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1
Platek, Tadeusz. "Analysis of Ripple Current in the Capacitors of Active Power Filters." Energies 12, no. 23 (November 25, 2019): 4493. http://dx.doi.org/10.3390/en12234493.
Повний текст джерелаАнотація:
This article provides formulae to determine the root mean square (rms) value of a capacitor current in an inductive-capacitive-inductive (LCL) filter used in a parallel active power filter (PAPF) circuit. The article presents an analysis of three components of the capacitor current: a component forced by the usually distorted voltage of the grid; a component forced by the nonlinear load current harmonics and harmonics in the output current of the PAPF that compensates them (a novel aspect presented in this document); and a component forced by the inverters of the PAPF containing carrier and sideband harmonics. The article also presents formulae for determining the rms value of current harmonics in dc-link capacitors forced by the ripple of the ac output current without load of the filter inverters (also novel to this document). The results of the analysis have been confirmed by simulation and experimental research of a commercial active filter consisting of two parallel interleaved voltage inverters. Elements of the LCL filter of the PAPF have been selected according to dependencies available in scientific and technical literature. In addition, the formulae presented in the article are used to verify the correctness of selection of capacitors from the point of view of their catalogue acceptable rms value of capacitor current.
2
Santo, H., P. H. Taylor, C. H. K. Williamson, and Y. S. Choo. "The relative-velocity version of the Morison equation for obstacle arrays in combined steady, low and high frequency motion." Journal of Fluid Mechanics 842 (March 7, 2018): 188–214. http://dx.doi.org/10.1017/jfm.2018.130.
Повний текст джерелаАнотація:
This paper revisits the problem of forces on obstacle arrays in combined waves, an in-line steady current and structural dynamic motions. The intended application is the design and re-assessment of dynamically responding offshore platforms. Planar grids of perforated plates are moved in forced motion on three scales through otherwise stationary water. A new analytical wave–current–structure blockage model is developed by building on the existing wave–current blockage model presented by Santo et al. (J. Fluid Mech., vol. 739, 2014b, pp. 143–178) using a similar set of experiments but with forced motion on two scales. The new model, which is an improved Morison relative-velocity formulation, is tested against the experimental data for a range of structural to wave oscillation frequency ratios, $f_{s}/f_{w}=2$, 2.5 and 3. For relatively small current speed ($u_{c}$) and oscillatory structural velocity ($u_{s}$) compared with the oscillatory wave velocity ($u_{w}$), the drag force time history on grids is well approximated by a summation of the wave drag and the current drag components independently, without a $u_{w}\times u_{c}$ cross-term, consistent with the previous model. The wave drag component contains an additional $u_{s}$ contribution, while the current drag component may or may not contain an additional $u_{s}$ contribution depending on $f_{s}/f_{w}$. The measured drag force is observed to be asymmetric in time due to biasing from the mean flow. This is supported by numerical simulation using a porous block as a numerical model of the grids, although the simulated force asymmetry is weaker. All these effects can be sufficiently accounted for in the analytical model. The new model is shown to fit the variation of the experimental forces and force harmonics in time well for a wide range of cases, requiring only calibration of the Morison type drag and inertia coefficients. In contrast, the industry-standard version of the Morison relative-velocity formulation cannot reproduce the variation of the measured force in time, so present practice should be regarded as inadequate for combined steady, low frequency and high frequency motion acting on obstacle arrays.
3
Ovcharenko, N. I., and R. V. Shitov. "Methods for the fast determination of forced component amplitude of a short-circuit current." Russian Electrical Engineering 79, no. 5 (May 2008): 254–57. http://dx.doi.org/10.3103/s1068371208050064.
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Huang, Bing Hua, Guang Song Yang, Ya Fen Wei, and Ying Huang. "Harmonic Analysis Method Based on Power Balance." Applied Mechanics and Materials 325-326 (June 2013): 1508–14. http://dx.doi.org/10.4028/www.scientific.net/amm.325-326.1508.
Повний текст джерелаАнотація:
Nonlinear differential equations are sometimes found by using harmonic balance principle. If it is based on the complex power balance theory, some much more correct and rational results can be obtained. Non-autonomous circuits sometimes include two components, the forced and the self-excited oscillation, they must satisfy respectively the balancing condition of complex power. When we study the nonautonomous circuit, two notable questions should be considered. On the one hand ,the existence of self-excited oscillation of the circuit which contains the dissipative elements depends on whether or not active power can maintain balance. The existence is closely related to the amplitude of excited current source. When the current source is strong enough, the original self-excited oscillation will thus disappear, leaving only a forced component. On the other hand, the existence of the self-oscillation of the lossless circuit which does not contain the dissipative elements is independent from the current amplitude of the excited source. The forced and self-excited oscillation components can simultaneously coexist unconditionally. chaos can easy be produced by the nonlinear coupling of the two harmonic components. The intrinsic attributes of the chaos can be sufficiently revealed with the help of this kind of lossless circuits.
5
Castro Fo, Belmiro Mendes de. "Wind driven currents in the channel of São Sebastião: winter, 1979." Boletim do Instituto Oceanográfico 38, no. 2 (1990): 111–32. http://dx.doi.org/10.1590/s0373-55241990000200002.
Повний текст джерелаАнотація:
Simultaneous 40 h low-passed wind, current and sea level data in the Channel of São Sebastião (CSS) and atmospheric pressure and sea level data in the South Brazil Bight (SBB) during winter of 1979 were analysed and compared. Currents in the CSS were predominantly northeastward, associated with frontal southerly winds. Current reversals occurred between meteorological disturbance passages. There were significant correlation between alongchannel components of wind and current, with a time lag of 12-18 h, wind leading; and between alongchannel component of current and sea level, with a time lag of 6-12 h, current leading. Most of the variance in the CSS series is concentrated in two frequency bands: 11-16 d and 3 d. SBB series also show high variance in those two bands. Coherences in those two bands show significant values when calculated between alongchannel components of wind and current, and sea level, in the CSS. Those three last signals were almost in phase in the 11-16 d band; and there was a lead of 16 h (25 h) by wind over current (sea level) in the 3 d band. There are several indications that in die subtidal band currents in the CSS are not totally locally forced.
6
Meiss, R. A. "Stiffness of active smooth muscle during forced elongation." American Journal of Physiology-Cell Physiology 253, no. 3 (September 1, 1987): C484—C493. http://dx.doi.org/10.1152/ajpcell.1987.253.3.c484.
Повний текст джерелаАнотація:
The stiffness of isometrically contracting mesotubarium superius and ovarian ligament smooth muscle from estrous female rabbits was measured continuously by using sinusoidal length perturbations (at 80 Hz, less than 15 microns peak to peak). Muscles were stimulated with alternating current fields, and all records were digitized using a microcomputer system. Phase-angle data were used to resolve computed stiffness into elastic and viscous components. Stiffness measurements were continued during long ramp-type stretches (up to 25% of muscle length) delivered as soon as force was maximal. To use the period of isometric tension development as a standard for comparison, the expected stiffness was computed during the long stretch. Stiffness was reduced in approximate proportion to the ramp stretch rate, and the reduction was confined largely to the elastic component. Cooling the muscle increased the stiffness deviation at a given stretch rate. It is proposed that the long stretch detaches cross bridges that can reattach to new sites as myofilaments shear past one another. At higher shearing speeds, less time is available for reattachment and stiffness is further reduced.
7
Mingalev, Oleg, Pavel Setsko, Mikhail Melnik, Igor Mingalev, Helmi Malova, and Alexey Merzlyi. "Force balance in current sheets in collisionless plasma." Solar-Terrestrial Physics 7, no. 2 (June 30, 2021): 11–21. http://dx.doi.org/10.12737/stp-72202102.
Повний текст джерелаАнотація:
In this paper, we derive a divergent form of the force balance equation for collisionless plasma in the quasineutrality approximation, in which the electric field and current density are excluded. For a stationary spatially one-dimensional current sheet with a constant normal component of the magnetic field and magnetized electrons, the general form of the force balance equation has been obtained for the first time in the form of a conservation law. An equation in this form is necessary for the correct formulation of boundary conditions when modeling asymmetric current sheets, as well as for the control of the stationarity of the numerical solution obtained in the model. Furthermore, the fulfillment of this equation is considered for two types of stationary configurations of a thin current sheet, which are obtained using a numerical model. The derived equation makes it possible to develop models of asymmetric current sheets, in particular current sheets on the magnetopause flanks in the magnetotail.
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Kim, Tae-in, Robert T. Hudspeth, and W. Sulisz. "CIRCULATION KINEMATICS IN NONLINEAR LABORATORY WAVES." Coastal Engineering Proceedings 1, no. 20 (January 29, 1986): 30. http://dx.doi.org/10.9753/icce.v20.30.
Повний текст джерелаАнотація:
A weakly nonlinear solution is presented for the two-dimensional wave kinematics forced by a generic wavemaker of variable-draft. The solution is valid for both piston and hinged wavemakers of variable draft that may be double articulated. The second-order propagating waves generated by a planar wave board are composed of two components; viz., a Stokes second-order wave and a second-harmonic wave forced by the wavemaker which travels at a different speed. A previously neglected time-independent solution that is required to satisfy a kinematic boundary condition on the wavemaker as well as a mixed boundary condition on the free surface is included for the first time. A component of the time-independent solution is found to accurately estimate the mean return current (correct to second-order) in a closed wave flume. This mean return current is usually estimated from kinematic considerations by a conservation of mass principle.
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Gning, Paul, Vincent Lanfranchi, and Nicolas Dauchez. "Influence of the multi-component electrical feed of air-core industrial reactors on their sound radiation." Acta Acustica 4, no. 4 (2020): 14. http://dx.doi.org/10.1051/aacus/2020015.
Повний текст джерелаАнотація:
High voltage devices such as dry-type air-core reactors are subjected to environmental noise standards. Their excitation is due to Lorentz forces originated from the magnetic field, created by the coil itself, combined with the feed current. The objective of this paper is to show how spectral components present in the supply current of industrial dry-type air-core reactors is likely to produce a significant acoustic radiation. First, the multi-component distribution of the Lorentz forces is established. Then, the multi-physics computation process allowing to determine the acoustic pressure induced by each force component is presented. Finally, two industrial reactors are studied: a single and a multi-layer coil. It is pointed out that significant acoustic emergence can be induced by the interaction between small current spectral components with the fundamental or with each other.
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Ivanov, I. A., D. R. Lyubarsky, A. A. Rubtsov, and E. V. Tuzlukova. "An Method for Determining the Amplitude of the Forced Periodic Component of the Transient Short-Circuit Current." Russian Electrical Engineering 92, no. 9 (September 2021): 529–34. http://dx.doi.org/10.3103/s106837122109008x.
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11
Fukutani, Atsuki, and Walter Herzog. "Current Understanding of Residual Force Enhancement: Cross-Bridge Component and Non-Cross-Bridge Component." International Journal of Molecular Sciences 20, no. 21 (November 4, 2019): 5479. http://dx.doi.org/10.3390/ijms20215479.
Повний текст джерелаАнотація:
Muscle contraction is initiated by the interaction between actin and myosin filaments. The sliding of actin filaments relative to myosin filaments is produced by cross-bridge cycling, which is governed by the theoretical framework of the cross-bridge theory. The cross-bridge theory explains well a number of mechanical responses, such as isometric and concentric contractions. However, some experimental observations cannot be explained with the cross-bridge theory; for example, the increased isometric force after eccentric contractions. The steady-state, isometric force after an eccentric contraction is greater than that attained in a purely isometric contraction at the same muscle length and same activation level. This well-acknowledged and universally observed property is referred to as residual force enhancement (rFE). Since rFE cannot be explained by the cross-bridge theory, alternative mechanisms for explaining this force response have been proposed. In this review, we introduce the basic concepts of sarcomere length non-uniformity and titin elasticity, which are the primary candidates that have been used for explaining rFE, and discuss unresolved problems regarding these mechanisms, and how to proceed with future experiments in this exciting area of research.
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Friocourt, Yann, Bruno Blanke, Sybren Drijfhout, and Sabrina Speich. "On the Dynamics of the Slope Current System along the West European Margin. Part II: Analytical Calculations and Numerical Simulations with Seasonal Forcing." Journal of Physical Oceanography 38, no. 12 (December 1, 2008): 2619–38. http://dx.doi.org/10.1175/2008jpo3745.1.
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Abstract The seasonality of the baroclinic slope current system along the western European margin in the Bay of Biscay and along the northern Iberian Peninsula is investigated in a joint analysis of an analytical model and numerical simulations with various forcings. A distinction is made between local winds and basin-scale winds, in which the effect of the latter is indirectly apparent through the basin-scale density gradients. The slope currents are mainly forced by the large-scale structure of the density field. The analysis indicates significant differences in the behavior of the uppermost slope current and of the deeper currents. At all depths, seasonal variations in the large-scale density structure of the ocean alter the strength of the slope currents but are not able to cause robust, long-lasting reversals. Reversals of the uppermost slope current appear to be caused by changes in the alongshore component of the local wind stress, provided that the opposing forcing from the density structure is weak enough. However, the deeper slope currents are not very much affected by the wind stress, so that flow reversals can be explained neither by the wind nor by seasonal changes in the density structure. A numerical simulation suggests that the reversals of the deeper slope currents are at least partly forced by seasonal changes in the flow upstream of the slope current system. The authors demonstrate that the larger part of these seasonal changes is associated with annual baroclinic Rossby waves caused by the seasonal cycle of the large-scale wind stress over the whole basin.
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Tripathi, Saurabh Mani, and Prakash Ji Barnawal. "Design and Control of a STATCOM for Non-Linear Load Compensation: A Simple Approach." Electrical, Control and Communication Engineering 14, no. 2 (December 1, 2018): 172–84. http://dx.doi.org/10.2478/ecce-2018-0021.
Повний текст джерелаАнотація:
AbstractThis paper presents a systematic procedure to design a simple control for a three-phase VSC-based static synchronous compensator (STATCOM) in order to overcome the problems caused by the presence of the non-linear load at the point of common coupling (PCC). The proposed control method regulates the STATCOM in such a way that the source quadrature current component is forced to be zero so that only the active current component is drawn from the source and the harmonic and reactive current demands of the non-linear load are met by the STATCOM. The tuning of the inner and outer loop PI controllers is carried out with the help of the modulus optimum and symmetric optimum criteria, respectively. At last, a few case studies are presented using MATLAB simulation to exemplify the success of the proposed control method.
14
Oraby, S. E., A. F. Al-Modhuf, and D. R. Hayhurst. "A Diagnostic Approach for Turning Tool Based on the Dynamic Force Signals." Journal of Manufacturing Science and Engineering 127, no. 3 (September 1, 2004): 463–75. http://dx.doi.org/10.1115/1.1948397.
Повний текст джерелаАнотація:
In the current work it is proposed a simple, and fast softwired tool wear monitoring approach, based upon the features of the time series analysis and the Green’s Function (GF) features. The proposed technique involves the decomposition of the force signals into deterministic component and stochastic variation-carrying component. Then, only the stochastic component is processed to detect the adequate autoregressive moving average (ARMA) models representing the tool state at every wear condition. Models are further reduced to form a more representative parameter, the “Green’s Function (GF).” This reflects the dynamic behavior of the tool prior to failure and, may provide a comprehensive and accurate measure of the damping variation of the cutting process subsystem at different forms of tool’s edge wear. As wear enters the high rate region, the cutting process is forced toward the instability domain where it tends to have less damping resistance. It is also explained how a system response surface can be generated based on its Green’s function. It is proposed that this concept can be the basis for a diagnostic technique for use with many systems.
15
Shay, Lynn K., Jorge Martinez-Pedraja, Thomas M. Cook, Brian K. Haus, and Robert H. Weisberg. "High-Frequency Radar Mapping of Surface Currents Using WERA." Journal of Atmospheric and Oceanic Technology 24, no. 3 (March 1, 2007): 484–503. http://dx.doi.org/10.1175/jtech1985.1.
Повний текст джерелаАнотація:
Abstract A dual-station high-frequency Wellen Radar (WERA), transmitting at 16.045 MHz, was deployed along the west Florida shelf in phased array mode during the summer of 2003. A 33-day, continuous time series of radial and vector surface current fields was acquired starting on 23 August ending 25 September 2003. Over a 30-min sample interval, WERA mapped coastal ocean currents over an ≈40 km × 80 km footprint with a 1.2-km horizontal resolution. A total of 1628 snapshots of the vector surface currents was acquired, with only 70 samples (4.3%) missing from the vector time series. Comparisons to subsurface measurements from two moored acoustic Doppler current profilers revealed RMS differences of 1 to 5 cm s−1 for both radial and Cartesian current components. Regression analyses indicated slopes close to unity with small biases between surface and subsurface measurements at 4-m depth in the east–west (u) and north–south (υ) components, respectively. Vector correlation coefficients were 0.9 with complex phases of −3° and 5° at EC4 (20-m isobath) and NA2 (25-m isobath) moorings, respectively. Complex surface circulation patterns were observed that included tidal and wind-driven currents over the west Florida shelf. Tidal current amplitudes were 4 to 5 cm s−1 for the diurnal and semidiurnal constituents. Vertical structure of these tidal currents indicated that the semidiurnal components were predominantly barotropic whereas diurnal tidal currents had more of a baroclinic component. Tidal currents were removed from the observed current time series and were compared to the 10-m adjusted winds at a surface mooring. Based on these time series comparisons, regression slopes were 0.02 to 0.03 in the east–west and north–south directions, respectively. During Tropical Storm Henri’s passage on 5 September 2003, cyclonically rotating surface winds forced surface velocities of more than 35 cm s−1 as Henri made landfall north of Tampa Bay, Florida. These results suggest that the WERA measured the surface velocity well under weak to tropical storm wind conditions.
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Razavian Amrei, Seyed Amin, Reza Vahdani, Mohsen Gerami, and Gholamreza Ghodrati Amiri. "Correlation Effects of Near-Field Seismic Components in Circular Metro Tunnels: A Case Study—Tehran Metro Tunnels." Shock and Vibration 2020 (May 30, 2020): 1–13. http://dx.doi.org/10.1155/2020/3016465.
Повний текст джерелаАнотація:
Seismic evaluation of underground structures such as tunnels requires nonlinear dynamic analysis, due to the complex dynamic behavior of soil and the interaction of soil and structure. Simulation of the seismic response of the structure using nonlinear dynamic analysis is possible only with proper acceleration time history. Considering the vertical component of the earthquake (such as near-fault earthquakes) on the site is an important factor to achieve real structural responses. In the current study, soil-tunnel system has been modeled in ABAQUS software, considering Mohr–Coulomb nonlinear model for soil and concrete damage plasticity model for tunnel lining. In order to investigate the effect of seismic components correlation under different combinations of loads on the acceleration, axial force, and maximum shear force in tunnel lining, nonlinear dynamic analysis has been performed under four near-field earthquakes with different horizontal and vertical component ratios, considering 15 load combinations. The results show that increasing the vertical-horizontal component ratio has an insignificant effect on the maximum horizontal acceleration experienced by the tunnel lining. Also, the results of axial forces and shear forces indicate that increasing the ratio of vertical to horizontal components of the earthquake is the most effective factor on the axial force response.
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Karakaya, Furkan, Özgür Gülsuna, and Ozan Keysan. "Feasibility of Quasi-Square-Wave Zero-Voltage-Switching Bi-Directional DC/DC Converters with GaN HEMTs." Energies 14, no. 10 (May 16, 2021): 2867. http://dx.doi.org/10.3390/en14102867.
Повний текст джерелаАнотація:
There are trade-offs for each power converter design which are mainly dictated by the switching component and passive component ratings. Recent power electronic devices such as Gallium Nitride (GaN) transistors can improve the application range of power converter topologies with lower conduction and switching losses. These new capabilities brought by the GaN High Electron Mobility Transistors (HEMTs) inevitably changes the feasible operation ranges of power converters. This paper investigates the feasibility of Buck and Boost based bi-directional DC/DC converter which utilizes Quasi-Square-Wave (QSW) Zero Voltage Switching (ZVS) on GaN HEMTs. The proposed converter applies a high-switching frequency at high output power to maximize the power density at the cost of high current ripple with high frequency of operation which requires a design strategy for the passive components. An inductor design methodology is performed to operate at 28 APP with a switching frequency of 450 kHz. In order to minimize the high ripple current stress on the output capacitors an interleaving is performed. Finally, the proposed bi-directional converter is operated at 5.4 kW with 5.24 kW/L or 85.9 W/in3 volumetric power density with air-forced cooling. The converter performance is verified for buck and boost modes and full load efficiencies are recorded as 97.7% and 98.7%, respectively.
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Vieira, Alexandre L. N., Raul D. S. G. Campilho, Francisco J. G. Silva, and Luís P. Ferreira. "Increasing the Environmental Sustainability of an Over-Injection Line for the Automotive Component Industry." Sustainability 13, no. 22 (November 16, 2021): 12692. http://dx.doi.org/10.3390/su132212692.
Повний текст джерелаАнотація:
Thermoplastic injection is currently employed in different industrial fields. This process has significantly evolved over the years, and injection machine manufacturers are continuously forced to innovate, to improve the energetic efficiency, aiming to reduce costs, improve competitiveness, and promote environmental sustainability. This work focuses on the development of a novel, profitable, and environmentally friendly plastic over-injection equipment of small metallic parts for the automotive industry, to be applied in a bowden cable production line, to cover the zamak terminations with plastic, or produce terminations entirely made of plastic. The work is based on an over-sized existing solution. The operating parameters required for the work are quantified, and all machine parts are designed separately to achieve the required functionality. Known approaches are finally used to perform the cost analysis, calculate the return on investment (ROI), and energetic efficiency, to substantiate the replacement of the current solution. The new equipment was able to increase the energetic efficiency of the current assembly line while keeping the required injection rates. An efficient and sustainable solution was presented, with a ROI of 1.2 years over the current solution. The proposed design is also applicable to different automated production lines that require this technology. Nowadays, this concept can be extended to all fields of industry that employ injection molding in their processes, enabling to integrate new manufacturing systems, and increasing energetic efficiency while reducing production costs.
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Ren, Lei, Stephen Nash, and Michael Hartnett. "Forecasting of Surface Currents via Correcting Wind Stress with Assimilation of High-Frequency Radar Data in a Three-Dimensional Model." Advances in Meteorology 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/8950378.
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This paper details work in assessing the capability of a hydrodynamic model to forecast surface currents and in applying data assimilation techniques to improve model forecasts. A three-dimensional model Environment Fluid Dynamics Code (EFDC) was forced with tidal boundary data and onshore wind data, and so forth. Surface current data from a high-frequency (HF) radar system in Galway Bay were used for model intercomparisons and as a source for data assimilation. The impact of bottom roughness was also investigated. Having developed a “good” water circulation model the authors sought to improve its forecasting ability through correcting wind shear stress boundary conditions. The differences in surface velocity components between HF radar measurements and model output were calculated and used to correct surface shear stresses. Moreover, data assimilation cycle lengths were examined to extend the improvements of surface current’s patterns during forecasting period, especially for north-south velocity component. The influence of data assimilation in model forecasting was assessed using a Data Assimilation Skill Score (DASS). Positive magnitude of DASS indicated that both velocity components were considerably improved during forecasting period. Additionally, the improvements of RMSE for vector direction over domain were significant compared with the “free run.”
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Bukhari, Syed Sabir Hussain, Ghulam Jawad Sirewal, Faheem Akhtar Chachar, and Jong-Suk Ro. "Dual-Inverter-Controlled Brushless Operation of Wound Rotor Synchronous Machines Based on an Open-Winding Pattern." Energies 13, no. 9 (May 2, 2020): 2205. http://dx.doi.org/10.3390/en13092205.
Повний текст джерелаАнотація:
In an open-winding machine, three-phase stator currents can be controlled such that the input armature currents may contain the third-harmonic current component in addition to the fundamental. Considering this attribute of open-winding patterns, a harmonic current field excitation technique for a wound rotor synchronous machine (WRSM) is proposed in this paper based on the control of time-harmonic magneto-motive force. Two inverters connected to both terminals of the stator winding are controlled so that the input armature current generates an additional third-harmonic current component. This third-harmonic component generates a vibrating magnetic field that induces a current in the specially designed rotor harmonic winding. The current is supplied as DC current to the rotor excitation winding to generate a rotor field by using a full-bridge diode rectifier in order to achieve brushless operation. The proposed dual-inverter-controlled brushless operation for a WRSM is executed in ANSYS Maxwell using 2-D finite element analysis to validate its operation and electromagnetic performance.
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Zhang, Wanchao, Yujie Zhou, Kai Wang, and Xiaoguo Zhou. "Forced Motion CFD Simulation and Load Refinement Evaluation of Floating Vertical-Axis Tidal Current Turbines." Polish Maritime Research 27, no. 3 (September 1, 2020): 40–49. http://dx.doi.org/10.2478/pomr-2020-0045.
Повний текст джерелаАнотація:
AbstractSimulation of the hydrodynamic performance of a floating current turbine in a combined wave and flow environment is important. In this paper, ANSYS-CFX software is used to analyse the hydrodynamic performance of a vertical-axis turbine with various influence factors such as tip speed ratio, pitching frequency and amplitude. Time-varying curves for thrust and lateral forces are fitted with the least squares method; the added mass and damping coefficients are refined to analyse the influence of the former factors. The simulation results demonstrate that, compared with non-pitching and rotating turbines under constant inflow, the time-varying load of rotating turbines with pitching exhibits an additional fluctuation. The pitching motion of the turbine has a positive effect on the power output. The fluctuation amplitudes of thrust and lateral force envelope curves have a positive correlation with the frequency and amplitude of the pitching motion and tip speed ratio, which is harmful to the turbine’s structural strength. The mean values of the forces are slightly affected by pitching frequencies and amplitudes, but positively proportional to the tip speed ratio of the turbine. Based upon the least squares method, the thrust and lateral force coefficients can be divided into three components, uniform load coefficient, added mass and damping coefficients, the middle one being significantly smaller than the other two. Damping force plays a more important role in the fluctuation of loads induced by pitching motion. These results can facilitate study of the motion response of floating vertical-axis tidal current turbine systems in waves.
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Marques, Ana C., Helena Dias, Sandro Matos, Bruno Sargaço, Ricardo Simoes, Aster De Schrijver, and João C. Bordado. "Polyurethane one-component foam formulation optimization for low free isocianate monomer content." Journal of Cellular Plastics 53, no. 2 (July 28, 2016): 167–79. http://dx.doi.org/10.1177/0021955x16639230.
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Recent changes in legislation have forced one-component foam producers to drop the amount of free monomeric isocyanate in their polyurethane systems. Also, it is required that commercial polyurethane aerosol cans exhibit at least one year of shelf life and polyurethane foams must be classified as B2 on the fire testing following DIN 4102. This paper reports on a systematic optimization study of polyurethane formulations dedicated to address these current industry requirements. A one-component foam system exhibiting simultaneously all of these parameters was achieved by reacting conventional diols, a relatively low-molecular weight monol (2-ethylhexanol), a flame retardant high-molecular weight monol (tris(bromoneopentyl)alcohol), a methylene diphenyl diisocyanate-based prepolymer (GreenAdduct 13), and a small amount of 2,4′-toluene diisocyanate. The use of monols allows producing prepolymers with low free methylene diphenyl diisocyanate by preventing chain extension and, therefore, avoiding extreme viscosity build-up. Toluene diisocyanate also promotes a lower viscosity inside the aerosol can, which enables the use of high enough quantities of high-molecular weight flame retardant monol to achieve a B2 fire test classification.
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Campi, S., S. J. Mellon, D. Ridley, B. Foulke, C. A. F. Dodd, H. G. Pandit, and D. W. Murray. "Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement." Bone & Joint Research 7, no. 3 (March 2018): 226–31. http://dx.doi.org/10.1302/2046-3758.73.bjr-2017-0193.r1.
Повний текст джерелаАнотація:
Objectives The primary stability of the cementless Oxford Unicompartmental Knee Replacement (OUKR) relies on interference fit (or press fit). Insufficient interference may cause implant loosening, whilst excessive interference could cause bone damage and fracture. The aim of this study was to identify the optimal interference fit by measuring the force required to seat the tibial component of the cementless OUKR (push-in force) and the force required to remove the component (pull-out force). Materials and Methods Six cementless OUKR tibial components were implanted in 12 new slots prepared on blocks of solid polyurethane foam (20 pounds per cubic foot (PCF), Sawbones, Malmo, Sweden) with a range of interference of 0.1 mm to 1.9 mm using a Dartec materials testing machine HC10 (Zwick Ltd, Herefordshire, United Kingdom) . The experiment was repeated with cellular polyurethane foam (15 PCF), which is a more porous analogue for trabecular bone. Results The push-in force progressively increased with increasing interference. The pull-out force was related in a non-linear fashion to interference, decreasing with higher interference. Compared with the current nominal interference, a lower interference would reduce the push-in forces by up to 45% (p < 0.001 One way ANOVA) ensuring comparable (or improved) pull-out forces (p > 0.05 Bonferroni post hoc test). With the more porous bone analogue, although the forces were lower, the relationship between interference and push-in and pull-out force were similar. Conclusions This study suggests that decreasing the interference fit of the tibial component of the cementless OUKR reduces the push-in force and can increase the pull-out force. An optimal interference fit may both improve primary fixation and decrease the risk of fracture. Cite this article: S. Campi, S. J. Mellon, D. Ridley, B. Foulke, C. A. F. Dodd, H. G. Pandit, D. W. Murray. Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement. Bone Joint Res 2018;7:226–231. DOI: 10.1302/2046-3758.73.BJR-2017-0193.R1.
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Czán, Andrej, Richard Joch, Michal Šajgalík, Jozef Holubják, Andrej Horák, Pavol Timko, Jan Valíček, Milena Kušnerová, and Marta Harničárová. "Experimental Study and Verification of New Monolithic Rotary Cutting Tool for an Active Driven Rotation Machining." Materials 15, no. 5 (February 22, 2022): 1630. http://dx.doi.org/10.3390/ma15051630.
Повний текст джерелаАнотація:
Forced rotation turning appears to be an effective machining method due to higher tool life, time efficiency and acceptable quality. Several studies have been carried out to investigate the basic characteristics of forced rotation machining. So far, tools are used whose design included several components. However, such tools may generate vibrations, which are undesirable in the process. In engineering practice, most vibration problems are solved by reducing the cutting parameters (cutting speed and feed rate), which reduces machining productivity. For this reason, a new type of monolithic rotary tool has been designed that eliminates the design complexity and high assembly accuracy requirements of current rotary tools. Based on the performed experimental research, it is possible to define the influence of cutting parameters on the cutting force. Next, the equation of the cutting force and the resulting roughness of the machined surface was determined. In the introduction, the results of the analysis of machining parameters with a rotary tool were added. The presented solution fundamentally validates the new monolithic tool for forced rotation technology and defines its application for different machining materials.
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Lee, Kwang-Ho, Tag-Gyeom Kim, and Yong-Hwan Cho. "Influence of Tidal Current, Wind, and Wave in Hebei Spirit Oil Spill Modeling." Journal of Marine Science and Engineering 8, no. 2 (January 22, 2020): 69. http://dx.doi.org/10.3390/jmse8020069.
Повний текст джерелаАнотація:
The purpose of this study is to investigate the effects of three external forces (tidal current, wind, and waves) on the movement of oil spilled during the Hebei Spirit oil spill accident. The diffusion of the spilled oil was simulated by using a random walk (RW) model that tracks the movement caused by advection-diffusion assuming oil as particles. For oil simulation, the wind drift current generated by wind and tidal current fields were computed by using the environmental fluid dynamics code (EFDC) model. Next, the wave fields were simulated by using the simulating waves nearshore (SWAN) model, and the Stokes drift current fields were calculated by applying the equation proposed by Stokes. The computed tidal currents, wind drift currents, and Stokes drift currents were applied as input data to the RW model. Then, oil diffusion distribution for each external force component was investigated and compared with that obtained from satellite images. When the wind drift currents and Stokes drift currents caused by waves were considered, the diffusion distribution of the spilled oil showed good agreement with that obtained from the observation.
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Phan, T. D., and B. U. Ö. Sonnerup. "Resistive tearing-mode instability in a current sheet with equilibrium viscous stagnation-point flow." Journal of Plasma Physics 46, no. 3 (December 1991): 407–21. http://dx.doi.org/10.1017/s0022377800016214.
Повний текст джерелаАнотація:
An analysis is presented of linear stability against tearing modes of a current sheet formed between two oppositely magnetized plasmas forced towards each other in two-dimensional steady stagnation-point flow. The velocity vector in this flow is confined to planes perpendicular to the reversing component of the magnetic field. The unperturbed state is an exact resistive and viscous equilibrium in which the resistive diffusion outwards from the current sheet is exactly balanced by the inward motion associated with the stagnation-point flow. Thus the behaviour of the tearing mode can be examined even when the resistive diffusion time is comparable to or smaller than the growth time of the instability. The linear ordinary differential equation describing the mode structure is integrated numerically. For large Lundquist number S and viscous Reynolds number Re the Furth-Killeen-Rosenbluth scaling of the growth rate is recovered with excellent accuracy. The influence of the stagnation-point flow on the tearing mode is as follows: (i) long-wavelength perturbations are stabilized so that the unstable regime falls between a short-wavelength and a long-wavelength marginal state; (ii) for sufficiently low Lundquist number (S < 12.25) the current sheet is completely stable to tearing-mode perturbations; (iii) the presence of high viscosity reduces the growth rate of the tearing instability. This effect is more important at small wavelength. Finally, application of the results from this study to the problem of solar-wind plasma flow past the earth's magnetosphere is briefly discussed.
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Santo, H., P. H. Taylor, C. H. K. Williamson, and Y. S. Choo. "Current blockage experiments: force time histories on obstacle arrays in combined steady and oscillatory motion." Journal of Fluid Mechanics 739 (December 17, 2013): 143–78. http://dx.doi.org/10.1017/jfm.2013.605.
Повний текст джерелаАнотація:
AbstractThis paper revisits the problem of forces on obstacle arrays in combined waves and an in-line steady current. The intended application is the design and reassessment of offshore platforms. A series of experiments are performed on planar grids moved in both steady and oscillatory motion through otherwise stationary water. Detailed comparisons are made to a wave-current–structure interaction model recently presented by Taylor, Santo & Choo (Ocean Engng, vol. 57, 2013, pp. 11–24). We present new features of the model and test these against the experimental data. For relatively small current speed (${u}_{c} $) compared with oscillatory velocity amplitude (${u}_{w} $) with phase angle ($\omega t$), the drag force time history on grids with solid area ($A$) and projected frontal area (${A}_{f} $) is well approximated by a summation of the wave drag and the current drag components independently, so there is no ${u}_{w} \times {u}_{c} $ cross-term. The wave drag component is proportional to $\cos \omega t\vert \cos \omega t\vert $, while the current drag component to $\vert \cos \omega t\vert $, i.e. it is phase-locked to the oscillatory wave crests. The form of the predicted time history is new, so much of this paper is occupied in testing the adequacy of this theoretical form both in terms of an improved Morison-type formulation and also in the precise variation of the experimental drag force in time. We show that the measured crest and trough peak values of the drag force are consistent with the force peaks and troughs of the model prediction. The odd frequency harmonics of the measured drag force scale as the square of the oscillatory velocity amplitude $({ u}_{w}^{2} )$ and on the total hydrodynamic area (${C}_{d} A$). The shape of the odd harmonics is very similar to that for a pure oscillatory motion without steady current, but there are also even frequency harmonics associated with the current component. The even harmonics of the force scale as the square of the current speed $({ u}_{c}^{2} )$ and on the ${A}_{f} $, not on the ${C}_{d} A$. All of the above features are identified within the experimental data, and provide considerable support for the new current blockage model.The new model is also shown to fit the entire force time history well for a wide range of individual cases, with different blockage ratio ($A/ {A}_{f} $) and number of grids, requiring only calibration of the Morison-type drag and inertia coefficients. In contrast, the industry-standard form of the Morison equation can only be matched at a single instant of the oscillation cycle, so present practice should be regarded as seriously inadequate for combined steady current and oscillatory flow acting on obstacle arrays.
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Karspeck, Alicia R., Steve Yeager, Gokhan Danabasoglu, Tim Hoar, Nancy Collins, Kevin Raeder, Jeffrey Anderson, and Joseph Tribbia. "An Ensemble Adjustment Kalman Filter for the CCSM4 Ocean Component." Journal of Climate 26, no. 19 (September 24, 2013): 7392–413. http://dx.doi.org/10.1175/jcli-d-12-00402.1.
Повний текст джерелаАнотація:
Abstract The authors report on the implementation and evaluation of a 48-member ensemble adjustment Kalman filter (EAKF) for the ocean component of the Community Climate System Model, version 4 (CCSM4). The ocean assimilation system described was developed to support the eventual generation of historical ocean-state estimates and ocean-initialized climate predictions with the CCSM4 and its next generation, the Community Earth System Model (CESM). In this initial configuration of the system, daily subsurface temperature and salinity data from the 2009 World Ocean Database are assimilated into the ocean model from 1 January 1998 to 31 December 2005. Each ensemble member of the ocean is forced by a member of an independently generated CCSM4 atmospheric EAKF analysis, making this a loosely coupled framework. Over most of the globe, the time-mean temperature and salinity fields are improved relative to an identically forced ocean model simulation without assimilation. This improvement is especially notable in strong frontal regions such as the western and eastern boundary currents. The assimilation system is most effective in the upper 1000 m of the ocean, where the vast majority of in situ observations are located. Because of the shortness of this experiment, ocean variability is not discussed. Challenges that arise from using an ocean model with strong regional biases, coarse resolution, and low internal variability to assimilate real observations are discussed, and areas of ongoing improvement for the assimilation system are outlined.
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Lam, Linda A., Sonia Mehta, Eleonora M. Lad, Geoffrey G. Emerson, J. Michael Jumper, and Carl C. Awh. "Intravitreal Injection Therapy: Current Techniques and Supplemental Services." Journal of VitreoRetinal Diseases 5, no. 5 (July 22, 2021): 438–47. http://dx.doi.org/10.1177/24741264211028441.
Повний текст джерелаАнотація:
Purpose: Intravitreal injection is the most frequently performed eye procedure in the world and is an essential component in the management of sight-threating retinal diseases and conditions. Given the seriousness and range of diseases treated and the risks of the procedure, retina specialists must weigh the pros and cons of each individual treatment. Complexities guiding injection treatment are multifaceted and involve patient-history review, careful examination, diagnostic testing selection and interpretation, customized medical decision-making, and follow-up considerations. Methods: This article by the Intravitreal Injection Task Force Committee of the American Society of Retina Specialists documents the intricacies and necessary components of the intravitreal injection procedure. Results: By expert consensus, the task force further recommends ancillary services and decision-making that may accompany intravitreal injection visits, when appropriate, to monitor response to treatment, adjust treatment, and manage additional considerations in the same or fellow eye. Conclusions: Retina specialists can optimize safety and therapeutic outcomes with individualized consideration and customization of intravitreal injection treatment for each patient.
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Zhu, Zhao Qing, Hang Qiu, and Guo Liang Dai. "Experimental Studies on Loads on a Single Pile under the Wave-Current Flow." Applied Mechanics and Materials 170-173 (May 2012): 529–32. http://dx.doi.org/10.4028/www.scientific.net/amm.170-173.529.
Повний текст джерелаАнотація:
Indoor model experiments were made to study loads on single pile under the wave-current flow. Take three different velocities of the current and three different diameters of piles in the experiments to get the variations of loads. Drag and lift forces were measured by a two-component balance. Analysis on experiment results shows that, both drag force and lift force increase with the increase of the pile diameter and the current velocity. The drag coefficient Cd increases with the increase of Kc number until Kc researches 12, when Kc is more than 12, Cd decreases with the increase of Kc; while the inertia force coefficient Cm decreases with the increase of Kc, when Kc is more than 12, Cmchanges little. And the lift coefficient shows no correlation with the Kc number.
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Kumar, Dushyant, Ali Zifan, and Ravinder K. Mittal. "Botox injection into the lower esophageal sphincter induces hiatal paralysis and gastroesophageal reflux." American Journal of Physiology-Gastrointestinal and Liver Physiology 318, no. 1 (January 1, 2020): G77—G83. http://dx.doi.org/10.1152/ajpgi.00238.2019.
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Background: Endoscopic intrasphincteric injection of Botox (ISIB) is used routinely for the treatment of achalasia esophagus and other spastic motor disorders. Studies show that the ISIB reduces the smooth muscle lower esophageal sphincter (LES) pressure. The esophageal hiatus, formed by the right crus of diaphragm, surrounds the cranial half of the LES and works like an external LES. We studied the effects of ISIB on the LES and hiatal contraction and gastroesophageal reflux (GER). Fourteen patients treated with ISIB were studied. Esophageal manometry-impedance recordings were performed before and after the ISIB. Hiatal contraction was assessed during tidal inspiration, forced inspiration, Müller’s maneuver, and straight leg raise. In 6 subjects, the manometry were repeated 6–12 mo after the ISIB. The esophagogastric junction (EGJ) pressure was measured at end expiration (LES pressure) and at the peak of maneuvers (hiatal contraction). Transdiaphragmatic pressure (pdi; force of diaphragmatic contraction) was measured at the peak of forced inspiration. GER was measured from the impedance recordings. The EGJ pressure at end expiration (LES pressure) decreased significantly after the Botox injection. The peak EGJ pressure at tidal inspiration, forced inspiration, Müller’s maneuver, and straight leg raise was also dramatically reduced by the ISIB. There was no effect of Botox on the pdi during forced inspiration. Seven of 10 subjects demonstrated GER during maneuvers following the ISIB. Six to 12 mo after ISIB, the LES and hiatal contraction pressure returned to the pre-ISIB levels. ISIB, in addition to decreasing LES pressure, paralyzes the esophageal hiatus (crural diaphragm) and induces GER. NEW & NOTEWORTHY The sphincter mechanism at the lower end of the esophagus comprises smooth muscle lower esophageal sphincter (LES) and skeletal muscle crural diaphragm (hiatus). Current thinking is that the endoscopic intrasphincteric injection of Botox (ISIB), used routinely for the treatment of achalasia esophagus, reduces LES pressure. Our study shows that ISIB, even though injected into the LES, diffuses into the hiatus and causes its paralysis. These findings emphasize the importance of esophageal hiatus as an important component of the antireflux barrier and that the ISIB is refluxogenic.
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Bialobrzheskyi, O. V., and D. Y. Rod`kin. "Distorting Electrical Power of the Alternating Current in the Simplest Circuit with a Diode." ENERGETIKA. Proceedings of CIS higher education institutions and power engineering associations 62, no. 5 (October 4, 2019): 433–44. http://dx.doi.org/10.21122/1029-7448-2019-62-5-433-444.
Повний текст джерелаАнотація:
The development of electric power industry is accompanied by an increase in the number of consumers subjected to loads with nonlinear characteristics. The arising problem of the distortion of electrical energy that takes place when the mentioned consumers are in operation is partially solved by using means of improving the quality of electrical energy. The increase in the share of small generating plants that are placed in the nodes of consumers exacerbates the interaction of non-linear loads, forming additional parallel streams of electrical energy. Distorted electrical power is not an indication to account. Existing views on distorting power are amenable to criticism. In the well-known works, the proposals for the assessment of power using the quadratic norm and the quadratic norms of its components have been grounded. For the analysis of processes of formation the components of electrical power, a diagram of the simplest circuit containing a series-connected source of electromotive force, resistors and a diode is considered; also, the circuit was conditionally separated into a source and a consumer. The analysis of the power formation of each circuit element is performed with the use of the expression of current and voltage, as periodic functions represented by the trigonometric form of Fourier series. The power components are separated with the use of the known interaction of harmonic components of current and voltage of different orders. For the circuit elements, the power components formed by current and voltage harmonics of the same order are selected as well as power components formed by current and voltage harmonics of different orders, in which, in their turn, the power components are selected that have the same order as the first ones. The power formed by the action of the latter group is proposed to be attributed to the distorting power and to account its action by the corresponding quadratic norm. A numerical calculation has been performed with a use of the specified power component distribution. Time diagrams illustrate the process of interaction of the power components, which–in the case of the diode–leads to no change in power over time.
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Shvaliuchynskyi, Vasyl, Serhii Skorodid, and Serhii Pochynok. "BATTLEFIELD AUTOMATIZATION: CURRENT STATE AND PROSPECTS OF DEVELOPMENT." ГРААЛЬ НАУКИ, no. 4 (May 14, 2021): 124–28. http://dx.doi.org/10.36074/grail-of-science.07.05.2021.023.
Повний текст джерелаАнотація:
Current state of the development and implementation of automated control systems in the defense forces is analyzed. Taking into account of experience, gained during antiterrorist operation (Joint Forces Operation), the specifics of control systems functioning has been given. It is defined that automated control system is being developed by creation of hierarchical structure separately for each component of defense forces and, above all, is aimed on meeting its own needs. The main activities which might provide a system approach to development and implementation of a single automated control system in the defense forces have been identified.
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Buikis, A., and H. Kalis. "CALCULATION OF ELECTROMAGNETIC FIELDS, FORCES AND TEMPERATURE IN A FINITE CYLINDER." Mathematical Modelling and Analysis 7, no. 1 (June 30, 2002): 21–32. http://dx.doi.org/10.3846/13926292.2002.9637174.
Повний текст джерелаАнотація:
The distribution of electromagnetic fields, forces and temperatures induced by a three‐phase axially‐symmetric system of electric current in a conducting cylinder of a finite length has been calculated. An original method was used to calculate the radial and axial components of the magnetic fields and the mean values of electromagnetic forces, as well as the azimuthal component of the electric field and of the mean curl of the electromagnetic forces. For finding the source term in the temperature equation we applied an approximation of the heat transport problem based on the finite‐difference method. Such a procedure allows one to calculate the distribution of temperatures inside the cylinder depending on that of currents in the wires.
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Bao, Ze Fu, Hai Feng Dai, Peng Zang, and Jiang Ping Wang. "Design and Application of Forced Heat Dispersing Device of Superdeep Drilling Rig in High Temperature." Advanced Materials Research 339 (September 2011): 561–65. http://dx.doi.org/10.4028/www.scientific.net/amr.339.561.
Повний текст джерелаАнотація:
The system about the eddy current brake in drilling rig is very important and friable component. The temperature will arise with the winch lift the heave object and break, which will affect the winch. The conventional drilling rigs are cooled by air blast or water circulation, which always can’t content the request of drilling rig winch brake system. For this situation, I am to design and manufacture the forced heat-dispersing unit for ZJ70/4500DZ drilling rig winch. This device unified the formerly forced-air cooling and water cooling characteristic, and what’s more, it consists of air cooler, water tank, water pump valves, manifold and instruments. It has lots of advantages, for example: structure compact, easy installation and maintenance and so on. The article in the bases of analyses the ZJ70 drilling rig winch system characteristic and the theory of the formerly heat-dispersing, to introduced the approach of design and composition design…
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Thomas, Leif, and Raffaele Ferrari. "Friction, Frontogenesis, and the Stratification of the Surface Mixed Layer." Journal of Physical Oceanography 38, no. 11 (November 1, 2008): 2501–18. http://dx.doi.org/10.1175/2008jpo3797.1.
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Abstract The generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air–sea fluxes and stresses. In this paper, it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum. A classic example is the strong restratification resulting from frontogenesis in regions of confluent flow. Frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving Ekman flows that differentially advect density. Ekman flow induced during spindown always tends to restratify the fluid, while wind-driven Ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front (i.e., directed against or with the geostrophic shear), respectively. Scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field. The scalings suggest and the numerical experiments confirm that for wind stress magnitudes, mixed layer depths, and cross-front density gradients typical of the ocean, wind-induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean. The experiments reveal that wind-induced destratification is weaker in magnitude than restratification because the stratification generated by up-front winds confines the turbulent stress to a depth shallower than the Ekman layer, which enhances the frictional force, Ekman flow, and differential advection of density. Frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down-front wind stress.
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GROENEWEG, J., and J. A. BATTJES. "Three-dimensional wave effects on a steady current." Journal of Fluid Mechanics 478 (March 10, 2003): 325–43. http://dx.doi.org/10.1017/s0022112002003476.
Повний текст джерелаАнотація:
Measurements in a laboratory flume have shown unexpected wave-induced changes in the vertical profile of the mean horizontal velocity. Two theoretical explanations for these changes have been proposed so far. One is based on a local force balance in the longitudinal direction and the other relies on secondary circulations in the cross-sectional plane. In this study, a two-dimensional (2DV lateral) model based on the so-called generalized Lagrangian mean (GLM) formulation has been developed to investigate the three-dimensional effect of waves on the steady current and in particular to investigate the validity of the two fundamentally different explanations. Formulations for the three-dimensional wave-induced driving force have been implemented in an existing 2DV non-hydrostatic numerical flow model. Computations for regular waves following and opposing a turbulent current over a horizontal bed have been carried out and the results are compared with both experimental results and results from an existing numerical model. The results clearly indicate predominance of the longitudinal component of the wave-induced driving force over the cross-sectional components. Although the 2DV model has only been applied to and verified with measurements in wave–current systems in a laboratory flume, the approach followed here is relevant for a wider class of problems of wave–current interactions.
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Mensink-Bout, Sara M., Trudy Voortman, Marsela Dervishaj, Irwin K. M. Reiss, Johan C. De Jongste, Vincent W. V. Jaddoe, and Liesbeth Duijts. "Associations of Plasma Fatty Acid Patterns during Pregnancy with Respiratory and Allergy Outcomes at School Age." Nutrients 12, no. 10 (October 7, 2020): 3057. http://dx.doi.org/10.3390/nu12103057.
Повний текст джерелаАнотація:
Fatty acids might play a role in asthma and allergy development as they can modulate immune responses. We examined among 4260 mother-child pairs participating in a population-based cohort the associations of maternal plasma fatty acid patterns during pregnancy with a child’s respiratory and allergy outcomes at school-age. In mid-pregnancy, 22 individual fatty acids were measured from maternal blood. Three patterns were previously identified by principal component analysis: A ‘high n-6 polyunsaturated fatty acid (PUFA)’, a ‘monounsaturated and saturated fatty acid’, and a ‘high n-3 PUFA’ pattern. At the age of 10 years, a child’s lung function was assessed by spirometry, current asthma and physician-diagnosed inhalant allergy by questionnaire, and inhalant allergic sensitization by skin prick tests. A higher ‘high n-6 PUFA’ pattern was associated with a higher forced expiratory volume in 1 s/forced vital capacity and forced expiratory flow after exhaling 75% of forced vital capacity (Z-score difference (95% CI) 0.04 (0, 0.07) and 0.04 (0.01, 0.07), respectively, per SD increase in the fatty acid pattern). We observed no associations of maternal fatty acid patterns with a child’s asthma or allergy outcomes. Our results showed limited associations of maternal patterns of high n-6 PUFA concentrations in pregnancy with a better lung function in school-aged children.
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Dumitru, Ștefan Marian. "Forced digitization due to the global pandemic." Proceedings of the International Conference on Business Excellence 15, no. 1 (December 1, 2021): 1243–50. http://dx.doi.org/10.2478/picbe-2021-0115.
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Abstract COVID-19 has produced dramatic consequences on the world economy, industry, and citizens. But digitization is also aiding many businesses to adapt and surmount the current situation caused by the pandemic. The increase in the utilization of technology in the everyday lives of people and businesses to cope with this exceptional state is a testimony of the digital acceleration process. This study examines the impact of the digital revolution processes in three areas: labor and social interactions, marketing and sales, and technology. The effect of digitalization is anticipated to be transversal to each domain and will inspire the emergence of new digital services and products centered on flexibility. Furthermore, new methods of working will encourage the demand for new talent irrespective of people’s geographical position. Furthermore, cybersecurity and privacy will grow to be two key components that will support the integrated growth of artificial intelligence, robotics, big data, and the Internet of Things technology.
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Bladh, R., M. P. Castanier, and C. Pierre. "Component-Mode-Based Reduced Order Modeling Techniques for Mistuned Bladed Disks—Part II: Application." Journal of Engineering for Gas Turbines and Power 123, no. 1 (April 2, 2000): 100–108. http://dx.doi.org/10.1115/1.1338948.
Повний текст джерелаАнотація:
In this paper, the component-mode-based methods formulated in the companion paper (Part I: Theoretical Models) are applied to the dynamic analysis of two example finite element models of bladed disks. Free and forced responses for both tuned and mistuned rotors are considered. Comprehensive comparisons are made among the techniques using full system finite element solutions as a benchmark. The accurate capture of eigenfrequency veering regions is of critical importance for obtaining high-fidelity predictions of the rotor’s sensitivity to mistuning. Therefore, particular attention is devoted to this subject. It is shown that the Craig–Bampton component mode synthesis (CMS) technique is robust and yields highly reliable results. However, this is achieved at considerable computational cost due to the retained component interface degrees of freedom. It is demonstrated that this problem is alleviated by a secondary modal analysis reduction technique (SMART). In addition, a non-CMS mistuning projection method is considered. Although this method is elegant and accurate, it is seen that it lacks the versatility and efficiency of the CMS-based SMART. Overall, this work shows that significant improvements on the accuracy and efficiency of current reduced order modeling methods are possible.
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Ridgway, C., E. R. Priest, and T. Amari. "Prominence sheets supported by constant-current force-free fields. II - Imposition of normal photospheric field component and prominence surface current." Astrophysical Journal 385 (February 1992): 718. http://dx.doi.org/10.1086/170978.
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Stein, J. L., D. Colvin, G. Clever, and C. H. Wang. "Evaluation of DC Servo Machine Tool Feed Drives as Force Sensors." Journal of Dynamic Systems, Measurement, and Control 108, no. 4 (December 1, 1986): 279–88. http://dx.doi.org/10.1115/1.3143795.
Повний текст джерелаАнотація:
Unmanned machine tools as part of an automated factory require reliable, inexpensive sensors to provide machine and process information to the controller. The electric current in the DC motor of a CNC machine tool can be inexpensively measured and used to calculate the tool/workpiece cutting force and the forces associated with drive system components. In order to characterize the bandwidth, sensitivity and accuracy of current monitoring on the feed system of a CNC lathe, a dynamic lumped parameter model of this sensor system is developed. The model is used to identify the system components that have a dominant effect on the behavior of the sensor. Tests were conducted in order to determine the model parameters, verify the model, and determine the signal-to-noise (S/N) ratio of the sensor. The bandwidth of this sensor is predicted to be 80 Hz. Tests show that the S/N ratio is low but can be improved by a trade-off with the system bandwidth. The bandwidth is limited by the characteristics of the SCR amplifier. In addition, the sensitivity and accuracy of calculating the feed force component of the cutting force from the total current used by the feed motor is limited by the pitch of the ball screw and friction coefficient variations in the slide. Feed system design changes, to improve the S/N ratio of the feed system as a tool and machine force sensor, are discussed.
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Tchouaha Tankoua, Aristide, Tobias Köhler, Jean Pierre Bergmann, Michael Grätzel, Philip Betz, and Dirk Lindenau. "Tool Downscaling Effects on the Friction Stir Spot Welding Process and Properties of Current-Carrying Welded Aluminum–Copper Joints for E-Mobility Applications." Metals 11, no. 12 (December 3, 2021): 1949. http://dx.doi.org/10.3390/met11121949.
Повний текст джерелаАнотація:
According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools—i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum–copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process.
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Worswick, Michael J., Ryan George, Alex Bardelcik, Luke Ten Kortenaar, and Duane Detwiler. "Thermal Processing History and Resulting Impact Response of a Hot-Formed Component with Tailored Properties – Numerical Study." Applied Mechanics and Materials 566 (June 2014): 34–40. http://dx.doi.org/10.4028/www.scientific.net/amm.566.34.
Повний текст джерелаАнотація:
The impact modeling of a hot-formed component with tailored mechanical properties is studied to understand the influence of the thermal processing history and how the final properties of the component will affect its impact response. This paper presents a numerical study of the forming and quenching process and subsequent impact simulations. The processing simulations serve to predict the final microstructure and hardness distribution within a lab-scale B-pillar component that is processed using a tool with separate heated and cooled regions. A remapping algorithm is used to translate the results of the forming simulation to the impact simulation. A strain-rate sensitive material model is applied to model the response of these tailored microstructures during impact events. A comparison between a component that is fully hardened and a tailored component with regions of lower strength but increased ductility is presented in this work. Simulations that do not consider the onset of fracture predict superior peak impact load and energy absorption of the fully martensitic component due to its higher overall strength. However, the bainitic regions within the tailored component exhibit much higher ductility. Current work is addressing the introduction of failure criteria into simulations of tailored hot stamped components under impact loading for which the tailored component is expected to demonstrate superior resistance to cracking relative to the fully hardened component.
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Mingalev, Oleg, Pavel Setsko, Mikhail Melnik, Igor Mingalev, Helmi Malova, and Alexey Merzlyi. "Force balance in current sheets in collisionless plasma." Solnechno-Zemnaya Fizika 7, no. 2 (June 30, 2021): 12–23. http://dx.doi.org/10.12737/szf-72202102.
Повний текст джерелаАнотація:
In this paper, we derive a divergent form of the force balance equation for collisionless plasma in the quasineutrality approximation, in which the electric field and current density are excluded. For a stationary spatially one-dimensional current sheet with a constant normal component of the magnetic field and magnetized electrons, the general form of the force balance equation has been obtained for the first time in the form of a conservation law. An equation in this form is necessary for the correct formulation of boundary conditions when modeling asymmetric current sheets, as well as for the control of the stationarity of the numerical solution obtained in the model. Furthermore, the fulfillment of this equation is considered for two types of stationary configurations of a thin current sheet, which are obtained using a numerical model. The derived equation makes it possible to develop models of asymmetric current sheets, in particular current sheets on the magnetopause flanks in the magnetotail.
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Poliak, O. "CURRENT REQUIREMENTS FOR THE COMPETITIVENESS OF THE HIGHER EDUCATION TEACHER." Visnyk Taras Shevchenko National University of Kyiv. Pedagogy, no. 1 (11) (2020): 35–37. http://dx.doi.org/10.17721/2415-3699.2020.11.08.
Повний текст джерелаАнотація:
The article is devoted to the problem of formation and development of competitiveness among teachers of higher education institutions. If the content and structure of professional competitiveness, defined by state standards, are formed without taking into account the personal qualities of the learning subject, its interests, abilities and are not determined by the professionalism of the teacher, it is impossible to lay the foundations of competitiveness and develop the ability to compete. The genesis of different approaches to the concept of competitiveness of the modern educator has been analyzed, in particular, in modern researches it is emphasized on: – managerial, psychological and pedagogical aspect of competitiveness. The process of forming the competitiveness of a teacher of a higher education institution, which includes its components, is outlined: = levels of development: a motivational and holistic component; emotional-volitional component; evaluation and adjustment component; = conditions of formation: the need to find such forms of work of the teacher, which would ensure the continuity of the process of his professional growth, development and introduction of multidimensional models of the organization of professional development, introduction of new educational technologies, participation in innovative activity; = development of a complex of properties of his personality necessary for a high level of professional activity. The activity of the teacher is characterized by pedagogical expediency by orientation, individually creative character in content and organization, choice of means; = ways of formation: a certain amount of knowledge, abilities, skills and continuous improvement of the state of theoretical, psychological-pedagogical, methodological and technological preparation; motives for professional self-improvement; the desire for selfrealization and self-affirmation of personality; professional growth; expanding horizons; increasing the level of development of all types of competences; the presence of cognitive interest; creating a positive image among students and colleagues; upgrading the qualification category during certification; receiving awards; raising personal rankings at different levels of subordination; improving professional competence; raising the level of organization of the educational process.
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Childs, D. W., and D. S. Moyer. "Vibration Characteristics of the HPOTP (High-Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine)." Journal of Engineering for Gas Turbines and Power 107, no. 1 (January 1, 1985): 152–59. http://dx.doi.org/10.1115/1.3239676.
Повний текст джерелаАнотація:
A review is presented of various rotordynamic problems which have been encountered and eliminated in developing the current flight engines and of continuing subsynchronous problems which are being encountered in developing a 109 percent power level engine. The basic model for the HPOTP, including the structural dynamic model for the rotor and housing and component models for the liquid and gas seals, turbine-clearance excitation forces, and impeller-diffuser forces, are discussed. Results from a linear model are used to examine the synchronous response and stability characteristics of the HPOTP, examining bearing load and stability problems associated with the second critical speed. Various seal modifications are examined and shown to have favorable consequences with respect to bearing reactions and stability. Differences between linear and nonlinear model results are discussed and explained in terms of simple models. The transient nonlinear model is used to demonstrate forced subsynchronous motion similar to that observed in test data for models which are lightly damped but stable. The subsynchronous motion results from bearing clearance nonlinearities. Simulation results indicates that synchronous bearing loads can be reduced but that sub-synchronous motion is not eliminated by seal modifications.
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Goldfine, N., D. Schlicker, Y. Sheiretov, A. Washabaugh, V. Zilberstein, and T. Lovett. "Conformable Eddy-Current Sensors and Arrays for Fleetwide Gas Turbine Component Quality Assessment." Journal of Engineering for Gas Turbines and Power 124, no. 4 (September 24, 2002): 904–9. http://dx.doi.org/10.1115/1.1477196.
Повний текст джерелаАнотація:
The conformable Meandering Winding Magnetometer (MWM®) eddy current sensors and MWM-arrays provide new inspection capabilities for gas turbine components. The sensors provide measurements of coating thickness and absolute electrical conductivity, which can capture features of interest for a population of components, e.g., for tracking fleetwide trends in quality and aging, failure evaluations, and correlating failure origins to features of specific fleet population segments. Inspection applications include metallic and nonmetallic coating thickness and porosity measurement, detection of cracks on complex surfaces, imaging and detection of small flaws, thermal degradation monitoring, and cold work quality assessment. For example, the U.S. Air Force uses the MWM for cold work quality control on all of the C-130 propeller blades that go through the Warner Robins ALC. For P-3 and C-130 propeller blades, trend analysis is being performed fleetwide. This paper describes MWM technology advances for absolute property measurements and specific capability demonstrations. Multifrequency quantitative inversion methods used for coating characterization are also used for characterization of process-affected zones, such as shot peen quality or titanium alpha case characterization.
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Shichev, P. S. "TO DEVELOPMENT OF A MEASURING SYSTEM AND METHODOLOGICAL SUPPORT FOR CONTROL OF TECHNICAL CONDITION OF CENTRIFUGAL PUMP UNITS." Kontrol'. Diagnostika, no. 282 (December 2021): 12–19. http://dx.doi.org/10.14489/td.2021.12.pp.012-019.
Повний текст джерелаАнотація:
The article discusses solutions to create an algorithm for specifying the value of diagnostic parameters and instrumentation of measuring systems for the method of diagnostics of electric driven cantilever centrifugal pumping units by analyzing the spectra of motor current and voltage. The simulation model of the unit was used to establish a quantitative relationship between the amplitudes of the frequency components of the current and voltage of the motor supply line and the dependence of the phase shift between the fundamental harmonics of the current and voltage signals when varying the pressure developed by the pump centrifugal pumping units. An algorithm has been formed that assumes two approaches to refining the amplitude of the informative frequency component of the current spectrum, taken depending on the set of measured parameters. Arrangements of measuring systems for diagnostics of the centrifugal pumping units are proposed both with minimal possibilities for assessing the state of nodes by the spectrum of the current of one of the phases of the power line of the electric motor, and with the extended functionality of the spectral analysis of signals of currents and voltages of three phases of the motor and the possibility of refining the diagnostic parameters in conditions of their distortion by the frequency components of the mains voltage.
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Lan, Xianjiang, Ren Ren, Ruopeng Feng, Lana C. Ly, Yemin Lan, Zhe Zhang, Nicholas Aboreden, et al. "ZNF410 Uniquely Activates the NuRD Component CHD4 to Silence Fetal Hemoglobin Expression." Blood 136, Supplement 1 (November 5, 2020): 54. http://dx.doi.org/10.1182/blood-2020-137564.
Повний текст джерелаАнотація:
Transcription factors typically regulate a large number of genes. Here we found that transcription factor ZNF410 binds and activates the expression of a single direct target gene, CHD4, to enforce the silencing of the fetal hemoglobin genes (HBG1 and HBG2) in adult erythroid cells. ZNF410 is a pentadactyl DNA binding protein that emerged from a DNA binding domain-focused CRISPR-Cas9 screen aimed at the identification of new regulators of fetal hemoglobin silencing. Depletion of ZNF410 specifically diminished CHD4 expression, leading to reactivation of the normally silent fetal globin genes in both human erythroid culture systems and a human-to-mouse xenotransplant model. Combining RNA-seq and ChIP-seq analyses revealed that CHD4 is the sole direct ZNF410 target gene in erythroid cells, which was further validated by rescue of fetal hemoglobin silencing and other transcriptional changes upon CHD4 restoration in ZNF410-deficient cells. ZNF410 ChIP-seq detected only eight high-confidence peaks with seven associated genes including CHD4. Most strikingly, the two most predominant peaks are located at the CHD4 locus, which contains two highly conserved, dense clusters of ZNF410 binding motifs. The two motif clusters appear to be unique in the human and mouse genomes. Moreover, among the seven ZNF410-bound genes, CHD4 was the only one whose expression was down-regulated upon ZNF410 depletion, indicating that CHD4 is the sole target of ZNF410. Electrophoretic mobility shift assays (EMSAs) showed that the zinc finger (ZF) domain of ZNF410 is necessary and sufficient for DNA binding. When overexpressed, the DNA binding profile of ZF domain alone is very similar to full length ZNF410. Indeed, forced expression of the ZF domain displaced endogenous ZNF410 at all binding sites, including the CHD4 locus. This reduced CHD4 expression to levels comparable to those in ZNF410 deficient cells (and activated the fetal globin genes) but had no effect on the other ZNF410 bound genes, again confirming target specificity. ZNF410 depletion or expression of the dominant negative acting ZF domain lowered CHD4 only by ~65%-70%, which is very well tolerated by erythroid cells, as determined by morphology, cell surface phenotyping, and gene expression profiling. This exposes the fetal globin genes as highly sensitive to CHD4 levels. Lastly, we solved the crystal structure of the ZF domain-DNA complex at 2.75Å resolution pinpointing the protein-DNA contacts and showing that each of the five ZFs make specific DNA contacts. In sum, to our knowledge, ZNF410 is the only transcription factor with just one direct functional target gene in erythroid cells. Given the strong impetus to reactivate fetal globin gene expression in patients with sickle cell disease and some forms of b-thalassemia, it might be possible to exploit the exceptionally high transcriptional selectivity of ZNF410 to raise fetal hemoglobin expression for the treatment of these hemoglobinopathies. Disclosures Weiss: Rubius Inc.: Consultancy, Current equity holder in private company; Cellarity Inc.: Consultancy, Current equity holder in private company; Novartis: Consultancy, Current equity holder in private company; Esperion Therapeutics: Consultancy, Current equity holder in private company; Beam Therapeuticcs: Consultancy, Current equity holder in private company. Blobel:Fulcrum Therapeutics: Consultancy; Pfizer: Research Funding.