Large Impact Pressure Research Articles

3D spirally coiled piezoelectric nanogenerator for large impact energy harvesting

Piezoelectric nanogenerator is an emerging technology that can convert irregular discrete mechanical energy in the environment into electricity, which provides a long-term continuous power supply solution for mobile distributed electronics. However, it is still difficult to effectively harvest the large impact mechanical energy. Here, we developed a new kind of three-dimensional spirally coiled piezoelectric nanogenerator (SC-PENG), which can effectively convert irregular axial impact forces into uniform radial pressures, and achieve large-scale impact mechanical energy harvesting (corresponding pressures range from 80 kPa to 6.32 MPa). Especially, under a large impact pressure of 3.05 MPa, the output current, voltage and the equivalent transfer charge density of SC-PENG is up to 196 μA, 36 V and 2550 μC m−2 respectively, which break the record of PENG among previous studies. The volume of the piezoelectric film and the corresponding volume charge density are 0.224 cm−3 and 580 nC cm−3, respectively. Moreover, factors such as particle connectivity and modulus of the piezoelectric film are explored in detail, which can further improve the electromechanical conversion capability of PENG. This work not only achieves high electrical output of PENG, but also paves an efficient strategy for large impact mechanical energy harvesting towards practical application.

Numerical modeling of sloshing flow interaction with an elastic baffle using SPHinXsys

Sloshing is a complex fluid motion with high non-linearity. Violent sloshing results in large impact pressure on the tank that may lead to structural damage. Sloshing suppression using anti-sloshing baffles and interaction mechanisms between structure and fluid attract attention increasingly among engineering applications. In this paper, the sloshing flow interaction with an elastic baffle is investigated both numerically and experimentally. SPHinXsys, an open-source library in the entire smoothed particle hydrodynamic (SPH) framework, is applied to study sloshing interaction with an elastic baffle. To validate SPHinXsys model, a series of experiments are performed in a rectangular tank. The quantitative comparisons between numerical results and experimental measurements on the time variation of free surface, pressure and baffle deformation are conducted. The diffusion process of the dye around the baffle in the experiment is recorded and simulated by the FSI solver coupled with the diffusion model. Then the velocity field for varying filling depths is investigated numerically. The total dynamic force acting on the baffle for different water depths is also discussed.

A new nature of microporous architecture with hierarchical porosity and membrane template via high strain rate collision

This paper presents the formation of an unusual porous structure at Al/Al interface joined by magnetic pulse welding. The porous structure consists of a hierarchical microporous architecture with pore size of less than 2 µm that represents more than 80% over the whole area, in which 38% of them are sub-micron size pores. It also exhibits ultra-thin wall, sufficiently thin enough to behave as an electron-transparent material with a wall thickness of 50 nm. The formation of this porous structure is attributed to a cavitation process of a molten material in three stages including, (1) nucleation, (2) growth and coalescence and (3) solidification. Further analysis of this cavitation process using a dedicated numerical simulation reveals that the nucleation and growth of pores may arise from vaporization governed by a rapid isothermal and isochoric expansion of liquid metal due to the high rate of depressurization. This result explains the potential mechanism of coalescence for the creation of the open porosity. The difference between cavitation onset and highly developed porous structure is attributed to the difference in depressurization during various welding conditions. Welding performed with high intense collision enables to have large impact pressure, therefore those welding conditions provide higher depressurization gap and severe fluid rupture due to significantly large inherent surface tension of the fluid. A fast solidification at a high cooling rate of 10 °C/ns enables to freeze the micropores and resulting with the solidified porous architecture.

Numerical simulation of sloshing with large deforming free surface by MPS-LES method

Moving particle semi-implicit (MPS) method is a fully Lagrangian particle method which can easily solve problems with violent free surface. Although it has demonstrated its advantage in ocean engineering applications, it still has some defects to be improved. In this paper, MPS method is extended to the large eddy simulation (LES) by coupling with a sub-particle-scale (SPS) turbulence model. The SPS turbulence model turns into the Reynolds stress terms in the filtered momentum equation, and the Smagorinsky model is introduced to describe the Reynolds stress terms. Although MPS method has the advantage in the simulation of the free surface flow, a lot of non-free surface particles are treated as free surface particles in the original MPS model. In this paper, we use a new free surface tracing method and the key point is “neighbor particle”. In this new method, the zone around each particle is divided into eight parts, and the particle will be treated as a free surface particle as long as there are no “neighbor particles” in any two parts of the zone. As the number density parameter judging method has a high efficiency for the free surface particles tracing, we combine it with the neighbor detected method. First, we select out the particles which may be mistreated with high probabilities by using the number density parameter judging method. And then we deal with these particles with the neighbor detected method. By doing this, the new mixed free surface tracing method can reduce the mistreatment problem efficiently. The serious pressure fluctuation is an obvious defect in MPS method, and therefore an area-time average technique is used in this paper to remove the pressure fluctuation with a quite good result. With these improvements, the modified MPS-LES method is applied to simulate liquid sloshing problems with large deforming free surface. Results show that the modified MPS-LES method can simulate the large deforming free surface easily. It can not only capture the large impact pressure accurately on rolling tank wall but also can generate all physical phenomena successfully. The good agreement between numerical and experimental results proves that the modified MPS-LES method is a good CFD methodology in free surface flow simulations.

Order Estimation of Physical Processes in Dynamics of Steam-Water Mixed Spray Cleaning Technique

We have been developing an innovative ultra-low environmental load cleaning technique by the use of steam-water mixed spray. We showed that this technique is quite effective in both cleaning and photo-resist stripping. We also found that the physical force associated with steam-water mixed spray is greater than that with air-water mixed spray; hence we proposed that the condensation plays an important role in this cleaning technique. In order to discuss further this mechanism, we perform the order estimation of physical processes in dynamics of liquid droplet moving in vapor flow impacting on a solid interface in this study. Results show that droplet impact velocity can be reduced while the droplet approaches to the solid surface. However, the vapor in the gap can condensate to either the liquid droplet or the solid surface with the velocity whose order of magnitude cannot be negligible compared to the impact velocity; hence the amount of vapor that should be pushed out from gap can be drastically reduced, This condensation results in the significant reduction of viscous force. This reduction of force with the existence of condensation reduces the impact velocity deceleration. Consequently significantly large impact pressure is generated.

Influence of excitation frequency on slosh-induced impact pressures of liquefied natural gas tanks

Liquid sloshing phenomena in No. 2 tank of 140 km3 liquefied natural gas (LNG) carriers have been studied numerically and experimentally. The scale of the model tank was selected as 1/55.9. Roll and pitch motions were tested. For measuring impact pressures, seventeen pressure sensors were installed on the tank model. A large number of excitation frequencies and filling heights were investigated. The experimental results showed that when the frequency of tank motion is close to the natural frequency of fluid inside the tank, large impact pressures may be caused. Resonance frequencies and maximum impact pressures of different filling height were presented. Among all the experimental situations, the maximum impact pressure always occurs at the place near 70% height of tank where should be especially concerned. A computational fluid dynamics (CFD) model was developed to simulate the sloshing in the tank. The model was based on the Reynolds-averaged Navier-Stokes (RANS) equations, with a standard κ-ɛ turbulence model. The volume of fluid (VOF) method was used to predict free surface elevations. Dynamic mesh technique was used to update the volume mesh. Computations for pressure time histories and peak pressures were compared to experimental results. Good agreement was observed.

Simulation of vocal fold impact pressures with a self-oscillating finite-element model

Vocal fold impact pressures were studied using a self-oscillating finite-element model capable of simulating vocal fold vibration and airflow. The calculated airflow pressure is applied on the vocal fold as the driving force. The airflow region is then adjusted according to the calculated vocal fold displacement. The interaction between airflow and the vocal folds produces a self-oscillating solution. Lung pressures between 0.2 and 2.5 kPa were used to drive this self-oscillating model. The spatial distribution of the impact pressure was studied. Studies revealed that the tissue collision during phonation produces a very large impact pressure which correlates with the lung pressure and glottal width. Larger lung pressure and a narrower glottal width increase the impact pressure. The impact pressure was found to be roughly the square root of lung pressure. In the inferior-superior direction, the maximum impact pressure is related to the narrowest glottis. In the anterior-posteriorfirection, the greatest impact pressure appears at the midpoint of the vocal fold. The match between our numerical simulations and clinical observations suggests that this self-oscillating finite-element model might be valuable for predicting mechanical trauma of the vocal folds.

Study on sloshing in cargo tanks including hydroelastic effects

The sloshing problem in cargo tanks is studied through experiments and numerical analysis. The fluid motion is described using a higher-order boundary element method and the structural response by a thin plate theory. It was found that hydraulic jumps are formed when the excitation frequency is close to the resonance frequency in the case of low filling depth. In the case of high filling depth, the flow resonates and hits the top of the tank, thus inducing a large impact pressure. The pressure on the flexible plate shows amplified initial peaks followed by oscillatory components, the frequency of which coincides with the natural frequencies of the plate in water as a result of hydroelastic effects.

鉱石運搬船の船首底衝撃による過渡振動曲げモーメントと波浪曲げモーメントから見た可航限界について

The theoretical study on the critical navigation of a ore carrier (L_<pp>=247m, C_b=0.824) has been carried out from the viewpoint of structural seaworthiness in longitudinal strength. The navigable wave conditions were obtained by the same procedure for the single screw container ship, previously reported. From the results, it is shown that whipping of full ship due to slamming grows rapidly at lower ship speed in head sea condition because of large impact pressure coefficient and flat fore bottom. And, wave bending moment in following sea condition is larger than in head sea condition, so that the operations of full ship in heavy seaways should be dicided with attentions not only to slamming but also to wave bending moment. From the comparison of navigable wave condition between the present ore carrier and the previous container ship, it is found that the difference of structural seaworthiness in longitudinal strength between them is not significant in seaway of longer average wave period.

On the Characteristics of Water Impact Pressures Acting on a Hull Surface Among Waves

In the previous paper, very violent impact pressures on stem were measured by the experiments in high transient water waves.In this paper, the authors continued the experiments in order to take a somewhat closer look at some aspects of water impact to clarify the roles of certain mechanisms. Both the impact on stem in full load condition and the impact on bottom in the ballast condition were investigated. Ship model was equipped with relative wave surface probe, so the relative velocity and angle between hull and wave surface were obtained.The following conclusions can be deduced from these studies : 1) Large impact pressures acting on hull surface can be explained by the fundamental natures that are taken by theories and experiments of the drop of the two dimensional body or the breaking waves on the vertical wall.2) The maximum value of impact pressure, PI, is considered to be proportional to square of relative velocity, Vn, and the coefficient of impact pressure, C=PI/ (1/2ρVn2), reaches 48 to 66 at the bottom, 17 at the stem.3) When the relative angle between hull and wave surface at the moment of impact, β, is large, the coefficient C tends to be proportional to the square of cot β, as the Wagner's theory. As decreases, it comes to be proportional to cot β, as the Chuang's experiments.4) When air is entrapped, large impact pressure occures, but at the stem air is hardly entrapped because of its shape.

Impact Pressure acting on Bow of Large Full Ships

The impact pressure acting on bow of large and full ship may be predicted by the following considerations. The ship motions are mainly due to the waves longer than ship but scarcely affected by the shorter waves. Therefore, the ship cruising in the ocean is oscillated violently by the swell (longer waves) and the velocity of the bow motion relative to wave surface becomes very large. Impacts on bow occur when short waves are superposed to the longer waves and collide with such oscillating ship. If the angle between the stem and the wave surface of the short waves is small, large impact pressure is produced. The slope of stem and bluntness of bow are considered to be main parameters controlling the amount of pressure and its frequency.At Nagasaki Experimental Tank, impact pressures on the model are measured in shorter waves superposed on longer waves or using models oscillated with frequency and amplitude corresponding to the condition in longer waves.