A machining tool can be subject to different kinds of excitations. The forcing may have external sources (such as rotating imbalance or misalignment of the workpiece) or it can arise from the cutting process itself (e.g. chip formation). We investigate the classical tool vibration model which is a delay-differential equation with a quadratic and cubic nonlinearity and periodic forcing. The method of multiple scales was used to derive the slow-flow equations. The resonance curves of the system are similar to those for the Duffing-equation, having a hardening characteristic. Stability analysis for the fixed points of the slow-flow equations was performed. Local and global bifurcations were studied and illustrated with phase portraits and direct numerical integration of the original equation. Subcritical Hopf, saddle-node and heteroclinic bifurcations were found.

The design process can be considered as series of decisions supported by modeling and simulation (M&S). Current developments aim at supporting this decision making with regard to increasing resources committed in the M&S process. To understand possible decision support, we conducted an empirical study in a car manufacturing company to map out the decision-making process during the development phase. A qualitative data analysis was performed to understand the difficulties and the needs expressed by decision makers. Industrial preliminary observations have shown that decisions regarding design issues are often postponed, causing iterations, and time and cost overruns in the development process. The study revealed that decisions are escalated to upper hierarchical levels as complexity and uncertainty increase and as the tradeoffs become impactful. A lack of knowledge about the M&S performance and limits, a lack of clarity due to design ambiguity, and uncertainty are more likely to cause iterations and delay. In addition, decision makers and stakeholders are sometimes unadvised of the influence of the decision under consideration on subsequent decisions and on the profit. These findings are interesting as they shed light in terms of decision supported needed in the future.

The marine rudder with leading-edge protuberances is numerically investigated by SST k-ω turbulence model in present investigations. The newly designed rudder has a sinusoidal leading-edge profile along the spanwise direction. The numerical results show that the newly designed rudder helps to improve the lift coefficient of the rudder. The efficiency of the rudder is improved by adopting the leading-edge protuberances. The results are analyzed by means of streamlines and pressure coefficient. The leading-edge protuberances can delay or overcome the stall. The effect of leading-edge protuberances on the pressure coefficient of pressure surface is very small. However, the pressure coefficient of the suction surface is changed in the vicinity of leading-edge.

At present, the power wagon is confronted with several problems: small brake torque at low speeds, output instability of random loading and slow response speed. Aiming at the existing problems of current control performance for loading system of power wagon, the paper proposes a back propagation (BP) neural net PID algorithm. The dynamic analysis of power wagon loading system was presented. A mathematical model of the loading system is established by use of the classical control theory. Through simulation and analysis, the dynamic response of the loading system is researched by using step signal, sine signal and field-load spectrum stochastic signal as system input respectively. Meanwhile, through MATLAB simulation experiment, compares and analysis with superiorities and characteristics between BP neural net PID control method and traditional PID control method. On the basis of this study, the power wagon was modified based on YTO-LX1304. The road test of the YTO-MF554 tractor traction property was performed on the concrete by using the power wagon. Experimental results show that the system output traction has a good follow effect in comparison with input load. The BP neural net PID algorithm can improve the system’s dynamical performance and its static accuracy in comparison with the traditional PID control. The simulation results show that system delay time is 0.12s and maximum overshoot is 3.8%. Road test results show that system delay time is 0.22s and maximum overshoot is 4.2%. The BP neural net PID algorithm has better control performance for second-order plant with time-delay time-varying system.

Geometric tolerances for new products are sometimes assigned without specific knowledge of the cost or feasibility of manufacturing them to the assigned tolerances, which can significantly drive up production costs and lead to delays and design revisions. We present an interactive tool that quickly estimates the manufacturability of assigned tolerances for additive manufacturing and a compact visualization to present this information to the designer. The designer can use the system to explore feasible build orientations and then adjust specified tolerance limits if all tolerances are not simultaneously achievable at a single orientation. After the designer is satisfied that the range of feasible orientations has been fully explored, a physical programming approach is used to identify a single orientation to best satisfy the designer’s preferences. The calculation and visualization of the results is done in real-time, enabling quick iteration. A test case is presented to illustrate the use of the tool.

Although active disturbance rejection control (ADRC) has demonstrated promising results in many applications, in some safety critical applications e.g. power plant, unmanned aerial vehicle, etc., it is often reluctant to switch from an existing control algorithm, either the traditional PID controller or other advanced control algorithms, to a new one. If the switching between the control algorithms can be made seamless, many more opportunities may open up. In this paper, the problem of making the switching to the ADRC smooth is studied. Previous attempts to solve the problem are not thorough enough, since only a second order system was addressed. A very simple and effective method is proposed based on analysis to make the transition seamless. The solution is very general, and can be applied to system of any order or even system with time-delay. At the core of the solution is the initialization of the “total disturbance”.

This paper investigates the controllability of distributed-order fractional systems with distributed delays. By using the controllability Gramian matrix and reduction to absurdity, a necessary and sufficient condition for the controllability of linear system is established, and a sufficient condition for the nonlinear system is obtained. Examples are given to illustrate the effectiveness of the theorems.

In this article, we investigate the nonlinear static and dynamic behavior of a clamped circular microplate in presence of imperfections. By taking in account the von Kàrmàn nonlinearity, the geometrical imperfections lead to a significant delay in static pull-in occurrence. Numerical simulations are performed in the frequency domain to study the dynamic behavior under primary resonance. A parametric analysis is conducted with respect to actuation voltages and initial deflection in order to capture the competition between hardening and softening behavior. Interestingly, we show that a geometric imperfection can change the type of nonlinear response from softening to hardening. In practice, the imperfection can be functionalized to enhance the performances of capacitive micromachined ultrasonic transducers.

This paper proposes a method for finding the optimal fixture layout to achieve acceptable gauge repeatability in the inspection process of a non-rigid part. Currently, there are no rigorous means of evaluating the effectiveness of a fixture layout for a part in terms of gauge repeatability until actual parts and gauges are available late in the product development process. Changes to the part design or modifications to the gauge at this late stage are usually costly and can result in program delays, incurring substantial costs. This paper proposes an approach to arrive at the best locator layout for gauge repeatability early in the part design phase thereby avoiding costly and time-consuming changes during the build phase. The method is implemented using a commercially available tolerance stack software with finite element analysis combined with a specially coded genetic algorithm. The method’s effectiveness is demonstrated through the improvement in gauge repeatability from an arbitrary datum scheme to the optimal datum scheme in a notional design problem as well as an actual production part. We also demonstrate that the commonly accepted datum scheme of using a primary plane along the largest dimension of a part may be highly suboptimal for gauge repeatability.

In this paper the dynamics of towed elastic wheels are studied with the help of the brush tyre model. To calculate the lateral deformation of the contact patch centre-line distributed time-delay is taken into account for the rolling parts, whereas parabolic limits are used to determine the deformation in case of side-slip. After linear stability analysis of the rectilinear motion the limit cycles of the non-smooth time-delayed system are calculated with the method of numerical collocation. With the help of bifurcation diagrams it is demonstrated how the periodic orbits develop from the linear stability boundary in a structure characteristic of piecewise-smooth systems. Moreover, it is shown that the contact memory effect and the dry friction yield bistable parameter ranges besides the linearly unstable domains. Namely, for one particular towing velocity a stable equilibrium corresponding to straight-line motion and a stable periodic orbit coexist resulting a hysteresis effect in the stability of the straight-line motion.

Amplitude death is a physical phenomenon that occurs in coupled systems where oscillation is dead and comes to fixed points. Based on the basic mechanical oscillators, a new kind of coupling named mechanical coupling is proposed to induce amplitude death. Both direct coupling and time delay coupling of mechanical oscillators are tested to be able to induce amplitude death. The amplitude death region is found to be influenced by the coupling strength. Numerical examples of lorenz oscillators and rossler oscillators are also simulated and found that the chaotic motion is induced to death with properly designed parameters. The significant practical applications of the new mechanism of amplitude death is discussed.

In this paper, period-3 motions in a double-well Duffing oscillator with time-delay are predicted by a semi-analytical method. The implicit mapping structures of period-3 motions are constructed through the implicit mappings obtained by discretization of the corresponding differential equation. Complex period-3 motions are predicted through nonlinear algebraic equations of the implicit mappings in the mapping structures and the corresponding stability and bifurcation are carried out through eigenvalue analysis. Numerical and analytical results of complex period-3 motions are obtained and the corresponding frequency-amplitude characteristics are presented.

An efficient numerical method, the fractional Chebyshev collocation method, is proposed for obtaining the solution of a system of linear fractional order delay-differential equations (FDDEs). It is shown that the proposed method overcomes several limitations of current numerical methods for solving linear FDDEs. For instance, the proposed method can be used for linear incommensurate order fractional differential equations and FDDEs, has spectral convergence (unlike finite differences), and does not require a canonical form. To accomplish this, a fractional differentiation matrix is derived at the Chebyshev-Gauss-Lobatto collocation points by using the discrete orthogonal relationship of the Chebyshev polynomials. Then, using two proposed discretization operators for matrix functions results in an explicit form of solution for a system of linear FDDEs with discrete delays. The advantages of using the fractional Chebyshev collocation method are demonstrated in two numerical examples in which the proposed method is compared with the Adams-Bashforth-Moulton method.

The ability to split femtosecond free electron laser pulses and recombine them with an adjustable delay has numerous scientific applications. In this work, we present a symmetrical multi-DOF motion system placed on a granite table for a wavefront-splitting based hard X-ray split-delay system at the Linac Coherent Light Source [1,2]. In order to achieve ultra-precision multi-DOF motion, a planar air bearing based linear stage is embedded into the system. It features setting the granite table as the reference plane and using flexure mechanisms to decouple the parasitic motion errors. In this application, it is located in the delay line for improving stability and accuracy during the delay adjustments in order to maintain spatial overlap between the two branches. Stiffness matrix derivation and analysis are also presented.

Structural Health Monitoring (SHM) systems become an integral part of most technical systems in recent years. An integration of SHM in technical systems is closely related to: i) providing the guaranteed service lifetime of a system, ii) scheduled/planned maintenance actions, and iii) optimized system operation. For these purposes, different system variables can be monitored and utilized for an estimation of aging level of the system. Monitored system variables are therefore correlated to stochastically occurring damage, indirectly also to Remaining Useful Lifetime (RUL). Among challenges related to SHM, high attention is given to the reduction of a large amount of measured data and its real-time signal processing. In this contribution, classification of damages in composite materials using measurements of Acoustic Emission (AE) is proposed. Here, Discrete Wavelet Transform (DWT) is applied to AE signal to identify different damages in composites. As AE-signal is found in high frequency bandwidth, the amount of data captured in a short time period is enormous. Consequently, the calculation of DWT of such signal requires processing time quite far from real time and delays the entire classification procedure. Due to this, real-time implementation of DWT is proposed to cope with huge amount of captured data in this case and to reduce the time required for signal processing. Using FPGA-based system, real-time implementation of DWT is shown. Obtained results are compared with the results of offline DWT calculation to prove the efficiency and accuracy of real-time implementation.

Defense in Depth (DiD) is a key design principle helping to improve the safety of complex systems in domains like nuclear power, oil and gas, and mining. DiD affects the basic design of the system because it contains requirements for isolation, diversity and safety divisions. If the DiD assessment happens late in the design process, there is a risk of costly redesign and project delays. To avoid this issue, this paper refines a set of early DiD assessment design rules and proposes a model-driven methodology for early assessment of the implementation of the DiD capabilities of a complex system design. The topology of the different design aspects of the system under study (mechanical, electrical, human factors, and others) and the dependencies between system elements are captured in a High Level Interdisciplinary Model (HLIM) that also holds DiD specific attributes. The resulting system model is assessed against the proposed set of DiD rules and requirements, and then it can be improved according to the results. The methodology is applied to a case study of an early nuclear power plant model of a spent fuel pool cooling system. The proof-of-concept software tool developed for early DiD assessment and presented in this paper is able to identify undesired dependencies between system elements of redundant systems, of different defense lines and other DiD related weaknesses. This provides practitioners with insights into potential vulnerabilities in the design and enables focused redesign to address the identified problems early in the design process.

Autonomous systems operating in dangerous and hard-to-reach environments such as defense systems deployed into enemy territory, petroleum installations running in remote arctic and off-shore environments, or space exploration systems operating on Mars and further out in the solar system often are designed with a wide operating envelope and deployed with control systems that are designed to both protect the system and complete mission objectives, but only when the on-the-ground environment matches the expected and designed for environment. This can lead to overly conservative operating strategies such as preventing a rover on Mars from exploring a scientifically rich area due to potential hazards outside of the original operating envelope and can lead to unanticipated failures such as the loss of underwater autonomous vehicles operating in Earth’s oceans. This paper presents an iterative method that links computer simulation of operations in unknown and dangerous environments with conceptual design of systems and development of control system algorithms. The Global to Local Path Finding Design and Operation Exploration (GLPFDOE) method starts by generating a general mission plan from low resolution environmental information taken from remote sensing data (e.g.: satellites, plane fly-overs, telescope observations, etc.) and then develops a detailed path plan from simulated higher-resolution data collected “in situ” during simulator runs. GLPFDOE attempts to maximize system survivability and scientific or other mission objective yield through iterating on control system algorithms and system design within an in-house-developed physics-based autonomous vehicle and terrain simulator. GLPFDOE is best suited for autonomous systems that cannot have easy human intervention during operations such as in the case of robotic exploration reaching deeper into space where communications delays become unacceptably large and the quality of a priori knowledge of the environment becomes lower fidelity. Additionally, in unknown extraterrestrial environments, a variety of unexpected hazards will be encountered that must to be avoided and areas of scientific interest will be found that must be explored. Existing exploratory platforms such as the Mars Exploratory Rovers (MERs) Curiosity and Opportunity either operate in environments that are sufficiently removed from immediate danger or take actions slowly enough that the signal delay between the system and Earth-based operators is not too great to allow for human intervention in hazardous scenarios. Using the GLPFDOE methodology, an autonomous exploratory system can be developed that may have a higher likelihood of survivability, can accomplish more scientific mission objectives thus increasing scientific yield, and can decrease risk of mission-ending system damage. A case study is presented in which an autonomous Mars Exploration Rover (MER) is generated and then refined in a simulator using the GLPFDOE method. Development of the GLPFDOE methodology allows for the execution of more complex missions by autonomous systems in remote and inaccessible environments.

Mathematical models predict limit cycle oscillations (LCOs) in postural sway when the combination of neuromuscular time-delay and feedback gains are excessively large. LCOs have been observed in the standing posture of various populations known to have longer time-delays including concussed young adults and adults with neuromuscular impairment such as multiple sclerosis (MS) and Parkinsons disease (PD) but not healthy controls. However, the relationship between feedback gain and time-delay that leads to these LCOs has yet to be explored experimentally. In this study, we examine the relationship between the time-delay of healthy adults and the onset of LCOs under altered visual feedback. We find that there is an inversely proportional correlation between feedback gain and intrinsic neuromuscular time-delay for which LCOs arise. This finding has implications for the assessment and diagnosis of neuromuscular related balance issues through a simple and invasive protocol similar to that used in this study.

Neurological disorders, a concussion, or aging can extend the time-delay in the human neuromuscular balance system; this time-delay increase has been shown [5] to be an important factor contributing to the loss of balance. However, commercial balance boards used to help improve individual’s balance deficiencies do not utilize time-delay as a tunable parameter. In order to systematically study stiffness and time-delay induced instabilities in standing posture, we developed an active balance board system with controllable torsional board stiffness, as well as an added controllable feedback time-delay of the torsional board. Using this dynamical system we confirmed the presence of two distinct mechanisms of instability: insufficient stiffness leading to tipping posture and excessive time-delays leading to limit cycle oscillations. We expect that this active balance board will allow for the early identification of an increased fall-risk, especially for subjects with extended time-delays and could help provide insights into how the human postural system adapts to various environments.

In this paper, the fractional Chebyshev collocation (FCC) method is proposed to design fractional delay controllers for linear systems with periodic coefficients. In our previous study, it was shown that this method can be successfully used to stabilize fractional periodic time-delay systems with the delay terms being of integer orders. In the current paper, it is shown that this method can be extended successfully to design fractional delay controllers for fractional periodic systems. For this propose, the solution of linear periodic systems with fractional delay terms is expressed in a Banach space. The short memory principle is used to show that the actual response of the system can be approximated by an approximated monodromy operator. The approximated monodromy operator yields the solution of a fixed length interval by mapping the solution of the previous interval with the same length. Usually obtaining the approximated monodromy operator is complicated or even impossible. The spectral radius of the approximated monodromy matrix indicates the asymptotic stability of the system. The efficiency of the proposed fractional delayed control is illustrated in the case of a second order system with periodic coefficients.