A Measurement of ‘Walking-the-Wall’ Dynamics: An Observational Study Using Accelerometry and Sensors to Quantify Risk Associated with Vertical Wall Impact Attenuation in Trampoline Parks

This study illustrates the application of a tri-axial accelerometer and gyroscope sensor device on a trampolinist performing the walking-the-wall manoeuvre on a high-performance trampoline to determine the performer dynamic conditions. This research found that rigid vertical walls would allow the trampolinist to obtain greater control and retain spatial awareness at greater levels than what is achievable on non-rigid vertical walls. With a non-rigid padded wall, the reaction force from the wall can be considered a variable force that is not constrained, and would not always provide the feedback that the trampolinist needs to maintain the balance with each climb up the wall and fall from height. This research postulates that unattenuated vertical walls are safer than attenuated vertical walls for walking-the-wall manoeuvres within trampoline park facilities. This is because non-rigid walls would provide higher g-force reaction feedback from the wall, which would reduce the trampolinist’s control and stability. This was verified by measuring g-force on a horizontal rigid surface versus a non-rigid surface, where the g-force feedback was 27% higher for the non-rigid surface. Control and stability are both critical while performing the complex walking-the-wall manoeuvre. The trampolinist experienced a very high peak g-force, with a maximum g-force of approximately 11.5 g at the bottom of the jump cycle. It was concluded that applying impact attenuation padding to vertical walls used for walking-the-wall and similar activities would increase the likelihood of injury; therefore, padding of these vertical surfaces is not recommended.

Viscous banding instabilities: non-porous viscous fingering

We demonstrate a novel instability found within unconfined viscous bands/rims, or free-surface flows involving a longitudinal viscosity contrast. Such instabilities may be described as viscous banding instabilities, non-porous viscous fingering instabilities or unconfined viscous fingering instabilities of free-surface flows involving the intrusion of a less viscous fluid into a band of more viscous fluid. A consequence of this work is that viscous fingering instabilities, widely known to occur in porous media following the seminal work of Saffman & Taylor (Proc. R. Soc. Lond. A, vol. 245, 1958, pp. 312–329), also occur in non-porous environments. Although the mechanism of the viscous banding instability is characteristically different from that of the Saffman–Taylor instability, there are important similarities between the two. The main similarity is that a viscosity contrast leads to instability. A distinguishing feature is that confinement, such as the rigid walls of a Hele-Shaw cell, is not necessary for viscous banding instabilities to occur. More precisely, Saffman–Taylor instabilities are driven by a jump in dynamic pressure gradient, whereas viscous banding instabilities, or non-porous viscous fingering instabilities, are driven by a jump in hydrostatic pressure gradient, directly related to a slope discontinuity across the intrusion front. We examine the onset of instability within viscous bands down an inclined plane, determine conditions under which viscous banding instabilities occur and map out a range of behaviours in parameter space in terms of two dimensionless parameters: the viscosity ratio and the volume of fluid ahead of the intrusion front.

BIM-TECHNOLOGY METHOD AND MODELS IN THE DESIGN OF THE AQUAPARK DOME STRUCTURE WITH WOODEN ARCHES

Тhe issues of designing a multi-volume dome structure for a water park using wooden arches as load-bearing structures are сonsidered. The complexity of the volumes and their joining lines, as well as the requirement to perform non-linear analysis of large-span timber elements at the request of Eurocode 5, make an information model with elements of BIM-technology necessary. It is noted that design using this technology is developing in the direction of taking into account all stages of the structure life cycle. Wood Information modeling is the most prepared for the use of BIM-technologies. This is due to the high factory readiness and complex digital technologies for the manufacture of modern wooden structures elements. During the design, an information model was formulated in the SAPFIR software package with the subsequent possibility of importing the model into the LIRA-SAPR software package. Additional steps were used to build the model: creating a 2D template in AutoCad with reference lines and the location of rigid walls on which the coating rests, and importing drawings into SAPFIR as a dxf-underlay; for all elements of the system located in the local coordinate system, auxiliary lines were built for the correct orientation of the plane in space; loads on curved surfaces were calculated in the PC Expri. For the further development of the nodes, 3D modeling was used with the transfer of the information model to the Tekla Structures PC as a specialized environment for the constructive section of the project. The presented calculation of a complex dome structure using wooden arches summarizes the approaches to the development of unique forms of structures using wood. The use of information models made it possible to reduce the time spent on design, to optimize the drawings, and also to significantly increase the complexity of the architectural and structural design of the structure and the design model, taking into account the nonlinear effects of wood.

A Setup for Microscopic Studies of Ultrasounds Effects on Microliters Scale Samples: Analytical, Numerical and Experimental Characterization

Sonoporation is the process of cell membrane permeabilization, due to exposure to ultrasounds. There is a lack of consensus concerning the mechanisms of sonoporation: Understanding the mechanisms of sonoporation refines the choice of the ultrasonic parameters to be applied on the cells. Cells’ classical exposure systems to ultrasounds have several drawbacks, like the immersion of the cells in large volumes of liquid, the nonhomogeneous acoustic pressure in the large sample, and thus, the necessity for magnetic stirring to somehow homogenize the exposure of the cells. This article reports the development and characterization of a novel system allowing the exposure to ultrasounds of very small volumes and their observation under the microscope. The observation under a microscope imposes the exposure of cells and Giant Unilamellar Vesicles under an oblique incidence, as well as the very unusual presence of rigid walls limiting the sonicated volume. The advantages of this new setup are not only the use of a very small volume of cells culture medium/microbubbles (MB), but the presence of flat walls near the sonicated region that results in a more homogeneous ultrasonic pressure field, and thus, the control of the focal distance and the real exposure time. The setup presented here comprises the ability to survey the geometrical and dynamical aspects of the exposure of cells and MB to ultrasounds, if an ultrafast camera is used. Indeed, the setup thus fulfills all the requirements to apply ultrasounds conveniently, for accurate mechanistic experiments under an inverted fluorescence microscope, and it could have interesting applications in photoacoustic research.

Influence of Vapor-Gas Cavity on Pressure Field in Closed Discharge Chamber with Rigid Walls

The pressure field in discharge chambers of a limited volume with deformable walls very often has a great influence on the efficiency of technological processes of deformation of sheet alloys; therefore, its determination is an urgent task. As a result of an electric discharge in the liquid filling the discharge chamber, in it, a cavity with a higher compressibility is formed than the liquid in the chamber. At the stage of the discharge, this cavity is filled with non-ideal plasma, and after the discharge, with liquid vapor and gases dissolved in it (vapor-gas cavity). Its pulsations form a pressure field in the discharge chamber. The moving boundary of the vapor-gas cavity creates great problems in calculating the pressure field in a liquid, especially after a large number of its pulsations. At present, the role of the vapor-gas cavity in the formation of the pressure field in the discharge chamber with a deformable wall, which is a sheet alloy plate, is insufficiently studied. Its definition is the purpose of this work. The study was carried out on the base of a previously developed mathematical model of an electric discharge in water, which in this work is supplemented with relations that significantly increase the accuracy of calculating the resistance of the discharge channel and the energy released in it. It was determined that the pulsations of the vapor-gas cavity provide pressure fluctuations in it in an antiphase with the average pressure in the liquid. In a discharge chamber with rigid walls, they decay slowly, but the presence of a deformable wall leads to a rapid decay of pressure fluctuations. In the previously developed mathematical model, the change in the optical transparency of the plasma was taken into account, and its significant effect on the pressure in the cavity and the pressure field in the liquid was determined.

Ordering and Dynamics of Interacting Colloidal Particles under Soft Confinement

Confinement can induce substantial changes in the physical properties of macromolecules in suspension. Soft confinement is a particular class of restriction where the boundaries that constraint the particles in a region of the space are not well-defined. This scenario leads to a broader structural and dynamical behavior than observed in systems enclosed between rigid walls. In this contribution, we study the ordering and diffusive properties of a two-dimensional colloidal model system subjected to a one-dimensional parabolic trap. Increasing the trap strength makes it possible to go through weak to strong confinement, allowing a dimensional transition from two- to one-dimension. The non-monotonic response of the static and dynamical properties to the gradual dimensionality change affects the system phase behavior. We find that the particle dynamics are connected to the structural transitions induced by the parabolic trap. In particular, at low and intermediate confinement regimes, complex structural and dynamical scenarios arise, where the softness of the external potential induces melting and freezing, resulting in faster and slower particle diffusion, respectively. Besides, at strong confinements, colloids move basically along one direction, and the whole system behaves structurally and dynamically similar to a one-dimensional colloidal system.

Evaluation of Deformation Characteristic of Railway Subgrade Using Reinforced Rigid Walls with Short Reinforcement under Repetitive and Static Loads

A full-scale reinforced subgrade for railways (RSR) was constructed, and repetitive and static load tests were performed to analyze the deformation characteristics of reinforced rigid walls with short reinforcements for railway subgrades that require strict displacement restrictions. Load test results were obtained for four sections, in which the reinforcement arrangement (vertical spacing and length) and wall-reinforcement connection method were applied differently, and the behavior of the reinforced rigid wall was observed according to each parameter. A repetitive load of 500 kPa and a static load of 1000 kPa were applied to the outside of the reinforcement area to evaluate the behavior of the subgrade when utilizing short reinforcement. The test results confirmed the reduction of the settlement and horizontal displacement of the wall, owing to the restraining effect of the short reinforcement and rigid wall. In addition, it was observed that the greater the applied load, the greater the influence of the reinforcement on the behavior of the subgrade; this pattern was more marked in loads above the yield of soil.