Free Fall Height Research Articles

CFD-FEM simulation of water entry of aluminium flat stiffened plate structure considering the effects of hydroelasticity

In this paper, the slamming loads and structural response of an aluminium flat stiffened-plate structure during calm water entry considering the hydroelasticity effects are studied by a partitioned CFD-FEM two-way coupled method. The target structure is simplified as one segment of an idealized ship grillage structure, comprising flat plate and stiffeners. The typical numerical results are analyzed such as vertical displacement, velocity, acceleration, impact loads, and structural stress of the flexible flat bottom grillage structure considering the hydroelasticity effect and air cushion effect in different free fall height conditions. Drop test results of the same structure and other existing numerical simulation data by both coupled and uncoupled solutions in the literature are used for comparison with the present numerical simulation results. This study provides a practical means to simulate the slamming behaviour and structural response of ship structures, which is useful for predicting ship hull stiffened panel loads and related structural design.

Experimental investigation on debris bed formation from metallic melt coolant interactions

Motivated by risk quantification of severe core meltdown accidents which may occur light water reactors, an extensive DEFOR (DEbris FORmation) test series with various molten oxidic materials was conducted previously at Royal Institute of Technology to investigate the characteristics of debris beds formed from oxidic melt-water interactions, which are important to the coolability of debris beds and thus the retention of core melt. Yet, little attention has been paid to metallic melt which exist in the core melt. The present study is intended to fill in the knowledge gap, i.e., to characterize metallic melt-water interactions when a melt jet falls into a deep water pool. Nine DEFOR-M tests are carried out to clarify the effects of melt jet diameter, free fall height and water pool depth on metallic debris formation characteristics. Molten tin of 20 kg is employed as the simulant of metallic melt. A melt sensor and a mass sensor are installed to detect the discharging period of coherent jet and the mass accumulation of debris bed, respectively. A high-speed camera is applied to record the process of jet breakup, debris fragmentation and solidification, and debris bed formation. The experimental results show that the water pool depth has a significant influence on steam explosion and debris bed formation characteristics. Moreover, the jet breakup length is sensitive to jet diameter and free fall height. Finally, the features of metallic debris beds are compared with those of oxidic ones in respects of debris bed's configuration and porosity, particles' morphology and size distribution.

Multi-layer casting of self-consolidating concrete: Influence of mortar rheology and casting parameters on the inter-layer bond strength

Inter-layer bond strength is a critical factor to achieve structurally sound monolithic concrete structures. This paper discusses the effects of the cementitious paste volume (CP%vol), structural build-up of mortar (Athixm), and their interactions with casting parameters (i.e., free fall height (HFF), and delay time) on the residual bond strength of multi-layer self-consolidating concrete. It is found that the residual bond strength can be improved by increasing the CP%vol and HFF, or by reducing the delay time and Athixm. Out of the factors investigated, Athixm has the largest effect on both the residual bond strength and the critical delay time.

EXPERIMENTAL AND ANALYTICAL STUDY ON THE IMPACT BEHAVIOR OF STEEL–CONCRETE COMPOSITE SLAB

Concrete structures have been widely used for many years to resist impact loads. Steel–concrete composite structures may be considered efficient structures in the emerging modern construction field. Hence, the main objective of this research was to study the impact behavior of steel concrete composite slabs with different shear connectors and compare them with conventional slabs. Seven specimens of dimensions 500 × 500 × 50 mm were cast, which included plain cement concrete slabs, two reinforced cement concrete slabs with steel mesh and steel rebars as reinforcement, and four steel-concrete composite slabs with four different shear connectors: stud, tee, angle, and channel connectors. The composite action was achieved using a steel decking sheet welded with connectors on which the concrete layer was poured at the top. The test setup was fabricated with slots provided for specimens with simply supported end conditions and a mild steel drop weight. The specimens were impacted at the center of the span by dropping a steel mass from a free fall height of 1 m. The number of blows corresponding to the initial cracking and ultimate failure stages was recorded. The parameters that were used to compare the specimens were the impact energy absorbed, crack pattern, crack width, and increase in impact energy from the first blow to the last blow. The experimental results were very close to the analytical results obtained using ANSYS. The experimental and analytical results showed that the composite slabs with channel connectors performed better than the others, and it was proven that the composite slabs performed better under impact loading than conventional slabs.

Experimental and Numerical Crashworthiness Study of a Full-Scale Composite Fuselage Section

This work deals with the development of an improved numerical model, based on the explicit finite element method, aimed at investigating the energy absorption capabilities of a full-scale composite fuselage section of a regional aircraft and the related biomechanical injuries affecting the passengers. The experiment, conducted within the Italian national research project named “Innovative and Advanced Verification and Certification methods,” consisted in a drop test of a fully equipped barrel performed at the Italian Aerospace Research Centre, according to the special conditions of the Federal Aviation Regulation Certification Specification 25. From a free-fall height of about 4 m, a ground contact impact velocity of was measured. The numerical model has been developed faithfully to the experiment. Numerical analysis results, in terms of global deformations, failures, local accelerations, and biomechanical injuries, have been compared with the experimental ones to assess the prediction capability of the proposed numerical modeling procedure with a focus on improved crashworthy components for certification by analysis future purpose.

Packing of wet monodisperse spheres

We experimentally investigated the packing of wet monodisperse spheres with controlled falling height. The packing fraction are found to decrease with smaller grain size and free fall height. A model describing the effects of interparticle force and falling height on packing fraction is developed by introducing a dimensionless length scale, representing the extent of particle rearrangement towards a denser state due to impacts of falling grains. A universal law is observed for both wet particles where capillary forces dominate and dry powders where van der Waals forces govern the packing behaviour. This study deepens the understanding of packing of cohesive spheres and provide a simple experimental method for generating granular media with tailored packing fraction.

Dynamics of impact cratering on granular bed by hydrogel sphere

A lot of studies on the dynamics of a granular impact cratering by a liquid drop have been carried out. However, the results so far are controversial due to the complex impact dynamics of a liquid drop, such as deformation, splash, and penetration into the granular bed. In this study, we focused on the dynamics of the granular impact cratering by a hydrogel sphere, which deforms without splashing and penetrating. We investigated the maximal deformation time of the sphere and the lift-off time of the grains. Both the maximal deformation time and the lift-off time are similar to each other and depend on the −1/2 power of the Young’s modulus of the hydrogel sphere. This power law of the maximum deformation time is the same as an impact of a gel sphere on a flat solid surface. The angle of the ejected curtain was evaluated. The angle is larger for the impact with small deformation of the sphere than that for the impact with large deformation, and the angle is less dependent on the free-fall height. We also investigated the distributions of the ejected grains using the grains dyed by a fluorescent dye. The distribution was visualized by the fluorescent images captured before and after the impact. At the crater rim, the number of the dyed grains flying to and away are balanced. The number of the dyed grains gathered at the dimensionless distance from the crater center of 1.15, where the distance is nondimensionalized by the crater radius, is the largest. This maximum value for the number of the gathered grains is larger for the impact with small deformation than that with large deformation. This result is consistent with the dependence of the impact mode on the angle of the ejected curtain.

Performance on the drop impact test of the cone capsule shaped portable tsunami lifeboat using penalty method contact analysis

In 2016, the Laboratory of Ship Structures and Construction Diponegoro University organized a research group to develop an alternative hull form for the tsunami lifeboat. The research group proposed a cone capsule shaped portable tsunami lifeboat to support tsunami evacuation system, especially to give a portable protection facility that easily accessed by disable person, senior citizens and children.In order to fulfill the requirement that the lifeboat structure should be able to withstand the impact load, the aimed of the study is focused on the performance of the drop impact test of the developed portable tsunami lifeboat using numerical simulation.The tsunami lifeboat has to maintain its structural integrity when dropped on 3m free fall height. The orientation configurations are considered for the numerical analysis includes end drop, side drop and reversed drop. The explicit finite element with penalty method contact analysis is used to evaluate the drop test performance.The results show that the maximum effective stress and plastic strain is found in the side drop condition.It is indicated that the side structure is more vulnerable than the top and bottom structure. The maximum absorbed rupture energy is occurred on the frame structure for reversed drop condition, however it is transmitted effectively to all of the connected frames, outer-shell and inner-shell structures. According to the results of simulation analysis, it can be concluded that the structure of the cone capsule tsunami lifeboat is reliable to withstand the severe load during the tsunami disaster.

Effect of structural buildup at rest of self-consolidating concrete on mechanical and transport properties of multilayer casting

Multilayer casting of self-consolidating concrete (SCC) can be critical in situations involving delays between the placements of successive lifts. In the absence of mechanical consolidation, the increase in structural buildup at rest (SBR) of existing SCC lift prior to the placement of a successive lift can lead to lift lines. Furthermore, the bond strength deteriorates across the bonded interphases. In this study, eight SCC mixtures with different levels of SBR were considered. The thixotropy of concrete was determined using standard workability test methods and inclined plane test. Flexural strength and water permeability were determined using composite specimens cast in two SCC lifts. The second lift was placed after given periods of rest up to 60 min. Composite specimens developed residual flexural strengths and water permeability resistance with minimum values of 56% and 2%, respectively, compared to reference samples. To secure 90% residual flexural strength and impermeability, delays up to 25 and 10 min can be tolerated, respectively, depending on SBR level of the existing SCC layer. Statistical models were established to predict the residual flexural strength and water permeability resistance between successive lifts. SCC with low level of SBR, having static yield stress up to 250 Pa after 15 min of rest and rate of SBR up to 2.5 Pa/min evaluated using the inclined plane test, can secure relatively high level of bond strength and impermeability providing that the delay time before casting successive lifts is limited to 20 and 5 min, respectively. The interphases bond of successive SCC lifts was found to be affected by intermixing level of the layers. Both can be increased by the reduction in SBR of existing lift when concrete is cast with a given free fall height.

Extremely Energetic Rockfalls

AbstractExtremely energetic rockfalls (EERs) are defined here as rockfalls for which a combination of both large volume and free fall height of hundreds of meters results in energy larger than about 80 GJ released in a short time. Examples include several events worldwide. In contrast to low energy rockfalls where block disintegration is limited, in EERs the impact after free fall causes immediate release of energy much like an explosion. The resulting air blast can snap trees hundreds of meters ahead of the fall area. Pulverized rock at high speed can abrade vegetation in a process of sandblasting, and particles suspended by the blast and the subsequent debris cloud may travel farther than the impact zone, blanketing vast areas. Using published accounts and new data, we introduce physically based models formulated on analogies with explosions and explosive fragmentation to describe EERs. Results indicate that a portion of the initial potential energy of the block is spent in rock disintegration at impact (typically 0.2%–18%), while other sources of energy loss (air drag, seismic, sound, and ground deformation) are negligible; consequently, more than 80% of the potential energy is converted to kinetic energy of the fragmented block (ballistic projection, shock wave, sand blast, and dust cloud). We also propose simple estimates for the flow of the dust cloud associated with an EER and its long settling time. The areal extent of the affected zone is estimated from the energy balance and an empirical power law relationship.

Analysis of Steam Explosion under Conditions of Partially Flooded Cavity and Submerged Reactor Vessel

A steam explosion in a reactor cavity makes a mechanical load of the pressure pulse, which can result in a failure of the containment isolation. To prove the integrity of the containment during the ex-vessel steam explosion, the effects of water conditions on a steam explosion have to be identified, and the impulse of a steam explosion has to be exactly assessed. In this study, the analyses for steam explosions were performed for the conditions of a partially flooded cavity and a submerged-vessel in a pressurized water reactor. The entry velocity of a corium jet for the scale of the test facility was varied to simulate the two plant conditions. The TEXAS-V code was used for simulating the phases of premixing and explosion, and the load of a steam explosion was estimated based on the pressure variation. The impulse of a steam explosion under the condition of a corium jet falling into water without a free-fall height is bigger than that under a free-fall height. The fragmented mass of corium in an explosion phase and the distribution of steam fraction are the main parameters for the total load of the steam explosion. This study is expected to contribute to analyses of a steam explosion for a severe accident management strategy.

A Study of Impact Energy on Eggshell Crack

The lengthy and irregular cracks occur when eggs are impacted. These egg samples with cracks can be used for thermal image to study the display of the crack. The purpose in the study was to analyse eggs impacted by free fall and measure the crack length with a self-developed image analysis system, further investigating the relationship between the impact energy and the crack length. The image analysis system comprised Image Import, Gray Level Processing, Binary Transform, Dilation and Labelling. Finally, all crack blocks could be obtained, as well as the area, perimeter and length could be determined. The test results showed that a height of free fall between 24-42 mm or an impact energy of 12-26 mJ would cause cracks similar to those when eggs were collected. The larger energy was, and the longer crack length was, presenting in linear relationship, as well as the egg source to the relation would be greatly influenced.

Some patients live after trauma: Re-examining the lethality of vertical deceleration injuries

Background Vertical deceleration injury is a unique urban phenomenon of blunt injury resulting in significant morbidity and mortality. Since evaluations began in the 1940s and more extensively in the 1980s through 2005, the fall height at which 50% of patients are expected to die (LD50) has been consistently estimated to be 40 ft (12.1 m) and historical reports suggest no patients were able to survive a fall greater than 50 ft (15.2 m). The aim of this study was to determine the current LD50 or survivable free fall height in comparison to historical reports. Study design The trauma database at an urban level one trauma center was reviewed for all falls from a significant height from January 2010 to December 2015. The data were stratified based upon the height of the fall. The height at which 50% of patients were expected to die was determined by logistic non-linear regression line plot. Results In total, 110 patients were identified, with 97 meeting criteria for inclusion into the study. Twelve patients fell from 60 ft (18.2 m) with six survivors. The calculated LD50 was 48 ft (14.8 m) when the heights of a story and floor were standardized to 10 ft (3 m); if the height was increased to 12 ft (3.7 m) per story, the LD50 would be 68 ft (20.1 m). Conclusions The survivable height, as well as the LD50 of vertical free falls, has increased as compared to previous studies. We assume that this is attributable to the advances in diagnostic imaging, interventional radiology therapies, critical care, and field management of these patients. A fall from 80 ft (24 m) exceeds the maximum threshold of force that the human body can withstand.

Rheological characterization of digested sludge by solid sphere impact

An impact method was applied to investigate the rheological characteristics of digested sludge and reveal its transient dynamics. A high-speed camera allowed visualizing the dynamic impact process and observing interaction between impacting sphere and targeted sludge. A damping oscillation was observed after the impact. The crater diameter followed an exponential function, while the crater depth varied as a logarithmic function of both sphere diameter and free fall height. Furthermore, the viscosity and elasticity of digested sludge were evaluated by establishing a simplified impact drag force model. The impact elastic modulus was consistent with the Young’s modulus measured by a penetrometer. The impact viscosity was reasonable as the estimated impact shear stress was greater than the yield stress of digested sludge resulting in the formation of crater. The impact method offers an alternative way to reveal the viscoelasticity of digested sludge through a dynamic process.

Sistemas de protección individual anticaídas sometidos a impacto. Simulaciones numéricas

Personal fall protection systems are set up by EN-363 to avoid or retain people falls safely (without relevant damages). They are the ultimate resource to prevent a fall after other measures being considered. This paper analyses the variables affecting the system behaviour: free fall height, length of retaining rope, stiffness and damping of retaining material, and worker weight. To this end, fall phenomenon has been simulated with finite elements dynamic models with an elastic rope and a rigid ballast. It allows obtain likely values of maximum forces on the injured and over the system during the impact. Results demonstrate the fundamental role of height fall vs. rope length rate (fall factor), which results more important than the fall height itself. The severe values obtained for maximum forces show that future research would include elastoplastic energy absorbers to decrease impact until reasonable values.

Development of a Hopper-Type Planting Device for a Walk-Behind Hand-Tractor-Powered Vegetable Transplanter

Purpose: In order to ensure that vegetable seedlings (with a soil block around their roots) are planted in an upright orientation after metering in a vegetable transplanter, they need to be dropped freely from a certain height. The walk-behind hand-tractor-powered machines do not have sufficient space to drop the seedlings from that height. In the present work, a hopper-type planting device was developed for the walk-behind hand-tractor-powered vegetable transplanter to ensure that the soil block seedlings are planted in an upright orientation. Methods: Various dimensionless terms were developed based on the dimensional analysis approach, and their effect on the planting of soil block seedlings in an upright orientation (planting efficiency) was studied. The optimum design dimensions of the hopper-type planting device were identified by the Taguchi method of optimization. Results: The ratio of the height of free fall to the sliding distance of the seedling on the surface of the hopper had the highest influence on planting efficiency. The planting efficiency was highest for plants with a height . The plant handling Froude number, in interaction with the design of the hopper-type planting device, also significantly affected the planting efficiency. Of the hopper design factors, the length of the slide of the seedlings on the surface of the hopper was most important, and induced sufficient velocity and rotation to cause the seedling to fall in an upright orientation. An evaluation of the performance of the planting device under actual field conditions revealed that the planting efficiency of the developed planting device was more than 97.5%. Conclusions: As the seedlings were fed to the metering device manually, an increase in planting rate increased missed plantings. The planting device can be adopted for any vegetable transplanter in which the seedlings are allowed to drop freely from the metering device.

Novel aspects on the segregation in quasi 2D piles

Abstract We present the results of an experimental study of granular segregation on a large number of rectangular grain piles built by dropping simultaneously glass beads of two different sizes. During the construction process, we control the height of the injection point, the amplitude and velocity of its displacement and the injection flow rate for each kind of grain. The final spatial distribution of the grains is determined by a quantitative image analysis. A phase diagram of the mixing state as a function of the experimental parameters is presented along with a quantification of the different types of segregation patterns. Contrary to the assertions of other authors, we clearly demonstrate here, that stratification phenomena may be observed even for beads with the same round shape but a different size. We also find that the free fall height of the grains, the ratio between the discharged masses of the different types of grains and the amplitude of the horizontal motion have the greatest influence on segregation.

An experimental-theoretical determination of the force and energy characteristics of the operating zones of magnetic separators

The dependences of the force of attraction of ferroparticles (spheres or bodies of irregular form) in a module of two opposed magnetic elements on the dimensions of the ferroparticles, the distance to the surface of the element and the spacing between them, are obtained experimentally and described functionally. Expressions are obtained for the boundary values of the specific ferroparticle capture energy in the threshold zone of the module, the velocity of its entrance into this zone and the free-fall height.

유체가 흐르는 가스파이프의 진동 특성

This work investigates the vibrational characteristics of the underground gas pipelines. Experiments were conducted to analyze the effects of various parameters on the vibrational characteristics from the emergency detection point of view. Influences of the various types of impact exerted on the pipe, height of free fall and measuring locations were analyzed. Especially, the difference between the vibrational signal generated by the direct impact on the pipe and the ambient noise was successfully identified. To validate the experimental observation, computer simulation was also performed with constant properties(elasticity, fluid velocity and internal pressure) which are directly conjectured from the accompanying experiment with a real pipe system.

Impact of a liquid drop on a granular medium: Inertia, viscosity and surface tension effects on the drop deformation

An experimental study of liquid drop impacts on a granular medium (glass beads) is proposed. Four fluids were used to vary physical properties: pure distilled water, water with glycerol at two concentrations 1:1 and 1:2v/v and water with surfactant (Tween 20) at the concentration of 0.1gl−1 (≈1 CMC). The drop free fall height was varied to obtain a Weber number (We) between 10 and 2000 and a Reynolds number (Re) between 100 and 13000. Different behaviors during the drop spreading, receding and absorption are highlighted as function of the fluids viscosity (μ) and surface tension (γ). The role plays by the surfactant on the drop behavior after impact was found significant especially when the kinetic energy was high. On the other hand, the final diameter of the drop was found insensitive to the viscosity of the fluid and the Weber number. The maximal spreading factor βmax=Dmax/D0 was found to scale as We14 for water+surfactant drops (γ≈36mJm−2, μ=1mPas) whereas for the other fluids (γ≈70mJm−2 but μ=1−19mPas) βmax∼We15. The boundary between splashing and non-splashing was determined using the splash parameter Kd=We1/2Re1/4. The threshold value Kds was found higher that for impact of liquid drops on solid dry substrates. Experimental absorption times are also commented and compared with a simplified theoretical model. Finally, the morphology of the craters is discussed and a relationship between the crater diameter and the drop kinetic energy at impact is presented.