Impact force measurement in Shirodhara

Investigating the use of contact electrical conductance for the measurement of particle impact force

<p>For the design of mitigation measures knowledge of debris-flow impact forces, usually estimated based on hydrostatic, hydrodynamic, or combined approaches, is essential. As these approaches are based on Newtonian fluids, they must be adjusted by empirical correction factors to account for the solid-fluid nature of debris flows. The values for the correction factors shown in the literature vary over a wide range and several studies showed a clear dependence with the Froude regime of debris flows.</p><p>To better understand the correction factors and to be able to calculate them using parameters that describe the flow behaviour a total of 32 experiments were conducted in the course of the project “Debris flow impact forces on bridge super structures (DEFSUP)”, funded by the Austrian Science Fund (FWF). Two different material compositions, different water contents as well as a total impact and a bypassing of the measuring block were tested.</p><p>The experimental setup designed within the project consists of a 4 m long semi-circular channel with a diameter of 300 mm and an inclination of 20°. The material is released from a rectangular reservoir in a dam-break scenario and accelerated with zero roughness on a length of 1.2 m and transferred to the semi-circle profile. The subsequently introduced roughness with a grain diameter of 1-2 mm generates a stationary phenomenological debris flow until it hits the measuring setup. With a starting volume of 50 kg, flow heights between 8 and 12 cm and velocities from 0.8 to 2.2 m/s were achieved according to the material composition and different water content. With these different mixtures a Froude-range from 0.6 to 3.6 was covered. In addition, normal stresses and pore water pressures were measured at the exact same point.</p><p>A detailed analysis of the measured impact forces together with the above mentioned measured parameters showed that the hydrodynamic correction factor is a constant mainly corresponding to the liquification ratio of the debris-flow mixture. Hence, the hydrodynamic correction factor can be regarded as a drag coefficient and seems to depend mainly on the internal friction of the flowing medium. At low Froude numbers measured impact forces exceed even a full momentum transfer if the mean bulk density is used for the calculation. This indicates that the impact forces can no longer be described by the hydrodynamic approach alone. For this reason, an additional pressure term based on a hydrostatic approach is considered in the combined concept. This additional pressure term depends on the dynamics of flow (Froude number) and can be modelled via a dynamic earth pressure coefficient.</p><p>The findings from these experiments contribute to a better prediction of debris-flows impact forces in terms of their material composition and flow behaviour.</p>

Abstract. Flexible barriers are being increasingly applied to mitigate the danger of debris flows. However, how barriers can be better designed to withstand the impact loads of debris flows is still an open question in natural hazard engineering. Here we report an improved large-scale physical modelling device and the results of two consecutive large-scale granular flow tests using this device to study how flexible barriers react under the impact of granular flows. In the study, the impact force directly on the flexible barrier and the impact force transferred to the supporting structures are measured, calculated, and compared. Based on the comparison, the impact loading attenuated by the flexible barrier is quantified. The hydro-dynamic approaches with different dynamic coefficients and the hydro-static approach are validated using the measured impact forces.

Laboratory measurements of impact forces of supercritical granular flow against mast-like obstacles

Impact of tsunami-borne debris causes a significant force on coastal structures. Tsunami bores can carry different geometrical shapes of floating debris, which are often the greatest cause of damage to inland structures. Despite such a serious threat, the impact of floating debris on structures has received limited attention. The objective of this paper is to introduce a new method for measuring the impact force of floating debris on the seaward wall of structures during tsunami events. This will improve the understanding of tsunami-borne debris impact forces on structures and increase the predictive capabilities required for estimates of such forces in design guidelines. The debris impact tests were conducted using two smart debris devices with different geometrical shapes. Impact accelerations and forces in the horizontal and vertical planes were investigated.

In the Tibetan Plateau, pronounced topographical relief (steep mountains and deep valleys) coupled with intense weathering processes generates highly fragmented slope surfaces, creating debris-flow source materials with exceptionally heterogeneous grain-size distributions. These conditions frequently produce debris flows that exhibit extraordinary impact forces which cause severe damage to sediment-trap dams. Through 27 sets of flume experiments that systematically varied the particle-size distribution ( d max ), bulk density ( γ ) and flume slope ( θ ), this study investigates the impact mechanisms of wide-graded debris flows on sediment-trap dams. The results demonstrate that debris-flow interactions with sediment-trap dams occur through three distinct phases: (1) impact run-up, (2) rotational backflow and (3) depositional back-silting. Lower bulk-density flows exhibited greater run-up heights and more pronounced phase differentiation. Measured impact forces ( F ) showed an inverse relationship with bulk density ( γ ↑→ F ↓), while displaying positive correlations with both slope gradient ( θ ↑→ F ↑) and maximum particle size ( d max ↑→ F ↑). This occurs because higher- γ flows experience increased internal shear resistance, resulting in a reduction in velocity. Steeper slopes enhance kinematic energy, while larger particles generate more concentrated momentum transfer during impact. Sensitivity analysis revealed that d max exerts dominant control over impact dynamics compared to γ and θ . These findings provide critical insights for sediment-trap dam design in high-altitude debris-flow mitigation systems.

Landslides and debris flows that occur around residential areas are considered, globally, as significant disasters that cause damage to human life and property. With terrain slope defining the flow characteristics of debris flows, flow depth, flow velocity, and impact force vary by time and distance. In particular, when a structure is located in the flow path of debris flows, the flow characteristics of debris flows vary by terrain slope and direction angle. To simulate the flow characteristics of these debris flows, the simulation results obtained by FLO-2D were analyzed with six-stage conditions for the research area. In the analysis, the flow depth, flow velocity, and impact force were estimated on the basis of the outlet of the research area in the presence and absence of structure(s) at certain distances. With this, the variation of the impact force in accordance with the variation of the flow depth of the debris flows was highly similar to the simulation results obtained by FLO-2D, when the correction index (α) of the suggested dynamic impact force equation was 0.3–0.4. There were sections where the estimated value of the impact force was overestimated near the outlet, and it was judged that the fixed values of the terrain factors (width, roughness coefficient, slope, etc.) caused the impact force to be overestimated. However, the correlation analysis showed that the correlation index was above the normal ranges in the suggested dynamic impact force equation for debris flows with the application of the terrain factors.

Software which corrects the dynamic error of force transducers in impact force measurements using their own output signal has been developed. The software corrects the output waveform of the transducers using the output waveform itself, estimates its uncertainty and displays the results. In the experiment, the dynamic error of three transducers of the same model are evaluated using the Levitation Mass Method (LMM), in which the impact forces applied to the transducers are accurately determined as the inertial force of the moving part of the aerostatic linear bearing. The parameters for correcting the dynamic error are determined from the results of one set of impact measurements of one transducer. Then, the validity of the obtained parameters is evaluated using the results of the other sets of measurements of all the three transducers. The uncertainties in the uncorrected force and those in the corrected force are also estimated. If manufacturers determine the correction parameters for each model using the proposed method, and provide the software with the parameters corresponding to each model, then users can obtain the waveform corrected against dynamic error and its uncertainty. The present status and the future prospects of the developed software are discussed in this paper.

How accurately do finite element models predict the fall impact response of ex vivo specimens augmented by prophylactic intramedullary nailing?

The contacts closing impact phenomenon of vacuum interrupter is a basic event in a vacuum circuit breaker, which reveals lots of information including impact force, bouncing duration, stress distribution and so on. The objective of this paper is to investigate the contacts impact phenomenon in a 126 kV vacuum circuit breakers. PVDF (polyvinyldene fluoride) piezoelectric sensors were used to measure impact force of a 126 kV vacuum circuit breaker at a closing velocity of 1.5 m/s. In addition, a finite element analysis simulation model of contacts impact in a 126 kV vacuum interrupters was set up by using ANSYS / LS-DYNA software. The experimental results showed that the maximum contacts impact force of a 126 kV vacuum circuit breaker was about 105 N at 1.5 m/s closing velocity, which is are in good agreement with the simulation results. And the simulation results also showed that the maximum impact force, durations of contact bounce and the maximum stresses of contact were related with some parameters of vacuum interrupter, such as contact shape, elastic modulus of contact material, impact velocity and contact spring force.

This is the first quantitative study of the impact force over the hips of volunteers who fell laterally from standing to a hard surface while wearing a hip protector. Protector pads were first tested with a drop weigh machine. Piezoelectric sensors were placed on the impact surface to record force-time curves with and without a pad covering the surface. Two types of pads transmitted only 9% of the force at a drop weight impact force of 13,372 N. Sensors were placed over the hip under a protective hip pad worn by 10 volunteers who deliberately fell from standing, to a concrete surface. Only 5% or less impact force was transmitted to the skin sensors, and no hip injuries occurred after 85 falls, providing evidence for the safety of such falls. Only transient skin pain and tenderness occurred in three volunteers. Force transmission through the pads was well below that required to fracture hips from cadavers with osteoporosis in vitro. There was variability in the reduction of force transmission among the volunteer subjects. A 1-month compliance study with 106 elderly subjects showed protector use for 70% to 95% of their hours out of bed.

Aerospace composite components require effective monitoring techniques to detect possible internal damage from impact events. To ensure reliable impact identification, sensor measurements can provide valuable information about impact energy and identify potential issues that may require further investigation. However, selecting the most appropriate sensor technology to measure impact force and energy is a challenge. In this article, a systematic and structured approach is presented to compare the expected performance of sensors and their metrological parameters in terms of their ability for impact identification in aerospace composites. The proposed methodology is demonstrated using an application example where fibre Bragg grating (FBG) are compared with piezoelectric (PZT) sensors through comprehensive tests. These tests include the correlation test, the sensitivity test, and the factor test. The correlation test showed a high agreement between FBG and PZT sensors in the time and frequency domain. The sensitivity test indicated a significant correlation between the signal features and the impact energy levels in the energy profiling diagrams, revealing nonlinearities and energy losses indicative of damage. Furthermore, these results emphasise the superior resolution of the FBG sensors and the comparable repeatability of the two sensor types. Finally, the factor test showed that FBG sensors are sensitive to different angles of incidence, while PZT sensors have a more stable directivity. Further analysis also showed that the signal strength of both sensor types decreases with increasing distance from the impact source. Overall, the proposed approach enables a thorough evaluation of the capabilities and limitations of both sensor types. Consequently, it provides information to make an informed decision on the most suitable sensor for impact monitoring systems.

Nonlinear analytical study of structural laminated glass under hard body impact in the pre-crack stage

The phenomenon of liquid droplets colliding with wetted solid surfaces is widely found in nature and in industrial applications. In this study, we experimentally investigated the phenomenon of a droplet colliding with a droplet-carrying solid surface. The impact force on the solid surface was measured with a high-precision piezoelectric sensor and the morphological changes during droplet collisions were captured with a highspeed camera. Experimental Results showed that in such collision, the spreading factor of the droplet and the impact force on the surface are substantially influenced by droplet Reynolds number and are slightly affected by droplet Weber number. At a high Reynolds number, an annular jet appears between the falling droplet and the deposited droplet during the initial stage of collision, and rapid droplet spreading and a multi-peaked impact force curve were measured. On the contrary, at a low Reynolds number, the collision only results in a single force peak with the disappearance of the annular jet. Additionally, a considerable reduction in both the spreading factor and velocity is observed. This alteration is due to the quite different viscous forces in the two types of droplet collision. Detailed analysis suggests that the droplet spreading process at high Reynolds numbers can be classified into three distinct stages: the buffering stage, the high-speed spreading stage, and the maximum spreading stage. Furthermore, the volumetric ratio of the deposited droplets to the falling droplets has only a slight influence on the impact process.

In order to investigate the possibility of impact punching in brittle materials, an experimental setup was developed. In the setup, a long bar as a punch was used to apply the impact load to the specimen plate and measure the applied impact force during the impact punching process. Impact punching tests with various shape of punches were performed in soda-lime glass and silicon wafer under a different level of contact pressure. The damage appearance after the impact punching was examined according to the applied contact pressure. The minimum contact pressure required for a complete punching in glass specimens without development of radial cracks around the punched hole was sought at each condition. The minimum contact pressure increased with increasing the thickness of specimens and decreasing the end radius of punches. The profile of impact forces was measured during the impact punching experiment, and it could explain well the behavior of the punching process in brittle material plates. The measured impact force increased with increasing the contact pressure applied to the plates.