The spreading of a viscous microdrop on a solid surface

The spreading of a liquid microdrop across a solid surface is examined using the interface formation model. This model allows for variable surface tension at constant temperature and a flow induced Maragoni effect, by incorporating irreversible thermodynamics into the continuum model. The model is solved for small Capillary number and small Reynolds number. This problem has been considered before for much larger drops in Shikhmurzaev (Phys Fluids 9:266, 1997a), which examined the spreading of a drop for ε = τ U _CL/R ≪ 1, where U _CL is the speed of the moving contact line across the solid surface, τ is the surface tension relaxation time of the viscous liquid, and R is a typical length scale for the size of the drop. This paper extends that work by examining ε = O(1), which will be shown to be the appropriate scaling for very small liquid drops, on the scale of micrometres or less.     

Experimental investigation of snakelike motions of a three-link mechanism

A three-link joint mechanism is considered, which is able to move on a flat rough surface by changing its configuration. A model for this mechanism is presented, and its control system is described. The results of experiments with the three-link robot for various motion modes are presented.     

Phase-field simulation of impingement and spreading of micro-sized droplet on heterogeneous surface

A numerical investigation on the impingement and spreading of a micro-sized droplet with nonzero impact velocities on a surface with heterogeneous wettability is presented in this paper. The numerical model was implemented through phase-field simulation with finite element formulation. A simple scheme based on interfacial phase-field function gradient was proposed to track the velocity of contact line which was required to specify the dynamic contact angle based on hydrodynamic theory and molecular kinetic approach. For a circular pattern with a higher wettability than the surrounding surface, the impinging droplet final spread diameter decreases with an increasing wettability contrast. The droplet conforms to the circular patterns with smaller diameters up to a threshold, which is dictated by the wettability of the surface surrounding the pattern. Impact velocity of the droplet affects the maximum spread diameter but not the final conformability to a wettability pattern. Impingement and anisotropic spreading of a droplet on a stripe pattern was also demonstrated in a three-dimensional simulation. The high wettability contrast between the inner and outer regions of the stripe pattern confines droplet spreading and elongates the droplet in the direction of the stripe. These simulations demonstrated the conditions for a jetted micro-sized droplet to be confined to a specific area through wettability patterning, which can potentially improve the precision of current inkjet printing technology.     

Experimental and numerical investigation of a large stroke compliant revolute joint

Microsystem Technologies - Aiming at designing of a large stroke compliant revolute joint, this article presents an effective design method from the aspects of numerical and experimental...     

Experimental investigation and numerical modeling of the thermal behavior of a micro-heater

In micro-heater, heat flux is generated by Joule effect thanks to short electric pulses. This leads to a rapid increase of the micro-heater temperature that reaches a few hundreds degree Celsius in a few microseconds. In addition to this, the cyclic nature of the energizing signal may cause an excessive heat accumulation and hence a reduction of the device life expectancy. It is thus of utmost importance to accurately model heat transfer in the whole device. This work focuses on a 200 dots per inch printing head system which consists of a row of micro-heaters. Structure and chemical composition of a single micro-heater are determined by scanning electron microscopy coupled to an EDX analyzer (energy dispersive X-ray spectrometry). These data are used to build a two dimensional numerical model which represents a micro-heater cross-section. This model gives the spatiotemporal evolution of the temperature field which highlights clearly the thermal loading phenomenon in the micro-heaters. In parallel, electric measurements are performed during the printing process to access to the actual power supplied to the micro-heaters. Infrared thermography was used to measure the thermal response of the micro-heaters to the electrical solicitation. The comparison of experimental and numerical results shows that the numerical model correctly predicts the thermal behavior of micro-heaters.     

Experimental investigation of a model of a vibration-driven robot with rotating masses

Vibration-driven robots with internal movable masses able to move on a rough surface using only harmonic oscillations of these masses are considered. Models of such robots are presented. The results of experiments with vibration-driven robots for different types of motion modes are presented.     

Experimental investigation of distributed navigation and collision avoidance for a robotic swarm

Artificial Life and Robotics - In this study, we focus on the navigation of a robotic swarm and perform an experimental investigation. A decentralized control method using only local information...     

Precision range image registration using a robust surface interpenetration measure and enhanced genetic algorithms

This paper addresses the range image registration problem for views having low overlap and which may include substantial noise. The current state of the art in range image registration is best represented by the well-known iterative closest point (ICP) algorithm and numerous variations on it. Although this method is effective in many domains, it nevertheless suffers from two key limitations: it requires prealignment of the range surfaces to a reasonable starting point; and it is not robust to outliers arising either from noise or low surface overlap. This paper proposes a new approach that avoids these problems. To that end, there are two key, novel contributions in this work: a new, hybrid genetic algorithm (GA) technique, including hill climbing and parallel-migration, combined with a new, robust evaluation metric based on surface interpenetration. Up to now, interpenetration has been evaluated only qualitatively; we define the first quantitative measure for it. Because they search in a space of transformations, GA are capable of registering surfaces even when there is low overlap between them and without need for prealignment. The novel GA search algorithm we present offers much faster convergence than prior GA methods, while the new robust evaluation metric ensures more precise alignments, even in the presence of significant noise, than mean squared error or other well-known robust cost functions. The paper presents thorough experimental results to show the improvements realized by these two contributions.     

The role of viscoelasticity in drop impact and spreading for inkjet printing of polymer solution on a wettable surface

We investigate here for the first time the entire deposition process of a sub-30 μm-sized polymer-containing drop on wettable surfaces over more than 7 decades of elapsed time, under conditions fully representative of inkjet printing. The drop deposition dynamics of a polystyrene solution on a highly or partially wettable surface are independent of the high-shear rheology of the fluid, while the final drop size is significantly affected by surface wettability. We show why the polymer chains do not become extended despite the high extension rate in drop spreading. This study provides a framework to evaluate the effects of viscoelasticity on the drop deposition process due to the presence of polymers in dilute solution.     

Experimental investigation and thermodynamic calculation of Ti-Co-Hf system

Phase relationship of Ti-Co-Hf ternary system, which may contribute to the development of both new Ti-based biomaterials and Co₁₁Hf₂ based rare-earth-free magnetic materials, have been studied by using Ti-Co-Hf diffusion triple and selected equilibrated alloys. Isothermal sections of the Ti-Co-Hf ternary system at both 1173 and 1073 K were experimentally determined by means of electron probe microanalysis (EPMA), scanning electron microscope (SEM) and X-ray diffraction (XRD). Meanwhile, structure refinements of three continuous solid solutions, i.e. Co(Ti, Hf)₂, Co₂(Ti, Hf) and BCC_B2 which were formed between CoTi₂ and CoHf₂, Co₂Ti(c) and Co₂Hf as well as CoTi and CoHf, respectively, were performed by Rietveld method. The stable temperature range of Co₁₁Hf₂ was revised to be from 1310 ± 12.5–1516 K. And Ti (about 3.7 at%) partly dissolves in Co₂₃Hf₆ at 1173 K while the solubility of Hf in Co₃Ti at both 1173 and 1073 K is relatively limited. Based on the available data of binary system, thermodynamic modeling of Ti-Co-Hf ternary system was carried out, with Co(Ti, Hf)₂, Co₂(Ti, Hf) and BCC_B2 being respectively described with models, (Co, Hf)₁(Co, Ti, Hf)₂, (Co, Ti, Hf)₂(Co, Ti, Hf)₁ and (Co, Ti, Hf, VA)_0.5(Co, Ti, Hf, VA)_0.5. A set of self-consistent thermodynamic parameters, which can reasonably reproduce the measured results, has been obtained.     

非线性卡尔曼滤波方法的实验比较

实际系统中存在的非线性因素和不确定性是实时状态测量以及不确定性估计算法需要解决的重要问题.以机器人系统中典型的动态目标观测问题为背景,采用多飞行机器人实验平台,分别针对EKF、UKF以及基于MIT规则的AUKF方法进行实验研究,并比较了上述方法的计算速度及估计精度等性能.最后,根据实验结果并结合其原理分析了每种方法的特性.     

Experimental investigation and thermodynamic calculation of Ti-Hf-Mn system

The phase relationship of Ti-Hf-Mn system was studied by diffusion triple and equilibrated alloy methods. The isothermal sections at 1373, 1273 and 1173 K for this system were constructed by means of electron probe microanalysis (EPMA) and X-ray diffraction (XRD) for the first time. No ternary phase was found in the system at all these temperatures. Six, seven and seven three-phase equilibria regions have been determined at 1373, 1273 and 1174 K, respectively. In this ternary system, the intermetallic compounds TiMn₂, HfMn₂ and HfMn exhibit wide solid solution range at those three temperatures. In particular, the solution range of Ti in HfMn phase decreases with the increase of temperature, from 30.5 at% at 1173 K to 26.5 at% at 1373 K. Based on all available experimental data, the Ti-Hf-Mn system was evaluated using the CALPHAD method. The calculation results are in excellent agreement with the experimental data.     

Experimental and numerical investigation of unsteady cavitating flows through a 2D hydrofoil

In the present study, firstly, the unsteady cavitating flows around a hydrofoil are studied based on the flow visualization and detail velocity measurement, a high-speed video camera is used to visualize the flow structures, and a particle image velocimetry (PIV) technique is applied to the measurement of the time-averaged and instantaneous velocity and vorticity fields. The results show that the unsteadiness of mass transfer process between the vapor and the two-phase regions is substantial, a self-oscilla...     

Experimental investigation on coverage performance of a chaotic autonomous mobile robot

In many autonomous mobile robotic missions the complete and fast coverage of the workspace, scanned by an unpredictable trajectory, plays a crucial role. To satisfy these special demands in the design of an autonomous mobile robot, a motion controller, based on the dynamical behavior of a known discrete chaotic system, the Logistic map, is presented in this paper. The proposed method is based on a microcontroller for realizing a chaotic random bit generator and converting the produced chaotic bit sequence, to the robot’s trajectory of motion. The experimental results confirm that this approach, with an appropriate sensor for obstacle avoidance, can obtain very satisfactory results in regard to the fast scanning of the robot’s workspace with unpredictable way.     

Experimental investigation of stochastic parafoil guidance using a graphics processing unit

Control of autonomous systems subject to stochastic uncertainty is a challenging task. In guided airdrop applications, random wind disturbances play a crucial role in determining landing accuracy and terrain avoidance. This paper describes a stochastic parafoil guidance system which couples uncertainty propagation with optimal control to protect against wind and parameter uncertainty in the presence of impact area obstacles. The algorithm uses real-time Monte Carlo simulation performed on a graphics processing unit (GPU) to evaluate robustness of candidate trajectories in terms of delivery accuracy, obstacle avoidance, and other considerations. Building upon prior theoretical developments, this paper explores performance of the stochastic guidance law compared to standard deterministic guidance schemes, particularly with respect to obstacle avoidance. Flight test results are presented comparing the proposed stochastic guidance algorithm with a standard deterministic one. Through a comprehensive set of simulation results, key implementation aspects of the stochastic algorithm are explored including tradeoffs between the number of candidate trajectories considered, algorithm runtime, and overall guidance performance. Overall, simulation and flight test results demonstrate that the stochastic guidance scheme provides a more robust approach to obstacle avoidance while largely maintaining delivery accuracy.     

Optimization of a fertilizer spreading process

An optimization method for accurate fertilizer application by centrifugal spreader is described. The cost functional is a distance between a prescribed dose and the distributed dose. The distributed dose is computed using a simplified spread pattern and the unknowns of the problem are three time-dependent parameters of the spreader: the average (distribution) center, the average (distribution) angle and the mass flow rate. In order to take into account the mechanical limits of the device, constraints are introduced in the form of bounds on the parameter functions and their time derivatives. Numerical experiments show that application errors can be significantly reduced for parallel tracks within a main field body.     

Design of a novel miniaturized bandstop frequency selective surface exhibiting polarization insensitivity and enhanced oblique stability

In this article, a miniaturized 2.5‐dimensional frequency selective surface (FSS) bandstop filter operating at 2.4 GHz is presented. The proposed FSS contains meander lines as well as metallic patches on top and bottom layer of FR‐4 substrate, and vertical vias are employed to connect the top and the bottom layers. The proposed configuration significantly reduced the size of unit cell to 0.040λ₀ × 0.040λ₀ (where λ₀ is the free space wavelength) at the desired frequency of 2.4 GHz. Additionally, this element arrangement assists in achieving fractional bandwidth of 140%. The measured ?10 dB bandwidth is from 1 to 4.5 GHz. The proposed FSS is polarization insensitive and highly angularly stable (up to 75°). The equivalent circuit model (ECM) of this FSS and related surface current distribution are also provided to understand its working mechanism. The design performance validation has been carried out through the construction and testing of a functional prototype. The full wave simulation, the ECM, and the measured results depict a promising agreement.