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Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7609
Author(s):  
Georg Baumann ◽  
Dominik Niederkofler ◽  
Christian Ellersdorfer ◽  
Florian Feist

Split Hopkinson bars are used for the dynamic mechanical characterisation of materials under high strain rates. Many of these test benches are designed in such a way that they can either be used for compressive or tensile loading. The goal of the present work is to develop a release mechanism for an elastically pre-stressed Split Hopkinson bar that can be universally used for tensile or compressive loading. The paper describes the design and dimensioning of the release mechanism, including the brittle failing wear parts from ultra-high strength steel. Additionally, a numerical study on the effect of the time-to-full-release on the pulse-shape and pulse-rising time was conducted. The results of the analytical dimensioning approaches for the release mechanism, including the wear parts, were validated against experimental tests. It can be demonstrated that the designed release concept leads to sufficiently short and reproducible pulse rising times of roughly 0.11 ms to 0.21 ms, depending on the pre-loading level for both the tension and compression wave. According to literature, the usual pulse rising times can range from 0.01 ms to 0.35 ms, which leads to the conclusion that a good average pulse rising time was achieved with the present release system.


2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Qi Zhong ◽  
Huiming Bao ◽  
Yanbiao Li ◽  
Haocen Hong ◽  
Bin Zhang ◽  
...  

AbstractIn hydraulic area, independent metering control (IMC) technology is an effective approach to improve system efficiency and control flexibility. In addition, digital hydraulic technology (DHT) has been verified as a reasonable method to optimize system dynamic performance. Integrating these two technologies into one component can combine their advantages together. However, few works focused on it. In this paper, a twin spools valve with switching technology-controlled pilot stage (TSVSP) is presented, which applied DHT into its pilot stage while appending IMC into its main stage. Based on this prototype valve, a series of numerical and experiment analysis of its IMC performance with both simulated load and excavator boom cylinder are carried out. Results showed fast and robust performance of pressure and flow compound control with acceptable fluctuation phenomenon caused by switching technology. Rising time of flow response in excavator cylinder can be controlled within 200 ms, meanwhile, the recovery time of rod chamber pressure under suddenly changed condition is optimized within 250 ms. IMC system based on TSVSP can improve both dynamic performance and robust characteristics of the target actuator so it is practical in valve-cylinder system and can be applied in mobile machineries.


2021 ◽  
Author(s):  
Shiv Kumar ◽  
Pauline Tourneur ◽  
Jonathan Adsetts ◽  
Michael Wong ◽  
Pachaiyappan Rajamalli ◽  
...  

Aiming to develop efficient blue-emitting thermally activated delayed fluorescence (TADF) compounds, we have designed and synthesized derivatives of the well-known sky-blue emitter 2CzPN that contain electron-accepting phosphine chalcogenide groups to stabilize the HOMO level relative to the pristine compound, thus increasing the HOMO-LUMO gap and blue-shifting the emission wavelength. By cyclic voltammetry, photophysical data and quantum-chemical calculations, it was found that polar solvents and matrices validated the proposed concept, but these trends were not recovered in non-polar media. The suitability of these 2CzPN derivatives in polar matrices for optoelectronic applications was explored with electrochemiluminescence (ECL) by measuring emission delays, radical stability, emission stabilities, emission efficiencies and emission spectra. Some of the 2CzPN derivatives showed an unprecedented delayed onset of the ECL, and delayed rising time to the ECL maximum, as well as long ECL emission decay. All of these mentioned delay times suggest that these luminophores primarily emit via organic long-persistent electrochemiluminescence (OLECL) mechanisms. The derivatization of the donor groups of the emitters affected both the radical stability and the predominant emission mechanism, providing important insight into their potential as emitters in solid-state electroluminescent devices.


Author(s):  
Muhammad Akmal Bahari ◽  
Zikri Abadi Baharudin ◽  
Tole Sutikno ◽  
Ahmad Idil Abdul Rahman ◽  
Mohd Ariff Mat Hanafiah ◽  
...  

The mechanism on how lightning detection system (LDS) operated never been exposed by manufacturer since it was confidential. This scenario motivated the authors to explore the issue above by using MATLAB to develop autoanalysis software based on the feature extraction. This extraction is intended for recognizing the parameters in the first return stroke, and compare the measurement between the autoanalysis software and the manual analysis. This paper is a modification based on a previous work regarding autoanalysis of zero-crossing time and initial peak of return stroke using features extraction programming technique. Further, the parameter on rising time of initial peak is added in this autoanalysis programming technique. Finally, the manual analysis using WaveStudio (LeCroy product) of those two lightning parameters is compared with autoanalysis software. This study found that the autoanalysis produce similar result with the manual analysis, hence proved the reliability of this software.


2021 ◽  
Vol 18 (3) ◽  
pp. 1-9
Author(s):  
Chau Kim Tran

Sensitivity analysis is an effective tool to determine the robustness of an assessment by examining the extent to which the results are affected by changes in input. In this study, the FAST method was applied to analyse the sensitivity to the earth dam failure process. Four (04) input variables were selected including breach development time, breach width, side slope, and initial breach position. The effects of these parameters on the two (02) outputs i.e., the maximum outflow, and rising time were assessed. The study was applied to 08 reservoirs with different capacities. The sensitivity analysis showed that the development time and initial breach location dominantly affect these outputs. Additionally, development time is the most important factor in rising time. The lateral slope has an insignificant effect on outputs. The effect of breach width can be neglected to rising time, however, its influence on maximum outflow is significant. The results of this study show the role of input variables in the flow hydrograph due to dam failure. Through this research, the workload of the breach parameter analysis process can be substantially reduced.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hongyun Wang ◽  
Cheng Bi ◽  
Yongju Zhang ◽  
Axiang Ji ◽  
Pengyuan Qiu

AbstractTransient behavior of a magnetorheological brake excited by step currents under compression-shear mode has been experimentally studied. The results show that the amplitude of the applied current had little effect on the rising time of transient torque, while the rising time was significantly affected by the rotational speed, the compressive speed and the compressive strain position. The falling time of transient torque was independent of the amplitude of the applied current, the compressive speed and the compressive strain position, and it was affected by the rotational speed. The falling time of the transient torque was much shorter than the rising time by a step current. The transient process of MR brake applied as a step current was different from a stable process pre-applied at constant current in different particle chain structure forming processes. In addition, the compressive processes applied in one step current and randomly on/off current were compared and experimentally verified: the particle chains in two processes both experienced the same evolutionary of transient torque. The results achieved in this study should be properly considered in the design and control of magnetorheological brake under compression-shear mode.


2021 ◽  
Vol 10 (2) ◽  
pp. 387
Author(s):  
Sharmin Akhtar ◽  
Rubel Ahmed ◽  
Arnaba Saha Chaity ◽  
Mutasim Billah

Novel coronavirus (nCoV) has created a new challenging situation all over the world. In Bangladesh, people are facing some difficulties to response the emergencies. There are so many people who are lacking of proper quarantine information and knowledge about prevention practices towards coronavirus disease 2019 (COVID-19). COVID-19 has created an experience of mental disorder like depression, anxiety, and stress. Although social media, newspaper, news, television has focused on this issue, still there is to be needed to identify the psychological effects like negative impact on our mind and behavioral changes during lockdown. An online survey of 248 respondents was conducted between April, 15 2020 and May, 15 2020. The aim of this study was to assess the relationship between higher knowledge of public regarding safety measures and depression among the adult population of Bangladesh during lockdown. This study focused on correlation between knowledge level and mental health condition like depression. About 50% respondents were felt high depression after the first announcement of lockdown in Bangladesh. Approximately 50% respondents stated that people of their locality were panicked, not panicked were 26.21% and the probability of getting panic were 23.79% due to COVID-19 during lockdown in Bangladesh. The respondents who had gathered a higher knowledge about precautions were associated with depression.


Author(s):  
NUR SULISTYAWATI ◽  
FAHMIZAL FAHMIZAL ◽  
IOTA NATHASYA

ABSTRAKMakalah ini menyajikan penjelasan tentang penerepan full state feedback menggunakan metode pole placement pada sistem buck converter dengan Motor DC. Penambahan komponen buck converter diharapkan dapat membantu menaikkan nilai efisiensi sistem dan memperpanjang umur komponen switch yang digunakan. Namun terkadang sistem ini masih memerlukan kendali untuk dapat memaksimalkan perfoma sistem baik dari segi rising time, settling time maupun error steady state dari sistem. Simulasi kendali full state feedback menggunakan pole placement disimulasikan dengan pemodelan buck converter dan motor DC menggunakan Simscape dan Simulink pada Matlab. Dari hasil simulasi diperoleh bahwa kendali pole placement mampu menghasilkan kondisi rising time 1.4508s, settling time 2.5729s sedangkan kendali LQR lebih lambat 0.9524s untuk rising time dan 4.3603s untuk settling time saat diuji dengan sinyal step. Selain itu, penambahan pre compensator (Nbar) telah membuat sistem mampu mencapai nilai referensi yang diharapkan (error steady state menuju nol).Kata kunci: Motor DC, Buck Converter, Pole Placement. ABSTRACTThis paper presents an explanation of the advanced full state feedback using the pole placement method in a buck converter system with a DC motor. The addition of buck converter components is expected to help increase the value of system efficiency and extend the life of the switch components used. However, sometimes this system still requires control to be able to maximize system performance in terms of both the rising time, the settling time and the steady state error of the system. Full state feedback control simulation using pole placement is simulated by modeling the buck converter and DC motor using Simscape and Simulink in Matlab. The simulation results show that the pole placement control is capable of producing a rising time of 1.4508s, settling time of 2.5729s, while LQR control is 0.9524s slower for rising time and 4.3603s for settling time when tested with step signals. In addition, the addition of a pre compensator (Nbar) has made the system able to reach the expected reference value (steady state error goes to zero).Keywords: DC Motor, Buck Converter, Pole Placement.


Acta Acustica ◽  
2021 ◽  
Vol 5 ◽  
pp. 33
Author(s):  
Tom Colinot ◽  
Christophe Vergez ◽  
Philippe Guillemain ◽  
Jean-Baptiste Doc

The lowest fingerings of the saxophone can lead to several different regimes, depending on the musician’s control and the characteristics of the instrument. This is explored in this paper through a physical model of saxophone. The harmonic balance method shows that for many combinations of musician control parameters, several regimes are stable. Time-domain synthesis is used to show how different regimes can be selected through initial conditions and the initial evolution (rising time) of the blowing pressure, which is explained by studying the attraction basin of each stable regime. These considerations are then applied to study how the produced regimes are affected by properties of the resonator. The inharmonicity between the first two resonances is varied in order to find the value leading to the best suppression of unwanted overblowing. Overlooking multistability in this description can lead to biased conclusions. Results for all the lowest fingerings show that a slightly positive inharmonicity, close to that measured on a saxophone, leads to first register oscillations for the greatest range of control parameters. A perfect harmonicity (integer ratio between the first two resonances) decreases first register production, which adds nuance to one of Benade’s guidelines for understanding sound production. Thus, this study provides some a posteriori insight into empirical design choices relative to the saxophone.


2020 ◽  
pp. 466-478

Release valves are commonly used to protect hydraulic legs against overload caused by rock bursts or bumps. Due to an essential role in ensuring safety in the working, an application of a release valve is conditioned by a positive yield test results of a leg equipped with such a valve. A method of leg yield testing, used in Poland, enables a complex determination of an impact of not only a release valve but also of the parameters of the hydraulic leg, determining its stiffness such as for example a volume of the under-the-piston space, which has an impact on an observed pressure increase. The subject of this publication covers cognitive tests oriented onto a determination of an impact of a release valve exclusively on the pressure changes observed in the leg. The results of the efficiency tests of spring valves (Stoiński, 2018) on a rammer are discussed. The difference between the maximum pressure in the under-piston area of the leg with the release valve and the maximum pressure generated by the same dynamic load in the leg without this valve was the measure of the valve operation's effectiveness. Dynamic load, realized on a rammer, is characterized by a longer increase time than in the case of dynamic load acting on a powered roof support unit from the floor. The time process of the force in the leg is then characterized by a short load rising time – tn, large load increment factor – Kd and the average load growth rate –wp,n. Referring to that aspect, the features of a release valve were analyzed in relation to the parameters characterizing dynamic load acting on a powered roof support unit from the floor. Parameters characterizing the effectiveness of the release valve, i.e. change in the leg load increment index –Kd and change in the rate of load increase –wpn were defined. The test stand for generating the load of such parameters using the explosive method is described. Comparison of effects of the dynamic load generated by firing the same mass and the same type of explosive on a hydraulic leg with a release valve and the leg without this valve was the test objective. The effectiveness of the spring valve and two gas valves are analyzed. It was found that despite a very short load rising time, the release valve reduces the load acting on the leg. The positive values of the Kd and wp,n indices are the evidence.


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