Performance of textured foil journal bearing considering the influence of relative texture depth

Both foil structure and surface texturing have been widely used to improve bearing performance. However, there is little research on their combination, namely, textured gas foil bearing. This paper adopts the Reynolds equation as the pressure governing equation of bump-type foil journal bearing to study the influence of textures located on the top foil. The Newton-Raphson iterative method and the perturbation method are employed to obtain static and dynamic characteristics, respectively. Thereafter, based on three texture distribution types, further analysis about the effect of the relative texture depth and the textured portion is carried out. The results indicate that an appropriate arrangement of textures could improve the performance of gas foil bearing. For #1 texture distribution, the maximum increment of load capacity could exceed 10% when ω = 1.4 × 105 r/min, ε = 0.2.

The Effect of Gurney Flap and Trailing-edge Wedge on the Aerodynamic Behavior of an Axial Turbine Blade

In this research, the effect of Gurney flap and trailing-edge wedge on the aerodynamic behavior of blunt trailing-edge airfoil Du97-W-300 which is equipped with vortex generator is studied. To do this, the role of Gurney flap and trailing-edge wedge on the lift and drag coefficient and also aerodynamic performance of the airfoil is studied. Validation of the numerical model is performed by comparison of the obtained results with those of experiment. Results show that before stall, Gurney flap leads to the increase in the aerodynamic performance in a wider range of angle of attack. Numerical findings reveal that the maximum increment for the aerodynamic performance is obtained at low angle of attack when trailing-edge wedge is employed. It is found that for the highest considered value of Gurney flap and trailing-edge wedge heights, where the highest values for the lift occur, the higher aerodynamic performance at low angle of attack is obtained when trailing-edge wedge is used and at high angle of attack, the Gurney flap results in a higher aerodynamic performance. It is also shown that when high aerodynamic performance is concerned, addition of Gurney flap to the airfoil leads to the higher value for the lift. Doi: 10.28991/HIJ-2021-02-04-03 Full Text: PDF

Comparative Study of Dynamic Stall between an Aircraft Airfoil and a Wind Turbine Airfoil in an Air–Particle Flow

Dynamic stall in clean air flow has been well studied, but its exploration in air–particle (air–raindrop or air–sand) flow is still lacking. The aerodynamic performance loss of aircraft (NACA0012) and wind turbine (S809) airfoils and their differences during the hysteresis loop at different pitching parameters are also poorly understood. As shown in this paper, the reduced frequency has little effect on the value of the maximum lift coefficient increment caused by particles, but a larger one can enhance the hysteresis effect and drag the angle of attack, at which the maximum increment is obtained, from the up stroke to the down stroke. The large lift coefficient increments of two airfoils and their difference also have a similar change trend with the reduced frequency. Compared to that of NACA0012 airfoil, the increments of S809 airfoil are obviously greater at three mean angles of attack, especially at 8°, which is the commonly used operating angle. In addition, the angle of attack, at which the maximum lift coefficient is obtained, can be significantly changed by particles in two regions: one is under the effect of deep stall, the other is under the effect of light stall at a low, reduced frequency.

Effect of Depth-Induced Breaking on Wind Wave Simulations in Shallow Nearshore Waters off Northern Taiwan during the Passage of Two Super Typhoons

Super Typhoons Maria (2018) and Lekima (2019) were adopted for this case study, although they only passed the northern offshore waters of Taiwan without making landfall. A direct modification technique was employed to create the atmospheric conditions for a wave-circulation model to hindcast large typhoon-driven waves. The radius of the modified scale (Rtrs) for a hybrid typhoon wind plays an important role in the significant wave height (SWH) simulations during the passage of typhoons. The maximum increment in peak SWH reached 3.0 m and 5.0 m in the deep ocean for Super Typhoons Maria (2018) and Lekima (2019), respectively if the Rtrs was increased from 4 × Rmax (radius of the maximum wind) to 7 × Rmax. The SWHs induced by the typhoon winds in the surf zone were more sensitive to different wave-breaking formulations used in the wave-circulation model. The maximum difference in peak SWH reached 2.5 m and 1.2 m for Super Typhoons Maria (2018) and Lekima (2019), respectively, when the wave-breaking formulations of BJ78 (proposed by Battjes and Janssen in 1978) and CT93 (proposed by Church and Thornton in 1993) were introduced to the wave-circulation model. The SWH simulations in the surf zone were insensitive to the wave-breaking criterion (γ) during the passage of typhoons. In shallow nearshore waters, the utilization of a constant γ for the wave-circulation model always produces peak SWHs that are smaller than those using γ based on local steepness or peak steepness.

234 Woodlands for Expanding the Grazing Opportunity for Small Ruminants in the Southeast: Challenges and Opportunities

Woodlands account for around 60 percent of the land cover in the Southeast and offer a great potential for expanding the grazing opportunity for small ruminants. However, such opportunities and challenges associated with woodland grazing have not been documented well. The objectives of this study were to 1) develop strategies for increasing understory-vegetation biomass and its utilization by small ruminants and 2) identify challenges associated with the use of small ruminants in woodland plots. The study was initiated in 2017 using six woodland plots (0.4-ha each) that consisted of southern pines, as the main timber species, and numerous non-pine species. Each plot was virtually divided into four sections, and each section was randomly allocated to one of the cutting treatments or control. Treatments included the cutting of non-pine species into one of the three heights from the ground surface: 0 m, 0.9 m, or 1.5 m, and the control section did not receive any cut. Samples of understory vegetation were collected during the production period of 2018 and 2019, dried, and weighed. Small ruminants were rotationally stocked in the plots and their behavior (feeding: grazing, browsing; non-feeding: loafing, lying, and debarking) and landscape-use pattern (time spent by animals in different treatments or control in performing various behaviors) monitored. The understory-vegetation biomass increased tremendously in treatments compared to the control (33%-160%), with maximum increment (100%-160%) occurring in the section that received 0-m cut. Animals spent much of their feeding time in sections that received 0-m and 0.9-m cut consuming much of the vegetation available within their reach (goats or goats-sheep mixed: 0–1.5 m; sheep: 0–1.1 m from the ground). They selected dry and less vegetated areas containing shelters and tree shade for resting, visited the least to the control, and did not impose any damage to timber trees.

Growth of Fagus sylvatica L. and Picea abies (L.) Karst. Seedlings Grown in Hiko Containers in the First Year after Planting

In forest management in Poland, there are no standards for the quality and suitability for planting seedlings produced in nursery containers; therefore, research contributing to the development of such guidelines is important. We investigated the growth reaction of European beech and Norway spruce seedlings growing in container technology one year after planting on an experimental forest plantation. The seedlings used in the study were three experimental variants grown in a container nursery differing in fertilization. Two heights of seedlings were measured, i.e., after the first growing season on the experimental plantation and the initial (obtained in the forest nursery), and the annual (AHI, cm) and relative height increments (RHI, %) were calculated. The regression of the RHI of seedlings to their initial height was calculated, and the equations obtained were used to determine the optimal range of seedling height at the stage of nursery growth at which they will achieve the maximum increment in the first year of growth on the plantation. The change from foliar fertilization to a mixed one affected beech and spruce seedling parameters; however, it did not affect the diversity of their survival on the experimental plantation. Higher seedlings planted on the experimental plantation were characterized by a smaller RHI. The optimal range for the height of seedlings obtained at the nursery stage of growing, which determined the maximum value of the AHI after the first year of growth after planting, was 18–36 cm for beech and 14–25 cm for spruce.

Target Registration Errors in Navigation-assisted Mandibular Surgery According to the Tracking Methods and the Type of Markers

Background: This study was conducted to evaluate the accuracy of navigation process according to the type of tracking methods and registration markers. The target registration errors (TREs) were measured at seven anatomical landmarks of the mandible for evaluation. Methods: Four different experiments were performed to obtain the TREs using two different tracking methods, the optical tracker (Polaris) and the electromagnetic (EM) tracker (Aurora), and two different types of registration markers, invasive and noninvasive markers. All comparisons of TREs were statistically analyzed using SPSS and Python-based statistical package (Pingouin). Results: The average TRE values obtained from the four different experiments were as follows: 1) 0.85 mm using invasive marker and Aurora, 2) 1.06 mm using invasive marker and Polaris, 3) 1.43 mm using noninvasive marker and Aurora, and 4) 1.57 mm using noninvasive marker and Polaris. All comparisons among the type of markers and the seven anatomical landmarks revealed statistically significant differences, except for the type of tracking system. Although the comparison between the modality of the tracking system showed no significant differences, the EM-based approach consistently demonstrated better performances than the optical type in all comparisons. Conclusions: This study demonstrates that, irrespective of the tracking modality, the invasive marker is a better choice in terms of accuracy. When using the noninvasive marker, it is important to consider the increased TREs. In the present study, the noninvasive marker caused a maximum increment of TREs of approximately 0.81 mm compared with the invasive marker. Furthermore, EM-based tracking using an invasive marker may result in the best accuracy for the mandible.

Thermal comfort under weightlessness: A physiological prediction

This study investigated the physiological thermal response of people under simulated weightlessness using a 6° head down bed rest (HDBR) model to ensure the human body functions in the weightlessness way. Thermal responses of six male participants were experimentally determined. The relationship between thermal comfort and heart rate variability (HRV) was also scrutinized. Physiological responses of participants under different environmental conditions were observed including core temperature, sweating, and most importantly, HRV. Elevated core temperatures were observed amongst participants, with a maximum increment of 0.5°C. The sweating of participants under simulated weightlessness was conspicuously retarded, requiring a 2–4°C increase in environmental temperature to start sweating. Body regional differences in the sweating were also observed. The HRV index ‘LF/HF’, which reflects the balance of the autonomous nervous system, was found to vary with the environment and closely associated with the variation in the thermal comfort scores. Participants under simulated weightlessness had higher mean LF/HF when they felt comfortable, and they preferred a warmer environment in comparison to under normal gravity condition. An altered thermoregulation of the human body under simulated weightlessness was indicated by our findings. The use of HRV index could provide a useful prediction of subjective thermal comfort under weightlessness.

Effect of Additivized Biodiesel Blends on Diesel Engine Performance, Emission, Tribological Characteristics, and Lubricant Tribology

This research work focuses on investigating the lubricity and analyzing the engine characteristics of diesel–biodiesel blends with fuel additives (titanium dioxide (TiO2) and dimethyl carbonate (DMC)) and their effect on the tribological properties of a mineral lubricant. A blend of palm–sesame oil was used to produce biodiesel using ultrasound-assisted transesterification. B30 (30% biodiesel + 70% diesel) fuel was selected as the base fuel. The additives used in the current study to prepare ternary fuel blends were TiO2 and DMC. B30 + TiO2 showed a significant reduction of 6.72% in the coefficient of friction (COF) compared to B30. B10 (Malaysian commercial diesel) exhibited very poor lubricity and COF among all tested fuels. Both ternary fuel blends showed a promising reduction in wear rate. All contaminated lubricant samples showed an increment in COF due to the dilution of combustible fuels. Lub + B10 (lubricant + B10) showed the highest increment of 42.29% in COF among all contaminated lubricant samples. B30 + TiO2 showed the maximum reduction (6.76%) in brake-specific fuel consumption (BSFC). B30 + DMC showed the maximum increment (8.01%) in brake thermal efficiency (BTE). B30 + DMC exhibited a considerable decline of 32.09% and 25.4% in CO and HC emissions, respectively. The B30 + TiO2 fuel blend showed better lubricity and a significant improvement in engine characteristics.

Photovoltaic Equalizer Based on Single-Input Multi-Output Push-Pull Converter

Component mismatch often happens in the module-series photovoltaic system(including centralized, string, multi-strings PV system) due to partial shadowing, which causes a large loss of power generation. Photovoltaic equalizer can process the differential power under the condition of mismatching through parallel power electronic converter without changing the existing photovoltaic system architecture, so that all the modules can work near their maximum power points, which can greatly improve the power generation of the system under the condition of mismatching. This paper proposes a photovoltaic equalizer based on single-input multi-output push-pull converter. The topology has the advantages of simple structure and less switching devices. Firstly, the paper introduces the partial shadowing problem of photovoltaic modules and the principle of photovoltaic equalizer. Then, the topological structure and working principle of the proposed photovoltaic equalizer system are analyzed in detail. Finally, the simulation and verification of the designed photovoltaic equalizer are carried out. The simulated results show that the proposed equalizer can greatly improve the generation capacity of photovoltaic system under mismatching conditions, and the maximum increment can be up to 41%.