Optimal Sensor Placement for Enhanced Efficiency in Structural Health Monitoring of Medium-Rise Buildings.

Output-only modal analysis using ambient vibration testing is ubiquitous for the monitoring of structural systems, especially for civil engineering structures such as buildings and bridges. Nonetheless, the instrumented nodes for large-scale structural systems need to cover a significant portion of the spatial volume of the test structure to obtain accurate global modal information. This requires considerable time and resources, which can be challenging in large-scale projects, such as the seismic vulnerability assessment over a large number of facilities. In many instances, a simple center-line (stairwell case) topology is generally used due to time, logistical, and economic constraints. The latter, though a fast technique, cannot provide complete modal information, especially for torsional modes. In this research, corner-line instrumented nodes layouts using only a reference and a roving sensor are proposed, which overcome this issue and can provide maximum modal information similar to that from 3D topologies for medium-rise buildings. Parametric studies are performed to identify the most appropriate locations for sensor placement at each floor of a medium-rise building. The results indicate that corner locations at each floor are optimal. The proposed procedure is validated through field experiments on two medium-rise buildings.

Numerical simulation of cable sheath damage detection based on torsional mode guided wave.

In view of the cracking, sag, and damage of sheath caused by the load effect and external force impact of power cable, the echo parameters of cable sheath damage detection based on the characteristics of torsional guided wave propagation are studied in this work. According to the Navier displacement equilibrium equation, the dispersion curve of a magnetostrictive guided wave of the cable sheath was solved, and the T(0,1) mode with a group velocity of 1198.8 m/s and no dispersion was selected. Furthermore, while considering the excitation frequency, loss rate, and direction of the damaged section, the displacement field and the echo characteristic parameters of guided wave in the cable sheath were solved. Moreover, by analyzing the time-domain signals of damaged section echo, the cubic fitting function for the loss rate of the damaged section and the damaged section echo coefficient were obtained, which can effectively characterize the quantitative relationship between the damaged location, size, and guided wave echo of the cable sheath.

Axial Stress Measurement of Steel Tubes Using Ultrasonic Guided Waves.

Axially loaded steel tubes are widely used as primary structural members in civil engineering structures. In this paper, a stress measurement method for axially loaded steel tubes is developed based on the linear relationship between the group velocity of guided waves in the steel tube and the stress of the steel tube. The propagation modes of guided waves in a typical steel tube are analyzed using semi-analytical finite element method. A torsional mode T(0,1) is adopted to conduct the measurement. Experiments are carried out to calibrate the linear relationship between the group velocity of guided waves in a steel tube and the stress of the steel tube. The calibrated linear relationship is verified by another round of experiments on the same steel tube specimen. There is an average error of 8.2% between the stresses predicted by the calibrated linear equation and those obtained from strain gauges. Via this study, the guided wave-based stress measurement method has been successfully extended to axially loaded steel tubes.

Experimental Characterization of the Torsional Damping in CFRP Disks by Impact Hammer Modal Testing.

Composite materials are widely used for their peculiar combination of excellent structural, mechanical, and damping properties. This work presents an experimental study on the dissipation properties of disk-shaped composite specimens exploiting vibration tests. Two different polymer matrix composites with the same number of identical laminae, but characterized by different stacking sequences, namely unidirectional and quasi-isotropic configurations, have been evaluated. An ad-hoc steel structure was designed and developed to reproduce an in-plane torsional excitation on the specimen. The main idea of the proposed approach relies on deriving the damping properties of the disks by focusing on the modal damping of the overall vibrating structure and, in particular, using just the first in-plane torsional deformation mode. Experimental torsional damping evaluations were conducted by performing vibrational hammer excitation on the presented setup. Two methods were proposed and compared, both relying on a single-degree-of-freedom (SDOF) approximation of the measured frequency response function (FRF).

Comparative studies between longitudinal and torsional modes in phacoemulsification, using active fluidics technology along with the intrepid balanced tip.

PURPOSE: To compare and report the intra- and postoperative outcomes of phacoemulsification between longitudinal (LPKE) and torsional (TPKE) mode, using active fluidics along with the intrepid balanced tip. METHODS: This single center prospective randomized comparative study comprised a total 108 consecutive eyes of 108 patients having senile cataract subdivided into nuclear opalescence (NO) grades II-IV according to the lens opacities classification system III (LOCS III). Cataracts of each grade were randomly assigned to two groups LPKE (n = 54) and TPKE (n = 54) mode, who were operated on by the same surgeon using same machine (Centurion® Alcon Laboratories, Inc., USA) having features of both active fluidics and intrepid balanced tip. Pre-, intra-, and postoperative evaluations were done independently by a different author, who was masked to the surgical procedures. Patients were evaluated on the postoperative days (PODs) 1, 7, 15, and 28. Intraoperative outcome measures were cumulative dissipated energy (CDE) and ultrasound time (UST). Postoperative outcome measures were endothelial cell loss (ECL), central corneal thickness (CCT), and best-corrected visual acuity (BCVA). RESULTS: Age, gender, and NO-grade distribution among two modes were comparable (P > 0.05). Difference of CDE and UST between modes were found to be significant (P < 0.001) in favor of TPKE with all NO-grades. TPKE mode performs better than LPKE mode with regard to ECL, CCT-change, and BCVA-change, although the differences were found to be insignificant (P > 0.05). CONCLUSION: When using active fluidics along with the intrepid balanced tip, TPKE mode appeared to be a more efficient mode of PKE with reduced mean UST and CDE across all NO-grades, as compared to LPKE mode. However, ECL, CCT-change, and BCVA-change were seemed to be comparable between the two modes.

Effect of torsional mode phacoemulsification on cornea in patient with age-related cataract / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To study the effect of torsional mode phacoemulsification on cornea in patient with age-related cataract.METHODS: Totally 161 age-related cataract patients (196 eyes) were assigned randomly to phacoemulsification by torsional mode(Group A) or conventional ultrasound mode (Group B) in our hospital from January 2012 to December 2014.The intraoperative data of effective ultrasound time(UST)and effective cumulative dissipated energy(CDE) were recorded.Postoperative outcomes and the change of the best corrected visual acuity(BCVA),corneal edema degree(CED),central corneal thickness(CCT) and endothelial cell count were also recorded and compared.RESULTS: For grade Ⅰ,Ⅱ,Ⅲ and Ⅳ nuclear density,the mean UST and mean CDE were significantly lower in Group A.The average BCVA of Group A was better than Group B at 1 and 7d after surgery.But at 30d postoperative,there was no statistical difference between these two groups(P>0.05).The corneal clarity and the mean change of central thickness showed significantly less corneal edema in Group A than Group B in 1 and 7d postoperatively.This difference was no longer found significantly at 30d after surgery(P>0.05).At 7 and 30d postoperative,the endothelial cells in Group B were lower than in Group A.CONCLUSION: By reducing the effective UST and CDE intraoperatively,the main effect of torsional mode phacoemulsification on cornea shows less damage to endothelium cells,and patients get better prognosis.But the damage to cornea by torsional mode phacoemulsification isn`t fundamentally solved.

Quantitative assessment of contact and non-contact lateral force calibration methods for atomic force microscopy.

Atomic Force Microscopy (AFM) has been widely used for measuring friction force at the nano-scale. However, one of the key challenges faced by AFM researchers is to calibrate an AFM system to interpret a lateral force signal as a quantifiable force. In this study, five rectangular cantilevers were used to quantitatively compare three different lateral force calibration methods to demonstrate the legitimacy and to establish confidence in the quantitative integrity of the proposed methods. The Flat-Wedge method is based on a variation of the lateral output on a surface with flat and changing slopes, the Multi-Load Pivot method is based on taking pivot measurements at several locations along the cantilever length, and the Lateral AFM Thermal-Sader method is based on determining the optical lever sensitivity from the thermal noise spectrum of the first torsional mode with a known torsional spring constant from the Sader method. The results of the calibration using the Flat-Wedge and Multi-Load Pivot methods were found to be consistent within experimental uncertainties, and the experimental uncertainties of the two methods were found to be less than 15%. However, the lateral force sensitivity determined by the Lateral AFM Thermal-Sader method was found to be 8-29% smaller than those obtained from the other two methods. This discrepancy decreased to 3-19% when the torsional mode correction factor for an ideal cantilever was used, which suggests that the torsional mode correction should be taken into account to establish confidence in Lateral AFM Thermal-Sader method.

Effect of torsional mode phacoemulsification on cornea in eyes with/without pseudoexfoliation.

AIM: To evaluate the effect of torsional mode phacoemulsification on central corneal thickness, corneal endothelial cell density, and morphology in eyes with/without pseudoexfoliation (PEX) syndrome. METHODS: Fourty-two consecutive patients with and 42 patients without PEX as a control group scheduled for cataract surgery was studied. Phacoemulsification, using OZiL IP system, was performed with quick chop technique. Using noncontact specular microscopy, the central endothelial cell density (ECD), coefficient of variation, percentage of hexagonal cells, and the central corneal thickness (CCT) were evaluated preoperatively and postoperatively at 1, 7 and 30d. RESULTS: The ECD in PEX syndrome was statistically significantly lower than that in the control group preoperatively and postoperatively (P≤0.001). Percentage change in ECD was statistically significantly higher in PEX than that in control group after surgery follow up (P≤0.04). There was no statistically significant difference between both groups comparing percentage of hexagonal cells and coefficient of variation in the cell size before and after the surgery. At 1 and 7d after surgery, percentage change in CCT was statistically significantly higher in PEX group than that in the control group (P≤0.041). CONCLUSION: Although torsional mode phacoemulsification and intraocular lens (IOL) implantation provided a safe and favorable surgical outcome in patients with/without PEX, torsional phacoemulsification led to significantly higher ECD loss in the PEX group than that in the control group during the whole follow up period. In addition, more corneal swelling in the PEX group than that in the control group during the early postoperative period has indicated that the corneal endothelium, in presence of PEX endotheliopathy, seems to be more susceptible to the effects of phacoemulsification surgery in eyes with PEX. The increased risk of anterior chamber manipulations in patients with PEX should be taken into account for an increased risk of bullous keratopathy.

Torsional mode phacoemulsification: effective, safe cataract surgery technique of the future.

PURPOSE: To compare various outcome measures using torsional mode and longitudinal mode in the phacoemulsification of cataract with different nuclear densities. SETTING: Magrabi Eye Hospitals, Kingdom of Saudi Arabia. DESIGN: A randomized comparative clinical study. MATERIALS AND METHODS: This study includes 200 eyes of 156 patients (100 in the ultrasound longitudinal "US" group and 100 in the torsional group). All eyes received AcrySof((R)) single piece intraocular lens (Alcon Surgical, Fort Worth, TX). The primary outcome measures were ultrasound time (UST), cumulative dissipated energy (CDE), and surgical complications. Postoperative outcome measures were the degree of corneal edema on the first postoperative day and final best corrected visual acuity (BCVA) and CCT (central corneal thickness). RESULTS: The differences in UST and CDE between subgroups of nucleus hardness were statistically significant (P < 0.01). The UST and CDE consistently increased in eyes with higher grades of nucleus density. On day one, the mean BCVA was 0.61 +/- 0.13 decimals in the ultrasound (US) group and 0.67 +/- 0.11 decimals in the torsional group (significant P < 0.05). Corneal edema was significantly less in the torsional group (P < 0.05). At 30 days, the mean BCVA was 0.94 +/- 0.22 decimals in the US group and 1.0 +/- 0.12 decimals in the torsional group but this difference was not statistically different (P > 0.05). CONCLUSIONS: The torsional mode provides an effective and safe method for cataract removal with lower energy usage as compared to longitudinal traditional phacoemulsification. However, the final visual outcome was similar for both study groups.

Clinical Outcomes of Cataract Surgery Using Torsional Mode Phacoemulsification and Soft Shell Technique

PURPOSE: To evaluate the additional protective effect of the soft shell technique on corneal endothelial cells in torsional mode phacoemulsification. METHODS: Torsional mode phacoemulsification was performed on 60 eyes in 38 patients who were diagnosed with moderate cataracts. Thirty eyes were assigned to the soft shell technique group, and a control group with 30 eyes using only cohesive viscoelastics was created to evaluate ultrasound (US) time, mean US intensity, cumulative dissipated energy (CDE), and amount of used balanced salt solution. Corneal endothelium and corneal thickness were measured before and after the procedure. RESULTS: There were no statistically significant differences in US time, mean US intensity, cumulative dissipated energy, and dosage of the balanced salt solution between the two groups. There were no statistically significant differences between the two groups in postoperative central corneal thickness. Corneal endothelial cell densities decreased significantly after surgery in both groups, but there were no statistically significant differences between the two groups. CONCLUSIONS: There are no significant differences in the intensity of ultrasound, the density of corneal endothelial cells or the thickness of the cornea between the two groups. Therefore, the soft shell technique is not needed under torsional mode phacoemulsification.

The efficiency and safety of torsional mode phacoemulsification for cataract extraction / 眼科

0.05).At post- operative 30 days and 90 days,ECD were(6.39?0.90)%,(6.54?1.24)% respectively in the torsional group and(13.17?1.78)%, (13.67?2.36)% respectively in the US group,the differences between two groups were statistically(P0.05).Conclusion The torsional mode may provide more effective lens re- moval with a lower level of phacoemulsification time and energy.It can reduce the ultrasound energy and the intraocular trauma.(Oph- thalmol CHN,2008,17:82-85)