k. liu

Surface roughness of ski suits can have a significant effect on the aerodynamic performance of ski jumping athletes. Herein, several typical surface roughness configurations are examined through numerical simulations. Force parameters such as lift, drag and pitching moment are analyzed to evaluate the aerodynamic performance of varying surface roughness. Furthermore, the athlete model is segmented into distinct body parts to conduct a comprehensive analysis of the aerodynamic contributions from each individual segment. Generally, the surface roughness has a significant effect on the aerodynamic performance during the flight phase. Specifically, the lift-drag ratio of the entire multibody system shows a trend of increasing first and then decreasing. Moreover, the trunk of the athlete plays a predominant role in generating aerodynamic forces during the flight phase. Therefore, when designing high-performance ski jumping suits, prioritizing the surface roughness of this part can be considered first. Flow structures are also presented to analyze the impact of these various surface roughness conditions. Notably, flow suppression near the back region of the athlete body can significantly reduce the resistance force in the horizontal direction. Consequently, this revelation of the impact mechanism of ski suit surface roughness on the aerodynamic performance of the multibody system can guide the design of appropriate ski suits, and will also assist athletes in achieving superior aerodynamic performance during flight.

The Reynolds number (Re) is an important parameter that can affect compressor performance. This study experimentally and numerically investigated the effect of Re variations on the efficiency and stall mechanisms for a three-stage axial flow compressor. In the experiment, the total pressure ratio, polytropic efficiency, and stalling mass flow rate were measured in a Re range varying from 1,100,000 to 55,000 to elucidate the Re effects. Unsteady three-dimensional numerical simulations were implemented to understand the stall mechanisms. The results indicate that the compressor efficiency and stall–pressure ratio begin to decrease remarkably as Re is reduced below a critical value, which is 220,000 in the case of the compressor studied. At a low Re, losses caused by the secondary flow near the hub and shroud increase remarkably, and the extended boundary layer separations at the blade suction surface further decrease the efficiency. The variation in Re changes the stall-initiated location. At higher Reynolds numbers, the interaction between the corner separation at the hub of stator 1 and the leakage flow through the blade tip gap induces a large vortex, which seriously blocks the blade passage. The blocking effect spreads to the aft stage and extends to higher spans, which results in the stall of the whole compressor. However, the blocking effect at the hub disappears at Re =55,000, and the interaction of the blade boundary layer separation near the shroud of rotor 1 and the tip leakage vortex causes a large blockage and then induces stall. The Re variation changes the radial flow transportation because of the varying effect on the aerodynamic performance of each blade element at different spans. This significantly influences the extent of the vortex near the end wall and ultimately changes the stall mechanisms.

The sport of half-pipe skiing, characterized by its dynamic maneuvers and high-speed descents, often faces challenges posed by unpredictable wind conditions.  To address this, an advanced wind-blocking system incorporating an air curtain capable of generating a jet flow is proposed. This pioneering design offers a dual advantage: the system can significantly reduce the windbreak size in the vertical dimension while maintaining a satisfactory wind-blocking effect. A comprehensive study is conducted to analyze the effects of the height of the windbreak and the jet emission angle from the air curtain. When the jet speed is 40 m/s, a 50° emission angle and a 2 m height of the windbreak result in an optimal wind-blocking effect. Furthermore, delving deeper to understand the underpinnings of this phenomenon, we discovered that a counterrotating vortex pair, which forms in the presence of this jet under crossflow conditions, plays a pivotal role in augmenting the wind-blocking capabilities of the system.

NatuAt present, radioactive seed implantation is a common treatment for prostate cancer, the TPS (treatment planning system) calculates the dose by adding the dose attributed to each source. However, the interseed attenuation effect would result in a difference between the actual dose and the calculated dose. The aim of this study was to identify the factors influencing the interseed attenuation effect.

I-125 seed sources were selected, and MC (Monte Carlo) method was used to simulate the dose distribution around seed sources. The results obtained from the linear addition of a single-source dose were compared with those obtained considering the interseed attenuation effect. The effects of the medium, source arrangement and source number on the dose were evaluated.

The MC simulation results for multiple seed sources are lower than those for linear additive doses in most areas. In different medium, the mean error caused by interseed attenuation effect is the smallest in adipose tissue (0.52%) and the largest in bone (1.41%). Taking four sources as examples, the maximum error is 9.34%, appearing in the plane where the source is located. The error decreases to 1.3% when the source is located 2 mm away from the source plane. The more scattered the sources are in space, the smaller the error will be.

A high atomic number and high-density medium will cause a high error. The area with a high error is mainly observed in the plane where the sources are located, the edge error of the source distribution area is larger.

In this paper, a bionic perception method of navel orange plucking position based on Fmincon and Proportional Differential (PD) angle control is proposed to solve the problems of wind disturbance and green branches in dynamic unstructured environment. Different from these algorithms that limited to two-dimensional images, this method realizes picking position perception in three-dimensional. Meanwhile, the perception method and the picking robot control algorithm are achieved simultaneously. Firstly, an optimal solution model of the global target rotation angle of the control system based on Fmincon is established to solve the angle optimization problem of robot target approach motion. Secondly, a bionic perception system of plucking position based on PD angle control is constructed to solve specific perception problems. Finally, a joint simulation platform for picking robots based on Solidworks, Adams, and Simulink is given; the validity and accuracy of the algorithm were verified. The experimental results show that the picking accuracy rate is 95%, the angle error of each mechanism and the displacement error are less than 0.5 degrees and 10mm, respectively. The total time from the optimized angle calculation to the system's stability is only about 0.33s. This method is suitable for the rapid perception of plucking position and active angle control of picking robots under dynamic unstructured environment.