Browsing by Author "Kim, Youdan"

Now showing 1 - 12 of 12
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    Analytic approach to impact time guidance with look angle constraint using exact time-to-go solution
    (American Society of Civil Engineers, 2023-12-12) Lee, Seokwon; Kim, Jinrae; Kim, Youdan; Cho, Namhoon
    This paper proposes an analytic approach for impact time control guidance laws against stationary targets using biased proportional navigation. The proposed guidance scheme realizes the impact time control in two different ways: the first approach directly uses the exact time-to-go error to satisfy both the impact time control and the field-of-view constraint, while the second approach adopts a look angle tracking law to indirectly control the impact time, with the reference profile of the look angle generated using the exact time-to-go solution. The stability properties of the proposed guidance laws are discussed, and numerical simulations are carried out to evaluate their performance in terms of accuracy and efficiency.
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    Collision avoidance strategies for unmanned aerial vehicles in formation flight
    (IEEE, 2017-06-13) Seo, Joongbo; Kim, Youdan; Kim, Seungkeun; Tsourdos, Antonios
    Collision avoidance strategies for multiple UAVs (Unmanned Aerial Vehicles) based on geometry are investigated in this study. The proposed strategies allow a group of UAVs to avoid obstacles and separate if necessary through a simple algorithm with low computation by expanding the collision-cone approach to formation of UAVs. The geometric approach uses line-of-sight vectors and relative velocity vectors where dynamic constraints are included in the formation. Each UAV can determine which plane and direction are available for collision avoidance. An analysis is performed to define an envelope for collision avoidance, where angular rate limits and obstacle detection range limits are considered. Based on the collision avoidance envelope, each UAV in a formation determines whether the formation can be maintained or not while avoiding obstacles. Numerical simulations are performed to demonstrate the performance of the proposed strategies.
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    Composite model reference adaptive control under finite excitation with unstructured uncertainties
    (IEEE, 2024-01-19) Cho, Namhoon; Shin, Hyosang; Kim, Youdan; Tsourdos, Antonios
    This paper presents an online parameter update algorithm in the context of composite model reference adaptive control based on intermittent signal holding to improve convergence properties of the parameters representing the unstructured uncertainties in the absence of persistent excitation. The present study extends the algorithm which was previously developed by considering only the structured uncertainties for which the basis functions are known a priori. The proposed extension utilises the Gaussian radial basis function neural network as the model for the uncertainty assuming appropriate placement of the local basis functions in the state space. A notable distinction from the case with full knowledge of the features constituting the linearly-parameterised uncertainty model is that the extended algorithm introduces a robustifying modification in the earlier phase of operation to deal with the inevitable learning residual.
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    Composite model reference adaptive control with parameter convergence under finite excitation
    (IEEE, 2017-08-09) Cho, Namhoon; Shin, Hyosang; Kim, Youdan; Tsourdos, Antonios
    A new parameter estimation method is proposed in the framework of composite model reference adaptive control for improved parameter convergence without persistent excitation. The regressor filtering scheme is adopted to perform the parameter estimation with signals that can be obtained easily. A new framework for residual signal construction is proposed. The incoming data is first accumulated to build the information matrix, and then its quality is evaluated with respect to a chosen measure to select and store the best one. The information matrix is built to have full rank after sufficient but not persistent excitation. In this way, the exponential convergence of both tracking error and parameter estimation error can be guaranteed without persistent oscillation in the external command which drives the system. Numerical simulations are performed to verify the theoretical findings and to demonstrate the advantages of the proposed adaptation law over the standard direct adaptation law.
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    Data-driven capturability analysis for pure proportional navigation guidance considering target maneuver
    (Springer, 2021-06-15) Lee, Suwon; Lee, Youngjun; Lee, Seokwon; Kim, Youdan; Han, Yongsu; Park, Jangseong
    A data-driven statistical analysis of the missile’s capture region is performed. The capture region is the region of the initial geometric configuration for pursuer missile against a target in which the missile can intercept the target while satisfying specific constraints. The statistical verification approach has advantages over the analytic approach in that it can deal with various guidance algorithms and target maneuver utilizing numerical simulator. In this study, the verification model is constructed using the Gaussian process regression model. The verification model computes the probability distribution of the target capture over the initial configuration space. The data-driven capturability analysis is conducted for the maneuvering target using the Gaussian process regression model. The capture region derived from the statistical model is compared with the analytic model, and the effectiveness of the active sampling algorithm is demonstrated.
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    Data-efficient active weighting algorithm for composite adaptive control systems
    (IEEE, 2022-08-09) Kim, Seong-hun; Lee, Hanna; Cho, Namhoon; Kim, Youdan
    We propose an active weighting algorithm for composite adaptive control to reduce the state and estimate errors while maintaining the estimation quality. Unlike previous studies that construct the composite term by simply stacking, removing, and pausing observed data, the proposed method efficiently utilizes the data by providing a theoretical set of weights for observations that can actively manipulate the composite term to have desired characteristics. As an example, a convex optimization formulation is provided, which maximizes the minimum eigenvalue while keeping other constraints, and an illustrative numerical simulation is also presented.
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    Design framework for optimizing waypoints of vehicle trajectory considering terminal velocity and impact angle constraints
    (Taylor and Francis, 2021-05-17) Kim, Youngil; Cho, Namhoon; Park, Jongho; Kim, Youdan
    Ballistic missiles often require the terminal velocity and impact angle to be confined to a certain region around a desired value considering a wide variety of uncertain initial conditions and operational ranges. This study presents a design framework to determine optimum waypoints that satisfy constraints for given launch conditions and mission profiles. As a systematic approach to this kinodynamic motion planning problem, the proposed framework deterministically samples the waypoints. The trajectory generated by the determined waypoints in consideration of various conditions satisfies the terminal constraint. Numerical simulations are performed to demonstrate the effectiveness of the proposed method.
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    Generalized analysis of biased proportional navigation guidance with fractional power error feedback
    (AIAA, 2022-06-03) Cho, Namhoon; Kim, Jinrae; Lee, Seokwon; Kim, Youdan
    This study presents a comprehensive analysis of biased proportional navigation guidance laws with variable gain in the bias command that achieve stationary target interception with a desired impact angle under the restriction of permissible look angle. More specifically, this study investigates the bias shaping approach, which takes the bias gain function given by a product of factors in range and look angle. The linear feedback and fractional power feedback of impact-angle error are considered for command structures. For each command form, this study examines the conditions that should be satisfied by the gain functions to guarantee mission accomplishment without violation of the constraints. The analysis particularly focuses on estimating the set of feasible initial or final conditions that ensure compliance with the constraints along the trajectory. Numerical simulation is performed for a range of initial and final flight-path angles to verify the analytical results. The findings of this study provide a general foundation for the design of a nonswitching guidance law for impact-angle control with limited look angle through shaping of gain profiles.
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    Generalized formulation of linear nonquadratic weighted optimal error shaping guidance laws
    (AIAA, 2019-12-29) Cho, Namhoon; Kim, Youdan; Shin, Hyosang
    This study presents a novel extension to the theory of optimal guidance laws represented by the nontraditional class of performance indices: nonquadratic-type signal Lp" role="presentation">Lp norm for the input weighted by an arbitrary positive function. Various missile guidance problems are generally formulated into a scalar terminal control problem based on the understanding of the predictor–corrector nature. Then, a new approach to derive the optimal feedback law, minimizing the nonquadratic performance index, is proposed by using the Hölderian inequality. The proposed extension allows a more general family of formulations for the design of closed-form feedback solutions to various guidance problems to be treated in a unified framework. The equivalence between the proposed approach and other design methodologies is investigated. In general, the type of input norm mainly determines the variability of input during the engagement while trading off against the rate of error convergence. The analytic solution derived in this study is verified by comparison with the solution from numerical optimization, and the effect of the exponent p" role="presentation">p in the performance index on the trajectory and command is demonstrated by numerical simulations.
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    Guidance of gliding vehicles with energy management based on approximate prediction of speed
    (2022-05-05) Cho, Namhoon; Kim, Youngil; Shin, Hyosang; Kim, Youdan
    This study presents a guidance method for flight vehicles gliding in the vertical plane to achieve desired position and velocity at the final time. The proposed guidance algorithm combines two decoupled elements to plan future flight trajectories satisfying the given constraints at each guidance update cycle: i) parametric path generator, and ii) approximate speed predictor. The parametric path generator is capable of producing an altitude profile as a parametric function of downrange by solving a convex optimisation problem considering only the shape properties of a flight path. An approximate method for predicting the future speed history endows the proposed guidance algorithm with the capability to address energy management objectives in trajectory planning. Provided that an altitude profile is specified by the parametric path generator and the lift-to-drag ratio model is known, the approximation neglecting gravitational acceleration turns the speed dynamics along the given path into a scalar linear first order ordinary differential equation, the form which admits a closed-form solution that can be represented by definite integrals. In this way, the proposed method opens a possibility to update the trajectory in flight to achieve the desired final speed by reducing the computational load due to speed prediction task, although the predicted speed contains approximation errors of certain degrees.
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    Online trajectory replan for gliding vehicle considering terminal velocity constraint
    (IEEE, 2022-08-08) Kim, Youngil; Cho, Namhoon; Park, Jongho; Kim, Youdan
    Controlling the terminal velocity can improve the effectiveness of guided missiles. In particular, a ballistic missile propelled by solid rocket motors can successfully accomplish its mission when it hits the target at an appropriate speed. In this study, a method for modifying the trajectory of gliding vehicle, i.e., gliding ballistic missiles is proposed to meet the terminal velocity constraint by reflecting the effects of the environment during a flight. The proposed framework consisting of trajectory generation and dynamic propagation compensates for errors due to uncertainties in real time. The trajectory generation step provides various trajectories that satisfy the given constraints based on information about the current state. The dynamic propagation step efficiently predicts the terminal velocity for each of the generated trajectories and finds the trajectory with the lowest terminal speed error. A numerical simulation is performed considering various conditions to demonstrate the performance of the proposed method.
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    Unified control parameterization approach for finite-horizon feedback control with trajectory shaping
    (IEEE, 2022-03-22) Cho, Namhoon; Park, Jongho; Kim, Youdan; Shin, Hyosang
    This study presents control parametrisation as a unifying framework for designing a linear feedback control law that achieves finite-time transfer of output as well as trajectory shaping. Representing control input as a linear combination of independent basis functions allows wide variability in the resultant feedback control laws through selection of the number and types of basis functions. Given an array of basis functions that meets the trajectory shaping necessities, the unified design approach proceeds with determination of the coefficients so that the predicted trajectory attains the desired output at the final time. The input evaluated with the coefficients found at each instance essentially turns out to be a linear state feedback policy with an additional feedforward term and time-dependent gains which is appropriate for practical use. The unified control parametrisation approach lends itself well to missile guidance applications with the expandability and direct trajectory shaping capability that it provides. To emphasise expandability of the framework, this study revisits the trajectory shaping guidance laws from the control parametrisation viewpoint and shows how the notion of specifying input basis functions not only generalises various existing methods but also enables further extensions. Furthermore, an application to integrated guidance and control illustrates the strength of design process in handling the shaping requirements more directly through construction of appropriate basis.