scholarly journals The impact of raindrops on Salvinia molesta leaves: effects of trichomes and elasticity

2021 ◽  
Vol 18 (185) ◽  
Author(s):  
Wilfried Konrad ◽  
Anita Roth-Nebelsick ◽  
Benjamin Kessel ◽  
Tatiana Miranda ◽  
Martin Ebner ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Water Repellency ◽  
High Water ◽  
Rain Water ◽  
Residual Water ◽  
Intense Rainfall ◽  
Salvinia Molesta ◽  
Aquatic Fern ◽  
The Impact

The floating leaves of the aquatic fern Salvinia molesta are covered by superhydrophobic hairs (=trichomes) which are shaped like egg-beaters. These trichomes cause high water repellency and stable unwettability if the leaf is immersed. Whereas S. molesta hairs are technically interesting, there remains also the question concerning their biological relevance. S. molesta has its origin in Brazil within a region exposed to intense rainfall which easily penetrates the trichome cover. In this study, drop impact on leaves of S. molesta were analysed using a high-speed camera. The largest portion of the kinetic energy of a rain drop is absorbed by elastic responses of the trichomes and the leaf. Although rain water is mostly repelled, it turned out that the trichomes hamper swift shedding of rain water and some residual water can remain below the ‘egg-beaters’. Drops rolling over the trichomes can, however, ‘suck up’ water trapped beneath the egg-beaters because the energetic state of a drop on top of the trichomes is—on account of the superhydrophobicity of the hairs—much more favourable. The trichomes may therefore be beneficial during intense rainfall, because they absorb some kinetic energy and keep the leaf base mostly free from water.

Simulation of drip-rain effects by tribofatigue loading

2020 ◽  
Author(s):  
A.A. Aliev ◽  
A.Yu. Ampilogov
Keyword(s):  
Polymer Coating ◽  
High Speed ◽  
Erosion Resistance ◽  
High Water ◽  
Contact Spot ◽  
Vertical Load ◽  
Rigid Substrate ◽  
Rain Drop ◽  
The Impact ◽  
Rain Erosion

The outer surfaces of aircraft are periodically subjected during flight to intense rain causing hydroerosion of the outer paintwork. The experimental evaluation of hydroerosion resistance is based on testing in high-speed water flow. The main drawback of such research is the bulkiness of the stands, high water and energy consumption, and, as a result, increased cost. As an alternative to drip-rain tests, their simulation by kinetically similar tribofatigue test according to the “ball on plate” scheme is proposed (vertical load is applied to the polymer coating on a rigid substrate through a steel ball). The process is cyclically repeated until the coating is worn to the specified thickness. The experimentally obtained tribofatigue characteristics then can be converted into close-meaning estimates of erosion resistance. CAAPCOAT-B274-ASP108 polyurethane, previously tested for rain erosion, was selected as the sample. For quantitative evaluation of the transition from drip-rain loading to equivalent tribofatigue one the contact mechanics formulas were used by calculating the force of the drip impact and the stress in the contact spot. Tribofatigue tests were conducted on the UMT-2 TriboLab unit. At equal calculated contact stress levels the wear rate under tribofatigue loading was almost 7 times higher compared to the conditions of rain-drop erosion. The reason may be a scale factor due to the actual difference in contact areas under drip and tribofatigue loading, as well as the failure to take into account the dynamics of waves after the impact of drops. The obtained results of tribofatigue tests can give an estimated value of the hydroerosion resistance of the coating.

scholarly journals Soft projectile impact forces measurement using Hopkinson bars: application to ice, artificial bird and rubber

2021 ◽  
Vol 250 ◽  
pp. 01008
Author(s):  
Ramón del Cuvillo ◽  
Jose Alfonso Artero-Guerrero ◽  
Jesús Pernas-Sánchez ◽  
Jorge López Puente
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Soft Materials ◽  
Peak Force ◽  
Video Cameras ◽  
Impact Forces ◽  
Compression Strain ◽  
Experimental Campaign ◽  
The Impact ◽  
Semiconductor Strain

This work presents an experimental campaign of impacts of soft projectiles to measure the induced force during the impact. Three different materials acting as soft impactors that could strike against a aeronautical structural component: ice, artificial bird and rubber have been impacted at several velocities against an aluminium Hopkinson bar. This device has been instrumented with semiconductor strain gauges that allow to obtain the induced compression strain. Additionally, all the impacts were recorded using high-speed video cameras, allowing the kinematic analysis of the projectile during the impact. After the results study, it has been concluded that there is a linear dependency between the kinetic energy and the peak force for all three materials. Added to that, it has been proved that the higher peak force corresponds to ice, despite the kinetic energy, followed by rubber and finally the artificial bird. In addition, while ice and artificial bird projectiles get radially dispersed after the impact, rubber spheres rebound due to its different behaviour. The obtained data is of great interest to design structures which could be subjected to impacts of soft materials such as aeronautic structures

Assessment of Diaphragm Wall's Structural Impact on Groundwater Hydrology

2011 ◽  
Vol 250-253 ◽  
pp. 1098-1104
Author(s):  
Te Hsing Chang
Keyword(s):  
Groundwater Level ◽  
High Speed ◽  
Vibration Reduction ◽  
High Water ◽  
Diaphragm Wall ◽  
Wall Structure ◽  
Groundwater Hydrology ◽  
Groundwater Levels ◽  
Diaphragm Walls ◽  
The Impact

The Southern Taiwan Science Park (STSP) is located between Hsinshi Township and Shanhua Township of Tainan County, with the newly-built, high-speed railway running through its eastern side. The low-frequency vibration which was generated by passing high-speed trains causes environmental disturbances to industries within the Park. To address this issue, the implementation of vibration-reduction project with detailed design and construction was provided. The diaphragm wall-type vibration reduction walls will be built along the borderline between Hsinshi Township and Shanhua Township to reduce the impact on industries. The diaphragm wall structure will block groundwater from flowing to affect the underground hydrology. This study was aimed to discuss and assess the best configuration for the vibration reduction effects and environmental impacts. Numerical analysis of the impacts on groundwater hydrology was conducted in two cases. The simulation results indicated that both sides of diaphragm walls developed gaps in groundwater levels. Hence, diaphragm walls effectively reduced adverse impacts on groundwater hydrology with openings at locations where underground pipelines ran. Such variations were within the scope of groundwater level of high water and low water periods. Therefore, surface runoff and land subsidence resulting from the diaphragm wall construction were not severe. As diaphragm walls were made of impermeable materials, pumping water nearby made the groundwater level drawdown effects worse. Groundwater level variations resulting from pumping water were far greater than the regional groundwater level variations after the establishment of diaphragm walls. Special attention must be paid to this situation in follow-up management.

Impact Resistance of Automobile Tires

1968 ◽  
Vol 41 (4) ◽  
pp. 1051-1064
Author(s):  
E. W. Lothrop
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Impact Resistance ◽  
Test Machine ◽  
Test Results ◽  
Laboratory Test Results ◽  
Breaking Energy ◽  
The Impact ◽  
The Relationship ◽  
Automobile Tires

Abstract The construction and operation of a high speed plunger test machine to determine the impact energy required to produce failure of automobile tires are described. The equipment has been designed to operate over an energy range of 1500 to 15,000 in. lb at preselected velocities between 40 and 100 mph and at preselected temperatures between 75 and 300° F. These ranges are adequate to permit the testing of passenger tires over a range of conditions simulating those encountered in high speed driving. The test machine consists of a pneumatic gun for propelling the plunger at an inflated tire, mounted in a temperature controlled cabinet, and photoelectric devices for measuring plunger velocity. In a test the kinetic energy of the plunger is increased in increments, until failure occurs. The minimum kinetic energy required to cause failure of the tire fabric is taken as a measure of the carcass breaking energy. Data on rayon and nylon cord tires indicate that the breaking energy of a tire is dependent on both speed and temperature and that the relationship between energy, speed, and temperature depends on the cord-reinforcing material in the tire. As a result it is impossible to predict the relative impact resistance of tires under use conditions on the basis of laboratory test results obtained with the standard static plunger test, in which the plunger penetrates the tire at 2 in./min at room temperature.

Motion Situation and Kinetic Energy Analysis for Ore Pass of Underground Mine

2011 ◽  
Vol 90-93 ◽  
pp. 383-386
Author(s):  
Yong Heng Huang ◽  
Ping Cao ◽  
Yi Xian Wang
Keyword(s):  
Kinetic Energy ◽  
High Speed ◽  
Impact Damage ◽  
Critical Value ◽  
Impact Angle ◽  
Underground Mine ◽  
Damaged Zone ◽  
Impact Kinetic Energy ◽  
The Impact ◽  
Ore Pass

The fragmentation of ore pass under loading belongs to one of the typical disaster in underground mine. This paper is concerned with the description and explanation of this phenomenon and presents brittle fragmentation for impact damage of rock block based on impact test, high-speed camera was used to study the relation between fragmentation and damage and the effect of the kinetic energy of projectile on them, the experimental results demonstrate that the damaged zone, invasion depth increase with the increase of the kinetic energy of projectile, but are influenced by the impact angle; the results show that prior to the impact kinetic energy reaches the critical value, the energy dissipation is mainly for damaged zone, when the impact kinetic energy increases to the critical value.

The formulation of the RANS equations for supersonic and hypersonic turbulent flows

2020 ◽  
pp. 1-31
Author(s):  
H. Zhang ◽  
T.J. Craft ◽  
H. Iacovides
Keyword(s):  
Kinetic Energy ◽  
Pressure Gradient ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
High Speed ◽  
Mean Flow ◽  
Rans Equations ◽  
Flow Equations ◽  
The Mean ◽  
The Impact

Abstract Accurate prediction of supersonic and hypersonic turbulent flows is essential to the design of high-speed aerospace vehicles. Such flows are mainly predicted using the Reynolds-Averaged Navier–Stokes (RANS) approach in general, and in particular turbulence models using the effective viscosity approximation. Several terms involving the turbulent kinetic energy (k) appear explicitly in the RANS equations through the modelling of the Reynolds stresses in such approach, and similar terms appear in the mean total energy equation. Some of these terms are often ignored in low, or even supersonic, speed simulations with zero-equation models, as well as some one- or two-equation models. The omission of these terms may not be appropriate under hypersonic conditions. Nevertheless, this is a widespread practice, even for very high-speed turbulent flow simulations, because many software packages still make such approximations. To quantify the impact of ignoring these terms in the RANS equations, two linear two-equation models and one non-linear two-equation model are applied to the computation of five supersonic and hypersonic benchmark cases, one 2D zero-pressure gradient hypersonic flat plate case and four shock wave boundary layer interaction (SWBLI) cases. The surface friction coefficients and velocity profiles predicted with different combinations of the turbulent kinetic energy terms present in the transport equations show little sensitivity to the presence of these terms in the zero-pressure gradient case. In the SWBLI cases, however, comparisons show that inclusion of k in the mean flow equations can have a strong effect on the prediction of flow separation. Therefore, it is highly recommended to include all the turbulent kinetic energy terms in the mean flow equations when dealing with simulations of supersonic and hypersonic turbulent flows, especially for flows with SWBLIs. As a further consequence, since k may not be obtained explicitly in zero-equation, or certain one-equation, models, it is debatable whether these models are suitable for simulations of supersonic and hypersonic turbulent flows with SWBLIs.

Vibration Influence of Artillery Autoloader Analysis and Testing

2013 ◽  
Vol 711 ◽  
pp. 540-544
Author(s):  
Jie Xing ◽  
Yin Xian Duo
Keyword(s):  
Kinetic Energy ◽  
Stationary State ◽  
High Speed ◽  
High Speed Photography ◽  
Working Mechanism ◽  
Positioning Accuracy ◽  
Muzzle Velocity ◽  
Exciting Source ◽  
Feeding Process ◽  
The Impact

The inconsistency of the projectile's seizing-bore stroke of the large caliber gun during feeding process will lead to differences of the volume of propellant chamber and starting pressure of projectiles.It will also affect guns' muzzle velocity and firing accuracy.In order to improve the positioning accuracy of projectiles in an arm-type autoloader,first of all,high speed photography was used and only to find that there will be vibrations of projectiles in the direction of gravity.The vibrations will consume kinetic energy of the projectile and contribute to inconsistency of the retaining force.By means of analyzing the working mechanism of the rammer,the motion relationship among the parts during ramming process came to clear eventually.Then the position of the exciting source which causes vibrations of the projectile can be determined by analyzing the force situation of the rammer in the stationary state and the state of motion,and next,testing the amplitude and frequency of the position using laser displacement sensor.Finally,the improved scheme was raised to eliminate the impact of the vibration on stability of ramming.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Case study: Prediction and field tests of railway noise and effects of a low-height noise barrier

2020 ◽  
Vol 68 (4) ◽  
pp. 303-314
Author(s):  
Yuna Park ◽  
Hyo-In Koh ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
...  
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Residential Areas ◽  
Railway Systems ◽  
Railway Noise ◽  
Sound Levels ◽  
Noise Barrier ◽  
The Difference ◽  
Reduction Effect ◽  
The Impact

Railway noise is calculated to predict the impact of new or reconstructed railway tracks on nearby residential areas. The results are used to prepare adequate counter- measures, and the calculation results are directly related to the cost of the action plans. The calculated values were used to produce noise maps for each area of inter- est. The Schall 03 2012 is one of the most frequently used methods for the production of noise maps. The latest version was released in 2012 and uses various input para- meters associated with the latest rail vehicles and track systems in Germany. This version has not been sufficiently used in South Korea, and there is a lack of standard guidelines and a precise manual for Korean railway systems. Thus, it is not clear what input parameters will match specific local cases. This study investigates the modeling procedure for Korean railway systems and the differences between calcu- lated railway sound levels and measured values obtained using the Schall 03 2012 model. Depending on the location of sound receivers, the difference between the cal- culated and measured values was within approximately 4 dB for various train types. In the case of high-speed trains, the value was approximately 7 dB. A noise-reducing measure was also modeled. The noise reduction effect of a low-height noise barrier system was predicted and evaluated for operating railway sites within the frame- work of a national research project in Korea. The comparison of calculated and measured values showed differences within 2.5 dB.

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