A Method for Quantitative Evaluation of Seismic Stability of Loess Slope Based on the Shaking Table Model Test

The large-scale shaking table model test, which can directly reproduce the process of slope instability and failure, is an important technical means for the prediction and evaluation of slope seismic stability. However, up to now, the systematic slope stability evaluation method based on the shaking table slope model test has not been established, which limits the application of the expensive shaking table model test in slope seismic design. Therefore, the slope stability evaluation method based on the model test needs to be developed and innovated. In this research, through three loess slope model tests with different rainfall, according to the change law of the peak value of transfer function spectrum, combined with the macrodestructive characteristics of the slope model, an accurate calculation method of the critical instability acceleration of the slope is proposed. Based on the behavior similarity theory, for the shaking table model test of slope whose soil cohesion cannot meet the similarity ratio, the reduction method of applying the critical instability acceleration obtained from the model test to prototype slope is proposed. Based on first-order natural frequency and damping ratio extracted from the TF spectrum curve, a calculation method for the stability factor Fs of loess slope based on the shaking table model test is proposed, and the stability factors of loess slope under the action of different seismic ground motion would be quantitatively calculated. The above methods provide another effective way for qualitative prediction and evaluation of seismic stability of loess slope.

Nonlinear dynamic analysis of multiple grooved water-lubricated journal bearings using attenuation rate interpolation method

Purpose The stringent requirements for environmental protection have induced the extensive applications of water-lubricated journal bearings in marine propulsion. The nonlinear dynamic analysis of multiple grooved water-lubricated bearings (MGWJBs) has not been fully covered so far in the literature. This study aims to conduct the nonlinear dynamic analysis of the instability for MGWJBs. Design/methodology/approach An attenuation rate interpolation method is proposed for the determination of the critical instability speed. Based on a structured mesh movement algorithm, the transient hydrodynamic force model of MGWJBs is set up. Furthermore, the parameters’ analysis of nonlinear instability for MGWJBs is conducted. The minimum water film thickness, side leakage, friction torque and power loss of friction are fully analyzed. Findings With the increase of speed, the journal orbits come across the steady state equilibrium motion, sub-harmonic motion and limit circle motion successively. At the limit circle motion stage, the orbits are much larger than that of steady state equilibrium and sub-harmonic motion. The critical instability speed increases when the spiral angle decreases or the groove angle increases. The minimum water film thickness peak is at the rotor speed of 4,000 r/min for the MGWJB with Sa = 0°. As rotor speed increases, the side leakage decreases slightly while the friction torque and the power loss of friction increase gradually. Originality/value Present research provides a beneficial reference for the dynamic mechanism analysis and design of MGWJBs.

Research on Arch Model and Numerical Simulation of Critical Water and Sand Inrush in Coal Mine near Unconsolidated Layers

With the continuous increase of the upper limit of coal mining, in mining areas near unconsolidated layers, water and sand inrush disasters occur from time to time, seriously threatening the safety of mine production. In this paper, the process of water and sand inrush accidents induced by mining near unconsolidated layers is analyzed using mechanical analysis and numerical simulation methods, based on the principle of silo unloading and arching and combined with actual water and sand inrush characteristics; the critical water and sand inrush arching mechanism is explained. The paper also proposed and established three critical arching mechanics models (interlocking arch, bonded arch, and transition arch), deduced the mathematical expression of interlocking arch and transition arch, and obtained the critical instability conditions of the arch and its influencing factors. The research results have guiding significance for the occurrence of water and sand inrush disasters and the judgment of the degree of damage in mining near unconsolidated layers.

Critical instability at moving keyhole tip generates porosity in laser melting

Laser powder bed fusion is a dominant metal 3D printing technology. However, porosity defects remain a challenge for fatigue-sensitive applications. Some porosity is associated with deep and narrow vapor depressions called keyholes, which occur under high-power, low–scan speed laser melting conditions. High-speed x-ray imaging enables operando observation of the detailed formation process of pores in Ti-6Al-4V caused by a critical instability at the keyhole tip. We found that the boundary of the keyhole porosity regime in power-velocity space is sharp and smooth, varying only slightly between the bare plate and powder bed. The critical keyhole instability generates acoustic waves in the melt pool that provide additional yet vital driving force for the pores near the keyhole tip to move away from the keyhole and become trapped as defects.

Thermosolutal Convection with a Navier–Stokes–Voigt Fluid

We present a model for convection in a Navier–Stokes–Voigt fluid when the layer is heated from below and simultaneously salted from below, the thermosolutal convection problem. Instability thresholds are calculated for thermal convection with a dissolved salt field in a complex viscoelastic fluid of Navier–Stokes–Voigt type. The Kelvin–Voigt parameter is seen to play a very important role in acting as a stabilizing agent when the convection is of oscillatory type. The quantitative size of this effect is displayed. Nonlinear stability is also discussed, and it is briefly indicated how the global nonlinear stability limit may be increased, although there still remains a region of potential sub-critical instability, especially when the Kelvin–Voigt parameter increases.

ІДЕНТИФІКАЦІЯ КАТЕГОРІЇ «НАЦІОНАЛЬНІ ДІЛОВІ КУЛЬТУРИ» ЯК ВИХІДНА ОСНОВА МІЖНАРОДНОГО ПІДПРИЄМНИЦТВА

Formulation of the problem. The dramatic aggravation of the situation in world commodity, financial and stock markets leads to critical instability of international business, which confirms the need to study the problematics of national business cultures. The aim of the research is to identify the pivotal category - "national business cultures" and to disclose its content. The subject of the research is the original epistemological basis of analysis and the defining phenomena that reveal the content of the category - "national business cultures". The methods of the research: unity of analysis and synthesis, ascent from concrete to abstract, method of comparative analysis. The hypothesis of the research - national business cultures embody a set of phenomena and processes that are multidisciplinary in content, with reproducibility in time and space with some modification in specific conditions. The statement of basic materials: on the basis of the analysis of the works of the founders of the theory of national business cultures (G. Hofstede, F. Trompenaars; R. Lewis; C. Rapaille) and their followers the essence of the components of the study of national business cultures: cross -cultural management, cross -cultural communications and cross -cultural marketing. The epistemologi cal postulates that are necessary for the categorical definition of the "national business cultures" concept are qualified: multifacetedness; determinants of the formation of national business cultures; the longevity and reproduction of national business cultures; property of identification and classification of differences of national business cultures; modification of forms of manifestations of national business cultures within specific time. The originality and practical significance of the research lays in clear authentication of the "national business cultures" category and identification of the defining components of cross-cultural entrepreneurship. Conclusions and perspectives of further research: national business cultures are a complex interdisciplinary phenomenon that focuses on a set of essential features not only of economic content but also of the institutional environment. The primary tasks of further development are to conduct applied empirical studies on the evaluation of Ukraine's national business culture.

Hydro-meteorological monitoring activities in Portofino Natural Park (Italy) as demonstrator of the H2020 RECONECT project: preliminary results

<p>The European Horizon RECONECT Project (Regenerating ECOsystems with Nature-based solutions for hydro-meteorological risk rEduCTion) aims to contribute to a European reference framework on NBS by demonstrating, upscaling and spreading large-scale NBS in rural and natural areas.</p><p>The Italian RECONECT demonstrator is set in the Portofino Natural Park, which represents a unique natural landscape element with high ecologic, social, and economic (touristic) value and severely endangered by hydro-meteorological hazards.</p><p>The Portofino Promontory is historically affected by geo-hydrological events. They can produce natural instability processes related to the interaction between meteorological phenomena and the geological environment, which can potentially cause loss of the exposed elements at risk, as happened in the past. The more frequent processes are: shallow landslides and flash floods, sea-storm surges, rockfalls and mud-debris flows. Often, different processes can occur simultaneously during an intense meteorological event, interacting each other and causing an avalanche effect.</p><p>This research introduces the NBS interventions proposed in the RECONECT case study of Portofino over two pilot catchments (San Fruttuoso and Paraggi basins), visited by thousands of tourists all over the year. The project envisages the setting up of meteorological-hydrological stations for studying and monitoring geomorphological processes.</p><p>In particular, RECONECT project foresees the selection, installation and operation of hydro-meteorological instruments that include three weather stations, two hydrometers and two cameras to monitor small and very steep catchments.</p><p>Monitoring activity include the use of remote sensing survey LIDAR data, orthophotography and infrared aerial photography, whose acquisition has been carried out in January 2020.</p><p>Remote sensing and monitoring data are used to quantitatively assess the morphological features and processes, allowing to: a) evaluate the critical-instability areas along the slope and channels and to support the reconstruction of dry stone walls of the widespread terraced areas; b) evaluate the potentially more susceptible source areas of mud-debris flows and the identification of thresholds in meteorological conditions.</p><p>In relation to future projections of natural, social and economic impacts of climate change, NBS represent a relevant mitigation and adaptation strategy for the Portofino case study, which may be upscaled at national and international level.</p>

Acoustic Emission investigation for avalanche formation and release: A case study of dry-slab avalanche event in Great Himalaya

Non-invasive monitoring of avalanche formation and release processes, through the use of Acoustic Emission (AE) technique, has been a research challenge since long time. In present investigation AE technique is implemented to monitor the avalanche formation and release processes through a case study of a natural avalanche event reported in Great Himalaya. The specialized AE sensor-arrestor arrays, established over the avalanche starting zone, in conjunction to a high speed multichannel AE acquisition system have successfully recorded the avalanche event passed through the course of instability development followed by release of avalanche. A new method is devised to compute the AE based instability index, and same has been applied to quantify the instability levels of a snowpack. The prominent AE parameters and instability indices are analyzed for different window scales with respect to different AE sensors. The effect of nivological and meteorological conditions and pit analyses collected during the avalanche formation process is also discussed. The critical instability was triggered possibly due to the excessive loading (during snowfall) of an unstable snowpack consisting of persistent weak layers which led to the avalanche release. An abnormal and abrupt increase in the AE activity was observed prior to the avalanche release. The increasing trends in instability indices have shown a good correlation to the avalanche formation and a sharp jump in instability index is attributed to a particular transition occurring across two different instability states of the snowpack. Thus, five conceptual states of snowpack are identified for instability evolution corresponding to four different transitions during avalanche formation and release processes.

Analysis on the Aeroelastic Stability of Open Cylindrical Shells in Subsonic Airflow Using the Theoretical and Two-way CFD/CSD Coupled Methods

The aeroelastic stability of an open cylindrical shell in subsonic airflow is analyzed. The equation of motion of the open cylindrical shell whose one surface is subjected to the subsonic airflow is established based on the Donnell shell theory and transformed into ordinary differential equations using Galerkin’s method. The linear potential flow theory is applied to derive the aerodynamic pressure. The natural frequencies of the aeroelastic system are obtained, from which the flow velocity for the open cylindrical shell under instability can be calculated. The effects of the material and geometric parameters on the critical instability velocity are discussed. Furthermore, the open cylindrical shell is modelled using the finite element software ANSYS. The time domain responses of the structure in subsonic airflow are calculated using the two-way CFD/CSD (computational fluid-structure dynamics) coupled method. From the results, it can be seen that with the increase of the thickness and elastic modulus of the shell, the critical instability velocity increases also. The open cylindrical shell with a smaller radius shows better aeroelastic properties than that with a larger radius. The time domain responses obtained by the CFD/CSD method are compared with those calculated by the theoretical method, and the results of these two methods have a good agreement with each othe