Derived Time Constants Research Articles

Effect of Delay on Control of Direct Resonance of Ships in Beam Waves Using a Proportional–Derivative Controller With Delay

Abstract A harmonically excited, single-degree-of-freedom time-delay system with cubic and quintic nonlinearities is studied. This system describes the direct resonance of a ship with an actively controlled antiroll tank (ART) that is subjected to beam waves. We consider low-, medium-, and high-freeboard ship models. A proportional–derivative (PD) controller with a constant time delay is assumed to operate the pump in the active ART system. The delay originates from the time required to pump fluid from one container to another, the inertia of large impeller blades and linkages, and the measurement and processing time of the roll-sensing unit. The stability boundary of the system, in the parametric space of the control gain and the delay, is derived analytically from the characteristic equation of the linearized system. We show that the area of the zero equilibrium region is inversely related to the derivative time constant of the PD controller; thus, we focus on a strictly proportional-gain controller. The spectral Tau method is used to identify the eigenvalues associated with the zero equilibrium since the rightmost eigenvalues determine the system's robustness to perturbations in the initial conditions. We use the method of multiple scales and harmonic balance to obtain the global bifurcation diagram in the space of the applied frequency and the amplitude of the response. Numerical simulations verify our analytical expressions. Study of the dynamics, stability, and control of the roll motion of ships is critical to avoid dynamic instabilities and capsizing.

HOLONIC CONTROL OF POULTRY HOUSE TRAVELLING HOPPER FEEDERS AND COMPARATIVE COST ANALYSIS

This work is aimed at applying holonic control system to poultry house travelling hopper feeders with the comparative cost analysis. It adopts HCBA which is suitable for controlling the reconfigurable automated processes. The feeder consists of parts for different types of poultry feeds dispensable from the feed reservoirs and carried around by travelling hoppers along the feed carts. The simulations were carried out using MATLAB and SIMATIC software. The responses of the speed of each traveling hopper were determined to be 1.04 sec, 1.91 sec and 0.0841% for rise time, settling time and percentage overshoot respectively. The parameters of the embedded controller in STEP 7 CONT_C FB41 data block translate to a constant gain of 10, integral time constant of 100 ms and derivative time constant of 280 ms. Visual results from the HMI show the system’s ability for customization, cooperation and autonomy for implementation of any poultry feeding program. The cost analysis shows that it is profitable for farm capacity of 10,000 birds and above with low labour cost and average annual energy cost of about N708,000. The feed wastage loss is reduced by 66% while depreciation is 10% as compared to cage system with belted conveyor feeder.

Fractional order automatic tuning of [formula omitted] controller for stable processes

This paper presents modified fractional order relay based automatic tuning of PIλD controller for stable processes with load disturbance. The modified relay comprises of PIλcontroller introduced with the ideal relay in series. The proportional gain of PIλ controller is assumed as unity and the integral time constant is chosen such that, the system attains minimum 0° phase margin. λ of PIλ controller helps in reducing the harmonics in the output which ultimately leads to improvement in the accuracy of the proposed scheme. The limit cycle, thus, obtained helps in extracting the critical frequency and peak amplitude which helps in controller design. The designing of PIλD controller is based on the measured parameters from modified relay. Subsequently, the derivative time constant is derived in the design of PIλD controller using phase margin criteria and Nyquist curve is used to obtain the proportional gain. The integral time constant for PIλD controller is same as that of PIλ controller for auto tuning test. The auto tuning method and PIλD controller design, thus proposed, is validated using typical examples through simulation.

Lack of tone in mouse small mesenteric arteries leads to outward remodeling, which can be prevented by prolonged agonist-induced vasoconstriction.

Inward remodeling of resistance vessels is an independent risk factor for cardiovascular events. Thus far, the remodeling process remains incompletely elucidated, but the activation level of the vascular smooth muscle cell appears to play a central role. Accordingly, previous data have suggested that an antagonistic and supposedly beneficial response, outward remodeling, may follow prolonged vasodilatation. The present study aimed to determine whether 1) outward remodeling follows 3 days of vessel culture without tone, 2) a similar response can be elicited in a much shorter 4-h timeframe, and, finally, 3) whether a 4-h response can be prevented or reversed by the presence of vasoconstrictors in the medium. Cannulated mouse small mesenteric arteries were organocultured for 3 days in the absence of tone, leading to outward remodeling that continued throughout the culture period. In more acute experiments in which cannulated small mesenteric arteries were maintained in physiological saline without tone for 4 h, we detected a similar outward remodeling that proceeded at a rate several times faster. In the 4-h experimental setting, continuous vasoconstriction to ~50% tone by abluminal application of UTP or norepinephrine + neuropeptide Y prevented outward remodeling but did not cause inward remodeling. Computational modeling was used to simulate and interpret these findings and to derive time constants of the remodeling processes. It is suggested that depriving resistance arteries of activation will lead to eutrophic outward remodeling, which can be prevented by vascular smooth muscle cell activation induced by prolonged vasoconstrictor exposure. NEW & NOTEWORTHY We have established an effective 4-h method for studying outward remodeling in pressurized mouse resistance vessels ex vivo and have determined conditions that block the remodeling response. This allows for investigating the subtle but clinically highly relevant phenomenon of outward remodeling while avoiding both laborious 3-day organoid culture of cannulated vessels and in vivo experiments lasting several weeks.

Influence of Heterogeneity on the Ultrafast Photoisomerization Dynamics of Pfr in Cph1 Phytochrome

Photoisomerization of a protein-bound chromophore is the basis of light sensing and signaling in many photoreceptors. Phytochrome photoreceptors can be photoconverted reversibly between the Pr and Pfr states through photoisomerization of the methine bridge between rings C and D. Ground-state heterogeneity of the chromophore has been reported for both Pr and Pfr. Here, we report ultrafast visible (Vis) pump-probe and femtosecond polarization-resolved Vis pump-infrared (IR) probe studies of the Pfr photoreaction in native and 13 C/15 N-labeled Cph1 phytochrome with unlabeled PCB chromophore, demonstrating different S0 substates, Pfr-I and Pfr-II, with distinct IR absorptions, orientations and dynamics of the carbonyl vibration of ring D. We derived time constants of 0.24ps, 0.7ps and 6ps, describing the complete initial photoreaction. We identified an isomerizing pathway with 0.7ps for Pfr-I, and silent dynamics with 6ps for Pfr-II. We discuss different origins of the Pfr substates, and favor different facial orientations of ring D. The model provides a quantum yield for Pfr-I of 38%, in line with ~35% ring D rotation in the electronic excited state. We tentatively assign the silent form Pfr-II to a dark-adapted state that can convert to Pfr-I upon light absorption.

Synthesis, structural characterization and VUV excited luminescence properties of LixNa(1−x)Sm(PO3)4 polyphosphates

Stoichiometric phosphors Li(x)Na(1−x)Sm(PO3)4(x = 0, 0.5, 1) were prepared in the solid state and were characterized at room temperature using X-ray diffraction, infrared and Raman spectroscopy. The obtained LiSm(PO3)4 and NaSm(PO3)4 polycrystalline samples are single-phased and have centrosymmetric monoclinic structure. The observed results show the presence of characteristic bands due to (PO2)− terminal and P−O−P bridging groups. However, the Li0.5Na0.5Sm(PO3)4 material seems to be a mixture of the Li and Na homologues. The VUV excitation and emission spectra of as-synthesized compounds were measured. It was found that the Sm3+ ions show an orange-red emission which corresponds to the group transitions 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, 11/2), with the strongest transition (4G5/2 → 6H7/2) peaking at around 597 nm. The decay curves were pure exponential. The derived time constants are comprise between 14 μs and 31 μs, the lowest value is for NaSm(PO3)4. The decays were modeled in the frame of fast diffusion model with a rough estimation of fast cross-relaxation mechanism which returns a cross-relaxation rate of 3–7 × 104 s−1 and diffusion constant of 1–2 × 10−9 cm2 s−1.

DYNAMIC SIMULATION AND COMPOSITION CONTROL IN A 10 L MIXING TANK

The open loop experiment of composition dynamic in a 10 L mixing tank has been successfully done inlaboratory. A 10 L tank was designed for mixing of water (as a stream-1) and salt solution (as astream-2 with salt concentration, c2 constant). An electric stirrer was employed to obtain uniformcomposition in tank. In order to keep the liquid volume constant, the system was designed overflow. Inthis work, 2 composition control configurations have been proposed; they are Alternative-1 andAlternative-2. For Alternative-1, the volumetric-rate of stream-1 was chosen as a manipulatedvariable, while the volumetric-rate of stream-2 was chosen as a manipulated variable for Alternative-2. The composition control parameters for both alternatives have been tuned experimentally. Thevolumetric-rate of manipulated variable was changed based on step function. The outlet stream’scomposition response (c3) to a change in the input volumetric-rate has been investigated. Thisexperiment gave Proportional Integral Derivative (PID) control parameters. The gain controllers Kc[cm6/(gr.sec)] for Alternative-1 and Alternative-2 are -34200 and 40459 respectively. Integral timeconstant ( tI) and Derivative time constant (tD) for both alternatives are the same, i.e. tI = 16 second,and tD = 4 second. Furthermore, closed loop dynamic simulation using computer programming wasalso done to evaluate the resulted tuning parameters. The developed mathematical model ofcomposition control system in a mixing tank was solved numerically. Such mathematical model wasrigorously examined in Scilab software environment. The results showed that closed loop responses inPID control were faster than those in P and PI controls.

Proper theoretical analysis of the oxygen wash-in kinetics of circle breathing systems

To correctly define the theoretical treatment of oxygen wash-in kinetics in circle breathing systems and reevaluate previously published results for the rate of change of oxygen concentration in a large animal circle breathing system. Theoretical analysis of previously published data. None. Previously published data for the rate of change of oxygen concentration in a large animal circle breathing system with two reservoir bag sizes (40 and 20 L) at three different flow rates (3, 6, and 10 L minute(-1)) were obtained from the original publication, via digital extraction, and analyzed to determine system time constants. The results of this analysis were compared to those originally reported and the level of mathematical agreement between experiment and theory was quantified. Theoretical time constants for the system with 40 L reservoir bag with flow rates of 3, 6, and 10 L minute(-1) were 16.4, 8.2, and 4.9 minutes, respectively. Experimentally derived time constants for this system with flow rates of 3, 6, and 10 L minute(-1) were 18.1, 9.2, and 5.4 minutes, respectively. Percent differences between experimental and theoretical time constants for this system with flow rates of 3, 6, and 10 L minute(-1) were 10.4, 12.2, and 10.2%, respectively. For the system with a 20 L reservoir bag and 6 L minute(-1) flow rate, the theoretical and experimentally derived time constants were 5.5 and 5.6 minutes, respectively, with a 1.8% difference. The average relative deviations between theory and experiment for the system at 6 L minute(-1) flow with a 40 or 20 L reservoir bag were 1.3% and 3.0%, respectively. Proper theoretical analysis of experimentally obtained data for the wash-in kinetics of oxygen into a large animal circle breathing system leads to improved mathematical agreement between theory and experiment when compared to the originally published results. Application of this method should allow more accurate prediction of the rate of change of oxygen concentration in anesthetic circuits.

Modeling Charge / Discharge Kinetics of the W' During Intermittent Exercise

The Critical Power model concerns the relationship between work rate (P, in watts) and fatigue, and includes two constants: the CP and the W'. These are related according to the equation (Whipp 1982): W' = (P-CP)t The CP is a power that can be maintained indefinitely on the basis of "aerobic" metabolism. The W' is a finite work capacity (in joules) available above CP (i.e. in the final sprint of a bicycle race), which is recharged curvilinearly (Ferguson 2010). Depletion of the W' results in extreme fatigue. Thus, knowledge of the W' can be helpful when developing a race strategy (Fukuba and Whipp 1999). PURPOSE: To develop a function to account for the kinetics of the W' during intermittent exercise, permitting constant monitoring of the athlete's "W' balance" remaining. METHODS: After determining GET, VO2max, CP and W', 6 recreationally active subjects carried out 5 separate exercise tests on an electronically braked ergometer. Each set was repeated until fatigue. 1: 60s of severe intensity exercise with 30s of 20W recovery 2: 60s of severe intensity exercise with 30s of moderate recovery 3: 60s of severe intensity exercise with 30s of heavy recovery 4: 60s of severe intensity exercise with 30s of severe recovery 5: A constant power trial in the severe domain The data were fit to the equation: where (t-u) = time between samples resulting in a depletion of W', and tc is the time constant of recharge, dependent on recovery power. The tc was varied by an iterative process until modeled W'balance = 0 at the time of fatigue. Derived time constants were plotted against %CP during recovery. RESULTS: Below CP, time constants of W' recharge were correlated with recovery power (r = 0.73). There was no correlation if recovery power exceeded CP. Time constants of W' recharge were correlated with the CP during 20W recovery (avg = 369s, SD = 23s, r = 0.86), moderate recovery (avg = 504s, SD = 115s, r = 0.55) and heavy recovery (avg = 579s, SD = 114s, r = 0.69), but not severe recovery or continuous severe exercise. CONCLUSION: It is possible to model the discharge and recharge of the W' during intermittent exercise. This could have important implications for the planning and real time monitoring of athletic performance.

Improved automatic tuning of PID controller for stable processes

This paper presents an improved automatic tuning method for stable processes using a modified relay in the presence of static load disturbances and measurement noise. The modified relay consists of a standard relay in series with a PI controller of unity proportional gain. The integral time constant of the PI controller of the modified relay is chosen so as to ensure a minimum loop phase margin of 30 ∘. A limit cycle is then obtained using the modified relay. Hereafter, the PID controller is designed using the limit cycle output data. The derivative time constant is obtained by maintaining the above mentioned loop phase margin. Minimizing the distance of Nyquist curve of the loop transfer function from the imaginary axis of the complex plane gives the proportional gain. The integral time constant of the PID controller is set equal to the integral time constant of the PI controller of the modified relay. The effectiveness of the proposed technique is verified by simulation results.

A study on adaptation of SBW parameters to individual driver’s steer characteristics for improved driver–vehicle system performance

This study focuses on the adaptation of steer-by-wire (SBW) parameters to the driver’s steer characteristics for a vehicle equipped with SBW system whereby steering gain and derivative time constant between the steering-wheel angle and the front-wheel-steer angle can be freely set. First of all, it presents a simple yet effective method to estimate the driver’s steer parameters from experimental data based on the general driver’s model. Driver’s parameters for young and aged drivers are compared. SBW parameters are then adapted to the identified driver’s parameters based on a simple analytical method, and its effect on the driver–vehicle system performance improvement is examined through an experimental study, for the case of aged drivers.

Optical bistability and pulsating behaviour in Silicon-On-Insulator ring resonator structures

We demonstrate optical bistability in a Silicon-On-Insulator two-bus ring resonator with input powers as low as 0.3mW. We evaluate the importance of the different nonlinear contributions and derive time constants for carrier and thermal relaxation effects. In some cases, we also observe pulsation due to interaction between the dominant nonlinear effects. Such a behaviour may be problematic for possible memory and switching operations. Alternatively, it could be used for (tunable) pulse generation.

Parameter comparison for low-noise Mo/Au TES bolometers

We describe a comparative investigation of the parameters of MoAu-bilayer TES bolometers designed for infrared detectors. A set of devices with variations in geometry were fabricated at the NASA/GSFC detector development facility. These detectors have different bilayer aspect ratios (providing differing normal state resistances and current densities), and have varieties of normal metal regions to study the effects of geometry on noise. These normal metal regions are oriented either parallel to or transverse to the direction of current flow, or both. The lowest noise detectors are found to have normal metal regions oriented transversely. For about a dozen different devices, we have measured a large set of parameters by means of a suite of tests. These include complex impedance measurements to derive time constants; IV curves to determine resistance and power; thermal conductance measurements; noise measurements as a function of device resistance; and direct resistance vs. temperature measurements.

Time-intensity-based volumetric flow measurements: an in vitro study

Ultrasonic contrast agents have been used to assist blood flow measurements. Several contrast-specific flow measurement techniques have been proposed during the last few years. Among them, a method based on relative enhancement of the backscattered signal as a function of time is of particular interest. This method is also known as the time-intensity method. The method is based on the indicator-dilution theory, and the time-intensity curve is used to derive blood flow-related parameters such as the flow rate and the blood mixing volume. Previous in vitro studies done by other research groups were mainly based on a perfusion model or an artery model. Results showed that several parameters derived from the time-intensity curve had a good correlation with the flow rate under certain conditions. However, the studies did not focus on factors such as mixing volume, mixing chamber configuration and different types of mixing chamber. In this paper, dependence of the time-intensity curve is further studied. Specifically, two types of blood-mixing chambers were constructed. One was a spherical compartment phantom with two different sizes (260 and 580 mL) and different inflow/outflow configurations. The other was a perfusion phantom consisting of dialysis cartridges with the volume ranging from 114 to 351 mL. The time intensities were also measured at both the input and the output of the mixing chamber. A commercial agent (Levovist®) and a self-made, albumin-based agent were used and the wash-out time constant and the mean transit time were derived for flow rates ranging from 500 to 1300 mL/min. For the perfusion phantom, results showed that the parameters had a good correlation with both the flow rate and the mixing volume. Results from the compartment phantom, on the other hand, indicated that the inflow/outflow configuration and the mixing size significantly affected the derived time constants. Potential applications of new volumetric flow estimation techniques based on both input and output intensities were also discussed. (E-mail: paichi@cc.ee.ntu.edu.tw)

Design of methanol Feed control in Pichia pastoris fermentations based upon a growth model.

The methylotrophic yeast Pichia pastoris is an effective system for recombinant protein productions that utilizes methanol as an inducer, and also as carbon and energy source for a Mut(+) (methanol utilization plus) strain. Pichia fermentation is conducted in a fed-batch mode to obtain a high cell density for a high productivity. An accurate methanol control is required in the methanol fed-batch phase (induction phase) in the fermentation. A simple "on-off" control strategy is inadequate for precise control of methanol concentrations in the fermentor. In this paper we employed a PID (proportional, integral and derivative) control system for the methanol concentration control and designed the PID controller settings on the basis of a Pichia growth model. The closed-loop system was built with four components: PID controller, methanol feed pump, fermentation process, and methanol sensor. First, modeling and transfer functions for all components were derived, followed by frequency response analysis, a powerful method for calculating the optimal PID parameters K(c) (controller gain), tau(I) (controller integral time constant), and tau(D) (controller derivative time constant). Bode stability criteria were used to develop the stability diagram for evaluating the designed settings during the entire methanol fed-batch phase. Fermentations were conducted using four Pichia strains, each expressing a different protein, to verify the control performance with optimal PID settings. The results showed that the methanol concentration matched the set point very well with only small overshoot when the set point was switched, which indicated that a very good control performance was achieved. The method developed in this paper is robust and can serve as a framework for the design of other PID feedback control systems in biological processes.

Feasibility study of time-intensity-based blood flow measurements using deconvolution.

Ultrasonic contrast agents have been used to enhance the acoustic backscattered intensity of blood and to assist the assessment of blood flow parameters. One example is the time-intensity method based on the indicator-dilution theory. In this case, a mixing chamber model can be employed to describe the concentration of the contrast agent as a function of time. By measuring the time intensities at both the input and output of the blood mixing chamber, blood flow information can be obtained if proper deconvolution techniques are applied. Note that most deconvolution techniques assume a linear and time invariant (LTI) system for the mixing of the contrast agent with blood. In this paper, the hypothesis that a blood mixing chamber is an LTI system was tested. Several aspects were studied. One aspect was the linear relationship between the concentration of the contrast agent and the backscattered intensity. The other aspect was the dependence of the derived time constants on the concentration. The concept of an effective mixing volume was also introduced and evaluated. Finally, the input and the output time constants were measured and compared to theory under the LTI assumption. Extensive experiments were performed. Two in vitro flow models were constructed and two contrast agents were used. Results indicated that the LTI assumption does not hold and quantitative flow estimation is generally not possible. Nonetheless, the indicator-dilution theory can still be applied if only relative measurements of the flow rate are required.

Analysis of Palierne’s emulsion model in the case of viscoelastic interfacial properties

The quantitative understanding of rheological experiments on compatibilized binary polymer blends requires the consideration of viscoelastic interfacial properties. The Palierne model offers these capabilities but a systematic analysis has not been performed yet. Starting from the Palierne model containing a Maxwell ansatz for complex interfacial shear or dilatational moduli and which considers a particle-size distribution function, we find that this model combines parameter and material functions in an ambiguous way. Consequently, a simplified version of the model—frequency-independent interfacial moduli and monomodal particle-size distribution—was introduced. Formulas have been derived for the relaxation times, the form relaxation time, and one additional still longer time which is associated with viscoelastic interfacial properties. We have found a good agreement between the predictions of the model and experimental data as well as the characteristic times in the relaxation time spectrum and the derived time constants for a PS/PMMA blend compatibilized with different amounts of a corresponding symmetric block copolymer. These results reveal that from the rheological point of view, the interface is of almost elastic nature, either shear or dilatational.

Fuzzy logic based set-point weight tuning of PID controllers

A methodology, based on fuzzy logic, for the tuning of proportional-integral-derivative (PID) controllers is presented. A fuzzy inference system is adopted to determine the value of the weight that multiplies the set-point for the proportional action, based on the current output error and its time derivative. In this way, both the overshoot and the rise time in set-point following can be reduced. The values of the proportional gain and the integral and derivative time constant are determined according to the well-known Ziegler-Nichols formula so that a good load disturbance attenuation is also assured. The methodology is shown to be effective for a large range of processes and is valuable for industrial settings since it is intuitive, it requires only a small extra computational effort, and it is robust with regard to parameter variations. The tuning of the parameters of the fuzzy module can be easily done by hand or by means of an autotuning procedure based on genetic algorithms.

New method for Shuttle Orbiter thermal analysis

A new, simplified, approximate method of on-orbit transient thermal analysis of complex operational space vehicles in varying environmental conditions is described. When applied to the Space Shuttle Orbiter simulation, the standard deviation of error in results compared with flight data for over 50 missions is typically between 5 and 10°F. The method requires first running detailed orbiter thermal mathematical models for a steady-state solution in a systematized variety of on-orbit Earth-sun orientations. These steady-state temperatures form a database that is loaded and permanently stored in a personal-computer-based program package. An exponential extrapolation method derived from a classical simplified energy balance and using empirically derived time constants is applied to convert from the steady-state temperature to the actual transient response. Now in use routinely for thermal analysis of the Space Shuttle Orbiter, the method has reduced the days of engineering manpower and hours of mainframe computer usage previously required to a simple, painless, and short session on a personal computer. The results, although approximate and sometimes limited in certain special situations, have been found generally to yield excellent agreement with flight data.

Characteristics and Performance of an Autotuning Proportional Integral Derivative Controller for Dissolved Oxygen Concentration

AbstractThe characteristics and performance of an autotuning proportional integral derivative (PID) controller developed by us have been investigated. The parameters for this controller, proportional gain, K, the integral time constant, Ti, and the derivative time constant, Td, are on‐line‐tuned by using heuristic rules, requiring no α priori tuning. The controller showed a stable and robust performance, even when only K was on‐line‐tuned. However, the dynamic (or time delay) of the membrane‐type dissolved oxygen (DO) probe caused oscillations in the DO concentration unless it was properly compensated. This required a prediction method. When all three controller parameters were on‐line‐adjusted, the DO probe dynamic could be effectively overcome with no separate prediction step.