848 research outputs found
Development of temperature-robust damage factor based on sensor fusion for a wind turbine structure
No full textWind power systems have gained much attention due to the relatively high reliability, maturity in technology and cost competitiveness compared to other renewable alternatives. Advances have been made to increase the power efficiency of the wind turbines while less attention has been focused on structural integrity assessment of the structural systems. Vibration-based damage detection has widely been researched to identify damages on a structure based on change in dynamic characteristics. Widely spread methods are natural frequency-based, mode shape-based, and curvature mode shape-based methods. The natural frequency-based methods are convenient but vulnerable to environmental temperature variation which degrades damage detection capability; mode shapes are less influenced by temperature variation and able to locate damage but requires extensive sensor instrumentation which is costly and vulnerable to signal noises. This study proposes novelty of damage factor based on sensor fusion to exclude effect of temperature variation. The combined use of an accelerometer and an inclinometer was considered and damage factor was defined as a change in relationship between those two measurements. The advantages of the proposed method are: 1) requirement of small number of sensor, 2) robustness to change in temperature and signal noise and 3) ability to roughly locate damage. Validation of the proposed method is carried out through numerical simulation on a simplified 5 MW wind turbine model.close
Chi-Sung's Contribution to Sung-hsiao（宋学）: Especially on his "Fei-han"
No full textChi-Sung (契嵩), a Buddhist priest of Sham-sect (禅宗) in the era of Sung (宋), was also a learned Confucian scholar. His "Fei-han (非韓)" was written to criticize the anti-Buddhistic views of Han-Yu (韓愈), -a noted Confucian scholar in the era of Tang (唐), - which are to be observed in his "Yuan-tao (原道)" and other writings. The author of this article intends, through the examination of Chi-Sung's opinions on "Chung-yang (中庸)" and "Chou-i (周易)", to see how and in what respect his new points of view influenced his contemporary Confucian scholars and, influencing them, contributed to the formation of new sect of learning in the era of Sung.Article信州大学文理学部紀要. 第1部, 人文・社会 9: 49-59(1960)departmental bulletin pape
Optimization of critical factors affecting the performance of an allergen chip for the analysis of an allergen-specific human IgE in serum
No full textA sensitive and multiplexed assay of allergen-specific human immunoglobulin E (IgE) is of great significance in the precise diagnosis of allergies. We report on the optimization of critical factors for chip-based analysis of IgE in human serum with a high reliability. Extracts of two mite species were used as model allergens, and were spotted onto a glass slide for the construction of an allergen chip. Respective allergen-specific IgE in human serum was analyzed by using biotinylated anti-human IgE and a streptavidin-Cy3 conjugate. Factors affecting the performance of the allergen chip were investigated and optimized. Especially, the effect of additives, the concentrations of biotinylated anti-human IgE and the streptavidin-Cy3 conjugate, the serum dilution factor, and the concentration of allergen extract as a capturing agent were examined in detail. Under the optimized conditions, a chip-based analysis for sera from 43 patients revealed a reliable and reproducible diagnosis of respective allergies, showing a good correlation with a conventional CAP assay
Decentralized Strategies for Monitoring Structures using Wireless Smart Sensor Networks
No full textDriven by the needs to address problems with our rapidly aging civil infrastructure, structural health monitoring (SHM) has arisen as an important tool to improve maintenance and operation. Introduced as a promising alternative to the traditional wired sensors, wireless smart sensors offer unique features (low cost, wireless communication, onboard computation, and small size) that enable deployment of dense array of sensors essential for assessing structural damage. The centralized data collection approach, which the wired sensor system commonly employs, is not suitable to wireless smart sensor networks (WSSNs) due to limitations in the wireless communication; decentralized data aggregation and processing is required in the WSSNs. Rather than collecting uncondensed raw sensor data at a centralized location, in-network data processing, made possible by the onboard computational capability of smart sensors, is utilized to condense the raw data and extract meaningful information. By transferring only the condensed data to the centralized location, data communication over the wireless links can be greatly reduced. Decentralized data aggregation approaches can be placed in two broad categories: (a) independent processing (each node processes sensor data independently), and (b) coordinated processing (sensor nodes collaborate to process sensor data by sharing information). This report outlines the implementation of both decentralized data aggregation approaches for the WSSNs employing Crossbow’s Imote2 smart sensor platform. Design considerations for developing WSSN applications are described herein, including network-wide flow and timing, fault-tolerant feature, and network topology to account for the decentralized data aggregation. WSSN applications introduced in this report can be downloaded at the Illinois SHM Project website (http://shm.cs.uiuc.edu).Submitted by Sung Han Sim ([email protected]) on 2009-11-21T21:39:22Z
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Sensory cue integration of visual and vestibular stimuli: a case study for 4D rides
No full textThis paper investigated human self-motion perception through the visual and vestibular sensory systems under the context of virtual reality (VR) and 4D. Consistently with general 4D riding applications, we designed and used sinusoidal motions as stimuli, which resembled simple roller coaster rides moving in three directions of pitch, surge, and heave. Based on the Bayesian integration model, we experimented to determine the uncertainty involved in the two sensory systems and their relative contributions. We factored in small sensory discrepancies between the visual and vestibular cues and visually noticeable obstacles that could distract viewers. We found that the vestibular system contributed more dominantly to the perception in the ratio of 7:3 than the vision, demonstrating vestibular capture. We also discovered that the visual scenes that contain eye-catching elements and pure optical flows can hamper self-motion perception while increasing the perceptual uncertainty. Our findings can serve as a basis for designing motion effects for VR and 4D applications, especially in situations where multiple sensory systems are stimulated simultaneously. © 2023, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.11Nsciescopu
Virtual Sensing for Structural Health Monitoring of Off-shore Structures
No full textDepartment of Urban and Environmental Engineering(Urban Infrastructure Engineering)Offshore structures are generally subjected to harsh environment with strong tidal current and wind loading, which demands robust and reliable Structural Health Monitoring (SHM) to avoid any catastrophic failure. The growing size, complexity, and harsh environment of offshore structures lead to difficulties in sensor deployment and maintenance. Response at critical locations in complex offshore rigs are inaccessible during sensor deployment. Moreover, their operational environment demands frequent sensor maintenance for uninterrupted monitoring. Virtual sensing addresses these issues by estimating unmeasured responses with the help of measured responses. This dissertation delineates a virtual sensing method based on Kalman state estimator to combine multi-sensor data under non-stationary random excitation. The estimation algorithm effectively uses the FE model of a structure to predict and fuse different type of structural response (acceleration, strain, and angular displacement). This study investigates various combinations of sensor fusion to improve the estimation accuracy. In addition, an erroneous model is purposefully used to support the robustness and practicality of estimator. The performance of virtual sensing is successfully verified with numerical and experimental test over simply-supported and bottom fixed off-shore structure. Test results conclude that the unmeasured responses are reasonably recovered form measured responses.ope
Concrete Static Stress Estimation Using Computer Vision-Based Digital Image Processing
No full textDepartment of Urban and Environmental Engineering (Urban Infrastructure Engineering)As increasing interests about structural safety due to occasionally occurring collapse of structures and social infrastructures, efforts to identify and monitor the current state of structure are also increasing. Recently, most structures have been built of concrete, so identification of safety level of concrete structures becomes a critical issue. One of such techniques is to evaluate the current stress state in concrete. This technique is essential in various fields involved in an investigation of tensile stress of tendons in pre- and post-tensioned structures, building remodeling which needs to remove bearing walls and adds other foundations, and identification of load distribution in enlarged concrete structures. In other words, current stress level in concrete is an important factor to check the safety level of the structures in service.
Although it is obvious that a technique for estimating the static stress level of concrete is essential, the method to identify the stress state of the currently used concrete structure is definitely limited. Several efforts for estimating the current stress state have been developed in previous research, including a stress-strain relationship based on elastic theory and a stress relaxation method (SRM) for concrete. These methods in the previous researches have made a certain contribution in this field but practical use in real structures is still inadequate. Therefore, an objective of this study is to develop a static stress estimation technique which can be applied to real concrete structures. This study proposes a method that can measure the static stress level of concrete by incorporating SRM and computer vision-based image processing. Applying a small damage to concrete specimen can release the current stress state and induce stress field change inside concrete around the damage. Computer vision-based measurement can measure the deformation due to this stress field change. This deformation measurement is used in the static stress estimation algorithm developed in this study. The proposed method is validated using several concrete specimens and consequently demonstrates the performance.clos
Performance Assessment of Concrete Crack Repairing Materials using PZT Transducers
No full textDepartment of Urban and Environmental Engineering (Urban Infrastructure Engineering)Concrete is a widely used material in construction of civil infrastructure engineerings such as dams, houses, bridges, and energy plants. Due to shrinkage, rapid dry of the concrete, and overload, cracks are usually generated on the concrete structures and can possibly cause durability-related issues and structural damages. Thus, the concrete crack is an important indicator of potential durability degradation and damage, and the crack should be monitored and repaired through regular maintenance. Indeed, identifying and repairing the concrete cracks using healing materials is important. While most research efforts to date have been devoted to investigation of crack locations and sizes and effective repair, few are evaluating the repairing performance. Therefore, to find an effective nondestructive evaluation (NDE) method for assessing the repairing performance of different healing materials is necessary. Meanwhile, the electro-mechanical impedance (EMI) employing the Piezoelectric Ceramic Lead Zirconate Titanate (PZT) is widely used in structural health monitoring (SHM) as an NDE method in the civil engineering field. The PZT-based EMI is usually applied to detect and locate structural damage in operation. This study used PZT EMI to extract the impedance, which was used as the damage indicator to evaluate the repairing performance of three different materials of the healing cement material from Intchem company, superabsorbent polymer (SAP), and epoxy. A comparison study on the different computation methods of damage index (the root-mean-square deviation (RMSD), the shift of resonance frequency (SRF) and the mean absolute percentage deviation (MAPD)) is also conducted. Results show that the increase of crack depth level and the completing process of repairing crack can be carried out by the change rates of the impedance (admittance) and the shifts of the resonance frequency of PZT sensor in the selected frequency range clearly. .ope
Finite Element Model Updating using Rotational Response
No full textDepartment of Urban Environmental Engineering (Urban Infrastructure Engineering)The Finite Element (FE) models have been used in civil, mechanical and aerospace engineering field for system identification and response simulation under various unexperienced loadings. However, the original FE models are difficult to use directly in simulation because the original FE model is different with the present state of actual structure. Therefore the FE models are updated to minimize the differences with real structure. In the existing FE model updating method, generally translational responses measured by accelerometers have been employed to identify the structural properties and update numerical model controlling parameter. This paper proposes FE model updating method only uses rotational response such as angular velocity measurement because the rotational response is more sensitive to damage than translational response in numerical analysis on simply supported beam. First sensitivity of translational and rotational response is investigated by sensitivity analysis on a numerical simply-supported beam. The FE model updating is carried out for a numerical simply-supported beam using an optimization algorithm which minimizes the gap between responses from the actual structure and the FE model reduce. The used responses in FE model updating are natural frequencies and rotational mode shape obtained from angular velocities measured by gyroscope sensor. The sensitivity analysis shows that rotational responses have higher sensitivity than translational responses to the structural and boundary condition changes. Then, the updated model using existing translational response from the experiment two FE models updated using translational and rotational responses are compared to validate he improvement by proposed FE model updating method. From the experiment, using rotational responses is a good enough in FE model updating compared to existing method, using translational responses.ope
LIGHTWEIGHT AGGREGATE CONCRETE USING PREPLACED CASTING METHOD
No full textDepartment of Urban and Environmental Engineering (Urban Infrastructure Engineering)Lightweight aggregate concrete (LWAC) has an advantage of decreasing the self-weight of the concrete structure, which has been used for concrete infrastructure. However, conventional mixing process can induce the quality problems of lightweight aggregate (LWA) destruction and segregation due to weak strength and low density. Moreover, the high-water absorption capacity of LWA causes the slump loss in the freshly mixed LWAC. In this dissertation, the preplaced casting method is applied to provide a solution of the aforementioned problems of conventional LWAC. It can be achieved by the unique manufacturing process of preplaced casting method by separating the aggregate placement and grout mixing. The preplaced aggregate concrete is fabricated by placing aggregates in the formwork and injecting specially mixed grout mixtures to fill the voids between the aggregate particles. Therefore, the crushing, segregation, and slump loss problems of conventional LWAC can be prevented. Moreover, preplaced casting method allows a large utilization of coarse aggregates, resulting in the density decrease of preplaced LWAC. In the literature, the investigation of preplaced aggregate concrete incorporating normal aggregate was mainly investigated for the repair work and construction of the dam. However, the properties of preplaced LWAC has not been sufficiently investigated. In this dissertation, the physical and mechanical characteristics of preplaced LWAC are analyzed with the evaluation of grout fluidity and filling ability to extend its applications in concrete infrastructures.
First of all, the physical and mechanical characteristic of preplaced LWAC were investigated. Because of the unique manufacturing process of preplaced aggregate concrete, the volume percentage of coarse aggregate is higher than the value of conventional concrete, up to 70%. The quasi-mono and multi-size particles of LWAs used in the dissertation had the volume percentage of 57-61%. Consequently, the density of preplaced LWAC was much lower than that of conventional normal vibrated and self-compacting LWAC. One of the experimental results of preplaced LWAC showed the density of 1,500 kg/m3 and compressive strength of 22 MPa. Compared to conventional normal vibrated concrete, the density of preplaced LWAC is decreased for given coarse LWA, approximately 22%. Other preplaced LWAC specimens incorporating similar bulk density of LWAs had a no big difference in the density. Even though compressive strength of preplaced LWAC is highly decreased compared to normal vibrated LWAC, approximately 30%, both density and compressive strength results of preplaced LWAC were satisfying the specification for structural LWAC.
The elastic properties of concrete are one of the important factors for the structural purpose. The elastic properties of concrete composites concrete influences those of the concrete. The elastic properties of aggregate, matrix, interfacial transition zone (ITZ), and homogenized phase can be used for predicting those of concrete using micromechanical analysis. However, preplaced aggregate concrete has a unique internal structure, fully connected aggregate skeleton. Moreover, the grout penetrated the dry-state LWA, composing an intermediate zone reinforced the aggregate network. These complex homogeneities were considered in a micromechanical four-phase model, from which we predicted the elastic properties of preplaced LWAC. In the model, the equivalent aggregate network was composed of the homogenized connected aggregate network and grout matrix. The thickness of the intermediate zone surrounding each aggregate particle was estimated by the iterative homogenization. The effective modulus of the aggregate network was increased by lowering the w/cm of the grout and stiffening LWAs, which consequently increased the elastic modulus of preplaced LWAC. The elastic properties of preplaced LWAC showed well correspondence with the predicted value. The researches about the physical and mechanical characteristics of preplaced LWAC are useful to understand the comprehensive hardened properties as well as extend its application in the construction filed.
The performance of preplaced aggregate concrete is highly related to the grout mix proportion and its filling ability. Because the smaller particles of LWA than NWA is essential to use high fluidity grout using a high dosage of superplasticizer, the optimized mix design is an important task obtaining target fluidity. The superplasticizer-based grout mix design can be possibly used for obtaining the high fluidity with a minimum amount of superplasticizer. The test was conducted by the analysis of the relation between the fluidity of grout mixture and the adsorption and consumption of superplasticizer polymers onto the surface of hydrating cement particles. Using 6 different PCEs, the critical dosage of superplasticizer was investigated measuring the saturation dosage of superplasticizer polymers. At the critical dosage, the fluidity of cement paste grout was highly increased for all cement paste samples with 6 different superplasticizers due to the abundant amount of adsorbed polymers generating strong dispersion force. Moreover, there was a small increase in the fluidity of cement paste at high PCE dosage. To obtain cost-effective and high fluidity grout, the dosage of superplasticizer should be used satisfying the critical dosage.
Because the grout filling determines the bonding between the aggregate and matrix by filling the interstitial voids, the determination of injectable flow range of grout mixtures is helpful to produce well compacted and quality ensured preplaced NWAC and LWAC. In case of severe filling problems, honeycombing can be easily observable by the visual inspection after demolding the concrete specimen. On the contrary, the internal voids of preplaced aggregate concrete cannot be identified by the same method. Therefore, the ultrasonic pulse velocity (UPV) method is applied to identify the remaining voids in preplaced aggregate concrete. The UPV test has been used for detecting the internal defects of concrete structures by detecting the wave velocity decrease spot. The results of the UPV test was verified with high-resolution inner structure scanning using ??-CT. Based on the reliable void detection analysis, well compacted preplaced aggregate concrete specimens were identified, and measuring the rheological properties of injectable grout mixtures was conducted to determine injectable grout flow range for a given aggregate. All this process can be applicable for determining injectable fluidity of grout mixtures in preplaced aggregate concrete, and helpful to produce high-quality concrete.
The findings of the dissertation provide comprehensive information on preplaced LWAC regarding the grout mix design, grout filling, and hardened properties. Considering the benefits of preplaced LWAC, the transportation cost of preplaced LWAC used precast product is highly decreased. Specifically, preplaced LWAC products would be suitable for polar regions where in-site concrete casting and hardening is difficult. Moreover, preplaced LWAC can be applicable for producing concrete railway, nuclear shield, and precast products. Therefore, it is expected that the investigations of preplaced LWAC would contribute to extending its applications in the concrete infrastructureclos
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