Artificial Disturbances Research Articles

Large-scale influence of numerical noises as artificial stochastic disturbances on a sustained turbulence

We investigate the large-scale influence of numerical noises as tiny artificial stochastic disturbances on a sustained turbulence. Using two-dimensional (2-D) turbulent Rayleigh–Bénard convection (RBC) as an example, we solve numerically the Navier–Stokes equations, separately, by means of a traditional algorithm with double precision (denoted RKwD) and the so-called clean numerical simulation (CNS). The numerical simulation given by RKwD is a mixture of the ‘true’ physical solution and the ‘false’ numerical noises that are random and can be regarded as a kind of artificial stochastic disturbances; unfortunately, the ‘true’ physical solution is mostly at the same level as the ‘false’ numerical noises. By contrast, the CNS can greatly reduce the background numerical noise to any a required level so that the ‘false’ numerical noises are negligible compared with the ‘true’ physical solution, thus the CNS solution can be used as a ‘clean’ benchmark solution for comparison. It is found that the numerical noises as tiny artificial stochastic disturbances could indeed lead to large-scale deviations of simulations not only in spatio-temporal trajectories but also even in statistics. In particular, these numerical noises (as artificial stochastic disturbances) even lead to different types of flows. The shearing convection occurs for the RKwD simulations, and its corresponding flow field turns to a kind of zonal flow thereafter; however, the CNS benchmark solution always sustains the non-shearing vortical/roll-like convection during the whole process of simulation. Thus we provide rigorous evidence that numerical noises as a kind of small-scale artificial stochastic disturbances have quantitatively and qualitatively large-scale influences on a sustained turbulence, i.e. the 2-D turbulent RBC considered in this paper.

Research on the Development Law of Pre-Mining Microseisms and Risk Assessment of Floor Water Inrush: A Case Study of the Wutongzhuang Coal Mine in China

Coal-mining areas are widely distributed in Northern China, but are under threat from confined water in the mining operation, resulting in a series of floor water- inrush hazards. Therefore, it is significant to effectively evaluate the floor water inrush to ensure safe and efficient coal mining. The 182602 working face of the Wutongzhuang coal mine served as the background for our research. The concept of “pre-mining microseisms” was proposed, and based on this, microseismic monitoring equipment was arranged on site. The correlation between microseismic events and the water abundance of an aquifer was analyzed, and a floor water inrush evaluation method was constructed based on the three elements of an aquifer and pre-mining microseisms. The main results are as follows: first, the microseismic events were excited by artificial disturbances before the mining of the working face including slurry diffusion and neighboring mining, which had the characteristics of sporadicity, clustering, and periodicity. Second, the regional distribution of water abundance was determined by taking the water inflow, water pressure, and grouting volume as the outward performance characteristics of water abundance in the Shanvuqing aquifer. Furthermore, the correlation coefficient between the pre-mining microseisms and the three elements of the aquifer (water inflow, water pressure, and grouting volume) was larger than 0.7. On this basis, an evaluation method associated with the water inrush risk along the strike of the working face was established based on pre-mining microseisms, dividing the working face into dangerous zones, suspected dangerous zones, and safe zones. Furthermore, pre-mining microseisms, water abundance, and structures were introduced as risk-evaluation indices, and the complete weight was calculated using an analytic hierarchy process and entropy-weight technique, before a vulnerability index model of floor water inrush was built. Finally, targeted treatment procedures were efficiently implemented to ensure the safe mining of working face 182602 due to the successful prediction of potential water risk zones. The research results provide scientific and technological support for pre-mining microseisms combined with water abundance as a technical method to prevent floor water inrush.

How soil meso‐/macro‐faunas orchestrate ecosystem multifunctionality under different artificial disturbance conditions in the Changbai Mountain region, China

AbstractBiodiversity‐ecosystem function relationships have been widely studied in the field of microorganisms in recent years. The research findings revealed that microorganisms positively influence multiple ecosystem functions in diverse ecosystem types. However, the previous studies have neglected the fact that biodiversity at higher trophic levels is also required in order to maintain ecosystem multifunctionality. Here, in this study, the relationships among soil macro/meso faunal diversity, soil functions (C, N, and P functions), and ecosystem multifunctionality under different artificial disturbance conditions were investigated. The results revealed a positive relationship between the soil meso‐faunal diversity and ecosystem multifunctionality in primary forest (PM), secondary forest (SF), and deforested land (DL). However, correlations between macro‐faunal diversity and ecosystem multifunctionality decreased as the intensity of artificial disturbances increased, and no significant relationships were found in the DL and cultivated land (CL). We suggested that the soil faunal size was the main factor affecting the predictive ability of meso‐ or macro‐ faunas, and the soil meso‐faunal diversity was more suitable than soil macro‐fauna to orchestrate the ecosystem multifunctionality. Further, we demonstrated that the relative effects of the soil functions on ecosystem multifunctionality were changed with the increasing disturbance intensities. We proposed that soil function and meso‐/macro‐faunas contribute to ecosystem multifunctionality in different ways under natural or artificial disturbances. It was concluded that the relative contributions of the soil meso‐/macro‐fauna to the ecosystem multifunctionality were manipulated by their size, soil functions, and disturbance intensities.

Distribution and diffusion thermodynamic characteristics of phosphorus at the interface between river sediment and water under the influence of artificial disturbance

Abstract Artificial disturbance affects the migration of phosphorus (P) at the interface between river sediments and water. In the present research, we sampled three sections of the Yitong River in Changchun City, China, in order to obtain representative samples of city, town, and rural reaches. Overlying water and sediment samples were obtained in September 2021 during the dry period. In our experiments, we determined the distribution of different forms of P, diffusion flux of P at the interface, as well as P adsorption parameters. The results showed that concentrations of four P species in the sediments followed the order: Ca-P > Fe-P > Acid extracted phosphorus > Alkali extracted phosphorus. The diffusion flux of -P in each reach was positive, showing that sediments were an important P source for the overlying water. The -P content in the interstitial water of sediments was significantly correlated with that in the overlying water. This indicated that P diffused into the overlying water in the form of -P under most circumstances. The adsorption parameters gradually decreased from upstream to downstream. These data indicated that potential for phosphorus release from downstream sediments was higher than that from upstream sediments. This likely occurred because, downstream, a greater artificial disturbance intensity is observed.

Carbon Sequestration Model Based on Multiple Linear Regression

Proper deforestation promotes the development of man and nature, so it is necessary to design models to calculate the amount of carbon sequestered and further determine the value of forests. According to the formula for calculating the carbon sequestration of forest and its affiliated forest products, we use the intensity of human disturbance as a single variable to construct a differential equation for the relationship between forest and wood product accumulation. Combining five major indicators such as rainfall, temperature, and tree species, we constructed a multiple linear regression model for carbon sequestration using the data obtained for fifteen forests worldwide. As a result, we established the relationship between carbon sequestration and the influencing factors, learned the significant effects of tree species and artificial disturbance intensity on carbon sequestration, and further established the optimal forest plan.

Landscape Pattern Vulnerability of the Eastern Hengduan Mountains, China and Response to Elevation and Artificial Disturbance

The eastern Hengduan Mountains are located in the transition zone between the Qinghai-Tibet Plateau and the Sichuan Basin and are important for global biodiversity and water conservation in China. However, their landscape pattern vulnerability index (LVI) and its influencing factors have not been systematically studied. Therefore, the spatial distribution patterns, LVI, and the landscape artificial disturbance intensity (LHAI) of Ganzi Prefecture were analyzed using ArcGIS software based on landscape data and Digital Elevation Model (DEM) digital elevation data. Then, the LVI response to LHAI and elevation was discussed. The results showed that Ganzi Prefecture was dominated by low- and middle-LVI areas, together accounting for 56.45% of the total area. LVI values were highest in the northern regions, followed by the southern and eastern regions. Batang and Derong counties had the highest LVI values. Most areas in Ganzi Prefecture had very low- or low-LHAI values, accounting for 81.48% of the total area, whereas high-LHAI areas accounted for 2.32% of the total area. Both the LVI and LHAI of Ganzi Prefecture had clustered distributions. Spearman analysis indicated that when elevation exceeded 4500 m, it was the most important factor affecting LVI and LHAI. In the range of 4500–5400 m, the relationship between elevation and LVI shifted from a weak positive correlation to a negative correlation, whereas LHAI was positively correlated with elevation. In addition, LVI also responded significantly to LHAI. However, the relationship kept changing as elevation increased. Hence, the ecological vulnerability of high elevation areas above 4500 m deserves greater attention. In addition, pasture areas in the upstream reaches of the Yalong River in the northern region, the coastal area in the downstream reaches of the Jinsha River in the southern region, and the eastern mining area, should be prioritized for protection and restoration. This research provides a basis for appropriate environmental planning mechanisms and policy protections at the landscape level.

Human activities changed organic carbon transport in Chinese rivers during 2004-2018

Rivers serve as regulators of global climate by releasing greenhouse gases, burying particulate carbon, and connecting different ecosystem carbon pools. However, long-term organic carbon (OC) transport features across different Asian rivers are not well known due to unavailable data. Based on routinely monitored environmental and hydrological data during 2004-2018, this study investigated the spatiotemporal variations in dissolved (DOC) and particulate OC (POC) transport across 41 rivers in China. Across different rivers, both DOC (1.35 – 16.8 mg/L) and POC (0.27 – 4.48 mg/L) concentrations covered wide ranges. The DOC content was high in the north and low in the south, with significantly higher (t test, p < 0.01) values for rivers north of 30°N (5.39 ± 3.66 mg/L vs. 2.39 ± 1.14 mg/L). Human activities greatly influenced the riverine DOC and POC distributions. The riverine ammonia nitrogen (NH+ 4-N) content was positively correlated with DOC (r = 0.81 and p < 0.01) and explained 85.59% of its spatial variation. High vegetation coverage had significant effects on decreasing the riverine POC content, with r = -0.55 and p < 0.05. During 2004-2018, water pollution prevention and control strategies decreased DOC concentrations in 60.98% of rivers; meanwhile, anthropogenic vegetation restoration and dam construction led to POC content decreases in 90.48% of rivers. Importantly, along with DOC and POC changes, increasing DOC/POC ratios were found in 90.48% of the rivers, with 42.86% being significant, which indicated that Chinese rivers are losing their Asian features of low DOC/POC ratios due to artificial disturbance. This study is significant for accurately quantifying greenhouse gas emissions, carbon burial, and OC export to estuaries by Chinese rivers.

Patterns and Driving Factors of Diversity in the Shrub Community in Central and Southern China

Climate, topography, and human activities are known to influence plant diversity. In the present study, species-abundance distribution (SAD) patterns of the shrub community were fitted, and the mechanism of contribution of 22 driving factors was assessed. The results showed that the α-diversity index exhibited no significant differences between artificial disturbance and the natural community. The Zipf and Zipf–Mandelbrot models were found to exhibit a good SAD fitting of the communities, thereby exhibiting a different diversity structure. It was observed that the SAD followed more than one rule, and the Zipf–Mandelbrot model was better than other models. The gradient boosting model indicated that precipitation in the wettest month, annual precipitation, and slope direction showed the strongest impact on plant richness. The indicator species of the artificial disturbance and natural community were identified from a multiple regression tree. Furthermore, an increase in species diversity was observed with a rise in latitude, exhibiting a single-peaked curve with increased altitude. β-diversity analysis indicated that both habitat filtering and the neutral effect influenced the establishment of the natural community, while the establishment of the artificial disturbance community was only affected by habitat filtering. Our study provides a better understanding of the ecological process of the maintenance of shrub-community diversity.

Numerical study of the impact of contact line with hysteresis on the Faraday instability

We report a numerical study of the contact-line effect on the Faraday instability. A momentum balance model is implemented to simulate the hysteresis of the meniscus. By using this model, a stick–slip-motion of the contact line happens on the lateral wall when a vertical vibration is exerted to the container. The numerical result further supports that the contact-line hysteresis can increase the natural frequency by inference. Besides, it can largely delay the timing of the onset because of an extra dissipation provided by the capillary effect. The growth rate can also be affected by the meniscus but the impact of the hysteresis seems limited. The presence of the meniscus is the reason why Faraday instability occurs without any artificial disturbance. Finally, a linear relation between the contact-angle range and the contact-line position is observed from our computation.

Assessment of the technical condition of the power supply of electronic airport security systems in the aspect of electromagnetic disturbances

Airports are classified as national critical infrastructure facilities mainly due to their strategic importance. Therefore, they require special protection for their functioning. These systems are not only influenced by factors related to the intensity of use but are also exposed to the influence of external and internal, natural and artificial electromagnetic disturbances. For the selected electronic security system (ESS) of the airport, a graph of relations in the system in terms of reliability and operation will be developed. Subsequently, it will enable mathematical analyses to obtain a system of equations describing the system. The obtained results of the reliability and operational analysis of the selected airport ESS, taking into account electromagnetic disturbances, made it possible to estimate the probabilities of the system being in the selected states. The introduction of the factor describing the level of the impact of electromagnetic disturbances on ESS allows for estimating the effectiveness of various solutions counteracting such interactions' effects. The presented reliability and operational analysis of the selected electronic security system used to protect the airport allowed us to estimate its most important reliability and operational parameters. The obtained dependencies make it possible to compare various electronic security systems solutions and select rational solutions for airport security.

Study of the sorting pattern of dredger fill under artificial disturbance based on the concealment degree.

This paper focuses on the sorting pattern of silt deposited at estuaries under artificial disturbance based on the concept of bidirectional concealment, which is introduced for such silt with similar particle size, low disturbance exposure angle, and difficult sorting. By establishing the relationship among the absolute concealment (Δi), the drag force coefficient ({C}_{mathrm{D}}), and the lift force coefficient ({C}_{mathrm{L}}) of highly concealed silt particles under disturbance and considering the concepts of disturbance intensity, disturbance direction, and particle concealment degree, the contribution equation for the effective depth (Y) of artificial disturbance in the deposited slurry is introduced, and the mechanical equation for the internal disturbance of silt is established. On this basis, the motion initiation probability for fine particles ({varepsilon }_{{d}_{i}}) is calculated using the Shields parameter (Thetac), and the theoretical model of plastic sandy silt sorting under artificial disturbance is derived from the Markov chain-based three-state transition. The method proposed in this paper can explain the bedload gradation of sandy silt under internal physical disturbance. The calculated data in this paper agrees well with that of the flume test on uniform sandy silt and the related sediment particle theories. Therefore, the clay particle transport pattern model in slurry under artificial disturbance based on the bidirectional concealment degree can explain the gradation changes of flow-plastic sandy silt under artificial disturbance, thus providing a theoretical basis for the research on the sorting of flow-plastic sandy silt under artificial disturbance.

Research on the Integrated Planning of Blue-Green Space towards Urban-Rural Resilience: Conceptual Framework and Practicable Approach

Facing the impacts of climate change and the ecological environmental problems caused by urbanization, urban-rural resilience is a new value goal of territorial space development. Blue-green space is an interconnected network system of natural and artificial green space and water bodies, which can dissolve the internal and external pressures of the system by way of mitigatory acceptance and adaptive interaction, reduce the impact of climate change and artificial construction disturbances, and provide diversified composite functions. By recognizing the connotation of the concept of blue-green space, its composite ecological functionality and its relationship with the value of urban-rural resilience, this paper constructs a conceptual framework for the integrated planning of blue-green space in urban and rural areas with “resilient objectives, resource identification, integrated configuration, differentiated regulation”. The paper proposes an integrated and coordinated multi-scale practicable approach of blue-green space planning (i.e., the construction of the blue-green corridor network, the configuration of blue-green open space, the allocation of blue-green infrastructure) and the regulation-based urban-rural transect, with the aim of improving the hydroecological performance and composite functional services in order to realize urban and rural resilience.

Dynamic Responses of a Pile with a Cap under the Freezing and Thawing Processes of a Saturated Porous Media Considering Slippage between Pile and Soil

The freezing/thawing stratification effect of seasonal factors or artificial disturbances in frozen soil regions has an important influence on the vertical vibration of the pile–soil–cap system. Taking into account the slippage between the pile and soil, a simplified layered analytical model of the vertical vibration of the pile–soil–cap system in a double-layered stratum under the freezing and thawing processes of a saturated porous medium was established, and the analytical solution of the dynamic response on the top of the pile cap was obtained. In this model, frozen saturated porous media and Biot’s porous media theory were used to simulate frozen soil and unfrozen soil, respectively. The validation of the slippage model was first verified by comparison with the results of the existing model tests. This was followed by a dynamic model test of the pile–soil–cap system in a self-made, ground-freezing system. In comparison with the analytical results and the experimental results of model tests under the freezing/thawing processes, the validation of the present model is further verified. A comprehensive parametric study reveals that the parameters of the frozen or thawed soil layer have significant effects on the amplitude–frequency curve of the vertical vibration of the pile foundation.

Species Richness, Abundance, and Productivity of Birds Along a Powerline Right-of-way within a Forested Landscape, Northeastern United States

Utility rights-of-way (ROW) serve as nesting areas and maintain a high diversity of early successional birds. ROW incorporating wire zone–border zone and integrated vegetation management can be used as examples of early successional habitat management for bird conservation more generally in the Northeastern United States, given artificial disturbances not created solely for natural resource conservation comprise approximately 80% of early successional habitats. The objective of our study was to determine the effect of herbicide and mechanical vegetation management approaches on the abundance, species richness, and reproductive success of breeding bird species occupying an electric transmission line ROW in central Pennsylvania. The overall abundance of birds was significantly lower within the wire and border management zones, following initiation of a new vegetation management cycle at State Game Lands (SGL 33) than in the years prior to management. Sections of ROW with no border zones contained the lowest abundance and species richness of breeding birds compared to sections with borders prior to the initiation of a new management cycle. Sections of ROW with no border zones and mowing sections had the lowest bird abundance and species richness of all ROW sections at the onset of a new management cycle, and contained the lowest number of bird species displaying evidence of breeding, both prior to and at the beginning of management cycles. Sections of ROW managed using herbicides were comparable or more beneficial to bird communities in terms of abundance, species richness, indices of productivity, and nesting success than sections maintained via mechanical treatments (mowing and hand cutting), both at the end and beginning of management cycles within a forested landscape in the central Appalachian Mountains and surrounding forested regions in the northeastern United States.

Measuring Organization of Large Surficial Clasts in Heterogeneous Gravel Beach Sediments

The natural stratification and interlocking “organization” of armored sediments in heterogeneous, coarse-grained, beaches provides protection and enhances habitat for borrowing sedentary megafauna and macrofauna such as hard-shelled clams. Here, we develop a novel metric for quantifying sediment organization of large surficial beach clasts through sedimentologic and photogrammetric analyses of 37 lower intertidal heterogeneous gravel beaches in western Prince William Sound, Alaska (USA). Grain size, photogrammetric, and Wolman Pebble Count clast-size data from 64, ~1-m2 study plots are combined into a clast-size-independent “Organization Metric” to quantify the degree of organization in the meshed arrangement of larger surficial sediments. This metric was validated through field manipulation experiments and comparisons of adjacent plots characterized by different clast sizes. Application of this metric to subsets of Prince William Sound beaches that underwent differential treatment following the Exxon Valdez oil spill reveals persistent physical effects of artificial beach disturbance even 21 years after the cleanup. This has important implications for beach management (e.g., cleaning or dredging) and for the diverse and productive sedentary megafaunal assemblages that live within these sediments. Overall, this study provides a new approach for quantifying organization of heterogenous coarse sediments in diverse natural settings; in particular, heterogenous gravel beaches.

Numerical and experimental study on the behavior of vortex rings generated by shock–bubble interaction

In this study, three-dimensional numerical simulations and experiments of the interaction between a normal shock and bubbles generated by the repetitive energy depositions of a laser pulse in a Mach 1.92 flow was conducted. As a result of the shock–bubble interaction, a vortex ring, caused by a baroclinic effect, was generated. Owing to the self-induced velocity field, the advection velocity of the vortex rings decreased with increasing laser pulse energy. In the experiments, when interactions among the vortex rings became strong, separations in transverse directions between adjacent bubbles were induced. This was reproduced through numerical simulations by imposing an artificial disturbance in the initial positions of the bubbles, i.e., by 5% of the bubble diameter in a transversal direction. The asymmetric behaviors of a row of vortex rings were classified into three patterns based on the ratio of the distance between the vortex rings to the size of the vortex rings (λ: inverse Strouhal number). In pattern 1, with λ &amp;gt;2.9, there was negligible interference between the vortex rings because the interval of the vortex rings was sufficiently large. In pattern 2, with λ = 0.97–1.2, separation in the vortex-ring rows appeared, and the separation angle increased as λ decreased. In pattern 3, with λ &amp;lt;0.62, the interference intensified, and the vortex rings collapsed, forming a turbulent flow behind the shock wave.

Efficacy of spotlights and thermal cameras to detect lions Panthera leo and spotted hyenas Crocuta crocuta depends on species and management regime

Accurate abundance estimates can contribute to effective management of large carnivore populations. Lion Panthera leo and spotted hyena Crocuta crocuta populations are frequently estimated at night by eliciting their approach using broadcasted vocalizations. Spotlights are typically used to observe these species on approach but can disturb animals and adversely affect counts. We compared the efficacy of spotlight with red filters and forward looking infrared (FLIR) thermal monocular to enumerate lions and spotted hyenas in Serengeti National Park (SNP; non‐hunted area) and Maswa Game Reserve (MGR; hunted area), Tanzania, during 2015–2017. We established 119 call‐in sites in SNP and 20 in MGR and conducted repeated call‐ins at 1–2 week intervals. During call‐ins we conducted systematic paired counts using both devices. We assessed the influence of device order, species, hunting regime and land cover on species counts. We found that FLIR was more efficacious for counting hyenas in MGR and spotlight for counting lions in SNP. We found evidence for temporary artificial light disturbance in MGR, as counts were higher when FLIR was used as the second device. Habitat type within 200 m of call‐in sites did not influence device performances. Greater spotlight efficacy in SNP is a likely consequence of lower perceived risk and less anthropogenic disturbance compared to MGR. To improve accuracy of counts and subsequent population estimates for lions and spotted hyenas, we recommend consideration of variation in device efficacy, based on species surveyed and management regime.

The Prototype of a Fast Vertical Ionosonde Based on Modern Software-Defined Radio Devices

The description and test results of the prototype of a fast ionosonde for the vertical sounding of the ionosphere, which makes it possible to record ionograms once a second, are presented. Such a high rate of registration of ionograms is required to study the fast processes of redistribution of electron concentration during heating experiments, for registration of fast quasiperiodic and moving ionospheric disturbances in the F, E, and Es layers. The key feature of the presented development is the usage of publicly available radio-electronic components. This provided a significant reduction in the cost of creating the prototype. In the current version, the prototype is based on the software-defined radio (SDR) devices Red Pitaya SDRlab 122-16 and LimeSDR. The test results showed that the quality of the ionograms recorded using the prototype is not worse than the quality of ionograms recorded using the professional CADI ionosonde. The low cost of the components allows providing multi-position registration of ionograms for determination the dynamics of natural and artificial ionospheric disturbances in 3D region of space at a lower expenses rate, as well as to create a network of ionospheric observation points with an increased number of ionosondes.

Fracture mechanism of tight sandstone under high and complex 3-D stress compression: Insights from acoustic emission

Tight sandstone gas (TSG) reservoirs are developed in large buried depths and complex geo-stress field environments. During exploitation, the surrounding rock of a drill well is often damaged or can collapse under artificial engineering disturbances. Understanding the failure mechanism of tight sandstone under high and complex three-dimensional (3-D) stress states is essential for the safe and efficient exploitation of TSG. In this study, using the stress Lode angle ( θ σ ) as a variable, failure experiments of low porosity sandstone specimens under various 3-D stress paths are performed, and the mechanical responses (e.g., stress–strain behavior, strength, fracture pattern, and acoustic emission characteristics) are analyzed. The results show that as θ σ increases, the strength of the specimen as well as the deviatoric stress required its failure decrease linearly, whereas its brittleness increases. The failure of the specimens is primarily due to numerous micro tensile cracks and a few macro shear cracks. θ σ significantly affects the cracking mode during failure. Acoustic emission (AE) parameters show that the failure process can be categorized into three stages within the time-to-failure window, among which Stage 2 (acceleration stage) can be regarded as the precursor stage of the ultimate failure of the specimen. The descriptive statistical results of AE energy show that uniaxial stress, hydrostatic stress, and true triaxial stress compression impose different effects on the damage mode of the specimens. Under the high 3-D stresses, the multiple fracture surfaces formed inside the specimen are intertwined to present several “X”-shaped fracture pairs. These findings facilitate the understanding of the failure mechanism of rock mass surrounding the wellbore, and of significance in stability designing in well trajectory of TSG reservoir actual development. • Stress Lode angles significantly affect cracking mode of tight sandstone. • Uniaxial stress, hydrostatic stress, and true triaxial stress compression impose different effects on damage mode of tight sandstone. • Precursor stage of tight sandstone ultimate failure under complex three-dimensional stress conditions can be identified through acoustic emission signals.

Numerical Investigation into the Transient Behavior of the Spike-Type Rotating Stall for a Transonic Compressor Rotor

In this paper, a numerical investigation into a spike-type rotating stall process is carried out considering a transonic compressor rotor (the NASA Rotor 37). Through solution of the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, the evolution process from an initially circumferentially-symmetric near-stall flow field to a stable stall condition is simulated without adding any artificial disturbance. At the near-stall operating point, periodic fluctuations are present in the overall flow of the rotor. Moreover, the blockage region in the channel periodically shifts from middle span to the tip. This fluctuating condition does not directly lead to stall, while the full-annulus calculation eventually evolves to stall. Interestingly, a kind of “early disturbance” feature appears in the dynamic signals, which propagates forward ahead of the rotor.