Dynamics and 2D temperature distribution of plasma obtained by femtosecond laser-induced breakdown

Recently, plasma produced by focusing femtosecond laser in gases has been introduced as an etching tool in materials processing. Proper control of the plasma in this application necessitates the apt understanding of the different morphological features of the plasma. In this contribution we show that, the plasma produced in air goes through several stages of morphological development – from ellipsoidal to spherical to toroidal plasma, whereas in argon, axial compression of an ellipsoidal plasma is observed. To explain this dissimilarity, we have quantified the temperature by emission spectroscopy (Planck analysis with Wien’s approximation). The evolution of temperature shows a triple exponential dependence in time which can be correlated with different stages of morphological changes of the plasma. Open Source Field Operation and Manipulation (OpenFOAM) simulations using experimentally determined temperature values show that – (i) the reverse pressure gradient propagates radially inwards and compresses the plasma in both air and argon and forms a localized high pressure zone at the center that generates a secondary pressure wave in air, but not in argon, and (ii) the baroclinic torque that is generated because of the Richtmyer-Meshkov instability, dominates the rate of vorticity in air, whereas effects of flow compressibility and velocity gradients dominate the vortices in argon. Knowledge of the initial state and the dynamics of the subsequent stages of the plasma formation can be utilized for control and optimization of laser-induced plasma applications.

Investigation on Flow Field Characteristics in an Open-Pit Coal Mine

In this paper, the atmospheric flow field characteristics in a deep open-pit mine are investigated numerically and theoretically. A theoretical model on the recirculation length based on the energy equation is used, a total variation diminishing (TVD) difference scheme with second order accuracy is used to solve the NS equations with a standard two-equation k-ε turbulence model. The effects of elevated inner dump on the flow field characteristics of the open-pit mine are analyzed detailly with the same inflow parameters. The results show that a recirculation zone exists in the open-pit mine due to the reflux from the high-pressure zone to the low-pressure zone. As the height of the inner dump increases, the flow becomes more complicated, the low-pressure zone and the recirculation zone becomes bigger. The elevated inner dump makes it difficult for the internal fluid to flow to the outside, which results in the increase of the dust concentration. At last, the influences of key parameters on flow filed are conducted by normalizing the depth of the lowest direct current flow on the windward slope. The sensitivity analysis is done by study each influencing factor. This paper offers an effective way to study the flow field characteristics in an open-pit coal mine, which is essential to the dust pollution control of open-pit mine.

Onset of northeast monsoon over South Peninsular India

The onset dates of the northeast monsoon over South Peninsular India are determined using the wind data at 850 hPa and 200 hPa, OLR, mean sea level pressure data for the domain 40° E to 120° E, 0° to 40° N. These three data sets are sourced from NCEP/NCAR reanalysis daily data sets. Further the daily grid point (0.25° Lat. × 0.25° Long.) rainfall data over India from Indian Meteorological Department is considered for delineation of rainfall pattern. The total length of the data of the above mentioned parameters is 21 years (1994 to 2014). Pentad distributions of the above parameters for the domain considered are prepared for examining the circulation patterns and rainfall activity. The pentads taken for the study are from 55th (28th September - 2nd October) pentad to 65th (17-21 November) pentad. In the determination of the northeast monsoon over South Peninsular India, the following points are considered: (i) The persistence of the northeasterlies at 850 hPa level, (ii) Occurrence of the rainfall over the South Peninsular India, (iii) Presence of east-west oriented trough [Intertropical Convergence Zone (ITCZ)] in the lower latitudes from Ethiopia region to Malaysia region passing through South Arabian Sea, southern region of South Peninsular India and South Bay of Bengal, (iv) The presence of low pressure over the southwest Bay of Bengal at the surface, (v) Persistence of a high pressure zone in northern latitudes of India (extending from the Saudi Arabia/Jordan region to the Head Bay of Bengal running through North Arabian Sea, Gujarat and Orissa), (vi) Presence of subtropical ridge at 200 hPa level around 17.5° N, (vii) Presence of north-south ridge over theeastern parts of China and (viii) Presence of relatively low OLR values over South Peninsular India when compared to the northern latitudes. If any pentad satisfies the above points, the middle date of the pentad is considered as the date of onset of northeast monsoon over South Peninsular India. If any pentad satisfies all the points except point number 2, importance is given to the persistence of northeasterlies and the middle date of the pentad will be declared as the onset date. By following the criteria, the dates of onset of northeast monsoon are determined for the latest 21 years. These dates are compared with those of the India Meteorological Department.

A Probabilistic High-Pressure Zone Model of Dynamic Ice Structure Interactions and Associated Ice-Induced Vibrations

During ice-structure interactions that are dominated by ice compressive failure, the majority of the ice loads are transmitted through localized contact regions known as high-pressure zones (hpzs). This paper presents a probabilistic modelling framework for dynamic ice-structure interaction based on the mechanics of hpzs. Individual hpzs are modelled as a nonlinear spring-damper system where the stiffness is modelled as a function of nominal strain, with the degree of softening depending on the average strain-rate. Both spalling and crushing failure mechanisms were assessed in the context of periodical sinusoidal response. For spall dominated failure, the model structure showed presence of frequency lock-in in the speed range of 100–125mm/s, beyond which the failure was found to be random in nature with lower amplitude of structural response. The amplitude was also found to be significantly influenced by structural parameters with structural damping having the highest contribution. For pure crushing, an estimated equilibrium layer thickness based on theoretical calculations also showed presence of frequency lock-in. The work highlights the importance of understanding the interplay between these mechanisms, as well as the role of ice conditions and structural parameters on the processes that dominate an interaction.

Simulation and Verification of Hydraulic Performance and Energy Dissipation Mechanism of Perforated Drip Irrigation Emitters

Drip irrigation has become an application trend of water-saving irrigation technology due to its excellent water-use efficiency. However, the energy dissipation form of the commonly used labyrinth channel is relatively simple, and the corresponding energy dissipation mechanism research is inadequate. This article proposes a new kind of channel structure of drip irrigation emitters based on the structure of scalariform perforation plates in plant xylem vessels. We establish a total of 16 sets of orthogonal structure schemes. Using numerical simulation and physical experiments, the hydraulic performance and energy dissipation mechanism of the perforated drip irrigation emitters (PDIE) are studied. The results show that the flow index of PDIE is 0.4665–0.5266. The hydraulic performance of PDIE in the high-pressure zone is the best, and the flow index is 0.4665–0.5046. As the pressure increases, the velocity of the flow of the upper perforation increases rapidly, the flow ratio decreases, the flow index decreases, and the hydraulic performance improves. To further verify the energy dissipation mechanism, a lower flow ratio and a better hydraulic performance were obtained through appropriately expanding the upper part of the upper perforation inlet to the channel boundary. The research sheds new insights for optimizing the hydraulic performance of PDIE. Results reported here provide a theoretical basis for the structural design of drip irrigation emitters and the energy dissipation mechanism research.

Effect of Eccentric Distance on Successive Dual-droplet Impacting a Super-hydrophobic Tube

Droplet impact is a common but significant phenomenon in industry. The CLSVOF (coupled level set and volume-of-fluid) method is used to numerically study the successive dual-droplet impacting a super-hydrophobic tube. For the impact velocity of 1.0 m/s, the effect of the eccentric distance on dynamic characteristics is analysed, the corresponding eccentric distances are 0.5, 1.0 and 2.0, respectively. In addition, the break-up during rebound is analysed with velocity field and pressure nephogram. Results show that, the eccentric distance hinders the spread during the initial period of spreading. With the increase in eccentric distance, more liquid gathers at the eccentric side and the liquid film might rebound easily without break-up under the same impact velocity. The break-up during rebound mainly depends on the local airflow and pressure difference. The high-pressure zone near the solid-liquid interface moves towards the eccentric side with the increase in eccentric distance.

Numerical Modelization of the Oil Film Pressure for a Hydrodynamic Tilting-Pad Thrust Bearing

This study analyses the hydrodynamic characteristic of the tilting pad thrust bearing. Research content is simultaneously solving the Reynolds equation, force equilibrium equation, and momentum equilibrium equations. Reynolds equation is solved by utilizing the finite element method with Galerkin weighted residual, thereby determines the pressure at each discrete node of the film. Force and momentums are integrated from pressure nodes by Gaussian integral. Finally, force and momentum equilibrium equations are solved using Newton-Raphson iterative to achieve film thickness and inclination angles of the pad at the equilibrium position. The results yielded the film thickness, the pressure distribution on the whole pad and different sections of the bearing respected to the radial direction. The high-pressure zone is located at the low film thickness zone and near the pivot location.

Ground Test and Numerical Simulation on Ground Effect of Ducted Propeller System

The aerodynamic performances of a ducted propeller system applied in a manned vertical takeoff and landing aircraft considering the ground effect are investigated. Based on the ground test and CFD simulation combined with sliding mesh technique, the thrust and power characteristics of the ducted propeller under different heights between the duct and ground are compared and analyzed, and the influence mechanism of the ground effect on the aerodynamic performance of the ducted propeller is detailed analyzed based on the CFD simulation results. The test and simulation results show that, the ground near the ducted propeller leads to a high-pressure zone to block the jet flow through the outlet of the duct, while an upward rebounded flow with the vortex rings is also generated to affect the aerodynamic forces and powers of both the duct and propeller. As the influence of the high-pressure zone, the thrust of the propeller increases. However, the thrust of the duct decreases when the rebounded flow is inhaled again into the duct. With the increase of the heights between the ground and the ducted propeller, the ground effect is weakened, and the power of the system recovers more quickly than the thrust. In general, the ground effect seriously affect the aerodynamic efficiency of the ducted propeller in near ground hover state, which should be mainly considered in the process of aerodynamic and conceptual design.

Triple Stapling Resection and J pouch anal Stapling Anastomosis for Ulcerative Colitis

Background: In 2017, we reported laparoscopic total proctocolectomy with J pouch anal anastomosis, which was created at the dentate line by our original procedure using staplers, Triple Stapling Resection and J pouch Anal Stapling Anastomosis (TSRJASA), for ulcerative colitis (UC) patients. UC patients have undergone TSRJASA since it was introduced in our institution. However, the feasibility and usefulness of TSRJASA for UC patients has not been elucidated.Methods: From January 2014 to December 2018, fourteen patients with ulcerative colitis, including three cases of concomitant cancer, who underwent TSRJASA were enrolled in this study. Anal manometry was performed using the Pock Monitor GMMS-100 system (STAR MEDICAL, INC., Tokyo, Japan) one year and two years after surgery. Maximum resting pressure, maximum squeeze pressure, and the length of the high-pressure zone were measured. Fecal incontinence was evaluated using the Wexner incontinence questionnaire.Results: J pouch anal anastomosis was created at the dentate line in all patients. In a manometric examination two years after surgery, maximum resting pressure was 75.3 (54-88) mmHg, maximum squeeze pressure was 125.0 (90-160) mmHg, and the length of the high-pressure zone was 39.6 (35-42) mm. Wexner score was 2.8 (1-4).Conclusion: TSRJASA seems to be a useful procedure for UC patients given its acceptable defecation function.

THE INFLUENCE OF TECHNOLOGICAL PARAMETERS OF THE EXTRUSION PROCESS AND TECHNICAL PARAMETERS OF AN EXTRUDER WITH ELASTIC SCREW ELEMENTS ON THE EXPANSION INDEX OF THE EXTRUDATE

The processing of feed by extrusion improves the level of absorption by animals. In the extruder, due to frictional forces, the grain mass is heated to a temperature of 120 ... 150 ° C and acquires thermoplastic properties. Due to the transition of the heated mass from the high-pressure zone to the atmospheric zone, adiabatic expansion occurs, as a result of which the volume of the extrudate increases due to the destruction of the granular structure of starch at the cellular level. The extrudate acquires a microporous structure, which contributes to a more complete absorption of nutrients by the animal body. The purpose of the work is to determine the rational values of the factors that most significantly influence the extrusion process and to evaluate the degree of their influence on the extrusion index of the grain mixture of cereals. The studies were performed using a sample of the model extruder section structure, the coils of the screw extruder can oscillate along its axis. A blend of corn, barley and winter wheat in a 5: 3: 2 ratio was used as the study object. The effect of the extruder parameters and modes on the extrudate expansion index was studied using the multivariate experiment planning method. The extrudate expansion index was defined as the ratio of the extrudate diameter to the diameter of the die. To study the process, the following factors were selected that most significantly influence the extrusion process and the extrudate expansion index: die diameter X1 (d, mm), relative humidity of the grain mixture X2 (W,%) and temperature of the extrusion process X3 (T, 0C). The levels of variation of the factors were as follows (initially recorded the zero level of factors, and after the interval of variation): X1 (6; 2 mm), X2 (16; 4%) and X3 (135; 25 0C). As a result of the conducted researches the following rational parameters and modes of operation of the extruder were established: diameter of die d = 4.9… 5.9 mm; humidity of grain mixture W = 17,7… 20%; the temperature of the extrusion process T = 140… 145 0C, and a die diameter of 4.9 ... 5, 9mm.