wind actions in cases of residential buildings. A very significant increase in stiffness is observed simply placing the anchors to the structure alternately to one side and the other of the structural element, and it is still more when there are wall ties between leaves, especially to a brickwork inner leaf.

Initiation, Development and Stabilization of Cavities during Tensile Deformation of Semicrystalline Polymers

By using polybutene-1 as a typical example, we illustrate the initiation, development and stabilization of cavities in the sample during tensile deformation. Samples with the same crystallinity, long spacing and crystalline lamellar thickness but very different sizes of spherulites were prepared via changing the melt history. Dimension of cavities during stretching the samples was determined by in situ ultra small angle X-ray scattering techniques. It turned out that the size of the cavities was bigger in the sample with larger spherulites than the one with smaller spherulites. The results show clear evidence of initiating cavities within crystalline phase at the grain-boundary of crystalline blocks, growing of cavities passing through parallel stacked lamellar crystals and amorphous layers and finally stablized by tilted lamellae at both ends of the plate-like cavities within the spherulites.

Study on Effects of The Shape of Cavitator on Supercavitation Flow Field Characteristics

The cavitator is the key part of the nose of the vehicle to induce the formation of supercavity, which has an important influence in the cavity formation rate, cavity shape and cavity stability. To study the influence of the shape on the supercavitation flew field characteristics, the cavity characteristics and the resistance characteristics of different shapes of cavitator under different working conditions are obtained by combining technical methods of numerical simulation and experimental research in water tunnel. The simulation results are contrast and analyzed with the test results. The analysis results show that : in terms of the cavity size, the inverted-conic cavitator can form the biggest cavity size, followed by the disk cavitator, and the truncated-conic cavitator is the least; in terms of the cavity formation speed, the inverted-conic cavitator has the fastest cavity formation speed, then is the truncated-conic cavitator, and the disk cavitator is the least; in terms of the drag characteristic, the truncated-conic cavitator has the maximum coefficient, disk cavitator is the next, the inverted-conic cavitator is the minimal. The research conclusion can provide reference and basis for the head shape design of supercavitating underwater ordnance and the design of hydrodynamic layout.

Investigating the Dynamics of Designed Ligand-Binding Proteins

Protein design constitutes a challenging but promising area in biochemistry. Custom-designed ligand-binding proteins, in particular, present promising applications in small-molecule sensing, diagnostics, and in therapeutic scavenging of toxic compounds. Some of the challenges in designing ligand-binding proteins lie in the creation of a binding site that results in high affinity interaction but is also pre-organized and does not collapse in the absence of ligand. Here, we use molecular dynamics simulations to assess the cavity stability and binding affinity of designed proteins that have been tested experimentally. Our apo simulations provide information on the cavity pre-organization while holo simulations indicate protein-ligand affinity and correlate well with experimental observations. The results obtained can be used to guide further steps in protein design and to select appropriate metrics for the prediction of binding affinity of future un-tested proteins, aiding the protein design methodology.

Telescope-based cavity for negative ion beam neutralization in future fusion reactors.

In future fusion reactors, heating system efficiency is of the utmost importance. Photo-neutralization substantially increases the neutral beam injector (NBI) efficiency with respect to the foreseen system in the International Thermonuclear Experimental Reactor (ITER) based on a gaseous target. In this paper, we propose a telescope-based configuration to be used in the NBI photo-neutralizer cavity of the demonstration power plant (DEMO) project. This configuration greatly reduces the total length of the cavity, which likely solves overcrowding issues in a fusion reactor environment. Brought to a tabletop experiment, this cavity configuration is tested: a 4mm beam width is obtained within a ≃1.5 m length cavity. The equivalent cavity g factor is measured to be 0.038(3), thus confirming the cavity stability.

Critical Length and Collapse of Interlayer in Rock Salt Natural Gas Storage

The existence of an interlayer has a significant effect on the stability of a rock salt gas storage cavity; therefore, an uncontrollable collapse of the interlayer would cause a series of issues. In this study, three types of mechanical instability criteria are comprehensively calculated. The limit radius of the interlayer is computed under different criteria, and the collapse radius of the interlayer is obtained by comparison. The calculation results of the mathematical model are highly accurate with respect to actual engineering logging data, in general with over 90% of accuracy. It is demonstrated that, besides the physical and mechanical characteristics of the sandwich, the location of the interlayer in the cavity and concentration of the brine also have an important effect on the collapse of the interlayer. The brine at the bottom of the cavity is nearly saturated. Therefore, an interlayer at this location does not easily collapse. The mathematical model established in this study is used in the seismic design and prediction of interlayer collapse during the construction of salt‐cavern gas storage facilities in China.

Stability and process parameter optimization for a vertical rotating ZnO-MOCVD reaction chamber

Developing an understanding of the cavity stability underlying the metalorganic chemical vapor deposition (MOCVD) of ZnO is critical to the fabrication of oxide-based devices. Therefore, computational fluid dynamics (CFD) was used to study the process parameters (e.g., the growth temperature, total gas flow, chamber pressure, and substrate speed) of the MOCVD H-type reaction chamber for four states in the cavity: buoyancy-induced flow, plug flow, rotating-plug flow, and rotating flow. Based on these states, criteria for determining stable and unstable flows were determined. These can be presented on the pressure–rotation rate spectrum, which can be used to visualize the effects of specific process parameters on the flow stability. In order to obtain a good film deposition rate in the stable flow state of the cavity, a response surface model and genetic algorithm were also used to optimize the process parameters. The coefficient of variation of the optimized ZnO film was reduced to 2%, which greatly improved the film quality. This study provides a comprehensive insight into the transport phenomena of the MOCVD H-type reaction chamber, including coupled heat and mass transfer and chemical reactions, and presents the optimal combination of parameters to provide a useful reference for obtaining high-quality thin films.