Drop Impact Simulation Research Articles

Simulation of drop impact on substrate with micro-wells

In this paper, we numerically investigate drop impact on a micro-well substrate to understand the phenomena of non-wettability. The simulation is carried out by solving three-dimensional incompressible Navier–Stokes equations using a density projection method and an adaptive grid refinement algorithm. A very sharp interface reconstruction algorithm, known as the moment-of-fluid method, is utilized to identify the multi-materials and multi-phases present in the computation domain. Our simulations predicted that a micro-well with a deep cavity can significantly reduce a solid–liquid contact in the event of drop impact. The results from the drop impact on the micro-well substrate are compared with results from drop impact on a flat substrate. Significant differences are observed between these two cases in terms of wetted area, spreading ratio, and kinetic energy. Our simulation shows that under the same conditions, a drop is more apt to jump from a micro-well substrate than from a flat surface, resulting in smaller wetted area and shorter contact time. Based on the simulation results, we draw a drop jumping region map. The micro-well substrate has a larger region than the flat surface substrate. Finally, we present a comparative analysis between a flat substrate and a substrate constructed with a dense array of micro-wells and, therefore, show that the array of micro-wells outperforms the smooth substrate with regard to non-wettability and drop wicking capability.

Numerical prediction of dynamic fracture strength of edge-mounted non-symmetric tempered glass panels under steel ball drop impact

Despite the well-known effects of loading rate and specimen size on glass strength, the fracture criterion of products containing tempered glass panels (TGPs) has been established based on the static fracture strength (SFS) of a standard-sized TGP due to procedural difficulties in determining large scale dynamic fracture strength (DFS). This impractical fracture criterion that has universally been adopted in industrial fields results in a use of excessive safety factor in product design and development process. In this work, large scale DFS of full-edge mounted TGPs is numerically predicted using ball drop impact (BDI) simulation, which realize in-service dynamic loading conditions and constraints. The numerical prediction results were verified by a remarkable correlation with a deformation deviation of 1.0–5.0% and stress deviation within about 6.9% comparing to BDI fracture test results. It was found that the average DFS derived in the practical BDI condition was 2.0 times higher than the average SFS derived in standard flexural test condition. We believe this study contributes to setting more efficient fracture criterion when designing or developing products in which TGPs are mounted, with emphasizing difference in glass strength derived from the in-service conditions and the standard test conditions.

The Dynamic Impact Response of 3D-Printed Polymeric Sandwich Structures with Lattice Cores: Numerical and Experimental Investigation.

This paper proposes a dynamic drop weight impact simulation to predict the impact response of 3D printed polymeric sandwich structures using an explicit finite element (FE) approach. The lattice cores of sandwich structures were based on two unit cells, a body-centred cubic (BCC) and an edge-centred cubic (ECC). The deformation and the peak acceleration, referred to as the g-max score, were calculated to quantify their shock absorption characteristic. For the FE results verification, a falling mass impact test was conducted. The FE results were in good agreement with experimental measurements. The results suggested that the strut diameter, strut length, number and orientation, and the apparent material stiffness of the lattice cores had a significant effect on their deformation behavior and shock absorption capability. In addition, the BCC lattice core with a thinner strut diameter and low structural height might lead to poor shock absorption capability caused by structure collapse and border effect, which could be improved by increasing its apparent material stiffness. This dynamic drop impact simulation process could be applied across numerous industries such as footwear, sporting goods, personal protective equipment, packaging, or biomechanical implants.

Numerical simulation and structure optimization of control rod drop impact in floating reactor

In order to simulate the impact of control rod assembly on upper grid plate of reactor core after emergency shutdown of offshore floating reactor, the structure size of upper grid plate was optimized. In this study, ADAMS simulation software was used to simulate the impact stress and strain of 50 mm and 100 mm thick upper grid plate with and without spring buffer at 0.5 m / s impact speed. Therefore, the thickness of the buffer plate on the grid can be reduced, and the simulation results show that the buffer plate can be optimized effectively.

Numerical Simulation of drop impact on immiscible quiescent liquid layers

Numerical Simulation of drop impact on immiscible quiescent liquid layers

3D Simulation of Drop Impact on Dry Surface Using SPH Method

The purpose of this paper is to present and illustrate a smoothed particle hydrodynamics (SPH) method to study the process of a drop impacting on a dry solid surface. SPH is a Lagrangian mesh-free particle method that offers advantages in modeling the evolution of the liquid surface during drop impact. A new surface tension model is used. The artificial viscosity is also used, which is demonstrated to be, approximately, a linear function of the dynamic viscosity of the liquid. The SPH method is used to simulate different liquid drops impacting on dry surfaces. The numerical results agree with experimental data obtained from the literature. The influence of various parameters on the drop impact, including impact velocity, diameter, viscosity, surface tension, and density of the drop, is also studied. The results show that the dimensionless spreading diameter of the drop increases if the impact velocity, diameter, or density increases, while the increase in viscosity and surface tension decreases the spreading diameter. The results indicate that the drop impact depends more strongly on the viscosity and impact velocity than on the diameter, surface tension, and density of the drop. In addition to the impact of a spherical drop, the impact of an ellipsoidal drop on a dry surface is also studied. The results show that the aspect ratio of the drop has a significant influence on the outcome of drop impact.

Researchers model high-speed drop impact on thin films

A new study details numerical simulation of high-speed drop impact on thin liquid films, applicable to aircraft icing, a known flight hazard.

Optimization of constitutive model parameters for simulation of polystyrene concrete subjected to impact

This article presents the results of a series of experimental testing and numerical modeling studies to optimize the parameters of a constitutive material model to accurately simulate the behavior of polystyrene crushable concrete during impact loading using LS-DYNA. Quasi-static compression tests and confined drop impact tests were conducted. To model the quasi-static compression tests, the response surface methodology was used to optimize Poisson’s ratio and friction angle in the pseudo-tensor model in LS-DYNA. Using the optimized model parameters, the simulated compression stress versus strain relationship showed an excellent agreement with those from the compression tests. To model the confined drop impact tests, the strain rate sensitivity parameter in LS-DYNA was optimized by comparing the drop impact simulations at different strain rate sensitivity values with the drop impact tests. This study suggests that the pseudo-tensor material model is potentially suitable for modeling crushable concrete. Although the optimized constitutive model parameters are specific for the polystyrene concrete mix used in this study, similar approach can be used to optimize model parameters for other polystyrene concrete mixes.

A computational framework for the analysis of rain-induced erosion in wind turbine blades, part I: Stochastic rain texture model and drop impact simulations

In the past decade, the power output of wind turbines has increased significantly. This increase has been primarily achieved through manufacturing larger blades resulting in high blade tip velocities and increased susceptibility to rain erosion. This paper is the first part in a two-part paper that presents a framework for the analysis of rain erosion in wind turbine blades. Two ingredients of the framework are presented. A stochastic rain texture model is developed to generate three-dimensional fields of raindrops consistent with the rainfall history at the turbine location by integrating the micro-structural properties of rain, i.e. raindrops size and spatial distribution with its integral properties such as the relationship between the average volume fraction of raindrops and rain intensity. An in-house GPU-accelerated computational fluid dynamics model of free-surface flows and a multi-resolution strategy are used to calculate the drop impact pressure as a function of time and space. An interpolation scheme is finally proposed to find the time evolution of impact pressure profile for any given drop diameter using the high fidelity simulation results, significantly reducing the computational cost. Other ingredients of the framework pertaining to drop impact-induced stresses and the blade coating fatigue life are presented in part II.

二相系格子ボルツマン法を用いた固体壁面上における液滴の衝突挙動解析

二相系格子ボルツマン法を用いた固体壁面上における液滴の衝突挙動解析

Development of drop impact simulation method of packaging cardboard cargo considering buckling of the buffer structure

Development of drop impact simulation method of packaging cardboard cargo considering buckling of the buffer structure

A Numerical-Experimental Method for Drop Impact Analysis of Composite Landing Gear

The special material performance, manufacturing process, machining behavior, and operating condition of composite materials cause uncertainties to inevitably appear in the mechanical properties of composite structures. Therefore, variability in mechanical properties must be considered in a mechanical response analysis of composite structures. A method is proposed in this paper to predict the dynamic performance of composite landing gear with uncertainties using experimental modal analysis data and nonlinear static test data. In this method, the nonlinear dynamic model of the composite landing gear is divided into two parts, the linear and the nonlinear parts. An experimental modal analysis is employed to predict the linear parameters with a frequency response function, and the nonlinear parameters caused by large deflection are identified by a nonlinear static test with the nonlinear least squares method. To check the accuracy and practicability of the method, it is applied to drop impact simulations and tests of composite landing gear. The results of the simulations are in good agreement with the test results, which shows that the proposed method is perfectly suited for the dynamic analysis of composite landing gear.

Drop test simulation and surrogate-based optimization of a dishwasher mechanical structure and its packaging module

A drop test simulation of the mechanical structure of a redesigned dishwasher is performed by using a detailed finite element (FE) model. The nonlinear explicit FE code LS-DYNA® is used for the drop impact simulations. The FE model is validated through real tests of two drop scenarios (vertical and inclined to the side). An optimization study is performed in order to determine the optimum design variables for better crash performance. The effects of geometric parameters and material properties on the weights of certain components (ie, dogleg plate and bottom foam) are investigated. A surrogate-based optimization approach is used to find optimum values for the dogleg plate thickness, bottom foam density and increment of the bottom foam height to minimize the weights of both components. Two different surrogate models are used to predict optimization problem constraints that have a crucial role in the crash performance of the dishwasher mechanical structure and packaging module: the polynomial response surface and radial basis functions. The results showed that the dogleg plate mass can be slightly reduced and the bottom foam mass can be significantly reduced in order to obtain the optimum dishwasher configuration and better crashworthiness. The weights of the dogleg plate and bottom foam could be lowered by as much as 5.95 and 24.8 %, respectively. Finally, multi-objective optimization is performed by minimizing a composite objective function that provides a compromise between the weights of both components. The results showed that weight reductions of 2.3 and 21.5 % could be obtained for the dogleg plate and bottom foam, respectively.

Simulation of liquid drop impact on dry and wet surfaces using SPH method

Spray–wall interactions occur in many combustion devices and have significant effects on mixture distribution and combustion quality. This paper describes an advanced numerical method, based on smoothed particle hydrodynamics (SPH), for predicting the detailed outcomes of drop–wall interactions. SPH is a Lagrangian mesh-free method suitable for capturing the surface evolution of a deforming liquid. In simulating the drop impact on a dry surface, the present model was able to predict the spread of the drop on the wall, and the evolution of the predicted wall film diameter agreed with the experimental data. In simulating the drop impact on a wet surface with an existing liquid film, the model captured the formation of the crown, the generation of secondary droplets, and the eventual receding of the crown. Results show that as the impact velocity increased, both the maximum crown height and the time to reach the maximum crown height increased. These predictions agreed with the measurements for various operating conditions. This agreement indicates that the present numerical method has the potential to accurately predict the details of spray–wall interactions in combustion system environments.

Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?

It is well known that a superhydrophobic surface may not be able to repel impacting droplets because of the so-called Cassie-to-Wenzel transition. It has been proven that a critical value of the receding contact angle (θR) exists for the complete rebound of water, recently experimentally measured to be 100° for a large range of impact velocities. On the contrary, in the present work, no rebound was observed when low-surface-tension liquids such as hexadecane (σ = 27.5 mN/m at 25 °C) are concerned, even for very low impact velocities and very high values of θR and low contact angle hysteresis. Therefore, the critical threshold of θR ≈ 100° does not sound acceptable for all liquids and for all hydrophobic surfaces. For the same Weber numbers, a Cassie-to-Wenzel state transition occurs after the impact as a result of the easier penetration of low-surface-tension fluids in the surface structure. Hence, a criterion for the drop rebound of low-surface-tension liquids must consider not only the contact angle values with surfaces but also their surface tension and viscosity. This suggests that, even if it is possible to produce surfaces with enhanced static repellence against oils and organics, generally the realization of synthetic materials with self-cleaning and antisticking abilities in dynamic phenomena, such as spray impact, remains an unsolved task. Moreover, it is demonstrated that the chemistry of the surface, the physicochemical interactions with the liquid drops, and the possible wettability gradient of the surface asperity also play important roles in determining the critical Weber number above which impalement occurs. Therefore, the classical numerical simulations of drop impact on dry surfaces are definitively not able to capture the final outcomes of the impact for all possible fluids if the surface topology and chemistry and/or the wettability gradient in the surface structure are not properly reflected.

緩衝構造の角部破壊を想定した段ボール梱包貨物の落下衝撃シミュレーションの開発

緩衝構造の角部破壊を想定した段ボール梱包貨物の落下衝撃シミュレーションの開発

Entropic lattice Boltzmann method for multiphase flows: Fluid-solid interfaces.

The recently introduced entropic lattice Boltzmann model (ELBM) for multiphase flows [A. Mazloomi M., S. S. Chikatamarla, and I. V. Karlin, Phys. Rev. Lett. 114, 174502 (2015)] is extended to the simulation of dynamic fluid-solid interface problems. The thermodynamically consistent, nonlinearly stable ELBM together with a polynomial representation of the equation of state enables us to investigate the dynamics of the contact line in a wide range of applications, from capillary filling to liquid drop impact onto a flat surfaces with different wettability. The static interface behavior is tested by means of the liquid column in a channel to verify the Young-Laplace law. The numerical results of a capillary filling problem in a channel with wettability gradient show an excellent match with the existing analytical solution. Simulations of drop impact onto both wettable and nonwettable surfaces show that the ELBM reproduces the experimentally observed drop behavior in a quantitative manner. Results reported herein demonstrate that the present model is a promising alternative for studying the vapor-liquid-solid interface dynamics.

Assessment of dynamic adaptive grids in Volume-Of-Fluid simulations of oblique drop impacts onto liquid films

Grid spacing dependence in three-dimensional numerical simulations of non-normal drop impact onto thin liquid films is assessed for different impingement angles and grid refinement levels. To describe the liquid phase dynamics, the Navier–Stokes equations are coupled to a Volume-Of-Fluid (VOF) model. Numerical simulations are performed with a modified version software OpenFOAM over a structured grid of hexaedra. Grid adaptation is carried out using an edge subdivision technique which results in non-conformal meshes. Grid convergence is assessed by monitoring integral parameters describing the dynamics of the post-impact free-surface waves. Starting from an initial grid spacing between D/8 and D/5, with D drop diameter, a refinement level of three is found to be sufficient to describe the diverse flow feature and to identify the splashing regime.

Impact Attenuation of Customized User-centered Bicycle Helmet Design

Bicycle helmets are currently available to cater to general head sizes, ranging from S/M and L/XL, but there is also a universal model that can fit all sizes through adjustable helmet strap. Numerous surveys addressed that wearing helmet is not comfortable and the current sizing did not accommodate various range of users, because the human head shapes and dimensions are different according to ethnic groups, age and gender. This paper describes impact attenuation of user-centred design approach, i.e by modifying the shape of the liner to improve fit of bicycle helmet in accordance to AS/NZS 2063:2008. Head scans of 15 participants from a selected control group were captured using Artec3D portable scanner, while bicycle helmets and J headform were scanned using Flexscan 3D scanning equipment. These participants were selected based on a grouping method referring to selected 37 landmarks on human head shape. A new headform for the control group was developed by aligning and combining all the involved head scans in Geomagic Studio 12. Several new helmets with different liner thickness were designed based on the new headform. A validated drop impact simulation model, developed using Abaqus FEA software, was used to conduct drop impact simulation of each customized helmet design. Thickness of each user-centred helmet models at 37 landmarks was also recorded and the peak linear acceleration (PLA) of the helmet at impact locations such as top, side and front area were measured. Results revealed that the PLA increases as the thickness of helmet liner decreases. The rate of increase of PLA as the helmet liner thickness decreases is different at each impact location; it was greater at front and side location compared to top impact location.

Finite Element Bicycle Helmet Models Development

Abstract Impact attenuation performance of three different range of commercial bicycle helmet were investigated in lateral drop impact test in accordance to AS/NZS 2063:2008, Australian/New Zealand Standard for bicycle helmet using numerical simulation and and experimental impact test. The aim of this research is to develop a simulation model of drop impact test, which to be used in further investigations of user-centred design approach of bicycle helmet. Three commercial bicycle helmet models were used in this study. All helmets and J headform were scanned using Flexscan 3D scanning equipment. Post-scan processing jobs of scanned geometry models such as helmet liner, shell and headform were conducted in Geomagic Studio 12. The experimental impact test is carried out using 2-wire drop test facility in accordance to the AS/NZS 2063:2008, Australian Standard for bicycle helmet. A few samples were cut from the liner of each helmet to determine the density of Expanded Polystyrene (EPS). Headform peak linear acceleration, impact duration and impact speed of each helmet were measured and recorded from the drop test. The scanned geometry models were imported into Abaqus. A drop impact simulation was developed based on the density and impact speed data obtained from the physical test. Inner liner of bicycle helmet, made from Expanded Polystyrene (EPS), was modeled using crushable foam properties, while headform and anvil were modeled as rigid bodies. Peak linear accelerations and impact duration of the headform on each helmet at three different impact locations of helmet were recorded. A robust correlation study using peak linear acceleration score, impact duration score and Pearson correlation coefficient between the data from physical test and numerical model was conducted. Good correlation scores (>80%) were achieved between the numerical model and experimental impact test in terms of headform peak linear acceleration and impact duration score, suggesting that the simulation model is in good correlation with those from physical test.