Transport Lag Research Articles

Model Based Tuning of Humidifying Processes with Transportation Lag

A humidifying system with varying transportation lag was studied experimentally. Various models were tried and the system fitted a first order plus dead time model with an error of ±5%. The humidity was measured using an on‐line Yokogawa hygrometer. From the model parameters, various controllers, such as PI, Smith predictor, IMC, and IMC PID were analyzed using Matlab. The closed loop performance was studied for both regulator and servo problems. Based on rise time, settling time, and overshoot, the present study concludes that the IMC controller is best suited for this process.

Active Flutter Suppression by Feedback Compensation of Transport Logs

A IRCRAFT wings are deigned to be flexible, and as a consequence of this feature they are known to be continuously oscillating under the action of wind loads leading to the well-known phenomenon of “flutter.” Flutter in wings was conventionally inhibited by passive design techniques based on altering the mass and stiffness distributions of the wing. However, the recent trend in building highly flexible aircraft has demonstrated the inadequacy of passive techniques for inhibiting the occurrence of flutter. To overcome the inadequacy of passive techniques in inhibiting the occurrence of flutter within the design envelope of the aircraft, a new technique, based on feedback control, was developed in the early 1970s, called “active flutter suppression.” Two distinct approaches emerged for the design of the control law for activeflutter suppression, the first based on optimal control, and the second approach [1], emerging from the concept of passivity, considers the energy flowing in and out of the “system.” There are several applications of this method to real aircraft, and [2] is archetypal of these examples. References [3,4] are typical examples in which the techniques based on the modeling methods were applied to the synthesis of optimal and near-optimal control laws for active flutter suppression. In this paper we propose a third approach towards controlling flutter. By careful consideration of the unsteady aerodynamic loading, those components that contribute to the delay in the growth of the loading in response to changes in the wingmotion are isolated. These delays or transport lags are then eliminated by an appropriate control law that ensures the constancy of circulatory component of the unsteady lift. With secondary compensation one could increase the flutter speed, which is the primary objective of active flutter suppression. Furthermore, the constancy of the circulatory component implies that the flow is less likely to separate and the circulation is more likely to remain steady. To evaluate the method we consider the archetypal problem of the typical section and implement such a control law. Themotivation for this work arose from the need to develop smart, flexibly actuated morphing control surfaces for future aircraft wings in low-speed flight. The method described in this paper can be routinely implemented with control surfaces. Morphing control surfaces can be deflected in a multitude of modes and the method itself is based on observations of bird flight.

Optimal Wide Area Controller and State Predictor for a Power System

An optimal wide area controller is designed in this paper for a 12-bus power system together with a Static Compensator (STATCOM). The controller provides auxiliary reference signals for the automatic voltage regulators (AVR) of the generators as well as the line voltage controller of the STATCOM in such a way that it improves the damping of the rotor speed deviations of the synchronous machines. Adaptive critic designs theory is used to implement the controller and enable it to provide nonlinear optimal control over the infinite horizon time of the problem and at different operating conditions of the power system. Simulation results are provided to indicate that the proposed wide area controller improves the damping of the rotor speed deviations of the generators during large scale disturbances. Moreover, a robust radial basis function network based identifier is presented in this paper to predict the states of a multimachine power system in real-time. This wide area state predictor (WASP) compensates for transport lags associated with the present communication technology for wide area monitoring of the electric power grid. The WASP is also robust to partial loss of information caused by larger than expected transport lags or even failed sensors throughout the network

THE EFFECTS OF NON-EQUILIBRIUM SEDIMENT TRANSPORT PROCESS ON INSTABILITY OF DUNEFORMATION

In order to enable accurate predictions of the formation of dunes, to predict the effect of non-equilibrium sediment transport process is important. The stochastic model has been known to be the non-equilibrium sediment transport formula which can describe the sediment transport lag behind the bed shear stress. In this study, we performed a linear stability analysis by the use of the stochastic model with the two dimentional Reynolds equations. The phase lag between the sediment transport and bed shear sterss is generated from step length on the sediment transport process, and the phase lag between the shear stress and flow velocity is generated from the fluid viscosity. The two phase lags are able to be theoretically predicted in this analysis. It is found that the instability of dune formation is shown by the balance of the two phase lags. We also performed a weakly nonlinear analysis. It is found that the dune-flat bed transition is charactrized by the subcritical bifurcation in the range of small bed slop and small step length.

An investigation on spill plume development and natural filling in large full-scale atrium under retail shop fire

This paper reports an investigation on the scenarios of the spill plume and the resultant natural filling in a full-scale atrium mock-up due to a retail shop fire. The study includes two aspects, i.e., the full-scale experiment and the numerical simulation. A spill plume model is proposed to predict the characteristic properties of the plume development in the atrium under a retail shop fire. Furthermore, to accurately predict the shop fire in the atrium, an improved zone model is developed combining the transport lag time model and the spill plume model. Besides validating the developed model by experiments, the case is also simulated by the established zone model, i.e., CFAST code, and the computational fluid dynamics model, i.e., FDS code. By both physical and numerical experiments, the process of natural smoke filling and the temperature rise in the atrium are investigated and well understood. It is found that a typical spill plume contains three regimes, i.e., the curved section out of the retail shop door, the line plume in the near field, and the axisymmetric plume in the far field. Predictions from the proposed empirical model for the spill plume and the resultant improved zone model compare favorably with the experiments. The study indicates that the atrium becomes very dangerous due to such shop fire if no smoke control employed. The ability of mechanical exhaust system in the atrium to mitigate the hazard of a retail shop fire is investigated as well.

Model Based IMC Controller for Processes with Dead Time

A system with varying transportation lags has been experimentally studied for modeling. Modeling is performed using a step test. The tracer is sodium chloride solution whose conductivity is measured using an online conductivity analyzer. Based on the step response, the model parameters are determined and the lag processes are represented by a first order plus dead time (FOPDT) model. For the models developed, an internal model control (IMC) scheme is designed. Performance comparison, based on rise time, settling time, and overshoot, is done among the designed IMC controllers, conventional PID controllers, and Smith Predictor controllers. The present study depicts that IMC controllers outperform PID and Smith Predictor controllers.

Using planning agreements to fund transport infrastructure

The use of planning agreements to provide funding for transport improvements required to support development proposals is discussed. The legislation and Government guidance referred to applies to England, but there is similar legislation and guidance applicable to Scotland and Wales. Planning policies since the late 1980s have required developments to be accessible by non-car modes of transport as well as by private vehicles and planning agreements are thus usually used to secure improvements to all transport modes. Planning agreements have been in use since the early 1970s and many agreements have secured highway improvements. These have usually been for single large-scale developments. Securing improvements needed to meet the cumulative impact of a number of developments has not been very successful with the result that many developments cause an impact but the necessary transport infrastructure has to be provided by the transport authorities. New Government advice issued in 2005 has made it clear that standard charges and pooling funding from several developments for the provision of transport infrastructure is acceptable. Some methods have been developed and are reviewed in the paper. Compared with the standard charge methods that have been developed for the provision of open space and educational facilities those for transport lag well behind. The result of this is that much needed funding for transport is not being collected.

各出力に大きさの異なるむだ時間を含む多変数系の状態予測器

Various actual systems include time delays due to measurement and/or computational delays, and transmission and transport lags. In this paper, the authors propose a state predictor for a certain class of multivariable systems including multiple output delays. The predictor consists of full-order observers, each estimates a past state from a delayed output, and finite interval integrators, which compensate the effect of the delays using state transition equations. The error of the state prediction converges to zero at the arbitrary rate adjusted by choosing a finite number of poles of the full-order observers. The output matrix used for observer design is not affected by the delays, whereas that of a conventional observer greatly depends on the length of the delays. Numerical examples of an integral process and an unstable process demonstrate that the errors of numerical computation in the proposed predictor are smaller than those in the conventional observer.

Suspended sediment transport along an idealised tidal embayment: settling lag, residual transport and the interpretation of tidal signals

We present semi-analytical solutions for suspended sediment concentration (SSC) and residual sediment transport in a simple mathematical model of a short tidal embayment. These solutions allow us to investigate in some detail the characteristic tidal and semi-tidal variation of SSC and the processes leading to residual sediment transport, including settling and scour lags, the roles of ‘local’ and ‘advective’ contributions, and the presence of internally or externally generated overtides. By interpreting the transport mechanisms in terms of the classic conceptual models of settling lag we clarify how these models may be expressed in mathematical terms. Our results suggest that settling lag is usually a more important process than scour lag, and that a local model which neglects advection may predict the direction of net sediment transport incorrectly. Finally, we discuss our results in the context of other transport processes and morphodynamic feedback.

Effect of Delay on the Stability of a Coupled Reactor−Flash System Sustaining an Elementary Non-isothermal Reaction

In this work, we investigate the stability of a continuous stirred tank reactor (CSTR) coupled to an isothermal, isobaric flash. The coupling is through the recycle of the reactant-rich stream from the downstream flash unit to the upstream reactor. We consider the first-order irreversible reaction A → B occurring non-isothermally in the CSTR. The main focus of this work is to investigate the effect of delay arising as a result of transportation lag from the reactor to the separator on the system stability. In the absence of delay, it has been clearly shown that the coupled system exhibits static and dynamic instability. The effect of delay on the stability of the coupled system is studied for the two classical control strategies: (i) The fresh feed flow rate, F0, is flow controlled and the reactor effluent flow rate, F, is used to control the molar holdup in the reactor, MR. (ii) The flow rate, F, is flow controlled, and F0 is used to control MR. It is shown that delay induces new regions of dynamic instability. The system switches from instability to stability and vice versa for these two control strategies as the delay is increased.

Transient analysis of reactant gas transport and performance of PEM fuel cells

The dynamic performance of PEM fuel cells is one of the most important criteria in the design of fuel cells with application to mobile systems. To study this issue, we extend our previous steady model of gas reactant transport to an unsteady one and employ it to examine the transient transport characteristics and the system performance of the PEM fuel cells. With the assumption of the two-dimensional mass transport in the cathode side of PEMFC, the effects of the channel width fraction, λ = ℓ c / ℓ b , the porosity of the gas diffuser layer, ɛ 1, and the surface overpotential of the catalyst layer, η, on the transient characteristics of the resultant current density and mass transport are focused in this work. It is disclosed that an increase in λ, or η may lead to a faster dynamic response for the fuel cell when the PEM fuel cell system is started up. Results of a typical case demonstrate that, although the dynamic response time may be as long as 10 s due to the mass transport lag, the fuel cell system needs only less than 0.4 s to reach the 90% response.

Transport and Time Lag of Chlorofluorocarbon Gases in the Unsaturated Zone, Rabis Creek, Denmark

Transport of chlorofluorocarbon (CFC) gases through the unsaturated zone to the water table is affected by gas diffusion, air–water exchange (solubility), sorption to the soil matrix, advective–dispersive transport in the water phase, and, in some cases, anaerobic degradation. In deep unsaturated zones, this may lead to a time lag between entry of gases at the land surface and recharge to groundwater. Data from a Danish field site were used to investigate how time lag is affected by variations in water content and to explore the use of simple analytical solutions to calculate time lag. Numerical simulations demonstrate that either degradation or sorption of CFC-11 takes place, whereas CFC-12 and CFC-113 are nonreactive. Water flow did not appreciably affect transport. An analytical solution for the period with a linear increase in atmospheric CFC concentrations (approximately early 1970s to early 1990s) was used to calculate CFC profiles and time lags. We compared the analytical results with numerical simulations. The time lags in the 15-m-deep unsaturated zone increase from 4.2 to between 5.2 and 6.1 yr and from 3.4 to 3.9 yr for CFC-11 and CFC-12, respectively, when simulations change from use of an exponential to a linear increase in atmospheric concentrations. The CFC concentrations at the water table before the early 1990s can be estimated by displacing the atmospheric input function by these fixed time lags. A sensitivity study demonstrates conditions under which a time lag in the unsaturated zone becomes important. The most critical parameter is the tortuosity coefficient. The analytical approach is valid for the low range of tortuosity coefficients (τ = 0.1–0.4) and unsaturated zones greater than approximately 20 m in thickness. In these cases the CFC distribution may still be from either the exponential or linear phase. In other cases, the use of numerical models, as described in our work and elsewhere, is an option.

Transport and Time Lag of Chlorofluorocarbon Gases in the Unsaturated Zone, Rabis Creek, Denmark

Transport of chlorofluorocarbon (CFC) gases through the unsaturated zone to the water table is affected by gas diffusion, air–water exchange (solubility), sorption to the soil matrix, advective–dispersive transport in the water phase, and, in some cases, anaerobic degradation. In deep unsaturated zones, this may lead to a time lag between entry of gases at the land surface and recharge to groundwater. Data from a Danish field site were used to investigate how time lag is affected by variations in water content and to explore the use of simple analytical solutions to calculate time lag. Numerical simulations demonstrate that either degradation or sorption of CFC‐11 takes place, whereas CFC‐12 and CFC‐113 are nonreactive. Water flow did not appreciably affect transport. An analytical solution for the period with a linear increase in atmospheric CFC concentrations (approximately early 1970s to early 1990s) was used to calculate CFC profiles and time lags. We compared the analytical results with numerical simulations. The time lags in the 15‐m‐deep unsaturated zone increase from 4.2 to between 5.2 and 6.1 yr and from 3.4 to 3.9 yr for CFC‐11 and CFC‐12, respectively, when simulations change from use of an exponential to a linear increase in atmospheric concentrations. The CFC concentrations at the water table before the early 1990s can be estimated by displacing the atmospheric input function by these fixed time lags. A sensitivity study demonstrates conditions under which a time lag in the unsaturated zone becomes important. The most critical parameter is the tortuosity coefficient. The analytical approach is valid for the low range of tortuosity coefficients (τ = 0.1–0.4) and unsaturated zones greater than approximately 20 m in thickness. In these cases the CFC distribution may still be from either the exponential or linear phase. In other cases, the use of numerical models, as described in our work and elsewhere, is an option.

Patterns of relationship between activity of sympathetic nerves in rabbits and rats

We used frequency domain analysis (power spectra, ordinary and partial coherence and phase spectra) of simultaneously recorded activity of postganglionic sympathetic nerves to investigate the construction of their central generators in rabbits and rats anesthetized with urethane. As found earlier in the cat, power spectra of sympathetic nerve discharge (SND) consisted of a wide-band component (1 to 10 Hz in rabbits and 1 to 15–20 Hz in rats) and superimposed cardiac and respiratory related peaks. The coherence between pairs of SNDs in the cardiac, vertebral, and renal nerves was significant over a wide range of frequencies, from 0 to 6–10 Hz in rabbits, and except for a sharp peak at the heart rate, was not explained by baroreceptor feedback. In rats, the coherence between distant nerves was relatively low (<0.2) except at the cardiac and respiratory frequencies. Analysis of partial coherences for the three nerves in rabbits revealed two main patterns; one characterized by dominance of the cardiac SND generator, and the other by strong coupling of the vertebral and cardiac SNDs, as compared with renal SND. Phase spectra of distant nerves contained a well-defined transportation lag corresponding to a delay of ∼70 ms between upper and lower thoracic spinal cord segments. At frequencies close to heart rate however, the phase was constant in most experiments indicating that different mechanisms are involved in transmitting wide band and oscillatory components of resting SND. The similarities between sympathetic oscillators in cats, studied previously in great detail, and rabbits preferred in recent behavioral studies allow the translation of knowledge between these two species.

Electrochemical detection in liquid flow analytical techniques: Characterization and classification (IUPAC Technical Report)

Abstract Liquid flow analytical techniques are classified, and definitions are provided of flow-injection analysis, segmented flow analysis, flow titration, continuous monitoring, liquid chromatography, and capillary electrophoresis. Electrochemical detection and flow through detection cells are characterized with respect to the surface and bulk detection. The detector performance is discussed in terms of its principal analytical parameters, such as detection limit and dynamic concentration range, as well as its dynamic characteristics, such as the response time, sampling frequency, transport lag, and long-term stability. Moreover, different detection modes are critically evaluated, including both potentiostatic and galvano-static techniques. Factors influencing sensitivity and detection limit, which include electronic and hydrodynamic approach, are also discussed. Different detector designs are critically reviewed, and the special features of electrochemical detectors for flow analytical techniques are emphasized.

Effect of Delay on the Stability of a Coupled Reactor−Separator System

In this work we investigate the behavior of a coupled reactor−separator system. The reactor considered is a continuous stirred tank reactor, and the coupling between the two units occurs via recycle of the reactant-rich stream (assumed to be the bottoms) from the downstream flash to the upstream reactor. We investigate two reactions: (i) an irreversible isothermal first-order reaction A → B and (ii) an elementary cubic autocatalytic isothermal reaction of the form A + 2B → 3B. The separator is modeled as a flash unit operating isothermally and isobarically. The feed to the flash is restricted to be a binary mixture. This uniquely fixes the composition of the two effluent streams, leaving the flash unit. The main focus in this work is to study the effect of delay arising from the transportation lag from the reactor to the separator. The behavior of the system is governed by delay differential equations. We want to study how the dynamic instability induced by delay crucially depends on the flow control strategy of the coupled reactor−separator system. It is shown that delay does not induce any instability if the fresh feed flow rate F0 is flow-controlled and the molar holdup is controlled using the reactor effluent flow rate F. In the second control strategy where the reactor effluent flow rate F is flow-controlled and the holdup is controlled using fresh feed flow rate F0, delay above a threshold value can induce instability for the two reaction systems considered. In the third control strategy, both F and F0 are flow-controlled and the holdup in the reactor is allowed to vary. Here again delay beyond a critical value can introduce a new region of instability for the isothermal first-order reaction, and it increases the region of dynamic instability for the cubic autocatalytic reaction. The main result of the paper is to demonstrate that some of the preferred control structures of Luyben that are stable can be rendered unstable by sufficiently large delay.

A nonlinear model study on the long‐term behavior of shore face–connected sand ridges

A morphodynamic model is analyzed to gain further knowledge about the finite amplitude behavior of shore face–connected sand ridges observed on storm‐dominated inner shelves. The present work elaborates on previous studies in which it was demonstrated that ridge formation may be due to an instability of a storm‐driven current moving over a sandy inner shelf with a transverse slope. Here, the long‐term evolution of the ridges is studied by performing a nonlinear stability analysis in which the physical variables are expanded in eigenmodes of the linear stability problem. New physical aspects are that the longshore pressure gradient in the momentum equations and settling lag in the suspended load sediment transport are incorporated. Furthermore, along‐shelf uniform shelf modes and subharmonic eigenmodes are accounted for. The model shows that after the transient stage the competition between the modes results in saturation behavior that is dominated by a few modes only. The characteristic height of the final bed forms increases with increasing transverse slopes of the shelf, while the timescale of transient behavior decreases. The longshore uniform modes, pressure gradient, and settling lag effects only have a minor effect on the dynamics. A process analysis reveals that the mechanism responsible for the saturation behavior is the sediment transport related to the bottom slope and the effect of small‐scale bed forms. Subharmonic modes significantly affect the transient behavior of the ridges and cause the final bed forms to have larger amplitudes and longer wavelengths.

FIELD EVALUATION OF RESPONSE TIMES FOR A VARIABLE RATE (PRESSURE–BASED AND INJECTION) LIQUID CHEMICAL APPLICATORS

This study investigated the field performance of a ground sprayer for applying chemicals at constant and variable application rates with both pressure–based and injection sprayer control technology. Evaluation of the variable rate chemical application system was performed by assessing the field application accuracy through instrumentation of the system to monitor sprayer chemical flow, sprayer field location, and sprayer speed. The data collected provided information for determining the sprayer application rate for each constant and variable rate application. The application system produced an average application rate within .2.25% of the desired application rate. The transport lag in the pressure–based variable rate technology is approximately 2 s due to GPS signal lag and control valve response lag. The average active ingredient lag time for the injection variable rate technology is based upon the flow rate of the carrier and ranged from 15 to 55 s. This transport lag varies however for each nozzle.

Assessment of open-loop rollover control of articulated vehicles under different manoeuvres

In this paper, a comprehensive three-dimensional heavy vehicle model is developed to investigate the effectiveness of an open-loop roll instability control. The steering system compliance, roll steer, bump steer, Ackerman steer and wrap steer are incorporated in the vehicle model, along with a comprehensive tyre model and ABS algorithm. Time delays due to a driver's reaction and the transportation lag of the braking system are characterized by a variable called the reaction delay. The rollover indicators in terms of roll safety factor, tractor and trailer lateral accelerations and roll angles, and the rearmost axle roll angle are investigated for their effectiveness for open-loop roll stability control in various cornering and evasive manoeuvres, road conditions, braking efforts, and different reaction delays.

Phase plane analysis of first-order system with transport lag

This correspondence presents some unfamiliar aspects of the phase plane method when applied to controlled systems containing transport lag. A simple example is used to illustrate the design of trajectories which can be obtained either from a numerical simulator or via a true setup. It is then shown that the usual phase plane trajectory of plant with pure delay provokes a spiral motion around the stable singular point.