Fast-time Simulation Research Articles

Model Order Reduction of Multi-Terminal Direct-Current Grid Systems

This paper proposes a methodology to develop a linear low-order model of a multi-terminal direct-current (MTDC) system connected to practically-sized offshore wind farm systems. The method individually linearizes the model of wind farm systems and subsequently performs model order reduction (MOR) using iterative rational Krylov algorithm (IRKA). This is, therefore, a modular approach and expandable to any number of wind farm connections. On the other hand, the model order and non-linearity of other components are retained. Effectiveness of the proposed method is demonstrated on an MTDC system connected to two large-scale wind farm models by comparing the responses obtained from the full order model (FOM) and reduced order model (ROM). From the simulation studies, it can be seen that the ROM obtained from proposed method is able to maintain high degree accuracy of FOM responses at a much faster simulation time, and hence this can help power system operation planning. Various control functionalities and strategies, different operating conditions and faults of the MTDC system are also considered to investigate robustness of the proposed method.

Segmented Standard Taxi Routes—A New Way to Integrate Remotely Piloted Aircraft into Airport Surface Traffic

The safe and orderly integration of unmanned aircraft in the airspace is surely among the most difficult challenges to be solved in the near future. However, a safe and fluid traffic management on the ground is not less important and not less challenging, as completely different aspects have to be considered here. Much less work has been done yet to solve this question. In the frame of the project Surface Management Operations (SuMO), a procedural solution has been developed to enable fully integrated unmanned airport ground movements while allowing air traffic controllers to guarantee a safe, orderly and expeditious flow of traffic. This concept is based on the idea of segmented standard taxi routes for unmanned aircraft, while maintaining current procedures for manned aircraft. From 2017 to 2019, a two-stage validation campaign validated this new solution. No concerns regarding safety or human factors issues were revealed. Access and Equity, as well as Interoperability, were found to be very satisfying. A fast time simulation of mixed manned and unmanned traffic, using the proposed solution, was almost as efficient as pure manned traffic and can easily be implemented at medium-size airports. This article provides information about the experimental setup and the conduction of both validations stages, and illustrates obtained results. It closes with a discussion and an outlook.

Review of Conflict Resolution Methods for Manned and Unmanned Aviation

Current investigations into urban aerial mobility, as well as the continuing growth of global air transportation, have renewed interest in Conflict Detection and Resolution (CD&R) methods. With the new applications of drones, and the implications of a profoundly different urban airspace, new demands are placed on such algorithms, further spurring new research. This paper presents a review of current CR methods for both manned and unmanned aviation. It presents a taxonomy that categorises algorithms in terms of their approach to avoidance planning, surveillance, control, trajectory propagation, predictability assumption, resolution manoeuvre, multi-actor conflict resolution, considered obstacle types, optimization, and method category. More than a hundred CR methods were considered, showing how most work on a tactical, distributed framework. To enable a reliable comparison between methods, this paper argues that an open and ideally common simulation platform, common test scenarios, and common metrics are required. This paper presents an overview of four CR algorithms, each representing a commonly used CR algorithm category. Both manned and unmanned scenarios were tested, through fast-time simulations on an open-source airspace simulation platform.

Carbon Footprint and Total Fuel Consumption Benefit Evaluation of a Proposed Decision Support System Algorithm for Istanbul Ataturk Airport Surface Movement Area

The continuous growth in air traffic volume causes extra operational fuel consumption due to serious ground delays at major airports. Effective ground movement management of aircraft plays an essential role in reducing or even eliminating these ground holds and congestions. Ground movement of aircraft is conventionally done by ground controllers using conventional techniques, which rely on static and short-term (dynamic) planning. Such planning usually overlooks possible in-flight delays, which lead to gate assignment problems (GAP) at destination airports. Ground movement decision support system is proposed as an alternative method to mitigate these problems. This system allocates available taxi paths to arriving and departing aircraft. Such a dynamic planning provides more robust taxi path assignment and delay management at the airports movement area especially in the peak hours. This study analyzes time benefits and time cost effects of this system using SIMMOD, which is a fast time simulation tool. In order to demonstrate the fuel consumption benefits of tactical taxi path allocation, two scenarios (baseline and alternative), have been generated and tested for Istanbul Ataturk Airport. Keywords: Airport Modeling, Carbon Footprint, Heuristic Algorithm, Airport Ground Delays, Air Traffic Management DOI: 10.7176/JSTR/6-04-06

On the Algorithmic Identification of Optimal Coarse-Grained Representations of Biomolecules

The ever increasing computer power, together with the improved accuracy of atomistic force fields, enables researchers to investigate biological systems at the molecular level achieving remarkable sizes and detail. However, the computational resources required to cover biologically relevant length and time scales are unavailable but to a few groups worldwide; furthermore, it is often the case that the physical and biological questions one tackles by means of computer simulations and in silico models remain unanswered even having access to cutting-edge technology, when multiple runs and/or fast simulation times are required. One of the most effective solutions to these limitations is offered by simplified, or coarse-grained, models of large biomolecules, capable of providing insightful information on the system's properties at a lower computational cost with respect to all-atom models. Generally, coarse-grained models employ a uniform mapping, that is, a given group of atoms (e.g. an amino acid or a nucleic acid basis) is mapped onto the same effective interaction site irrespectively of its specific environment, properties, and role. Consequently, relevant fine-grained detail is removed or poorly embedded in these models, with detrimental consequences for the realistic and accurate representation of the system. An alternative to this intuitive yet limiting strategy is the usage of non-uniform mappings in which the resolution of the system can vary depending on local as well as global features. In this talk I will make the case for this kind of approaches, presenting and discussing algorithmic procedures developed to identify the representation of a given system which optimally describes it, distributing the atomistic detail and the crude coarse-grained simplification so as to balance efficiency and accuracy.

Navigation in Restricted Channels Under Environmental Conditions: Fast-Time Simulation by Asynchronous Deep Reinforcement Learning

This paper proposes an efficient method, based on reinforcement learning, to be used as ship controller in fast-time simulators within restricted channels. The controller must operate the rudder in a realistic manner in both time and angle variation so as to approximate human piloting. The method is well suited to scenarios where no previous navigation data is available; it takes into account, during training, both the effect of environmental conditions and also curves in channels. We resort to an asynchronous distributed version of the reinforcement learning algorithm Deep Q Network (DQN), handling channel segments as separate episodes and including curvature information as context variables (thus moving away from most work in the literature). We tested our proposal in the channel of Porto Sudeste, in the southern Brazilian coast, with realistic environment scenarios where wind and current incidence varies along the channel. The method keeps a simple representation and can be applied to any port channel configuration that respects local technical regulations.

Simulation-Based Evolutionary Optimization of Air Traffic Management

In the context of aerospace engineering, the optimization of processes may often require to solve multi-objective optimization problems, including mixed variables, multi-modal and non-differentiable quantities, possibly involving highly-expensive objective function evaluations. In Air Traffic Management (ATM), the optimization of procedures and protocols becomes even more complicated, due to the involvement of human controllers, which act as final decision points in the control chain. In this article, we propose the use of computational intelligence techniques, such as Agent-Based Modelling and Simulation (ABMS) and Evolutionary Computing (EC), to design a simulation-based distributed architecture to optimize control plans and procedures in the context of ATM. We rely on Agent-Based fast-time simulations to carry out offline what-if analysis of multiple scenarios, also taking into account human-related decisions, during the strategic or pre-tactical phases. The scenarios are constructed using real-world traffic data traces, while multiple optimization variables governed by an EC algorithm allow to explore the search space to identify the best solutions. Our optimization approach relies on ad-hoc multi-objective performance metrics which allow to assess the goodness of the control of aircraft and air traffic regulations. We present experimental results which prove the viability of our approach, comparing them with real-world data traces, and proving their meaningfulness from an Air Traffic Control perspective.

Navigation simulations as support to lock approaches design. Application to Ampsin-Neuville new lock, Meuse, Belgium

The existing 136 × 16 m lock at Ampsin-Neuville, on River Meuse, Belgium, is close from saturation. A new lock, sized 225 × 25 m, has been designed in order to increase the capacity and will soon be built. Site constraints are significant: existing lock on the outer side of a river bend, limited space between existing lock and weir, hydropower station on the left bank, etc. Two layouts were successively tested in details: (1) replacing the right hand pass of the weir by the new lock, and building a new spillway around the hydropower station; and (2) building the new lock on the location of the existing 136 × 16 m lock, with use of a secondary lock to maintain navigation during works. Civil engineering studies were supported by different nautical simulations. Fast-time simulations were used in a first stage, with the ClusterTool software (DST), to check the availability of waiting berths in each design, with no current. In a second stage, real-time simulations were performed on the SANDRA simulator at DST, to check manoeuvrability with current. Lastly, manoeuvring times were used in capacity simulations, using IMDC-Locks software (IMDC). In particular, the capacity of the secondary lock of the second layout had to be tested. All the results collected helped to choose the appropriate design for the new lock, and to optimize future operation rules.

A Mindset-Based Evolution of Unmanned Aircraft System (UAS) Acceptance Into the National Airspace System (NAS)

The main goal of this research is to evaluate the Air Traffic Controller (ATCo) workload considering the Unmanned Aircraft System (UAS) integration into the National Airspace System (NAS) through fast-time simulations, and including futuristic scenarios in which the ATCo is familiar with manned and unmanned aircraft, i.e., different ATCo mindsets are considered. As these professionals play an essential role in optimizing the airspace operation, maintaining their workload at an acceptable level is essential. However, the integration of new technologies, such as UAS, may present an impact on safety levels from the workload perspective. In this context, the Technology Maturity Level (TML), which is a systematic metric/measurement system that supports assessments of the familiarity of a particular aircraft with ATCos, is proposed. The experiments showed that the integration of UAS into the NAS should be conducted gradually.

Conservative multirate multiscale simulation of multiphase flow in heterogeneous porous media

Accurate and efficient simulation of multiphase flow in heterogeneous porous media motivates the development of space-time multiscale strategies for the coupled nonlinear flow (pressure) and saturation transport equations. The flow equation entails heterogeneous high-resolution (fine-scale) coefficients and is global (elliptic or parabolic). The time-dependent saturation profile, on the other hand, may exhibit sharp local gradients or discontinuities (fronts) where the solution accuracy is highly sensitive to the time-step size. Therefore, accurate flow solvers need to address the multiscale spatial scales, while advanced transport solvers need to also tackle multiple time scales. This paper presents the first multirate multiscale method for space-time conservative multiscale simulation of sequentially coupled flow and transport equations. The method computes the pressure equation at the coarse spatial scale with a multiscale finite volume technique, while the transport equation is solved by taking variable time-step sizes at different locations of the domain. At each coarse time step, the developed local time-stepping technique employs an adaptive recursive time step refinement to capture the fronts accurately. The applicability (accuracy and efficiency) of the method is investigated for a wide range of two-phase flow simulations in heterogeneous porous media. For the studied cases, the proposed method is found to provide 3 to 4 times faster simulations. Therefore, it provides a promising strategy to minimize the tradeoff between accuracy and efficiency for field-scale applications.

Time-Efficient Integrated Electrothermal Model for a 60-kW Three-Phase Bidirectional Synchronous DC–DC Converter

This article introduces an accurate and fast electrothermal model to calculate power loss and junction temperature of power electronic devices in a three-phase dc–dc converter, and to simulate converter dynamics during a simulated drive cycle. The proposed electrothermal model calculates power loss and junction temperature by representing the three-phase dc–dc converter dynamics within a drive cycle using a three-phase state-space average model. The three-phase state-space average model is modified to represent converter dynamics when one or two phases are off , in addition to the phase transition dynamics. The existing electrothermal models can either represent converter dynamics but are too slow for long simulations like drive cycles, or they reduce the simulation time at the expense of junction temperature accuracy. Furthermore, the existing electrothermal models in the literature are for inverters and single-phase dc–dc converters. The proposed electrothermal model combines the advantages of fast simulation time with accurate estimation of junction temperature. The power loss calculated by the proposed method is verified by a switching Simulink/PLECS model, and the mosfet temperature estimation is validated experimentally using a 60-kW three-phase bidirectional boost converter under steady-state conditions and a custom drive cycle. The efficiency of the three-phase converter is measured experimentally and compared with the efficiency calculations from the proposed electrothermal model.

A Universal SPICE Field-Effect Transistor Model Applied on SiC and GaN Transistors

This paper presents a universal SPICE model for field-effect transistors, which is independent from technology and semiconductor material. The created behavioral simulation model is based on a set of collected measurement data. The temperature-dependent output characteristics are modeled using a hybrid approach consisting of lookup tables and analytical equations. This leads to fast simulation times and very high accuracy. The validity for the static temperature-dependent behavior of this approach is verified for one SiC and one GaN transistor using the respective datasheet curves. The transistors nonlinear capacitances are modeled in dependence of their inter-electrode voltages. In order to verify the validity in the dynamic range, the universal model is applied to a GaN high-electron-mobility transistor. Double pulse measurements are used for the dynamic validation at a characterized measurement test bench regarding its parasitic elements. Therewith a proper validation of the simulation model at switching transients as low as 5 ns is achieved.

Development of Analog Behavioural Model of BiMOSFET

Behavioural modelling of a power semiconductor device offers many advantages to an application engineer as it is possible to model the device from the available datasheet without a detailed knowledge of the fabrication process. The development of an analog behavioural model for a BiMOSFET is undertaken here by using the Hammerstein model. The Hammerstein model is developed with static and dynamic block sub-blocks and is designed to respond for varying temperatures.The datasheet values of Ic and Vceare utilized to derive the static linear block,while the dynamic block is modelled as Hammerstein current source.The developed model of the BiMOSFET has been verified for its terminal characteristics through OrCAD simulations and hardware testing. The developed model of BiMOSFETexhibits fast simulation times with reasonable accuracy. The hardware testing is carriedout with BiMOSFET IXBF55N300 by observing its currents and voltages under the variation of gate voltage at constant collector emitter voltage and variation of collector emitter voltage at constant gate voltage.

Integrating Air and Near Space Traffic Management for aviation and near space

Commercial space transportation is becoming more affordable and accessible. Consequently, we expect to see significant expansion of commercial space launch activities in the coming decade. As space vehicles travel through airspace during the launch and re-entry stages, they potentially disrupt the regular operations of traditional users. This paper estimates the potential economic and operational impacts of commercial space horizontal launch activities on airlines under various launch scenarios using predictive fast-time simulation modeling, focusing on Cecil Air and Space Port in Jacksonville (Florida) and the rules governing the national airspace system (NAS) in the United States. Our results indicate that the existing 4-hour airspace closure rule impacts a significant number of flights, resulting in flight time delays, additional flight distance and fuel burn, as well as other direct operating costs. Safely reducing the duration of airspace closures could serve as a simple solution to mitigate the impacts on airlines and other traditional NAS users. More importantly, treating our studied launch vehicle as an aircraft and opening its departure/arrival corridor to air traffic during a horizontal launch and return would potentially reduce the impacts on airlines significantly, depending on the location of the spaceport, planned flight paths and the trajectory of the launch.

Time- and space-parallel simulation of air traffic networks

Computer simulations are widely used to design and evaluate air traffic systems. A fast time simulation capability is essential to effectively explore the consequences of decisions in airspace design, air traffic management, and operations. A parallel simulation approach is proposed to accelerate fast time simulation of air traffic networks that exploits both temporal and spatial parallelisms. A time-parallel algorithm is first described that simulates different time intervals concurrently and uses a fix up computation that exploits the scheduled nature of commercial air traffic to address the problem of dependencies between time segments. The time-parallel algorithm is then extended with a space-parallel simulation approach using Time Warp to simulate each time segment in parallel thereby increasing the amount of parallelism that can be exploited. The time and space-parallel algorithms are evaluated using a simulation of the U.S. National Airspace System (NAS). Experimental data is presented demonstrating that this approach can achieve greater acceleration than what can be achieved by exploiting time-parallel or space-parallel simulation techniques alone.

Analyzing the Departure Runway Capacity Effects of Integrating Optimized Continuous Climb Operations

Performing Continuous Climb Operation (CCO) procedures enable the reduction of the environmental footprint and the improvement of the trajectory efficiency when individually operated. However, its operation may affect negatively the overall operational efficiency at Terminal Manoeuvring Areas (TMAs). The estimation of capacity is a matter of paramount importance to all airport planning and analyzing the capacity effects of this particular operational technique on a certain scenario will definitely help on evaluating its potential applicability. In this paper, departure runway capacity at the Adolfo Suárez Madrid-Barajas airport was operationally evaluated when introducing CCOs. The considered trajectories consisted of multiobjective optimized CCOs based on the optimal control theory, using the pseudospectral direct numerical method. These scenarios allowed addressing of the incremental variations of CCOs versus conventional departures, through fast time simulation, with the objective to assess the effects on the operations.

Trajectory Specification for Terminal Airspace: Conflict Detection and Resolution

Trajectory Specification is a method of specifying aircraft trajectories with tolerances such that the position at any given time in flight is constrained to a precisely defined bounding space. The bounding space is defined by tolerances relative to a reference trajectory that specifies position as a function of time. The tolerances are dynamic and are based on the aircraft navigation capabilities and the traffic situation. Trajectory Specification can guarantee safe separation for an arbitrary period of time even in the event of an air traffic control (ATC) system or datalink failure. It can help to achieve the high level of safety and reliability needed for ATC automation, and it can reduce the reliance on tactical ATC backup systems during normal operation. This paper presents algorithms and software for detecting and resolving conflicts between specified trajectories in the terminal airspace serving a major airport. In a fast-time simulation of a full day of traffic in a major terminal airspace, all conflicts were resolved in near real time, demonstrating the computational feasibility and the preliminary operational feasibility of the concept.

Determination of the Risk of Location the Quay for Large Steel Components Handling in Vicinity of the Fairway Using the Fast-Time Simulation Method

AbstractThe paper presents the use of the Fast-Time navigational simulator to verify the location of designed elements of navigational infrastructure in vicinity of a high traffic fairway. The aim of the study is to perform the analysis of navigational safety in vicinity of newly constructed quay placed to the east of the island Ostrow Brdowski. The Quay is intended handling of large steel structures. The Fast-Time simulation is performed to evaluate the safety of the navigation passage through the fairway along the quay for the future use of vessels which length may exceed 260 m. This kind of simulation method has been implemented to make a statistical analysis based on a large amount of data, the collection of which would be very expensive and time consuming using a Real-Time simulator.

Modelling and Simulating Airport Surface Operations with Gate Conflicts

ABSTRACTThe Surface Operations Simulator and Scheduler (SOSS) is a fast-time simulation of the airport surface used to rapidly develop and test new surface scheduling concepts. Gate conflicts present a challenge for surface scheduling. A late departure pushback or early arrival sharing the same gate can cause a gate conflict, which if left unmanaged, can lead to surface gridlock. Surface scheduling concepts that meter departures at their gates can increase the likelihood of gate conflicts. In real operations, hardstand areas are used to temporality park aircraft out of the way to avoid gate conflicts. New SOSS models and functionality for hardstand operations were developed to simulate gate conflict management approaches using hardstands to temporarily park either the arrival or departure out of the way of the other. Four gate conflict management approaches were simulated with surface scheduling and their effects on surface operations were compared. The four gate conflict management approaches each allowed a unique subset of resolution actions including early departure pushback, sending the departure to the hardstand, and sending the arrival to the hardstand. The gate conflict management approaches allowing arrivals to be sent to the hardstand were found to be most successful in resolving the gate conflicts and maintaining scheduler performance measured by takeoff time predictability.

Constant speed optimal reciprocal collision avoidance

In this article, the Optimal Reciprocal Collision Avoidance (ORCA) algorithm is modified to make it work for speed constrained aircraft. The adaptation of ORCA to aircraft conflict resolution shows that when the speed norm is constrained, aircraft flying within the same speed range with small angle converging trajectories tend to remain on parallel tracks, preventing a resolution of the conflict. The ORCA algorithm is slightly modified to avoid this behavior. In the new algorithm called CSORCA (Constant Speed Optimal Reciprocal Collision Avoidance), the directions of the semi-plane used to calculate the conflict free maneuvers are modified when the relative speed vector is in the semi-circular part of the conflicting area. After explaining the reasons that make the original algorithm fail in the constant speed environment, the modification made on the algorithm is detailed and its impact on a simple example is shown. The new strategy is also compared to an Add-Up strategy close to the Airborne Separation Assurance System (ASAS) strategy found in the literature. Hundreds of fast time simulations are then performed to compare the two versions of the algorithm for different traffic densities in the horizontal plane. In these simulations the speed norm is first constrained. The aircraft can only change direction with a limited turning rate. Simulations with released speed constraints are then performed to compare the behavior of both algorithms in a more general environment. In all the scenarios tested, CSORCA is more efficient than ORCA to solve conflicts.