• Tunnel and Underground Space
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• v.24 no.5
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• pp.335-343
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• 2014

Room-and-pillar mining method is one of the most popular underground mining method in the world. If the room-and-pillar mining method is able to be adopted in civil works, it would be highly probable to reduce underground construction costs and to expand a underground structure in use. Therefore, this study aims to analyze the design procedure of unsupported rock pillars which are indispensable to ensure the stability of a room-and-pillar underground structure. Parametric studies on their key design parameters are also carried out for 125 different kinds of design conditions. From the study, the width of a rock pillar is found to show a linear relationship with its corresponding safety factor. The safety factor of a unsupported rock pillar decreased drastically like a negative exponential function as the ratio of room width to pillar width increases in the same rock strength condition. Based on the parametric studies, a design chart to simply evaluate the geometric design parameters of a unsupported rock pillar satisfying a design safety factor is also proposed in this study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.219-237
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• 2020

Rapid economic development and urban population growth have been increasing the necessity for underground space exploration and utilization due to the need of upgrading and expanding the existing infrastructures. TBM has been widely used to construct underground structures with high advance rate and minimal ground disturbance. Two important design parameters, which are available thrust capacity and cutterhead torque, should be estimated for any project in addition to proper selection of TBM type. However, the conventional thrust force and torque estimation model only depends on the empirical equation, which hinders the design process of the optimal thrust hydraulic system and the appropriate hydraulic components. In this study, four thrust and torque calculation models are derived and explained. For TBM design practice, the four estimation models are compared and discussed.

• Tunnel and Underground Space
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• v.24 no.2
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• pp.155-165
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• 2014

Multiple thermal energy storage (TES) caverns can be used for storing thermal energy on a large scale and for a high-aspect-ratio heat storage design to provide good thermal performance. It may also be necessary to consider the use of multiple caverns with a reduced length when a single, long tunnel-shaped cavern is not suitable for connection to aboveground heat production and injection equipments. When using multiple TES caverns, the separation distance between the caverns is one of the significant factors that should be considered in the design of storage space, and the optimal separation distance should be determined based on a quantitative stability criterion. In this paper, we described a numerical approach for determining the optimal separation distance between multiple caverns for large-scale TES utilization. For reliable stability evaluation of multiple caverns, we employed a probabilistic method which can quantitatively take into account the uncertainty of input parameters by probability distributions, unlike conventional deterministic approaches. The present approach was applied to the design of a conceptual TES model to store hot water for district heating. The probabilistic stability results of this application demonstrated that the approach in our work can be effectively used as a decision-making tool to determine the optimal separation distance between multiple caverns. In addition, the probabilistic results were compared to those obtained through a deterministic analysis, and the comparison results suggested that care should taken in selecting the acceptable level of stability when using deterministic approaches.

• Smart Structures and Systems
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• v.23 no.6
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• pp.579-587
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• 2019

In this paper, pounding tuned mass dampers (PTMDs) were designed to mitigate the multi-mode vortex-induced vibration (VIV) of stay cable utilizing the viscous-elastic material's energy-dissipated ability. The PTMD device consists of a cantilever metal rod beam, a metal mass block and a specially designed damping element covered with viscous-elastic material layer. Wind-tunnel experiment on VIV of stay cable model was set up to validate the effectiveness of the PTMD on multi-mode VIV mitigation of stay cable. By analyzing and comparing testing results of all testing cases, it could be verified that the PTMD with viscous-elastic pounding boundary can obviously mitigate the VIV amplitude of the stay cable. Moreover, the installed location and the design parameters of the PTMD device based on the controlled modes of the primary stay cable, would have a certain extent suppression on the other modal vibration of the stay cable, which means that the designed PTMDs are effective among a large band of frequency for the multi-mode VIV control of the stay cable.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.60-70
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• 1999

The longitudinal stability characteristics of a Wing-In-Ground Effect Craft are quite different from that of the conventional airplane due to the existence of force and moment derivatives with regard to height. This stability characteristics plays a great role in designing a safe and efficient WIG due to its potential danger in sea surface proximity. The static and dynamic stability criteria are derived from the motion equations of WIG in the framework of small disturbance theory and discussed in the paper. The static and dynamic stability analyses of a 20-passenger WIG are conducted based on the wind tunnel test data and the dynamic motion behaviors are investigated for the change of the design parameters. Finally, the flying quality of the 20-passenger WIG is analysed at the cruising condition according to the military regulations.

• Geomechanics and Engineering
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• v.29 no.3
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• pp.249-258
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• 2022

A disc cutter is an excavation tool on a tunnel boring machine (TBM) cutterhead; it crushes and cuts rock mass while the machine excavates using the cutterhead's rotational movement. Disc cutter wear occurs naturally. Thus, along with the management of downtime and excavation efficiency, abrasioned disc cutters need to be replaced at the proper time; otherwise, the construction period could be delayed and the cost could increase. The most common prediction models for TBM performance and for the disc cutter lifetime have been proposed by the Colorado School of Mines and Norwegian University of Science and Technology. However, design parameters of existing models do not well correspond to the field values when a TBM encounters complex and difficult ground conditions in the field. Thus, this study proposes a series of machine learning models to predict the disc cutter lifetime of a shield TBM using the excavation (machine) data during operation which is response to the rock mass. This study utilizes five different machine learning techniques: four types of classification models (i.e., K-Nearest Neighbors (KNN), Support Vector Machine, Decision Tree, and Staking Ensemble Model) and one artificial neural network (ANN) model. The KNN model was found to be the best model among the four classification models, affording the highest recall of 81%. The ANN model also predicted the wear rate of disc cutters reasonably well.

• International Journal of Ocean System Engineering
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• v.1 no.2
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• pp.110-119
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• 2011

Numerical and experimental studies were performed to investigate the aerodynamic performance of a thin wing in close vicinity to the ground. The vortex lattice method (VLM) was utilized to simulate the wing in ground (WIG) effect, which included freely deforming wake elements. The numerical results acquired through the VLM were compared to the experimental results. The experiment entailed varying the ground clearance using the DHMTU (Department of Hydromechanics of the Marine Technical University of Saint Petersburg) wing and the WIG craft model in the wind tunnel. The aero-dynamic influence of the design parameters, such as angles of attack, aspect ratios, taper ratios, and sweep angles were studied and compared between the numerical and experimental results associated with the WIG craft. Both numerical and experimental results suggested that the endplate augments the WIG effect for a small ground clearance. In addition, the vortex lattice method simulated the wake deformation following the wing in the influence of the ground effect.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.311-318
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• 2001

RQD is used to evaluate the degree of fracture in the rock mass and is also used as input into rock mass classification scheme, such as RMR and Q-system. However there are some drawbacks of the RQD caused by anisotropy and calculation length. Thus it is important to understand the variation of RQD in 3-D space in order to evaluate the properties of rock mass. The main purpose of this study is to reveal the distribution of RQD in the equal-angle stereo net, to investigate the effects of scanline length and joint frequency and to inquire the effect on the selection of rock mass strength parameters in the numerical analysis. Analysis has been extended to field joint survey data using same method. The results can be applied to contribute for more accurate interpretation of the results of engineering geological survey for better design and construction work.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.97-100
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• 2008

Various flyers in nature have attracted great interests with a recent need for developing versatile and small-size flight vehicles. In the present study, we focus on the flying fish which has been observed to glide a long distance just above a seawater surface. Since previous studies have depended on the field observation or measurement of the physical parameters only, quantitative data of the flying fish flight has not been provided so far. Therefore, we evaluate the wing performance of the flying fish in gliding flight by directly measuring the lift, drag and pitching moment on real flying fish models (Cypselurus hiraii) in a wind tunnel. In addition, we investigate the roles of wing morphology like the enlarged pectoral and pelvic fins, and lateral dihedral angle of pectoral fins. With both the pectoral and pelvic fins spread, the lift-to-drag ratio is larger and the longitudinal static stability is enhanced than those with the pelvic fins folded. From the glide polar, we find that the wing performance of flying fish is equivalent to those of medium-size birds like the petrel, hawk and wood duck. Finally, we examine the effect of water surface underneath the flying fish and find that the water surface reduces the drag and increases the lift-to-drag ratio.

• Tunnel and Underground Space
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• v.14 no.2
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• pp.97-107
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• 2004

Various kinds of rock mass properties, which can be obtained from laboratory tests as well as field tests, can be reasonably applied to the design of earth structures. An extrapolation technique can be used for this application and it generally guarantee its quality from a sufficient amount of test results because it is based on the RMR value in most cases. When the confident RMR can not be obtained because of the insufficient testing results, the Monte Carlo Simulation technique can be introduced fer deducing the proper RMR and this assessed RMR can be reused fur the major input parameters. Authors' proposed method can be verified from the comparison between the results of numerical analysis and the evidences of field site.