Experimental Techniques最新文献

Climate significantly affects the performance of building materials and its changing patterns are posed to increasingly exacerbate the projected impacts. Prevention strategies are indeed necessary to ensure avoiding excessive degradation and serious damage to the built environment. In this context, innovative and accessible methodologies and tools are required to investigate and characterize the interaction between material properties and climatic factors. This paper presents an innovative device for the simulation of natural ventilation, relative humidity and temperature fluctuations and for evaluating the performance of building materials subjected to different environmental scenarios. The presented results include the design, construction and validation of a small-scale wind tunnel (2 m × 1.8 m ca. vertical orientation). Key findings outline the adequacy of the tool in reproducing a stable, quality airflow with the following characteristics: achievable operational airflow speed ranges between 0.2 and 0.7 m/s, safe operational temperature is included between 10℃ and 35℃ and allowable operational relative humidity varies between 30 and 99%. Advantages and limitations for laboratory applications are outlined in the paper and future work is also suggested.

It is of great significance for the safe operation of oil equipment to know the influence of particle size and concentration on the time-averaged velocity of oil. The oil with different particle size and concentration were tested using particle image velocimetry (PIV) measurement technology in an exceedingly square tube, the instant velocity vector information of the oil flow field was non-inheritable, and the time-averaged velocity distributions were analyzed along the flow direction and normal direction. The results showed that the flow time-flow-averaged velocity of the oil-containing particles is a quasi-parabola shape along the normal direction, and its variation amplitude increases with the decrease of the particle concentration and reaches the highest value when the particle size is 25 μm. The normal time-flow-averaged velocity has the extreme value along the normal direction when the particle concentration is low, and the variation range is large; when the normal position ranges from 0 to 0.2 and above 0.2, the unidirectional of the normal time-flow-averaged velocity of the oil is reversed. The distribution of the flow time-normal-averaged velocity along the flow direction is also a quasi-parabolic shape, and its variation amplitude is more uneven with the decrease of particle concentration. Similarly, the distribution of the normal time-normal-averaged velocity along the flow direction increases with the decrease of particle concentration, and this trend is more obvious when the particle size is 25 μm. These changes make the motion characteristics of the oil unstable, which is not conducive to the stable realization of the function of the oil equipment, so the presence of particles in the oil has an important impact on the motion characteristics of the oil and even the accurate and reliable operation of the equipment.

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.

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.