Prediction Of Collapse Research Articles

Impact of sleeping position, gravitational force & effective tissue stiffness on obstructive sleep apnoea

Accurate prediction of deformation and collapse of the upper airway during breathing is required for effective and personalised treatment of obstructive sleep apnoea (OSA). While numerical modelling techniques such as fluid–structure interaction (FSI) are promising, an outstanding challenge is to accurately predict the deformation of the airway during breathing and thus the occurrence of OSA. These difficulties arise because the effective stiffness of the soft tissue in the human upper airway varies due to neuromuscular effects on the stiffness of the underlying muscles. In addition, both the elasticity and anisotropy of the soft tissues along the upper airway are poorly characterised. Finally, gravitational effects on anatomic features are yet to be considered. In this study, a validated FSI technique is introduced that allows prediction of the extent and position of the major deformation in the upper airway. This technique is used to analyse the behaviour of the upper airway in the two most common sleeping positions and for a range of effective tissue stiffnesses. The results demonstrate that sleeping position, gravity and soft tissue stiffness (used here as a proxy for neuromuscular effects) are the main factors that affect upper airway collapse. Therefore, this study provides new insights into the mechanisms of OSA and a new methodology that significantly advances the patient-specific treatment of OSA.

The effect of triaxiality on finite element deletion strategies for simulating collapse of full-scale steel structures

Collapse prediction of steel structures should incorporate a finite element model that accounts for ductile fracture through material separation in critical structural members. Finite element deletion approaches have been used successfully in the past to account for fracture in steel members. However, the current common approach in collapse modeling of steel structures, a constant critical strain strategy (CS), typically requires recalibration when used with different structural configurations due to the fact that it does not account for triaxiality, which is a primary parameter in ductile fracture. To better predict structural response of steel structures undergoing collapse, it is important to study the effect of triaxiality on fracture in steel structures. A new finite element deletion approach that accounts for triaxiality was previously proposed, calibrated, and validated in small steel specimens for use in predicting collapse of steel structures. In this approach, fracture initiation is modeled using Void Growth Model (VGM) and the subsequent softening of the material to element deletion is modeled by a Hillerborg model. This paper describes the change of triaxiality, equivalent plastic strain, and other parameters during the duration of the loading, influencing the strategies implemented and provides explanation for the performance shown. In addition, the paper examines the effect of triaxiality on accurately predicting fracture in steel structures through comparison of VGM to CS strategy with validation in simulations of full-scale structural steel connection and frame tests without recalibration. The VGM strategy provided an accurate prediction based on calibration to test results that are most widely available for different types of structural steels, while CS strategy frequently provided less accurate results. The VGM strategy thus allows for an accurate collapse modeling of steel structures for use by researchers, code developers, and practitioners who address collapse of steel structures.

Robustness assessment of planar steel frames caused by failure of a side column under localized fire

SummaryProgressive collapse of a building structure under fire is a disaster that may cause heavy casualties and serious economic loss. However, there is a lack of codified method to assess fire‐induced progressive collapse of building structures. A global–local analysis method (GLAM) has recently been proposed by the authors and their colleagues to assess progressive collapse of steel buildings under localized fire, and its application on fire scenarios that causes one inner column to fail has been verified. This paper extends the application of GLAM to fire scenarios that causes a side column to fail in a planar steel frame. The predictions of the GLAM were validated against the results obtained from nonlinear dynamic analysis of the whole frame model. Besides, effects of location of the heated column at different storeys and load level of the frame were also studied. The results show that GLAM gives the same collapse predictions to the case studies with detailed nonlinear dynamic analysis. The differences between the critical load obtained from GLAM and that provided by the nonlinear dynamic analysis is within 7%. Therefore, GLAM has good applicability on robustness assessment of planar steel frames caused by failure of a side column under localized fire.

Acoustic Emission Simulation on Coal Specimen Subjected to Cyclic Loading

The damage and failure state of the loaded coal and rock masses is indirectly reflected by its acoustic emission (AE) characteristics. Therefore, it is of great significance to study the AE evolution of loaded coal and rock masses for the evaluation of damage degree and prediction of collapse. The paper mainly represents a numerical simulation investigation of the AE characteristics of coal specimen subjected to cyclic loading under three confining pressures, loading‐unloading rates, and valley stresses. From the numerical simulation tests, the following conclusions can be drawn: (1) The final cycle number of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure, followed the valley stress. With the increase in confining pressure or valley stress, the cycle number tends to increase. However, the loading‐unloading rate has a little influence on it. (2) The AE counts of coal specimen subjected to cyclic loading are greatly influenced by the confining pressure and the valley stress. With the increase in the confining pressure, the cumulative AE counts at the 1st cycle tend to increase but decrease at a cycle before failure; with the decrease in the valley stress, the cumulative AE counts per cycle increase in the relatively quiet phase. However, the loading‐unloading rate has a little influence on it. (3) The failure mode of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure. Under the uniaxial stress state, there is an inclined main fractured plane in the coal specimen, under the confining pressures of 5 and 10 MPa, the coal specimen represents dispersion failure. The loading‐unloading rate and valley stress have little influence on it. (4) The AE ratio is proposed, and its evolution can better reflect the different stages of coal specimen failure under cyclic loading. (5) The influence of confining pressure on the broken degree of coal specimen subjected to cyclic loading is analyzed, and the higher the confining pressure, the more broken the failed coal specimen.

The use of the shock index to predict hemodynamic collapse in hypotensive sepsis patients: A cross-sectional analysis.

Objectives:Septic shock, defined as sepsis with hypotension not responding to fluid resuscitation or requiring vasopressor support, results in the worst outcomes in sepsis patients. This subtype of the patient is often difficult to detect. The shock index (SI) has demonstrated the potential for predicting hemodynamic compromise and collapse and predicting patient outcomes in multiple medical and surgical settings. In our study, we assessed the utility of the SI as a hemodynamic screening tool to identify patients likely to fail to respond to fluids and ultimately to be diagnosed with septic shock.Methodology:A single-center cross-sectional analysis of patients presenting with hypotension and septicemia over 1 year. The study was conducted using the electronic medical records of the emergency department patients presenting to King Saud University Medical City. The charts were reviewed from 2 May 2015 to 24 April 2016 using the local medical registry. The study was approved by the hospital institutional review board (IRB). Data extraction was performed using a standardized form.Results:The area under the curve was 0.77 (P < 0.001) for the prediction of hemodynamic collapse. An initial SI ≥0.875 had a sensitivity of 81% and a specificity of 72% for the identification of patients in whom fluid resuscitation would fail.Conclusions:Based on our findings, we found that the SI was a reliable screening tool for the identification of hypotensive patients with sepsis who would ultimately be diagnosed with septic shock.

Transition from stable column to partial collapse during the 79 cal CE P3 Plinian eruption of Mt. Pelée volcano (Lesser Antilles)

Explosive volcanic eruptions commonly form sustained Plinian columns that collapse at some stage producing dangerous pyroclastic density currents (PDC) on the ground. Numerical and laboratory models of volcanic plumes show that the conditions leading to total column collapse are strongly controlled by the amount of exsolved gas at the source and the mass eruption rate. However, column collapse is rarely total and the volcanic jet often separates in a dense collapsing part feeding PDC and a buoyant rising plume spreading volcanic gases and pyroclasts in the atmosphere. This transitional regime has been directly observed and/or inferred from the structure of the deposits for several past eruptions, but the number of cases for which the partial collapse regime is described in detail, including the 79 CE Vesuvius, and the 186 CE Taupo eruptions, remains too small to fully constrain physical models. Here, we present a detailed reconstruction of the time evolution of the P3 eruption at Mt. Pelée volcano (Martinique, Lesser Antilles) that underwent partial column collapse in order to discuss the mechanisms controlling the eruption dynamics and improve the volcanological database on transitional eruptions. The P3 eruptive succession consists of seven major phases that produced a total of 1 km3 dense rock equivalent (DRE) of deposits (i.e., VEI 5 event), starting with a thick pumice fall deposit (0.1 km3 DRE) overlain by alternating pyroclastic density current (PDC) (0.7 km3 DRE) and pumice fall deposits (0.2 km3 DRE). We use physical models together with field data on deposit dispersal, thickness, and grain-size distribution to reconstruct the dynamical evolution of the volcanic column. Our results show that the mass eruption rate (MER) increased from 1.2 × 108 to 1.7 × 108 kg s−1 during the initial phase producing a 28 to 30 km-high Plinian plume. The MER later reached up to 2.5 × 108 kg s−1 and the column entered the partial collapse regime characterized by the formation of a small (i.e., 12 to 17 km-high) ash plume and contemporaneous PDCs mainly channelized in three paleo-valleys. These estimates are used together with published data on magmatic water contents in glass inclusions to decipher the mechanisms leading to partial collapse. The P3 eruption column collapsed due to an increase in mass eruption rate and a decrease in gas content. A similar evolution was also inferred for the 1300 CE P1 and 280 CE P2 eruption deposits, revealing a systematic behavior in the recent Plinian eruptions of Mt. Pelée volcano. The comparison of model predictions of column collapse and field data reveals a good agreement for the P1, P2, P3 and Taupo eruptions, but not for the 79 CE Vesuvius eruption where thermal disequilibrium between gas and pyroclasts most likely strongly affected the column dynamics.

A NEW GROUND MOTION RECORD SELECTION PROCEDURE BASED ON THE EFFECTS OF SPECTRAL SHAPE AND PERIOD ELONGATION

One of the most prevalent ground motion Intensity Measures (IMs) is the spectral acceleration at the fundamental period of the structure. Previous research has shown that vectorizing scalar IMs leads to a more reliable structural response, particularly in the nonlinear region and near collapse. Furthermore, nonlinear behavior of ductile structures results in an elongation in the "effective period" of the structure. Therefore, this paper proposes a new approach for selecting ground motion records considering the effect of spectral shape and period elongation. This method contains two disaggregation analyses at the fundamental and elongated period of the structure. Nonlinear dynamic analysis is conducted on a set of reinforced concrete moment resisting frames designed based on ACI 318-05 as representatives of modern structures. Results show a considerable decrease in the median collapse prediction, margin against collapse and dispersion of the structural response. The presented approach can give a better prediction for the vulnerability of the structure toward collapse.

A combined SHM/IDA method for assessing collapse capacity and risk in subsequent ground motions

Prediction of building collapse due to significant seismic motion is a principle objective of earthquake engineers, particularly after a major seismic event when the structure is damaged and decisions may need to be made rapidly concerning the safe occupation of a building or surrounding areas. Traditional model-based pushover analyses are effective, but only if the structural properties are well understood, which is not the case after an event when that information is most useful. This paper combines hysteresis loop analysis (HLA) structural health monitoring (SHM) and incremental dynamic analysis (IDA) methods to identify and then analyse collapse capacity and the probability of collapse for a specific structure, at any time, a range of earthquake excitations to ensure robustness. This nonlinear dynamic analysis enables constant updating of building performance predictions following a given and subsequent earthquake events, which can result in difficult to identify deterioration of structural components and their resulting capacity, all of which is far more difficult using static pushover analysis. The combined methods and analysis provide near real-time updating of the collapse fragility curves as events progress, thus quantifying the change of collapse probability or seismic induced losses very soon after an earthquake for decision-making. Thus, this combination of methods enables a novel, higher-resolution analysis of risk that was not previously available. The methods are not computationally expensive and there is no requirement for a validated numerical model, thus providing a relatively simpler means of assessing collapse probability immediately post-event when such speed can provide better information for critical decision-making. Finally, the results also show a clear need to extend the area of SHM toward creating improved predictive models for analysis of subsequent events, where the Christchurch series of 2010–2011 had significant post-event aftershocks.

New Plastic Analysis Procedure for Collapse Prediction of Braced Frames by Means of Genetic Algorithm

AbstractThe analysis of frames and the determination of their collapse mechanisms and related loads are desirable for structural designers and also attractive for researchers. Plastic analysis meth...

An elastic stability-based method to predict the homogenized hoop elastic moduli of reinforced thermoplastic pipes (RTPs)

The homogenized hoop elastic moduli are key parameters of RTPs that must be considered in the buckling collapse predictions and pipe designs. However, it is difficult to give an accurate analytical solution due to the material anisotropy of RTPs. To address this problem, a novel method is proposed based on the classical elastic stability theory and NASA SP-8007 formula. This method is under the assumption that the critical pressures of homogenized RTPs equal the critical pressures calculated by the classical lamination theory and Donnell-type stability differential equations. One advantage of this method is that it could simultaneously consider the extensional response, the bending response, and the extensional-bending coupling response of laminates in the calculation of homogenized hoop elastic moduli. Meanwhile, it gives a more concise formula form and doesn’t involve successive iterations in comparison with the existing homogenization method. Numerical simulations of the crushing case were used to verify the effectiveness of the proposed method. Compared with numerical results and the existing homogenization method, the proposed method was found to give accurate results. Furthermore, the effects of fiber’s winding angles and thickness-radius ratios, and the proportional relations between the homogenized hoop elastic moduli and the reciprocal of radii were investigated.

Prediction of Collapse Using Patient-Specific Finite Element Analysis of Osteonecrosis of the Femoral Head.

ObjectiveTo develop a prediction method for femoral head collapse by using patient‐specific finite element analysis of osteonecrosis of the femoral head (ONFH).MethodsThe retrospective study recruited 40 patients with ARCO stage‐II ONFH (40 pre‐collapse hips). Patients were divided into two groups according to the 1‐year follow‐up outcomes: patient group without femoral head collapse (noncollapse group, n = 20) and patient group with collapse (collapse group, n = 20). CT scans of the hip were performed for all patients once they joined the study. Patient‐specific finite element models were generated based on these original CT images following the same procedures: segmenting the necrotic lesion and viable proximal femur, meshing the computational models, assigning different material properties according to the Hounsfield unit distribution, simulating the stress loading of the slow walking gait, and measuring the distribution of the von Mises stress. Receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive performance of the maximum level of the von Mises stress. The optimal cut‐off value was selected based on the Youden index and the corresponding predictive accuracy was reported as well.ResultsThe mean level of the maximum von Mises stress in the collapse group was 2.955 ± 0.539 MPa, whereas the mean stress level in the noncollapse group was 1.923 ± 0.793 MPa (P < 0.01). ROC analysis of the maximum von Mises stress found that the area under the ROC curve was 0.842 (95% CI: 0.717–0.968, P < 0.01). The maximum Youden index was 0.60, which corresponded to two optimal cut‐off values: 2.7801 MPa (sensitivity: 0.70; specificity: 0.90; predictive accuracy: 80.00%; LR+: 7), and 2.7027 MPa (sensitivity: 0.75; specificity: 0.85; predictive accuracy: 77.50%; LR+: 5).ConclusionFinite element analysis is a potential method for femoral head collapse prediction among pre‐collapse ONFH patients. The maximum level of the von Mises stress on the weight‐bearing surface of the femoral head could be a good biomechanical marker to classify the collapse risk. The collapse prediction method based on patient‐specific finite element analysis is, thus, suitable to apply to clinical practice, but further testing on a larger dataset is desirable.

Development of a new voltage stability index and its implementation considering voltage measurement uncertainty

In this study, a new method is proposed to analyse steady-state voltage stability under load variations. This method combines a weighted sum of two voltage stability indices: one derived from power flow equations, and another from the decay of voltage magnitudes. The weight value of each index is updated using an algorithm based on a backwards Euler approximation. In addition, the impact of uncertainty related to voltage measurements on the prediction of voltage instability is mathematically quantified using this new index. The obtained formula shows a reduction in the capability of the proposed stability index in predicting voltage instability when the amplitude of measurement uncertainties increases. Thus, an appropriate filtering technique is added in parallel to the developed index, which proves to reduce the adverse impacts due to uncertain measurements. Simulation studies are performed using four test cases: 5-bus, IEEE 14-bus, IEEE 57-bus, and IEEE 118-bus systems. The obtained results show that the proposed index, named as global voltage stability index, is effective when compared to other voltage stability indices such as voltage collapse prediction index, voltage collapse index, and local Thevenin index.

Application of SPH-DEM coupled method to failure simulation of a caisson type composite breakwater during a tsunami

During the 2011 Mw9.0 Tohoku Earthquake, caisson breakwaters in several ports experienced severe tsunami damage. Such failures were probably caused by a combination of scouring and seepage destruction of foundations and by large horizontal forces caused by the tsunami. We use a coupled Smoothed Particle Hydrodynamics (SPH) – Distinct Element Method (DEM) analysis method based on locally averaged equations of motion to analyze scouring and seepage flow phenomena at caisson-type breakwaters during the tsunami. Permeability tests and numerical simulations verified the coupled analysis methods that calculate the forces between solid and liquid phases. Numerically simulated triaxial tests determined the numerical parameters. Experimental simulations of caisson-type breakwater failures under centrifugal conditions validated the numerical method. Numerical simulations of the collapse process in the breakwaters agreed fairly well with experimental results at centrifugal acceleration fields. Thus, the SPH-DEM analysis method is applicable for predictions of collapse or failure in composite type breakwaters during a tsunami.

Propinquity of voltage collapse prediction for power system using indices

Continuous assessment of voltage stability is vivacious in safeguarding the electrical power system (EPS) operation. The final outcome of voltage instability is proximity to voltage collapse. The critical operating conditions of the transmission lines may possibly lead to voltage collapse with certain disturbances in electrical power supply. Quite a lot of Voltage Stability Indices (VSIs) have been technologically advanced in to estimate the proximity to voltage collapse. A few VSIs are computationally efficient, while the rest are said not to accomplish as expected under all circumstances. The study recommends a voltage stability index such as Composite Severity Index (CSI) and New Voltage Stability Index (NVSI) which are vigorous based on its theoretical nitty-gritties. The recommended index has been meritoriously tested on IEEE 30 bus and IEEE 118 bus test system under various operating conditions in order to weigh its efficacy. Also, it is shown that CSI and NVSI index could be used for estimating the distance to Voltage Collapse Point (VCP). The validation is done with Lmn, LQP and FVSI indices. The results designate its possibilities for the assessment of voltage stability.

Prediction of pipeline collapse due to hydrostatic pressure

PurposeThe purpose of this paper is to present a finite element method (FEM) model that predicts the collapse pressure of the majority of the gas/petroleum pipelines worldwide. More specifically, it refers to pipelines with diameter to wall thickness (D/t) ratios between 15 and 45. The model’s results were evaluated on the basis of the DNV-OS-F101 offshore pipeline design code.Design/methodology/approachA series of FEM simulations were conducted using a 2D model created in the ANSYS’ software environment considering both the plane strain and the plane stress approach. The corresponding values of the collapse pressure for pipes with different value sets of D/t and ovality were calculated in Python (programming language) according to the DNV equations. Given that the pipeline’s resistance to collapse is governed by geometric imperfections and material properties, amongst others, the influence of other crucial factors, such as ovality, eccentricity, hardening modulus and the chemical composition (pipe’s steel grade) was examined.FindingsThe FE model approaches very closely the DNV calculations. Although the effect of the hardening modulus and pipe’s steel grade, respectively, was found to be insignificant on the pipeline’s collapse, it turned out that the lower the D/t ratio was the bigger the influence of these factors appeared. The D/t ratio does not affect the pipe’s sensitivity in eccentricity, because for a pipe with the same characteristics and eccentricity, but with higher ovality, the decrease in collapse pressure was found to be lower.Originality/valueA 2D FEM which estimates collapse pressure and simultaneously takes into account the effect of various factors is less time-consuming and costly than the full-scale pipe collapse tests in pressure chambers.

Prediction of risk in submarine tunnel construction by multi-factor analysis: A collapse prediction model

Collapse is a major threat in tunnel construction. How to predict collapse risk accurately and timely is a complicated problem. In this paper, a non-linear mathematical model is applied to obtain the potential risk indices for a submarine tunnel using statistical analysis based on previous submarine tunnels, such as the Seikan tunnel and Xiang’an tunnel. Rough set theory is used to screen risk indices, determine each indicator value, and classify risk factors. Traditional weight calculation methods that are overly dependent on expert experience and other subjective factors are optimized and improved. Based on the frequency of each risk factor, the objective weight value of each risk index is determined according to weight back analysis theory. The ideal point method is used to calculate the collapse risk level. Predictions made by this new method are consistent with the actual tunnel collapse risk levels. This new method provides theoretical and technical basis for effectively predicting tunnel collapse.

Universal thermodynamic properties of the intracluster medium over two decades in radius in the X-COP sample

Context.The hot plasma in a galaxy cluster is expected to be heated to high temperatures through shocks and adiabatic compression. The thermodynamical properties of the gas encode information on the processes leading to the thermalization of the gas in the cluster’s potential well and on non-gravitational processes such as gas cooling, AGN feedback, shocks, turbulence, bulk motions, cosmic rays and magnetic field.Aims.In this work we present the radial profiles of the thermodynamic properties of the intracluster medium (ICM) out to the virial radius for a sample of 12 galaxy clusters selected from thePlanckall-sky survey. We determine the universal profiles of gas density, temperature, pressure, and entropy over more than two decades in radius, from 0.01R500to 2R500.Methods.We exploited X-ray information fromXMM-Newtonand Sunyaev-Zel’dovich constraints fromPlanckto recover thermodynamic properties out to 2R500. We provide average functional forms for the radial dependence of the main quantities and quantify the slope and intrinsic scatter of the population as a function of radius.Results.We find that gas density and pressure profiles steepen steadily with radius, in excellent agreement with previous observational results. Entropy profiles beyondR500closely follow the predictions for the gravitational collapse of structures. The scatter in all thermodynamical quantities reaches a minimum in the range [0.2 − 0.8]R500and increases outward. Somewhat surprisingly, we find that pressure is substantially more scattered than temperature and density.Conclusions.Our results indicate that once accreting substructures are properly excised, the properties of the ICM beyond the cooling region (R &gt; 0.3R500) follow remarkably well the predictions of simple gravitational collapse and require few non-gravitational corrections.

Prediction of spray collapse in multi-hole gasoline direct-injection fuel injectors

A parametric study was conducted to predict the conditions leading to spray collapse in multi-hole gasoline direct-injection fuel injectors using computational fluid dynamics simulations. The computational fluid dynamics simulations were performed using an in-house multi-dimensional code that accounts for thermal non-equilibrium and entrainment of the non-condensable gas and coupled with primary atomization. The simulations were performed for a fixed injection pressure and fuel temperature on nine different six-hole injectors. The parameters were varied to include the effects of the ratio of the ambient pressure to the saturation pressure (Pa/Ps), the drill angle, and the diameters of the nozzle and the counter bore, respectively, on the spray. The findings indicate that spray collapse results from a combination of the nozzle geometry, the thermodynamic conditions of the fuel, and the ambient pressure. Spray collapse was observed in injectors with a narrow arrangement of the nozzle holes under extreme flash-boiling conditions with very low ambient pressures and in the case of non-flash-boiling conditions with very high ambient pressures.

Bending collapse of dual rectangle thin-walled tubes for conceptual design

In engineering, the bending deformations of thin-walled tubes mostly are under three-point loading. However, for the dual rectangle thin-walled tube (DRTWT), the theoretical prediction of the three-point bending collapse is still an unsolved problem. In this paper, the three-point bending collapse of the DRTWT is innovatively investigated using theoretical prediction and experimental verification. The global energy equilibrium theory is applied to derive the bending characteristic of the DRTWT. It is assumed that all the bending energy is absorbed and distributed along the hinge lines and in the toroidal surfaces during the bending collapse. The analytical results show good agreement with the experimental results. Finally, a simplified bumper structure of automobile is created by using beam elements and spring elements with the derived bending characteristics, which can effectively replace the detailed finite element model (FEM) to accelerate the crashworthiness design of automotive structure at the conceptual design stage.

Reliability of collapse simulation – Comparing finite and applied element method at different levels

Numerical prediction of progressive collapse of buildings due to extreme loading is still a challenging task. However, increased computational power makes it nowadays possible to analyze not only small-scale connections and mid-size building elements, but also full buildings with considerable height and complexity. The present paper compares the results of Finite Element Method (FEM) and Applied Element Method (AEM) simulations to experimental results when performing blast or earthquake analysis on those three scales. The aim is to highlight which level of physical detail and complexity is required to predict progressive collapse numerically, and which level of accuracy can be expected. For the full scale level, the progressive collapse of the Pyne Gould Corporation Building in Christchurch, New Zealand, was simulated and compared to the final collapse shape. It is shown that the FEM is able to predict the structural response of small scale models well, but fails to achieve realistic collapsed shapes in case of the large structure, whereas the AEM shows convincing results in all cases.