Measurement and Analysis of Roadway Deformation and Stress under Mining-Induced Stress

Small coal pillars, which are used to protect roadways, have a significant influence on mining operations and roadway stability and safety. Consequently, the optimal width of coal pillars that provides suitable performance under mining-induced stress must be determined accurately. Based on the deformation data of the surrounding rock along the gob roadway of the 13318 working face in Xieqiao Coal Mine, we analyzed the surface deformation data of the roadway and the displacement of the deep surrounding rock of the roadway under the action of mining-induced stress herein. The separation fractures of the low side of the roadway can be divided into four zones: 0–2 m, 2–5 m, 5–9 m, and 9–11 m. The absolute displacement of the surrounding rock relative to the center of the roadway in the 0–2 m zone was large, and the displacement region in the side of the roadway extended from 0 m to 11 m. The separation fractures of the high side of the roadway can be divided into three zones: 0–3 m, 3–5 m, and 5–5.5 m. The absolute displacement of the surrounding rock relative to the center of the roadway in the 0–3 m zone was large, whereas the deformation separation of the coal pillar was small. The surrounding rock in the 5–5.5 m zone also exhibited absolute displacement relative to the center of the roadway. Furthermore, the stress increased faster on the low side of the roadway than the high side; the core stress region on the high side occurred at approximately 3 m, whereas that on the low side occurred at approximately 8 m. The findings obtained herein can help determine the optimal preset width of small pillars.

Absolute Displacement-Based Formulation for Peak Inter-Story Drift Identification of Shear Structures Using Only One Accelerometer

Only one accelerometer is used in this paper for estimating the maximum inter-story drifts and time histories of the relative displacements of all stories of multi-degree-of-freedom (MDOF) shear structures under seismic excitation. The calculation based on the data of one sensor using a conventional method is unstable, and when modal coordinates are used, higher modes should be included, which is different from the estimation based on the responses recorded by many accelerometers. However, the parameters of the higher modes of structures are difficult to obtain from structures under small excitations. To overcome this difficulty, the recorded absolute acceleration is converted into the absolute displacement, and a state-space equation is formulated. Numerical simulations of a nine-story structure were conducted to check the applicability, robustness against environmental noise, and optimal installation location of the accelerometer of the proposed approach. In addition, the effects of the higher modes were analyzed in terms of the number of accelerometers and type of response. Finally, the proposed approach was validated in a simple experiment. The results indicate that it can accurately estimate the time histories of the relative displacements and maximum inter-story drifts of all floors when one accelerometer is used and just the first two modal parameters are incorporated in the model. Furthermore, the approach is robust against environmental noise.

Outdoor recreation experiences at Diamond Lake, Oregon (USA), before, during and after a biological disruption.

This chapter examines recreational displacement in response to a unique management and biological event: the introduction of the non-native cyprinid tui chub (Gila bicolor pectinifer) into Diamond Lake. The study demonstrates the behavioural reactions of visitors in response to a management action or a 'controlled' decision to intervene in the impacts of the invasive tui chub. About half of the Diamond Lake visitors who still visit the lake exhibited some temporal and/or spatial displacement behaviours. Visitors at Diamond Lake dealt with the lake's closure by remaining at the lake but participating in another activity (activity substitution) or by moving to an alternative location to continue their primary activity (spatial displacement/resource substitution). More than one-third of all Diamond Lake visitors chose not to recreate during that period (temporal displacement) and 17% changed both their activity and location (absolute displacement).

Outdoor recreation experiences at Diamond Lake, Oregon (USA), before, during and after a biological disruption.

This chapter examines recreational displacement in response to a unique management and biological event: the introduction of the non-native cyprinid tui chub (Gila bicolor pectinifer) into Diamond Lake. The study demonstrates the behavioural reactions of visitors in response to a management action or a 'controlled' decision to intervene in the impacts of the invasive tui chub. About half of the Diamond Lake visitors who still visit the lake exhibited some temporal and/or spatial displacement behaviours. Visitors at Diamond Lake dealt with the lake's closure by remaining at the lake but participating in another activity (activity substitution) or by moving to an alternative location to continue their primary activity (spatial displacement/resource substitution). More than one-third of all Diamond Lake visitors chose not to recreate during that period (temporal displacement) and 17% changed both their activity and location (absolute displacement).

Διερεύνηση της συμπεριφοράς και προτάσεις σχεδιασμού κατασκευών σε σεισμούς κοντινού πεδίου

Στην παρούσα διατριβή αναπτύχθηκε μια νέα μέθοδος για τον προσδιορισμό των παλμών ταχύτητας που εντοπίζονται κυρίως ε καταγραφές στην περιοχή κοντά στο ρήγμα. Η μέθοδος χρησιμοποιεί το κυματίδιο των Mavroeides & Papageorgiou (2003) και προσδιορίζει τα χαρακτηριστικά του παλμού (περίοδο Tp, εύρος A, αριθμό κύκλων γ, φάση ν και χρονική θέση) με μια αυτοματοποιημένη μέθοδο, για την οποία έχει αναπτυχθεί κατάλληλο λογισμικό. Η μέθοδος προσδιορίζει την περίοδο του παλμού από το γινόμενο των φασμάτων ταχυτήτων και μετακινήσεων, ενώ οι υπόλοιπες παράμετροι του κυματιδίου προσδιορίζονται με τη βοήθεια της Αθροιστικής Απόλυτης Μετακίνητης (Cumulative Absolute Displacement - CAD) και τη διασυσχέτιση των χρονοϊστοριών παλμού και καταγραφής. Η αξιοπιστία της μεθόδου ελέγχθηκε με τη βοήθεια των αποτελεσμάτων της μελέτης του Baker (2007). Επειδή διαπιστώθηκε ότι σε αρκετές περιπτώσεις υπάρχουν περισσότεροι του ενός σημαντικοί παλμοί, όπως υποστηρίζουν και άλλοι ερευνητές, η μέθοδος επεκτάθηκε για τον εντοπισμό τους. Η επέκταση γίνεται αφαιρώντας αλγεβρικά τη χρονοϊστορία ταχυτήτων του παλμού από αυτή της καταγραφής, και χρησιμοποιώντας το σήμα που εναπομένει για την επανάληψη της μεθόδου. Κατά την εξαγωγή παλμών διαπιστώθηκε ότι τα κριτήρια σημαντικότητας του 1ου παλμού δεν μπορούν να εφαρμοστούν για τους υπόλοιπους, και διατυπώθηκε ένα νέο κριτήριο για τη σημασία των παλμών, σύμφωνα με το οποίο οι επόμενοι παλμοί είναι σημαντικοί εφόσον συμπίπτουν χρονικά με τον πρώτο και βρίσκονται στο πρώτο τμήμα αυτού. Βασιζόμενοι στη διαπίστωση της σημασίας της διάρκειας του 1ου παλμού, προτάθηκε η αντικατάσταση της καταγραφής από το τμήμα αυτής που αντιστοιχεί στον 1ο παλμό, εφόσον η περίοδος της κατασκευής που εξετάζεται δεν ξεπερνά πάνω από 50% την περίοδο του παλμού. Στη συνέχεια, πραγματοποιήθηκε στατιστική διερεύνηση των παραμέτρων του παλμού, και διαπιστώθηκε συσχέτιση της περιόδου με το μέγεθος και την απόσταση, του εύρους με την απόσταση ενώ οι παράμετροι γ και ν διαπιστώθηκε ότι δεν συσχετίζονται με κάποιες μεταβλητές και προβλέπονται μέσα από κατανομές (γάμμα και ομοιόμορφη αντίστοιχα). Τέλος, προτάθηκε η τροποποίηση του φάσματος σχεδιασμού ανάλογα με την απόσταση κατά Joyner-Boore και το μέγεθος του σεισμού. Η περίοδος ορίζει τις νέες περιόδους Tc, Td, ενώ το εύρος τη φασματική ψευδοταχύτητα και από αυτή την φασματική ψευδοεπιτάχυνση

The nonlinear vibrations of a vertical hard gyroscopic rotor with nonlinear characteristics

The paper considers an impact of viscous linear and cubic nonlinear damping of the elastic support on nonlinear vibrations of a vertical hard gyroscopic unbalanced rotor, taking into account nonlinear stiffness of the support material. Analyzing the research results shows that linear and cubic nonlinear damping can significantly suppress the resonance peak of the fundamental harmonic, eliminate the jumping phenomena of the nonlinear system. In non-resonance areas where the velocity is higher than the critical one, cubic nonlinear damping, unlike linear one, can slightly suppress amplitude of the rotor vibration. Therefore, in the high-velocity area, only nonlinear damping can maintain performance of a vibration isolator. In resonance area, an increase in linear or cubic nonlinear damping significantly suppresses the ability to absolute displacement. In non-resonance area, where the rotational velocity is lower than the critical one, they have almost no impact on ability to absolute displacement. In high velocity area, an increase in nonlinear damping may slightly increase the moment of force transmissibility, but linear damping has almost no impact on it. The obtained results can be successfully used to produce passive vibration isolators used for damping the vibrations of rotary machines, including gyroscopic ones.