Presence Of External Pressure Research Articles

Numerical Simulation of the Failure Localization for Rock Massive Under Rock Pressure Conditions During Explosive Mining with Charges of Industrial Explosives

The complication of geomechanical conditions with an increase in the depth of field development requires improved calculations of drilling and blasting parameters based on studies of the patterns of changes in the stress-strain state and fragmentation of the blasted massif with an increase in rock pressure in various directions. This paper presents the results of studies of a section of a rock mass with a bare surface under conditions of flat deformation by the smoothed-particle hydrodynamics (SPH) method when blasting blasthole charges of sparing and crushing action. Regularities of change in time and space of the destruction zones of the massif and stresses with the formation of cracks as a result of the impact of an explosion in the presence of external pressure and in its absence are established. The results of calculations of the influence of physical and mechanical properties on the trigger effect of the destruction of the blasted rock are presented. To obtain preliminary estimates of the growth and branching of crack-like defects in real rocks under plane deformation conditions, numerical experiments were carried out. Diffraction patterns of fracture development on cracks filled with sand are obtained.

The effect of external pressure & magnetic field in star formation: The critical mass model

Theoretical work addressing the role of external pressure with magnetic fields in collapsing molecular clouds is important in building a comprehensive theory of star formation(SF). In many SF studies turbulence, magnetic fields, and self-gravity are described as the key dynamical processes involved in SF. However, the importance of external pressure in collapsing strongly magnetized clouds has not yet been particularly explained. Magnetic fields transport excess angular momentum from the central core while external pressure compresses the cloud. Thus the outflow of angular momentum, and on the other hand, the compression made by external pressure are the cause for matter falling onto the central core from the envelope. Therefore, external pressure facilitates the collapse of gas and the inflow of matter. In this work, we show theoretically how the strong magnetic field is dragged inward by the external pressure during the core collapse and formulate the critical mass of the core in the presence of external pressure.

Does COVID-19 infection increase the risk of pressure injury in critically ill patients?: A narrative review.

Patients with severe COVID-19 may have endothelial dysfunction and a hypercoagulable state that can cause skin damage. In the presence of external pressure on the tissues, the local inflammatory process regulated by inflammatory cytokines can increase and prolong itself, contributing to the formation of pressure injury (PI). PI is defined as localized damage to the skin or underlying tissues. It usually occurs as a result of intense and/or prolonged pressure in combination with shear. The aim of the study is to perform a narrative review on the physiological evidence of increased risk in the development of PI in critically ill patients with COVID-19.In patients with severe COVID-19 a pattern of tissue damage consistent with complement-mediated microvascular injury was found in the lungs and skin of critically ill COVID-19 patients, suggesting sustained systemic activation of complement pathways. Theoretically, the same thrombogenic vascular changes related to COVID-19 that occur in the skin also occur in the underlying tissues, making patients less tolerant to the harmful effects of pressure and shear. Unlike the syndromes typical of acute respiratory illnesses and other pathologies that commonly lead to intensive care unit admission, COVID-19 and systemic viral spread show that local and systemic factors overlap. This fact may be justified by current epidemiological data showing that the prevalence of PI among intensive care unit patients with COVID-19 was 3 times higher than in those without COVID-19. This narrative review presents physiological evidence to suggesting an increased risk of developing PI in critically ill patients with COVID-19.

Doping site induced alteration of incommensurate antiferromagnetic ordering in Fe-doped MnNiGe alloys

The magnetic structure of Fe-doped MnNiGe alloys of nominal compositions ${\mathrm{MnNi}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{Ge}$ and ${\mathrm{Mn}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{NiGe}$ has been explored through detailed neutron powder diffraction (NPD) study in ambient and high-pressure (6 kbar) conditions. Both these alloys crystallize with ${\mathrm{Ni}}_{2}\mathrm{In}$-type hexagonal structure (with $P{6}_{3}/mmc$ space group) at room temperature and undergo a martensitic transition to low-temperature TiNiSi-type orthorhombic structure (with space group $Pnma$). Both the alloys show incommensurate antiferromagnetic ordering at the low-temperature martensitic phase. However, the modulation of the magnetic structures depends strongly on the doping site of Fe. The incommensurate propagation vector $\mathbf{k}$ for ${\mathrm{MnNi}}_{0.75}{\mathrm{Fe}}_{0.25}\mathrm{Ge}$ and ${\mathrm{Mn}}_{0.85}{\mathrm{Fe}}_{0.15}\mathrm{NiGe}$ alloys are found to be (0.1790(1),0,0) and (0.1543(3),0,0), respectively at 1.5 K, and these remain almost unchanged with increasing sample temperature under ambient conditions. The application of the external pressure results in a significant effect on both martensitic transition temperature and low-temperature magnetic structure. The propagation vectors $\mathbf{k}$ for both the alloys show a monotonic decrease with increasing sample temperature in the presence of external pressure. Interestingly, no sign of the magnetically ordered hexagonal austenite phase was observed in any alloys down to the lowest measurement temperature.

Analysis of newly developed fractal-fractional derivative with power law kernel for MHD couple stress fluid in channel embedded in a porous medium

Fractal-fractional derivative is a new class of fractional derivative with power Law kernel which has many applications in real world problems. This operator is used for the first time in such kind of fluid flow. The big advantage of this operator is that one can formulate models describing much better the systems with memory effects. Furthermore, in real world there are many problems where it is necessary to know that how much information the system carries. To explain the memory in a system fractal-fractional derivatives with power law kernel is analyzed in the present work. Keeping these motivation in mind in the present paper new concept of fractal-fractional derivative for the modeling of couple stress fluid (CSF) with the combined effect of heat and mass transfer have been used. The magnetohydrodynamics (MHD) flow of CSF is taken in channel with porous media in the presence of external pressure. The constant motion of the left plate generates the CSF motion while the right plate is kept stationary. The non-dimensional fractal-fractional model of couple stress fluid in Riemann–Liouville sense with power law is solved numerically by using the implicit finite difference method. The obtained solutions for the present problem have been shown through graphs. The effects of various parameters are shown through graphs on velocity, temperature and concentration fields. The velocity, temperature and concentration profiles of the MHD CSF in channel with porous media decreases for the greater values of both fractional parameter alpha and fractal parameter beta respectively. From the graphical results it can be noticed that the fractal-fractional solutions are more general as compared to classical and fractional solutions of CSF motion in channel. Furthermore, the fractal-fractional model of CSF explains good memory effect on the dynamics of couple stress fluid in channel as compared to fractional model of CSF. Finally, the skin friction, Nusselt number and Sherwood number are evaluated and presented in tabular form.

Mathematical modeling determination coefficient of magneto-optical absorption in semiconductors in presence of external pressure and temperature

The calculation of the coefficients of magneto-optical absorption in semiconductors at different temperatures and pressures is carried out. A formula for the temperature dependence of the oscillations of the combined density of states by the Kane dispersion law is obtained. Mathematical modeling has been carried out that determines the magneto-optical absorption coefficient in semiconductors in the presence of external influences. A new method for determining the magneto-optical absorption coefficient in semiconductors in the presence of pressure and temperature is proposed. The correspondence of simulation results with experimental data is shown.

Gravitational instability of non-isothermal filamentary molecular clouds in presence of external pressure

ABSTRACT Filamentary molecular clouds are omnipresent in the cold interstellar medium. Observational pieces of evidence show that the non-isothermal equations of state describe the filaments properties better than the isothermal one. In this paper, we use the logatropic and the polytropic equations of state to study the gravitational instability of the pressure-confined filaments in presence of a uniform axial magnetic field. To fully explore the parameter space, we carry out very large surveys of stability analysis that cover filaments with different radii in various magnetic fields. Our results show that for all the equations of state the instability of thinner filaments is more sensitive to the magnetic field variations than the thicker ones. Moreover, for all the equations of state, an intermediate magnetic field can entirely stabilize the thinner filaments. Albeit for the thicker ones, this effect is suppressed for the magnetic field stronger than B ≃ 70 μG.

Shearing of granular materials in a confined split-bottom Couette cell

Formation of shear bands is one of the most remarkable phenomena in the dynamics of granular matter. Several parameters have been so far identified to influence the behavior of the shear bands. We carried out experiments to investigate the evolution of the shear bands in the split-bottom Couette cell in the presence of confining pressure. We employed the Particle Image Velocimetry (PIV) to characterize the shear band both in the absence and presence of external pressure. Our results show that the location and width of the shear band are affected by both the confining pressure and the filling height. The shear zone evolves towards the middle of the cylinder and expands to a broader region with increasing applied pressure or filling height; also the angular velocity decreases relative to the rotation rate of the bottom disk. Our findings are consistent with prior empirical observations on the formation of wide shear bands at free surfaces.

What is Wrong with the Hungarian Legal System and How to Fix it

Institutions are made up of the interplay of three components: (1) formal rules, (2) actual practices and (3) narratives. However, lawyers in post-socialist countries do not see law through institutionalist lenses, but often nurture a false and simplistic idea of the law: they consider it to be the sum of rules, disregarding often the actual practices of the rules’ addressees and narratives attached to the law (encompassing everything from the raison d’etre and goal of the institution, its symbolism, the public discourse surrounding it, and social attitudes towards the institution). This restricted view makes Hungarian lawyers blind and to a certain extent also defenceless against recent authoritarian tendencies. Institution-building has been a moderately successful feat in Hungary. To put it more pessimistically, it has partially failed since the end of socialism, in particular when it comes to actual practices and narratives. In the Hungarian context, consideration of the problems of institution-building suggests two general conclusions: on the one hand, the lack of unison among the individual elements (rules, practices, narratives) renders institutions less stable and consequently less capable of inducing compliance with the law; on the other, the institutions that have been established have failed to deliver prosperity to the political community. This paper describes the constitution-making of 2010/11 from the perspective of institution-building. This institutionalist view of the law yields two main specific findings: (1) Historical experience shows that besides honest determination, the radical institutional overhaul of a complete legal system can only be successful in the presence of external pressure, the effect of which has unfortunately decreased with Hungary’s accession to the EU. That is, institution-building should go hand-in-hand with effective international and EU obligations undertaken in more sober political moments to guarantee that the political community will not later enter into a self-destructive mode. (2) Taking elements beyond mere rules more consciously into account, such as actual practices and narratives in the realm of legislation, the application of the law and legal training would ideally result in the gradual reinforcement of substantive cultural elements. This, however, requires political action, more precisely the adjustment of formal rules. Since this is not in the interest of the incumbent decision-makers, overcoming the impasse seems unlikely for the time being.

Assessment of the contribution of internal pressure to the structural damage in a hydrogen-charged Type 316L austenitic stainless steel during slow strain rate tensile test

The aim of this study is to provide a quantification of the internal pressure contribution to the SSRT properties of H-charged Type-316L steel tested in air at room temperature. Considering pre-existing penny-shaped voids, the transient pressure build-up has been simulated as well as its impact on the void growth by preforming JIc calculations. Several void distributions (size and spacing) have been considered. Simulations have concluded that there was no impact of the internal pressure on the void growth, regardless the void distribution since the effective pressure was on the order of 1 MPa during the SSRT test. Even if fast hydrogen diffusion related to dislocation pipe-diffusion has been assessed as a conservative case, the impact on void growth was barely imperceptible (or significantly low). The effect of internal pressure has been experimentally verified via the following conditions: (I) non-charged in vacuum; (II) H-charged in vacuum; (III) H-charged in 115-MPa nitrogen gas; (IV) non-charged in 115-MPa nitrogen gas. As a result, the relative reduction in area (RRA) was 0.84 for (II), 0.88 for (III), and 1.01 for (IV), respectively. The difference in void morphology of the H-charged specimens did not depend on the presence of external pressure. These experimental results demonstrate that the internal pressure had no effect on the tensile ductility and void morphology of the H-charged specimen.

QUANTUM-MECHANICAL STUDY OF FRICTION IN NANOCONTACTS

The quantum-mechanical approach (the density functional theory and the pseudopotential method) is used to study the friction in the aluminum–aluminum, aluminum–tungsten, and tungsten–tungsten nanopairs on the atomic level in the presence of external pressure. Nanopairs were constructed from crystalline nanoslabs and crystalline nanorods of rectangular cross section. The nanoslabs had infinite periodic structures in the X and Y directions; the nanorods were periodic in the Y direction. The process of friction was studied by reducing a rod and a slab to an equilibrium contact with subsequent step-by-step shift of the rod relative to the slab along the X direction. The rod was located above the slab (in the Z direction). The total energy of the system was calculated on each step. The friction force was calculated as a ratio of the change in the total energy to the value of the rod shift step. The pressure force was applied to the rod in the Z direction. The coefficient of friction was calculated as a ratio of the friction force to the pressure force. Observation of the behavior of atoms showed that for all the nanopairs studied the process of friction is accompanied by the processes of deformation and destruction. Both components of a nanopair are subjected to deformation, whereas destruction is observed only in the nanorods. Aluminum rods are subject to the maximum deformations and destructions in both aluminum–aluminum and aluminum–tungsten pairs. The tungsten rods are not destroyed; deformations in them and in tungsten slabs are minimal. The friction coefficients in the aluminum–aluminum pairs decrease with increasing pressure, and they increase in the aluminum–tungsten and tungsten–tungsten pairs.

HOW GALACTIC ENVIRONMENT REGULATES STAR FORMATION

ABSTRACT In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.

Finite element analysis of UOE manufacturing process and its effect on mechanical behavior of offshore pipes

• We simulate the UOE forming process, using finite elements and an advanced plasticity model. • We present results for geometrical imperfections and anisotropy induced by the UOE forming process. • We investigate the effect of cold-forming on the performance of UOE pipes under external pressure, tension and bending. • We compare the structural performance of UOE pipes with the performance of seamless pipes. • We examine the efficiency of a simplified methodology for determining the structural capacity of a UOE pipe. Thick-walled steel pipes during their installation in deep-water are subjected to a combination of loading in terms of external pressure, bending and axial tension, which may trigger structural instability due to excessive pipe ovalization. The resistance of offshore pipes against this instability depends on imperfections and residual stresses due to the line pipe manufacturing process. The present study examines the effect of UOE line pipe manufacturing process on the structural response and resistance of offshore pipes during the installation process using advanced finite element simulation tools. The cold bending induced by the UOE process is simulated rigorously and, subsequently, the application of external pressure and structural loading (bending or axial force) is modeled, until structural instability is reached. A parametric analysis is conducted, focusing on the effects of line pipe expansion on the structural capacity of the pipe. The results show that there exists an optimum expansion at which the highest pressure capacity is achieved. The effect of the axial tension on the pressure capacity of the pipe is examined as well. The influence of the line pipe expansion on bending capacity in the presence of external pressure is also identified. Finally, a simplified methodology is employed, accounting for the material anisotropy induced by the manufacturing process, capable of determining the structural capacity of a UOE pipe in a simple and efficient manner with good accuracy, using more conventional modeling tools.

Interactive Buckling Tests of Externally Pressurized Stiffened Bent Pipelines

The paper reports an experimental study on the collapse of long uniformly pressurized ring-stiffened bent pipelines. Bending in the presence of external pressure is experienced by pipelines during their installation and operation. The buckling aptitude of shells is dependent on two leading geometric ratios, i.e. the length to radius and radius to thickness. In this paper, four different ring-stiffened steel pipeline specimens were tested to collapse. The evolution of the specimens behavior that has been recorded in the presence of a uniform external pressure is outlined. A thin-walled pipeline is sensitive to buckling phenomena when it experiences locally a compressive stress. It is often considered that its behavior under bending is rather similar to pure compression, but very few are the experimental investigations that precise the real behavior of it. A comparison of experimental data to empirical formulae and design recommendations is finally achieved. Consequently, it has been found that with using ring stiffeners the structure behavior against the combination of loads is improved in all loading paths. Also it has been found that buckle propagation in all manners occurs suddenly and dynamically and the amount of initial bending moment is not serious in defining the number of buckling modes. Also, the considerable effects of a longitudinal spot weld line on the buckling strength and mode shapes are verified.

Numerical tool to model collapse of polymeric liners in pipelines

Polymeric liners are widely used in the gas and oil transportation industry. They provide improved corrosion resistance to metallic tubes and they also are used in rehabilitation of deteriorated pipelines. Oil derived gases permeate across the liner wall; which during rapid depressurization produce external pressure that in many cases lead to buckling collapse of the liner. A number of simple models to calculate critical pressure for buckling collapse are available, but these models do not account for surface or geometrical defects that are usually present in liners under service conditions. The non-linear characteristics of the problem generate convergence issues that make it difficult for classical FEM to reproduce the actual behavior of experimental curves. This paper is concerned with simulation of the buckling collapse of HDPE liners. Three ways to raise and resolve the issue of liner collapse have been used in this study. Two of them, the General Static Model and the Riks Static Method have been used before for similar simulations. Innovatively in this work, a non-conventional approach to finite element analysis (FEA) which makes use of hydrostatic elements has been tried for the first time. This approach has the inherent advantage of allowing the use of time-dependent material constitutive models. Three types of constitutive models were considered to model HDPE stress–strain behavior: elastic, ideal elastic–plastic and an elastic-strain hardening plastic model that takes into account the complete deformation curve determined from uniaxial tensile experiments. Validation of the simulations are made by comparing the results with analytical, or semi-analytical models and with results from previous publications. The collapse of polymeric liners in the presence of external pressure is adequately reproduced by the finite elements method (FEM) models developed.

Combined effect of hydrostatic pressure and magnetic field on the martensitic transition in the Ni49CuMn34In16alloy

The combined effect of hydrostatic pressure and magnetic field on the martensitic transition in the Ni${}_{49}$CuMn${}_{34}$In${}_{16}$ alloy is investigated through a study of electrical resistivity. It is shown that a combination of an external pressure of 2 kbar and a magnetic field of 20 kOe can produce a magnetoresistance (MR) of \ensuremath{\sim}24% in the Ni${}_{49}$CuMn${}_{34}$In${}_{16}$ alloy at the ambient temperature of 296.5 K. The volume change in the alloy across the austenite-to-martensite phase transition is estimated to be \ensuremath{\sim}0.4%, which shows the potential of the alloy in near room-temperature actuator applications. The phase diagrams depicting the detailed field and pressure dependence of the characteristic temperatures associated with austenite-martensite phase transition are constructed from the experimental data. The results indicate that the strain fields produced in the Ni${}_{49}$CuMn${}_{34}$In${}_{16}$ alloy are different when the alloy is cooled under externally applied pressure from what they are when the alloy is cooled in ambient pressure. These changed strain fields appear to influence the scattering of conduction electrons and the dynamics of the austenite-to-martensite phase transition in the alloy in the presence of external pressure. The present results may be useful for finding a guideline for generating chemical pressure (obtained through the partial substitution of atoms in the system) leading to newer NiMnIn alloys with room temperature functional properties.

Coarse-graining microscopic strains in a harmonic, two-dimensional solid: Elasticity, nonlocal susceptibilities, and nonaffine noise

In soft matter systems the local displacement field can be accessed directly by video microscopy enabling one to compute local strain fields and hence the elastic moduli in these systems using a coarse-graining procedure. We study this process in detail for a simple triangular, harmonic lattice in two dimensions. Coarse-graining local strains obtained from particle configurations in a Monte Carlo simulation generates nontrivial, nonlocal strain correlations (susceptibilities). These may be understood within a generalized, Landau-type elastic Hamiltonian containing up to quartic terms in strain gradients [K. Franzrahe, Phys. Rev. E 78, 026106 (2008)10.1103/PhysRevE.78.026106]. In order to demonstrate the versatility of the analysis of these correlations and to make our calculations directly relevant for experiments on colloidal solids, we systematically study various parameters such as the choice of statistical ensemble, presence of external pressure and boundary conditions. Crucially, we show that special care needs to be taken for an accurate application of our results to actual experiments, where the analyzed area is embedded within a larger system, to which it is mechanically coupled. Apart from the smooth, affine strain fields, the coarse-graining procedure also gives rise to a noise field (χ) made up of nonaffine displacements. Several properties of χ may be rationalized for the harmonic solid using a simple "cell model" calculation. Furthermore the scaling behavior of the probability distribution of the noise field (χ) is studied. We find that for any inverse temperature β, spring constant f, density ρ and coarse-graining length Λ the probability distribution can be obtained from a master curve of the scaling variable X=χβf/ρΛ(2).

Effect of pressure on the phase diagrams and dynamic properties of easy-plane antiferromagnets

Phase diagrams and dynamic properties of strongly anisotropic, easy-plane antiferromagnets in the presence of external pressure are studied. It is demonstrated that the phase with tensorial order parameter is possible in the system. Spectra of bound magnetoelastic waves are studied in the vicinity of the phase transition points.

Stability of pressurized long inelastic cylinders under radial transverse loads

In the present paper, the structural capacity of relatively thick inelastic steel cylindrical tubes under external or internal pressure and concentrated radial loads is investigated, through a rigorous finite element analysis, as well as using a simplified analytical model. For zero pressure, the tubes exhibit inelastic cross-sectional deformation and are capable of dissipating a significant amount of plastic energy. The energy absorption capacity, as well as the ultimate transverse load, are reduced in the presence of external pressure. The effects of internal pressure are also examined. Results are reported in the form of load-deflection curves for different pressure levels. In addition, collapse envelops showing the interaction of pressure versus radial transverse loads are presented. The conclusions of this study are important for the structural integrity of cylindrical steel tubulars for pipeline and other offshore applications.

Bifurcation Buckling Versus Limit Load Instabilities of Elastic-Plastic Tubes Under Bending and External Pressure

Abstract Commonly used procedures for installing offshore pipelines can induce substantial bending to the line in the presence of external pressure. These combined loads can lead to catastrophic collapse of the structure. For typically used steels and higher diameter-to-thickness ratios (D/t), bending is limited by a bifurcation type of instability; for lower D/t values, the structures exhibit limit load types of instabilities. Similar distinctions can be made for bending in the presence of external pressure. Previous work (Corona and Kyriakides, 1988) addressed primarily the limit load types of instabilities. In this paper, this analysis is extended to include bifurcation instabilities. The predictions from the two types of analyses are critically compared to experimental results and recommendations about the regime of applicability of each are made.