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外文翻譯---頻率和錨固長(zhǎng)度對(duì)超聲波在錨桿中傳播行為的影響-展示頁

2025-01-24 02:20本頁面
  

【正文】 ydependent and some frequencyindependent. The total attenuation is the sum of the contributions of all in?uencing factors [14], and this relationship applies to both bulk waves and guided waves: (2)where is the attenuation coef?cient of the ith ponent caused by the ith factor, is the travel distance affected by the ith factor, is the amplitude ratio after attenuation of the ith ponent, If is the same for all factors, then wehave or (3)where is the total attenuation coef?cient.According to the cause, attenuation may be grouped into the following categories:(a) Dissipative attenuation: An energy loss due to nonelastic resistance of the medium. It increases with thewave travel distance and may bee profound over a long distance depending on the material property. This type of attenuation in steel is generally very low pared to that in rocks. As shown later, it can beignored in practice for guided waves traveling in rock bolts due to the low resistance of steel and the short bolt length (1–3 m).(b) Dispersive attenuation: An energy loss due to deformation of waveform during wave propagation, a characteristic that distinguishes guided waves from bulk waves. The phenomenon of wave deformation is calledenergy dispersion.(c) Spreading attenuation: An energy loss which occurs at the interface between the bolt and the grouting material. As a guided wave reaches the interface, not all of the wave energy can be re?ected at the interface. Part of the energy passes through the interface and is transmitted into the grouted material, a phenomenon called energy leakage.Therefore, it can be reasonably assumed that attenuation in grouted rock bolts consists of two major ponents。 Attenuation。英文原文Effects of frequency and grouted length on the behavior of guided ultrasonic waves in rock bolts. Zoua, Y. Cui, V. Madengaa, C. ZhangAbstractExperiments were conducted to study the behavior of guided waves in free and grouted rock bolts. Ultrasonic waves with frequencies from 25 to 100 kHz were used as excitation inputs. Tests were ?rst conducted on free bolts to help understand the behavior of guided waves in nongrouted bolts. The effects of wave frequency and grouted length on the group velocity and attenuation of the guided ultrasonic waves were then evaluated. The test results indicated clear but different trends for the group velocity in the free and the grouted bolts. The attenuation in free bolts was not affected by bolt length and frequency. However, in grouted bolts it increased with frequency and grouted length. It was also found that the two main sources of attenuation are the setup energy loss, which has a ?xed quantity for a speci?c type of test setup, and the dispersive and spreading energy loss which varies with frequency and bolt Elsevier Ltd. All rights reserved.Keywords: Rock bolts。 Guided waves。 Amplitude。dispersive and spreading attenuation, both of which are frequencydependent. The total attenuation in grouted rock bolts should thus be the sum of the two ponents and in future will be referred to as DISP attenuation.It should be pointed out however, that as observed during our laboratory tests, the amplitude decay and the energy loss of guided waves recorded during tests of rock bolts in laboratory are not solely from the DISP attenuation. Another important ponent is the energy loss due to refraction at the contact surfaces between the bolt sample and the equipment. Theoretically, when a wave reaches an interface adjoining a medium which does not transmit mechanical waves (., vacuum or air), no refraction occurs and all energy is re?ected rock bolt test, transducers are attached to the bolt sample, which is in contact with the testing frame (., a table or a rack). It is at these contact surfaces that some energy is inevitably refracted, causing energy loss. This type of energy loss, as shown later, is expected to be constant and is of a ?xed quantity for a speci?c type of test setup. In future it will be called setup energy loss. As a result, the recorded amplitude decay and energy loss during rock bolt tests will be greater than what is actually caused by the DISP attenuation.An ongoing research program at Dalhousie University is aimed at studying the characteristics of guided waves in grouted rock bolts. Effects of wave frequency and grouted length on the behavior of guided ultrasonic waves in free bolts and grouted bolts have been studied. The achieved results are strikingly convincing. The details are given below.2. Experiments of guided ultrasonic wave testsAn understanding of the ultrasonic wave characteristics in free bolts (nongrouted bolts) is essential to the study of the behavior of guided ultrasonic waves in grouted bolts. In this research, both free bolts and grouted bolts were tested.. Test samplesThe test samples included two free bolts and three grouted bolts of various lengths. The free bolts were bare steel bars. The grouted bolts were made by casting a cylindrical concrete block around a steel bar to simulate the grouted rock bolts in the ?eld (). In these tests the bolts were not tensioned. The sample sizes and other descriptions are given in Table 1. The two free bolts (samples 1 and 2) were used to study the effects of bolt length and frequency on the behavior of guided ultrasonic waves, particularly the setup energy loss due to equipment setup. The three grouted bolts (samples 3–5) with varying grouted lengths were used to investigate the effects of frequency and grouted length on the attenuation of guided ultrasonic waves.. Test instruments and experiment descriptionThe instruments used in the study included a Handyscope HS3 (a data acquisition device with a wave generator), an ampli?er, two transducers, and a puter. The equipment setup is illustrated in . The HS3 unit has the capability of generating ultrasonic signals with varying frequencie
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