Present Simulation Results Research Articles

Obstacle avoidance and trajectory optimisation for an autonomous vessel utilising MILP path planning, computer vision based perception and feedback control

In this study, we investigated autonomous vessel obstacle avoidance using advanced techniques within the Guidance, Navigation, and Control (GNC) framework. We propose a Mixed Integer Linear Programming (MILP) based Guidance system for robust path planning avoiding static and dynamic obstacles. For Navigation, we suggest a multi-modal neural network for perception, demonstrating the identification of obstacle type, position, and orientation using imaging sensors. Additionally, the paper compares an error-based PID control strategy and a Model Predictive Control (MPC) scheme as well. This evaluation aids in better evaluating their performance and determining their applicability within the GNC scheme. We detail the implementation of these systems, present simulation results, and offer a performance evaluation using an experimental dataset. Our findings, analysed through qualitative discussion and quantitative performance indicators, contribute to advancements in autonomous navigation and the control strategies to achieve it.

Roughness-Induced Transition in Supersonic Boundary Layers with Wall Heating and Cooling Effects

The laminar–turbulent transition of a supersonic boundary layer induced by an isolated roughness element is investigated using direct numerical simulation, BiGlobal linear stability theory, and the three-dimensional parabolized stability equation. Cylindrical and diamond-shaped roughness elements are investigated in combination with different wall temperatures. Direct numerical simulations show that the cylinder configuration induces an earlier transition than the diamond configuration, with the interaction between the separated shear layer and the counter-rotating vortices causing the transition. BiGlobal analysis and the parabolized stability equation confirm the existence of two unstable instability modes in the wake region, namely, a symmetric mode and an antisymmetric mode, with the former being strongly dominant. The wall cooling and heating effects are studied by changing the wall temperature. Wall heating lifts the inlet boundary layer and weakens the separated shear layer. This, in turn, weakens the wake instability and delays the transition. The antisymmetric model disappears as the wall heating increases. Wall cooling accelerates the transition by enhancing the distortion of the roughness wake, resulting in stronger instabilities. Finally, the Reynolds number based on the momentum defect is used to define the transition criterion, and this is found to be in good agreement with the present simulation results.

Online as-Built Building Information Model Update for Robotic Monitoring in Construction Sites

Today, automated techniques for the update of as-built Building Information Models (BIM) make use of offline algorithms restricting the update frequency to an extent where continuous monitoring becomes nearly impossible. To address this problem, we propose a new method for robotic monitoring that updates an as-built BIM in real-time by solving a Simultaneous Localization and Mapping (SLAM) problem where the map is represented as a collection of elements from the as-planned BIM. The suggested approach is based on the Rao-Blackwellized Particle Filter (RBPF) which enables explicit injection of prior knowledge from the building’s construction schedule, i.e., from a 4D BIM, or its elements’ spatial relations. In the methods section we describe the benefits of using an exact inverse sensor model that provides a measure for the existence probability of elements while considering the entire probabilistic existence belief map. We continue by outlining robustification techniques that include both geometrical and temporal dimensions and present how we account for common pose and shape mistakes in constructed elements. Additionally, we show that our method reduces to the standard Monte Carlo Localization (MCL) in known areas. We conclude by presenting simulation results of the proposed method and comparing it to adjacent alternatives.

Analysis of the Spread of Covid-19 via Atangana-Baleanu Fractional Derivatives

We study the spread of the epidemic via Atangana-Baleanu Fractional Derivatives. We present the mathematical analysis and formulation of a fractional model for the epidemic. The existence and uniqueness of the solution for the proposed model are proved. The study also investigates the existence of disease-free equilibrium and analyzes its stability properties. To validate the theoretical results, we provide a numerical scheme for the fractional model and present various simulation results. These results can serve as a valuable resource in developing strategies to mitigate the spread of the epidemic.

Numerical Simulation of Soliton Propagation Behavior for the Fractional-in-Space NLSE with Variable Coefficients on Unbounded Domain

The soliton propagation of the fractional-in-space nonlinear Schrodinger equation (NLSE) is much more complicated than that of the corresponding integer NLSE. The aim of this paper is to discover some novel fractal soliton propagation behaviors (FSPBs) of this fractional-in-space NLSE. Firstly, the exact solution is compared with the present numerical solution, and the validity and accuracy of the present numerical method are verified. Secondly, the effect of fractional derivatives on soliton propagation is explored through the present numerical simulation results. At the same time, the present method is extended to the three-dimensional fractional-order NLSE. Finally, some novel FSPBs of the fractional-in-space NLSE are given.

State-Difference Feedback Control for Discrete-Time Takagi–Sugeno Fuzzy Descriptor Systems with Parameter Uncertainties and External Noises

This research focuses on the development of state-difference feedback controllers for discrete-time (DT) nonlinear descriptor systems. Discrete-time nonlinear DA systems consist of difference and algebraic equations and play a crucial role in describing dynamic behavior and capturing the constraints or relationships within the system. However, analytical stability may pose additional challenges due to the unique characteristics of the system. Utilizing fuzzy model-based techniques, the DT nonlinear DA system discussed in this study can be effectively represented using the Takagi–Sugeno (T-S) fuzzy model. After linearizing the nonlinear system through the T-S fuzzy model, traditional linear control techniques become applicable. These techniques are then applied to T-S fuzzy systems to establish stability criteria. This article chooses the Lyapunov function as the method used to analyze system stability. Additionally, we use a free-weighting matrix to introduce additional degrees of freedom. In summary, this paper presents simulation results and discussions to verify the effectiveness of the proposed design approach.

A novel fast roll-off bandpass frequency selective surface for stealth applications

A novel frequency selective surface (FSS)-based spatial bandpass filter for TM-polarized waves is reported. The unit cell of the proposed FSS consists of a dielectric substrate with two conducting layers on opposite sides. One magnetic resonator is placed on the top conducting layer, while two pairs of electric resonators are positioned on the bottom conducting layer to provide a fast roll-off bandpass characteristic. The simulated values of the −3 dB to −10 dB roll-off factor (RF) for the proposed structure are 140 and 280 dB/GHz on the lower and upper sides of its passband, respectively. To validate the simulation results of the proposed structure, a prototype of the FSS-based filter was fabricated and tested experimentally. Furthermore, the present simulation results are benchmarked with the band-pass FSSs reported in the literature, demonstrating an advantage of the proposed filter over the filters mentioned in previous works.

Combined magnetic field evolution in neutron star cores and crusts: ambipolar diffusion, Hall effect, and Ohmic dissipation

ABSTRACT Neutron star magnetic field evolution is mediated through the Hall effect and Ohmic dissipation in the crust while ambipolar diffusion is taking place in the core. These effects have been studied in detail in either part of the star, however, their combined, simultaneous evolution and interplay has not been explored in detail yet. Here, we present simulation results of the simultaneous evolution of the magnetic field in the core due to ambipolar diffusion and the crust due to Hall effect and Ohmic decay, under the assumption of axial symmetry. We find that a purely poloidal field generates a toroidal field in the crust, due to the Hall effect, that sinks into the core. A purely toroidal field remains toroidal and spreads into the core and the crust. Finally, for a mixed poloidal–toroidal field, the north–south symmetry is broken due to the Hall effect in the crust, however, ambipolar diffusion, tends to restore it. We examine the role of ambipolar diffusion to the magnetic field decay and we compare the rate of the conversion of magnetic field energy into heat, finding that it enhances the magnetic field decay in neutron stars.

Investigation of Large Scale Traveling Atmospheric/Ionospheric Disturbances Using the Coupled SAMI3 and GITM Models

AbstractWe present simulation results of the vertical structure of Large Scale Traveling Ionospheric Disturbances (LSTIDs) during synthetic geomagnetic storms. These data are produced using a one‐way coupled SAMI3/Global Ionosphere Thermosphere Model (GITM) model, where GITM provides thermospheric information to SAMI3 (SAMI3 is Another Model of the Ionosphere), producing LSTIDs. We show simulation results which demonstrate that the traveling atmospheric disturbances (TADs) generated in GITM extend to the topside ionosphere in SAMI3 as LSTIDs. The speed and wavelength (600–700 m/s and 10º–20° latitude) are consistent with LSTID observations in storms of similar magnitudes. We demonstrate the LSTIDs reach altitudes beyond the topside ionosphere with amplitudes of <5% over background which will facilitate the use of plasma measurements from the topside ionosphere to supplement measurements from Global Navigation Satellite System in the study of Traveling Ionospheric Disturbances (TIDs). Additionally, we demonstrate the dependence of the characteristics of these TADs and TIDs on longitude.

CFD-FEM simulation of water entry of aluminium flat stiffened plate structure considering the effects of hydroelasticity

In this paper, the slamming loads and structural response of an aluminium flat stiffened-plate structure during calm water entry considering the hydroelasticity effects are studied by a partitioned CFD-FEM two-way coupled method. The target structure is simplified as one segment of an idealized ship grillage structure, comprising flat plate and stiffeners. The typical numerical results are analyzed such as vertical displacement, velocity, acceleration, impact loads, and structural stress of the flexible flat bottom grillage structure considering the hydroelasticity effect and air cushion effect in different free fall height conditions. Drop test results of the same structure and other existing numerical simulation data by both coupled and uncoupled solutions in the literature are used for comparison with the present numerical simulation results. This study provides a practical means to simulate the slamming behaviour and structural response of ship structures, which is useful for predicting ship hull stiffened panel loads and related structural design.

Dynamics of off-axis injection near the coupling resonance at PETRA IV

The PETRA IV project will have a storage ring with an ultra-low natural emittance of 20 pm rad. For an off-axis injection scheme with working points at the difference resonance, it is critical to ensure that the vertical excursion caused by transversal coupling does not affect injection efficiency. In this contribution, we present simulation results of an off-axis injection near the coupling resonance, which provides equal equilibrium emittances. The advantages and disadvantages of such a scheme are discussed.

Swarm intelligence algorithms for optimising sliding wear of nanocomposites

This paper presents simulation results obtained by a set of modern algorithms adhering to swarm intelligence for minimising wear rate in the case of A356/Al2O3 nanocomposites produced using a compocasting process. Grey wolf optimisation (GWO) algorithm, moth-flame optimisation (MFO) algorithm, dragonfly algorithm (DA) and whale optimisation algorithm (WOA) were the algorithms under examination. A full quadratic regression equation that predicts wear rate, as the optimisation objective by considering reinforcement content, sliding speed, normal load and reinforcement size as the independent process parameters, was utilised as the objective function. Simulation results obtained by the selected algorithms were quite promising in terms of fast convergence and global optimum result arrival, thus prompting to further investigation of applying swarm intelligence to general problem-solving aspects related to tribology.

Dynamic Investigations of Grid Connected Fixed-Speed Wind Turbine During Grid Faults

Especially during grid faults, grid code requirements for wind power integration have become a key element in improving grid efficiency and reliability. Under severe problems for network operation, wind turbines are expected to continue operating and supporting the grid during frequency restoration. This paper presents simulation results of a fixed-speed grid-connected wind turbine under various short-circuit current contributions. Fault analysis is carried out by studying the grid side line to ground fault, double line fault, double line to ground fault, and three phase fault involving ground and without ground. The obtained current waveforms are analyzed to explain the behavior, such as the rate of decay and peak values. Variations of active and reactive power during post-fault conditions and faulty conditions are investigated. Moreover, recommendations for switchgear and protection equipment are performed.

Fuel Melting Simulation with FRAPCON/FRAPTRAN Codes for the Power-to-Melt-and-Maneuverability Simulation Exercise and Consideration of Model Modifications

This paper presents simulation results of earlier fuel melting tests (xM3 and HBC4) performed under the power-to-melt-and-maneuverability (P2M) simulation exercise organized within the Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) framework for irradiation experiments. The simulations were performed using the single-rod performance analysis code FRAPCON/FRAPTRAN as a contribution of the Central Research Institute of Electric Power Industry (CRIEPI) to the P2M simulation exercise. To this end, the base irradiation of each sample was simulated using FRAPCON software, and the calculated result was used to define the initial state of the transient simulations; the xM3 and HBC4 ramp tests were simulated using FRAPTRAN. Fuel melting was not predicted for xM3, and the melting radius was underestimated for HBC4 using the original version of FRAPTRAN. The value of the fuel/cladding gap conductance was modified to obtain results that satisfy the experimental measurement of the melting radius. In this paper, the simulation results are compared with experimental results, and the causes for discrepancy between the simulation and experiment results are discussed. The necessary improvements for FRAPTRAN to achieve a better simulation of fuel melting are also discussed. These results can help calibrate codes against high-temperature behavior and improve fuel melting modeling toward the planned P2M power ramp tests.

Adaptation of the turbulence model to the heat transfer in a rod bundle

Fast neutron reactors using liquid metal or gas coolants are one of the most actively studied fields of research. Increased safety requirements and insufficient knowledge of the thermohydraulic characteristics of these coolants require validation of RANS simulations via information from experiments or DNS. This information can also be applied to improve the RANS turbulence model ifnecessary.In this paper, a series of thermohydraulic DNS simulations of the uniformly heated rod bundle with a relative pitch of 1.4 have been performed to improve RANS. A total of 12 test cases with four different Prandtl numbers of Pr = 0.0043, 0.0154, 0.0324 and 0.71, which correspond to liquid metals and gas, and three Reynolds numbers of Re = 2500, 5000 and 10,000 are considered. The present simulation results show good agreement with the experimental and DNS data. It is revealed that the intermittent flow regime forms at Re = 2500. Furthermore, the turbulent Prandtl number is structured with a maximum of up to y+≈25 and, from y+≈50 onwards, in most cases takes on a constant value. By increasing the Prandtl or Reynolds number, the average value of the turbulent Prandtl number tends to be 1.0. It was also revealed that the turbulent contribution to heat transfer is linear to the Reynolds number for the selected coolant. A new formula for the temperature profile was also obtained, which shows better agreement with DNS data compared to its analogues.As a result, the selected RANS model has been improved (the maximum integral error dropped from 49% to 4%) by the new model of the turbulent Prandtl number and by introducing model coefficients from DNS.

Security bipartite synchronization of MASs resilient to DoS attacks

This paper considers the security bipartite synchronization problem of nonlinear multi-agent systems (MASs) under the impact of denial-of-service (DoS) attacks. Notice that malicious attackers may block the neighbor information transmission among agents, which will reduce the efficiency of the distributed control strategy and even paralyze the entire system. In order to eliminate the impact of DoS attacks on the stability of MASs, this paper represents the first attempt to solve the security bipartite synchronization problem with the help of a distributed leader state observer. An observer that can obtain the leader state estimation is established, and the control strategy constructed based on the observer can eliminate the impact of DoS attacks. Theoretical analysis shows that the control strategy proposed in this paper can realize the security bipartite synchronization of the system under the impact of DoS attacks. The validity of the proposed results is verified by several presented simulation results.

A high-resolution, 3D groundwater-surface water simulation of the contiguous US: Advances in the integrated ParFlow CONUS 2.0 modeling platform

Large-scale, high-resolution hydrologic modeling is an important tool to address questions of water quantity, availability, and potential recharge. Continental-to-Global scale models, particularly those that include groundwater, are growing in number. However, many of these approaches simplify aspects of the system and the connections between surface water and groundwater. The ParFlow CONUS modeling platform is a large-scale, hyper-resolution, hydrologic model that relies on the integrated solution of 3D partial differential equations that describe groundwater, soil, and 2D surface water flow. The prior version, ParFlow CONUS 1.0, was the first large-scale hydrologic model that included an explicit treatment of lateral groundwater flow for the contiguous US (CONUS). Here, we present the ParFlow CONUS 2.0 integrated hydrologic model. This model extends to the coastlines and contributing basins for CONUS and is consistent with the NOAA National Water Model. Here we document the roughly five years of technical development of this platform, present steady-state simulation results, rigorously compare these results to the prior ParFlow CONUS 1.0 simulations, and evaluate the model performance based on observations. Simulated water table depth and streamflow were evaluated using more than 635 K observations from USGS monitoring wells, other compiled groundwater datasets, and NHD and USGS streamflow gauges. Our results demonstrate improvement in both groundwater and surface water simulations over the prior generation model for all USGS Hydrologic Unit Code (HUC) basins. These results suggest that this current generation hydrologic model has good to excellent streamflow performance over the entire CONUS, with almost half of the HUC subbasins exhibiting excellent performance based on normalized root-square error (RSR). These results suggest that the current generation model approaches good performance for water table depth over the CONUS, a metric not usually compared directly at all in large-scale studies, with good-to-excellent performance exhibited over some HUC regions. We also delineate two regions that influence model performance, one where microtopography around streams dominates (D2), and another where a mix of subsurface heterogeneity and topographic gradients dominate (D1). Improvements in topography from CONUS1 to CONUS2 generally result in better streamflow and water table depth performances. Advancements in the subsurface depth and structure also produce better water table estimates.

3D model for inertial cavitation bubble dynamics in binary immiscible fluids

The physics of cavitation bubbles in water has been extensively studied for over a century. However, our understanding of bubble dynamics in binary immiscible fluids, such as a water-oil system, is limited. These systems have recently gained a lot of interest due to their relevance in modern medical treatment, emulsification, and the food industry. In this study, we establish an accurate and inexpensive three-dimensional boundary integral (BI) model for inertial cavitation bubble dynamics in binary immiscible fluid systems. Our novel scheme for solving velocities on the flow boundaries, expressed in a matrix form, can be easily extended to complex situations where multiple bubbles are generated in different phases. Additionally, we employ a density potential method and a weighted moving least-squares method to maintain a high level of mesh regularity. Our results demonstrate that the proposed 3D model is comparable in accuracy to a 3D axisymmetric model by comparing it against analytical solutions and the results obtained from an axisymmetric model. Furthermore, we compare our numerical simulations against a purposely conducted experiment for the bubble-droplet interaction, and excellent agreement is achieved. For the first time, we present simulation results of two-bubble interactions with an initially flat fluid-fluid interface and inside a droplet surrounded by a second fluid. We also reveal the dependences of the two-bubble morphologies, flow patterns, and jet velocities on the density ratio between the two phases. Finally, we find a significant difference in the mechanism of fluid mixing by multiple bubbles compared to that of a single bubble case.

Multiple imputation for non-monotone missing not at random data using the no self-censoring model.

Although approaches for handling missing data from longitudinal studies are well-developed when the patterns of missingness are monotone, fewer methods are available for non-monotone missingness. Moreover, the conventional missing at random assumption-a natural benchmark for monotone missingness-does not model realistic beliefs about the non-monotone missingness processes (Robins and Gill, 1997). This has provided the impetus for alternative non-monotone missing not at random mechanisms. The "no self-censoring" model is such a mechanism and assumes the probability an outcome variable is missing is independent of its value when conditioning on all other possibly missing outcome variables and their missingness indicators. As an alternative to "weighting" methods that become computationally demanding with increasing number of outcome variables, we propose a multiple imputation approach under no self-censoring. We focus on the case of binary outcomes and present results of simulation and asymptotic studies to investigate the performance of the proposed imputation approach. We describe a related approach to sensitivity analysis to departure from no self-censoring. We discuss the relationship between missing at random and no self-censoring and prove that one is not a special case of the other. Finally, we discuss extensions to non-binary data settings. The proposed methods are illustrated with application to a substance use disorder clinical trial.

Investigation on the effects of asphalt mixes and their combinations on asphalt mix shear strength by 3D discrete element method

ABSTRACT This study investigated the effects of asphalt mixes and their combinations on the asphalt mix shear strength (SS) by a three-dimensional (3D) discrete element method (DEM). The uniaxial penetration test (UPT) for testing the asphalt mix SS was succinctly depicted. 3D micromechanical models used to predict the asphalt mix SS were built through X-ray computed tomography and discrete particle model implemented in particle flow code in three dimensions (PFC3D). The effects of asphalt mixes and their combinations on the SS were analysed on the basis of these models. Simulation results were proven against laboratory UPTs. As shown, the presented simulation results were in good agreement with the laboratory results, and the deviations between them were below approximately 6%, and most were less than 4%. The SS of high modulus asphalt mixes was greater than that of SBS-modified asphalt mixes and rubber-modified asphalt mixes. The asphalt mix SS increased with the increase in aggregate size, and it decreased with the rise in void content. The double-layer asphalt mix SS was more remarkably influenced by the bottom asphalt layer. The crumb rubber content also affected the rubber-modified the asphalt mix SS. The rubber-modified asphalt mix SS increased with the rise in crumb rubber content.