Water impact analysis of space shuttle solid rocket motor by the finite element method

Preliminary analysis showed that the doubly curved triangular shell elements were too stiff for these shell structures. The doubly curved quadrilateral shell elements were found to give much improved results. A total of six load cases were analyzed in this study. The load cases were either those resulting from a static test using reaction straps to simulate the drop conditions or under assumed hydrodynamic conditions resulting from a drop test. The latter hydrodynamic conditions were obtained through an emperical fit of available data. Results obtained from a linear analysis were found to be consistent with results obtained elsewhere with NASTRAN and BOSOR. The nonlinear analysis showed that the originally assumed loads would result in failure of the shell structures. The nonlinear analysis also showed that it was useful to apply internal pressure as a stabilizing influence on collapse. A final analysis with an updated estimate of load conditions resulted in linear behavior up to full load

A wirelessly programmable actuation and sensing system for structural health monitoring

Wireless sensor networks promise to deliver low cost, low power and massively distributed systems for structural health monitoring. A key component of these systems, particularly when sampling rates are high, is the capability to process data within the network. Although progress has been made towards this vision, it remains a difficult task to develop and program ’smart’ wireless sensing applications. In this paper we present a system which allows data acquisition and computational tasks to be specified in Python, a high level programming language, and executed within the sensor network. Key features of this system include the ability to execute custom application code without firmware updates, to run multiple users’ requests concurrently and to conserve power through adjustable sleep settings. Specific examples of sensor node tasks are given to demonstrate the features of this system in the context of structural health monitoring. The system comprises of individual firmware for nodes in the wireless sensor network, and a gateway server and web application through which users can remotely submit their requests

Bayesian model updating using incomplete modal data without mode matching

This study investigates a new probabilistic strategy for model updating using incomplete modal data. A hierarchical Bayesian inference is employed to model the updating problem. A Markov chain Monte Carlo technique with adaptive random-work steps is used to draw parameter samples for uncertainty quantification. Mode matching between measured and predicted modal quantities is not required through model reduction. We employ an iterated improved reduced system technique for model reduction. The reduced model retains the dynamic features as close as possible to those of the model before reduction. The proposed algorithm is finally validated by an experimental example. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Damage detection with small data set using energy-based nonlinear features

This study proposes a new algorithm for damage detection in structures. The algorithm employs an energy-based method to capture linear and nonlinear effects of damage on structural response. For more accurate detection, the proposed algorithm combines multiple damage sensitive features through a distance-based method by using Mahalanobis distance. Hypothesis testing is employed as the statistical data analysis technique for uncertainty quantification associated with damage detection. Both the distance-based and the data analysis methods have been chosen to deal with small size data sets. Finally, the efficacy and robustness of the algorithm are experimentally validated by testing a steel laboratory prototype, and the results show that the proposed method can effectively detect and localize the defects

Sparse generalized pencil of function and its application to system identification and structural health monitoring

ingularity expansion method (SEM) is a system identification approach with applications in solving inverse scattering problems, electromagnetic interaction problems, remote sensing, and radars. In this approach, the response of a system is represented in terms of its complex poles; therefore, this method not only extracts the fundamental frequencies of the system from the signal, but also provides sufficient information about system's damping if its transient response is analyzed. There are various techniques in SEM among which the generalized pencil-of-function (GPOF) is the computationally most stable and the least sensitive one to noise. However, SEM methods, including GPOF, suffer from imposition of spurious poles on the expansion of signals due to the lack of apriori information about the number of true poles. In this study we address this problem by proposing sparse generalized pencil-of-function (SGPOF). The proposed method excludes the spurious poles through sparsity-based regularization with ℓ1-norm. This study is backed by numerical examples as well as an application example which employs the proposed technique for structural health monitoring (SHM) and compares the results with other signal processing methods

Impact of dyslipidemia on cardiovascular risk stratification of hypertensive patients and association of lipid profile with other cardiovascular risk factors: results from the ICEBERG study

Giray Kabakci1, Nevres Koylan2, Baris Ilerigelen3, Omer Kozan4, Kemalettin Buyukozturk2 on behalf of the ICEBERG Investigators1Hacettepe University, Hacettepe School of Medicine, Department of Cardiology, Ankara, Turkey; 2Istanbul University, Istanbul School of Medicine, Department of Cardiology, Istanbul, Turkey; 3Istanbul University, Cerrahpasa School of Medicine, Department of Cardiology, Istanbul, Turkey; 4Dokuz Eylul University, Dokuz Eylul School of Medicine, Department of Cardiology, Izmir, TurkeyBackground: Hypertension, dyslipidemia, and other cardiovascular risk factors are linked epidemiologically, clinically, and metabolically. Intensive/Initial Cardiovascular Examination regarding Blood Pressure levels, Evaluation of Risk Groups (ICEBERG) study focuses on the effect of dyslipidemia on cardiovascular risk evaluation and association of lipid profile with other risk factors.Patients and methods: The ICEBERG study consisted of two sub-protocols: ICEBERG-1, conducted at 20 university hospitals (Referral Group) and ICEBERG-2, conducted at 197 primary healthcare centers (Primary Care Group). Sub-protocol had two patient profiles: patients previously diagnosed with essential hypertension and under medical treatment (Treated Group) and patients with systolic blood pressure ≥130 mmHg or diastolic blood pressure ≥85 mmHg, with no antihypertensive treatment for at least 3 months before inclusion (Untreated Group). Dyslipidemia was evaluated and cardiovascular risk stratification was performed according to ESC/ESH guidelines.Results: More than half of the treated and untreated subjects were classified into high or very high cardiovascular risk groups. In a total of 1817 patients, the percentage of patients in “high” plus “very high” added risk groups increased to 55.2% in Treated Referral Group (p < 0.001), to 62.6% in Untreated Referral Group (p = 0.25) and to 60.7% in Untreated Primary Care Group (p < 0.001), by re-evaluation of patients’ lipid values.Conclusions: Serum lipid levels are useful in stratifying hypertensive patients into cardiovascular risk groups more accurately, for appropriate antihypertensive treatment.Keywords: hypertension, dyslipidemia, cardiovascular diseas

Structural Health Monitoring from the Window Seat of a Passenger Airplane

Recent advances in computer vision and graphics have shown that regular, monocular cameras and video (e.g. cell phone cameras and Digital SLRs) can be used to identify the resonant frequencies of structures, and even image visually subtle operational deflection shapes. This paper is offered as a teaser for that work, focusing specifically on an example that may be of interest to people in the structural health monitoring (SHM) community. The discussion is high-level, and presented in an intentionally casual tone (much of the paper presents an anecdote-about recovering the operational deflection shape of an airplane wing using a cell phone and a dish sponge-using the first person). Our hope is to make this text as accessible and painless to read as possible, with hopes of introducing readers from different engineering disciplines to our related work in computer vision and graphics

Continuous Monitoring of High‐Rise Buildings Using Seismic Interferometry

The linear seismic response of a building is commonly extracted from ambient vibration measurements. Seismic deconvolution interferometry performed on ambient vibrations can be used to estimate the dynamic characteristics of a building, such as its shear-wave velocity and its damping. The continuous nature of the ambient vibrations allows us to measure these parameters repeatedly and to observe their temporal variations. We used 2 weeks of ambient vibrations, recorded by 36 accelerometers that were installed in the Green Building at the Massachusetts Institute of Technology campus, to monitor the shear wavespeed and the apparent attenuation factor of the building. Because of the low strain of the ambient vibrations, we observed small speed changes followed by recoveries. We showed that measuring the velocity variations for the deconvolution functions, filtered around the fundamental-mode frequency, is equivalent to measuring the wandering of the fundamental frequency in the raw ambient vibration data. By comparing these results with local weather parameters, we showed that the air humidity is the dominating factor in the velocity variations of the waves in the Green Building, as well as the main force behind the wandering of the fundamental mode. The one-day periodic variations are affected by both the temperature and the humidity. The apparent attenuation, measured as the exponential decay of the fundamental-mode waveforms, is strongly biased due to the amplitude of the raw vibrations and shows a more complex behavior with respect to the weather measurements. We have also detected normal-mode nonlinear interaction for the Green Building, likely due to heterogeneity or anisotropy of its structure. We found that the temporal behavior of the frequency singlets may be used for monitoring.Royal Dutch-Shell Group (through MIT Energy Initiative)National Science Foundation (U. S.) (Grant Grant EAR-1415907

A Novel Structural Assessment Technique to Prevent Damaged FRP-Wrapped Concrete Bridge Piers from Collapse

Repairing deteriorated concrete bridge piers using externally wrapped fiber reinforced polymer (FRP) composites have been proven as an effective approach. This technique has also been applied to low-rise building structures. Failures in FRP-wrapped concrete structures may occur by flexural failures of critical sections or by debonding of FRP plate from the concrete substrate. Debonding in the FRP/adhesive/concrete interface region may cause a significant decrease in member capacity leading to a premature failure of the system. In this chapter, a novel structural assessment technique aiming at inspecting the near-surface FRP debonding and concrete cracking of damaged FRP-wrapped concrete bridge piers to prevent the structures from collapse is presented. In the first part of this chapter, failure mechanisms of FRP-wrapped concrete systems are briefly discussed. The second part of this chapter introduces a novel structural assessment technique in which far-field airborne radar is applied. In this development, emphasis is placed on inspection of debonding in glass FRP (GFRP)-wrapped concrete cylinders, while the technique is also applicable to beams and slabs with bonded GFRP composites. Physical radar measurements on laboratory specimens with structural damages were conducted and used for validating the technique. Processed experimental measurements have shown promising results for the future application of the technique. Finally, research findings and issues are summarized.National Science Foundation (U.S.) (Grant CMS-0324607)Lincoln Laborator

A robust nanoscale experimental quantification of fracture energy in a bilayer material system

Accurate measurement of interfacial properties is critical any time two materials are bonded—in composites, tooth crowns, or when biomaterials are attached to the human body. Yet, in spite of this importance, reliable methods to measure interfacial properties between dissimilar materials remain elusive. Here we present an experimental approach to quantify the interfacial fracture energy Γ[subscript i] that also provides unique mechanistic insight into the interfacial debonding mechanism at the nanoscale. This approach involves deposition of an additional chromium layer (superlayer) onto a bonded system, where interface debonding is initiated by the residual tensile stress in the superlayer, and where the interface can be separated in a controlled manner and captured in situ. Contrary to earlier methods, our approach allows the entire bonded system to remain in an elastic range during the debonding process, such that Γ[subscript i] can be measured accurately. We validate the method by showing that moisture has a degrading effect on the bonding between epoxy and silica, a technologically important interface. Combining in situ through scanning electron microscope images with molecular simulation, we find that the interfacial debonding mechanism is hierarchical in nature, which is initiated by the detachment of polymer chains, and that the three-dimensional covalent network of the epoxy-based polymer may directly influence water accumulation, leading to the reduction of Γ[subscript i] under presence of moisture. The results may enable us to design more durable concrete composites that could be used to innovate transportation systems, create more durable buildings and bridges, and build resilient infrastructure.National Science Foundation (U.S.) (Grant CMS-0856325