Search Results (12)

Drawing from a broad and multifaceted stream of educational research and practice that has gradually emerged in recent decades within science education field, widely known as Inquiry-Based Science Education (IBSE), the current study aims to extend its boundaries within the special education field. In particular it aspires to investigate to what extent teachers foster IBSE characteristics and accommodate the specific learning characteristics of students with autism when they are called to teach them projectile motion and the concept of force. To fulfill this goal, seven secondary school physics teachers with a background in special education were recruited to develop lesson plans on mechanics for high-functioning autistic adolescents. Our findings indicate that these teachers exhibit varying levels of engagement, with certain aspects of IBSE being applied more consistently than others. Notably, the nature of the content appears to play a significant role in shaping this variability. The findings show that teachers tend to demonstrate different levels of engagement, with some aspects of IBSE being more consistently applied than others. Interestingly, the nature of the content appears to play a significant role in influencing this variability. The findings of the current study are likely to contribute to teaching and learning science content to students that with autism spectrum disorder. Full article

For a spinning projectile, coning motion induced by disturbances during flight can have a unique impact on the lateral force and yawing moment, which may further affect flight stability and maneuverability. The flow over a coupled spinning–coning projectile and a spinning projectile was numerically simulated by solving the unsteady Reynolds-averaged Navier–Stokes (URANS) equation with an implicit dual-time stepping method and a spinning–coning coupled motion model established through a dynamic mesh technique. The variation in transient and time-averaged aerodynamic characteristics with the angle of attack (AoA), dimensionless spin rate, and dimensionless cone rate was analyzed, and the specific effect of coning motion on the lateral force and yawing moment was revealed. Based on these findings, the yawing moment term in traditional angular motion theory was modified, and the flight response to the initial disturbance was discussed. The results indicate that the time-averaged lateral force and yawing moment of the spinning–coning coupled projectile are multiplied compared with those of the spinning projectile and vary linearly with the dimensionless spin rate and cone rate. The main factors affecting the lateral force are the coning motion-induced effective angle of sideslip (AoS), asymmetric expansion waves, and asymmetric vortices. The much larger yawing moment induced by spinning–coning coupled motion can more easily cause AoA divergence and flight instability. Full article

Sabots are vital to the successful launch of hypervelocity projectiles (HVPs), supporting and protecting the projectile’s flight body within the barrel. After the projectile exits the muzzle, aerodynamic forces induce relative motion between the sabot and the flight body, termed ‘sabot discard’. During this process, there are complex aerodynamic interactions between the sabot and flight body. These interactions impact the flight body’s flight stability and accuracy. This research focuses on an HVP with a two-segment sabot at Mach 7.2, employing the unstructured overset grid method and three-degree-of-freedom model to investigate the impact of the angle of attack (AOA) on the discard. At the AOA = 0 Deg, the sabot segments’ movement is symmetric, causing fluctuations in the flight body’s drag. However, at AOAs $\ne$ 0 Deg, the sabot segments’ movement becomes asymmetric. The upper sabot segment accelerates while the lower one decelerates, causing significant fluctuations in drag and lift, and prolonged disturbance. As the AOA increases, both asymmetry and disturbances intensify. Notably, at the AOA = 8 Deg, the absolute value of the discard angle difference between the upper and lower sabot segments reaches 45 Deg. Considering the AOA’s impact, it is advisable to maintain the AOA for HVP sabot discard in the range of [−2, 2] Deg. Full article

To simulate the launching process of missile complex flow, movement, and constraint states, a multifield coupling model is put forward based on a computational fluid dynamics (CFD) method. In this coupled model, a CFD method is used to solve the three-dimensional compressible transient flow, and the six-degree motion of the launching platform is considered, and the virtual contact method is used to deal with the constraint states of the guideway and the slider. The active force and moment are applied to the launching platform to simulate its rolling, pitching, and heaving motions under the 5-level waves. Collision detection is carried out through the minimum clearance distance between the slider and the guideway, and the contact force is handled by a modified Herz collision model. In the problem of launching a missile from the water surface, the change characteristics of the flow field, the load response characteristics, and the relative motion laws of the missile and the launching platform during the catapulting process are investigated. The results show that the motion laws of the projectile and the launch tube in the constrained direction are the same, and the established coupling model is able to simulate the launch separation process of the missile in the constrained state. In addition, the effect of wind load on the missile ejection process is analyzed using the coupled model. Full article

The bending deformation can affect the lateral force of spinning projectiles with large aspect ratios, thus interfering with their flight stability. Based on the established spin–deformation coupling motion model, the unsteady Reynolds averaged Navier–Stokes (URANS) equations are solved to simulate the flow over a large−aspect−ratio projectile undergoing spin and spin−deformation coupling motion by using the dual−time stepping method and dynamic mesh technique, obtaining the lateral force. Furtherly, the flow mechanism is analyzed for the changed lateral force induced by the bending deformation. The results indicate that the variation of transient lateral force for the head of a projectile is consistent with that of the deformation−induced additional sideslip angle; affected by the deformation−induced compression wave and expansion wave, the time−averaged lateral force for the middle of a projectile will be increased at small angles of attack, but changed little at large angles of attack; at small angles of attack, the change trend of transient lateral force for the tail of a projectile is similar to that of additional angle of attack caused by the deformation; at large angles of attack, the characteristic of phase lag is presented between the transient lateral force for the tail of a projectile and the additional sideslip angle. Full article

Obvious aeroelastic deformation occurs in spinning projectiles with large slenderness ratio, which seriously affects flight stability and maneuverability. This paper investigates the aeroelastic response of spinning projectiles with large slenderness ratio under supersonic speed. Based on a dynamic mesh method, an unsteady numerical simulation method is developed to study the aeroelasticity of spinning projectiles by coupling aerodynamics and structural dynamics. The numerical simulation method is well validated by the experimental results of AGARD 445.6 wing flutter. Then, the aeroelastic response of spinning projectiles with large slenderness ratio is numerically explored under different flight conditions. The aeroelastic response is obtained, revealing the presence of beat vibrations and variations in response frequency. Furthermore, the influence mechanism of flight conditions on the aeroelastic response is analyzed. The results suggest that the coupling of the first two modes of the projectile caused by the spinning motion leads to the occurrence of beat vibrations in the aeroelastic response; the coupling degree of the first two modes decreases as the angle of attack increases and it increases with the increase in spinning speed; and the time−averaged deformation caused by the time−averaged aerodynamic force is beneficial to the convergence of the aeroelastic response of spinning projectiles, while the rotation−induced Magnus effect is counterproductive. Full article

The study of the water entry of successively fired projectiles under a wave environment is of great significance for the development and application of supercavitation weapons. In this paper, the supercavitating flow field of two successively fired projectiles entering water under different wave conditions is numerically simulated by the volume of the fraction model considering the cavitation of water. The motion of projectiles is handled by the overlapping grid technology and the simulated projectiles have six degrees of freedom. The effects of different wave phases and wave heights on the supercavitating flow field and the dynamic loads of the projectiles are studied. The research results show that the wave phase has an effect on the evolution and size of the supercavitation and the effect of the wave phase on the water splash above the free surface is more obvious. The peak of the drag force of the first projectile under conditions of different wave phases with 0.12 m wave height can be reduced by about 50% compared with that under the no-wave condition. The wave phases have an effect on the peak of the drag coefficient, and for the first projectile the peak under the condition of the 180° phase is about 40% lower than that of the 0° phase. The peak of the drag coefficient of the first projectile decreases with the increase in wave height. When the wave height increases from 0.0 m to 0.05 m, the peak value decreases by about 45%. For all conditions, regardless of wave phases or wave heights, the peak of the drag coefficient of the second projectile is obviously much lower than that of the first projectile. Accordingly, the decrease in the velocity of the second projectile is far slower than that of the first one. Negative values of the drag coefficient on the second projectile are observed when the second projectile enters the cavity of the first one. Full article

Addressing the problem of the influence of surface properties on the cavity in the process of a moving body entering water, especially the problems of water entry speed and the cavitation evolution of the round-head, air-delivered projectile that has many practical applications, a self-designed launch platform and high-speed camera were used, and the MK46 was used as a prototype to conduct scaled model experiments with different head form types and different surface properties. This paper describes the general process of the moving body entering the water and the generation of the cavity. The relationship between the re-injection flow, the local cavity number and the cavity stability is discussed. At the same time, the effects of head shape, launch velocity and surface wettability on the cavity evolution and motion characteristics were analyzed, including 0°, 57°, 70°, 90° and 180° hemispherical angle-head projectiles with speeds of 2.2 m/s and 3.95 m/s, so as to observe the cavity development and ballistics. The results show that hydrophobic surfaces are more prone to cavities when entering water vertically at low speeds. The influencing factors of water entry ballistics are often the combined effects of head shape, water entry speed and water entry angle. The speed of the hydrophilic surface models with head hemisphere angles of 57 degrees and 70 degrees entering the water is the fastest. This provides a reference for us to design the shape of the projectile. The internal relationship between the cavity shape and the ballistic characteristics is based on the premise that the cavity will complicate the force on the model. The cavity affects the ballistic characteristics of the model by affecting the forces on the model. Full article

In order to reduce the x-direction and Y-direction displacement disturbance of the barrel and improve the firing accuracy, based on Bernoulli Euler’s theoretical assumption of beam and taking M134 barrel machine gun as the calculation model, the pre-stress modal analysis and optimization of cantilever supported rotor under unbalanced force and moving mass are carried out in this paper. The main work of this paper is as follows: (1) M134 physical model is established, and the unbalanced force in the motion process of projectile in bore is solved by interior ballistic theory; (2) Based on the unbalanced rotor theory, the barrel vibration model considering the projectile weight and acceleration is established; (3) The critical speed model of high-speed rotating system is established, and the critical speed is determined by finite element modal analysis to determine the rigid/flexible state of barrel components in different speed regions; (4) Based on the above model, take the x-direction and Y-direction displacement of the barrel as the output value, and take the elastic modulus of the barrel, the relative position between the barrel hoop and the fuselage components and the cross-sectional area as the variable values, carry out the optimization design, and verify the firing accuracy before and after optimization through experiments. Full article

High-speed supercavitating projectiles receive tremendous hydrodynamic force when flying underwater in tail-slap mode, and have obvious structural deformation and structural vibration. To study the motion characteristics of high-speed supercavitating projectiles, a bidirectional fluid-structure interaction model was established, and validated by comparing with the existing results. The motion, supercavitation flow field, and structural deformation response process of a supercavitating projectile were numerically investigated under the conditions of initial speed within 800–1600 m/s. It was found that the tail-slap motion of high-speed supercavitating projectiles is correlated with a high-frequency structural vibration. Further, the amplitude of the structural vibration increases with the initial speed. When flying with an initial speed higher than 1200 m/s, supercavitating projectiles encounter a great structural deformation under the action of the huge hydrodynamic load, which exerts a significant influence on the motion characteristic, and even destroys the trajectory stability. Thus, the supercavitating projectile cannot be regarded as a rigid body any more, and the structural response effect must be considered. Full article

This paper presents an explanation of why a spinning football rotates so that the spin axis remains nearly aligned with the velocity vector, and approximately parallel to the tangent to the trajectory. The paper derives the values of the characteristic frequencies associated with the football’s precession and nutation. The paper presents a graphical way of visualizing how the motions associated with these frequencies result in the observed “wobble” of the football. A solution for the linearized dynamics shows that there is a minimum amount of spin required for the motion to be stable and for the football not to tumble. This paper notes the similarity of this problem to that of spun projectiles. The results show that the tendency of a football to align itself with and rotate with the velocity vector is associated with an equilibrium condition with a non-zero aerodynamic torque. The torque is precisely the value required for the football to rotate at the same angular rate as the velocity vector. An implication of this is that a release with the football spin axis and velocity vector aligned (zero aerodynamic torque) is not the condition that results in minimum motion after release. Minimum “wobble” occurs when the ball is released with its symmetry axis slightly to the right or left of the velocity vector, depending on the direction of the spin. There are additional forces and moments acting on the football that affect its trajectory and its stability, but it is not necessary to consider these to explain the tendency of the ball to align with the velocity vector and to ”wobble.” The results of this paper are equally applicable to the spiral pass in American football and the screw kick in rugby. Full article

The “super-gun” class of weaponry has been around for a long time. However, its unusual physics is largely ignored to this day in mainstream physics. We study an example of such a “super gun”, the “Paris gun”. We first look into the historic accounts of the firing distance of such a gun and try to reconcile it with our physical understanding of ballistics. We do this by looking into the drag component in the equations of motion for ballistic movement, which is usually neglected. The drag component of the equations of motion is the main reason for symmetry breaking in ballistics. We study ballistics for several air density profiles and discuss the results. We then proceed to look into the effects of muzzle velocity as well as mass and ground temperature on the optimal firing angle and firing range. We find that, even in the simplest case of fixed air density, the effects of including drag are far reaching. We also determine that in the “sensible” range of projectile mass, the muzzle velocity is the most important factor in determining the maximal firing range. We have found that even the simplest of complications that include air density, shifts the optimal angle from the schoolbook’s 45-degree angle, ground temperature plays a major role. While the optimal angle changes by a mere two degrees in response to a huge change in ground temperature, the maximal distance is largely affected. Muzzle velocity is perhaps the most influential variable when working within a sensible projectile mass range. In the current essay, this principle is described and examples are provided where students can apply them. For each problem, we provide both the force consideration solution approach and the energy consideration solution approach. Full article