Solution In Dynamic Environment Research Articles

A Novel Control Architecture Based on Behavior Trees for an Omni-Directional Mobile Robot

Robotic systems are increasingly present in dynamic environments. This paper proposes a hierarchical control structure wherein a behavior tree (BT) is used to improve the flexibility and adaptability of an omni-directional mobile robot for point stabilization. Flexibility and adaptability are crucial at each level of the sense–plan–act loop to implement robust and effective robotic solutions in dynamic environments. The proposed BT combines high-level decision making and continuous execution monitoring while applying non-linear model predictive control (NMPC) for the point stabilization of an omni-directional mobile robot. The proposed control architecture can guide the mobile robot to any configuration within the workspace while satisfying state constraints (e.g., obstacle avoidance) and input constraints (e.g., motor limits). The effectiveness of the controller was validated through a set of realistic simulation scenarios and experiments in a real environment, where an industrial omni-directional mobile robot performed a point stabilization task with obstacle avoidance in a workspace.

Dynamic evolutionary multiobjective optimization for open-order coil allocation in the steel industry

In terms of improving coil resource utilization and customer satisfaction, most steel companies are still far behind in these quality objectives and need significant improvements. Scientific approaches to production and operations planning are critical to improve its situation. Motivated by this phenomenon, this study investigates a challenging operations decision problem on allocating open-order coils to customer orders in the steel industry. In this article, a dynamic multiobjective optimization model is formulated to optimize the total mismatching costs, surplus inventory and coil utilization considering various practical dynamisms, such as production changes and unscheduled arrivals of new customer orders. To address this problem, we propose a multiobjective evolutionary algorithm based on knee-driven change response strategy and Pareto local search mechanism, so called KPLSEA. This proposed approach, which combines the information of decision-making stages with the evolutionary search, significantly reduces the computational cost and promotes the evolutionary search to converge quickly. Extensive experiments are performed on real-world production benchmark instances. Computational comparisons with other state-of-art algorithms validate that the proposed algorithm could generate effective and practical solutions in dynamic environments as well as provide the decision makers with a satisfied near-optimal solution.

Risk-aware Fine-grained Access Control in Cyber-physical Contexts

Access to resources by users may need to be granted only upon certain conditions and contexts, perhaps particularly in cyber-physical settings. Unfortunately, creating and modifying context-sensitive access control solutions in dynamic environments creates ongoing challenges to manage the authorization contexts. This article proposes RASA, a context-sensitive access authorization approach and mechanism leveraging unsupervised machine learning to automatically infer risk-based authorization decision boundaries. We explore RASA in a healthcare usage environment, wherein cyber and physical conditions create context-specific risks for protecting private health information. The risk levels are associated with access control decisions recommended by a security policy. A coupling method is introduced to track coexistence of the objects within context using frequency and duration of coexistence, and these are clustered to reveal sets of actions with common risk levels; these are used to create authorization decision boundaries. In addition, we propose a method for assessing the risk level and labelling the clusters with respect to their corresponding risk levels. We evaluate the promise of RASA-generated policies against a heuristic rule-based policy. By employing three different coupling features (frequency-based, duration-based, and combined features), the decisions of the unsupervised method and that of the policy are more than 99% consistent.

A distributed method for dynamic multi-robot task allocation problems with critical time constraints

This paper considers the task allocation problems in a distributed multi-robot system under critical time constraints. Considering the requirement of distributed computing, many existing distributed heuristic task allocation approaches tend to trap in local optimal and cannot obtain high-quality solutions. For a dynamic task allocation problem in a multi-robot system, not only the task information and the robot state may be subject to changes, but also the network status. That is, robots that each robot can communicate with may change over time, and sometimes there may even be no robots that it can communicate with. To solve these problems, a dynamic grouping allocation method is proposed. It builds upon the state-of-the-art consensus-based auction algorithms, extending them in both task inclusion phase and consensus phase. First, a cluster-first strategy and a task inclusion procedure that can be easily applied to the task inclusion phase of the algorithms are proposed, so that the solution quality of each iteration of the algorithms are significantly improved with a reasonable amount of computation. In addition, to increase the exploration capabilities, a proportional selection method is used in the task inclusion procedure when it is likely to trap in a local optimal. Second, the block-information-sharing strategy is used to avoid the possible conflicts that dynamic changes may bring. Numerical simulations demonstrate that the proposed method can provide conflict-free solutions in dynamic environments and can achieve outstanding performance in comparison with the state-of-the-art algorithms.

Interactive Heuristic D* Path Planning Solution Based on PSO for Two-Link Robotic Arm in Dynamic Environment

This paper is devoted to find an intelligent and safe path for two-link robotic arm in dynamic environment. This paper focuses on computational part of motion planning in completely changing dynamic environment at every motion sample domains, since the local minima and sharp edges are the most common problems in all path planning algorithms. In addition, finding a path solution in a dynamic environment represents a challenge for the robotics researchers, so in this paper, a proposed mixing approach was suggested to overcome all these obstructions. The proposed approach methodology for obtaining robot interactive path planning solution in known dynamic environment utilizes the use of modified heuristic D-star (D*) algorithm based on the full free Cartesian space analysis at each motion sample with the Particle Swarm Optimization (PSO) technique. Also, a modification on the D* algorithm has been done to match the dynamic environment requirements by adding stop and return backward cases which is not included in the original D* algorithm theory. The resultant interactive path solution was computed by taking into consideration the time and position changes of the moving obstacles. Furthermore, to insure the enhancement of the final path length optimality, the PSO technique was used. The simulation results are given to show the effectiveness of the proposed method.

Research on backbone node deployment for Wireless Mesh Networks in dynamic environments

Wireless Mesh Network is a type of wireless networks in which demands of bandwidth for users has mobility. The backbone node placement of wireless mesh networks in a dynamic scenario is investigated, and the TSDPSO algorithm is used to adapt the dynamic environment, which updates node deployment location to adapt to changes in demand if it detects environmental changes at the beginning of the cycle time. In order to meet the demands of bandwidth for users and network connectivity, particle swarm optimization algorithm is employed to select the gateway location, then nodes to the backbone network is added constantly until all requirement is covered. The experimental results show that algorithm could get effective solution in dynamic environment.

A Stochastic Game-Theoretic Approach for Interference Mitigation in Small Cell Networks

In this letter, we investigate the distributed channel selection for interference mitigation in small cell networks considering the random deployment and dynamic on-off activity. Game theory is adopted to analyze the distributed and interactive decision making, and the problem is formulated as an exact potential game, in which the Nash equilibrium (NE) minimizes the expected network interference, either globally or locally. Furthermore, we design a fully distributed, no-regret channel selection algorithm to find the NE solution in dynamic environment.

Evolutionary Algorithm with Diversity-Reference Adaptive Control in Dynamic Environments

Evolutionary algorithms (EAs) can be used to find solutions in dynamic environments. In such cases, after a change in the environment, EAs can either be restarted or they can take advantage of previous knowledge to resume the evolutionary process. The second option tends to be faster and demands less computational effort. The preservation or growth of population diversity is one of the strategies used to advance the evolutionary process after modifications to the environment. We propose a new adaptive method to control population diversity based on a model-reference. The EA evolves the population whereas a control strategy, independently, handles the population diversity. Thus, the adaptive EA evolves a population that follows a diversity-reference model. The proposed model, called the Diversity-Reference Adaptive Control Evolutionary Algorithm (DRAC), aims to maintain or increase the population diversity, thus avoiding premature convergence, and assuring exploration of the solution space during the whole evolutionary process. We also propose a diversity models based on the dynamics of heterozygosity of the population, as models to be tracked by the diversity control. The performance of DRAC showed promising results when compared with the standard genetic algorithm and six other adaptive evolutionary algorithms in 14 different experiments with three different types of environments.

An adaptive optimization technique for dynamic environments

The use of evolutionary algorithms (EAs) is beneficial for addressing optimization problems in dynamic environments. The objective function for such problems changes continually; thus, the optimal solutions likewise change. Such dynamic changes pose challenges to EAs due to the poor adaptability of EAs once they have converged. However, appropriate preservation of a sufficient level of individual diversity may help to increase the adaptive search capability of EAs. This paper proposes an EA-based Adaptive Dynamic OPtimization Technique (ADOPT) for solving time-dependent optimization problems. The purpose of this approach is to identify the current optimal solution as well as a set of alternatives that is not only widespread in the decision space, but also performs well with respect to the objective function. The resultant solutions may then serve as a basis solution for the subsequent search while change is occurring. Thus, such an algorithm avoids the clustering of individuals in the same region as well as adapts to changing environments by exploiting diverse promising regions in the solution space. Application of the algorithm to a test problem and a groundwater contaminant source identification problem demonstrates the effectiveness of ADOPT to adaptively identify solutions in dynamic environments.

Dynamic hierarchical algorithms for document clustering

In this paper, two clustering algorithms called dynamic hierarchical compact and dynamic hierarchical star are presented. Both methods aim to construct a cluster hierarchy, dealing with dynamic data sets. The first creates disjoint hierarchies of clusters, while the second obtains overlapped hierarchies. The experimental results on several benchmark text collections show that these methods not only are suitable for producing hierarchical clustering solutions in dynamic environments effectively and efficiently, but also offer hierarchies easier to browse than traditional algorithms. Therefore, we advocate its use for tasks that require dynamic clustering, such as information organization, creation of document taxonomies and hierarchical topic detection.