• Smart Structures and Systems
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• v.6 no.3
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• pp.183-196
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• 2010

Monitoring and economical design of alternative energy generators such as wind turbines is becoming increasingly critical; however acquisition of the dynamic output data can be a time-consuming and costly process. In recent years, low-cost wireless sensors have emerged as an enabling technology for structural monitoring applications. In this study, wireless sensor networks are installed in three operational turbines in order to demonstrate their efficacy in this unique operational environment. The objectives of the first installation are to verify that vibrational (acceleration) data can be collected and transmitted within a turbine tower and that it is comparable to data collected using a traditional tethered system. In the second instrumentation, the wireless network includes strain gauges at the base of the structure. Also, data is collected regarding the performance of the wireless communication channels within the tower. In both turbines, collected wireless sensor data is used for off-line, output-only modal analysis of the ambiently (wind) excited turbine towers. The final installation is on a turbine with embedded braking capabilities within the nacelle to generate an "impulse-like" load at the top of the tower. This ability to apply such a load improves the modal analysis results obtained in cases where ambient excitation fails to be sufficiently broad-band or white. The improved loading allows for computation of true mode shapes, a necessary precursor to many conditional monitoring techniques.

• Tribology and Lubricants
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• v.32 no.1
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• pp.1-8
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• 2016

This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.

• Journal of Aerospace System Engineering
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• v.14 no.1
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• pp.16-20
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• 2020

The fatigue happening during the road riding of the vehicle and for the moment the aircraft lands on the runway is closely related to the life cycle of the landing gear, the airframe, the vehicle's suspension, etc. The multiple loads acting on the wheel are longitudinal, lateral, vertical, and braking forces. To study the dynamic characteristics and fatigue stiffness of the vehicle, the dynamic fatigue simulator generally has been used to represent the real road vibration in the lab. It can save time and cost. In hardware, the critical factor in the hydraulic fatigue simulator structure is to decouple each axis and to endure several load vibration. In this paper, the inverse kinematic analysis method derives the magnitude of movement of the hydraulic servo actuator by the coupling after rendering the maximum movement displacement in the axial direction at the center of the dummy wheel. The result of the analysis is that the coupling between the axes is weak to reproduce the real road vibrations precisely.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.305-310
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• 2013

In general, it is difficult to measure dynamic responses of a bridge with stepwise increasing speed of a train during commercial service on a high speed railroad. However, before opening the 2nd stage of the Gyeongbu high speed railroad, there was an opportunity for field tests and measurements of the bridge with stepwise increasing speed(from 170km/ h to 315km/h). The measured responses were compared with the results of a developed bridge/train interaction analysis. Although good agreement was found throughout almost the entire range of speeds, relatively large differences were found in the vicinity of the critical speed at which resonance behavior of the bridge occurs. To investigate the cause of this, reanalyses are performed with re-estimated damping ratios from field tests.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.265-274
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• 2018

The increasing use of curved beams in buildings, vehicles, ships, and aircraft has prompted studies directed toward the development of an accurate method for analyzing the dynamic behavior of such structures. The stability behavior of elastic curved beams has been the subject of a large number of investigations. Solutions of the relevant differential equations have been obtained traditionally using standard finite difference or finite element methods. These techniques require a great deal of computer time as the number of discrete nodes becomes relatively large under the conditions of complex geometry and loading. One of the efficient procedures for the solution of partial differential equations is the method of differential quadrature. The differential quadrature method (DQM) has been applied to a large number of cases to overcome the difficulties of the complex algorithms of programming for the computer, as well as the excessive use of storage due to the conditions of complex geometry and loading. The in-plane buckling of curved beams considering the extensibility of the arch axis was analyzed under uniformly distributed radial loads using the DQM. The critical loads were calculated for the member with various parameter ratios, boundary conditions, and opening angles. The results were compared with the precise results by other methods for cases, in which they were available. The DQM, using only a limited number of grid points, provided results that agreed very well (less than 0.3%) with the exact ones. New results according to diverse variations were obtained, showing the important roles in the buckling behavior of curved beams, and can be used in comparisons with other numerical solutions or with experimental test data.

• International Journal of Computer Science & Network Security
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• v.21 no.11
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• pp.345-353
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• 2021

Cloud computing represent a new era of computing that's forms through the combination of service-oriented architecture (SOA), Internet and grid computing with virtualization technology. Virtualization is a concept through which every cloud is enable to provide on-demand services to the users. Most IT service provider adopt cloud based services for their users to meet the high demand of computation, as it is most flexible, reliable and scalable technology. Energy based performance tradeoff become the main challenge in cloud computing, as its acceptance and popularity increases day by day. Cloud data centers required a huge amount of power supply to the virtualization of servers for maintain on- demand high computing. High power demand increase the energy cost of service providers as well as it also harm the environment through the emission of CO₂. An optimization of cloud computing based on energy-performance tradeoff is required to obtain the balance between energy saving and QoS (quality of services) policies of cloud. A study about power usage of resources in cloud data centers based on workload assign to them, says that an idle server consume near about 50% of its peak utilization power [1]. Therefore, more number of underutilized servers in any cloud data center is responsible to reduce the energy performance tradeoff. To handle this issue, a lots of research proposed as energy efficient algorithms for minimize the consumption of energy and also maintain the SLA (service level agreement) at a satisfactory level. VM (virtual machine) consolidation is one such technique that ensured about the balance of energy based SLA. In the scope of this paper, we explore reinforcement with fuzzy logic (RFL) for VM consolidation to achieve energy based SLA. In this proposed RFL based active VM consolidation, the primary objective is to manage physical server (PS) nodes in order to avoid over-utilized and under-utilized, and to optimize the placement of VMs. A dynamic threshold (based on RFL) is proposed for over-utilized PS detection. For over-utilized PS, a VM selection policy based on fuzzy logic is proposed, which selects VM for migration to maintain the balance of SLA. Additionally, it incorporate VM placement policy through categorization of non-overutilized servers as- balanced, under-utilized and critical. CloudSim toolkit is used to simulate the proposed work on real-world work load traces of CoMon Project define by PlanetLab. Simulation results shows that the proposed policies is most energy efficient compared to others in terms of reduction in both electricity usage and SLA violation.

• International Journal of High-Rise Buildings
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• v.1 no.1
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• pp.37-51
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• 2012

New generation of tall and complex buildings systems are now introduced that are reflective of the latest development in materials, design, sustainability, construction, and IT technologies. While the complexity in design is being overcome by the availability and advances in structural analysis tools and readily advanced software, the design of these buildings are still reliant on minimum code requirements that yet to be validated in full scale. The involvement of the author in the design and construction planning of Burj Khalifa since its inception until its completion prompted the author to conceptually develop an extensive survey and real-time structural health monitoring program to validate all the fundamental assumptions mad for the design and construction planning of the tower. The Burj Khalifa Project is the tallest structure ever built by man; the tower is 828 meters tall and comprises of 162 floors above grade and 3 basement levels. Early integration of aerodynamic shaping and wind engineering played a major role in the architectural massing and design of this multi-use tower, where mitigating and taming the dynamic wind effects was one of the most important design criteria established at the onset of the project design. Understanding the structural and foundation system behaviors of the tower are the key fundamental drivers for the development and execution of a state-of-the-art survey and structural health monitoring (SHM) programs. Therefore, the focus of this paper is to discuss the execution of the survey and real-time structural health monitoring programs to confirm the structural behavioral response of the tower during construction stage and during its service life; the monitoring programs included 1) monitoring the tower's foundation system, 2) monitoring the foundation settlement, 3) measuring the strains of the tower vertical elements, 4) measuring the wall and column vertical shortening due to elastic, shrinkage and creep effects, 5) measuring the lateral displacement of the tower under its own gravity loads (including asymmetrical effects) resulting from immediate elastic and long term creep effects, 6) measuring the building lateral movements and dynamic characteristic in real time during construction, 7) measuring the building displacements, accelerations, dynamic characteristics, and structural behavior in real time under building permanent conditions, 8) and monitoring the Pinnacle dynamic behavior and fatigue characteristics. This extensive SHM program has resulted in extensive insight into the structural response of the tower, allowed control the construction process, allowed for the evaluation of the structural response in effective and immediate manner and it allowed for immediate correlation between the measured and the predicted behavior. The survey and SHM programs developed for Burj Khalifa will with no doubt pioneer the use of new survey techniques and the execution of new SHM program concepts as part of the fundamental design of building structures. Moreover, this survey and SHM programs will be benchmarked as a model for the development of future generation of SHM programs for all critical and essential facilities, however, but with much improved devices and technologies, which are now being considered by the author for another tall and complex building development, that is presently under construction.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.993-999
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• 2008

A girder height limitation is the critical parameter for rapid construction of bridge deck and construction space limitation especially in urban area such as high population area and high density habitats. A standard post-tensioned I-shaped concrete girder usually demands relatively higher girder height in order to retain sufficient moment arm between compression force and tensile force. To elaborate this issue, a small U-shaped section with wide flanges can be used as a possible replacement of I-shaped standard girder. This prestressed concrete box girder allows more flexible girder height adjustment rather than standard I-shaped post-tensioned girder plus additional torsion resistance benefits of closed section. A 30m-long, 1.7m-high and 3.63m-wide actual small prestressed concrete box girder is designed and a laboratory test for its static behaviors by applying 6,200kN amount of load in the form of 4-point bending test was performed. The load-deflection curve and crack patterns at different loading stage are recorded. In addition, to extracting the dynamic characteristics such as natural frequency and damping ratio of this girder, several excitation tests with artificial mechanical exciter with un-symmetric mass are carried out using operational frequency sweep-up. Nonlinear finite element analysis of this 4 point bending test under monotonic static load is investigated and discussed with aids of concrete damaged plasticity formulation using ABAQUS program.

• The KIPS Transactions:PartC
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• v.14C no.6
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• pp.519-524
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• 2007

One of the most important issues on the sensor network with resource limited sensor nodes is prolonging the network lifetime by effectively utilizing the limited node energy. The most representative mechanism to achieve a long lived sensor network is the clustering mechanism which can be further classified into the single hop mode and the multi hop mode. The single hop mode requires that all sensor nodes in a cluster communicate directly with the cluster head(CH) via single hop md, in the multi hop mode, sensor nodes communicate with the CH with the help of other Intermediate nodes. One of the most critical factors that impact on the performance of the existing multi hop clustering mechanism is the cluster size and, without the assumption on the uniform node distribution, finding out the best cluster size is intractable. Since sensor nodes in a real sensor network are distributed non uniformly, the fixed size mechanism may not work best for real sensor networks. Therefore, in this paper, we propose a new dynamic size multi hop clustering mechanism in which the cluster size is determined according to the distance from the sink to relieve the traffic passing through the CHs near the sink. We show that our proposed scheme outperforms the existing fixed size clustering mechanisms by carrying out numerical analysis and simulations.

• Convergence Security Journal
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• v.16 no.2
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• pp.19-23
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• 2016

The design, management, and operation of network infrastructure have evolved during the last few years, leveraging on innovative technologies and architectures. With such a huge trend, due to the flexibility and significant economic potential of these technologies, software defined networking (SDN) and network functions virtualization (NFV) are emerging as the most critical key enablers. SDN/NFV enhancing the infrastructure agility, thus network operators and service providers are able to program their own network functions (e.g., gateways, routers, load balancers) on vendor independent hardware substrate. They facilitating the design, delivery and operation of network services in a dynamic and scalable manner. In NFV, the management and orchestration (MANO) orchestrates other specific managers such as the virtual infrastructure manager (VIM) and the VNF Manager (VNFM). In this paper, we examine the contents of these NFV MANO systematically and proposes a security system in a virtualized environment.