共查询到20条相似文献，搜索用时 62 毫秒
1.
环境不确定性是企业财务柔性存在的前提,而财务柔性是主动适应和有效处理环境不确定性的必然选择.本文在对环境不确定性和财务柔性度量的基础上,设计了财务柔性与环境不确定性的匹配度模型,提出在环境不确定性情况下,要对企业的财务柔性实施动态管理. 相似文献
2.
知识联盟的本质是一种战略联盟,也是企业获取知识的重要方式。但现实中普遍存在的战略联盟不稳定现象受到越来越多的关注。在考虑成员决策柔性和联盟收益不确定的情况下,通过构建定量分析模型,对联盟的不稳定性进行了分析研究,重点是对联盟成员退出联盟的条件及时机进行分析和研究。结果表明,成员企业基于决策柔性的等待行为及收益不确定性的加大会促进联盟的稳定;而由于联盟契约的不完全性所导致的专用性投资不足,则会导致联盟的不稳定。 相似文献
3.
C.M. Leech 《Journal of The Franklin Institute》1980,309(2):65-90
The equations of motion of a rigid body are developed in body fixed axes; the aerodynamic forces and moments are expressed as elements of a Taylor series in the six kinematic rates (body velocities and spins). Stability is approached firstly by forcing Jacobi elliptic functions into the equations of motion; stability criteria follow either as unconditional system stability or as a conditional criterion dependent upon the launch conditions. Stability is also considered by way of the motion invariants and their relation to kinetic energy. Three basic systems are considered and numerical integration gives detailed system responses; pertubation of the various aerodynamic effects changes the responses and the stability from unconditional stability to instability or conditional stability. 相似文献
4.
Wongphaka Wongrat Ali Elkamel Peter L. Douglas Ali Lohi 《Journal of The Franklin Institute》2011,348(7):1318-1338
Rice drying synthesis is an essential operation that has to be done carefully and cost-effectively. Rice is harvested at high moisture content and hence must be dried within 24 h for safe storage. However, improper drying can cause fissuring in the rice grain, and thus greatly reduce its market value. Multi-pass drying systems are therefore used to gradually bring moisture content to desired level.The problem of rice synthesis, considered in this study, seeks the configuration of units and their corresponding operating conditions that maximize rice quality. This problem is formulated as a mixed-integer dynamic optimization problem. The integer part of the problem reflects process alternatives while the dynamic part originates from nonlinear differential-algebraic equations describing the drying behavior of a rice grain.Clearly such a formidable problem is not easy to solve. Hence, we propose an approach that makes use of two algorithms: a genetic algorithm to search for the best configuration of units and a control vector parameterization approach that optimizes the operating conditions for each configuration. We demonstrate the effectiveness of the approach on a case study. 相似文献
5.
《Journal of The Franklin Institute》2019,356(10):5260-5273
Fuzzy Sliding Mode Control (FSMC) algorithms have been widely studied and implemented to combine the robustness of the classical sliding mode control with lower chattering levels, but industrial implementation requires a robustness measurement such as the stability margins. Due to the significance of stability margins in control systems, the computation of the phase Margin (PM) and gain margin (GM) in FSMC has already been proposed with the self-sustained oscillations considered as an unstable behavior. However, a procedure to obtain the desired PM and GM from the FSMC design itself has not been developed yet. Hence, in this study, a method to design FSMC algorithms with desired PM and GM is presented. The describing function (DF) and harmonic balance (HB) techniques were used to identify the limit cycles; then, a step-by-step process to tune the FSMC parameters was provided. Examples and simulations are presented to validate the proposed method. 相似文献
6.
In this paper, we investigate the stability and periodicity of a class of state-dependent switched systems with all unstable subsystems by means of energy analysis. We firstly transform the unstable subsystems reversibly into the form of second order mechanical systems, and then construct energy functions by calculating the sum of kinetic and potential energies of each subsystem. After that, two switching lines, derived from the lines with the largest and smallest energy drops, make the stable phase trajectory approach to the equilibrium point at the fastest speed. In addition, we explore possible dynamic behaviors of the switched system under a pair of switching line including asymptotic stability, instability and periodicity. Furthermore, based on the bisection method and nested intervals theorem, we design a state-dependent switching law, which makes the switched system periodic initiated from a stable switching law. Finally, numerical simulation examples are provided to illustrate the effectiveness and less conservativeness of the proposed method with practical significance. 相似文献
7.
Emmanuel Bernuau Denis Efimov Wilfrid Perruquetti Andrey Polyakov 《Journal of The Franklin Institute》2014
The paper is reviewing the tools to handle high-order sliding mode design and robustness. The main ingredient is homogeneity which can be checked using an algebraic test and which helps us in obtaining one of the most desired properties in sliding mode control that is finite-time stability. This paper stresses some recently obtained results about homogeneity for differential inclusions and robustness with respect to perturbations in the context of input-to-state stability. Lastly within this framework, most of the popular high-order sliding mode control schemas are analysed. 相似文献
8.
Nuno Gil 《Research Policy》2007,36(7):980-999
This study defines a project safeguard as the design and physical development work needed to ensure, or enhance, the embedding of a real option in complex products and systems (CoPS). Safeguards operationalize optionlike strategic thinking at implementation. I examine safeguarding investments through an in-depth multiple-case study of 12 options embedded across 5 projects encompassed by an airport expansion programme. This includes options to phase out delivery (stage-option), grow capacity (growth-option), and switch operational regime (switch-option). Passive safeguards only involve design work, whereas active safeguards involve both design and physical execution. The analysis shows how the confluence between the uncertainty of option exercising and the modularity of the relevant functional elements in relation to the CoPS architecture affects the attractiveness of safeguarding. High uncertainty makes safeguarding less attractive as it can lead to sunk costs that may not pay off over the CoPS operating life. Conversely, high modularity increases the attractiveness of safeguarding because (1) safeguards can be limited to marginal investments at the interfaces between the functional elements with other CoPS subsystems, and (2) the stability of modular design rules increases the likelihood that safeguards remain valid over time. Safeguards build options into integrative CoPS. This flexibility and redundancy makes them resilient to change stemming from option exercising if uncertainties resolve favourably in the future. 相似文献
9.
An exo-atmospheric interception scenario between an accelerating missile and its target is investigated. It is assumed that the maneuvering acceleration is obtained by instantaneous rotation of the missile's body to the required attitude. Two different guidance laws are derived for such an interceptor using the sliding mode control methodology. The difference is in the definition of the sliding surface enforcing different trajectories for the interceptor. It is shown that if this surface is chosen as the zero-effort-miss of the well-known proportional navigation guidance law, then the missile is commanded to point its acceleration vector along the line-of-sight and consequently fly along a curved trajectory. For the second guidance law, a unique sliding surface is chosen enforcing the missile to fly on a straight line towards collision, after the initial heading error is nulled. The performance of the guidance laws is analyzed and compared using a nonlinear two dimensional simulation. It is shown that on top of enforcing a different flight geometry for the interceptor, the use of the new guidance to collision sliding mode guidance law can enhance the capture zone of the interceptor. 相似文献
10.
This paper develops numerical strategies which enable the constrained incremental Newton-Raphson scheme to handle the static response of structure to loading fields with completely generalized histories. This is made possible through the use of specially warped hyperelliptic constraint surfaces which control successive or clustered load steps in the vicinity of loading events with specific timing schedules. Such an approach enables improved convergence and stability characteristics. Due to the generality of the methodology, pre- and postbuckling behaviour caused by both kinematic and material nonlinearity can be handled. To demonstrate the scheme, the results of several bench-mark problems are also presented. These include situations involving nonlinear kinematics as well as highly history-dependent elastic-plastic and thermoelastic-plastic material behaviour. 相似文献
11.
Qitong Zou Xusheng Mu Hongkun Li Rui Huang Haiyan Hu 《Journal of The Franklin Institute》2021,358(5):2642-2660
Flying-wing unmanned aerial vehicles have received extensive attention over the past decade because of their excellent aerodynamic and stealth performance. However, the aeroelastic interaction problems among unsteady aerodynamics, flight dynamics, and structural dynamics, such as the body-freedom flutter, are still open. This paper presents the study of a robust control scheme for active body-freedom flutter suppression of a flexible flying-wing unmanned aerial vehicle. The control objective is to expand the boundary of body-freedom flutter and to enhance the control robustness to external unknown disturbance simultaneously. The paper begins with the modeling procedure of a parameter-varying aeroservoelastic plant for the design of control law. Then, it presents how to synthesize a robust controller so as to suppress the flutter instability for a wide flight range of dynamic pressures. Afterwards, the paper shows how to analyze the flutter stability of the closed-loop system and the robustness of the controller, respectively. The numerical results demonstrate that the proposed robust controller can not only expand the flutter boundary of the unmanned aerial vehicle by 30%, but also exhibit the strong robustness to external disturbance. 相似文献
12.
13.
Integrated guidance and autopilot design for a chasing UAV via high-order sliding modes 总被引：1，自引：0，他引：1
Takeshi Yamasaki S.N. Balakrishnan Hiroyuki Takano 《Journal of The Franklin Institute》2012,349(2):531-558
Integrated guidance and control (IGC) approaches exploit the synergy between guidance and control designs. This study focuses on the integrated guidance and control (autopilot) design for a chasing Uninhabited Aerial Vehicle (UAV) against a target aircraft. A second-order sliding structure with a second-order sliding mode (SOSM) including a high-order sliding mode (HOSM) observer for the estimation of the uncertain sliding surfaces is selected to develop an integrated guidance and autopilot scheme. In order to make the design synthesis easier, intermediate control variables for partial derivatives of a sliding surface are carefully selected. The resulting sliding surface structure is simple and sufficient to relate the actuator input to the sliding surface. The potential of the proposed method is demonstrated through an aircraft application by comparing its simulation performance, number of tuning parameters used, and information needed for its implementation with an approach where the guidance law and the controller are designed separately. 相似文献
14.
由于人为因素,订单出错是常有的事。采用计算机订单管理系统,能充分发挥计算机精准的特性及擅长处理大数据量的能力,保证处理过程的正确性。该系统基于B/S架构,使用面向对象C#语言和.net框架开发,并充分利用了.net的OO特性,结合MS SQL SERVER,在开发过程中运用多层结构的设计思想（表现层、业务逻辑层、数据访问层）,是一个高内聚、低耦合的MIS系统,能有效的帮助企业实施企业信息化管理,节约运营成本。 相似文献
15.
由于云搜索服务的灵活度和稳定性无法满足需求,厦门大学图书馆决定应用Elasticsearch重构站内搜索。通过环境部署、索引配置、数据导入、索引错误处理等步骤,厦门大学图书馆成功实现了基于Elasticsearch的站内搜索,且在功能、界面等方面有所改进。据此进一步提出,Elasticsearch未来可应用于大数据环境,成为数字图书馆的私有云搜索引擎。 相似文献
16.
L. Piroddi 《Journal of The Franklin Institute》2012,349(3):826-844
Nonlinear control with feedforward neural networks is usually designed by means of model based control strategies, which make explicit use of (direct or inverse) models of the controlled system. In this framework, a typical control problem consists in reducing the effects of the inevitable errors introduced by neural network approximation. In a non-adaptive setting, modeling errors can be compensated by hybrid control schemes, where the approximate neural controller is complemented with an integral type regulator connected in parallel. However, in this way, the model based control paradigm is partially lost and stability properties of the control system may be degraded. In this paper a stability analysis of such hybrid schemes is performed, which shows that control system stability can be achieved provided each of the two control blocks obeys a specific condition. Furthermore, a modified hybrid scheme is proposed to enhance the cooperation between the two control blocks: a nonlinear static filter is employed to modulate the integral action so that it becomes significant only when the neural controller has approached the equilibrium. Stability analysis is extended to this case. The hybrid scheme where the two control blocks are connected hierarchically in cascade is finally discussed. 相似文献
17.
Photo-crosslinkable gelatin methacrylate (GelMa) microspheres are applicable to deliver cells or drugs in biological or biomedical applications. To fabricate GelMa microdroplets, a flow focusing technique with advantages of size control and rapid production was used in a T-junction microfluidic device. Instability played an important role in promoting microdroplet uniformity. 5 wt. % GelMa prepolymer solution mixed with cells affected cell-induced instability. At low flow rate ratio of GelMa to mineral oil below 0.200, stability was maintained regardless of GelMa concentration (5 and 8 wt. %) and cell presence, which led to uniform microdroplet generation. In contrast, instability at high flow rate ratio above 0.200 was worsened by cell presence and unstable jetting length, resulting in the generation of non-uniform cell-laden microdroplets. Therefore, the effect of cell-induced instability on microdroplet generation was minimized at a low flow rate ratio. 相似文献
18.
We explore how risk management and design flexibility interplay in major (infrastructure) projects, using the £4.2bn Terminal 5 project to expand London's Heathrow airport. By juxtaposing these two conceptual frames, we unearth the conditions under which they can be complements for managing the tension between efficiency and effectiveness central to these projects. Building design flexibility - through modular or safeguarded integral architectures - increases adaptability to accommodate evolving requirements which is necessary to attain effectiveness. Efficiency, in turn, demands risk management to deliver the project ‘on time, within budget’. We explain variation in the interplay between the two approaches, highlighting the moderating role of the developer's relationship with the customer. Strong co-operation, particularly in a stable environment, encourages investments in design flexibility. Risk management practices prevail when co-operation breaks down. Another insight is that co-location and continuity of key project staff are themselves inadequate conditions to sustain co-operation. 相似文献
19.
Distributed cooperative controller design considering guidance loop and impact angle 总被引：1，自引：0，他引：1
This paper presents an integrated distributed cooperative guidance and control scheme for multiple missiles to attack a single target simultaneously at desired impact angles. The scheme is divided into two parts: individual part and cooperative part. For the individual part, partial integrated guidance and control method is adopted to generate the elevator deflection (which is a realistic control input) to ensure that the missiles fly along their respective desired line of sight and hit the target; this is in contrast to previous works which analyze only the engagement dynamics and use missile accelerations as the control input, however, the proposed controller also considers the missile dynamics, thus enabling the implementation of an autopilot. For the cooperative part, using only information from adjacent missiles, the proposed distributed cooperative controller can make all missiles hit the target simultaneously. Hence in this scheme, each missile can hit the target at desired angles and at the same time, thus achieving salvo attack. Simulations are performed to verify the effectiveness of the scheme. 相似文献
20.
The paper considers planar interception engagements against maneuverable targets using a linearized kinematic model with constant velocities. Both the interceptor and the target have bounded controls and first-order linear dynamics. Due to the linearization, the duration of the interception is prescribed. The target dynamics is fixed, but the interceptor has variable structure dynamics, switching from one mode to another once during the engagement. For such engagements the capture zone of a given linear feedback control is constructed. Numerical examples demonstrate that proper change of the interceptor dynamic mode leads to an enlarged capture zone. 相似文献