Propeller Efficiency - Simple Methods

In order to produce thrust, the air needs to be accelerated by the propulsor (the propeller or the jet engine). The more the air gets accelerated from flight speed v = v_1 to exit speed v_4 (i.e. the higher v_4/v_1), the lower the efficiency. However, without accelerating the air, no power or thrust is produced. The efficiency depends on the non-dimensional thrust, called thrust loading, c_S, which is a function of aircraft speed. Disc loading k_P is calculated from power, P air density, rho and propeller disc area, A_S. k_P is independent of speed and as such a good characteristic parameter of a propeller. Together, this makes the propulsive efficiency a function of disc loading, k_P and flight speed, v. Further losses come from angular momentum. The efficiency calculated considering angular momentum in addition dependents on the ratio of forward speed, v and tip speed u (v/u). A constant speed propeller can run at a favorable speed for the piston or turboprop engine at a limited Mach number of the blade tips. At higher speeds, v and also v/u increases and hence required engine torque. This increases the angular momentum and reduces the efficiency. At low speeds, the ratio v_4/v_1 gets unfavorably high and the efficiency is low. At zero speed v_4/v_1 goes to infinity and the efficiency to zero. For an example calculation, optimum efficiencies were obtained at v/u between 3 and 5 depending on disc loading. Not considered is the limited lift-to-drag ratio (L/D) of the propeller blades and losses at blade tip (which could be accounted for by a performance factor between 0.85 and 0.9).

Effect of Finishing Diet and Lairage Time on Steers Welfare in Uruguay

The objective of this experiment was to evaluate the effect of two different pasture-based finishing strategies and lairage time on steers welfare in Uruguayan conditions. Sixty Hereford (H) and Braford (B) steers were assigned to two different diets for finishing purposes: (D1) native pasture plus corn grain (1% of live weight) (H n = 15, B n = 15) and (D2) high-quality pasture (H n = 15, B n = 15). The average daily gain was registered every 14 days, and temperaments were individually assessed one week before slaughter by three individual tests: crush score, flight time and exit speed, building a multicriterial temperament index (TIndex). Animals were slaughtered the same day in two groups (50% from D1 and 50% from D2 in each group) after traveling for 3.5 h and staying 15 (long lairage) and 3 h (short lairage) in the lairage pens, respectively. The behaviors were observed during lairage, and physiological indicators were used to assess stress at the farm after transport, after lairage and at slaughter. Bruises incidence and final pH were registered at the abattoir as a means of assessing the overall animal welfare. Calmer animals had higher average daily gains with no differences either between diets or between breeds. Calmer animals also had a lower stress response during all preslaughter stages, regardless of the time in lairage. Transport did not imply psychological stress (cortisol) for any slaughter group, but physical stress was evident after transport in both groups through NEFA and CPK increases. Bruise incidences did not differ between lairage groups. The short lairage group did not have enough time to cope with the environment before slaughter, with the consequent deleterious effects on the carcass pH. Animals from the long lairage group had a higher metabolic response shown through NEFA values, but they had enough time to rest and recover overnight, reaching final pH values lower than 5.8, considered the upper limit of the normal range. According to this experiment, with pasture-based animals without fasting on the farm and after 3.5 h of transportation, a resting period of 15 h in lairage should be better than a 3-h one.

The effect of spin level and ball exit speed on forearm muscle activity in the tennis forehand stroke

Elbow tendinopathy injuries are very common in tennis players. One of the commonly accepted theories describing the development of elbow tendinopathy in tennis is based on stiffness of the forearm skeletal muscle units and their repetitive overuse in the forehand stroke. Our objective was to use a novel microcontroller based wearable device to compare the influence of different forehand spin levels (flat, topspin and lob) and ball exit speed on forearm muscle activity in the potential onset of elbow tendinopathy in experienced adult tennis players. Peak normalised extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscle activity corresponding to each forehand shot and ball exit speed were determined and analysed. For the ECR shots (flat = 121, topspin = 272 and lob = 273) by 8 players, Kruskal-Wallis test (p < 0.001) and Post-Hoc tests revealed a significant difference between the flat and topspin spin levels (p < 0.01) and flat and lob spin levels (p < 0.001). For the FCR shots (flat = 125, topspin = 301 and lob = 303) by 9 players, Kruskal-Wallis test showed no significant difference between the three spin levels. For the corresponding ball speed, the Kruskal-Wallis (p < 0.001) and subsequent Post-Hoc (p < 0.001) showed that flat hits had the significantly highest ball speed followed by topspin then lob accordingly for both muscles included shots. Our results suggest that coaches could consider recommending players to hit forehands with topspin in order to potentially reduce the risk of developing lateral elbow tendinopathy.

Effect of air pockets in drug delivery in jet injections

Needle-free jet injections are actuated by a pressure impulse that can be delivered by different mechanisms, and the resultant jets are (102) m/s. Here, we report on the effect of entrapped air bubbles since filling procedures for pre-filled ampoules can induce bubbles, especially for viscous fluids. We use spring-piston devices as the principal actuation mechanism and vary both the location and size of the initial bubble. We find that the bubble location does have a statistically significant (p < 0.05) effect on the jet exit speed, based upon the volumetric flow rate. However, we reveal subtle features such as intermittent atomization when the gas pockets pass through the orifice and de-pressurize, which leads to spray formation and a temporary increase in jet dispersion, both of which can lead to product loss during an injection. These results have implications for the development of prefilled ampoules for jet injection applications.

EXPERIMENTAL STUDY ON PERFORATION OF BRITTLE LAYERED OBSTACLES

An experimental study of the process of perforation of plates made of brittle materials by rigid strikers has been carried out. The strikers were accelerated to the required speed with a pneumatic gun. Both homogeneous plates and obstacles from several plates glued together, put together without gluing, or spaced relative to each other were considered as targets. The results of experiments on the perforation of plexiglass plates by rigid spherical bodies at impact velocities of 100–200 m/s are presented. Qualitative features of the fracture at different velocities of impact are revealed. For the samples considered, it was found that spaced plates reduce the velocity of the striker during penetration more effectively than the same plates putted together. A set of experiments were also carried out on perforation of two combined plates made of various brittle materials: plexiglass, ceramics, artificial stone (polyacryl, quartz) by a rigid spherical striker for a velocity range of 200–350 m/s. For each considered combination of plates, a ballistic limit (ballistic limit velocity, BLV, at which the striker penetrates the obstacle with zero exit speed) was experimentally established, which characterizes the protective properties of the barrier. The effect on the ballistic limit of the order of the layers was studied. As a result, it was found that for all selected pairs of materials, a larger ballistic limit was achieved when a less dense and less brittle plexiglass layer was located behind a denser plate (made of ceramic or artificial polyacrylic or quartz stone). The reverse order of the layers led to a decrease in the ballistic limit in all cases. Photographs illustrating the nature of the destruction of the plates are presented.

Influence of Mg Content on Deformability of AlMg Alloys during Extrusion

In this study the research on deformability of AlMg alloys with high Mg contents in extrusion was carried out. The different shapes from AlMg alloys containing 3.5%, 4.5% and 5.5% of Mg were extruded on 500 T semi-industrial press by using one-hole and multi-hole flat dies. The extrudates surface quality was under investigations in relation with the temperature-speed parameters of the extrusion process. The metal exit speed was estimated depending on the extrudates shape, wall thickness and Mg content. The alloy’s border solidus and liquidus temperatures were also determined.

Development of a Variable Diameter Synthetic Jet Actuator

Synthetic jet actuators use oscillating motion near a fixed orifice to produce a net axial momentum flux with zero net mass flux. Through strategic application, these devices can provide flow control, propulsive thrust, and impingement cooling. To improve this performance, a new actuator has been designed with a variable orifice size, which can potentially increase exit flow speeds. The jet is generated using a pneumatic cylinder, which is oscillated linearly near an orifice. The opening consists of a camera aperture, whose diameter can decrease by a factor of 18 with the aid of a second pneumatic cylinder. The system is capable of operating at frequencies up to 5 Hz while maintaining full piston stroke, and the phase between the piston and orifice motion can be varied from 0 to 180 degrees. The flow structure is investigated using phase-locked particle image velocimetry (PIV), which shows that simultaneous constriction of the exit can substantially increase the exit speed. The initial design is used with air flow but will be extended to water applications in the future.

Correlation Relationships between Properties of Brick Body and their Use in Building Practice

The regular exit check of the brick products is an important step as to meet the quality in brickworks. These products are characterized by pore and lightweight brick body, therefore, their physical properties depend primarily on the specific characteristics their pore structure. We can determine on the basis of one well-known property and the correlation relationships other characteristics of the brick body, since there is an assumption that these properties between themselves "connected". Authors propose to use this knowledge in the exit speed check directly at the factory. In this case could be monitored only one property and one that can be quickly and reliably determined, such as thermal conductivity of using an apparatus Isomet. It is then possible to set for the existence of a correlation function between thermal conductivity and compressive strength of brick body at regular intervals compressive strength without using a hydraulic press.

Research of Baseball’s Best Batting Position Changes with the Selection of Material of Baseball

From the aspect of the fastest exit speed of the ball and through the collision model of mechanics, we analyzed the best hitting point which results in the fastest exit speed of the ball and the change of the best hitting point. Based on this model, we gave a very practical definition of the sweet spot, and we also found out the effect of the baseball bat’s material on the sweet spot. The distances from the best hitting point to the end of the baseball bat result from the three different materials, which are the bat’s original material, aluminum and the corked material. Through the sensitivity analysis, three parameters affecting the hitting position resulting in the ball’s fastest exit speed are the weight of the bat, the center of mass and the moment-of-inertia. In the process of the three parameters’ calculation, the infinitesimal method is used. As can be found out that the length of the sweet spot results from the corked and the aluminum are much longer than results from the original material. The longer the length of sweet spot, the possibility that the hitter hits the fast ball is higher. Also ball hit by the aluminum bat is faster than that hit by the bat made out of the original material. The above analysis can explain that why the aluminum bat and corked bat are prohibited by Major League Baseball