Increasing Drop Height Research Articles

Rigid-Body Water–Surface Impact Dynamics: Experiment and Semianalytical Approximation

An experimental study of the dynamics of a generic rigid body during water impact and an equivalent-radius approximate analytical procedure is developed and calibrated in this study. The experimental tests in a wave basin covered a range of drop heights using a 1/6th-scale model of a practical water-landing object prototype for two drop mechanisms to determine the water impact and contact effects. The first mechanism involved a rope and pulley arrangement, while the second mechanism employed an electromagnetic release to drop the rigid body. Hydrodynamic parameters including peak acceleration and touchdown pressure were measured and the maximum impact/contact force was estimated for various entry speeds (corresponding to various drop heights) and weights of the rigid body. Results from the tests show that the impact acceleration and touchdown pressure increases approximately linearly with increasing drop height and the data provides conditions that keep impact accelerations under specified limits for the rigid-body prototype. The experimentally measured maximum accelerations were compared with classical von Karman and Wagner approximate closed-form solutions. In this study, an improved approximate solution procedure using an equivalent radius concept integrating experimental results with the von Karman and Wagner closed-form solutions is proposed and developed in detail. The resulting semianalytical estimates are calibrated against experimental results and found to provide close matching.

Response characteristic of acceleration forces in loose-fill cellulose insulation material caused by impact tests

Using a wall element filled with loose-fill cellulose insulation a settling test according to the draft standard ISO CD 18393, method B was performed. The drop height and the hardness of the absorber of the test stand were varied. Acceleration was measured at the bottom of the wall element and on three levels inside the insulation. Results show that certain maximum values are not exceeded inside the insulation, although acceleration at the bottom of the wall element is rising with increasing drop height and absorber hardness. Fast-Fourier-transform of the acceleration signals shows that only low frequencies mostly below 100 Hz are transferred into the insulation body while higher frequencies were absorbed by the insulation material.

Dynamic postural stability for double-leg drop landing

Dynamic postural stability has been widely studied for single-leg landing, but seldom considered for double-leg landing. This study aimed to evaluate the dynamic postural stability and the influence mechanism of muscle activities during double-leg drop landing. Eight recreationally active males and eight recreationally active females participated in this study and dropped individually from three heights (0.32 m, 0.52 m, and 0.72 m). Ground reaction force was recorded to calculate the time to stabilisation. Electromyographic activities were recorded for selected lower-extremity muscles. A multivariate analysis of variance was carried out and no significant influence was found in time to stabilisation between genders or limb laterals (P > 0.05). With increasing drop height, time to stabilisation decreased significantly in two horizontal directions and the lower-extremity muscle activities were enhanced. Vertical time to stabilisation was not significantly influenced by drop height. Dynamic postural stability improved by neuromuscular change more than that required due to the increase of drop height. Double-leg landing on level ground is a stable movement, and the body would often be injured before dynamic postural stability is impaired. It is understandable to protect tissues from mechanical injuries by the sacrifice of certain dynamic postural stability in the design of protective devices or athlete training.

Preparation of a Large Size Granular Specimen Using a Rainer System with a Porous Plate

Abstract In this study, a rainer system capable of forming a large homogeneous granular specimen is introduced. A series of laboratory tests is carried out in order to study the performance of the proposed system. The features of the rainer system used in this study are the adoption of a porous plate and the air-pluviation without changing the deposition intensity. Without a porous plate, the rainer induces an insignificant density increase with increasing drop height, providing a dense to very dense specimen. However, the rainer with a porous plate produces a medium dense to dense specimen, with a drastic density increase at drop heights of 10–40 cm and a progressively reduced rate of density increase at larger drop heights. It is shown that the density obtained by using a porous plate rainer with a 70 cm drop height is similar to that achieved by using a conventional rainer with a 10 cm drop height. It is concluded that the use of a conventional rainer that adopts a porous plate significantly widens the range of density achievable even without an alteration in the deposition intensity. It is also concluded that using the rainer with a porous plate significantly improves the vertical and horizontal homogeneities of the specimen. The relative density evaluated from the measured cone resistance appears to provide a reasonable estimation at depths of 40–80 cm. The profile of shear wave velocity measured using bender elements seems to accurately reflect the vertical non-uniformity of the specimen.

Approach run increases preactivation and eccentric phases muscle activity during drop jumps from different drop heights

The purpose of this study was to investigate the effects of a horizontal approach run and drop height on the activation of lower extremity muscles during drop jumps. Ten participants performed drop jumps from drop heights of 15, 30, 45 and 60 cm with zero (standing), one, two, and three approach run steps. The EMG activities of the Gluteus Maximus (GM), Rectus Femoris (RF), Biceps Femoris (BF), Vastus Lateralis (VL), Tibialis Anterior (TA), Gastrocnemius (GA) and Soleus (SO) were recorded, full-wave rectified, and averaged (aEMG) during the preactivation (50 ms before touchdown), downward, and push-off phases. Increasing drop height did not enhance the muscle activation level of any examined muscles except GA. During the preactivation phase, the aEMG of all muscles except TA increased with the number of approach run steps. The aEMG of RF, BF, VL, and SO also increased with the number of approach run steps during the downward phase, while no aEMG changes were observed during the push-off phase. These results suggest that a horizontal approach run preceding the drop jump is an effective strategy for increasing the muscle preactivation level, which contributes to a higher level of muscle activity during the eccentric contraction phase and could potentially contribute to the reported higher power output during the concentric contraction phase.

Impact resistance of fibre-reinforced concrete

Fibre reinforcement increases the toughness of plain concrete under static compressive loading. The compressive toughness of fibre-reinforced concrete (FRC) under impact loading has not, however, previously been investigated. The current paper reviews the behaviour of high-strength fibre-reinforced concrete under uniaxial compressive impact loading. An instrumented drop weight impact machine was used to carry out compressive impact tests on various FRC systems with compressive strengths ranging from about 60 MPa to 120 MPa. The deformations of the FRC cylinders were determined using a high-speed video camera system. As expected, the compressive strength was found to increase with increasing drop height (or impact velocity). The dynamic compressive toughness was also found to increase with increasing drop height and with increasing matrix strength. It was observed that the mode of failure of the FRC was dependent upon the properties of the matrix and of the fibres, as well as on the drop height. Thus, the dynamic compressive toughness of FRC appeared to be dependent on the constitutive behaviour of the matrix, the fibre type and volume, the impact velocity and the mode of failure.

Experimental Investigation of Air Entrainment in Free-Falling Particle Plumes

Powders and granulated solids are widely used in industrial bulk solids storage, handling, and transportation systems. Such bulk materials handling operations frequently involve a falling stream of material. During such a process, the surrounding air is induced to flow with the falling particle stream, forming a particle-driven plume. Herein, experimental research results are reported on this fundamental problem, focusing in particular on the velocity profile of air entrained by the free-falling particles. This investigation shows that the velocity profile of the induced air can be modeled as a Gaussian distribution. The radius of the particle plume is found to increase linearly with increasing drop height, and it also increases with increasing bulk solid mass flow rate. Comparisons are made with other entrainment flows, such as jets and plumes, and it was found that air entrainment and hence the angle of spread of the particle-driven plumes was much less than for the other entrainment flows. The angles of spread of the particle-driven plumes were found to be in the range 1.3° < θ s < 1.8° as compared to θ s ≈ 5.7° for miscible plumes arising from sources of heat, for example. In addition, the centerline velocity of the induced air in the particle plumes was found to increase significantly with increasing drop height. Results from high-speed digital video records show that the bulk material does not dilate in a uniform manner as it falls, and a series of distinct particle clouds form in the core of the particle-driven plume. These clouds eventually disperse over a sufficiently large drop height.

Immediate Damage to The Blood-Spinal Cord Barrier Due to Mechanical Trauma

Primary damage to the blood-spinal cord barrier (BSCB) is a nearly universal consequence of spinal cord injury that contributes significantly to the overall pathology, including the introduction of reactive species that induce cytotoxicity as well as secondary insults on the BSCB itself. We have characterized quantitatively the extent and severity of primary, physical disruption of the BSCB in adult rats 5 min after graded trauma induced with the Impactor weight-drop model of spinal cord contusion. Animals were injured by dropping a 10-g mass 12.5, 25, or 50 mm (n(level) = 8) on to the exposed mid-thoracic spinal cord. The volume of extravasation of three markers of distinct size--fluorescently labeled hydrazide ( approximately 730 Da), fluorescently labeled bovine serum albumin ( approximately 70 kDa), and immunohistochemically labeled red blood cells ( approximately 5 microm in diameter)--were quantified in both the gray and white matter. The results indicate that spinal cord trauma causes immediate, non-specific vascular changes that are well-predicted by mechanical parameters. Extravasation volume increased significantly with increasing drop height and decreasing marker size. Extravasation volumes for all three markers were greater in gray matter than in white matter, and were better correlated to the rate of spinal cord compression than to the depth of spinal cord compression, which suggests that tissue-level strain rate effects contribute to primary spinal cord microvasculature pathology. The relationship between the response of the spinal cord and the injury pattern points towards opportunities to control the distribution and extent of injury patterns in animal models of spinal cord injury through a precise understanding of model and tissue biomechanics, as well as potential improvements in means of preventing spinal cord injury.

Contribution of the tendinous tissue to force enhancement during stretch–shortening cycle exercise depends on the prestretch and concentric phase intensities

When the prestretch intensity and concentric work are increased in stretch–shortening cycle (SSC) exercises, the utilization of the elastic energy can increase during the concentric phase. In order to further understand this process during SSC exercises, the interaction between fascicle–tendinous tissues (TT) of the vastus lateralis (VL) muscle was examined under different prestretch and rebound intensity drop jumps. Ten male subjects participated in the study. Direct VL fascicle lengths ( N = 10) and in vivo patellar tendon force ( N = 1) were measured together with the electromyographic (EMG) activity of VL during the trials. With increasing drop height but the same rebound height condition, the TT stretch increased during the early braking phase with a subsequent increase in its recoil during the early push-off phase. This occurred concomitantly with decreased fascicle shortening and EMG activation. However, with the increased rebound height but the same drop height condition, the fascicles were stretched less during the late braking phase with higher EMG activation. In this situation, TT could be stretched more by the tension provided by fascicles. Consequently, the TT recoil increased during the late push-off phase. These observations confirm that there can be an intensity specific fascicle–TT interaction during SSC exercises.

Interaction between fascicle and tendinous tissues in short-contact stretch-shortening cycle exercise with varying eccentric intensities

The interaction between fascicle and tendinous tissues (TT) in short-contact drop jumps (DJ) with three different drop heights [low (Low), optimal (OP), and high (High)] was examined with 11 subjects. The ground reaction force (F(z)) and ankle and knee joint angles were measured together with real-time ultrasonography (fascicle length) and electromyographic activities of the medial gastrocnemius (MG) and vastus lateralis (VL) muscles during the movement. With increasing drop height, the braking force and flight time increased from Low to OP (P < 0.05). In High, the braking force increased but the flight time decreased compared with OP (P < 0.05). During contact of Low and OP conditions, the length of muscle-tendon unit and TT underwent lengthening before shortening in both MG and VL muscles. However, the two muscles differed in the fascicle behaviors. The MG fascicles behaved isometrically or shortened, and the VL fascicles underwent lengthening before shortening during contact. In High, the TT lengthening in both muscles decreased compared with OP (P < 0.05). The rapid stretch occurred in the MG fascicles but not in VL fascicles during the braking phase. The elastic recoil ratio decreased in both muscles with increasing the intensity during DJ. These findings demonstrated that TT underwent lengthening before shortening during DJ. However, the efficacy of elastic recoil decreased with increasing the drop intensity. The effective catapult action in TT can be limited by the drop intensity. In addition, the measured muscles behaved differently during DJ, providing evidence that each muscle may have a specific means of fascicle-TT interaction.

Comparative performance of playground surfacing materials including conditions of extreme non-compliance

Objective: A recent case series study found that only 4.7% of 402 playgrounds in which arm fractures occurred in Victorian schools complied with the recommended 20 cm depth of tanbark....

The static and impact behaviour of polymer composite sandwich beams

The static and dropped weight impact performance of polymer composite sandwich beams has been investigated in a three-point bend configuration. The skin materials examined included woven fabrics of glass, carbon and aramid fibre, as well as glass chopped strand mat. The core materials were Coremat ™ (resin-impregnated non-woven polyester) and Aeroweb ™ aluminium honeycomb. Polyester and epoxy resin matrices were used. The static failure modes of beams with various core and skin combinations are discussed. The dominant failure modes for both glass/Coremat and glass/Aerolam ™ beams involved upper skin failure in the vicinity of the penetrator. The dropped weight impact performance of the latter two types of beam, at impact speeds of up to 7.5 m s −1, was investigated. The Coremat-cored beams showed marked rate dependence effects, with failure energies reducing to a minimum at a given drop height and then increasing again with increasing drop height. The honeycomb-cored beams showed only slight rate dependence. The dynamics of the beam tests are discussed in terms of mass spring models and times to failure in the upper skins highlighted.

The fracture toughness of concrete under impact loading

The fracture toughness of plain concrete, high strength concrete, and concrete reinforced with fibrillated polypropylene fibers was studied. Single-edge notched beams, of dimensions (l×w×d) 1400×100×125 mm, were loaded dynamically in 3-point bending, using an instrumented drop weight impact machine. Fracture energies and dynamic fracture toughness (K ID) values were determined, using three different drop heights of the impact hammer. It was found that, for all three types of concrete, K ID increased with increasing drop height; the fracture toughness values under impact loading were much higher than those obtained in static tests. There were also dramatic increases in the fracture energies under impact loading.

加工用トマト果実の物理的性質に関する研究

The physical behavior under drop impact of the fruits of tomato for processing was investigated to elucidate the resistivity of the fruits against impact load.1. Impact force and impact energy accompanied by the dropping increased with increasing drop height or fruit weight. The impact energy was relatively large in the varieties of oblate fruits (H-1409, Kagome 70, ES-58) and the smallest in those of pear-shaped fruits (Super Roma V.F., Chico) among the examined varieties.2. The hardness of the fruits was decreased by suffering the drop impact, and the decrease in the hardness became pronounced with an increase in impact. The degree of deformation accompanied by impact was distinguished in the varieties of round or oblate fruits, whereas it was not distinguished in those of pear-shaped or lengthy fruits.3. The frequency of occurrence of injured fruits increased with increasing drop height. The damage index of the fruits increased with increasing fruit-shape index and fruit weight.The critical impact energy for the occurrence of injured fruits was comparatively high in Chico, AT 70/24, and Super Roma V. F. among the examined varieties. Accordingly, the resistivity against impact load was higher in the varieties of pear-shaped or lengthy fruits than in those of oblate or round ones.The resistivity of each variety decreased with a progress in maturity of fruits.