Terminal Angle Research Articles

Virtual target approach-based optimal guidance law with both impact time and terminal angle constraints

Virtual target approach-based optimal guidance law with both impact time and terminal angle constraints

Anatomic Variation of Type III Right Testicular Venous Drainage: A Case Report

The testicular vein exhibits variations in number, course, and insertion. Such differences may enhance the risk of varicocele and complication in patients by impairing testicular drainage. The following is a case report of the abnormal drainage of the right testicular vein (RTV) draining into the right renal vein (RRV). The incidence, course, insertion, and termination angle of the testicular veins were measured with a 150 mm digital Vernier dial microcaliper, and photographs were taken by Canon EOS 70D using a 100mm macro lens. In one out of seven cadavers (14.28%), the right testicular vein (RTV) drained into the right renal vein (RRV) (Type III) rather than into the inferior vena cava (IVC) at a 90° angle 0.4 cm from the IVC. The double (medial and lateral) left testicular veins (LTV) drained into the left renal vein (LRV) at a 62° angle 5 cm from the IVC. The understanding of type III RTV drainage or course can provide crucial data for surgeons in order to prevent complications during right-sided varicocele surgery.

A new three-dimensional fixed time sliding mode guidance with terminal angle constraints

In this paper, a continuous fixed-time guidance law with terminal angle constraints considering coupled dynamics is proposed for intercepting maneuvering targets in three-dimensional space. First, a fast fixed-time nonsingular sliding manifold is designed to guarantee the line-of-sight angle tracking errors and angular rates to zero in a fixed time. Next, a novel sliding mode reaching law is proposed to weaken the chattering phenomenon and guarantee guidance system states converge to sliding mode manifold in a fixed time. Finally, numerical simulations are conducted to validate the effectiveness and superiority of the proposed guidance law.

Missile guidance with assisted deep reinforcement learning for head-on interception of maneuvering target

In missile guidance, pursuit performance is seriously degraded due to the uncertainty and randomness in target maneuverability, detection delay, and environmental noise. In many methods, accurately estimating the acceleration of the target or the time-to-go is needed to intercept the maneuvering target, which is hard in an environment with uncertainty. In this paper, we propose an assisted deep reinforcement learning (ARL) algorithm to optimize the neural network-based missile guidance controller for head-on interception. Based on the relative velocity, distance, and angle, ARL can control the missile to intercept the maneuvering target and achieve large terminal intercept angle. To reduce the influence of environmental uncertainty, ARL predicts the target’s acceleration as an auxiliary supervised task. The supervised learning task improves the ability of the agent to extract information from observations. To exploit the agent’s good trajectories, ARL presents the Gaussian self-imitation learning to make the mean of action distribution approach the agent’s good actions. Compared with vanilla self-imitation learning, Gaussian self-imitation learning improves the exploration in continuous control. Simulation results validate that ARL outperforms traditional methods and proximal policy optimization algorithm with higher hit rate and larger terminal intercept angle in the simulation environment with noise, delay, and maneuverable target.

A novel data-driven air balancing method with energy-saving constraint strategy to minimize the energy consumption of ventilation system

Air balancing is a key technology to reduce energy consumption of ventilation system and improve the quality of indoor living environment. So far, most of the existing data-driven non-iterative air balancing methods only focus on the prediction of terminal damper angle to supply appropriate airflow, but they do not pay attention to the energy-saving constraint of fan voltage and terminal damper. Therefore, their energy efficiencies are not high enough. In this paper, energy-saving constraint strategy of low fan voltage and small damper friction resistance is considered and a novel data-driven non-iterative air balancing model with energy-saving constraint strategy is proposed. The model parameters can be trained by the proposed optimization algorithm inputting acquisition data. Then, given a design airflow rate, the required fan voltage and terminal damper angle can be predicted by the trained model to achieve accurate air balancing control with high energy efficiency. The performance validation of the proposed method is executed on our experimental duct system with five terminals. Compared with the current air balancing method, the proposed method can improve energy saving potential up to 13.7%, while keeping accurate air balancing within 10% relative error standard.

Sensor-Based Robust Incremental Three-Dimensional Guidance Law with Terminal Angle Constraint

In this work, a robust incremental three-dimensional (3D) guidance law is proposed considering terminal angle constraint against maneuvering targets. As a stepping stone, the line-of-sight (LOS) tracking error dynamics is employed for the 3D guidance law design. A sliding variable is constructed such that its first-order derivative excludes the relative range in the perturbation, which avoids the unboundedness of system perturbation induced by target maneuvers near collision. A time-varying version of the sliding variable is designed to accelerate convergence of the LOS tracking errors and avoid large initial sliding variables. Then, two guidance laws are derived as a benchmark via the nonlinear dynamic inversion (NDI)-based sliding mode control (NDI-SMC) and NDI-based time-varying sliding mode control (NDI-TVSMC), respectively. To further improve guidance robustness with reduced system perturbation, the sensor-based incremental nonlinear dynamic inversion (INDI) control is used to design the INDI-SMC-based and INDI-TVSMC-based guidance laws. The sensor-based guidance laws exploit the LOS angular acceleration and guidance command output at the latest step, which result in smaller guidance gains to reject the perturbation than the NDI guidance laws. Numerical simulations in various cases and comparison studies are conducted to verify the effectiveness and robustness of the proposed method.

Three-dimensional time-varying sliding mode guidance law against maneuvering targets with terminal angle constraint

This paper deals with the problem of intercepting maneuvering targets with terminal angle constraints for missiles subjected to three-dimensional non-decoupling engagement geometry. To achieve the finite-time interception and satisfactory overload characteristics, a time varying sliding mode control methodology is developed based on a time base generator function. The main feature of the proposed guidance law guarantees the Line-of-Sight (LOS) angles to converge to small neighborhoods of the desired values at the interception time. First, a fractional power extended state observer is used to estimate the unknown target acceleration, which can significantly reduce the adaptive switching gain. The fractional power extended state observer enjoys the advantage of better noise tolerance. Then, a newly designed sliding mode surface is constructed by introducing a time base generator function and the time-varying sliding mode guidance law is developed based on this time-varying sliding surface. The proposed guidance law significantly reduces the overload magnitudes. Numerical simulations are carried out to verify the performance of the proposed guidance law.

Distributed adaptive cooperative time-varying formation tracking guidance for multiple aerial vehicles system

Distributed adaptive cooperative time-varying formation tracking guidance problems of multiple aerial vehicles system against a maneuvering target are investigated. Different from the former results, the proposed cooperative guidance strategies are based on distributed time-varying formation tracking theories. Firstly, the leader aerial vehicle is designed to achieve interception with desired terminal attack angle, which provides a reference trajectory. The uncertain dynamic items and target's uncertain maneuver have been compensated. For the follower aerial vehicles, the distributed cooperative time-varying formation tracking guidance laws are raised. Adaptive distributed extended state observers are introduced to estimate the leader vehicle's states and input information. Then, an algorithm is shown for determining guidance parameters of cooperative guidance laws. Thirdly, the properties and the stabilities of the algorithm are discussed in detail. Finally, a simulation experiment is performed for showing the feasibility and effectiveness of achieved results.

Fundamental Understanding of Tea Growth and Modeling of Precise Tea Shoot Picking Based on 3-D Coordinate Instrument

Tea is a popular beverage worldwide and also has great medical value. A fundamental understanding of tea shoot growth and a precision picking model should be established to realize mechanized picking of tea shoots with a small product loss. Accordingly, the terminal bud length (Lbud), tea stem length (Lstem), terminal bud angle (αbud), tea stem angle (αstem), and growth time (t) were considered as the key growth parameters; the sum of the vertical lengths of the terminal bud and stem (ξ), the picking radius (r), and the vertical length of the stem (Zstem) were considered as the picking indexes of the tea shoots. The variations in growth parameters with time were investigated using a 3-D coordinate instrument, and the relationships between the growth parameters and the picking indexes were established using an artificial neural network (ANN). The results indicated that the tea growth cycles for periods P1, P2, P3, P4, P5, and P6 were 14, 7, 6, 4, 4, and 6 d, respectively. A growth cycle diagram of the tea growth was established. Moreover, a 5-2-12-3 ANN model was developed. The best prediction of ξ, r, and Zstem was found with 16 training epochs. The MSE value was 0.0923 × 10−4, and the R values for the training, test, and validation data were 0.99976, 0.99871, and 0.99857, respectively, indicating that the established ANN model demonstrates excellent performance in predicting the picking indexes of tea shoots.

Electrocardiographic biomarkers to predict atrial fibrillation in sinus rhythm electrocardiograms

ObjectiveEarly prediction of atrial fibrillation (AF) development would improve patient outcomes. We propose a simple and cheap ECG based score to predict AF development.MethodsA cohort of 16 316 patients was...

Three-dimensional terminal angle constraint finite-time dual-layer guidance law with autopilot dynamics

Considering the problem of intercepting a target at desired terminal angles in the three-dimensional (3D) space, this paper proposes a finite-time dual-layer guidance law with consideration of the second-order autopilot dynamics. The proposed guidance law owns a cascaded structure, which is divided into an outer system and an inner system. To achieve the finite-time convergence, the outer and inner controllers are developed based on the nonsingular terminal sliding mode control. With the aid of the command filter, which can compute the first and the second derivatives of the virtual signal simultaneously, the design procedure of the fourth-order guidance system is simplified into two steps. Moreover, extended state observers are used to estimate the unknown target maneuver and the acceleration derivative of the missile, which facilitates the real implementation. Simulation results verify the performance of the proposed guidance law.

Adaptive fault recovery strategy of LCC‐MMC based hybrid HVDC

Hybrid HVDC consisting of line commutated converter (LCC) on rectifier side and modular multilevel converter (MMC) on inverter side is the favourable future trend of HVDC projects utilising the advantages of both converter technologies. However, fault clearing and adaptive restart capabilities of such hybrid HVDC are not much investigated in the literature. In this paper fault clearing of hybrid HVDC transmission line is investigated using mechanical DC breaker at MMC terminal and forced firing angle retardation at LCC terminal. Then, the characteristics of the line voltages are analysed during the fault blocking states of converters to clear the transient fault. Characteristics of the line voltages of LLC rectifier have shown prominent difference under permanent and temporary fault states, and also dependent on the severity of fault. Therefore, based on line voltage characteristics, a restart strategy is proposed for hybrid HVDC which is adaptive to the fault characteristics. Several PSCAD/EMTDC based simulation studies are conducted to validate the proposed fault recovery strategy. Simulation results validate the effectiveness of the proposed strategy for hybrid HVDC under DC line faults.

Three-dimensional impact angle constrained distributed cooperative guidance law for anti-ship missiles

This paper investigates the problem of distributed co-operative guidance law design for multiple anti-ship missiles in the three-dimensional (3-D) space hitting simultaneously the same target with considering the desired terminal impact angle constraint. To address this issue, the problem formulation including 3-D nonlinear mathematical model description, and communication topology are built firstly. Then the consensus variable is constructed using the available information and can reach consensus under the proposed acceleration command along the line-of-sight (LOS) which satisfies the impact time constraint. However, the normal accelerations are designed to guarantee the convergence of the LOS angular rate. Furthermore, consider the terminal impact angle constraints, a nonsingular terminal sliding mode (NTSM) control is introduced, and a finite time convergent control law of normal acceleration is proposed. The convergence of the proposed guidance law is proved by using the second Lyapunov stability method, and numerical simulations are also conducted to verify its effectiveness. The results indicate that the proposed cooperative guidance law can regulate the impact time error and impact angle error in finite time if the connecting time of the communication topology is longer than the required convergent time.

A Practical Optimal Guidance Scheme Under Impact Angle and Terminal Acceleration Constraints

This paper proposes a practical optimal guidance law that can handle terminal angle and acceleration constraints while providing robustness against uncertainty in autopilot dynamics. Building upon a well-established linear-quadratic optimal guidance framework, we first derive an energy-minimizing guidance scheme that nullifies terminal acceleration called optimal guidance law with impact angle and terminal acceleration constraints (OGL–IATA). Then, a practical modification to OGL–IATA is proposed to deal with the stability degradation of OGL–IATA due to unmodeled high-order autopilot dynamics. The modification primarily features feedback of pseudo-acceleration that is computed by passing the true acceleration signal through approximate missile dynamics; this simple modification is demonstrated to improve the stability margin of the guidance loop. Numerical examples of nonlinear engagement kinematics demonstrate the performance and the robustness characteristics of the proposed practical guidance scheme.

Study on project trajectory of air-to-ground missile with strapdown seeker under multi constraints

The air-to-ground missile with strapdown seeker may have the problems, including small field of view(FOV), limited overload, and fall angle constraint. To solve the above mentioned problem, a phased guidance scheme is proposed. In this scheme, the attack trajectory is divided into the following six stages, including glided stage, fall angle constraint stage, target acquisition and adjustment stage, terminal guidance stage and blind zone stage. The glided stage is designed to increase range, the terminal fall angle is attained ahead of time at fall angle constraint stage. The aim of target acquisition and adjustment stage is to adjust the missile attitude, so that the target will fall within the FOV of the seeker. It creates good condition to capture the target for strapdown seeker. In the terminal stage, the guidance law of proportional navigation and attitude track are used to fit the needs of FOV constraint and attack accuracy. The simulation result shows that the project trajectory can solve the application of attacking moving targets for air-to-ground missile with strapdown seeker under multi constraints.

Optimal Guidance Law for Intercepting the Active Defense Aircraft with Terminal Angle Constraint

For the scenario where the target can actively defend against the attacking missile, an optimal guidance law for the attacking missile that can simultaneously evade the defending missile and intercept the target is proposed. To increase lethality of the attacking missile, the terminal angle constraint is considered. Assuming that the defending missile and the target is using a known control strategy, the guidance law design problem for the attacking missile is formulated as an optimal control problem with inequality constraint. General solution of the problem is derived for arbitrary order dynamics of the adversaries. Then first-order dynamics of the three players are considered and an analytic solution is presented. Numerical simulations are carried out to demonstrate the high performance of the proposed guidance law.

Rapid Algorithm for Generating Entry Landing Footprints Satisfying the No-Fly Zone Constraint

An online estimation algorithm of landing footprints based on the drag acceleration-energy profile is proposed for an entry hypersonic vehicle. Firstly, based on the Evolved Acceleration Guidance Logic for Entry (EAGLE), drag acceleration-energy profiles are designed. To track the drag acceleration-energy profile obtained by the interpolation, a drag acceleration tracking law is designed. Secondly, based on the constraint model of the no-fly zone, flying around strategies are proposed for different conditions, and a reachable area algorithm is designed for no-fly zones. Additionally, by interpolating the minimum and maximum drag acceleration profiles, the terminal heading angle constraint is designed to realize the accurate calculation of the minimum and maximum downrange ranges by adjusting the sign of the bank angle. In this way, the distribution of landing footprints is more reasonable, and the boundary of a reachable area is more accurate. The simulation results under typical conditions indicate that the proposed method can calculate landing footprints for different situations rapidly and with the good adaptability.

Dynamics and Environmental Characteristics of Spin Labels in a KvAP Voltage Sensor by Molecular Dynamics Simulations.

The nitroxide spin label is the most widely used probe for electron paramagnetic resonance (EPR) spectroscopy studies of the structure and function of biomolecules. However, the role of surrounding environments in determining the dynamics of nitroxide spin labels in biological complex systems remains to be clarified. This study aims to characterize the dynamics and environmental structure of spin labels in the voltage-sensing domain (VSD) of a KvAP potassium channel by means of molecular dynamics (MD) studies. MD simulations for unlabeled and 132 spin-labeled KvAP-VSD models (spin labels introduced at positions 20-151) were carried out in a phospholipid bilayer to evaluate conformational dynamics of nitroxide spin-label side chains in the VSD. Structural flexibility, conformational freedom, and orientation of the spin-label side chains were investigated in relation to their dynamics in different microenvironments. The analysis of MD data showed that the attached spin-label probe did not severely perturb the protein dynamics. The conformational freedoms of the nitroxide side chain vary with the physical structure of the surrounding environments. The two terminal dihedral angles of the nitroxide side chain tend to cluster and adopt several preferred rotameric states. From the nearest-neighbor analysis, the spin label can be exposed to either a homogeneous or heterogeneous environment with various exposure scenarios. The dynamical movement of KvAP-VSD is high at a water-exposed site, moderate in the membrane, and low in the protein core. Understanding the structure and dynamics behaviors of spin labels helps to manage the experimental uncertainty and avoid misleading interpretation in relation to the protein structure.

A novel adaptive three-dimensional finite-time guidance law with terminal angle constraints for interception of maneuvering targets

ABSTRACT In this paper, a novel adaptive three-dimensional finite-time guidance law is proposed to achieve the interception of maneuvering targets. The proposed guidance law considers terminal angle constraints and the coupled nonlinear dynamics of the three-dimensional missile-target interception scenario. Adaptive control technique and sliding mode control theory are applied to design the guidance law. More specifically, the designed adaptive law can ensure sliding mode manifold fast reach a predefined region and weaken the chattering phenomenon without the upper bounds of target maneuvers. Furthermore, the line-of-sight angle tracking errors and the line-of-sight angular rates can achieve finite-time convergence via the designed nonsingular fast terminal sliding mode controller. Therefore, the accurate interception of the missile against maneuvering targets can be achieved via the proposed guidance law. Numerical simulations show the effectiveness and superiority of the proposed guidance law.

A Novel Air Balancing Method for HVAC Systems by a Full Data-Driven Duct System Model

Air balancing is an important technique in heating, ventilation, and air conditioning (HVAC) applications to achieve accurate air supply for satisfactory indoor air quality and better energy saving performance. The existing air balancing methods are usually based on a hybrid duct system model, which includes a data-driven duct system model between terminal flow and static pressure, and an American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) damper model between static pressure and terminal damper angle. Most of the existing methods just focus on how to improve the accuracy of the former part (i.e., the data-driven duct system model), whereas neglecting the latter. However, it is found that the ASHRAE damper model cannot exactly reflect the characteristics of the actual dampers in practice and may lead to unavoidable modeling errors. To fix this issue, this article develops a full data-driven duct system (FD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> S) model to directly reveal the relationship between the terminal flow and terminal damper angle in the whole duct system. As a result, the desired terminal damper angle under the design flow conditions can be more accurately predicted. Besides, since the proposed method directly models the relationship between terminal flow and terminal damper angle, it avoids installing extra pressure sensors and reduces the operating cost. Besides, the proposed FD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> S model greatly reduces the model complexity compared with the previous hybrid model. The proposed FD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> S model-based air balancing method is fully tested on three real duct systems, and the results proved the effectiveness and generality of the proposed FD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> S model-based air balancing method.