Ow Control Research Articles

Review of multiport isolated bidirectional converter interfacing renewable and energy storage system

<p>Multi port converters increasingly gain prominance in the recent past to interface renewable energy sources like photovoltaic cells, fuel cells with the load. Energy storage elements like battery and supercapacitors nd major place as an additional and alternate sources in systems with primary renewable energy sources to overcome its intermittency issues. As these energy storage element's charging and discharging cycles are to be controlled, an isolated bidirectional converter topology with transformer is used. The galvanic isolation provided by the high frequency ac link transformers in partly isolated and fully isolated topologies makes these converters most preferrable in high power applications like electric vehicles. A comprehensive review is performed on various three port partly isolated and fully isolated topologies addressed by dierent research groups. The key contributions on soft switching for reducing switching losses and improving overall converter efficiency with help of resonant elements are discussed. In addition, control strategies for power ow control with enhanced soft switching of partly isolated converters are highlighted. A summary of converter topologies is provided comparing power rating, device count, soft switching resonant elements and efficiency which gives an idea for selection of suitable topology for the desired system requirement.</p>

DYNAMIC LOAD ON CYLINDER SURGE TANKS OF DIVERSION HYDROELECTRIC POWER STATIONS UNDER SEISMIC IMPACT

The necessity of construction of surge tanks for diversion hydroelectric power stations with pressure derivation is substantiated in the article. These tanks as a part of water-conveyance headrace are essential to protect a long pressure tunnel from pressure boost under hydraulic shock and in consequence from additional charges for tunnel walls underpinning. It is to be noted that diversion hydroelectric power stations are often erected in mountainous area and surge tanks are situated on the turning point of water-conveyance headrace. This position allows to lower surge tank and to keep construction costs down. The examples show that it is preferable to construct surge tanks on the surface of the earth. It is to be noted that these structures constructive elements are exposed to static water pressure and water dynamic load due to water fl ow control through aggregates under power consumption changes of hydroelectric power station . At the same time in mountainous area surge tanks can also be exposed to dynamic loads because of seismic impact. The article gives the solution for determination of impulse and convective components of hydrodynamic pressure at vertical walls of metal cylinder tank in the case of horizontal seismic impact. The proposed solution clarifi es well-known calculation methods and allows to perform an accurate design calculation of potential loads and to choose necessary geometric parameters that ensure tank reliability.

Velocity field measurements on high-frequency, supersonic microactuators

The resonance-enhanced microjet actuator which was developed at the Advanced Aero-Propulsion Laboratory at Florida State University is a fluidic-based device that produces pulsed, supersonic microjets by utilizing a number of microscale, flow-acoustic resonance phenomena. The microactuator used in this study consists of an underexpanded source jet that flows into a cylindrical cavity with a single, 1-mm-diameter exhaust orifice through which an unsteady, supersonic jet issues at a resonant frequency of 7 kHz. The flowfields of a 1-mm underexpanded free jet and the microactuator are studied in detail using high-magnification, phase-locked flow visualizations (microschlieren) and two-component particle image velocimetry. These are the first direct measurements of the velocity fields produced by such actuators. Comparisons are made between the flow visualizations and the velocity field measurements. The results clearly show that the microactuator produces pulsed, supersonic jets with velocities exceeding 400 m/s for roughly 60 % of their cycles. With high unsteady momentum output, this type of microactuator has potential in a range of ow control applications.

Flow Control Of Impingement JetsAnd Wall Jets

The purpose of this article is to provide useful information on the fl ow control technology of impingement jets in gas turbines and to discuss the recent trends in the passive and active fl ow control of impingement jets based on recent advancements. The temperature level in a gas turbine fi eld is so high that innovative developments in material and cooling technology are needed for usage in the hot sections. Therefore, innovative cooling systems will be employed in the future. Smart actuators for fl ow control of the jet impingement, which can be used under severe temperature and pressure conditions, will also be provided based on the progress in related technologies.

Active and Passive Flow Control of Turbomachines

Turbomachines are used in a wide range of applications. Increasing the efficiency and operating range of turbomachines reduces fuel consumption of gas turbine power plants and other applications. Over the years, many attempts have been made to achieve these objectives. e present special issue addresses these goals with special emphasis on active and passive �ow control techniques. is special issue compiles 7 original research articles that describe active and passive �ow control techniques applied to different types of turbomachines. e theme for this special issue is set by J. P. Gostelow et al. ey describe various types of vortices encountered in a transonic turbine nozzle blade passage. Active and passive control of these vortices is essential to improve the performance of turbines. ere are two more papers on control of turbine �ows. e paper by R. Da Soghe et al. describes aerothermal analysis of a turbine casing impingement cooling system. T. Matsunuma and T. Segawa systematically varied the input voltage of plasma actuators to reattach the simulated boundary layer on the suction surface of a turbine at a low Reynolds number. e low-pressure turbine of aircra gas turbine power plants operating at high altitudes operates at low Reynolds numbers. Losses in turbines operating at low Reynolds numbers increase rapidly due to large separation occurring on the suction surfaces of the turbine blades. Many researchers used dielectric barrier discharge (DBD) plasma actuators to actively control �ow separation, tip clearance �ows, and so forth in turbines and other turbomachinery components. e present paper by T. Matsunuma and T. Segawa is a great addition to the available data that addresses the effects of input voltage to plasma actuators on �ow control effectiveness. Two papers describe active and passive �ow control techniques applied to centrifugal compressors. A. Marsan et al. numerically investigated boundary layer suction technique applied to the radial diffuser of a transonic centrifugal compressor. ey had presented an efficient control technique, which used a suction mass �ow rate of 0.1% of global mass �ow to increase the compressor operating range by 40%. T. Hirano et al. experimentally investigated a passive nozzle injection system to control surge and rotating stall in high speed centrifugal compressors. ey demonstrated optimum circumferential position of the injection nozzle. S. Kyparissis and D. Margaris tested impellers with three different leading edge angles to optimize the leading edge angle to reduce cavitation development and enhance the performance of a centrifugal pump. Active and passive �ow control techniques are being extensively investigated in the primary components of turbomachinery. However to further improve the performance of turbomachinery, active and passive �ow control techniques need to be applied to secondary components of turbomachines, such as seals. e last paper of the special issue by M. �hang et al. addresses leakage �ow characteristics of seals used in reactor coolant pumps. ey had numerically shown that helical groove seal controls the leakage along the front surface of the impeller face due to its higher resistance than the circumferential grooved seal. It is hoped that this special issue will provide useful information to wide readership from academia, industry and research establishments and inspire new and more efficient control techniques.

On-off and PI Control of Methane Gas Production of a Pilot Anaerobic Digestion Reactor

A proposed feedback control system for methane ow control of a real pilot anaerobic digestion reactor fed with dairy waste is designed and analyzed using the modied Hill model, which has previously been adapted to the reactor. Conditions for safe operation of the reactor are found using steady-state responses of dynamic simulations, taking into account the upper limit of the volatile fatty acids (VFA) concentration recommended in the literature. The controllers used are standard process controllers, namely the on-o controller and the PI controller. Several PI controller tuning methods are evaluated using simulations. Two methods are favoured, namely the Skogestad method, which is an open loop method, and the Relaxed Ziegler-Nichols closed loop method. The two methods give approximately the same PI settings. Still, the Skogestad method is ranged rst as it requires less tuning time, and because it is easier to change the PI settings at known changes in the process dynamics. Skogestad’s method is successfully applied to a PI control system for the real reactor. Using simulations, the critical operating point to be used for safe controller tuning is identied.

Nanofluidic Chips: Real‐Time Template‐Assisted Manipulation of Nanoparticles in a Multilayer Nanofluidic Chip (Small 19/2011)

The cover picture conceptualizes nanoparticles, quantum dots, or biomolecules being controlled in a multilayer, nanofl uidic chip architecture using electrokinetic forces to capture, hold, and release them by controlling the potential difference across the channels. The nanomaterials are delivered into the top microfl uidic channel and are captured onto the vertical nanochannels. Such dynamic control of the fl ow and placement of nanomaterials in a biocompatible, aqueous environment will have a profound impact on the fi elds of nanoplasmonics, nanophotonics, and medicine. With this architecture it is possible to capture and align nanoparticles into a 2D structure. For more information, please read the Full Paper “Real-Time Template-Assisted Manipulation of Nanoparticles in a Multilayer Nanofl uidic Chip” by L. Pang, Y. Fainman, and co-workers, beginning on page 2750.

Flow Control as a Stochastic Optimal Control Problem with Incomplete Information

A nonlinear stochastic control problem related to ow control is considered. It is assumed that the state of a link is described by a controlled hidden Markov process with a finite state set, while the loss ow is described by a counting process with intensity depending on a current transmission rate and an unobserved link state. The control is the transmission rate, and it has to be chosen as a nonanticipating process depending on the observation of the loss process. The aim of the control is to achieve the maximum of some utility function that takes into account losses of the transmitted information. Originally, the problem belongs to the class of stochastic control problems with incomplete information; however, optimal filtering equations that provide estimation of the current link state based on observations of the loss process allow one to reduce the problem to a standard stochastic control problem with full observations. Then a necessary optimality condition is derived in the form of a stochastic maximum principle, which allows us to obtain explicit analytic expressions for the optimal control in some particular cases. Optimal and suboptimal controls are investigated and compared with the ow control schemes used in TCP/IP (Transmission Control Protocols/Internet Protocols) networks. In particular, the optimal control demonstrates a much smoother behavior than the TCP/IP congestion control currently used.

Dynamic Stall Control Using a Model-Based Observer

Dynamic stall control is of interest for its potential to enhance the performance of rotorcraft. The experiments described used pulsed vortex generator jets, shown previously to prevent separation on steady wings and airfoils, to delay dynamic stall on a rapidly pitching airfoil. In tests performed on a NACA-0012 airfoil at low Reynolds numbers, the jets yielded a 25‐ 35% increase in the lift coefe cient achievable without moment stall. Next, a differential equation model of the dynamic stall process was derived and experimentally validated. Models of this form enable the application of well-known control theory to the design of e ow control systems. In the e nal round of experiments, a state observer based on the mathematical model detected incipient dynamic stall. A controller used the stall prediction to operate the pulsed jets only when needed to prevent stall. The controller turned the jets off for the remainder of the oscillation cycle. The controller only operated the jets for about 25% of the pitch cycle, so that the best lift increases of the early experiments could be achieved with only 25% of the air mass e ow.

Compressibility and Excitation Location Effects on High Reynolds Numbers Active Separation Control

The effects of compressibility and excitation slot location on active separation control at high Reynolds numbers are explored. The model, which was tested in a cryogenic pressurized wind tunnel, simulates the upper surface of a 20% thick Glauert‐ Goldschmied-type airfoil at zero angle of attack. The boundary layers on the model are turbulent becausethetunnelsidewallboundary layere owsoverit.Withoutcontrol,thee ow separatesatthehighly convex area of the model and a large turbulent separation bubble is formed. Periodic excitation was applied to control the separation bubble. Two alternative blowing slot locations, as well as the effect of compressibility and steady suction or blowing, were studied. During the test, the chord Reynolds numbers ranged from 1.1 £ £10 7 to 3£ £10 7 and the Mach numbers ranged from 0.25 to 0.7. It was found that excitation must be introduced slightly upstream of the separation region at low Mach number. Introduction of excitation upstream of the shock wave is more effective than at its foot. Compressibility reduces the ability of steady mass transfer and periodic excitation to control the separation bubble, but periodic excitation has an effect on the integral parameters, which is similar to that observed in low Mach numbers. Blowing becomes more effective than suction at transonic speeds, whereas the opposite was found in low Mach numbers. The data presented provide a proper validation case for unsteady numerical design tool that will enable exploring the full potential of unsteady e ow control.

Control of a Miniducted-Fan Unmanned Aerial Vehicle Using Active Flow Control

An experimentalstudy of thecontrol of the e owe eld around thestatorvanes of a new miniducted-fan unmanned aerial vehicle (UAV) using synthetic jet actuators is presented. As a result, a new control approach of the UAV is proposed in which active e ow control can be used instead of moving control surfaces and articulated rotor blade. Therefore, the UAV’ s propulsion and control systems are reduced to a single moving part, a e xed pitch propeller. This mechanical simplicity makes the active e ow control application particularly attractive for development of mini- and micro-UAVs. The directional and rotational control of the UAV (0.5 m in diameter and 0.15 m in height ) can be obtained by controlling the e ow within the duct. This can be achieved by the activation of surface e uidic actuators based on synthetic jet technology that are located downstream from a miniature passive obstruction. The synthetic jets are e ush mounted on a set of four e xed stators located downstream from the propeller. In the present work the e owe eld around the stator vanes is studied using particle image velocimetry at different radial locations, where the geometrical angle of attack of the stator vanes is e xed at 10 deg and the propeller rotational speed is either 4300 or 6200 rpm. Velocity measurements in the near wake are also obtained, and the data show that as a result of the actuation the cross-stream extent of the wake and its velocity dee cit are signie cantly reduced and the e ow is quasi-steady.

Mixing Enhancement of Compressible Jets by Using Unsteady Microjets as Actuators

Lateralsteady/unsteadyinjectionofanarrayofmicrojets,whichareplacedalongthecircumferenceofthenozzle exit of a primary jet at equal intervals of azimuthal angle, was studied experimentally to clarify the characteristics of mixing and noise of compressible primary jets. Two modesof the microjets wereinvestigated: axisymmetric and antisymmetric injections. Fully expanded and underexpanded primary jets issued from a convergent nozzle are considered in thepresent study. Theunsteady microjets wereinjectedata Strouhal number Srof0.16, based on the nozzle exit diameter and the velocity at the nozzle exit, for two cases of total mass injection: 4 and 6% of primary jet mass e ow rate. Results of the mean e owe eld showed that the antisymmetric injection has a higher spreading ratethan the steady and unsteady axisymmetric injections in terms of centerlinevelocity decay. Thoseresults were cone rmed from linear stability analysis, which showed that antisymmetric modes for natural disturbances are more unstable in the downstream region than the corresponding axisymmetric modes. Moreover, reduction in the radiated noise was observed in steady axisymmetric injection. Thus, these results suggest that unsteady microjets have the potential for future use as a device for shear e ow control.

From the modelling of driver's behavior to hydrodynamic models and problems of traffic flow

1.IntroductionThe optimization and control of trac ow along a road or networks of roads,eitherhighwaysorurbanstreets,isaninterestingandchallengingeldofinteractionsbetweenmathematicsandengineeringsciences.Dealingwithsuchaproblemmaytakeadvantage of suitable models which describe the evolution in time and space of theowconditions:cardensityandvelocity.Duetoseveraleconomicalandsocialmotivations,theliteratureonthistopicisvastandcharacterizedbycontributionscoveringmodellingaspects,statementofproblems,qualitative analysis and simulations related to applications. On the other hand, mod-ellinghasnotyetreachedasatisfactorylevelsothatfurtheranalysisandimprovementsmay be necessary in order to reach the standards needed by the qualitative analysisrelated to applications. The aim of this paper consists in providing a critical analysissuitabletoopennewresearchperspectivesintheeld.Some books and review paper provide a useful background. The interested readermayrefertothebooksbyPrigogineandHerman[50]onkineticmodels,byLeutzback[40], mainly devoted to microscopic and hydrodynamic modelling, and to the surveypapersbyKlaretal.[28],KlarandWegener[30],andHelbingetal.[26].Theabovesurveypapersreportthemostrecentliteratureonthistopic.

Switched Real-Time Ethernet with Earliest Deadline First Scheduling—Protocols, Trafic Handling and Simuation Analysis

There is a strong interest of using the cheap and simple Ethernet technology for industrial and embedded systems. This far, however, the lack of real-time services has prevented this change of used network technology. This paper presents enhancements to full-duplex switched Ethernet for the ability of giving throughput and delay guarantees. The switch and the end-nodes controls the real-time tra.c with Earliest Deadline First (EDF) scheduling on the frame level. No modi.cation to the Ethernet standard is needed in the network that supports both real-time and nonreal- time TCP/IP communication. The switch is responsible for admission control where feasibility analysis is made for each link between source and destination. The switch broadcasts Ethernet frames regularly to clock synchronize the end nodes and to implement .ow control for non-real-time tra.c. We have characterized the performance of the network in terms of channel acceptance ratio by simulations with di.erent number of nodes connected to the switch.

Development of Piezoelectric Actuators for Active Flow Control

The development of piezoelectric actuators for active e ow control is discussed. The type of actuators considered consists of a single sheet of piezoceramic material bonded to the underside of a shim: a “ unimorph” e ap design. Existing theoretical beam models are extended to incorporate a linear strain distribution in the composite unimorph beam structure. This model is combined with an optimization scheme to design a e ap that maximizes the tip dee ection per unit voltage for a given bandwidth. The optimization model is then used to design a piezoelectric actuator. The model predictions compare favorably to measurements of the actuator frequency response function. A sample application to control of separated e ow from a backward-facing step is also described, in which the actuator is installed at the origin of the free shear layer. Detailed hot-wire measurements, together with dimensional analysis, reveal the physical mechanism responsible for the e uid-structure coupling. A quasi-static model based on the solid-body displacement of the incoming shear layer accurately describes the peak streamwise velocity perturbations produced by the actuator. This model leads to a proportional relationship between the e ap tip displacement, the incoming boundary-layer proe le parameters, and the streamwise velocity e uctuations produced by the actuator.

Flow Control: The Future

The subject of e ow control, particularly reactive e ow control, is broadly introduced, leaving some of the details to other papers in this special volume of the Journal of Aircraft . The ability to manipulate a e owe eld actively or passively to effect a desired change is of immense technological importance. In general, methods of control to achieve transition delay, separation postponement, lift enhancement, drag reduction, turbulence augmentation, and noise suppression are sought for both wall-bounded and free-shear e ows. An attempt is made to present a unie ed view of the means by which different methods of control achieve a variety of end results. The important advances in the e eld of e ow control that took place during the past few years are discussed. Spurred by the recent developments in chaos control, microfabrication and neural networks, reactive control of turbulent e ows is now in the realm of the possible for future practical devices. HEability to manipulate a e owe eld actively or passively to effect a desired change is of immense technological importance, and this undoubtedly accounts for the subject being more hotly pursuedbyscientistsandengineersthananyothertopicine uidmechanics.The potential benee ts of realizingefe cient e ow-controlsystems range from saving billions of dollars in annual fuel costs for land, air,and seavehiclesto achieving economically andenvironmentally more competitive industrial processes involving e uid e ows. Methodsofcontroltoeffecttransitiondelay,separationpostponement,lift enhancement, drag reduction, turbulence augmentation, and noise suppression are considered. Prandtl 1 pioneered the modern use of e ow control in his epoch-making presentation to the Third International Congress of Mathematicians held at Heidelberg, Germany. In just eight pages, Prandtl introduced the boundary-layer theory, explained the mechanics of steady separation, opened the way for understanding the motion of real e uids, and described several experiments in which the boundary layer was controlled. He used active control of the boundary layer to show the great ine uence such control can exert on the e owpattern. Specie cally, Prandtl used suction to delay boundary-layer separation from the surface of a cylinder. NotwithstandingPrandtl’ s 1 success,aircraftdesignersinthethree decades following his convincing demonstration were accepting lift anddragofairfoilsaspredestinedcharacteristicswithwhichnoman could or should tamper. 2 This predicament changed mostly due to the German research in boundary-layer control pursued vigorously shortly before and during World War II. In the two decades following the war, extensive research on laminar e ow control, where the boundary layer formed along the external surfaces of an aircraft is kept in the low-drag laminar state, was conducted in Europe and the UnitedStates,culminatinginthesuccessfule ighttestprogramofthe X‐21,wheresuctionwasusedtodelaytransitiononasweptwingup to a chord Reynolds number of 4 :7£10 7 . The oil crisis of the early 1970s brought renewed interest in novel methods of e ow control to reduce skin-friction drag even in turbulent boundary layers. In the 1990s, the need to reduce the emissions of greenhouse gases and to constructsupermaneuverablee ghterplanes,faster/quieterunderwater vehicles, and hypersonic transport aircraft, for example, the U.S. National Aerospace Plane, provides new challenges for researchers in the e eld of e ow control.

Compressible Dynamic Stall Control: Comparison of Two Approaches

The approaches of compressible dynamic stall control using real-time airfoil adaptation and slatted airfoils are compared. Each method attempts to solve the unsteady e ow separation and the underlying causes differently. The approaches lead to unexpected results: For the slatted airfoil, dynamic stall alleviation on the main airfoil with a fully stalled slat occurred, and for the shape adapting airfoil, leading-edge attached e ow with trailing-edge separation was obtained. In both cases, no dynamic stall vortex was present. As can be expected, the control effectiveness of each method varies over the full cycle and depends on the Mach number due to the new factors introduced by the use of the methods. These issues are addressed. conditions. At low Reynolds numbers and Mach numbers, it arises from a large leading-edge adverse pressure gradient. At slightly highervaluesofthesequantities,whenthelocale owbecomessuper- sonic, the mechanism changes to that due to an interaction between the local supersonic e ow and the laminar separation bubble, at very low pressure gradients. Tripping the airfoil causes dynamic stall again from the strong leading-edge adverse pressure gradient. At higher Mach numbers, shock-induced separation initiates dynamic stall. A rotor blade encounters a variety of freestream conditions de- pending on the local e ow conditions. Hence, it may see dynamic stall arisingfromany of these causes. In general,athigher Reynolds numbers, two main mechanisms, the adverse leading-edge pressure gradient and the shock-induced separation, can be expected to pre- vail. It is imperative that any dynamic stall e ow control schemes that are developed be robust and effective against all dynamic stall onset mechanisms over the full range of e ow conditions observed in the rotor e ight envelope. Specie c to dynamic stall control is that the unsteady vorticity e uxincreasesdramaticallywhenanairfoilisrapidlypitchedpastthe staticstallangle.Thisisparticularlyinterestingbecauseoneeffectof unsteadinessistoreducetheequivalentangleofattackfortheairfoil, which is responsible for the delay of stallmeasured.Eventually,this unsteady vorticity abruptly coalesces into the dynamic stall vortex.

Progress on the Use of Compliant Walls for Laminar-Flow Control

Thispaperreviewsand assessestherecentprogresstoward making theuseofcompliantwallsa practicalmethod of laminar-e ow control. Three main areas are covered. First, the current understanding of the vitally important e ow-induced surface instabilities is assessed. Some new results are included. Then the optimization of multiplepanel compliant walls is considered. New numerical simulation results are included showing that short compliant panels are very effective in suppressing Tollmien ‐Schlichting waves. It is found that for marine applications appropriately designed multiple-panel compliant walls are capable of suppressing Tollmien ‐Schlichting waves to indee nitely high Reynolds numbers. Finally, the feasibility of using compliant walls for laminar-e ow control in aeronautical applications is assessed. It is found that, although there is no reason in principle why compliant walls cannot be used in air, in practice exceptionally delicate walls are required to obtain the necessary match between thee uid and structural inertias. Theresulting lack ofrobustness forsuch walls isdeemed to make them completely impractical for aeronautical applications.

Exploring the Feasibility of Pulsed Jet Separation Control for Aircraft Configurations

This paper describes experiments aimed at demonstrating the effectiveness of pulsed vortex generator jets (PVGJs) in controlling separation on aircraft wings. The demonstration is accomplished by applying the jets to two relevant cone gurations and evaluating their effectiveness in a wind tunnel. The jet design and placement for both experiments was based on parametric studies described in a previous paper. In the e rst application, pulsed jets prevented separation over the wings on a three-dimensional lambda-wing e ghter cone guration at low speeds and high angles of attack. This experiment shows that the e ow control method can enhance the lift, and hence the maneuverability, of advanced e ghters in post-stall e ight. The lambda-wing experiments also demonstrated that jets can be operated asymmetrically for lateral maneuvering control at high angles of attack. The second set of experimentstestedhigherspeed ranges, applying jets to an airfoilsection in an M =0.3‐0.5 e ow.Thiscone guration is relevant to subsonic cruise. The results show that PVGJs can increase lift and lift-to-drag ratios, but they were less effectiveat supercriticalspeedswhereseparation isinduced by hingelineshocks. In all cases, thejetsincreased lift over their effective range although their drag effect was small.

Multiple On-Off Valve Control for a Launch Vehicle Tank Pressurization System

Pressure control inside the propellant tanks of a pump-fed space launch vehicle is almost always a e ight-critical task. Pressures are commonly controlled by admitting helium from high-pressure reservoirs into the propellant tank free volumes, or ullages. Controlled pressures must often satisfy the competing needs of engine net positive suction head, e ight dynamic pressures, tank structural stability, and tank maximum expected operating pressure. Heliume owsareusuallygovernedbyeitherregulators,proportionalvalves,oron ‐offsolenoidvalvesimplementing relay logic leading to control limit cycles. A new control scheme using on ‐off solenoid valves to approximate the performance of a proportional e ow control valve has been synthesized for both stages of a space launch vehicle. This control system uses the same valves required by a competing limit cycle system but signie cantly improves system robustness in the face of system uncertainties, including initial engine oute ow rates, ullage volumes, and helium-to-propellant heat transfer rates. Simulations indicate ullage pressures can be maintained within a 5-psi band at all times, despite the slow 25-Hz data communication rate assumed for this vehicle. Furthermore, the control logic provides a simple way to incorporate additional feedback signals such as engine pressure into the control loop to further improve tracking accuracy.