Stability analysis of partially filled tanker trucks using a finite element modeling approach

The point of rollover for a tanker truck carrying fluid cargo is of great importance due to the catastrophic nature of accidents involving such vehicles. Payloads are often toxic or flammable, thus, predicting the threshold of rollover effectively is of great value. Furthermore, the liquid load shift caused by fluid slosh amplifies the propensity of these vehicles to rollover.;This research presents an approach for determining the threshold of rollover stability of a specific tanker truck by using finite element analysis methods, specifically the software program ANSYS. This approach allows the consideration of many variables which had not been fully considered in the past, including nonlinear spring behavior and tank flexibility. The program uses simple mechanical pendulums to simulate the fluid sloshing affects, beam elements to match the torsional and bending stiffness of the tank, and spring damper elements to represent the suspension.;The finite element model of the tanker truck is validated using data taken by the U.S. Army Aberdeen Test Center (ATC) on a M916AI tractor/Etnyre model 60PRS 6000 gallon trailer combination. ATC tested the actual tanker truck both statically and dynamically to provide data as inputs for the tanker truck model. The outputs from the computer model and the real truck are shown to corroborate, thus validating the method of analysis. The approach is then expanded to include a double lane change maneuver derived from a cycloidal path.;The main conclusions are drawn in two forms. First, the model is shown to corroborate with the experimental data taken from the actual tanker truck. Secondly, a series of both actual and hypothetical simulations are made to determine the critical velocity for the given maneuver. These are presented for a constant radius turn and for double lane change maneuvers

Application of systems engineering principles to the development of a hydraulic control system for an automatic transmission

Thesis (S.M.)--Massachusetts Institute of Technology, System Design and Management Program, 2008.Includes bibliographical references (p. 71).Product development in the automotive industry has evolved around the design of components. The organization is established around components and people have a very component centric perspective on problem solving. This has led to local optimization of individual components, while the larger system spirals out of control. The penalty is often measured in terms of development time and cost. New programs are given autonomy to make independent choices without regard for what other programs are doing, which leads to a wide variety of architectures put into place. Program managers and functional managers have different prioritizations. Furthermore, new designs are provided by a separate organization from the group responsible for implementation. They have a very different value system and are unaware of the difficulties experienced in the implementation phase. This type of practice leads to programs nearing production deadlines with poorly optimized systems. Engineers must relearn due to the lack of standardization across program. The team absorbs additional resources from within to fix issues prior to launch. The robbing of resources leads to delays in subsequent programs and the cycle repeats itself. These issues are partly cultural, part organizational, part due to lack of understanding of systems engineering. A new organization is designed, which strengthen the systems perspective and give power to a new role in the organization, the Systems Engineer. The Systems Engineer is chartered with global optimization of the entire system, which includes both functional aspects as well as business aspects like resource availability, development cost and time. They are responsible for developing the complete system, from concept to final implementation. The Design Structure Matrix (DSM) shows the boundaries of the system and reveals new areas where the Systems Engineer can influence the design at lower cost to the organization.(cont.) The Robustness Checklist, standardization and Systems Architecture provide Systems Engineers tools to change from a component mindset to a systems mindset and to optimize the system as a whole.by Matthew J. Aquaro.S.M

Human Immunodeficiency Virus Impairs Reverse Cholesterol Transport from Macrophages

Several steps of HIV-1 replication critically depend on cholesterol. HIV infection is associated with profound changes in lipid and lipoprotein metabolism and an increased risk of coronary artery disease. Whereas numerous studies have investigated the role of anti-HIV drugs in lipodystrophy and dyslipidemia, the effects of HIV infection on cellular cholesterol metabolism remain uncharacterized. Here, we demonstrate that HIV-1 impairs ATP-binding cassette transporter A1 (ABCA1)-dependent cholesterol efflux from human macrophages, a condition previously shown to be highly atherogenic. In HIV-1–infected cells, this effect was mediated by Nef. Transfection of murine macrophages with Nef impaired cholesterol efflux from these cells. At least two mechanisms were found to be responsible for this phenomenon: first, HIV infection and transfection with Nef induced post-transcriptional down-regulation of ABCA1; and second, Nef caused redistribution of ABCA1 to the plasma membrane and inhibited internalization of apolipoprotein A-I. Binding of Nef to ABCA1 was required for down-regulation and redistribution of ABCA1. HIV-infected and Nef-transfected macrophages accumulated substantial amounts of lipids, thus resembling foam cells. The contribution of HIV-infected macrophages to the pathogenesis of atherosclerosis was supported by the presence of HIV-positive foam cells in atherosclerotic plaques of HIV-infected patients. Stimulation of cholesterol efflux from macrophages significantly reduced infectivity of the virions produced by these cells, and this effect correlated with a decreased amount of virion-associated cholesterol, suggesting that impairment of cholesterol efflux is essential to ensure proper cholesterol content in nascent HIV particles. These results reveal a previously unrecognized dysregulation of intracellular lipid metabolism in HIV-infected macrophages and identify Nef and ABCA1 as the key players responsible for this effect. Our findings have implications for pathogenesis of both HIV disease and atherosclerosis, because they reveal the role of cholesterol efflux impairment in HIV infectivity and suggest a possible mechanism by which HIV infection of macrophages may contribute to increased risk of atherosclerosis in HIV-infected patients

Role of CCL3L1-CCR5 Genotypes in the Epidemic Spread of HIV-1 and Evaluation of Vaccine Efficacy

Polymorphisms in CCR5, the major coreceptor for HIV, and CCL3L1, a potent CCR5 ligand and HIV-suppressive chemokine, are determinants of HIV-AIDS susceptibility. Here, we mathematically modeled the potential impact of these genetic factors on the epidemic spread of HIV, as well as on its prevention.Ro, the basic reproductive number, is a fundamental concept in explaining the emergence and persistence of epidemics. By modeling sexual transmission among HIV+/HIV- partner pairs, we find that Ro estimates, and concordantly, the temporal and spatial patterns of HIV outgrowth are highly dependent on the infecting partners' CCL3L1-CCR5 genotype. Ro was least and highest when the infected partner possessed protective and detrimental CCL3L1-CCR5 genotypes, respectively. The modeling data indicate that in populations such as Pygmies with a high CCL3L1 gene dose and protective CCR5 genotypes, the spread of HIV might be minimal. Additionally, Pc, the critical vaccination proportion, an estimate of the fraction of the population that must be vaccinated successfully to eradicate an epidemic was <1 only when the infected partner had a protective CCL3L1-CCR5 genotype. Since in practice Pc cannot be >1, to prevent epidemic spread, population groups defined by specific CCL3L1-CCR5 genotypes might require repeated vaccination, or as our models suggest, a vaccine with an efficacy of >70%. Further, failure to account for CCL3L1-CCR5-based genetic risk might confound estimates of vaccine efficacy. For example, in a modeled trial of 500 subjects, misallocation of CCL3L1-CCR5 genotype of only 25 (5%) subjects between placebo and vaccine arms results in a relative error of approximately 12% from the true vaccine efficacy.CCL3L1-CCR5 genotypes may impact on the dynamics of the HIV epidemic and, consequently, the observed heterogeneous global distribution of HIV infection. As Ro is lowest when the infecting partner has beneficial CCL3L1-CCR5 genotypes, we infer that therapeutic vaccines directed towards reducing the infectivity of the host may play a role in halting epidemic spread. Further, CCL3L1-CCR5 genotype may provide critical guidance for optimizing the design and evaluation of HIV-1 vaccine trials and prevention programs