Process Control Flow Research Articles

Model checking programs in process-oriented IEC 61131-3 Structured Text

The process-oriented programming is a paradigm based on the process concept where each process is a concurrent finite state machine inside. The paradigm is intended for PLC (programmable logic controllers) developers to write Industry 4.0-enabled software. The poST language is a promising process-oriented extension of the IEC 61131-3 Structured Text (ST) language designed to provide a conceptual consistency of the PLC source code with technological description of the process under control. This language combines the advantages of FSM-based programming with the standard syntax of the ST language. We propose transformational semantics of poST providing rules for translation of poST language statements to Promela — the input language of the SPIN model checker. Following these semantic rules, our Xtext-based translator outputs a Promela model for the poST program. Our contribution is the poST transformational semantics and the method for automatic generation of the Promela code from poST control programs. The resulting Promela program is ready to be verified with SPIN model checker against linear temporal logic requirements to the source poST program. In the paper we provide an overview of related work, as well as a brief description of the poST and Promela languages. Further, the Promela poST translation rules cover control flow statements, process creation and state management constructs, and timeout management. Then we define service processes for modeling the external environment and managing high-level LTL specifications. Then we present the main ideas of implementing the translator poST to Promela. We also illustrate our approach using the example of a system for managing electricity consumption and production, including renewable sources.

Correctness Notions for Petri Nets with Identifiers

A model of an information system describes its processes and how resources are involved in these processes to manipulate data objects. This paper presents an extension to the Petri nets formalism suitable for describing information systems in which states refer to object instances of predefined types and resources are identified as instances of special object types. Several correctness criteria for resource- and object-aware information systems models are proposed, supplemented with discussions on their decidability for interesting classes of systems. These new correctness criteria can be seen as generalizations of the classical soundness property of workflow models concerned with process control flow correctness.

ЕКСПОРТ АГРОПРОДУКЦІЇ ЗА ВИДАМИ ТРАНСПОРТУ

In the conditions of martial law, the importance of export of agricultural products is increasing, as Ukraine remains an agrarian country and guarantees the food security of the world. Therefore, the research of various aspects of agribusiness remains relevant. The article used a set of different methods of scientific knowledge, namely logical, descriptive, system-structural and others. An essential-conceptual analysis of the term “logistics” was carried out based on approaches to considering this concept at the macro- and micro-levels. The expediency of using a general approach to the definition of the term “logistics” is substantiated, as it covers a wider range of content. The significant role of innovations, technologies and information flows for improving the quality of logistics systems is noted. The definition of the term “agrologistics” has been formed, which takes into account the specifics of the agro-industrial complex. One of the special characteristics of logistics in agriculture, unlike other industries, is that the efficiency of logistics systems of agribusiness entities depends on the degree of continuity of management, organization and flow control processes and the level of digitization of these processes, as well as on the development of logistics infrastructure. The export of agricultural products by means of transport is outlined, with an analysis of the factors and conditions for choosing sea, rail or road transport. The conditions of international trade according to Incoterms are described. Detailed requirements and rules based on EXW (Ex Works), CPT (Freight/Carriage Paid Before), FCA (Free Carrier), DDU (Delivery Duty Free), DAF (Delivery to Border), FOB (Free on Board) and they are distributed by types of transport. The current state of export of agricultural products by types of transport in Ukraine is assessed, the important role of sea transport in agribusiness is determined. The main tasks facing agro-enterprises to improve the state of agro-logistics and boost exports have been formulated. Transport costs make up the largest share of export costs, therefore, the establishment of agro-logistics policy, the search for new strategies and solutions can give an impetus to the development of agricultural business entities of Ukraine. A conclusion was made about opportunities and threats for the further development of agribusiness in Ukraine.

Dynamic Stall Control for a Vertical-Axis Wind Turbine Using Plasma Actuators

Dynamic stall is a major challenge for vertical-axis wind turbines (VAWTs) as it negatively impacts the aerodynamic performance of VAWTs, resulting in a reduction in net power output from the turbines. This study explores the use of alternating current dielectric barrier discharge plasma actuators for controlling dynamic stall on a VAWT. The flow control process is resolved using a two-dimensional unsteady Reynolds-averaged Navier–Stokes equations simulation with a Reynolds stress turbulence model adopted. The macro-effect of the plasma discharge on mean flow is modeled by an empirical body force model. The detailed flow actuation procedure is simulated. Numerical results show that the flow control process is dominated by the spanwise vortices, which result from the interaction between the plasma discharge and separated flow. The spanwise vortices not only prevent the development of a leading-edge separation bubble into a dynamic stall vortex, but also suppress the flow separation at the trailing edge. The application of plasma forcing has been found to greatly enhance the aerodynamic performance of the turbine in terms of the moment coefficient and averaged power coefficient of the turbine blades. Furthermore, we examine how the positioning of the plasma actuators and the freestream wind velocity affect flow control. The optimal actuation location is determined, and the plasma actuators are seen to be able to substantially enhance the net power output of the blades at all freestream speeds.

Thermal examination of chemical interaction and thermophoretic diffusion of Williamson fluid flow across Riga Plate surface with nonlinearity radiation flux

The purpose of this research is to investigate the thermophoretic diffusion and chemical reaction on steady magnetized Williamson fluid flow, heat, and mass transfer along a Riga surface in the presence of variable thermal properties. By imposing the appropriate similarity technique, the system of higher-order formulas has been transformed from partial order into ordinary order. An efficient numerical technique named the classical Keller box scheme has been incorporated to solve these dimensionless coupled non-linear ordinary differential equations. The obtained results are visualized graphically with physical justification. In addition to that, we validated the obtained outcomes by comparing them to earlier literature, and we identified an excellent match, supporting the reliability of the present method. We discovered from our analysis that acceleration in the values of Williamson fluid and viscosity leads to enhancement in both velocity plots. Also, the material and stretching parameters have a major role in the fluid flow control process.

Data-aware conformance checking with SMT

Conformance checking is a key process mining task to confront the normative behavior imposed by a process model with the actual behavior recorded in a log. While this problem has been extensively studied for pure control-flow processes, data-aware conformance checking has received comparatively little attention. In this paper, we tackle the conformance checking problem for the challenging scenario of processes that combine data and control-flow dimensions. Concretely, we adopt the formalism of data Petri nets (DPNs) and show how solid, well-established automated reasoning techniques from the area of Satisfiability Modulo Theories (SMT) can be effectively harnessed to compute conformance metrics and optimal data-aware alignments. To this end, we introduce the CoCoMoT (Computing Conformance Modulo Theories) framework, with a fourfold contribution. First, we show how SMT allows to leverage SAT-based encodings for the pure control-flow setting to the data-aware case. Second, we introduce a novel preprocessing technique based on a notion of property-preserving clustering, to speed up the computation of conformance checking outputs. Third, we show how our approach extends seamlessly to the more comprehensive conformance checking artifacts of multi- and anti-alignments. Fourth, we describe a proof-of-concept implementation based on state-of-the-art SMT solvers, and report on experiments. Finally, we discuss how CoCoMoT directly lends itself to further process mining tasks like log analysis by clustering and model repair, and the use of SMT facilitates the support of even richer multi-perspective models, where, for example, more expressive DPN guards languages are considered or generic datatypes (other than integers or reals) are employed.

A CFD Modelling Approach for the Operation Analysis of an Exhaust Backpressure Valve Used in a Euro 6 Diesel Engine

Harvesting residual thermal energy from exhaust gases with thermoelectric generators is one of the paths that are currently being explored to achieve more sustainable and environmentally friendly means of transport. In some cases, thermoelectric generators are installed in a by-pass configuration to regulate the mass flow entering the thermoelectric generator. Some manufacturers are using throttle valves with electromechanical actuators and electronic control in the exhaust pipe to improve techniques for active control of pollutant emissions in reciprocating internal combustion engines, such as the exhaust gas recirculation. The above-mentioned circumstances have motivated the approach of this work: computational fluid dynamics (CFD) modelling of the operation of a throttle valve used for establishing adequate exhaust backpressure conditions to achieve the low pressure exhaust gas recirculation in Euro 6 engines. The aim of this model is to understand the flow control process with these types of valves in order to incorporate them in an exhaust system that will include two thermoelectric generators used to convert residual thermal energy into electrical energy. This work presents a computational model of the flow through the throttle valve under different temperatures and mass flow rates of the exhaust gas with different closing positions. For all cases, the values of the pressure drop were obtained. In all cases studied, the level of agreement between the modelled and experimental results exceeds 90%. The developed model has helped to propose a correlation to estimate the mass flow rate of exhaust gas from easily measurable quantities.

Special Issue “Active Flow Control Processes with Machine Learning and the Internet of Things”

The desired changes in flow characteristics are obtained by flow control, which implies manipulating flow behavior such as drag reduction, mixing augmentation, or noise attenuation, employing active or passive devices [...]

Towards a novel EMHD dissipative stagnation point flow model for radiating copper-based ethylene glycol nanofluids: An unsteady two-dimensional homogeneous second-grade flow case study

A novel EMHD dissipative second-grade nanofluid flow model is proposed exclusively in this numerical inspection for radiating copper-based ethylene glycol nanofluids to reveal the dynamical and thermal aspects of the studied homogeneous mixture during its unsteady two-dimensional stagnation point flow towards a horizontal electromagnetic actuator. Based on admissible physical assumptions and authenticated experimental correlations, the governing PDEs and BCs are derived appropriately for the nanofluid flow problem under consideration. After numerous rearrangements and non-dimensionalization treatments, the resulting ODEs and BCs are handled computationally with the help of a robust GDQ algorithm under the parametric control of several influencing factors, whose strengthening magnitudes affect probably the flow control process and heat transport mechanism. In this context, it proved graphically that the nanoparticles’ loading process exhibits dissimilar dynamical and thermal impacts as compared with the influences of the nanoparticles’ diameter size. Besides, the resistive dynamical effect of the utilized electromagnetic actuator reinforces thermally the enhancing role of the thermal radiative heat flux and Joule’s heating process within the nanofluidic medium.

Semantics-aware mechanisms for control-flow anonymization in process mining

Information systems support the execution of business processes. As part of that, data about process execution is recorded in event logs, which can be used to analyse the control-flow of the respective processes. However, such data may contain personal information on process stakeholders that is protected by privacy regulations. Process analysis based on event logs shall, therefore, employ anonymization techniques. In this paper, we introduce two approaches to anonymize the recorded control-flow of a process. Specifically, we present SaCoFa and SaPa as two techniques to anonymize the result of trace-variant queries over an event log. Unlike existing techniques that achieve differential privacy through randomized noise insertion, our techniques rely on noise insertion mechanisms that incorporate a process’ semantics, thereby avoiding easily-recognizable noise. Both techniques take different design choices, though. SaCoFa anonymizes a trace-variant distribution directly, thereby focusing on utility preservation at the expense of potentially changing the number of a traces in the result considerably. SaPa, in turn, anonymizes a trace-variant distribution indirectly, through play-out of an anonymized directly-follows distribution. This way, the number of traces in the result is close to the original log, but the drop in utility may become larger due to using only local control-flow information. However, our experiments demonstrate that both approaches strike a better balance of preserving the utility of an event log compared to existing techniques.

JShellDetector: A Java Fileless Webshell Detector Based on Program Analysis

Fileless webshell attacks against Java web applications have become more frequent in recent years as Java has gained market share. Webshell is a malicious script that can remotely execute commands and invade servers. It is widely used in attacks against web applications. In contrast to traditional file-based webshells, fileless webshells leave no traces on the hard drive, which means they are invisible to most antivirus software. To make matters worse, although there are some studies on fileless webshells, almost all of them are aimed at web applications developed in the PHP language. The complex mechanism of Java makes researchers face more challenges. To mitigate this attack, this paper proposes JShellDetector, a fileless webshell detector for Java web applications based on program analysis. JShellDetector uses method probes to capture dynamic characteristics of web applications in the Java Virtual Machine (JVM). When a suspicious class tries to call a specific sensitive method, JShellDetector catches it and converts it from the JVM to a bytecode file. Then, JShellDetector builds a Jimple-based control flow graph and processes it using taint analysis techniques. A suspicious class is considered malicious if there is a valid path from sources to sinks. To demonstrate the effectiveness of the proposed approach, we manually collect 35 test cases (all open source on GitHub) and test JShellDetector and only two other Java fileless webshell detection tools. The experimental results show that the detection rate of JShellDetector reaches 77.1%, which is about 11% higher than the other two tools.

Investigation of flow separation control over airfoil using nanosecond pulsed plasma actuator

A detailed investigation of flow separation control over a stalled NACA 0015 airfoil model using pulsed nanosecond dielectric barrier discharge (NS-DBD) plasma actuator is conducted through combined large eddy simulation (LES), dynamic mode decomposition (DMD) and experimental particle image velocimetry (PIV) measurement possibly for the first time. Airfoil flow at chord-based Reynolds number (Re) of Re = 6.3 × 104 is considered. It is found that the interplay of the residual heat due to the nanosecond plasma discharge with external flow causes the generation of vortices through the baroclinic and vortex dilation mechanisms and finally promotes the formation of large-scale vortical structures that dominate the early-stage evolution of the flow control process. One of the most important findings of this work is that the flow control mechanisms are not universal but depend on the forcing frequencies of plasma actuation, and are categorized into three different types. Meanwhile, three-dimensional DMD analysis of LES datasets is performed and the output of modal analysis helps provide more physical insights into flow control and determine the optimum forcing frequency. Depending on the value of forcing frequency, the global or local resonance of the forced flow with the periodic plasma actuation occurs. The plasma forcing at any frequencies in the range 1≤F+≤20 produces pronounced flow control authority except for that at F+=20. Moreover, the optimum forcing frequency is identified and its relationship with the inherent characteristic frequencies of the baseline flow is established based on DMD analysis. It is found that the most favorable control effect is achieved when the plasma excitation frequency is high and very close to the characteristic frequency of the separated shear layer in the unforced baseline flow.

Data-Based Flow Rate Prediction Models for Independent Metering Hydraulic Valve

Accurate valve flow rate prediction is essential for the flow control process of independent metering (IM) hydraulic valve. Traditional estimation methods are difficult to meet the high-precision requirements under the restricted space of the valve. Thus data-based flow rate prediction method for IM valve has been proposed in this study. We took the four-spool IM valve as the research object, and carried out the IM valve experiments to generate labeled data. Picking up the post-valve pressure and valve opening as input, we developed and compared eight different data-based estimation models, including machine learning and deep learning. The results indicated that the SVR and DNN with three hidden layers performed better than others on the whole dataset in the trade-off of overfitting and precision. And MAPE of these two models was close to 4%. This study provides further guidelines on high-precision flow rate prediction of hydraulic valves, and has definite application value for development of digital and intelligent hydraulic systems in construction machinery.

Development of a novel two-dimensional(2D) three-way(3W) fuel flow control servo valve with constant pressure difference

To solve the problems of large volume, and low integration of traditional electro-hydraulic servo valve with constant pressure differential fuel metering device, a new two-dimensional three-way constant pressure differential fuel flow control servo valve (2D3WFFCSV) is developed. It innovatively adopts the advantages of lightweight of “two-dimensional hydraulic technology”, The constant differential pressure function and flow regulation function are integrated into a two-dimensional (2D) main spool with two degrees of freedom (rotational and axial degrees of freedom). The flow control process of 2D3WFFCSV is as follows: firstly, the armature of the torque motor and the two-dimensional piston are coaxially installed at the end of the two-dimensional piston, so the torque motor can directly drive the two-dimensional piston to rotate; secondly the “hydraulic servo screw mechanism”, which can amplify the power, is used to drive the two-dimensional piston to move in line; Finally, a pair of conversion mechanisms (roller group and spiral track conversion mechanism) are converted into the angular displacement of 2D main spool to control the area of flow valve port. The axial degree of freedom of 2D main spool realizes the function of constant differential pressure. To improve the flow control accuracy of the servo valve, the axial position of the 2D piston is detected by the linear displacement sensor (LVDT), and the signal is transmitted to the controller to realize the closed-loop control. To explore its open-loop characteristics, the mathematical models of torque motor, two-dimensional piston and main spool are established to obtain its open-loop transfer function. Then the AMESIM simulation model is built. To optimize the design of the system, through the dynamic simulation of the system, the influence of key parameters on the dynamic response of the system can be studied. An experimental study is carried out to verify the design feasibility of the servo valve. The experimental results show that under the condition of no-load and full-scale input, the closed-loop delay of the servo valve is 1.84%, the linearity is 2.14%, the step response time is 43 ms, and the dynamic frequency response is 38 Hz. The newly developed 2D3WFFCSV has the advantages of high integration, small size, light weight (801.5 g) and high response and control accuracy. It can replace the constant differential pressure, metering valve and hydraulic servo valve in the aeroengine fuel regulator.

Process analysis and control flow design of the 1kW @ 4.5K helium refrigerator for NNBI

A helium cryogenic system with a cooling capacity of 1kW@4.5K was designed in order to support the NNBI(Negative ion based Neutral Beam Injection system) test facility, cryopumping test facility and beam source test facility, which consists of a helium compressor with its storage and recovery system, 1kW@4.5K helium refrigerator, a cryogenic distribution valve box, cryogenic transfer lines and a helium Dewar, etc. Based on the SIMATIC S7-1500H PLC, the cryogenic control system can realize seven major operational modes, including the independent refrigeration mode and independent liquefaction mode, etc. On the basis of process analysis, the control flow of the NNBI helium cryogenic system in each operational modes was designed and will be presented in this paper. It will direct the control system to realize automatic control in multiple operational modes.

Control flow versus communication: comparing two approaches to process modelling

PurposeBusiness process modelling integrates and visualizes relevant information essential for managing day-to-day business operations. It plays a critical role in the design and execution of business transformations. Recognizing the role of process modelling, a large number of modelling languages, methods and techniques have been developed, each offering diverse advantages and having inherent limitations. Traditional and popular process modelling approaches focus on the exact specification of the control flow of business processes, whereas more recent approaches like Subject-oriented Business Process Management (S-BPM) are focused on the communication between process participants. This study aims to provide comparative insights about these two approaches through their experimental application. This study does so by comparing Business Process Model and Notation (BPMN); a control flow approach, with S-BPM; a communication approach, with a specific focus on their suitability for novice modellers.Design/methodology/approachThis paper reports on an exploratory experiment that compares BPMN to S-BPM. Applying cognitive load theory, this study compares the experiences and outcomes of novice process modellers, assessing perceived ease of use, model quality (syntactic and semantic) and modelling efficiency (time to model) across the two approaches.FindingsStudy results show that S-BPM (a communication approach) led to significantly better user performances for process modelling than BPMN (a control flow approach). This study points to how a different modelling approach such as S-BPM could be either considered as an alternative or to complement the more popular control flow approach BPMN. This observation was especially relevant for modelling contexts where domain experts are novice process modellers.Originality/valueThis study provides the first empirical evidence that communication approaches like S-BPM could outperform modelling approaches which are control-flow based (i.e. BPMN), especially when being used by novice process modellers who hold the domain and process knowledge. This study uses this as a springboard to present important considerations for practice and guide future process modelling research.

Measuring Similarity for Data-Aware Business Processes

Business process similarity measures are of vital importance for process repository management applications, such as process query, process recommendation, and process clustering. Most existing approaches measure process similarity by relying on control-flow structures only. This article investigates the role of data in process similarity measure. To incorporate data-flow information into business process control flow, it proposes a data-aware workflow net (DWF-net) by extending the classical workflow net with data reading and writing semantics. Then, we introduce three types of similarity measures, i.e., data item set-based similarity, data operation set-based similarity, and data-aware behavior-based similarity, to quantify the similarity of data-aware business processes from different perspectives. Next, a methodology is introduced to help process analysts apply these three measures in a systematical way. Finally, we evaluate the effectiveness and applicability of the proposed similarity measures by a group of comparative experiments.

Fluid flow state estimation from sparse sensor measurements using convolutional neural network

State estimation from limited measurements can widely be found in various fields such as engineering, biology, and economics. In fluid mechanics, it has also contributed for flow control and experimental data processing. However, its application to fluid flows is particularly difficult due to their nonlinearities and high-degrees of freedom in space and time. Neural networks (NNs) have recently been recognized as a powerful tool to tackle the aforementioned challenges. In this presentation, we examine the applicability of NNs to various fluid flow estimations from a practical viewpoint. We use three types of unsteady laminar and turbulent flows for the present demonstration: flow around a square cylinder, turbulent channel flow, and transitional boundary layer. We utilize convolutional neural network (CNN) to estimate velocity fields from sensors arranged in a cross-section. We assess the practicability of the models by investigating physical quantities required for the input and robustness against lack of sensors. In addition, the effectiveness of several approaches to increase the robustness of the models is also examined.

Flow separation control over an airfoil using continuous alternating current plasma actuator

The flow separation control over an NACA 0015 airfoil using continuous alternating current (AC) dielectric barrier discharge (DBD) plasma actuator is investigated experimentally and numerically. This work is intended to report some observations made from our experiment, to which little attention is paid in the previous studies, but which is thought to be important to the understanding of control of complex flow separation with AC DBD. To this end, the response of separated flow to AC plasma actuation is visualized through the time-resolved particle image velocimetry (PIV) measurement, whereas numerical simulation is carried out to complement the experiment. The flow control process at chord-based Reynolds number (Re) of 3.31 × 105 is investigated. It is found that the response of external flow to plasma forcing is delayed for up to tens of milliseconds and the delay time increases with angle of attack increasing. Also observed is that at the intermediate angle of attack near stall, the forced flow features a well re-organized flow pattern. However, for airfoil at high post-stall angle of attack, the already well suppressed flow field can recover to the massively separated flow state and then reattach to airfoil surface with the flow pattern fluctuating between the two states in an irregular manner. This is contrary to one’s first thought that the forced flow at any angles of attack will become well organized and regular, and reflects the complexity of flow separation control.

Control and Commissioning of a Subcooled Helium Cryogenic Testing Platform with Cold Compressors

The subcooled helium cryogenic testing platform with cold compressors has been operated successfully in the end of 2018 at the Institute of Plasma Physics, Chinese Academy of Sciences (CASIPP). It is the first subcooled helium cryogenic system based on the cryogenic decompression technique in China, which has been designed and constructed over two years by our own team. The subcooled helium cryogenic testing platform was designed to provide the 4.5 K supercritical helium for the helium forced-flow cooling with one helium circulating pump, and provide the 3 K subcooled helium with two cold compressors in series. It consists of one 2.5 kW@4.5 K helium refregeator and one distribution valve box where the helium circulating pump and the cold compressors installed on it. This paper will present the process control flow of the distribution system and the design parameters of two cold compressors. During the commissioning, the startup and stop control flow of the two cold compressors have been determined. And their operation and control were performed within the safe operation area in the performance map. The testing result shows the lowest temperature and pressure of the saturated helium bath, and indicates the subcooled helium system has an equivalent refrigeration power greater than the design value of 700 W@3 K. The commissioning experience will help the reconstruction of the subcooled helium system for EAST Tokamak in future to enhance the cryogenic stability in higher magnetic field.