Vehicle Payload Research Articles

Modeling and Analysis of Automotive Antilock Brake Systems Subject to Vehicle Payload Shifting

The steerability and stability of vehicles must be maintained during emergency stopping and evasive driving maneuvers on degraded road surfaces. The introduction of antilock brake and traction control systems (ABS/TCS) has expanded the envelope of safe vehicle operation for the majority of drivers. These mechatronic systems combine an electronic controller with wheel speed sensors, an electro-mechanical hydraulic brake actuator, and in some instances, engine intervention through the engine control unit, to regulate wheel slip. The development of ABS systems has traditionally depended on extensive in-vehicle testing, at cold weather proving grounds, which contribute to lengthy product development cycles. However, recent attention has been focused on the use of simulation and hardware-in-the-loop strategies to emulate test conditions in a controlled setting to shorten product design time and methodically address critical safety issues. In this paper, the effect of transient load shifting due to cargo movement on ABS performance in light-duty vehicles will be investigated. Analytical and empirical mathematical models are presented to describe the chassis, tire/road interface, wheel, brake modulator, and cargo dynamics. Two strategies, a model-free table lookup and model-based discrete nonlinear controller, are presented to regulate the ABS modulator's operation. These vehicle and controller dynamics have been integrated into a simulation tool to investigate the effect of transient weight transfers on the vehicle's overall stopping distance and time. Representative numerical results are presented and discussed to quantify the ABS systems' performance for various loading and operating conditions.

Fabrication of glassy carbon spools for utilization in fiber optic gyroscopes

A gyroscope is a device that measures the angular charges that could damage electronic circuits in the velocity of its reference coordinate system relative to an system. inertial system. An inertial platform comprises at least three gyroscopes and three acceleration sensors [1,2]. A In this work, a furfuryl alcohol resin with a viscosity of vehicle equipped with this system is able to find its way 3000 mPa s at 258C is used in the fabrication of the spool. and position in space. An interferometric fiber gyro This resin is polymerized with the addition of 2.5% of the comprises a Sagnac interferometer in its basic configuracatalyzer para-toluenesulfonic acid, with homogenization tion [4]. This kind of sensor has been a good solution for by manual agitation as long as necessary to make sure that high resolution measurement of angular velocity, mainly no trace of the catalyzer could be observed over the resin for its high sensitivity, electromagnetic immunity, and surface. The resin is centrifuged at 3000 rev. /min for 40 reduced size and weight. It can be found in aircrafts, min. After transference to the mold, it is left to rest at spatial vehicles, satellites, missiles, ships, oil perforation room temperature for 24 h. Then it is placed in the oven at drills, and automobiles [5]. 608C for 2 h. And to conclude the cure cycle, it is kept in A fundamental component in a fiber optic gyroscope the oven at 808C for 2 h. (FOG) is the fiber optic coil. It is usually wound on a rigid Spool machining is realized before carbonization, using spool, which should have the following desirable characconventional machining techniques. A 70-mm-diameter teristics: tubular oven is used in the carbonization thermal treatment. Maximum temperature was 10008C with an average • low density, since a reduced sensor mass allows for a heating rate of 58C/h. higher vehicle payload, especially in aerospace applicaElectrical resistivity (r ) measurements concerning the e tions; samples treated up to 10008C were made by the four point • low thermal expansion coefficient, aiming to keep the method with equipment built in the Materials Division of deformation of the optical fiber to a minimum when Centro Tecnico Aeroespacial (CTA). temperature increases; The apparent specific mass (d) of the material was • low electrical resistivity, to avoid undesirable static determined from the quotient of the spool mass to its volume. This implies that apparent specific mass is an average value including the pores within the material. Rugosity profiles obtained yielded parameters of maxi*Corresponding author. Tel.: 155-12-3947-6420; fax: 155mum (R ), average (R ) and apparent (R ) rugosity, this max z a 12-3947-6405. being the average height between all peaks and valleys on E-mail addresses: cyntia.paula@embraer.com.br (C.C. de the material surface. Paula), edsonbotelho@directnet.com.br (E. Cocchieri Botelho), mirabel@iae.cta.br (M.C. Rezende). Material hardness was measured using a digital hardness

Comparison of Glideback and Flyback Boosters

The aim of the present study is to investigate alternative reusable launch vehicle concepts and to provide a comparison of two different vehicle cone gurations. The e rst concept vehicle uses airbreathing engines to perform a powered booster e yback mission, whereas the second concept employs only aerodynamic lift to achieve booster e yback. The optimization software employs a system parameter optimization, in conjunction with a trajectory parameter optimization, to calculate the optimal mass split and corresponding optimal trajectory. A reference mission is used to comparelaunch vehicle payloads fora e xed grossliftoffweight, assuming launch from Woomera Prohibited Area, South Australia. The payload for a vehicle using a powered e yback strategy is found to be considerably higher than that obtained by a vehicle employing an aerodynamic glide return e ight.

Toward Adapting HDM-III Model to Local Conditions: Lessons from a Case Study in Tanzania

Drawing from a case study in Tanzania, a generic approach to the problem of the desirability and scope of recalibrating the HDM-III model for local application is presented. On the basis of the three key factors of locational sensitivity, parameter impact on the model output, and the availability of calibration resources, candidate parameters for calibration are recommended for the case region. The roughness progression factor was found to have the highest impact on the net present value (NPV) of life-cycle costs. The roughness-age, cracking progression, and pathole progression factors were found to be the next influential on the NPV, with elasticity values of 0.7 to 0.8. From these results the study recommended a priority list in allocating recalibration efforts. The study findings suggest that calibration of rutting, cracking initiation, and raveling can be given low priority where resources are constrained. Considerations in choosing the appropriate vehicle operating cost (VOC) model for local conditions are highlighted. The Brazil set of VOC relationships is recommended for many applications; however, recalibration for these equations is highly desirable. Recent changes in automotive technology (with increased engine power, higher gross vehicle weights and payloads, improved fuel efficiency and tire technology, etc.) are raising the question of obsolescence of the Brazil VOC relationships. This issue may pose the most important challenge to the next evolution of HDM-III.

Innovations on a Quartz Crystal Micronbalance Frost-Point Hygrometer

The authors describe a hygrometer based on a quartz crystal (QC) microbalance. The hygrometer is based on frost accumulation rather than adsorption. Previous designs are improved in two ways. First, a radial flow geometry makes it possible to quantitatively remove water from an airstream and therefore measure water vapor by measuring the rate of frost accumulation as well as by measuring the frost point. Second, a thin-film copper-constantan electrode on the QC measures the temperature of the front surface of the QC while still allowing measurement of the oscillation frequency. The hygrometer design is appropriate for frost points between about −1 00° and −40°C, and a future implementation could be used on a lightweight balloon or unmanned aerial vehicle payload.

Vibration Isolation of Launch Vehicle Payload and Its Subsystem

Passive base vibration-control systems for reducing the transfer of orbiter vibration energy to its payload during liftoff are studied. The launch vehicle payload is modeled as a nonuniform flexible structure, and its sensitive subsystem is treated as a single-degree-of-freedom system. Two modified designs for trunnions are suggested for the vibration-control system. These modified trunnions make use of rubber bearings with and without trunnion friction. The performance of these base vibration control systems for protecting the Space Shuttle payload and its sensitive subsystem during liftoff is evaluated. A sinusoidal excitation and the Space Transportation System mission 41 (STS-41) \iZ-direction liftoff acceleration are used as dynamic input of the orbiter. Effects of the trunnion friction and flexibility on the vibration of payload and its subsystem are studied, and the results are compared with those in the absence of the base vibration-control systems.

Implementation of Acoustic Blankets in Energy Analysis Methods with Application to the Atlas Payload Fairing

Energy analysis methods are commonly used to predict the vibroacoustic response of a spacecraft inside a launch vehicle payload fairing during liftoff. The payload fairing wall is often lined with acoustic blankets which can be difficult to model. This paper shows the development of a practical working method for accurately representing acoustic blankets in a VAPEPS statistical energy analysis model. A clear scaling relationship between the acoustic absorption coefficient and the blanket thickness is established. The scaling procedure is demonstrated using two sets of data for different absorption materials. The absorption data are implemented in VAPEPS by converting them to frequency-dependent damping loss factors. A post-processing procedure is derived to account for the increase in transmission loss due to the addition of the blanket layer. The entire process is used to predict the noise reduction in a VAPEPS model of the Atlas 14-ft-diameter payload fairing. Comparisons to ground-test and flight data for the blanketed fairing are presented to validate the procedure.

Composite active suspension for automotive vehicles

This article describes the development of a composite controller for an active suspension system. This consists of two controllers operating together over different frequency ranges. The first of these is required to cancel out the low-frequency dynamic loads experienced during cornering and braking in order to maintain a level vehicle platform. The second is required to isolate the car body from vibrations caused by the high-frequency road profile. Furthermore, the vibration controller is based on a fully adaptive control algorithm. This enables the suspension to auto-tune to different vehicle payloads, tyre stiffnesses and other parameter variations experienced during progressive wear, and to adapt to the varying road frequency spectrum. Simulations were performed on a quarter car (one wheel) suspension model and the results obtained demonstrated the potential benefits of composite and adaptive control in active suspension design.

Rarefied-flow aerodynamics measurement experiment on the Aeroassist Flight Experiment vehicle

The rarefied-flow aerodynamics measurement experiment, which is expected to measure the rarefied-flow flight regime with an accelerometer on the aeroassist flight experiment, is discussed. The experiment concept and mission plans are examined and the experiment configuration is illustrated. The experiment plans include flight measurements of aerodynamic force and moment coefficients throughout the rarefied regime to verify ground-to-flight extrapolation techniques. In addition, the experiment includes the study of acceleration rates and the effects of attitude variation. The experiment is also expected to evaluate the determination of vehicle mass properties to study robust control theory formulations which are applicable to special return aeroassisted orbital transfer vehicle payloads.

Analysis of Active and Semi-Active Vehicle Suspensions Fitted with a Pneumatic Self-Energizing Levelling Device

A pneumatic self-energizing self-levelling (SESL) device is proposed in schematic form and a theoretical analysis of it is carried out. The unit allows the design suspension working space to be maintained once steady state operating conditions have been reached. Conventional passive, semi-active and fully active suspensions are all disadvantaged by variable vehicle payloads. An investigation is carried out to determine what advantages are to be gained by combining the SESL unit with each of these types of suspension. Computing simulations have been used to show that for large payloads it has the ability to: (a) improve the performance of a conventional passive suspension, (b) reduce the power requirements of a fully active system and (c) maintain the performance of a semi-active system close to that of a fully active system for a wide range of payloads. It is concluded that the SESL device has most to offer when it is used in conjunction with a semi-active system containing a variable-rate switchable damper.

Launch Vehicle Payload Interface Response

A method has been developed by which an estimate of the launch vehicle/payload interface response is derived from the interface responses obtained from missions with the identical launch vehicle but different payloads. This method requires the knowledge of the launch vehicle eigenvalues, interface modal displacements, and the dynamic characteristics of the payloads. No other launch vehicle information is required. The organization responsible for the payload is able to perform loads and responses analysis resulting from a payload change without interfacing with the launch vehicle organization. SPACE mission often utilizes an existing launch vehicle for a new payload designed for a specific mission; such will be the case for future Shuttle missions. The dynamic design loads for the payload are obtained by performing a transient analysis of the analytical dynamic model of the coupled payload and launch vehicle. Each analysis iteration for a specific payload configuration is expensive and time consuming. The combined dynamic model of the payload/launch vehicle is not only large and complex, but the time duration of one iteration is extensive because of the number of different organizations involved. The proposed methodology allows the payload organization to estimate the dynamic loads for a design iteration independent of other organizations. It should be noted that the proposed method can also be applied to the general class of subsystems coupled to relatively large vehicles such as the guidance system on a missile and the auxiliary power unit on an aircraft. This method will make a significant contribution to the time- critical development of subsystems constrained by complex technical and project interfaces. The procedure assumes that the acceleration time history at the payload/launch vehicle is available from past flight measurements or analyses, the dynamic characteristics of the launch vehicle do not change, the forcing function on the launch vehicle can be approximated by a delta function, and the mass of the payload is small compared to the mass of the launch vehicle. These assumptions are realistic for most projects for design/analysis iterations. Historically, during the payload design phase, the payload/launch vehicle interface accelerations have been defined as a sine wave input or a shock spectrum.1'2 Both methods essentially eliminate the time dependency of the interface response. In the past 10 years, estimates of spacecraft interface ac- celerations measured from flight data have been used as an input forcing function to the payload to obtain more realistic estimates of the dynamic loads. At the Jet Propulsion Laboratory similar procedures were used on the Ranger, Surveyor, Mariner, and Viking Projects. In 1971, Caughey3 investigated the potential error in this procedure by assuming that the interface acceleration is invariant as the payload is modified. The study indicates that the error can be very large and is dependent on the dynamic characteristics of the system.

Trajectory Requirements for Comet Rendezvous

Future spacecraft mission for short period comets rendezvous, considering trajectory requirements and launch vehicle payload capabilities

Comparative Analysis of Acoustic Testing Techniques

Current progress on research under NASA contract is detailed. Empirical acoustic-vibration energy. transforms are compared to state-of-the-art analytical results for progressive wave and reverberant acoustic excitation. Structural specimens vary from homogenous plane panels to reinforced cylindrical elements. Analytical results and experimental capabilities are briefly reviewed. A comparison of theory and test is performed with analytical assumptions maintained explicit. Emphasis is placed on pressure field coherency, spatial variations, and probable damage potential. Recommendations for subsequent efforts are provided. The culmination of this program of research is to improve design and utilization of acoustic test facilities for environmental testing of advanced space vehicle payloads and equipment and ultimately to optimize component performance relative to weights, volume, and packaging, etc. [This research program supported by NASA, George C. Marshall Space Flight Center.]