The Impact of Midlevel Shear Orientation on the Longevity of and Downdraft Location and Tornado-like Vortex Formation within Simulated Supercells

Despite an increased understanding of environments favorable for tornadic supercells, it is still sometimes unknown why one favorable environment produces many long-tracked tornadic supercells and another seemingly equally-favorable environment produces only short-lived supercells. One relatively unexplored environmental parameter that may differ between such environments is the degree of backing or veering of the midlevel shear vector, especially considering that such variations may not be captured by traditional supercell or tornado forecast parameters. We investigate the impact of the 3-6 km shear vector orientation on simulated supercell evolution by systematically varying it across a suite of idealized simulations. We found that the orientation of the 3-6 km shear vector dictates where precipitation loading is maximized in the storms, and thus alters the storm-relative location of downdrafts and outflow surges. When the shear vector is backed, outflow surges generally occur northwest of an updraft, produce greater convergence beneath the updraft, and do not disrupt inflow, meaning that the storm is more likely to persist and produce more tornado-like vortices (TLVs). When the shear vector is veered, outflow surges generally occur north of an updraft, produce less convergence beneath the updraft, and sometimes undercut it with outflow, causing it to tilt at low levels, sometimes leading to storm dissipation. These storms are shorter lived and thus also produce fewer TLVs. Our simulations indicate that the relative orientation of the 3-6 km shear vector may impact supercell longevity and hence the time period over which tornadoes may form.

Negative potential energy content analysis in cracked rotors whirl response

Appearance of transverse cracks in rotor systems mainly affects their stiffness content. The stability of such systems at steady-state running is usually analyzed by using the Floquet’s theory. Accordingly, the instability zones of rotational speeds are dominated by negative stiffness content in the whirl response in the vicinity of critical rotational speeds. Consequently, an effective stiffness measure is introduced here to analyze the effect of the crack and the unbalance force vector orientation on the intensity of negative potential and stiffness content in the whirl response. The effective stiffness expression is obtained from the direct integration of the equations of motion of the considered cracked rotor system. The proposed effective stiffness measure is applied for steady-state and transient operations using the Jeffcott rotor model with open and breathing crack models. The intensity of negative potential and stiffness content in the numerical and experimental whirl responses is found to be critically depending on the propagation level of the crack and the unbalance force vector orientation. Therefore, this can be proposed as a crack detection tool in cracked rotor systems that either exhibit recurrent passage through the critical rotational speeds or steady-state running.

Negative Potential Energy Content Analysis in Cracked Rotors Whirl Response

Appearance of fatigue cracks in rotor systems mainly affects their stiffness content. The stability of such systems at steady-state running is usually analyzed by using the Floquet’s theory. Accordingly, the instability zones of rotational speeds are dominated by negative stiffness content in the whirl response in the vicinity of critical rotational speeds. Consequently, an effective stiffness measure is introduced here to analyze the effect of the crack and the unbalance force vector orientation on the intensity of negative potential and stiffness content in the whirl response. The effective stiffness expression is obtained from the direct integration of the equations of motion of the considered cracked rotor system. The proposed effective stiffness measure is applied for steady-state and transient operations using the Jeffcott rotor model with open and breathing crack models. The intensity of negative potential and stiffness content in the numerical and experimental whirl responses is found to be critically depending on the propagation level of the crack and the unbalance force vector orientation. Therefore, this can be proposed as a crack detection tool in cracked rotor systems that either exhibit recurrent passage through the critical rotational speeds or steady-state running.

Use of the Lyapunov Functions for Calculating the Locally Optimal Control of a Thrust Vector during Low-Thrust Interorbital Transfer

Abstract— This paper presents a method for locally optimal control of the thrust vector of the electric propulsion system (EPS) for a spacecraft that performs a multiturn interorbital transfer from the initial elliptical orbit into a geostationary orbit (GSO). The control represents the time dependences of the angles that characterize the EPS thrust vector orientation in space. Here, it is assumed that the EPS is always on. The proposed control algorithm belongs to the class of feedback control algorithms and is based on using the Lyapunov functions. Numerical examples are presented, which characterize the operability of the proposed control technique. Considerable attention is paid to the comparison of given solutions with the optimal solutions obtained within the framework of the maximum principle formalism.

ORGANIZATIONAL AND METHODOLOGICAL PROVISIONS OF STRATEGIC AUDIT OF ECONOMIC ACTIVITY OF ENTERPRISES ENTERPRISING ACTIVITIES

In order to form methodical principles of internal strategic audit of activity the development of homogeneous well-known principles of economic audit through adaptation of specific principles is offered. The research was based on the functional-vector orientation of the objects of strategic audit, highlighting two levels of differentiation: 1 - level - types of economic activity of the granite mining enterprise (production and administrative activities); Level 2 - vectors within each of the above activities (strategic environment, development strategy, strategic gaps). This approach will allow covering as much as possible all the important provisions of the strategy for the development of granite mining companies, which will contribute to a more thorough study and support the likelihood of the latter or its refutation. The article forms a descriptive model of specific methodological tools for strategic audit of granite mining enterprises, which provides segmentation of the latter in terms of the 2nd level of differentiation of internal strategic audit of granite mining enterprises. In order to identify the risks of internal strategic audit of granite mining enterprises, their classification is formed. For the final formalization of the developed organizational and methodological provisions of the internal strategic audit of the granite mining enterprise, the structure of the Standard of the internal strategic audit of the granite mining enterprise has been developed. Keywords: audit, granite mining enterprises, strategic audit, granite mining activity.

Voltage controlled Néel vector rotation in zero magnetic field

Multi-functional thin films of boron (B) doped Cr2O3 exhibit voltage-controlled and nonvolatile Néel vector reorientation in the absence of an applied magnetic field, H. Toggling of antiferromagnetic states is demonstrated in prototype device structures at CMOS compatible temperatures between 300 and 400 K. The boundary magnetization associated with the Néel vector orientation serves as state variable which is read via magnetoresistive detection in a Pt Hall bar adjacent to the B:Cr2O3 film. Switching of the Hall voltage between zero and non-zero values implies Néel vector rotation by 90 degrees. Combined magnetometry, spin resolved inverse photoemission, electric transport and scanning probe microscopy measurements reveal B-dependent TN and resistivity enhancement, spin-canting, anisotropy reduction, dynamic polarization hysteresis and gate voltage dependent orientation of boundary magnetization. The combined effect enables H = 0, voltage controlled, nonvolatile Néel vector rotation at high-temperature. Theoretical modeling estimates switching speeds of about 100 ps making B:Cr2O3 a promising multifunctional single-phase material for energy efficient nonvolatile CMOS compatible memory applications.

Reversible hydrogen control of antiferromagnetic anisotropy in α-Fe2O3

Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe2O3 (haematite) – now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe2O3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe2O3.

Grid Side Inverter Control for a Grid Connected Synchronous Generator Based Wind Turbine Experimental Emulator

This paper describes the real time implementation and control of a wind energy conversion chain emulator based on a synchronous generator (SG) using a full-scale power converter configuration. The proposed structure consists of the mechanical coupling of two 1.5 kW machines, a DC motor which emulates the static-dynamic behaviors of a three-blade wind turbine with a horizontal axis including an ideal gearbox, and a synchronous generator that ensures the electromechanical conversion and manages the different operating modes. The aim of the first part in this work is the design and the implementation of the control of the grid side converter in order to control the flow of the produced/consumed active and reactive power (PGSC / QGSC) in both directions between the generator and the grid. An improved experimental grid voltage vector-orientation control algorithm (VOC) is investigated and applied to the grid inverter to control the GSC powers independently and instantly. The control algorithms are implanted in C, using dSPACE DS1104 control board to drive the 6-IGBT’s inverter. The experimental results validate the effectiveness of the proposed control scheme of the GSC.