基于准分布式FBG传感器的均质材料内部应变测试的试验研究

采用环氧树脂材料作为试验载体,使用没有任何保护性封装的、运用波分复用技术在同一光纤上刻入三个布拉格光栅的基础FBG传感器,来监测液体树脂流动及固化成型的全过程,并使用固化成型的环氧树脂板进行三点弯曲试验。将所得数据与有限元模拟数值解进行比较,来验证在去除封装、将传感器自身应变影响降到最低的情况下,FBG传感网络是否依然能够有效地反映出试验对象在各种情况下的内部应变。本文给出了FBG光纤光栅在逐级静力荷载加载下材料内部三点弯曲的应变图,并通过数值计算分析了未封装光纤在复合材料内部受力过程中的力学性能。     

Numerical Simulation and Experimental Validation of the Turbulent Combustion and Perlite Expansion Processes in an Industrial Perlite Expansion Furnace

A computational code has been developed based on a Eulerian–Lagrangian approach in order to model the combustion and the motion of perlite particles in a vertical expansion furnace. The expansion of a single particle, which takes place during its motion in the furnace, has been modeled by taking into account the perlite chemical composition and the gradual variation of the temperature distribution inside the grain. Experiments, performed in a perlite expansion plant, have been used to validate the computational results. The operational characteristics of a perlite expansion furnace have been measured and have served as inlet conditions for the numerical simulation of the combustion and perlite expansion processes.The good agreement between measurements and predictions indicates that the developed computational tool can be used to optimise the perlite expansion process leading to reduced fuel consumption with increased productivity.     

基于光学和扫描显微平台的微尺度实验力学检测技术和装置研究

本文基于光学和扫描显微平台,介绍了本研究组在微尺度实验力学检测技术和设备方面的最新研究成果。在检测技术方面涉及显微散斑干涉技术、微标记阵列检测技术、晶粒变形分析技术、光学探针动静态变形分析技术;在检测系统和装置方面介绍了新近开发的双视场薄膜检测系统、散斑微干涉系统、微标记检测平台、AFM和SEM单轴拉伸装置、三维微定位与加载系统、微力传感器及其标定装置、微动平台驱动装置等。探讨了微尺度实验力学检测中的问题和新的检测技术,给出了一些典型的应用和相关装置。     

运七飞机座舱的压电主动振动控制实验研究

由于实验规模与复杂性的限制 ,将压电材料用于实际飞机振动主动控制的实验研究极少 ,因而缺少对其实用潜力的探讨。为评估压电陶瓷在实际飞机结构上用于减振的可行性和效果 ,以运七飞机座舱壁板为试件 ,实地进行了基于准独立模态控制策略的主动振动控制实验 ,取得理想的控制效果 ;表明了建模和控制方法的正确性与有效性 ,同时反映出压电结构的应用潜力和前途是十分广阔的     

含冲击损伤高强中模碳纤维复合材料层压板压缩剩余强度分析与试验验证

论文以碳纤维复合材料层压板为研究对象,发展了一种模拟复合材料层压板冲击及冲击后压缩的一体化数值分析方法．基于Puck 失效准则和粘聚区模型描述层内损伤与层间损伤,分别采用基于断裂能的双线性型、函数型以及直接折减型等不同损伤折减方法构建了层内损伤预测与演化模型;建立了碳纤维复合材料冲击后压缩数值仿真模型,通过开展不同能量冲击后压缩试验,验证了所发展的数值分析方法的有效性;研究结果表明,采用Puck 失效准则和基于断裂能的双线性损伤演化模型预测冲击后压缩强度时具有较高精度．     

Development and Validation of a New Model for In Situ Foam Generation Using Foamer Droplets Injection

Transport in Porous Media - Foam generation and transport in porous media are a proven method to improve the sweep efficiency of a flooding fluid in enhanced oil recovery process and increase the...     

Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Experimental Mechanics - Various nonlinear system identification methods applicable to distributed nonlinearities have been developed over the last decade. However, many of them are not eligible to...     

High-Resolution 3D FIB-SEM Image Analysis and Validation of Numerical Simulations of Nanometre-Scale Porous Ceramic with Comparisons to Experimental Results

The development of focused ion beam-scanning electron microscopy (FIB-SEM) techniques has allowed high-resolution 3D imaging of nanometre-scale porous materials. These systems are of important interest to the oil and gas sector, as well as for the safe long-term storage of carbon and nuclear waste. This work focuses on validating the accurate representation of sample pore space in FIB-SEM-reconstructed volumes and the predicted permeability of these systems from subsequent single-phase flow simulations using a highly homogeneous nanometre-scale, mesoporous (2–50 nm) to macroporous (>50 nm), porous ceramic in initial developments for digital rock physics. The limited volume of investigation available from FIB-SEM has precluded direct quantitative validation of petrophysical parameters estimated from such studies on rock samples due to sample heterogeneity, large variations in recorded sample pore sizes and lack of pore connectivity. By using homogeneous synthetic ceramic samples we have shown that lattice-Boltzmann flow simulations using processed FIB-SEM images are capable of predicting the permeability of a homogeneous material dominated by 10–100 nanometre-scale pores (similar, albeit simpler, to those in natural samples) at the much larger scale where permeability measurements become practical. This result shows the LB flow simulations can be used with confidence in pores at this scale allowing future work to focus on sample preparation techniques for samples sensitive to drying and multiple FIB-SEM site selection for the population of larger-scale models for heterogeneous systems.     

Experimental and Numerical Analysis of an In-Plane Shear Specimen Designed for Ductile Fracture Studies

An in-plane shear specimen made of dual phase steel designed for ductile fracture studies is presented and then analyzed experimentally and numerically. In the experiment, digital image correlation (DIC) technique is utilized to measure the deformation of the specimen. Based on the implicit nonlinear FE solver Abaqus/Standard, numerical analysis of the specimen is performed by using plane stress and solid elements respectively. The elongation of the specimen’s gauge length and the shear strain distribution within the shear zone are compared between the experimental and numerical results and a general good agreement is obtained. Thereafter, based on calculated results, the stress state of the shear zone is investigated in detail. It is shown that the shear stress is dominant within the shear zone despite of the emergence of normal stresses. The deformation is concentrated in the shear zone, where the incipient fracture is most likely to occur. The stress triaxiality and the Lode parameter at the fracture initiation are found to be maintained at a relatively low level, which implies that the stress state achieved by the specimen is close to pure shear. The present study demonstrates that the proposed in-plane shear specimen is suitable for investigation of the fracture behavior of high strength materials under shear stress states.     

An Experimental and Numerical Study of Relative Permeability Estimates Using Spatially Resolved $$T_1$$- z NMR

Relative permeability is a key characteristic describing flow properties of petroleum reservoirs, aquifers and water retention of soils. Various laboratory methods, typically categorised as steady-state, unsteady-state and centrifuge are used to measure relative permeability and may lead to different results. In recent years, 1D MRI, NMR \(T_2\) and \(T_1\) profiling have been applied for the characterisation of rock cores. It has been shown that spatially resolved NMR in conjunction with centrifuge technique may provide high-quality capillary pressure curves. Combining Burdine and Brooks–Corey models enables estimation of relative permeability from capillary pressure curves. This approach assumes a strong relationship between capillary pressure and relative permeability known to be complex. Here we compare a generalised approach of Green, which relies on saturation profiles set by various capillary drainage techniques, to a NMR relaxation approach. Comparisons are performed experimentally and numerically using three sandstone rocks to test the influence of rock morphology. The numerical part includes simulation of a centrifuge capillary drainage by applying morphological drainage transforms on high-resolution 3D tomograms. \(T_1\) responses along the sample are simulated using a random walk technique. The NMR relaxation-based approach is then compared to LBM simulated relative permeability and to experiment. The study confirms the applicability of NMR relaxation methods for relative permeability estimation of water-wet rocks and validates a numerical approach against experiment.     

Experimental and Numerical Investigation of Swirl Induced Self-Excited Instabilities at the Vicinity of an Airblast Nozzle

We report on the experimental and numerical investigation of swirl induced self-excited instabilities in the form of precessing helical structures at the vicinity of an Airblast Atomiser. Within the scope of this work, the increase of the knowledge of the fundamental factors governing the precessing vortex core phenomenon (PVC) (Gupta et al. 1984) by applying dual air-flow Airblast nozzles is aimed. This study concentrates on the experimental investigation of the impact of important parameters of a combustor system on the performance characteristics of this instability. In particular, in terms of this work the properties of the PVC are determined by applying two different Airblast Atomisers, one of them producing an attached swirl flame, and another producing a lifted swirl flame. Measurements are also performed for a confined and a non confined flame, aiming to determine the impact of the confining duct on the performance of the PVC. In order to gain some further knowledge, regarding the impact of this aerodynamic instability on combustion of gaseous fuel, the features of PVC are experimentally identified under reacting conditions, by employing a laser light sheet (LLS) measurement technique. By applying the LLS measurement technique, further investigation on the nature of the PVC is also attempted. The power spectral density (PSD) function of the flow field was determined on the basis of raw data provided by 3D Laser Doppler Anemometry (3D-LDA). In order to validate the measurement technique as well as the nature of the instability, the planar Mie-Scattering of the flow was evaluated by employing a high speed camera performing at 12 kHz. The precessing character of the flow was also confirmed by means of a numerical simulation using the 3D Reynolds Stress Model (3D-RSM). The results of the numerical investigation provided some useful information concerning the onset of the instability within the primary swirler as well as its size and amplitude. According to this analysis, a high frequency instability was confirmed within a region of about one burner diameter downstream of the burner exit. Finally an evaluation of the (LDA) method in terms of providing accurate (PSD) was performed for the case of a swirl flow field.     

An Investigation of the Seismic Behaviour of an Ancient Masonry Bastion Using Non-Destructive and Numerical Methods

Determining the structural behavior of masonry structures is a challenge due to their lack of homogeneity. The seismic behavior of masonry structures is especially complex. The aim of this study was to examine the structural behavior of Za?anos Bastion using both experimental and numerical methods. The Operational Modal Analysis technique, including the Enhanced Frequency Domain Decomposition Method, and the Stochastic Subspace Identification Method were used to illustrate experimentally the dynamic characteristic of the bastion. A finite element model was developed using ANSYS software in order that the dynamic characteristics of the bastion, including natural frequencies and mode shapes, could be calculated numerically. Seismic analysis was carried out using the 1999 Kocaeli earthquake ground motion record to determine the linear and nonlinear seismic behavior of the bastion. The Turkish Earthquake Code and its general technical specifications were used to evaluate the seismic results. The results show that the maximum and minimum principal stresses exerted on the masonry components exceeded the code requirements at some points, but in general the requirements for the stresses were satisfied.     

A Combined Experimental and Numerical Study of Laminar and Turbulent Non-piloted Oxy-fuel Jet Flames Using a Direct Comparison of the Rayleigh Signal

In the present study laminar and turbulent oxy-fuel jet flames are investigated both experimentally and numerically with emphasis on the direct comparison of the Rayleigh signal. The Rayleigh signal was measured for both flame setups, correcting for background light appropriately. Two downstream regions were recorded for the laminar flame and three for the turbulent flame. Equivalently, the signal was processed numerically based on the numerical species data and temperature. The laminar flame was used for validating the procedure of processing the Rayleigh signal. Both the numerical species data and the temperature are known from detailed simulations, so a predicted Rayleigh signal can easily be obtained. Further, the influence of the choice of the kinetic mechanism, radiation and diffusion model was investigated. In contrast, in the turbulent Large Eddy Simulation, the Rayleigh signal has to be computed using an appropriate turbulence-chemistry interaction model in order to obtain the Reynolds-filtered Rayleigh signal which is of non-linear nature. In the present investigation, the Rayleigh signal was incorporated in the flamelet/progress variable approach. The statistics of the experimental and numerical Rayleigh signal were then compared. The proposed procedure of directly comparing the experimental and predicted Rayleigh signal was shown to be advantageous in model validation especially in turbulent flame configurations. The procedure enables accurate model validation across an entire 2D field of view whilst using a realistic fuel-oxidizer combination and reducing experimental complexity.     

Numerical and Experimental Investigation of the Influence of the Wake Behind an Injector Frame on Jet Dilution in a Crossflow

In this paper, a mixing of gases through square Jets issuing normally Into a CrossFlow (JICF) is investigated by means of both numerical simulation and experiment. The jets are emitted by two injectors mounted at the top and bottom of an Injector Frame (IF) which is installed at the center of an Eiffel type wind-tunnel. This jet configuration makes it possible to approximate an industrial gas mixer placed at the center of a pipe. Large Eddy Simulation based on the Smagorinsky model is used, enabling characterization of the mean and fluctuating velocities as well as the oscillating flow frequencies. Different diagnostic techniques, such as Laser Doppler Anemometry and Particle Image Velocimetry are employed for validating the numerical models, and a good agreement between prediction and experiment is obtained. In the numerical simulation, introduction of a passive scalar through the jet makes it possible to show three dilution phenomena. They are generated respectively by the wake of the IF, the jet/wake assemblage and the jets alone in function of the momentum flux ratio between jet and crossflow. Influence of the various parameters on the mixing process between the jets and the crossflow is identified. The numerical results show that if the IF wake is suppressed with the presence of a trailing edge behind the IF, classical formation of Counter-rotating Vortex Pair is found.