Shock and Vibration http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Impulse Force Balance for Ultrashort Duration Hypersonic Test Facilities Sun, 24 May 2015 11:31:46 +0000 http://www.hindawi.com/journals/sv/2015/803253/ This paper presents the measurement of side force, pitching, and yawing moments on a model, using an accelerometer force balance, in a short duration hypersonic shock tunnel. The test model is a blunt-nosed, flapped delta wing, mounted on a support sting through a force balance. The flexible rubber bushes constituting the balance allow the model to float freely on the sting during the test. The accelerometers were located in the model to record accelerations in the directions of interest. The model was tested in shock tunnel at Mach 8 at different angles of incidence with the freestream. Dynamic calibration of the test assembly was carried out for the acquisition of impulse response functions for the above components of force and moments, using an impulse hammer. The convolution technique was applied to derive the impulse response functions. The accelerometer outputs from the model in the hypersonic freestream were processed using the respective impulse response functions to derive the unknown aerodynamic force and moments. The newly adopted convolution technique has been found very effective for data reduction from accelerometer force balances developed for shock tunnel applications. P. Singh, V. Menezes, K. J. Irimpan, and H. Hosseini Copyright © 2015 P. Singh et al. All rights reserved. Numerical Tests on Failure Process of Rock Particle under Impact Loading Sun, 24 May 2015 11:30:53 +0000 http://www.hindawi.com/journals/sv/2015/678573/ By using numerical code RFP (dynamic version), numerical model is built to investigate the failure process of rock particle under impact loading, and the influence of different impact loading on crushing effect and consumed energy of rock particle sample is analyzed. Numerical results indicate that crushing effect is good when the stress wave amplitude is close to the dynamic strength of rock; it is difficult for rock particle to be broken under too low stress wave amplitude; on the other hand, when stress wave amplitude is too high, excessive fine particle is produced, and crushing effect is not very good on the whole, and more crushing energy is consumed. Secondly, in order to obtain good crushing effect, it should be avoided that wavelength of impact load be too short. Therefore, it is inappropriate to choose impact rusher with too high power and too fast impact frequency for ore particle. Yu-Jun Zuo, Qin Zhang, Tao Xu, Zhi-Hong Liu, Yue-Qin Qiu, and Wan-Cheng Zhu Copyright © 2015 Yu-Jun Zuo et al. All rights reserved. Study on Dynamic Disaster in Steeply Deep Rock Mass Condition in Urumchi Coalfield Sun, 24 May 2015 07:31:48 +0000 http://www.hindawi.com/journals/sv/2015/465017/ The possible mining seismicity (MS) and its prediction are important for safety and recovery optimization of mining in steep-heavy-thick rock mass condition. The stress-lever-rotation-effect (SLRE) model of fault-like mobilization was proposed preliminarily. Some innovation monitoring technique approaches for mining seismicity assessment were successfully fulfilled at Wudong Mine of Urumchi Coalfield, China. The characteristics on acoustic-seismic-wave index indicated the spatial-temporal-strength and stress redistribution of steeply deeper-heavy thick coal and rock masses. Applications in field investigations showed that the innovation monitoring (in time and space) of these instruments could provide important information about the performance of mining disturbed structures (heading and steep pillar) during caving of competent overlying roof strata. The prediction and evaluation for mining seismicity were applicable and valid. Operating practice showed that mining efficiency was raised and conspicuous economic benefit was obtained. This approach provides essential data for assessing mining seismicity, coal burst, dynamic hazard prevention, and deep mining potential. Xing-Ping Lai, Mei-Feng Cai, Fen-Hua Ren, Peng-Fei Shan, Feng Cui, and Jian-Tao Cao Copyright © 2015 Xing-Ping Lai et al. All rights reserved. An Experiment Monitoring Signals of Coal Bed Simulation under Forced Vibration Conditions Thu, 21 May 2015 14:13:17 +0000 http://www.hindawi.com/journals/sv/2015/693612/ An experiment simulating coal seam under forced vibration conditions was conducted. Acceleration response and microseism signal during the experiment were collected and analyzed. It is found that, with an increasing amount of vibration, the natural frequency of the specimen decreases, and this phenomenon reflects fractures appearing in the specimen. Acceleration response signals show that peaks in shock excitation frequency and shock excitation acceleration affect the acceleration response, which reflects damage to the specimen. When shock excitation frequency nears natural frequency, the acceleration response first decreases and then increases. When resonance occurs, it reaches its maximum value. As shock excitation acceleration peaks increase, the acceleration response peak of the specimen also increases. We conclude that destruction is mainly concentrated in the coal seam evidenced by specimen destruction situation. Then shock excitation frequency and shock excitation acceleration influence on microseism signals were analyzed by Hilbert-Huang transform. By receiving these signals and analyzing their characteristics, it is beneficial to develop new methods to predict disasters underground dynamically in the future. Chengwu Li, Po Hu, Tianbao Gao, Yingfeng Sun, Shengyang Shao, and Qifei Wang Copyright © 2015 Chengwu Li et al. All rights reserved. Simulation of the Load Evolution of an Anchoring System under a Blasting Impulse Load Using FLAC3D Thu, 21 May 2015 14:11:04 +0000 http://www.hindawi.com/journals/sv/2015/972720/ A limitation in research on bolt anchoring is the unknown relationship between dynamic perturbation and mechanical characteristics. This paper divides dynamic impulse loads into engineering loads and blasting loads and then employs numerical calculation software FLAC3D to analyze the stability of an anchoring system perturbed by an impulse load. The evolution of the dynamic response of the axial force/shear stress in the anchoring system is thus obtained. It is revealed that the corners and middle of the anchoring system are strongly affected by the dynamic load, and the dynamic response of shear stress is distinctly stronger than that of the axial force in the anchoring system. Additionally, the perturbation of the impulse load reduces stress in the anchored rock mass and induces repeated tension and loosening of the rods in the anchoring system, thus reducing the stability of the anchoring system. The oscillation amplitude of the axial force in the anchored segment is mitigated far more than that in the free segment, demonstrating that extended/full-length anchoring is extremely stable and surpasses simple anchors with free ends. Xigui Zheng, Jinbo Hua, Nong Zhang, Xiaowei Feng, and Lei Zhang Copyright © 2015 Xigui Zheng et al. All rights reserved. Mechanism of Roof Shock in Longwall Coal Mining under Surface Gully Thu, 21 May 2015 13:08:08 +0000 http://www.hindawi.com/journals/sv/2015/803071/ The paper presents an interpretation on the abnormal roof shock in longwall coal mining under gullies using physical modeling, numerical modeling, and mechanical analysis. The modeling results show that the roof movement causes the shock load onto the stope in longwall coal mining under surface gully. The triggering mechanism of shock load depends on the direction of the face retreat with respect to the bottom of the surface gully. The slope tends to slide along the interface plane with a long periodical weighting intervals when mining towards the bottom of the gully (downslope direction), while the overburden strata may be split into blocks and tend to topple towards the free face of gully when mining away from the bottom of the gully (upslope direction). The mechanical models showed that, during the period of mining in downslope direction, planar sliding and key fragmental blocks cause a sudden roof shearing off which could result in shock load and, during the period of mining in upslope direction, the overburden blocks may become unstable due to shearing off which could resulted in large shock pressure onto the stope. Gangwei Fan, Dongsheng Zhang, and Xufeng Wang Copyright © 2015 Gangwei Fan et al. All rights reserved. A Case Study of Damage Energy Analysis and an Early Warning by Microseismic Monitoring for Large Area Roof Caving in Shallow Depth Seams Thu, 21 May 2015 13:03:18 +0000 http://www.hindawi.com/journals/sv/2015/709459/ Shallow depth coal seams are widely spread in Shendong mining area, which is located in the Northwestern region of China. When working face is advanced out of concentrated coal pillar in upper room and pillar goaf, strong strata behaviors often cause support crushing accidents, and potentially induce large area residual pillars instability and even wind blast disaster. In order to predict the precise time when the accident happens, guaranteeing life-safety of miner, microseismic monitoring system was for the first time applied in shallow coal seam. Based on damage mechanics correlation theory, the damage energy model is established to describe relationship between damage level and cumulative energy of microseismic events. According to microseismic monitoring data of two support crushing accidents, the damage energy model is verified and an effective early warning method of these accidents is proposed. The field application showed that the early warning method had avoided miners suffering from all support crushing accidents in Shigetai coal mine. Like Wei, Qingxin Qi, Hongyan Li, Bin Zhang, Yongren Wang, and Linghai Kong Copyright © 2015 Like Wei et al. All rights reserved. The Microphone Feedback Analogy for Chatter in Machining Thu, 21 May 2015 09:57:06 +0000 http://www.hindawi.com/journals/sv/2015/976819/ This paper provides experimental evidence for the analogy between the time-delay feedback in public address systems and chatter in machining. Machining stability theory derived using the Nyquist criterion is applied to predict the squeal frequency in a microphone/speaker setup. Comparisons between predictions and measurements are presented. Tony Schmitz Copyright © 2015 Tony Schmitz. All rights reserved. A Comparison of Mine Seismic Discriminators Based on Features of Source Parameters to Waveform Characteristics Thu, 21 May 2015 09:55:41 +0000 http://www.hindawi.com/journals/sv/2015/919143/ To find efficient methods for classifying mine seismic events, two features extraction approaches were proposed. Features of source parameters including the seismic moment, the seismic energy, the energy ratio of S- to P-wave, the static stress drop, time of occurrence, and the number of triggers were selected, counted, and analyzed in approach I. Waveform characteristics consisting of two slope values and the coordinates of the first peak and the maximum peak were extracted as the discriminating parameters in approach II. The discriminating performance of the two approaches was compared and discussed by applying the Bayes discriminant analysis to the characteristic parameters extracted. Classification results show that 83.5% of the original grouped cases are correctly classified by approach I, and 97.1% of original grouped cases are correctly classified by approach II. The advantages and limitations pertaining to each classifier were discussed by plotting the event magnitude versus sample number. Comparative analysis shows that the proposed method of approach II not only has a low misjudgment rate but also displays relative constancy when the testing samples fluctuate with seismic magnitude and energy. Ju Ma, Guoyan Zhao, Longjun Dong, Guanghui Chen, and Chuxuan Zhang Copyright © 2015 Ju Ma et al. All rights reserved. The Mechanism and Application of Deep-Hole Precracking Blasting on Rockburst Prevention Thu, 21 May 2015 09:48:50 +0000 http://www.hindawi.com/journals/sv/2015/625691/ The mechanism of preventing rockburst through deep-hole precracking blasting was studied based on experimental test, numerical simulation, and field testing. The study results indicate that the deep-hole precracking could change the bursting proneness and stress state of coal-rock mass, thereby preventing the occurrence of rockburst. The bursting proneness of the whole composite structure could be weakened by the deep-hole precracking blasting. The change of stress state in the process of precracking blasting is achieved in two ways: (1) artificially break the roof apart, thus weakening the continuity of the roof strata, effectively inducing the roof caving while reducing its impact strength; and (2) the dynamic shattering and air pressure generated by the blasting can structurally change the properties of the coal-rock mass by mitigating the high stress generation and high elastic energy accumulation, thus breaking the conditions of energy transfer and rock burst occurrence. Zhenhua Ouyang, Qingxin Qi, Shankun Zhao, Baoyang Wu, and Ningbo Zhang Copyright © 2015 Zhenhua Ouyang et al. All rights reserved. Damage Characteristics of Surrounding Rock Subjected to VCR Mining Blasting Shock Thu, 21 May 2015 09:45:27 +0000 http://www.hindawi.com/journals/sv/2015/373021/ For limiting the damage range caused by explosive shock loads in vertical crater retreat (VCR) mining, the blasting damage characteristics of surrounding rock were studied by two methods: numerical simulation and ultrasonic testing. Combined with the mining blasting in Dongguashan Copper Mine of China, the VCR blasting shock characteristics under different conditions are obtained by using LSDYNA. Based on statistical fracture mechanics and damage mechanics theories, a damage constitutive model for rock mass subjected to blasting shock load was established. Then by using the fast Lagrange analysis codes (FLAC3D), the blasting damage characteristics of surrounding rock were analyzed by applying the blasting shock loads obtained from the VCR mining and the damage zone is obtained. At last, the relationship between the amount of explosives and the radius of damaged surrounding rock mass was discussed, and its formula was also derived. The research provides a theoretical basis for rationally controlling stope boundaries and optimizing mining blasting parameters. Nan Jiang, Chuanbo Zhou, Xuedong Luo, and Shiwei Lu Copyright © 2015 Nan Jiang et al. All rights reserved. Numerical Investigation of Rockburst Effect of Shock Wave on Underground Roadway Thu, 21 May 2015 07:23:46 +0000 http://www.hindawi.com/journals/sv/2015/867582/ Using UDEC discrete element numerical simulation software and a cosine wave as vibration source, the whole process of rockburst failure and the propagation and attenuation characteristics of shock wave in coal-rock medium were investigated in detail based on the geological and mining conditions of 1111(1) working face at Zhuji coal mine. Simultaneously, by changing the thickness and strength of immediate roof overlying the mining coal seam, the whole process of rockburst failure of roadway and the attenuation properties of shock wave were understood clearly. The presented conclusions can provide some important references to prevent and control rockburst hazards triggered by shock wave interferences in deep coal mines. Cai-Ping Lu, Guang-Jian Liu, Hong-Yu Wang, and Jun-Hua Xue Copyright © 2015 Cai-Ping Lu et al. All rights reserved. Warning Method of Coal Bursting Failure Danger by Electromagnetic Radiation Thu, 21 May 2015 07:19:14 +0000 http://www.hindawi.com/journals/sv/2015/583862/ Electromagnetic radiation (EMR) can reflect the stress state and deformation level of coal, yet its warning indexes correlated with coal properties and roof caving is poorly understood. The laboratory observations of EMR effects of coal samples bursting failure and in situ investigations in the process of roof caving are presented in this paper. EMR peak with increasing stress is discussed when the failure of coal samples happens, which provides an explanation to EMR signals positively correlated well with the stress loaded. The linearly increasing relation is also found between EMR intensity and the uniaxial compressive strength, and EMR maximum amplitudes and pulses behave a logarithmic accretion tendency with bursting energy indexes of coal. By in situ investigations, it is well found that EMR amplitude can effectively warn coal deformation and failure based on the critical value 120 mV proposed from experiments. Guang-Jian Liu, Cai-Ping Lu, Hong-Yu Wang, Peng-Fei Liu, and Yang Liu Copyright © 2015 Guang-Jian Liu et al. All rights reserved. Blast-Induced Damage on Millisecond Blasting Model Test with Multicircle Vertical Blastholes Thu, 21 May 2015 07:19:02 +0000 http://www.hindawi.com/journals/sv/2015/504043/ To investigate the blast-induced damage effect on surrounding rock in vertical shaft excavation, 4 kinds of millisecond blasting model tests with three-circle blastholes were designed and carried out with excavation blasting in vertical shaft as the background. The longitudinal wave velocity on the side of concrete model was also measured before and after blasting. Then blast damage factor was then calculated by measuring longitudinal wave velocity before and after blasting. The test results show that the blast-induced damage factor attenuated gradually with the centre of three-circle blastholes as centre. With the threshold value of 0.19 for blast-induced damage factor, blast-induced damage zones for 4 kinds of model tests are described and there is an inverted cone blast-induced damage zone in concrete model. And analyses of cutting effect and blast-induced damage zone indicate that in order to minimize the blast-induced damage effect and ensure the cutting effect the reasonable blasting scheme for three-circle blastholes is the inner two-circle blastholes initiated simultaneously and the outer third circle blastholes initiated in a 25 ms delay. Qin-yong Ma, Pu Yuan, Jing-shuang Zhang, Rui-qiu Ma, and Bo Han Copyright © 2015 Qin-yong Ma et al. All rights reserved. Multi-Index Monitoring and Evaluation on Rock Burst in Yangcheng Mine Thu, 21 May 2015 07:15:34 +0000 http://www.hindawi.com/journals/sv/2015/624893/ Based on the foreboding information monitoring of the energy released in the developing process of rock burst, prediction system for rock burst can be established. By using microseismic method, electromagnetic radiation method, and drilling bits method, rock burst in Yangcheng Mine was monitored, and a system of multi-index monitoring and evaluation on rock burst was established. Microseismic monitoring and electromagnetic radiation monitoring were early warning method, and drilling bits monitoring was burst region identification method. There were three identifying indexes: silence period in microseismic monitoring, rising period of the intensity, and rising period of pulse count in electromagnetic radiation monitoring. If there is identified burst risk in the workface, drilling bits method was used to ascertain the burst region, and then pressure releasing methods were carried out to eliminate the disaster. Yunliang Tan, Yanchun Yin, Shitan Gu, and Zhiwei Tian Copyright © 2015 Yunliang Tan et al. All rights reserved. Effects of Fine Gangue on Strength, Resistivity, and Microscopic Properties of Cemented Coal Gangue Backfill for Coal Mining Thu, 21 May 2015 07:11:44 +0000 http://www.hindawi.com/journals/sv/2015/752678/ The cemented coal gangue backfill (CGB) in coal mining is normally made of gangue (particle size of 0–15 mm), fly ash, cement, and water. In this study, the effects of the weight content (ranging from 20% to 60%) of fine gangue (0–5 mm) on the microscopic characteristics, resistivity, and compressive strength of CGB were investigated at 3 d and 28 d curing times, respectively. The test results indicate that the strengths of the CGB, regardless of the curing time, increased with fine gangue content changing from 20% up to 40%. Further increase in fine gangue introduced a decrease in the strength. Another observation is that, at 3 days, a general increasing trend of CGB resistivity was noted with fine gangue content. At 28 days, the resistivity of CGB decreased with increase in the fine gangue content. Correlations between the resistivity and compression strength of CGB show a concave pattern, which attribute to the various micromechanism influenced on the resistivity and strength of CGB with different fine gangue content. It indicates that using resistivity to derive strength of CGB is not appropriate. Tingye Qi, Guorui Feng, Yanrong Li, Yuxia Guo, Jun Guo, and Yujiang Zhang Copyright © 2015 Tingye Qi et al. All rights reserved. Study on Monitoring Rock Burst through Drill Pipe Torque Thu, 21 May 2015 06:28:29 +0000 http://www.hindawi.com/journals/sv/2015/371948/ This paper presents a new method to identify the danger of rock burst from the response of drill pipe torque during drilling process to overcome many defects of the conventional volume of drilled coal rubble method. It is based on the relationship of rock burst with coal stress and coal strength. Through theoretic analysis, the change mechanism of drill pipe torque and the relationship of drill pipe torque with coal stress, coal strength, and drilling speed are investigated. In light of the analysis, a new device for testing drill pipe torque is developed and a series of experiments is performed under different conditions; the results show that drill pipe torque linearly increases with the increase of coal stress and coal strength; the faster the drilling speed, the larger the drill pipe torque, and vice versa. When monitoring rock burst by drill pipe torque method, the index of rock burst is regarded as a function in which coal stress index and coal strength index are principal variables. The results are important for the forecast of rock burst in coal mine. Zhonghua Li, Liyuan Zhu, Wanlei Yin, and Yanfang Song Copyright © 2015 Zhonghua Li et al. All rights reserved. Instantaneous Rock Blasting Wave and Its Microscopic Characteristics during Interaction with Concrete Wed, 20 May 2015 16:48:02 +0000 http://www.hindawi.com/journals/sv/2015/318286/ This paper uses improved technology for dynamic strain measurement to investigate the dynamic strain signals of blasting wave action tested in the range of 8–16 cm from the central blast. Based on the blasting mechanism and on the analysis of signal characteristics, blasting waves are recognized and divided into three zones, namely, shock wave zone, stress wave zone, and gas-expanding zone. This paper studies the relationships between stress, strain, and time of every zone. The tensile and compressive stresses of stress wave are considered. After the blasting test, four cracks from the borehole center toward the minimum burden appear at the model surface. The relationship between blasting wave and concrete damage is analyzed. Shaoqin Huang, Lifeng Luan, Wanli Xing, and Qunyi Liu Copyright © 2015 Shaoqin Huang et al. All rights reserved. Distribution of Side Abutment Stress in Roadway Subjected to Dynamic Pressure and Its Engineering Application Wed, 20 May 2015 16:41:54 +0000 http://www.hindawi.com/journals/sv/2015/929836/ The borehole stress-meter was employed in this study to investigate the distribution of the side abutment stress in roadway subjected to dynamic pressure. The results demonstrate that the side abutment stress of the mining roadway reaches a peak value when the distance to the gob is 8 m and the distribution curve of the side abutment stress can be divided into three zones: stress rising zone, stress stabilizing zone, and stress decreasing zone. Further numerical investigation was carried out to study the effect of the coal mass strength, coal seam depth, immediate roof strength, and thickness on the distribution of the side abutment stress. Based on the research results, we determined the reasonable position of the mining roadway and the optimal width of the barrier pillar. The engineering application demonstrates that the retention of the barrier pillar with a width of 5 m along the gob as the haulage roadway for the next panel is feasible, which delivers favorable technological and economic benefits. Yao Qiangling, Zhou Jian, Li Yanan, Tan Yingming, and Jiang Zhigang Copyright © 2015 Yao Qiangling et al. All rights reserved. Chatter Prediction for Variable Pitch and Variable Helix Milling Wed, 20 May 2015 14:37:55 +0000 http://www.hindawi.com/journals/sv/2015/419172/ Regenerative chatter is a self-excited vibration that can occur during milling, which shortens the lifetime of the tool and results in unacceptable surface quality. In this paper, an improved semidiscretization method for modeling and simulation with variable pitch and variable helix milling is proposed. Because the delay between each flute varies along the axial depth of the tool in milling, the cutting tool is discrete into some axial layers to simplify calculation. A comparison of the predicted and observed performance of variable pitch and variable helix against uniform pitch and uniform helix milling is presented. It is shown that variable pitch and variable helix milling can obtain larger stable cutting area than uniform pitch and uniform helix milling. Thus, it is concluded that variable pitch and variable helix milling are an effective way for suppressing chatter. Yong Wang, Taiyong Wang, Zhiqiang Yu, Yue Zhang, Yulong Wang, and Hengli Liu Copyright © 2015 Yong Wang et al. All rights reserved. Study on Low-Frequency TEM Effect of Coal during Dynamic Rupture Wed, 20 May 2015 14:28:34 +0000 http://www.hindawi.com/journals/sv/2015/189569/ Dynamic loads provided by the SHPB test system were applied to coal specimens, and the TEM signals that emerged during coal rupture were recorded by the TMVT system. Experiments on coal-mass blasting rupture in excavating workface were also carried out, and the emerged TEM signal was analyzed. The results indicate that the low-frequency TEM signals were detected close to the coal specimens under high strain dynamic load applied by the SHPB, initially rising sharply and dropping rapidly, followed by a small tailing turbulence. And the field test results obtained during coal blasting process coincided with the results from the SHPB tests. Furthermore, its initial part shaped like a pulse cluster had a more pronounced tail and lasted even longer. And the generation mechanism of the low-frequency TEM effect was analyzed. It suggests that the low-frequency TEM effect of coal during dynamic rupture is contributed by the fractoemission mechanism and the resonance or waveguide effects. Because its wavelength is longer than the higher ones, the low-frequency TEM has a good anti-interference performance. That can expand the scope and performance of the coal-rock dynamic disaster electromagnetic monitoring technique. Cheng-wu Li, Chuan Wang, Bei-jing Xie, Xiao-yuan Sun, and Xiao-meng Xu Copyright © 2015 Cheng-wu Li et al. All rights reserved. Bolt Pull-Out Tests of Anchorage Body under Different Loading Rates Wed, 20 May 2015 14:28:14 +0000 http://www.hindawi.com/journals/sv/2015/121673/ Based on the force analysis and mechanical transmission mechanism of grouting bolts, the self-developed test apparatus for interfacial mechanics is used to study the distribution rule of axial force and interfacial stress of bolts in anchorage body. At the same time, pull-out tests of anchorage body are simulated with the particle flow code software , and stress distribution and failure patters are researched under different loading rates. The results show that the distribution of axial force and interfacial shear stress is nonuniform along the anchorage section: axial force decreases, shear force increases first and then decreases, and the maximum value of both of them is closed to the pull-out side; with the increase of loading rates, both of axial force and interfacial shear stress show a trend of increase in the upper anchorage section but changes are not obvious in the lower anchorage section, which causes serious stress concentration; failure strength of pull-out and loading rates show a linear correlation; according to loading rates’ impact on the anchoring effect, the loading rates’ scope can be divided into soft scope ( mm/s), moderate scope (10 mm/s < < 100 mm/s), and strong scope ( mm/s). Tong-bin Zhao, Wei-yao Guo, Yan-chun Yin, and Yun-liang Tan Copyright © 2015 Tong-bin Zhao et al. All rights reserved. Acoustic Emission Behavior of Rock-Like Material Containing Two Flaws in the Process of Deformation Failure Wed, 20 May 2015 13:47:11 +0000 http://www.hindawi.com/journals/sv/2015/167580/ Many sudden disasters (such as rock burst) by mining extraction originate in crack initiation and propagation. Meanwhile a large number of shock waves are produced by rock deformation and failure. With the purpose of investigating crack coalescence and failure mechanism in rock, experimental research of rock-like materials with two preexisting flaws was performed. Moreover, the AE technique and photographic monitoring were adopted to clarify further the procedure of the crack coalescence and failure. It reveals that AE location technique can record the moments of crack occurrences and follow the crack growth until final failure. Finally, the influence of different flaw geometries on crack initiation strength is analyzed in detail. This research provides increased understanding of the fracture mechanism of mining-induced disasters. Quan-Sheng Liu, Jie Xu, Bin Liu, and Jing-Dong Jiang Copyright © 2015 Quan-Sheng Liu et al. All rights reserved. Experimental Study on Anisotropic Strength and Deformation Behavior of a Coal Measure Shale under Room Dried and Water Saturated Conditions Wed, 20 May 2015 13:37:45 +0000 http://www.hindawi.com/journals/sv/2015/290293/ This paper presents an experimental investigation of anisotropic strength and deformation behavior of coal measure shale. The effect of two factors (i.e., anisotropy and water content) on shale strength and deformation behavior was studied. A series of uniaxial and triaxial compression tests were conducted on both room dried and water saturated samples for different lamination angles. The test results indicate that (1) the compressive strength, cohesion, internal friction angle, tangent Young’s modulus, and axial strain corresponding to the peak and residual strengths of room dried specimens exhibit anisotropic behavior that strongly depends on the orientation angle ; (2) in comparison to the room dried samples, the compressive strength and Young’s modulus as well as the anisotropy are all reduced for water saturated specimens; and (3) the failure mechanism of the samples can be summarized into two categories: sliding along lamination and shearing of rock material, with the type occurring in a particular situation depending strongly on the lamination orientation angles with respect to the major principal stress. According to the findings, it is strongly recommended that the effect of anisotropy and water content on the strength and deformation behavior of the rock must be considered in ground control designs. Jingyi Cheng, Zhijun Wan, Yidong Zhang, Wenfeng Li, Syd S. Peng, and Peng Zhang Copyright © 2015 Jingyi Cheng et al. All rights reserved. Dynamic Effect and Control of Key Strata Break of Immediate Roof in Fully Mechanized Mining with Large Mining Height Wed, 20 May 2015 13:31:06 +0000 http://www.hindawi.com/journals/sv/2015/657818/ This paper puts forward the concept of key strata in immediate roof (KSIF) and studied the dynamic effect and control mechanism of KSIF. The results show that KSIR controls the caving of its upper immediate roof strata; the break of KSIR has direct dynamic impact on its lower strata and this impact increases along with the increase of the thickness and hardness of the KSIR and the decrease of the distance to the working seam. The KSIR and main roof can easily form the bilayer structure “Cantilever-Masonry beam.” Support work load is affected by the position, thickness, and hardness of KSIR. The support work load increased on the condition of increase of the thickness and hardness of KSIR and the decrease of the distance to the face. Yuan Yong, Tu Shihao, Zhang Xiaogang, and Li Bo Copyright © 2015 Yuan Yong et al. All rights reserved. Blasting Vibration Safety Criterion Analysis with Equivalent Elastic Boundary: Based on Accurate Loading Model Wed, 20 May 2015 13:24:45 +0000 http://www.hindawi.com/journals/sv/2015/604683/ In the tunnel and underground space engineering, the blasting wave will attenuate from shock wave to stress wave to elastic seismic wave in the host rock. Also, the host rock will form crushed zone, fractured zone, and elastic seismic zone under the blasting loading and waves. In this paper, an accurate mathematical dynamic loading model was built. And the crushed zone as well as fractured zone was considered as the blasting vibration source thus deducting the partial energy for cutting host rock. So this complicated dynamic problem of segmented differential blasting was regarded as an equivalent elastic boundary problem by taking advantage of Saint-Venant’s Theorem. At last, a 3D model in finite element software FLAC3D accepted the constitutive parameters, uniformly distributed mutative loading, and the cylindrical attenuation law to predict the velocity curves and effective tensile curves for calculating safety criterion formulas of surrounding rock and tunnel liner after verifying well with the in situ monitoring data. Qingwen Li, Lan Qiao, Gautam Dasgupta, Siwei Ma, Liping Wang, and Jianghui Dong Copyright © 2015 Qingwen Li et al. All rights reserved. Vibration Control by Means of Piezoelectric Actuators Shunted with LR Impedances: Performance and Robustness Analysis Tue, 19 May 2015 08:20:49 +0000 http://www.hindawi.com/journals/sv/2015/704265/ This paper deals with passive monomodal vibration control by shunting piezoelectric actuators to electric impedances constituting the series of a resistance and an inductance. Although this kind of vibration attenuation strategy has long been employed, there are still unsolved problems; particularly, this kind of control does suffer from issues relative to robustness because the features of the electric impedance cannot be adapted to changes of the system. This work investigates different algorithms that can be employed to optimise the values of the electric components of the shunt impedance. Some of these algorithms derive from the theory of the tuned mass dampers. First a performance analysis is provided, comparing the attenuation achievable with these algorithms. Then, an analysis and comparison of the same algorithms in terms of robustness are carried out. The approach adopted herein allows identifying the algorithm capable of providing the highest degree of robustness and explains the solutions that can be employed to resolve some of the issues concerning the practical implementation of this control technique. The analytical and numerical results presented in the paper have been validated experimentally by means of a proper test setup. M. Berardengo, A. Cigada, S. Manzoni, and M. Vanali Copyright © 2015 M. Berardengo et al. All rights reserved. Compliance Matrix of a Single-Bent Leaf Flexure for a Modal Analysis Mon, 18 May 2015 14:42:21 +0000 http://www.hindawi.com/journals/sv/2015/672831/ We present a compliance matrix for a single-bent leaf flexure (SBLF) that shows the relationships between the deformations and the six-axis loads applied to the SBLF. Higher-order beam theory that considers the variable shear and warping effect is considered in bending. The partially restrained warping at the junction between elements is also considered in torsion. The total strain energy is calculated, and the complete compliance matrix is derived by using Castigliano’s second theorem. Sensitivity analyses over the compliance elements are performed and verified via finite element analysis (FEA). The results show that the derived compliance elements are in good agreement with FEA, with errors of less than 7.6%. We suggest that theoretical compliance elements considering variable shear and warping in bending and partially restrained warping in torsion give highly accurate design equations representing the compliant mechanism of the SBLF. The present work could be used in a modal analysis of a single-bent leaf flexure. Nghia-Huu Nguyen, Moo-Yeon Lee, Ji-Soo Kim, and Dong-Yeon Lee Copyright © 2015 Nghia-Huu Nguyen et al. All rights reserved. Adaptive Neural-Sliding Mode Control of Active Suspension System for Camera Stabilization Sun, 17 May 2015 11:45:11 +0000 http://www.hindawi.com/journals/sv/2015/542364/ The camera always suffers from image instability on the moving vehicle due to the unintentional vibrations caused by road roughness. This paper presents a novel adaptive neural network based on sliding mode control strategy to stabilize the image captured area of the camera. The purpose is to suppress vertical displacement of sprung mass with the application of active suspension system. Since the active suspension system has nonlinear and time varying characteristics, adaptive neural network (ANN) is proposed to make the controller robustness against systematic uncertainties, which release the model-based requirement of the sliding model control, and the weighting matrix is adjusted online according to Lyapunov function. The control system consists of two loops. The outer loop is a position controller designed with sliding mode strategy, while the PID controller in the inner loop is to track the desired force. The closed loop stability and asymptotic convergence performance can be guaranteed on the basis of the Lyapunov stability theory. Finally, the simulation results show that the employed controller effectively suppresses the vibration of the camera and enhances the stabilization of the entire camera, where different excitations are considered to validate the system performance. Feng Zhao, Mingming Dong, Yechen Qin, Liang Gu, and Jifu Guan Copyright © 2015 Feng Zhao et al. All rights reserved. A Cable-Passive Damper System for Sway and Skew Motion Control of a Crane Spreader Tue, 12 May 2015 08:32:34 +0000 http://www.hindawi.com/journals/sv/2015/507549/ While the crane control problem is often approached by applying a certain active control command to some parts of the crane, this paper proposes a cable-passive damper system to reduce the vibration of a four-cable suspended crane spreader. The residual sway and skew motions of a crane spreader always produce the angle deflections between the crane cables and the crane spreader. The idea in this paper is to convert those deflections into energy dissipated by the viscous dampers, which connect the cables and the spreader. The proposed damper system is effective in reducing spreader sway and skew motions. Moreover, the optimal damping coefficient can be found analytically by minimizing the time integral of system energy. The numerical simulations show that the proposed passive system can assist the input shaping control of the trolley motion in reducing both sway and skew responses. La Duc Viet and Youngjin Park Copyright © 2015 La Duc Viet and Youngjin Park. All rights reserved.