Monotone difference approximations for the simulation of clarifier-thickener units

Clarifier-thickener units treating ideal suspensions can be modeled as an initial-value problem for a nonconvex scalar conservation law whose flux depends on a vector of discontinuous parameters. This problem can be treated by the well-known Engquist-Osher scheme if the discontinuous parameters are discretized on a grid staggered against that of the conserved variable. We prove convergence of this scheme to a weak solution of the problem and illustrate its application to the clarifier-thickener setup by a numerical example.     

Computer-based simulation subsystem for versatile testing of 40 MW gas-turbine units

The testing of gas-turbine units of ground applications and their control systems is discussed. Today, such units are often based on refurbished commercial air-engines. It is offered to include a subsystem for computer simulation of gas-turbine units in the traditional scheme of tests taking into account characteristics of ground loading. The paper offers to supplement the traditional testing system with a simulation subsystem allowing for terrestrial load characteristics.     

Predicting real-world ergonomic measurements by simulation in a virtual environment

Virtual reality techniques have been increasingly used for ergonomic applications. However, it is always important to know whether the results obtained in a virtual environment (VE) are representative of a real environment (RE) ones. This paper presents our preliminary experimental results on the relationship between ergonomic measurements in VE and RE for some typical “drilling” tasks. The same tasks were carried out by thirty male manufacturing factory workers in both VE and RE. Five evaluation indices - three objective (elbow angle, maximum force capacity reduction, and task completion time) and two subjective (BPD - Body Part Discomfort and RPE - Rated Perceived Exertion) - were used to evaluate the similarities between VE and RE for the selected “drilling” tasks. Four of these indices (all except elbow angle) were significantly higher (p < 0.05) in VE than in RE, which indicates that subjects experienced more discomfort and grew fatigued more quickly in VE. However, linear correlations (Pearson’s rho: 0.635-0.807) between VE and RE were found for two of the five indices (BPD and maximum force capacity reduction).

Relevance to industry

Using digital mock-ups and virtual reality simulations, industrial work activities can be evaluated to identify potential ergonomic problems during an early design stage, which reduces design time and costs, increases quality and improves customer satisfaction. A validated linear relationship can provide a reference for work design in virtual reality.     

RESP-24: a computer program for the investigation of 24-h breathing abnormalities in heart failure patients

In this paper, we describe a computer program (RESP-24) specifically devised to assess the prevalence and characteristics of breathing disorders in ambulant chronic heart failure patients during the overall 24 h period. The system works on a single channel respiratory signal (RS) recorded through a Holter-like portable device. In the pre-processing stage RESP-24 removes noise, baseline drift and motion artefacts from the RS using a non-linear filter, enhances respiratory frequency components through high-pass filtering and derives an instantaneous tidal volume (ITV) signal. The core processing is devoted to the identification and classification of the breathing pattern into periodic breathing (PB), normal breathing or non-classifiable breathing using a 60 s segmentation, and to the identification and estimation of apnea and hypopnea events. Sustained episodes of PB are detected by cross analysis of both the spectral content and time behavior of the ITV signal. User-friendly interactive facilities allow all the results of the automatic analysis procedure to be edited. The final report provides a set of standard and non-standard parameters quantifying breathing abnormalities during the 24 h period, the night-time and the day-time, including the apnea/hypopnea index, the apnea index, the total time spent in apnea or in hypopnea and the prevalence of non-apneic and apneic PB. The accuracy of these measurements was appraised on a data set of 14 recordings, by comparing them with those provided by a trained analyst. The mean and standard deviation of the error of the automatic procedure were below respectively 6 and 8% of the reference value for all parameters considered and the mean total classification accuracy was 92%. In most cases, the individual error was <12%. We conclude that measurements provided automatically by the RESP-24 software are suitable for screening purposes and clinical trials, although a preventive check of signal quality should be recommended.     

Predicting piezometric water level in dams via artificial neural networks

The safety control of dams is based on measurements of parameters of interest such as seepage flows, seepage water clarity, piezometric levels, water levels, pressures, deformations or movements, temperature variations, loading conditions, etc. Interpretation of these large sets of available data is very important for dam health monitoring and it is based on mathematical models. Modelling seepage through geological formations located near the dam site or dam bodies is a challenging task in dam engineering. The objective of this study is to develop a feedforward neural network (FNN) model to predict the piezometric water level in dams. An improved resilient propagation algorithm has been used to train the FNN. The measured data have been compared with the results of FNN models and multiple linear regression (MLR) models that have been widely used in analysis of the structural dam behaviour. The FNN and MLR models have been developed and tested using experimental data collected during 9 years. The results of this study show that FNN models can be a powerful and important tool which can be used to assess dams.     

Predicting split decisions of coding units in HEVC video compression using machine learning techniques

Multimedia Tools and Applications - In this work, we propose to reduce the complexity of HEVC video encoding by predicting the split decisions of coding units. We use a sequence-dependent approach...     

基于Relief特征选择的心衰死亡率预测

提出心衰死亡率预测系统,预测心衰病人本次住院后30天内死亡率。基于上海曙光医院提供的心衰病人信息,首先对原始数据和特征进行预处理。由于特征的冗余性,再选用经典的Relief特征选择算法筛选出重要的心衰特征,最后选用bp-SVM算法来实现死亡率预测。实验结果证明,死亡率预测系统可以达到较高的性能并通过提供决策信息,辅助医生治疗病人。医生可以根据系统预测的病人死亡率的高低,采取不同的治疗方式,提高临床诊断结果和医院的资源分配。     

Conditional mutual information-based feature selection for congestive heart failure recognition using heart rate variability

Feature selection plays an important role in pattern recognition systems. In this study, we explored the problem of selecting effective heart rate variability (HRV) features for recognizing congestive heart failure (CHF) based on mutual information (MI). The MI-based greedy feature selection approach proposed by Battiti was adopted in the study. The mutual information conditioned by the first-selected feature was used as a criterion for feature selection. The uniform distribution assumption was used to reduce the computational load. And, a logarithmic exponent weighting was added to model the relative importance of the MI with respect to the number of the already-selected features. The CHF recognition system contained a feature extractor that generated four categories, totally 50, features from the input HRV sequences. The proposed feature selector, termed UCMIFS, proceeded to select the most effective features for the succeeding support vector machine (SVM) classifier. Prior to feature selection, the 50 features produced a high accuracy of 96.38%, which confirmed the representativeness of the original feature set. The performance of the UCMIFS selector was demonstrated to be superior to the other MI-based feature selectors including MIFS-U, CMIFS, and mRMR. When compared to the other outstanding selectors published in the literature, the proposed UCMIFS outperformed them with as high as 97.59% accuracy in recognizing CHF using only 15 features. The results demonstrated the advantage of using the recruited features in characterizing HRV sequences for CHF recognition. The UCMIFS selector further improved the efficiency of the recognition system with substantially lowered feature dimensions and elevated recognition rate.     

Predicting and evaluating the post-assembly shape of thin-walled components via 3D laser digitization and FEA simulation of the assembly process

Three-dimensional (3D) laser digitization has become a critical research field and a widely used technique for product quality inspection in the manufacturing and medical industries during the last decade. One common application of this technology is to analyze whether the final shape of an assembly component fulfills the designer’s geometric specifications. This task is currently performed by digitizing the component’s surface after mounting it into its final assembly or on a special testing frame. In order to speed up this process a new computational method is proposed for inspecting the final shape of an assembly component by virtually mounting it into the assembly, without the physical assembling process taking place. The developed computational method employs laser digitization to measure the initial shape of the assembly component and then finite element analysis (FEA) to predict its post-assembly shape. First, a laser-digitized dense mesh is smoothed and decimated to make it suitable for FEA. Material properties of the component, if not available, are then determined by a calibration process, and specific displacement boundary conditions are applied to reproduce the assembly process. After FEA is executed, the quality of the simulated post-assembly shape is checked using visualization tools such as light-reflection patterns and contour plots of the distance between the computed geometry and the target computer-aided design (CAD) geometry. Moreover, the accuracy of the proposed method is validated by comparing the simulated post-assembly shape with the actual post-assembly shape measured after physically assembling the component. Experiments show that the average distance between simulated shape and actual shape varies from 0.3 mm to 0.6 mm for objects with a characteristic size of a half meter, and that the isophotes and height fields of reflection (HFR) based indices are reduced up to 50%. The proposed method can thus predict the final shape of an assembled component well without assembling it, reducing the time and the cost of product quality inspection.     

Recommendations for dispatching emergency vehicles under multitiered response via simulation

Emergency medical service (EMS) systems provide medical care and transportation. While many real‐world systems use multiple vehicle types to attend different call priorities, few guidelines exist about which vehicles to allocate in multitiered responses where more than one vehicle is sent per call. This paper makes recommendations for multiple‐unit dispatch to multiple call priorities based on simulation optimization and heuristics. The objective is to maximize the overall expected survival probability of patients classified as “life‐threatening”. We assume two types of medical units and three call priorities; and that information may be updated when the medical unit arrives on‐scene. First, we study the optimal dispatching policies through several examples. Numerical results show that dispatching while considering call priorities, rather than dispatching the closest units, improves EMS system effectiveness. A heuristic algorithm is developed for large‐scale problems. A comparison between the heuristic and closest policy is demonstrated using real‐world data.     

高速多层板过孔分析与仿真

过孔效应已经成为制约高速PCB设计的关键因素之一,介绍了高速PCB设计中过孔对信号完整性的影响,尤其对于高速多层板过孔的特性进行了详细分析,并采用软件对多层印刷电路板上的过孔模型进行了仿真,着重分析了Stub对过孔传输特性所产生的影响,以及Back-drilling工艺的优势,仿真结果对高速PCB设计具有实际指导作用.     

Accelerated simulation method for estimating the probability of functional failure in high-reliability systems

We consider a class of systems whose required performance is described by a stochastic process (t), t 0. An accelerated simulation method is proposed for estimating the probability that at some time instant t [0, T] the required performance exceeds the available performance. A numerical example is considered.Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 30–41, July–August, 1991.     

Issues in the mining of heart failure datasets

This paper investigates the characteristics of a clinical dataset using a combination of feature selection and classification methods to handle missing values and understand the underlying statistical characteristics of a typical clinical dataset. Typically, when a large clinical dataset is presented, it consists of challenges such as missing values, high dimensionality, and unbalanced classes. These pose an inherent problem when implementing feature selection and classification algorithms. With most clinical datasets, an initial exploration of the dataset is carried out, and those attributes with more than a certain percentage of missing values are eliminated from the dataset. Later, with the help of missing value imputation, feature selection and classification algorithms, prognostic and diagnostic models are developed. This paper has two main conclusions: 1) Despite the nature of clinical datasets, and their large size, methods for missing value imputation do not affect the final performance. What is crucial is that the dataset is an accurate representation of the clinical problem and those methods of imputing missing values are not critical for developing classifiers and prognostic/diagnostic models. 2) Supervised learning has proven to be more suitable for mining clinical data than unsupervised methods. It is also shown that non-parametric classifiers such as decision trees give better results when compared to parametric classifiers such as radial basis function networks(RBFNs).     

Safety life analysis under the required failure possibility constraint for structure involving fuzzy uncertainty

For ensuring safety service of structure under fuzzy uncertainty, some efficient methods are proposed for analyzing safety life under the constraint that the actual time-dependent failure possibility (TDFP) less than the target failure possibility. The direct dichotomy method is firstly established to solve the safety life. Since the direct dichotomy method needs to iterate the TDFP at all searching points of the safety life and results in large computational cost, the equivalent constraint method (ECM) is established to solve the safety life. In ECM, the equivalence between the constraint of the actual TDFP and the equivalent constraint of the lower boundary of the minimum of the response function is strictly proved by the reduction to absurdity. By equivalently replacing the constraint of the actual TDFP with that of the lower boundary of the minimum of the output response, the computational cost for estimating the safety life is greatly reduced. Two solutions of the safety life based on the ECM are established. One is ECM based dichotomy method. The other is ECM based Newton method, where a simplified derivative solution is deduced to reduce the computational cost. After the implementations of solving the safety life are given in detail, several examples are used to verify the rationality of the established safety life analysis model and the efficiency of the methods for solving safety life.     

On the simulation of failure mechanisms in steel structures

The paper reports on the results of some recently performed numerical and physical experiments with steel structures. The experiments consisted of a bolt pull-out from a steel plate and the loading of different geometric arrangements of a trapezoidal stiffener of a steel orthotropic plate. Both numerical and physical experiments have been performed until full material failure. The simulations have been performed using LS-DYNA, a commercial finite element code. The paper discusses several modelling and numerical problems that have to be solved for the successful simulation. The simulation results are compared with the results of the physical experiments.     

Timing control points via simulation for production systems under random disturbances

The paper deals with the problem of production control with disturbances. The problem is applied to semi-automated production systems where the advancement of the process cannot be measured continuously but only in preset control (inspection) points. It is assumed that the production process can be simulated within a time interval of arbitrary size. Given the target amount needed, the due date, the routine control point, the actual accumulated production observed at that point, and the preset confidence probability (chance constraint) of meeting the deadline on time, the decision-maker has to determine the next control point. On-line control has to be carried out as rarely as possible but without missing the moment when the tendency to deviate from the planned trajectory may endanger meeting the due date on time under a chance constraint. Determining the next control point is carried out via simulation with a constant time step. At each intermediate check-point, decision-making based on sequential statistical analysis has to be undertaken, either.(a) to proceed further and to examine the next check-point; or(b) to determine the check-point under consideration as the last moment before the production process deviates from its target subject to the chance constraint. Thus, the next routine control point is determined.     

Stochastic resource allocation using a predictor-based heuristic for optimization via simulation

Some combinatorial stochastic resource allocation problems lack algebraically defined objective functions and hence require optimization via simulation as a mechanism for obtaining good solutions. For this class of problems, we propose a new predictor-based heuristic that uses a distance criterion to perform the solution search. To demonstrate our solution approach, we apply this heuristic to the problem of selecting the proper design configuration of an unmanned aerial system (UAS) fleet so as to maximize mission effectiveness. We compare our approach to black box optimization via simulation approaches (two tabu search-based procedures and a greedy heuristic) and glean both methodological and practical insights.     

虚拟手术中心脏跳动仿真技术研究

提出一种可实时运行的基于示例形状匹配的心脏跳动仿真方法,该方法通过简单的示例形态来控制心脏跳动过程中发生的形变行为。形变描述符被用来唯一定义形变对象的形变,并利用该描述符将形变优选空间表示为示例形态的线性组合。在每个时间步长中,当前的形变描述符被线性投影到示例歧管上,然后当计算目标位置时其被用于修改每个局部区域的静止形态。实验证明该方法能够真实地反映心脏的形变效果,达到实时模拟心脏跳动的目的。     

Importance sampling in systems simulation: a practical failure?

A network of servers, known as a grading in telecommunication engineering, is simulated in order to estimate the probability of a customer being “blocked”: all servers busy. Since blocking is a very rare event (1‰ to 5% chance), importance sampling was considered for reduction of the simulation variance. The basic idea of importance sampling is first explained by means of a non-dynamic system. For dynamic systems a method was proposed by Bayes in 1970, which is related to the “virtual measures” published by Carter and Ignall in 1975. For simple queuing systems, we derive the resulting variance, using the renewal or regenerative property of such systems. For our practical “grading” system several alternative importance regions are investigated. For practical reasons we choose to start an importance region immediately after a call gets blocked (not a renewal state). The analysis and simulation experiments for the resulting estimator yielded the estimated optimal length of the importance region and the optimal number of replications of the region. Unfortunately, a net increase in variance resulted.