Impact Load Characteristics Research Articles

Research on the Force Characteristics and Structural Optimization of Mine Antioutburst Door under the Influence of Coal and Gas Outburst Impact Airflow

In order to deeply explore the destructive effect of the impulsive airflow on the mine antioutburst door when coal and gas outbursts occur in underground coal mines, a large-scale coal and gas outburst dynamic effect simulation experiment device is used to carry out the coal and gas outburst disaster simulation experiment. The impact load and deformation characteristics of the antioutburst door under the impact airflow during coal and gas outburst are analyzed, and the experimental results are discussed in depth through numerical simulation analysis and field example analysis. Based on this, the internal and external causes of the damage of the antioutburst door on the coal mine site are analyzed, the key technologies that need to be solved in the design of the antioutburst door’s disaster resistance are studied, and the overall design of the structure optimization design of the antioutburst door is proposed. The research results show that after coal and gas outburst, the pressure on the antioutburst door will rise and fall, and the fluctuation will be greater. Under the same installation position, the farther the antioutburst door is from the protruding point, the less pressure it bears. In the middle and late stages of the outburst, intermittent negative pressure of the gas at the antioutburst door appeared. The key technologies for the design of the antioutburst door and its disaster resistance mainly include that strengthen theoretical and experimental research on the formation mechanism of outburst shock waves in mines, the interaction mechanism between disaster shock loads and dampers, and the magnitude of disaster expected shock loads; optimize the structure of the antioutburst door size, the width of the contact surface between the air door and the door wall, the stress distribution of the air door under impact load, the design of the safety hole, and the locking device; and improve the disaster monitoring and alarm capabilities of the antioutburst door and collect changes in antioutburst door pressure in real time. The research results provide a theoretical basis and technical support for the optimization of the antishock performance of underground antioutburst doors in coal mines and have important practical significance for improving the disaster resistance of the ventilation system.

Ship hull slamming analysis with smoothed particle hydrodynamics method

In the marine and ocean engineering area, the water-entry process is a typical problem of fluid-solid interaction, which involves complex phenomenon such as the large deformation of free surface and considerable structure movement. In this process, the predicting impact load and summarizing the evolution law of the free surface deformation have important reference significance for the hull structure design. To address this issue, numerical simulations are carried out using a robust Smoothed Particle Hydrodynamics (SPH) model. The accuracy of the present SPH model is firstly validated by simulating the water entry of bow-flare section in two and three dimensions, respectively. Then, we investigate the variation characteristics of impact load and the evolution of free surface during the entry of the bow-flare ship section with different roll angles (θ=0∘∼20.3∘). Attention is focused on the flow separating phenomenon and the spray jet on the free surface. Finally, the water entry of a three dimensional ship hull is simulated. The velocity and pressure of flow field are analyzed and some conclusions are drawn.

Experimental Study on the Unsteady Characteristics and the Impact Performance of a High-Pressure Submerged Cavitation Jet

High-pressure submerged cavitation jet is widely used in the fields of material peening, petroleum drilling, and ocean engineering. The impact performance of the jet with intensive cavitation is related to the factors such as working condition and the nozzle geometry. To reveal the relationship between the nozzle divergent angle and the jet pressure on the unsteady characteristics of the jet, high-speed photography with frame rate of 20000 fps is used to record the image of the cavitation clouds. Grayscale analysis algorithm developed in MATLAB is used to study the effects of injecting condition on the special structure, unsteady characteristics, and shedding frequency of the cavitation bubbles. The impact load characteristics of the cavitation jet with different cavitation numbers and stand-off distances are recorded using a high-response pressure transducer. It is found that the cavitation number is the main factor affecting the cavitation morphology of the submerged jet. The lower the cavitation number is, the more intense the cavitation occurs. The outlet divergent angle of the convergent-divergent nozzle also has a significant influence on the development of the cavitation clouds. In the three nozzles with the outlet divergent angles of 40°, 80°, and 120°, the highest bubble concentration is formed usinga nozzle with a divergent angle of 40°, but the high-concentration cavitating bubbles are only distributed in a very small range of the nozzle outlet. The cavities generated by using the nozzle with a divergent angle of 80° can achieve good results in terms of concentration and distribution range, while the nozzle with divergent angle of 120° has lower cavitation performance due to the lack of the constraint at the outlet which intensifies the shear stress of the jet. According to the result of frame difference method (FDM) analysis, the jet cavitation is mainly formed in the vortex structure generated by the shearing layer at the nozzle exit, and the most severe region in the collapse stage is the rear end of the downstream segment after the bubble cloud sheds off. The impact load of the cavitation jet is mainly affected by the stand-off distance of the nozzle from the impinged target, while the nozzle outlet geometry also has an effect on the impact performance. Optimizing the stand-off distance and the outlet geometry of the nozzles is found to be a good way to improve the performance of the cavitation jet.

Experimental investigation for characteristics of wave impact loads on a vertical cylinder in breaking waves

In this study, a series of model tests was conducted to investigate the characteristics of wave impact loads and the associated air bubble effects on a vertical circular cylinder with various pressure and force sensors installed in a 2D wave flume. Spilling and plunging waves, generated by the focusing wave method, induced wave impact loads on the cylinder, and these loads were measured by the sensors, which had different natural frequencies and sensing areas. Each test condition was repeated 20 times to verify the repeatability of the impact loads and their effects. The air bubble effects were investigated by analyzing the time histories of the impact forces and pressures, and the effects were related to the natural frequency and sensing area of the sensors. The air bubble effects were observed to increase as the breaking wave developed more at the position of the cylinder. The generated waves and impact loads were also observed to change significantly when even a small noise occurred in the displacement of the wavemaker.

Performance assessment of reinforced concrete columns under vehicle impact load using P‐I diagram

AbstractP‐I diagrams are widely used for structures subjected to blast loads. In the same manner, structures subjected to vehicle impact load, such as bridge columns, could potentially take advantages of the P‐I diagram if the dynamic characteristics of vehicle impact load and bridge columns are well considered. In the paper, the performance of bridge columns and hence the use of P‐I diagram is evaluated under vehicle impact load. The main tasks of the paper are (1) to determine the dynamic characteristics of vehicle impact load through finite element method, and three simplified load shapes are obtained including isosceles triangle, right triangle, and rectangular shapes; (2) to investigate structural failure modes under various shear‐bending ratios and impact loads; (3) to establish the damage index based on the residual axial capacity of bridge columns and to obtain P‐I diagrams at different damage levels of bridge columns under vehicle impact load; (4) to parametrically analyze the effects on the impulse asymptotic and the peak load asymptotic of P‐I diagrams, including column diameter, stirrup reinforcement ratio, longitudinal reinforcement ratio, and strength of the concrete. Finally, a simplified calculation method of P‐I diagrams is proposed to evaluate the performance of bridge columns under vehicle impact load.

Experimental and numerical investigation of the frequency-domain characteristics of impact load for AUV during water entry

Autonomous underwater vehicles (AUVs) are subjected to a very large impact load during the water-entry process, which may damage the structure of the vehicle and affect its motion trajectory. In this paper, five kinds of models with different nose shapes are tested under different water-entry velocities and angles, and the impact acceleration signals are obtained by a sensor. First, the accuracy of the experimental data is verified by comparison with the velocity obtained by the high-speed camera. Then, the ensemble empirical mode decomposition (EEMD) method combined with modal analysis is used to analyse the acceleration signal composition. Subsequently, a numerical simulation model based on the arbitrary Lagrangian Eulerian (ALE) method to describe the water-entering process of the vehicle is established, and the accuracy and capability of the numerical algorithm is verified by comparison with the experimental data. Finally, the frequency-domain characteristics of the impact load are analysed through the shock response spectrum (SRS) method. The result shows that the maximum acceleration shock spectrum of the impact load is related to the peak pulse width of the impact load and independent of the peak value. The smaller the pulse width is, the larger the inflection point frequency and magnification of the shock response spectrum are. The inflection point frequency of the shock response spectrum usually corresponds to the second-order bending natural frequency of the vehicle. The conclusions in this paper will be useful for the design and analysis of the water-entry impact structure of AUVs.

Numerical evaluation of the hydrodynamic impact characteristics of the air launched AUV upon water entry

In this paper, water entry process of air launched AUV is investigated by employing fully coupled finite element method and arbitrary Lagrange–Euler formulation (FEM-ALE) and using penalty coupling technique. Numerical model is established to describe the hydrodynamic characteristics and flow patterns of a high-speed water entry AUV. The effectiveness and accuracy of the numerical simulation are verified quantitatively by the experiments of the earlier study. Selection of suitable advection method and mesh convergence study is carried out during experimental validation process. It is found that appropriate mesh size of impact domain is crucial for numerical simulations and second-order Van Leer advection method is more appropriate for high speed water entry problems. Subsequently, the arbitrary Lagrange–Euler (ALE) algorithm is used to describe the variation laws of the impact load characteristics with water entry velocities, water entry angles and different AUV masses. Dimensionless impact coefficient of AUV at different velocities calculated using ALE method is compared with SPH results. This reveals that ALE method can also simulate the water entry process accurately with less computational cost. This research work can provide beneficial reference information for structure design of AUV and for selection of the water entry parameters.

An Acoustic Discrimination Method for Impact Load Based on Artificial Neural Network

In order to meet the engineering requirements of non-contact measurement of impact load and realize the intelligent identification of its characteristic parameters, this paper attempts to establish a method to analyze and learn the audio characteristics generated by accidental loads, such as impact and explosion, and to identify the impact load characteristics in reverse. The method, which is based on energy conservation, momentum conservation and strokes law, used p-norm in mathematics to extract the basic characteristics of impact load, and the frequency analysis to find the inevitable connection between the audio characteristics impulse-induced and the impact load characteristics. At last, “Acoustic Discrimination for Impact Load Identification (ADII)” by adopting the functions of artificial neural networks about learning, categorization and generalization was implemented.

Evaluation of remaining fatigue life of concrete sleeper based on field loading conditions

The main functions of the sleepers in ballasted tracks include transferring loads, securing rail gauge and maintaining railway track geometry. Sleepers can be manufactured using timber, concrete, steel or other engineered materials, but concrete is most commonly used around the world. There are a number of researches on the impact load characteristics and the ultimate load carrying capacity of prestressed concrete sleepers, but research on the fatigue life of prestressed concrete sleepers is very limited. A prestressed concrete sleeper's fatigue damage is mainly due to the repeated loads derived from dynamic wheel-rail interactions, especially when either wheel or rail irregularity is present. Fatigue failure is thus a time-dependent limited state where a concrete sleeper accumulates damage to a failure point over its service life. Concrete sleepers could usually suffer from the dynamic fatigue loading spectra throughout their whole lives, and simultaneously, both static and dynamic load-carrying capacities of concrete sleepers degrades over time. Therefore, a fatigue life assessment is an important and complicated research frontier. Field loading conditions, material time-dependent and dynamic properties, and the dynamic bending moments of prestressed concrete sleepers are quantitatively analysed in this study. This paper also presents an updated fatigue life assessment method for concrete sleepers, and provides a case study based on actual field loading conditions and the time-dependent behaviour of materials. The new insights obtained from this study will improve concrete sleeper maintenance and inspection criteria, and provide a new reference for a rational dynamic design principle of railway concrete sleepers and bearers.

The Research on Bus Voltage Stabilization Control of Off-Grid Photovoltaic DC Microgrid under Impact Load

The solar power generation includes certain randomness and volatility, coupled with dynamic load involved in power fluctuations, which renders microgrid having certain unplanned instantaneous power during the process of real-time operation, so as to affect the stability of DC bus voltage. This paper, through constructing a model of off-grid photovoltaic DC microgrid under impact load characteristics, aiming at the fluctuate problems of the DC bus voltage caused by impact load, puts forward a fast response of hybrid energy-storing system composed of supercapacitors and batteries and superiors peak regulation capability to shave the peak and fill the valley of the microgrid. The researches on the strategy of double closed-loop voltage stabilization of blended energy storage system are made and the shortcomings of the double closed-loop voltage control of voltage and electricity are analyzed. And based on this, the tactics of new and double closed-loop voltage control of inner ring of power and the energy outer ring of DC bus capacitance are put forward and examined by simulation and experiment. The experiments prove that this method can more effectively suppress the influence of the fluctuations of impact load power on the DC bus voltage and further improves the system’s stability.

Numerical study on the cavity characteristics and impact loads of AUV water entry

The high-speed water entry process of an autonomous underwater vehicle (AUV) has a strong impact nonlinearity, and a cavity formed by air and water will often be generated as part of the entry process. The shape of the water-entry cavity plays an important role in the load characteristics and stability of the water-entry trajectory. In this paper, a numerical model for describing the cavity and impact load characteristics of a high-speed water-entry AUV is established. The simulation results such as cavity shape and impact load are compared with experimental data. The good agreement between the numerical results and those of the experiments reveals the accuracy and capability of the numerical algorithm. Subsequently, the arbitrary Lagrange-Euler (ALE) numerical algorithm is used to simulate and analyse the variation laws of the cavity characteristics and impact loads with different head shapes, water-entry velocities, water-entry angles and angles of attack. The results obtained in this study can provide a good reference for the trajectory control and structural design of the AUV.

Understanding the impact loading characteristics of a badminton lunge among badminton players.

BackgroundThe rapid and repetitive badminton lunges would produce strenuous impact loading on the lower extremities of players and these loading are thought to be the contributing factors of chronic knee injuries. This study examined the impact loading characteristics in various groups of badminton athletes performing extreme lunges.MethodsFifty-two participants classified into male skilled, female skilled, male unskilled, and female unskilled groups performed badminton lunge with their maximum-effort. Shoe-ground kinematics, ground reaction forces, and knee moments were measured by using synchronised force platform and motion analysis system. A 2 (gender) x 2 (skill-level) factorial ANOVA was performed to determine the effects of different gender and different playing levels, as well as the interaction of two factors on all variables.ResultsMale athletes had faster approaching speed (male 3.87 and female 1.08 m/s), longer maximum lunge distance (male 1.47 and female 1.16 m), larger maximum (male 215.7 and female 121.65 BW/s) and mean loading rate (male 178.43 and female 81.77 BW/s) and larger peak knee flexion moment (male 0.75 and female 0.69) compared with female athletes (P < 0.001). Unskilled athletes exhibited smaller footstrike angle (skilled 45.78 and unskilled 32.35°), longer contact time (skilled 0.69 and unskilled 0.75 s), larger peak horizontal GRF (skilled 1.61 and unskilled 2.40 BW), smaller mean loading rate (skilled 150.15 and unskilled 110.05 BW/s) and larger peak knee flexion moment (P < .05; skilled 0.69 and unskilled 0.75 Nm/BW) than the skilled athletes. In addition, the interaction indicated greater peak GRF impact in female unskilled athletes compared with female skilled athletes (P < 0.001; female skilled 2.01 and female unskilled 2.95 BW), while there was no difference between male participants (P > 0.05; male skilled 2.19 and male unskilled 2.49 BW).ConclusionsThese data suggested that male athletes and/or unskilled athletes experience greater impact loading rates and peak knee flexion moment during lunge compared with female and skilled athletes, respectively. This may expose them to higher risk of overuse injuries. Furthermore, female unskilled athletes seemed to be more vulnerable to lower extremity injuries.

Analytical Solutions for Stochastic Vibration of Orthotropic Membrane under Random Impact Load.

Orthotropic membrane materials have been applied in the numerous fields, such as civil engineering, space and aeronautics, and mechanical engineering, among others. During their serving lifespan, these membranes are always facing strong stochastic vibrations induced by the random impact load such as hail, heavy rain, and noise, among others. In this paper, the stochastic vibration problem of orthotropic membrane subjected to random impact load is investigated. The statistical characteristics of random impact load are initially obtained based on the stochastic pulse theory. Then, the Von Karman theory is applied to model the nonlinear vibration of membrane with geometric nonlinearity, which is then used to derive and solve the corresponding fokker–plank–kolmogorov (FPK). The theoretical model developed is validated by means of experiment study and monte carlo simulation (MCS) analysis. The effects of variables like pretension force, velocity of impact load, and material features on stochastic dynamic behavior of membranes are discussed in detail. This exposition provides theoretical framework for stochastic vibration control and design of membranes subjected to random dynamic load.

Experimental research on impact loading characteristics by full-scale airplane impacting on concrete target

To investigate the impact loading characteristic during an airplane impacting process, an experiment of a full-scale airplane impacting on a movable concrete target was carried out, using a rocket slid propulsion facility. In the experiment, an on-off signal measurement system was used to monitor the airplane’s impacting velocity; the total impacting process as well as the fragment dispersion of the airplane’s wreckage were recorded by a high-speed photography system. Moreover, five accelerometers were installed on the reverse side of the target to measure its acceleration, from which the impact force-time history can be obtained. Moreover, two storage airborne accelerometers were placed on the airplane’s tail to measure the acceleration history of the airplane, from which both the crushing force-time history and the crushing force distribution along the fuselage can be obtained. It is found that the measured impact force-time history is in good agreement with that calculated using the modified Riera impact loading model. This verifies the reliability of using the modified Riera model to predict the impact force acting on the target during the airplane impacting process, and the value of the correction coefficient α in the Riera model can also be determined. In addition, it is observed that, except at the initial moment, the ratio of the crushing impulse to the impacting one remains roughly a constant, which makes it possible to further simplify the Riera model by getting rid of the crushing force distribution curve.

Fatigue Life Assessment Method for Prestressed Concrete Sleepers

Concrete sleepers are one of the most important applications of a railway track system. Researchers have previously studied the impact load characteristics and ultimate load carrying capacity of a prestressed sleeper but research on the fatigue life of prestressed concrete sleepers is limited. Prestressed concrete sleeper fatigue damage is mainly due to the accumulation of defects, caused by the repeated load of wheel-rail interaction. Fatigue load, fatigue characteristics and the existing design methods of prestressed concrete sleeper are summarized in this paper. The commonly used fatigue assessment methods of concrete structures are also evaluated. Based on the results of former research result, this article presents a convenient fatigue life assessment method for a prestressed concrete sleeper, and contrasts with the test results. The insight information gained can be used to evaluate the service performance and predict the fatigue life of the concrete sleeper, as well providing design flexibility and broadening the design principle. The outcome of this study may also improve the rail track maintenance and inspection criteria, in order to establish an appropriate track condition monitoring network in practice.

The energy-based failure mechanism of reticulated domes subjected to impact

To systematically study and determine the failure mechanism of reticulated domes when subjected to impact, ANSYS/LSDYNA was utilized to establish a functional and effective finite-element analysis method for the impact responses of reticulated domes. The impact load characteristics imposed on reticulated domes under three types of failure modes were analyzed, and the peak value and duration time were compared. Based on structural deformation and the node velocity at critical moments during impact, the collapse of reticulated domes is classified into three stages in light of energy transfer and conversion: impulse application, energy transfer, and conversion and dissipation. On this basis, and using the single-layer Kiewitt-8 reticulated dome as an example, the characteristics of energy transfer and conversion of the impact-induced failure processes were quantitatively analyzed. Consequently, the energy-based failure mechanism of reticulated domes subjected to impact is revealed.

Characteristics Analysis of Load Caused by Punching Pile Construction of Highway Bridge Pile Foundation

The characteristics of impact loads caused by punching pile construction of highway bridge pile foundation and the propagation law of vibration wave in the soil were researched. Combined with site monitoring vibration signal which is generated by the bridge pile foundation construction of Zhang Shi Expressway across the Shaanxi Beijing pipeline, signal waveforms of the punching pile construction and blasting construction were analyzed contrastively. It expounded the characteristics of impact loads, and deduced the mathematical expressions of impact loads. On the basis of the analysis model, through the numerical simulation, the propagation law of vibration wave in the soil caused by the impacting point source excitation was revealed. Thus, it indicates that because of the buried pipeline, the local gradient of vibration wave velocity field increased in the area between the vibration source and the pipeline, but decreased in the far direction.

Fatigue Strength and Damage Mechanisms of Laser Welded Structural Carbon Steel Sheets

Laser welding is one of advanced and promising joining technologies of metallic materials, characteristic by numerous advantages in comparison with conventional welding processes. The technology still can be considered as fairly new and so, investigations are needed to reach optimum properties of welds in specific application cases, depending on welding parameters. Certification welding procedures usually require to demonstrate sufficient microstructure, mechanical, impact loading and other characteristics, but not fatigue resistance, which is essential for welded dynamically loaded structures. The paper contains results of fatigue resistance investigation of laser welded 10 mm thick sheets of a carbon structural S 355 steel. High cycle fatigue tests were performed after optimizing laser welding parameters. Resulting endurance limit of the welds and heat affected zone was higher than that of basic material. However, high scatter of results and different damage mechanisms were shown for different load amplitudes. The results are discussed on the basis of fractographical analyses, which provided some quite interesting details about crack initiation mechanisms.

Failure behaviors of reinforced concrete beams subjected to high impact loading

To attain a better understanding of the failure behavior of reinforced concrete (RC) beams under impact load, series of high speed impact experiments were performed using an instrumented drop-weight impact machine. The test program was successful in providing a substantial volume of test data including impact loads, mid-span deflections, crack profiles and strains. These data was analyzed, focusing on the impact load characteristics and the impact behaviors of RC beams. Various characteristic values and their relationships were investigated such as the drop height, the static flexural load-carrying capacity, the input impact energy and the beam response values. Two empirical formulas were proposed to estimate the maximum and residual deflection of the beam based on the static flexural load-carrying capacity and the input impact energy. The applicability of the proposed equations was confirmed by comparison with the experimental results obtained by other researchers.

Application of Improved Bingham Model in Braking Large-Mass Unidirectional Impact Loading Problem

Aimed at braking large-mass unidirectional impact loading problem, the impact loading characteristics has been analyzed and a mechanical model has been established. A new improved Bingham model has been proposed to solve the problem of big error in traditional Bingham model in low-velocity region. Unlike the traditional Bingham model, there are two different kinds of expression of damping force on both low-velocity and high-velocity region in the improved Bingham model. Thus, the accuracy of the model has some improvement, and it has been verified with simulation.