Experimental and numerical investigations of particle suspension suppression mechanisms for a particle-suppression device in a stirred liquid bath

Particle suspension in a turbulent flow can seriously affect the performance of manufactured products in many industrial processes in which the motion of particles cannot be modeled using the numerical method because of the enormous number of particles. Therefore, in this study, a full-scale computational fluid dynamics (CFD) simulation and a 1/5 scaled-down water model experiment were employed to investigate the flow pattern and dynamic behavior of particles in a continuously stirred vessel system. Based on the understanding of the suspension mechanism of settling particles, a particle-suppression device was designed to realize the harmless movement and deposition of particles. The results showed that the flow guidance and division mechanisms of the particle-suppression device led to the inhibition of particle suspensions. In addition, the optimal parameter combination for the device from the water model experiment combined with the orthogonal experimental design, resulted in a 98.3% reduction in the concentration of suspended particles. The suspension of particles was effectively suppressed, which improves product quality and production efficiency. Reliable results can be achieved by combining CFD simulations and water model experiments.     

颗粒阻尼的动态特性研究

颗粒阻尼技术已经成功的应用于多个领域抑制振动。然而,由于颗粒阻尼复杂的碰撞和摩擦减振机理,很难预测其减振特性。本文建立了颗粒阻尼的粉体力学模型,并用于研究颗粒阻尼容器的截面形状及尺寸关系对其减振特性的影响。通过试验研究,揭示了颗粒阻尼的非线性阻尼特性,并应用等效阻尼的原理提出了合理的颗粒阻尼的等效数学模型。     

Propagation of steel corrosion in concrete: Experimental and numerical investigations

This paper focuses on experimental and numerical investigations of the propagation phase of reinforcement corrosion to determine anodic and cathodic Tafel constants and exchange current densities, from corrosion current density and corrosion potential measurements. The experimental program included studies on RC specimens with various binder compositions, concrete cover thicknesses, and concrete cover crack widths. Modelling and fitting of experimental data using an electrochemical model allowed for the determination of parameters, which are key parameters for electrochemical modelling tools. The numerical model was, furthermore, used to identify electrochemical parameters, which are independent of concrete cover thickness and crack width and at the same time allow for determination of the corrosion current density and corrosion potential of concrete structures within an acceptable error.Very good comparisons between the experimentally measured and numerically simulated corrosion current densities and corrosion potentials were found for the various RC specimens. Anodic and cathodic Tafel constant between 0.01 and 0.369 V/dec and 0.01 and 0.233 V/dec, respectively, were found in the present study through numerical simulations of the experimental data. Anodic and cathodic exchange current densities ranged from 1.0E–12 to 1.0E–09 A/mm² and 1.0E–12 to 1.1E–09 A/mm², respectively.     

软内壁颗粒阻尼器阻尼特性试验研究

在垂直简谐激励条件下,利用稳态能量流法对颗粒阻尼器的阻尼特性进行了试验研究.试验结果表明:对于由3 mm大颗粒组成的浅床颗粒阻尼器,其损耗功率随激振加速度的增加而单调递增,而由0.8 mm小颗粒组成的厚床颗粒阻尼器,其损耗功率随激振加速度的增加先递增而后突然递减而后再递增;在阻尼器容器内壁粘贴一层橡胶材料后,阻尼器具有...     

Experimental and numerical investigations on full-scale adhesively bonded timber trusses

Timber architecture, taking advantage of modern production techniques, is increasingly moving towards free forms; however, traditional joining techniques are not yet adapted to echo the new expression at the level of the details. This paper reports on adhesively bonded joints as a way to help architects fully unleash their creative potential. For this purpose, experimental and numerical investigations on full-scale adhesively bonded timber trusses were performed, in which adhesive bonds were compared to traditional doweled connections. The adhesively bonded trusses achieved significantly higher failure load and stiffness. Tests on small clear specimens were conducted to determine input parameters for finite element analyses. The sole timber connection was characterised, giving valuable insights into the mechanical behaviour of this truss component. At this end, the influence of the embedded length of the applied sleet plates was experimentally determined, delivering data to benchmark the subsequent dimensioning method. The trusses were then modeled and excellent agreement was found between numerical and experimental results. Finally, a dimensioning method, based on a realistic multi-axial failure criterion coupled with size effects was implemented and yielded very good agreement when with experimental results. The reported investigation demonstrates the high potential of adhesive bonding in timber structures.     

Experimental and numerical investigations on compressive properties of porous twisted wire materials

Wire diameter, sintering parameter, and porosity have great influences on porous structures and compressive properties of the stainless steel porous twisted wire materials with 30–92% porosities. Finer wires, higher sintering temperature, and longer sintering time will lead to narrower pore-size distributions, more compact porous structures, and stronger compressive yield strength. A random pore model and a twisted wire framework model are put forward to simulate the compressive process. The compressive deformation mechanism is a continuous densification process. The simulated and experimental stress-strain curves all exhibit elastic stage, plastic yield platform stage, and final densification stage.     

Experimental and numerical investigations for the free vibration of cantilever trapezoidal plates

Abstract

Based on the advantages of non‐contact and full field measurement, the optical technique called amplitude‐fluctuation electronic speckle pattern interferometry (AFESPI) with an out‐of‐plane setup is employed to investigate the free vibration of cantilever trapezoidal plates with various taper ratios and sweep‐back angles. Twenty different plate configurations are analyzed, including triangular and trapezoidal plates, and the first seven vibration modes of each plate are measured. The AF‐ESPI method is very convenient for measuring vibrating objects because no contact is required in contrast to classical modal analysis using accelerometers. Based on the fact that clear fringe patterns will appear only in resonance, both resonant frequencies and corresponding mode shapes can be obtained experimentally using the present technique. Numerical calculations by finite element method are also performed and the results are compared with the experimental measurements. Excellent agreements are obtained for both results of resonant frequencies and mode shapes. The influences of taper ratios and sweep‐back angles on the vibration behavior of cantilever trapezoidal plates are also demonstrated in terms of the dimensionless frequency parameter.     

Experimental and numerical investigation on the shape approximation of rice particle by multi-sphere particle models

In this study experimental and numerical investigations on the mechanical and flow behavior of the multi-sphere (MS) rice particles with different degrees of shape approximation are conducted. This work aims to provide a better understanding of the adaptability of the degree of the shape approximation. The results indicated that rice particles can be approximated using the MS models with axi-symmetric ellipsoid shape. Furthermore, the angularity factor, AF, can be used to quantify the degree of shape approximation. As AF decreases, the degree of shape approximation increases. Finally, selection of the shape approximation scheme depends on the application of granular materials. Specifically, for the static and dynamic mechanical behavior of the single particle, the degree of shape approximation should not be strictly accurate, but should be appropriately rough. However, for the static and dynamic flow behavior of the particle assembly, the degree of shape approximation should be accurate.     

Experimental investigations of the laws of energy dissipation during dynamic deformation of nanocrystalline titanium

The mechanical and thermodynamic characteristics of nanocrystalline (NC) titanium have been experimentally studied under the conditions of dynamic compression at a strain rate of (2–5) × 10³ s⁻¹. The samples of NC titanium were cut from a rod processed by equal-channel angular pressing and had a characteristic grain size of 300 nm. It is established that a 25% increase in the dynamic limit of elasticity in the NC titanium (compared to an initial coarse-grained sample) is accompanied by qualitative changes in the process of energy absorption and dissipation in the material. The amount of dissipated energy remains approximately constant and independent of the rate and amplitude of loading in the entire range of strain rates studied.     

Experimental and numerical investigations of low velocity impact on functionally graded circular plates

This paper addresses low-velocity impact behaviour of functionally graded clamped circular plates. An experimental work was carried out to investigate the impact behaviour of FG circular plates which is composed of ceramic (SiC) and metal (Al) phases varying through the plate thickness by using a drop-weight impact test system. The influence of the compositional gradient exponent and impactor velocity on the contact forces and absorbed energies was concentrated on the tests. The explicit finite element method, in which a volume fraction based elastic–plastic model (the TTO model) was implemented for the functionally graded materials, was used to simulate their drop-weight impact tests. Effective material properties at any point inside FGM plates were determined using Mori–Tanaka scheme. The experimental and numerical results indicated that the compositional gradient exponent and impactor velocity more effective on the elasto-plastic response of the FG circular plates to a low-velocity impact loading. The comparison at the theoretical and experimental results showed that the use of the TTO model in modelling the elasto-plastic behaviour of FG circular plates results in increasing deviations between the numerical and experimental contact forces for ceramic-rich compositions whereas it becomes more successful for metal-rich compositions.     

Experimental and numerical investigations on the eccentric vortex of the cross flow fan

The effects of an eccentric vortex on the performance of a cross flow fan for air-conditioning is evaluated experimentally and numerically. Based on the two-dimensional computational analysis using commercial CFD software, and experimental measurements, a new design is proposed for the inlet guide vanes. The new design reduces vortex shedding from the fan blades, thereby reducing the size of the eccentric vortex, which results in improved fan efficiency. The new design improves the performance of the cross flow fan marginally by 4.6% at a maximum volumetric flow rate of 10.5 m³ min⁻¹.     

Experimental and numerical modeling of particle levitation and movement behavior on traveling-wave electric curtain for particle removal

Traveling-wave electric curtain (EC) has been developed for potential application in particle removal/shield on solar panels and other surfaces. Levitation and transport of a particle in a traveling-wave electric field were simulated. Results show that levitation directions/angles and levitation trajectories differ because of the difference in starting positions and starting times. The particles in the two positive acceleration regions are levitated in opposite directions, and the particles distributed on the dielectric surface are levitated and transported successively rather than simultaneously. Movement trajectories are complex and affected by various factors. In the current paper, movement trajectories are modeled to analyze which motion modes are advantageous or disadvantageous to particle removal. This process is beneficial to elucidate the mechanism of particle removal and provide a guidance for movement control by designing appropriate operating parameters.     

颗粒碰撞阻尼的时效性研究

颗粒碰撞阻尼是一种被动式振动控制器,其中颗粒材料在冲击过程中的尺度和形貌变化必然对其减振性能产生重要影响。文中初次探讨了带有中值粒度为35微米的锌颗粒的颗粒碰撞阻尼器在96小时内对正弦激励悬臂梁的阻尼减振的时效性。研究证明,主系统的响应在所考察的时间历程内出现了三次微幅上升,它是锌颗粒材料在冲击作用下结构和能态变化的结果。首先,随着冲击的进程,颗粒的冷焊效应阻碍了冲击器的运动速度,降低了冲击器的动量交换功能。第二,颗粒应变能和层错能的下降降低了系统的不可逆能耗。第三,颗粒的细化使其本身缺陷减少,进一步细化的难度增加,也使得系统内的不可逆能耗不断减小。这是主系统的响应随着振动历程出现了两次阶跃性微幅上升的主要原因。     

Experimental and numerical investigations of bonding interface behavior in stationary shoulder friction stir lap welding

Stationary shoulder friction stir lap welding (SSFSLW) was employed to weld 2024 aluminum alloy. A coupled Eulerian-Lagrangian (CEL) model was developed to investigate the lap interface behavior during SSFSLW. Numerical results of material movement and equivalent plastic strain were in good agreement with the experimental work. With increasing welding speed, the distances from the hook tip to the top surface of the upper workpiece on the retreating side (RS) and the advancing side (AS) increase, while the distance between two wave-shaped alclads decreases. A symmetric interface bending is observed on the AS and the RS during plunging, while the interface bending on the AS is bigger than that on the RS during welding. The peak temperature of the interface on the AS is higher than that on the RS. The equivalent plastic strain gradually increases as the distance to the weld center decreases, and its peak value is obtained near the bottom of the weld.     

Experimental and numerical investigations of void damage in aluminum alloy welds under thermal cycling condition

Experimental and numerical investigations on thermal cycling induced void damage in aluminum alloy welds are presented. Microstructural and fractographic observations demonstrate that void nucleation around the second phase particles governs the damage process. A modified void nucleation model is presented to characterize the effect of thermal cycling assisted voiding. The physical simulation technique and finite element calculations are applied respectively to determine the local mechanical properties and damage parameters of the different parts of the welded joint. This model is successfully implemented in the finite element code to describe the void damage evolution of the welded joint under thermal cycling conditions.     

Compressive damage mechanism of GFRP composites under off-axis loading: Experimental and numerical investigations

Experimental and computational studies of the microscale mechanisms of damage formation and evolution in unidirectional glass fiber reinforced polymer composites (GFRP) under axial and off-axis compressive loading are carried out. A series of compressive testing of the composites with different angles between the loading vector and fiber direction were carried out under scanning electron microscopy (SEM) in situ observation. The damage mechanisms as well as stress strain curves were obtained in the experiments. It was shown that the compressive strength of composites drastically reduces when the angle between the fiber direction and the loading vector goes from 0° to 45° (by 2.3–2.6 times), and then slightly increases (when the angle approaches 80–90°). At the low angles between the fiber and the loading vector, fiber buckling and kinking are the main mechanisms of fiber failure. With increasing the angle between the fiber and applied loading, failure of glass fibers is mainly controlled by shear cracking. For the computational analysis of the damage mechanisms, 3D multifiber unit cell models of GFRP composites and X-FEM approach to the fracture modeling were used. The computational results correspond well to the experimental observations.     

Experimental and numerical investigations on fracture process zone of rock–concrete interface

A crack propagation criterion for a rock–concrete interface is employed to investigate the evolution of the fracture process zone (FPZ) in rock–concrete composite beams under three‐point bending (TPB). According to the criterion, cracking initiates along the interface when the difference between the mode I stress intensity factor at the crack tip caused by external loading and the one caused by the cohesive stress acting on the fictitious crack surfaces reaches the initial fracture toughness of a rock–concrete interface. From the experimental results of the composite beams with various initial crack lengths but equal depths under TPB, the interface fracture parameters are determined. In addition, the FPZ evolution in a TPB specimen is investigated by using a digital image correlation technique. Thus, the fracture processes of the rock–concrete composite beams can be simulated by introducing the initial fracture criterion to determine the crack propagation. By comparing the load versus crack mouth opening displacement curves and FPZ evolution, the numerical and experimental results show a reasonable agreement, which verifies the numerical method developed in this study for analysing the crack propagation along the rock–concrete interface. Finally, based on the numerical results, the effect of ligament length on the FPZ evolution and the variations of the fracture model during crack propagation are discussed for the rock–concrete interface fracture under TPB. The results indicate that ligament length significantly affects the FPZ evolution at the rock–concrete interface under TPB and the stress intensity factor ratio of modes II to I is influenced by the specimen size during the propagation of the interfacial crack.     

Experimental and numerical investigations of the impact behaviour of composite frontal crash structures

The present paper deals with the lightweight design and the crashworthiness analysis of a composite impact attenuator for a Formula SAE racing car, in order to pass homologation requirements. The analysed impact attenuator is manufactured by lamination of prepreg sheets in carbon fibres and epoxy matrix, particularly used for sporting applications, and has a very similar geometry to a square frusta, so as to obtain a progressive and controlled deformation. During the design, attention was focused on the material distribution and gradual smoothing, but also on the lamination process, which can heavily affect the energy absorption capability. To reduce the development and testing costs of a new safety design, computational crash simulations for early evaluation of safety behaviour under vehicle impact test were carried out. The dynamic analysis was therefore conducted both numerically, using an explicit finite element code such as LS-DYNA, and experimentally, by means of an appropriately instrumented drop weight test machine, in order to validate the model in terms of deceleration values during crushing. To assess the quality of the simulation results, a comparative analysis was initially developed on simple CFRP composite tubes subjected to dynamic axial loading. The numerical analysis was conducted using both shell and solid elements, in order to reproduce not only the brittleness of the composite structure but also the effective delamination phenomenon. Both the analyses show a good capacity to reproduce the crushing process; this is confirmed by the fact that model estimated displacements and accelerations are in close agreement with observed values for these variables. This confirms the quality of the methodology and approach used for the design of a racing car impact attenuator.