携帯型キネマティックGNSSを用いたスキージャンプの飛行計測

Ski jumping is a sport which competes the flight distance and the flight form, and jumpers attempt to fly as far as possible. In the regulations for ski jumping competition, the outstretched fabric must show a medium air permeability of a minimum of 40 liters per m2/sec under 10 mm of water pressure. However, the effect of the air permeability of ski jumping suits on aerodynamic characteristics has not been completely clarified yet. The purpose of this study is to investigate the effect of air permeability of jumpsuit fabrics on aerodynamic characteristics, and three types of fabric with different air permeability are examined from aerodynamic point of view. The wind tunnel experiments were carried out using the fabric clothed elliptic cylinder. The aerodynamic forces and velocity distribution were measured for four fabrics with different air permeability.

Described in this paper is an investigation on the aerodynamic characteristics of a full-scale realistic supersonic rocket-sled in operating conditions. The scale adaptive simulation (SAS), coupled with the layer dynamic mesh method, as well as a rocket-sled test, is employed here to present the detailed aerodynamic characteristics. The method used, overcoming the disadvantages of the wind tunnel test and the numerical blowing method, presents the realistic aerodynamic characteristics of an operating rocket-sled. Considering the realistic geometry, the effects of the sled-beam, supports, rails, fasteners, and sink on the aerodynamic characteristics of a supersonic rocket-sled are systematically studied. The aerodynamic characteristics, in terms of the transient flow structures, momentum transport process, lift and drag force, the aerodynamic characteristic frequency is considered at Mach numbers ( Ma ) of 1.5, 2, 2.5 and 3, while the corresponding test results are obtained at Ma of 1.5, 2, and 2.5. The results found show that the bow shock and compression waves of the rocket-sled are reflected at the multi-facilities, causing the complex wave structures, vortex shedding and aerodynamic characteristics. Compared with the simplified flat ground condition, the increase of 818% in the time-averaged lift of the rocket-sled is induced by the full-scale realistic multi-facilities at Ma = 2. The fasteners on the ground contribute to the increase of the lift, while the rail is not helpful. The sink on the ground produces a dramatically asymmetrical flow field which is revealed by the fraction coefficient and limiting streamlines of the rocket sled surface. In addition, the reflected compression waves are significantly enhanced by the periodically fixed fasteners, resulting in the periodic characteristics of the lift and drag force. The PSD (Power Spectral Density) analysis of the pressure, lift and drag force is employed to illustrate the characteristic frequency. The dominant frequencies of the rocket-sled at Ma = 1.5, 2, 2.5 and 3 are 407.6 Hz, 544.6 Hz, 679.9 Hz and 817.2 Hz, respectively. The results provide a reference for avoiding the resonance between the rocket-sled in operation and the rail.

Horizontal penetration in granular media is ubiquitous, from tunneling and geotechnical site investigation, to root growth and the locomotion of burrowing animals in nature. This contribution couples the discrete element method (DEM) with ant colony optimisation, a heuristic optimisation algorithm, to find the optimal tip shapes to minimise drag and lift forces during horizontal penetration. The tip which minimizes drag has a slender profile with a low tip curvature, to give a drag force that is $$15.6\%$$ 15.6 % lower compared to a conventional CPT intruder, however this shape induces a downwards force that increases with intruder depth. Conversely, the tip that minimizes lift is blunt, with a high tip curvature and short width, and reduces the drag and lift forces by $$4.5\%$$ 4.5 % and $$30.8\%$$ 30.8 % (respectively) compared to the CPT. The lift and drag forces are competing optimisation objectives, thus the tip shape with the optimal trade-off between drag and lift forces can be established using Pareto optimality. The Pareto optimal tip shape reduces the drag and lift forces by $$10.7\%$$ 10.7 % and $$19.4\%$$ 19.4 % respectively, and is strikingly similar to the profile of a sandfish. This contribution shows that when a common goal exists, bio-inspired solutions can offer an optimal solution to engineering applications. We also show the potential to integrate DEM simulations within an optimization framework to develop innovative design solutions.

Abstract. GNSS stands for Global Navigation Satellite System and is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. The advantage of having access to multiple satellites is accuracy, redundancy, and availability at all the times. Though satellite systems do not often fail, if one fails GNSS receivers can pick up signals from other systems. If the line of sight is obstructed, having access to multiple satellites is also a benefit. GPS (Global Positioning System, USA), GLONASS (Global Navigation Satellite System, Russia), BeiDou (Compass, China), and some regional systems are positioning systems that are usually used. In recent years with the development of the UAVs and GNSS receivers, it is possible to manage an accurate PPK (Post Processing Kinematic) networks with a GNSS receiver mounted on a UAV to achieve the position of images principal points WGS1984 and to reduce the need for GCPs. But the most important challenge in a PPK task is, which a combination of different GNSS constellations would result in the most accurate computed position in checkpoints. For this purpose, this study focused on a PPK equipped UAV to map an open pit (Golgohar mine near Sirjan city). For the purpose, different combination of GPS, GLONASS and BeiDou used for position computed. Results are plotted and compared and found out having access to multiple constellations while doing a PPK task would bring higher accuracies in building photogrammetric models although it may cause some random error due to the higher values of noise while the number of the satellites increases.

Kinematic Analysis of the Take-Off and Start of the Early Flight Phase on a Large Hill (HS-134 m) during the 2009 Nordic World Ski Championships The take-off is often considered the most significant and difficult phase of a ski jump. Thus, the purpose of this study was to compare three groups of ski jumpers representing different skill levels during the execution of the take-off and start of the early flight phase in ski jumping. A total of 30 athletes, recruited from competitors performing ski jumps on an HS-134 m jumping hill, were categorized into three groups based on jump-length execution. Two-dimensional (2-D) kinematic data were collected from the lower extremities, trunk, and skis of the ski jumpers. Findings indicated that the ski jumpers with shorter jump length demonstrated significantly smaller in-run velocity (p < .05), while the elite and mediocre level ski jumpers exhibited a significantly faster shift of the thigh at the transition from take-off into the early flight of the jump (p < .05) than did the low-level ski jumpers. In addition, the centre of body mass (CoM) of the elite group shifted significantly more forward over the skis (p < .01) than did that of the other two groups. Finally, interindividual differences existed among ski jumpers at similar performance levels. The largest coefficients of variation (CVs) were found for the position changes of the trunk and shank behind the jumping hill edge.

Relative importance of the lift force on heavy particles due to turbulence driven secondary flows

Ski jumping flight skill analysis based on high-speed video image

Direct numerical simulations of the shear flow over assemblies of uniformly sized, solid spheres attached to a flat wall have been performed using the lattice-Boltzmann method. The random sphere assemblies comprised monolayers, double layers and triple layers. The Reynolds number based on the sphere radius and the overall shear rate was much smaller than 1. The results were interpreted in terms of the drag force (the force in the streamwise direction) and lift force (the force in the wall-normal direction) experienced by the spheres as a function of the denseness of the bed and the depth of the spheres in the bed. The average drag and lift forces decay monotonically as a function of the surface coverage of the spheres in the top layer of the bed. The sphere-to-sphere variation of the drag and lift forces is significant due to interactions between spheres via the interstitial fluid flow.

Unmanned aerial vehicles (UAVs) are being increasingly used to provide high resolution imagery which, through photogrammetric method Structure-from-Motion (SfM), can be used for high resolution topographic reconstruction. PPK (Post-Processing Kinematic) positioning solution offers the potential of accurate image georeferencing without ground control points (GCPs). By integrating consumer-grade cameras and an onboard RTK/PPK GNSS receiver, we managed to have a low-cost and effective approach involving topographic change-detection. Here, we evaluated the positional accuracy and reproducibility of DSMs generated from PPK-SfM workflow with two camera setups by conducting multiple UAV surveys over a test field. Our results showed that the PPK solution has the same accuracy (mean: ca. 0.01 m, RMSE: ca. 0.03 m) as the more traditional georeferencing method based on ground control points. Furthermore, our results indicated that camera properties (i.e. focal length, resolution, sensor quality) have a large impact on the accuracy: a DSLR camera (Canon EOS), with 0.63 cm px-1 GSD, had 0.011 m planimetric error and 0.012 m altimetric error; while a cheap and light Action camera (GoPro) with 3.11 cm px-1 GSD had 0.019 m planimetric error and 0.024 m altimetric error at the same flight height. The repeatability of DSM construction was assessed by a DoD (DEMs of Difference) analysis. The LoD95% and LoDmin were ca. ±0.08 m and ca. ±0.04 m for the DSLR camera and ca. ±0.16 m and ca. ±0.08 m for the action camera (for a flight altitude of 45 m). The level of detection substantially improved when reducing the UAV flight altitude. We found that tie point density greatly controlled the error of the topography reconstruction for the DSLR camera. By exploiting the relation between error and tie point density, we demonstrated that a spatially explicit DoD threshold, according to the local surface condition, can greatly improve surface change detection. Volume estimation was conducted over the plowing area and obtained comparable results from DSLR and action camera datasets. Overall, the application of a PPK-UAV workflow provides a high-precision and high-efficiency solution in surveying and geomorphological applications.

Analysis of aerodynamic characteristics of car diffuser for dissimilar diffuser angles on Sedan’s using CFD

In this paper we propose and derive expressions for the drag and lift forces in a two-phase particulate mixture. The analysis is limited to two-dimensional laminar flows. In the Section after the Introduction, a brief review of the single particle approach is provided; it is then shown that in most multiphase flow problems some generalization of these forces acting on a single particle is used. We then describe a different way of defining the lift force and the drag force, an approach used in non-Newtonian fluid mechanics. In the following Section, the essential equations of Mixture Theory are provided and the specific approach of [1] is used. In this scheme, the lift force is part of the interaction mechanisms, which are to be modeled as constitutive parameters. In the final Section, we derive an expression for the lift force, whereby it is shown that the normal component of the force acting on the body, obtained by integrating the traction vector of the mixture acting on a single isolated particle, will give us the desired expression for the lift force in multi-component flows.

The primary objective of this study is to investigate the effect of slip mechanisms in nanofluids through scaling analysis. The role of nanoparticle slip mechanisms in both water- and ethylene glycol-based nanofluids is analyzed by considering shape, size, concentration, and temperature of the nanoparticles. From the scaling analysis, it is found that all of the slip mechanisms are dominant in particles of cylindrical shape as compared to that of spherical and sheet particles. The magnitudes of slip mechanisms are found to be higher for particles of size between 10 and 80 nm. The Brownian force is found to dominate in smaller particles below 10 nm and also at smaller volume fraction. However, the drag force is found to dominate in smaller particles below 10 nm and at higher volume fraction. The effect of thermophoresis and Magnus forces is found to increase with the particle size and concentration. In terms of time scales, the Brownian and gravity forces act considerably over a longer duration than the other forces. For copper-water-based nanofluid, the effective contribution of slip mechanisms leads to a heat transfer augmentation which is approximately 36% over that of the base fluid. The drag and gravity forces tend to reduce the Nusselt number of the nanofluid while the other forces tend to enhance it.

An investigation into the aerodynamic characteristics has been presented for a bio-inspired flapping wing aircraft. Firstly, a mechanism has been developed to transform the usual rotation powered by a motor to a combined flapping and pitching motion of the flapping wing. Secondly, an experimental model of the flapping wing aircraft has been built and tested to measure the motion and aerodynamic forces produced by the flapping wing. Thirdly, aerodynamic analysis is carried out based on the measured motion of the flapping wing model using an unsteady aerodynamic model (UAM) and validated by a computational fluid dynamics (CFD) method. The difference of the average lift force between the UAM and CFD method is 1.3%, and the difference between the UAM and experimental results is 18%. In addition, a parametric study is carried out by employing the UAM method to analyze the effect of variations of the pitching angle on the aerodynamic lift and drag forces. According to the study, the pitching amplitude for maximum lift is in the range of 60°~70° as the flight velocity decreases from 5 m/s to 1 m/s during landing.

In this paper, we present the concept and main mission of the Crabster, an underwater walking robot. The main focus is on the modeling of drag and lift forces on the legs of the robot, which comprise the main difference in dynamic characteristics between on-land and underwater robots. Drag and lift forces acting on the underwater link are described as a function of the relative velocity of the link with respect to the fluid using the strip theory. Using the translational velocity of the link as the rotational velocity of the joint, we describe the drag force as a function of joint variables. Generalized drag torque is successfully derived from the drag force as a function of generalized variables and its first derivative, even though the arm has a roll joint and twist angles between the joints. To verify the proposed model, we conducted drag torque simulations using a simple Selective Compliant Articulated Robot Arm.

The widespread use of multicopters, in particular quadcopters, in the civil, industrial and defense sectors necessitates the improvement of their aerodynamic characteristics in order to increase maneuverability, energy efficiency, load carrying capacity and reduce noise level. One of the key elements affecting these characteristics is the design of the propellers. Despite significant progress in the research of propellers for classical aviation, research for multicopters remains quite limited.The aim of the work is to conduct a comparative aerodynamic analysis of four three-dimensional models of the HQProp V1S 7x3.5x3 propeller using the modern SolidWorks Flow Simulation software. The research methodology involves computer modeling of three-dimensional models of the real propeller, created by the author using the master-model method and the shell method, as well as 3D models obtained from specialized internet resources.The main parameters of the analysis are the distribution of air flow velocities, pressure distribution, calculation of lift and drag force, as well as the influence of the angle of attack on the aerodynamic properties of the studied samples. The results of mathematical calculations demonstrate the differences between the models.The scientific novelty and practical significance of the research is that the author obtained original data on the aerodynamic characteristics of 3D models of the HQProp V1S 7x3.5x3 propeller, which were not previously published in the open press. The mathematical modeling technique used and the results obtained thanks to it will be used in the future to design new, more advanced propeller models, which will contribute to improving the overall efficiency of the UAV.