Computational Submodels Research Articles

A filtering-based methodology for assessing evacuation performance in layout of complex infrastructures

Evacuation is a performance matter in buildings design, and this study provides a framework for assessing the performance of complex architectural layouts for emergency egress. First, a theoretical framework is inspired by advanced estimation methods and extended to a performance model with spatial and computational sub-models. The spatial sub-model abstracts the floorplan as a geometric network. The computational sub-model is consisted of: filtering parameters, routing algorithm, and bottleneck importance calculation. A criterion called ‘Bottleneck Importance (BI)’ is introduced and formulated, which shows the effect of obstruction in each position in route on the evacuation performance of the floor. The model is applied in a case study, and outputs made it possible to analyse the performance of exits in-floor evacuation, frequent positions in the evacuation route, the topological relationship with performance, especially at intersections, and the effect of blocking in egress corridors and cause of obstructions.

Uncertainty propagation in risk and resilience analysis of hierarchical systems

A novel formulation is proposed for uncertainty propagation in risk and resilience analysis of hierarchical systems. The main challenges are related to the complexity of hierarchical systems’ computational workflow and high-dimensional probability space. The computational workflow in regional risk and resilience analysis consists of many interconnected sub-models to predict future hazards, the reliability and functionality of physical systems, and the recovery of disrupted services. The complexity of the computational workflow limits the number of model evaluations for uncertainty propagation. In contrast, the computational workflow contains many sources of uncertainty that demand extensive model evaluations to accurately estimate their effects. The proposed formulation in this paper consists of a multi-level uncertainty propagation approach to reduce the problem dimensionality and a variables-grouping approach to reduce the number of model evaluations. The idea of the multi-level uncertainty propagation is to break down the high-dimensional problem into several low-dimensional ones, one for each level of the hierarchy in the computational workflow. The proposed variables-grouping approach provides an adaptive refinement of uncertainty propagation to identify the influential uncertain input data and computational sub-models. The paper illustrates the proposed formulation through a well-known academic problem and regional risk and resilience analysis of a community.

Continuous-flow pump model study: the effect on pump performance of pump characteristics and cardiovascular conditions

This model study evaluates the effect of pump characteristics and cardiovascular data on hemodynamics in atrio-aortic VAD assistance. The model includes a computational circulatory sub-model and an electrical sub-model representing two rotary blood pumps through their pressure-flow characteristics. The first is close to a pressure generator-PG (average flow sensitivity to pressure variations, -0.047lmmHg(-1)); the second is closer to a flow generator-FG (average flow sensitivity to pressure variations, -0.0097lmmHg(-1)). Interaction with VAD was achieved by means of two interfaces, behaving as impedance transformers. The model was verified by use of literature data and VAD onset conditions were used as a control for the experiments. Tests compared the two pumps, at constant pump speed, in different ventricular and circulatory conditions: maximum ventricular elastance (0.44-0.9mmHgcm(-3)), systemic peripheral resistance (781-1200gcm(-4)s(-1)), ventricular diastolic compliance C p (5-10-50cm(3)mmHg(-1)), systemic arterial compliance (0.9-1.8cm(3)mmHg(-1)). Analyzed variables were: arterial and venous pressures, flows, ventricular volume, external work, and surplus hemodynamic energy (SHE). The PG pump generated the highest SHE under almost all conditions, in particular for higher C p (+50%). PG pump flow is also the most sensitive to E max and C p changes (-26 and -33%, respectively). The FG pump generally guarantees higher external work reduction (54%) and flow less dependent on circulatory and ventricular conditions. The results are evidence of the importance of pump speed regulation with changing ventricular conditions. The computational sub-model will be part of a hydro-numerical model, including autonomic controls, designed to test different VADs.

IABP Timing and Ventricular Performance - Comparison between a Compliant and a Stiffer Aorta: A Hybrid Model Study Including Baroreflex

The aim of this study was to investigate the effects of the intra aortic balloon pump (IABP) and of aortic compliance on left ventricular performance, including the effects of baroreflex control. The study was conducted using a hybrid cardiovascular simulator, including a computational cardiovascular sub-model, a hydraulic sub-model of the descending aorta, and a baroreflex computational sub-model. A 40 cc balloon was inserted into a rubber tube component of the hydraulic sub-model. A comparative analysis was conducted for two aortic compliances (C1 = 2.4 and C2 = 1.43 cm3/mmHg, corresponding to an aortic pulse pressure of 23 mmHg and 35 mmHg, respectively), driving the balloon for different trigger timings. Under C1 conditions, the IABP induced higher effects on baroreflex activity (decrement of sympathetic efferent activity: 10% for C1 and 14.7% for C2) and ventricular performance (increment of cardiac output (CO): 3.7% for C1 and 5.2% for C2, increment of endocardial viability ratio (EVR): 24.8% for C1 and 55% for C2). The best balloon timing was different for C1 and C2: inflation trigger timing (from the dicrotic notch) -0.09 s for C1 and -0.04 s for C2, inflation duration 0.25 s for C1 and 0.2 s for C2. Early inflation ensures better EVR, CO, and an increment of the afferent nerve activity, hence causing peripheral resistance and heart rate to decrease. The best balloon timing depends on aortic compliance, thus suggesting the need for a therapy tailored to the specific conditions of individual patients.

Hybrid Model Analysis of Intra‐Aortic Balloon Pump Performance as a Function of Ventricular and Circulatory Parameters

We investigated the effects of the intra-aortic balloon pump (IABP) on endocardial viability ratio (EVR), cardiac output (CO), end-systolic (V(es)) and end-diastolic (V(ed)) ventricular volumes, total coronary blood flow (TCBF), and ventricular energetics (external work [EW], pressure-volume area [PVA]) under different ventricular (E(max) and diastolic stiffness) and circulatory (arterial compliance) parameters. We derived a hybrid model from a computational model, which is based on merging computational and hydraulic submodels. The lumped parameter computational submodel consists of left and right hearts and systemic, pulmonary, and coronary circulations. The hydraulic submodel includes part of the systemic arterial circulation, essentially a silicone rubber tube representing the aorta, which contains a 40-mL IAB. EVR, CO, V(es), and V(ed), TCBF and ventricular energetics (EW, PVA) were analyzed against the ranges of left ventricular E(max) (0.3-0.5-1 mm Hg/cm(3)) and diastolic stiffness V(stiffness) (≈0.08 and ≈0.3 mm Hg/cm(3), obtained by changing diastolic stiffness constant) and systemic arterial compliance (1.8-2.5 cm(3)/mm Hg). All experiments were performed comparing the selected variables before and during IABP assistance. Increasing E(maxl) from 0.5 to 2 mm Hg/cm(3) resulted in IABP assistance producing lower percentage changes in the selected variables. The changes in ventricular diastolic stiffness strongly influence both absolute value of EVR and its variations during IABP (71 and 65% for lower and higher arterial compliance, respectively). V(ed) and V(es) changes are rather small but higher for lower E(max) and higher V(stiffness). Lower E(max) and higher V(stiffness) resulted in higher TCBF and CO during IABP assistance (∼35 and 10%, respectively). The use of this hybrid model allows for testing real devices in realistic, stable, and repeatable circulatory conditions. Specifically, the presented results show that IABP performance is dependent, at least in part, on left ventricular filling, ejection characteristics, and arterial compliance. It is possible in this way to simulate patient-specific conditions and predict the IABP performance at different values of the circulatory or ventricular parameters. Further work is required to study the conditions for heart recovery modeling, baroreceptor controls, and physiological feedbacks.

Cornell Net Carbohydrate and Protein System: A model for precision feeding of dairy cattle

The Cornell Net Carbohydrate and Protein System (CNCPS) predicts cattle requirements and nutrient supply for site-specific situations. This paper describes the CNCPS version 6 (CNCPSv6), which represents a re-engineering and updating of CNCPS version 5 with the following objectives: (1) improve the organization of the model and user interface to improve speed and accuracy in formulating diets for a herd of dairy cattle, (2) expand the carbohydrate pools to include sugars, soluble fibers, and organic and volatile fatty acids, (3) integrate a fat model to account for ruminal lypolization and biohydrogenation, and absorption of fatty acids in the small intestine, and (4) update the computational sub-models with new information. The CNCPSv6 model was re-designed using object-oriented programming in which physiological functions ( e.g. growth, lactation, pregnancy) and anatomical compartments ( e.g. rumen, intestines) were programmed as objects. The interface uses farm, location, and group flow, which decreases the number of inputs required per cattle group and allows for more rapid evaluation of diets, feed requirements, and nutrient excretion by location, group, and herd. The revised implementation of the body reserves sub-model allows accounting for fluxes in energy reserves when formulating diets. Updated equations and coefficients include the prediction of rumen ammonia balance and feed passage rates, indigestible DM, MP lactation efficiency, and DMI. The CNCPSv6 was evaluated with data from individually fed lactating dairy cows from three independent studies. As implemented, CNCPSv6 accounted for a similar proportion of the variation (86%) in first limiting (ME or MP) milk production as CNCPSv5 but with a lower bias (1% versus 4%, respectively). We concluded the re-designing and updating of the CNCPS improved its ability to formulate and evaluate a feeding program for a herd of dairy cattle with greater accuracy and efficiency.

Verification and Validation for Laminar Hypersonic Flowfields, Part 2: Validation

A validation methodology is applied to the laminar Mach 8 e ow over a spherically blunted cone. Validation of the overall computational model is performed via surface pressure comparisons with experimental data. Careful attention is paid to the submodels in the computational simulations and the assumptions in the experimental data analysis. The computational submodels for molecular viscosity and thermal conductivity are validated by comparisons to experimental data, whereasthevibrational nonequilibrium submodel is validated by comparing to published results using the vibrational master equation. The thermodynamic state of the hypersonic wind-tunnel nozzleisexamined,and argumentsaremadeforthepresenceofasignie cantamountofvibrationalnonequilibrium in thetunnel. Afterextensiveinvestigation, a 1.4% errorwasdiscovered in thefreestream static pressure originally reported in the experiment. Accounting for this error, along with the experimental uncertainty and estimated numerical error, agreement was found for surface pressure within 1.5%. The remaining errors are likely due to e owe eld nonuniformities in the tunnel, which are estimated using tunnel pitot calibration data and the method of characteristics.