Sliding mode control and Lyapunov based guidance law with impact time constraints

This paper analyses the issue of impact time control of super-cavitation weapons impact fixed targets which mainly refer to the ships or submarines who lost power, but still have combat capability. Control over impact time constraints of guidance law(ITCG) is derived by using sliding mode control(SMC) and Lyapunov stability theorem. The expected impact time is realized by using the notion of attack process and estimated time-to-go to design sliding mode surface(SMS). ITCG contains equivalent and discontinuous guidance laws, once state variables arrive at SMS,the equivalent guidance law keeps the state variables on SMS,then the discontinuous guidance law enforces state variables to move and reach SMS. The singularity problem of ITCG is also analyzed. Theoretical analysis and numerical simulation results are given to test the effectiveness of ITCG designed in this paper.

A hybrid proportional navigation based two-stage impact time control guidance law

To improve applicability and adaptability of the impact time control guidance(ITCG) in practical engineering, a twostage ITCG law with simple but effective structure is proposed based on the hybrid proportional navigation, namely, the pureproportional-navigation and the retro-proportional-navigation.For the case with the impact time error less than zero, the first stage of the guided trajectory is driven by the retro-proportionalnavigation and the second one is driven by the pure-proportionalnavigation. When the impact time error is greater than zero, both of the stages are generated by the pure-proportional-navigation but using different navigation gains. It is demonstrated by twoand three-dimensional numerical simulations that the proposed guidance law at least has comparable results to existing proportional-navigation-based ITCG laws and is shown to be advantageous in certain circumstances in that the proposed guidance law alleviates its dependence on the time-to-go estimation, consumes less control energy, and adapts itself to more boundary conditions and constraints. The results of this research are expected to be supplementary to the current research literature.

Impact time control guidance against maneuvering targets based on a nonlinear virtual relative model

Aiming at the problem of high-precision interception of air-maneuvering targets with impact time constraints,this paper proposes a novel guidance law based on a nonlinear virtual relative model in which the origin is attached to the target.In this way,the original maneuvering target is transformed into a stationary one.A polynomial function of the guidance command in the range domain with two unknown coefficients is introduced into the virtual model,one of the coefficients is determined to achieve the impact time constraint,and the other is determined to satisfy a newly defined virtual look angle constraint.For meeting the terminal constraints simultaneously,the guidance command can finally be obtained.The resulting solution is represented as a combination of proportional navigation guidance-like term which is aimed to meet the zero miss distance constraint,a bias term for impact time control by adjusting the length of the homing trajectory,and an additional term for target maneuvers.Numerous simulations demonstrate that the proposed law achieves an acceptable impact time error for various initial conditions against different types of maneuvering targets and shows more effective performance in comparison with those of other existing guidance laws.

Trajectory reshaping based guidance with impact time and angle constraints

This study presents a novel impact time and angle constrained guidance law for homing missiles. The guidance law is first developed with the prior-assumption of a stationary target, which is followed by the practical extension to a maneuvering target scenario. To derive the closed-form guidance law, the trajectory reshaping technique is utilized and it results in defining a specific polynomial function with two unknown coefficients. These coefficients are determined to satisfy the impact time and angle constraints as well as the zero miss distance. Furthermore, the proposed guidance law has three additional guidance gains as design parameters which make it possible to adjust the guided trajectory according to the operational conditions and missile's capability. Numerical simulations are presented to validate the effectiveness of the proposed guidance law. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

Impact time control using biased proportional navigation for missiles with varying velocity

A feasible guidance scheme with impact time constraint is proposed for attacking a stationary target by missiles with time-varying velocity.The main idea is to replace the constant velocity with the future mean velocity;therefore, the existing time-to-go estimation algorithm of the proportional navigation guidance law can be improved to adapt to varying conditions.In order to obtain the prediction of the velocity profile, the velocity differential equation to the downrange is derived, which can be numerically integrated between the current downrange and the target position by the on-board computer.Then, a third-order polynomial is introduced to fit the velocity profile in order to calculate the future mean velocity.At the beginning of each guidance loop, the future mean velocity is predicted and the time-to-go information is updated, based on which a novel biased proportional navigation guidance law is established to achieve the impact time constraint.Finally,numerical simulation results verified the effectiveness of the time-to-go estimation algorithm and the proposed law.

Optimal three-dimensional impact time guidance with seeker’s field-of-view constraint

This paper proposes a new three-dimensional optimal guidance law for impact time control with seeker’s Field-of-View(FOV) constraint to intercept a stationary target. The proposed guidance law is devised in conjunction with the concept of biased Proportional Navigation Guidance(PNG). The guidance law developed leverages a nonlinear function to ensure the boundedness of velocity lead angle to cater to the seeker’s FOV limit. It is proven that the impact time error is nullified in a finite-time under the proposed method. Additionally, the optimality of the biased command is theoretically analyzed. Numerical simulations confirm the superiority of the proposed method and validate the analytic findings.

Two-phase guidance law for impact time control under physical constraints

An impact-time-control guidance law is required for the simultaneous attack of suicide attack unmanned aerial vehicles.Based on the nonlinear model,a two-phase guidance strategy is proposed.The impact time is derived in a simple analytical form of initial states and switching states,and it can be controlled by switching at an appropriate range.Firstly,a two-phase guidance law is designed to make the magnitude of the heading error decrease monotonically from its initial value to zero.And then,the feasible interval of the switching ranges and of the impact times under the acceleration constraint are given analytically in sequence.Furthermore,a general form of twophase guidance law is proposed,which allows the magnitude of the heading error to increase in the first phase,to improve the applicability of the methodology.Having the same structure as proportional navigation guidance with a time-varying gain,the proposed algorithms are simple and easy to implement.The corresponding feedback form is presented for realistic implementation.When a predefined impact time is taken within its permissible set,the constraints on the acceleration and fieldof-view will not be violated during the interception.Finally,simulations validate the effectiveness of the methodology in impact time control and salvo attack.

Guidance law with impact time and impact angle constraints

A novel closed-form guidance law with impact time and impact angle constraints is pro- posed for salvo attack of anti-ship missiles, which employs missile＇s normal acceleration （not jerk） as the control command directly. Firstly, the impact time control problem is formulated as tracking the designated time-to-go （the difference between the designated impact time and the current flight time） for the actual time-to-go of missile, and the impact angle control problem is formulated as tracking the designated heading angle for the actual heading angle of missile. Secondly, a biased proportional navigation guidance （BPNG） law with designated heading angle constraint is constructed, and the actual time-to-go estimation for this BPNG is derived analytically by solving the system differential equations. Thirdly, by adding a feedback control to this constructed BPNG to eliminate the time-to-go errorthe difference between the standard time-to-go and the actual time-to-go, a guidance law with adjustable coefficients to control the impact time and impact angle simultaneously is developed. Finally, simulation results demonstrate the performance and feasibility of the proposed approach.

Leader-following cooperative guidance law with specified impact time

The problem of guidance law is investigated for multiple interceptors to attack a target cooperatively.A leader-following cooperative guidance strategy is presented to render the leader and the followers reach the target at specified impact time.The guidance law of leader is given to meet the demand of specified impact time.The arrival time is synchronized by enforcing the ranges-to-go of followers keep consensus with that of leader.The convergence time bound is estimated without dependence on the initial states,since the proposed leader-following cooperative guidance law is fixed-time convergent.The simulation is developed to validate the availability of proposed cooperative guidance law.

An experimental analysis on the turnover time of railway freight transportation based on the impact strength of factors

Based on the factors impact strength model(FISM), we studied on calculation formulas of influence strength and key elements of FISM, and analyzed the turnover time of railway freight transportation of China. The results show that wagon transfer time is the most critical factor among the three subjective factors of wagons turnover time. The FISM based analysis of wagon transfer time show that the wagon turnover time is significantly correlated with transit time with resorting. Among the seven factors of detention time of transit time with resorting, the time of waiting to departing, converging, and waiting to break-up are key factors, while the time of make-up, break-up, arrival and departure are general factors. We carried out one empirical research based on the data of Baoji East Railway Station in 2015. The results of empirical research and FISM are consistent completely.

Impact angle control over composite guidance law based on feedback linearization and finite time control

The impact angle control over guidance(IACG) law against stationary targets is proposed by using feedback linearization control(FLC) and finite time control(FTC). First, this paper transforms the kinematics equation of guidance systems into the feedbackable linearization model, in which the guidance law is obtained without considering the impact angle via FLC. For the purpose of the line of sight(LOS) angle and its rate converging to the desired values, the second-order LOS angle is considered as a double-integral system. Then, this paper utilizes FTC to design a controller which can guarantee the states of the double-integral system converging to the desired values. Numerical simulation illustrates the performance of the IACG, in contrast to the existing guidance law.

A TIME DOMAIN BOUNDARY ELEMENT METHOD FOR WATER-SOLID IMPACT ANALYSIS

A reciprocal theorem of dynamics for potential flow problems is first derived by means of the Laplace transform in which the compressibility of water is taken into account. Based on this theorem, the corresponding time-space boundary integral equation: is obtained. Then, a set of time domain boundary element equations with recurrence form is immediately formulated through discretization in both time and boundary. After having carried out the numerical calculation two solutions are found in which a rigid semicircular cylinder and a rigid wedge with infinite length suffer normal impact on the surface of a half-space fluid. The results show that the present method is more efficient than the previous ones.

重复冲击下砂岩的动态响应试验研究

高速动能水击压裂可借助聚能水锤效应实现强动载泄入性液压冲击,具有高峰值压力、高加载速率、重复多次渐进扩缝等优势,其中聚能流体贯入性冲击下岩石损伤-破裂的演化机制是该技术优化设计的核心问题。为此,采用岩石动态冲击损伤模拟试验装置,开展高速动能水击压裂破岩试验,分析不同加载速率、冲击次数、冲击组合等对岩石破裂形态的影响规律。结果表明:单次高速动能水击破岩中,随着加载速率的提高,岩石破坏依次呈现出近孔眼破碎损伤(8.5 MPa/ms)、微裂缝聚并串联成宏观裂纹(13.4 MPa/ms)、流体楔入形成脆性崩裂裂缝(15.5 MPa/ms)三种模式;在小峰值压力、低加载速率重复冲击下,岩石损伤破坏呈现近孔眼损伤(1~2次)-裂缝起裂扩展(3~5次)-应力挤压破碎(6~10次)三个阶段,随着冲击次数的增加,孔眼周围损伤加剧,形成3~40 mm(贯穿岩样)不等长的裂缝;“先低后高”组合加载速率冲击方式下,前期重复低速率冲击可在孔眼周围形成微裂纹损伤而又不会产生破碎压实,随后借助单次高加载速率聚能冲击,实现大体积高压流体在微裂纹内的快速楔入,激发多条径向深穿透裂缝,同时该组合冲击方法还可实现主裂缝两侧基质扩容增渗和相交分支缝网,实现改造效果的最大化。

A simple criterion for finite time stability with application to impacted buckling of elastic columns

The existing theories of finite-time stability depend on a prescribed bound on initial disturbances and a prescribed threshold for allowable responses. It remains a challenge to identify the critical value of loading parameter for finite time instability observed in experiments without the need of specifying any prescribed threshold for al- lowable responses. Based on an energy balance analysis of a simple dynamic system, this paper proposes a general criterion for finite time stability which indicates that finite time stability of a linear dynamic system with constant coefficients during a given time interval [0, tf] is guaranteed provided the product of its maximum growth rate （determined by the maximum eigen-root pl 〉0） and the duration tf does not exceed 2, i.e., pltf 〈2. The proposed criterion （pltf=2） is applied to several problems of impacted buckling of elastic columns： （i） an elastic column impacted by a striking mass, （ii） longitudinal impact of an elastic column on a rigid wall, and （iii） an elastic column compressed at a constant speed （＂Hoff problem＂）, in which the time-varying axial force is replaced approximately by its average value over the time duration. Comparison of critical parameters predicted by the proposed criterion with available experimental and simulation data shows that the proposed criterion is in robust reasonable agreement with the known data, which suggests that the proposed simple criterion （pltf---2） can be used to estimate critical parameters for finite time stability of dynamic systems governed by linear equations with constant coefficients.

有限视场下的攻击时间和角度多约束制导律

针对精确打击任务存在导引头视场受限这一过程约束的制导问题,提出了一种考虑视场限制以及攻击角度和时间多种约束的制导律.首先,在以比例导引项实现精确命中的基础上,利用最优控制理论,采用弹目距离加权控制能耗形式的指标函数,设计了攻击角度控制项,并推导了相应的剩余飞行时间解析预测表达式.其次,基于最优误差动力学方法,设计了攻击时间相关的控制项,保证了攻击时间误差的有限时间收敛.同时,针对导引头视场有限的问题,分析了各控制项对前置角收敛性的影响,利用特定的限制函数确保前置角在整个制导过程中始终处于有效视场内,并给出了前置角的有界性及收敛性证明.数学仿真结果验证了所提出制导律对多约束制导问题的有效性.

虑及控制机构运动关联的柱塞泵动态特性研究

针对柱塞泵建模过程中因函数简化控制机构及其运动关系而造成的误差大、不精准问题,提出基于控制机构运动关联的非简化建模方法。结合柱塞泵的控制原理,利用AMESim搭建功率-压力-电比例复合控制的柱塞泵仿真模型。通过对压力、电流和转速的组合控制,对柱塞泵的控制特性进行仿真测试,得到与理论研究相吻合的动态特性曲线。进一步通过台架试验对柱塞泵进行测试,试验结果表明:柱塞泵在实际工作中存在响应时间,系统流量在液压系统开启和闭合瞬间存在冲击振荡。对比两种建模思想的仿真结果,非简化模型最大相对误差分别为3.51%和5.08%,平均相对误差分别为1.74%和1.98%,均小于简化模型。柱塞泵建模准确,为实现产品性能优化和系统数字孪生提供了模型支撑。

DETECTION OF EARLY RUB-IMPACT IN ROTORS VIA HIGHER-ORDER TIME-FREQUENCY ENTROPY

Due to the calculation problem of classical methods (such as Lyapunovexponent) for chaotic behavior, a new method of identifying nonlinear dynamics with higher-ordertime-frequency entropy (HOTFE) based on time-frequency analysis and information theorem is proposed.Firstly, the meaning of HOTFE is defined, and then its validity is testified by numericalsimulation. In the end vibration data from rotors are analyzed by HOTFE. The results demonstratethat it can indeed identify the early rub-impact chaotic behavior in rotors and also is simpler tocalculate than previous methods.

2024年全国荔枝生产形势分析与管理建议

据2024年3月底的调查,全国荔枝种植面积785.13万亩,基于成花情况预测2024年全国荔枝总产量178.10万t,比上年减产45.94%。其中,广东87.64万t,广西41.61万t,海南22.81万t,福建11.78万t,云南7.83万t,四川6.43万t,广东、广西减产幅度较大。如以5月之前、5—7月、7月之后作为荔枝早、中、晚熟划分时间节点,今年国家荔枝龙眼产业技术体系综合试验站覆盖区域早、中、晚熟比例为47.1∶41.9∶11.0。分品种产量预测,‘妃子笑’62.85万t,‘黑叶’18.30万t,‘怀枝’9.35万t,‘白糖罂’7.99万t,‘桂味’5.05万t,‘双肩玉荷包’2.61万t,‘大红袍’1.79万t,‘白蜡’1.52万t,‘糯米糍’1.57万t。‘黑叶’‘怀枝’‘桂味’‘糯米糍’‘鸡嘴荔’等中、晚熟品种减产幅度达60%~80%。分析认为,末次秋梢成熟期偏迟和暖冬是影响今年荔枝成花的主要原因,并据此提出了相关管理技术建议。