Experimental Techniques最新文献

In the present study, an experimental platform is developed to study the behavior of the injected jet in a gas cross-flow applicable to different categories of fluid mechanics such as combustion. In all tests, water and air are used as jet and cross-flow gas, respectively. The main target of this work is to cover the higher range of momentum ratios and Weber numbers for the presentation of a more accurate equation for jet trajectory. To achieve a desirable scale of experiments, the range of momentum ratio is considered from 5 to 211 and the Weber number of gasses in all tests is between 1.1–19.1. For data mining and measurements, the shadowgraph method is used. It is shown that by increasing the momentum ratio (about 84%), the breakup point height is increased (about 94%). Three different types of breakups were observed in the tests. It observed that as the Weber number increases, the type of jet column mechanism changes. It also revealed that the type of breakup mechanism would not have a significant effect on the jet trajectory. In addition, it demonstrated that the momentum ratio parameter would have a decisive role in the direction of jet motion, and as the momentum ratio increases, the jet column height increases. Finally, an equation for the trajectory of jet flight under all test conditions is presented.

This paper deals with the determination of numerical and experimental buckling loads for circular plates. In the study, plates made of isotropic material and laminated composites were taken into consideration. For the experimental part of the study, a buckling apparatus for circular plates (BACIP) was designed and manufactured to apply radial compression on plates simply supported along the outer edge, which was the most important aspect of the study. Experimental buckling loads were determined by connecting this apparatus to a tension machine. ANSYS software based on the Finite Element Method (FEM) and the analytical buckling load formula found in textbooks were also used for the determination of the numerical and analytical buckling loads. The effects of parameters such as plate thickness, number of layers, cutout sizes, and so on on critical buckling loads were investigated within the scope of the work. Comparisons of analytical, theoretical and experimental buckling loads were presented in both graphical and tabular form. The results of the experimental and theoretical buckling were found to be comparatively compatible.

Accurate estimation of rotational frequency response functions (FRFs) is an essential element of successful structural coupling. It is well known that the experimental estimation of structural excitations is very difficult with current technology. This paper proposes a scheme to improve the performance of the frequency-based substructuring (FBS) method by estimating unmeasured FRFs, including those corresponding to rotational degrees of freedom, from a set of experimentally determined translational FRFs. More specifically, the modal parameters extracted by modal analysis (EMA) from the experimentally determined FRFs are used for model updating, modal expansion and FRF synthesis. For this purpose, an approximate modelling approach is proposed, where a simplified and approximate finite element model (ASFE) is developed and updated to accurately reproduce the experimental responses. A modal expansion basis is then constructed from the ASFE to expand the mode shapes using the system equivalent reduction and expansion process (SEREP). FRF synthesis is then used to derive unmeasured translational and rotational FRFs. The synthesised FRFs within the frequency range of interest agree well with the experimental FRFs. The synthesised full FRF matrix is then used with the FBS method to derive the response model for the coupled structure in a bottom-up modelling approach.

This paper analyzes the rigid body tilting of the spinning disc with a spline-guided boundary condition. Firstly, a comprehensive dynamic model of the flat disc is built to illustrate the general forces during rigid body tilting. On this basis, the tilting model of deformed discs is derived by introducing the shape function. Also, the model accounts for friction at the spline interface, constraints on the tilting angle, and the impact force experienced with the boundary during the tilting motion. A test rig is designed to evaluate the accuracy of the model, and the similarity between experimental and simulated signals is compared in both the time domain and frequency domain. The results show that the rotational speed increases the spectral amplitude associated with boundary impact, whereas disc deformation contributes to variations in the frequency bands of spectral peaks, resulting in the emergence of spectral peaks at higher frequencies.

Floor vibration-based methods to track human activity are becoming popular for applications in healthcare monitoring, security, and occupant detection. Popular techniques such as time of arrival (TOA) methods face wave dispersion and multiple-path fading challenges for localization. Data-driven methodologies such as the FEEL Algorithm rely exclusively on the system dynamic properties, an advantage over other methods. However, FEEL’s calibration process requires recording force input to the structure, which can become labor-intensive and time-consuming for applications that require a high localization accuracy and does not require force estimates. An alternative approach is proposed to use the system’s acceleration response exclusively, creating an output-to-output transfer function. This modification was tested against the 3575 impact Human-Induced Vibration Benchmark dataset containing seven impact types across five locations, the same dataset FEEL was originally developed with. The results demonstrated the acceleration-calibrated FEEL effectiveness with 99.9% localization accuracy compared to force-calibrated FEEL’s accuracy of 96.4%.

In order to significantly reduce the defects of hole-making on Carbon Fiber Reinforced Plastics (CFRP), a scheme on the variable parameter helical milling experiments was carried out. First, the helical milling process was analyzed. Second, using the response surface methodology (RSM) in the experiments, the max exit tear value, aperture diameter and surface roughness Ra at the intermediate area were analyzed and the optimum combination of parameters was obtained: spindle speed 8962 r/min, helical speed 60 r/min, and pitch 0.207 mm at the hole entry and exit areas; spindle speed 6242 r/min, helical speed 87 r/min, and pitch 0.205 mm at the hole intermediate area. Last, the effect of milling direction on hole-making was obtained: up milling at the hole entry and exit areas and down milling at the hole intermediate area. The superiority of variable parameter helical milling experiment was verified: there were fewer defects such as burrs and tears at hole entry and exit areas; and the surface roughness Ra was 6.39% lower, the aperture deviation was from + 0.011 mm to -0.007 mm at the hole intermediate area. Therefore, the quality of hole-making by the variable parameter helical milling scheme was significantly improved.

Plastic processing operations of ferromagnetic materials may cause significant mechanical stress, which has a strong impact on its final magnetic behavior. In this paper, the magneto-mechanical correlations between the stress-strain behavior and magnetic Barkhausen noise emission in three typical steels subjected to uniaxial tension were studied comparatively, the tensile damage and fracture morphology of each sample was identified by magnetic measurements and scanning electron microscopy. The results show that the characteristics values of Barkhausen noise envelope can be approximated by a parabolic function of the carbon content experimentally and theoretically. In the elastic region, the Barkhausen noise response exhibits progressive growth with increasing strain, and reaches saturation at a critical point for the stress-induced magnetic anisotropy. However, once plastic deformation occurs, the Barkhausen noise signal intensity appears a downward trend until specimen failure, because the increasing dislocation tangles further hinder the domain wall motion. According to the mapping of Barkhausen noise eigenvalues, the location of tensile cracking is determined with a very satisfactory agreement. This indicates that the magnetic Barkhausen noise technique can be used for the nondestructive quantitative evaluation of elastoplastic deformation and failure location of ferromagnetic products.