The physics remote laboratory: Implementation of an experiment on Standing Waves

There always have been some hurdles when it comes to the adequate use of didactical experimental activities in science education, such as the lack of proper training, insufficient time, and inadequate infrastructure. At this very moment, the pandemic has taught us that there may be also circumstances in which the traditional laboratory and the traditional activities are just not possible, thus online operable experiments might constitute a viable alternative for the practical lessons in higher education. In this paper, we discuss the development and the implementation of a remote-controlled didactical experiment on Standing Waves largely used in the physics basic program offered to the engineering courses. The development has combined applied knowledge from different areas, i.e. electric and electronics engineering, and computer science. In order to ascertain the experiment consistency, we have gathered data from the wave propagation speed and from the corresponding tension applied to the string and performed a χ-square linear fit in order to determine the correlation between the logarithm of both parameters. The experiment was successfully implemented and has been accessed by hundreds of different users from more than 30 different countries ever since. It has also been largely employed in practical activities at the university and has shown no significant signs of instability. It exhibited a total latency time inferior to 0.8 seconds on average and the results drawn from data it provides have shown to be accurate, within less than 0.8% of deviation with respect to the theoretical results.

EXPONENTIAL STABILITY OF LAMINATED BEAM WITH CONSTANT DELAY FEEDBACK

In this article, we consider a system of laminated beams with an internal constant delay term in the transverse displacement. We prove that the dissipation through structural damping at the interface is strong enough to exponentially stabilize the system under suitable assumptions on delay feedback and coefficients of wave propagation speed.

Using Dynamic Pressure Response for Erosion Detection in Hydraulic Tubes and Hoses

Numerical simulations were performed to study the feasibility of erosion detection in hydraulic tubes and hoses using fluid dynamic pressure response analysis. Reflected pressure signals caused by wall thinning were studied to locate and quantify pipe defects. Simulations were conducted for steel pipes as well as hoses. Results showed that for a steel pipe, since the stiffness of the fluid is much less than the pipe material’s, a very big change of wall thickness is needed to have a meaningful change in wave propagation speed and therefore the dynamic pressure response. For hoses, the wall stiffness is much less than steel pipes, hence it is more feasible to detect changes in stiffness. A dataset of 10 000 dynamic pressure impulse responses from samples with randomly generated eroded geometries was calculated to train a gated recurrent unit (GRU) neural network. Results showed that under perfect conditions (no noise), we are able to detect an eroded section’s location, length, and change in wave propagation speed with relative errors of 2.69%, 4.88%, and 3.79%, respectively. The changes in the wave propagation speed was also categorized into three classes of low, mild, and severe erosion with the accuracy of 97.3%. Under more practical conditions including sensor noise, the accuracy of erosion detection is degraded, especially in the case of steel tubing. By retraining the model with noisy data, the drop in the accuracy is compensated to about 96%.

Evaluation of dynamic behaviour of porous media including micro-cracks by ordinary state-based peridynamics

Reliable evaluation of mechanical response in a porous solid might be challenging without any simplified assumptions. Peridynamics (PD) perform very well on a medium including pores owing to its definition, which is valid for entire domain regardless of any existed discontinuities. Accordingly, porosity is defined by randomly removing the PD interactions between the material points. As wave propagation in a solid body can be regarded as an indication of the material properties, wave propagation in porous media under an impact loading is studied first and average wave speeds are compared with the available reference results. A good agreement between the present and the reference results is achieved. Then, micro-cracks are introduced into porous media to investigate their influence on the elastic wave propagation. The micro-cracks are considered in both random and regular patterns by varying the number of cracks and their orientation. As the porosity ratio increases, it is observed that wave propagation speed drops considerably as expected. As for the cases with micro-cracks, the average wave speeds are not influenced significantly in random micro-crack configurations, while regular micro-cracks play a noticeable role in absorbing wave propagation depending on their orientation as well as the number of crack arrays in y-direction.

Wave Propagation and Structural Health Monitoring Application on Parts Fabricated by Additive Manufacturing

Additive manufacturing (AM) applications have been steadily increasing in many industry sectors. AM allows creating complex geometries inside of a part to leave some space empty, called infills. Lighter parts are manufactured in a shorter time with less warpage if the strength of the part meets the design requirements. While the benefits of structural health monitoring (SHM) have been proven in different structures, few studies have investigated SHM methods on AM parts. In this study, the relationship between wave propagation and infill density has been studied for the additively manufactured polymer parts. The propagation of surface waves is monitored by using piezoelectric elements. Four rectangular parts are manufactured by using the material extrusion method with 20%, 40%, 60%, and 100% rectilinear infill densities. Four piezoelectric elements were attached on the surface of each beam, one for excitation and three for monitoring the response of the part at equal distances on each part. The results demonstrated that the surface waves diminish faster at parts with lower densities. The received signal in the part with totally solid infills showed about 10 times higher amplitudes compare with the part with 20% infill. The surface response to excitation (SuRE) method was used for sensing the loading on the part. Also, the wave propagation speed was calculated with exciting parts with a pulse signal with a 10-microsecond duration. The wave propagation speed was almost the same for all infill densities.

Influence of the applied pressure of the transducer on the propagation speed of the ultrasonic wave in wood

The non-destructive wave propagation technique is used to estimate the wood’s modulus of elasticity. The propagation speed of ultrasonic waves is influenced by some factors, among them: the type of transducer used in the test, the form of coupling and the sensitivity of the transducers. The objective of the study was to evaluate the influence of the contact pressure of the transducers on the ultrasonic speed. Ninety-eight tests were carried out on specimens of the species Eucalyptus grandis, with dimensions of 120 × 120 × 50 mm. The calibration of the pressure exerted by the transducer was controlled by a pressure gauge using a previously calibrated load cell. The robust statistical analysis allowed to validate the experimental results and to obtain consistent conclusions. The results showed that the wave propagation speed is not influenced by the pressure exerted by the transducer.

Coastal windstorms create unsteady, unpredictable storm surges in a fluvial Maine estuary

Storm surges create coastal flooding that can be damaging to life and property. In estuaries with significant river influence (fluvial), it is possible for tides, storm surge, and river discharge to interact and enhance surges relative to the immediate coast. These tide-surge-river interactions were previously identified in a fluvial Maine estuary as higher frequency (>four cycles per day) oscillations to storm surge which were proposed to be incited by enhanced friction and resonance during certain windstorm events (Spicer et al. 2019). The relative contributions to tide-surge-river interaction from atmospheric forcing variables (wind, barometric pressure, and externally generated surge) remains unclear. This work seeks to decompose and analyze a recent windstorm surge event to better isolate the effects of atmospheric forcing on tidesurge- river interaction. Results show total storm surges in the fluvial estuary to be two times larger than at the estuary mouth because of tide-surge-river interaction. Analysis indicated at least 50% of the magnitude of tide-surge-river interactions are created by non-tidal forcing, in the form of wind, enhancing frictional energy in the estuary. The remaining tide-surge-river interaction is likely a result of changes in tidal wave propagation speed due to surge deepening the mean estuary water level.

Analytical and Optimization Study of Propagation and Reduction of Wave in Granular Sand by DEM Method

In this research, the discrete element method has been used to analyze wave propagation and to investigate the factors affecting wave reduction in granular soils. The method of discrete elements is important because of the possibility of preparing completely similar specimens and examining the effect of changes in a certain parameter on the Behavior of the specimens. This method also provides an understanding of the changes that have occurred at the micro-scale of granular materials that are not achievable with other laboratory and numerical methods. To model the specimens, a set of disks with specific granulation has been used for two-dimensional studies. PFC 2D software has been used to perform simulations and related analyzes such as interparticle force. The DEM code in MATLAB is used to check the wave depreciation. In this research, the optimization process was performed using experimental data and the Taguchi method using the DEM method. The results of this study show that there is a direct relationship between the number of particle set contacts and the wave propagation speed. Also, material properties such as particle density are the most important parameters affecting wave velocity. The results of the method (DEM) are done with PFC 2D software and a comparison between the results of this method with the solution methods used by other researchers is shown to be a good match.

Augmented HLL Riemann solver including slope source term for 1D mixed pipe flows

In this paper, the augmented version of finite volume HLL solver, including source terms developed in Murillo and García-Navarro (2010, 2012), is extended to free-surface and pressurized mixed pipe flows over complex and frictional topography. This augmented HLL Riemann solver is employed for the flux approximation at the cell interface, where source terms are split into two parts based on the wave propagation speed. The friction term is treated using a splitting implicit method to maintain stability over dry beds. The Preissmann slot method is adopted to reproduce pressurized flow in the conduit. The performances of the numerical model are investigated by several numerical tests and compared with existing methods showing clear improvements.

The influence of hemodialysis-induced preload changes on the propagation speed of natural shear waves

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation - Flanders (FWO) Background Shear wave elastography (SWE) is a novel ultrasound technique based on the detection of transverse waves travelling through the myocardium using high frame rate echocardiography. The propagation speed of these shear waves is dependent on the stiffness of the myocardium. Previous studies have shown the potential of SWE for the non-invasive assessment of myocardial stiffness. It is unclear, however, if preload changes lead to measurable changes in the shear wave propagation speed in the left ventricle. In patients undergoing hemodialysis, the volume status is acutely changed. In this way, the effect of preload changes on shear wave speed can be assessed. Purpose The aim of this study was to explore the influence of preload changes on end-diastolic shear wave propagation speed. Methods Until now, 6 patients (age: 80[53-85] years; female: n = 2) receiving hemodialysis treatment were included. Echocardiographic images were taken before and every hour during a 4 hour hemodialysis session. Left ventricular parasternal long-axis views were acquired with an experimental high frame rate ultrasound scanner (average frame rate: 1016[941-1310] Hz). Standard echocardiography was performed with a conventional ultrasound machine. Shear waves were visualized on tissue acceleration maps by drawing an M-mode line along the interventricular septum. Shear wave propagation speed after mitral valve closure (MVC) was calculated by measuring the slope of the wave pattern on the acceleration maps (Figure A). Results Over the course of hemodialysis, the systolic (141[135-156] mmHg vs. 165[105-176] mmHg; p = 0.35 among groups) and diastolic blood pressure (70[66-75] mmHg vs. 82[63-84] mmHg; p = 0.21 among groups), heart rate (56[54-73] bmp vs. 57[50-67] bpm; p = 0.76 among groups), E/A ratio (1.6[0.7-1.8] vs. 1.2[0.6-1.4]; p = 0.43 among groups) and E/e’ (14[9-15] vs. 9[8-13]; p = 0.24 among groups ) remained the same. The ultra-filtrated volumes are shown in Figure B. The shear wave propagation speed after MVC gradually decreased during hemodialysis (6.7[5.4-9.7] m/s vs. 4.4[3.6-9.0] m/s; p = 0.04 among groups) (Figure C). There was a moderate negative correlation between shear wave speed and the ultra-filtrated volume (r=-0.63; p < 0.01) (Figure D). Conclusion The shear wave propagation speed at MVC significantly decreased over the course of hemodialysis and correlated to the ultra-filtrated volume. These results indicate that alterations in left ventricular preload affect the speed of shear waves at end-diastole. End-diastolic shear wave speed might therefore be a potential novel parameter for the evaluation of the left ventricular filling state. More patients will be included in the future to further explore these findings. Abstract Figure.