Rollover Problem Research Articles

Sovereign Debt in the Twenty-first Century

How will sovereign debt markets evolve in the twenty-first century? We survey how the literature has responded to the eurozone debt crisis, placing “lessons learned” in historical perspective. The crisis featured: (i) the return of debt problems to advanced economies, (ii) a bank–sovereign “doom loop” and the propagation of sovereign risk to households and firms, (iii) rollover problems and self-fulfilling crisis dynamics, (iv) severe debt distress without outright sovereign defaults, (v) large-scale sovereign bailouts from abroad, and (vi) creditor threats to litigate and hold out in a debt restructuring. Many of these characteristics were already present in historical debt crises and are likely to remain relevant in the future. Looking forward, our survey points to a growing role of sovereign bank linkages, legal risks, domestic debt and default, and of official creditors, due to new lenders such as China as well as the increasing dominance of central banks in global debt markets. Questions of debt sustainability and default will remain acute in both developing and advanced economies. (JEL E58, F33, F34, G01, G21, H63, N20)

Fasting the stabilization response for prevention of tractor rollover using active steering: Controller parameter optimization and real-vehicle dynamic tests

The rollover problem is prominent for a small tractor under complicated road conditions. The application of active steering (AS) technology is an effective approach to solve this problem. A lateral stability index based on the critical position is proposed and improved. Sliding mode control (SMC) technology based on an exponential terminal sliding mode surface is studied by considering the parameter changes and external disturbances in the rollover process of the tractor, which further accelerates the system’s response speed. A real vehicle test platform was built taking into account the limitations of the few real vehicle dynamic tests in current studies. Real vehicle dynamic tests with varying speeds, slopes, and obstacles were conducted for various road pavements and typical off-road pavements. For road pavements, the results demonstrated that the maximum roll angle of the tractor was 15.94 % less than with that under uncontrolled. For typical off-road pavements, AS control effectively restrained rollover accidents under non-extreme conditions, and SMC reduced the time the tractor was in the critical rollover region by 35.98 % on average compared with PID control. The stability region boundary of a small tractor was defined, and the stable driving region of a tractor on various slopes is obtained. This study provides a specific theoretical basis and implementation plan for guiding the research of tractor active safety technology.

Optimal sales and production rollover strategies under capacity constraints

Firms regularly replace their old product generation by a newer generation to sustain and increase their market share and profit. The product rollover problem of deciding on the number of old products to be pre-produced before the introduction of the new generation, and then deciding on the prices, sales volumes, and production volumes of the old and the new generation during the introduction under capacity constraint is considered.Production capacity limitations are common during the introduction period of a new product. We provide the first study that examines how a production capacity constraint affects the optimal decisions. The optimal decisions for a deterministic period-based model are provided in closed-form.A single sales/production rollover strategy implies that the sales/production of the old generation is discontinued before introducing the new generation. With a dual sales/production rollover strategy, the old and the new generation are sold/produced simultaneously. Depending on the capacity shortage, there are two types of mitigation actions: (i) increasing the prices, (ii) changing the sales and/or production rollover strategies with pre-production while adjusting the prices accordingly. If the capacity is unlimited, aligned sales and production rollover strategies are always optimal. We establish the conditions under which limited capacity leads to a combination of a single production rollover with a dual sales rollover strategy. We show that the selection of optimal rollover strategies is non-monotone in the available capacity. This implies that a change in the rollover strategy in response to limiting capacity has to be revoked for more severe capacity shortages.

Sovereign Debt in the 21st Century: Looking Backward, Looking Forward

How will sovereign debt markets evolve in the 21st century? We survey how the literature has responded to the eurozone debt crisis, placing “lessons learned” in historical perspective. The crisis featured: (i) the return of debt problems to advanced economies; (ii) a bank-sovereign “doom-loop” and the propagation of sovereign risk to households and firms; (iii) roll-over problems and self-fulfilling crisis dynamics; (iv) severe debt distress without outright sovereign defaults; (v) large-scale sovereign bailouts from abroad; and (vi) creditor threats to litigate and hold out in a debt restructuring. Many of these characteristics were already present in historical debt crises and are likely to remain relevant in the future. Looking forward, our survey points to a growing role of sovereign-bank linkages, legal risks, domestic debt and default, and of official creditors, due to new lenders such as China as well as the increasing dominance of central banks in global debt markets. Questions of debt sustainability and default will remain acute in both developing and advanced economies.

Sovereign Debt in the 21st Century: Looking Backward, Looking Forward

How will sovereign debt markets evolve in the 21st century? We survey how the literature has responded to the Eurozone debt crisis, placing “lessons learned” in historical perspective. The crisis featured: (i) the return of debt problems to advanced economies; (ii) a bank-sovereign “doom-loop” and the propagation of sovereign risk to households and firms; (iii) roll-over problems and self-fulfilling crisis dynamics; (iv) severe debt distress without outright sovereign defaults; (v) large-scale “sovereign bailouts” from abroad; and (vi) creditor threats to litigate and hold out in a debt restructuring. Many of these characteristics were already present in historical debt crises and are likely to remain relevant in the future. Looking forward, our survey points to a growing role of sovereign-bank linkages, legal risks, domestic debt and default, and of official creditors, due to new lenders such as China as well as the increasing dominance of central banks in global debt markets. Questions of debt sustainability and default will remain acute in both developing and advanced economies. Institutional subscribers to the NBER working paper series, and residents of developing countries may download this paper without additional charge at www.nber.org.

A Novel Roll and Pitch Estimation Approach for a Ground Vehicle Stability Improvement Using a Low Cost IMU.

Onboard attitude estimation for a ground vehicle is persuaded by its application in active anti-roll bar design. Conventionally, the attitude estimation problem for a ground vehicle is a complex one, and computationally, its solution is very intensive. Lateral load transfer is an important parameter which should be taken in account for all roll stability control systems. This parameter is directly related to vehicle roll angle, which can be measured using devices such as dual antenna global positioning system (GPS) which is a costly technique, and this led to the current work in which we developed a simple and robust attitude estimation technique that is tested on a ground vehicle for roll mitigation. In the first phase Luenberger and Sliding mode observer is implemented using simplest roll dynamics model to measure the roll angle of a vehicle and the validation of results is carried using commercial software, CarSim® (CarSim, Ann Arbor, MI, USA). In the second phase of research, complementary and Kalman filters have been designed for attitude estimation. In the third phase, a low-cost inertial measurement unit (IMU) is mounted on a vehicle, and both the complementary filter (CF) and Kalman filter (KF) are applied independently to measure the data for both smooth and uneven terrains at four different frequencies. We compared the simulated and real-time results of roll and pitch angles obtained using the complementary and Kalman filters. Using the proposed method, the achieved root mean square error (RMSE) is less than 0.73 degree for pitch and 0.68 degree for roll, with a sample time of 2 ms. Thus, a warning signal can be generated to mitigate roll over. Hence, we claim that our proposed method can provide a low-cost solution to the roll-over problem for a road vehicle.

Financial Fragility in Retail-NBFCs

This study examines the financial fragility of the Retail Non-Banking Financial Companies (Retail-NBFCs) sector. We show that the liquidity crunch in Retail-NBFCs stemmed from their over-dependence on short-term wholesale funding from Liquid Debt Mutual Funds (LDMFs) and the low level of high-quality liquid investments in the LDMF sector. While such reliance worked well in good times, it generated significant short-term debt rollover problems for Retail-NBFCs during times of stress. The key reason for the inability of Retail-NBFCs to roll over commercial paper was the transmission of systemic risk from Retail-NBFCs to the LDMF sector. Anticipating defaults by Retail-NBFCs, mutual fund investors exited from the LDMF sector. The low levels of high-quality liquid assets in the LDMF sector were insufficient to withstand the concerted redemption pressure by investors and made the LDMF sector reluctant to roll over short-term debt of Retail-NBFCs. We develop a robust tool (Health Score) to estimate financial fragility in a Retail-NBFCs and find that it can predict the constraints on external financing (or rollover risk) faced by these firms.

Optimal Sales and Production Rollover Strategies under Capacity Constraints

Firms regularly replace their old product generation by a newer generation to sustain and increase their market share and profit. The product rollover problem of deciding on the number of old products to be pre-produced before the introduction of the new generation, and then deciding on the prices, sales volumes, and production volumes of the old and the new generation during the introduction under capacity constraint is considered. Production capacity limitations are common during the introduction period of a new product. We provide the first study that examines how a production capacity constraint affects the optimal decisions. The optimal decisions for a deterministic period-based model are provided in closed-form. A single sales/production rollover strategy implies that the sales/production of the old generation is discontinued before introducing the new generation. With a dual sales/production rollover strategy, the old and the new generation are sold/produced simultaneously. Depending on the capacity shortage, there are two types of mitigation actions: (i) increasing the prices, (ii) changing the sales and/or production rollover strategies with pre-production while adjusting the prices accordingly. If the capacity is unlimited, aligned sales and production rollover strategies are always optimal. We establish the conditions under which limited capacity leads to a combination of a single production rollover with a dual sales rollover strategy. We show that the selection of optimal rollover strategies is non-monotone in the available capacity. This implies that a change in the rollover strategy in response to limiting capacity has to be revoked for more severe capacity.

Model predictive rollover prevention for steer-by-wire vehicles with a new rollover index

ABSTRACTRecent advances in active safety systems provide new opportunities to handle rollover problems more efficiently. This paper presents a Model Predictive Control (MPC) strategy for rollover prevention through active front steering. A new Rollover Index (RI) and a specified vehicle model are proposed to realise an effective rollover prevention approach. The new RI is represented by vehicle parameters and state variables so that it can be readily incorporated into the MPC objective function. Using a barrier cost function, the proposed MPC controller limits vehicle maneuvers within a safe region of rollover without sacrificing vehicle maneuverability under normal conditions. The roll dynamics, the tire nonlinearity, the lateral load transfer, and the road bank are considered for vehicle modelling to provide appropriate actions at the threshold of a rollover. An affine tire model is used to handle tire nonlinearity in the MPC structure. A high-fidelity CarSim model for an SUV is employed to evaluate the proposed RI and the MPC controller. Simulation results show the reliability of the proposed RI and the effectiveness of the proposed rollover prevention controller for different rollover situations.

Assessment of ground vehicle tankers interacting with liquid sloshing dynamics

This paper presents an assessment of the problems encountered with the design, dynamics and stability of road tankers. Generally, the research activities pertaining to these problems may be classified into three groups, liquid sloshing dynamics in moving containers, trucks dynamics carrying solids, and dynamic coupling of liquid-vehicle systems. The modal analysis of liquid free surface for circular, elliptic and generic cross-section geometries is presented together with the corresponding equivalent mechanical models. Considering popularity of horizontal elliptic cross-section tanks, the trammel equivalent pendulum received extensive research activities and the main results are discussed. Design optimisation of the liquid container cross-section and the passive and active control of liquid sloshing approaches are used by engineers to minimise rollover problem. The most difficult problem of road tankers is the coupling dynamics of liquid and vehicle dynamics under different conditions such as braking and lateral acceleration; in this view, computer numerical simulations have been developed.

Evaluating the rollover propensity of trucks—A roundabout example

The rollover propensity of SUVs and trucks has long been recognized as a potential safety issue. The propensity may increase with the growing number of roundabouts that are being built on high-speed roadways designed for 50mi/h or higher. This paper presents a research methodology developed to evaluate the rollover propensity of trucks on existing roundabouts and other roads with tight curves and high-speed traffic. The research objective was accomplished by developing an advanced 3D model of rollover that is applicable to field observations of the undisturbed behavior of multiple vehicles. This model was supplemented with a nonintrusive method of data collection based on recording video from a remote location and a novel method of extracting the data from the video material and processing it to generate the input required by the rollover model. The method is demonstrated in this paper on an example roundabout by evaluating the rollover propensity of semi-trailers in daytime and nighttime conditions. The results indicate that the drivers observed in nighttime conditions compensated well for the challenging conditions by driving more cautiously, which led to their rollover propensity at night being lower than during the day. The method was found useful for timely detection of the potential rollover problem without waiting for crashes.

The Combined Control of the Steering and Braking System of the Vehicle Rollover Avoidance Control

This paper analyzed vehicle rollover dynamic model when vehicle steering and rollover is occurring, which based on basic vehicle rollover problems. Three-degree-of-freedom vehicle roll model which considering roll angle was established, and physical quantities of model were analyzed. Input and output quantities were analyzed based on vehicle roll model, feedback quantities were determined, too. Controller state reset was added into traditional controller switch module so as to avoid undesired instantaneous pulse which appeared during switching. Three-degree-of-freedom vehicle roll model was put up in Simulink, Controller parameters set was tuned and I/O data were prepared to optimize control effect. The control method in this paper was verified finally.

The newly updated FMVSS 216 roof crush modelling and analysis

There is no doubt that rollovers are more complicated than planar crashes and attributed injury mechanisms are still debated among original equipment manufacturers (OEMs), design engineers, safety experts, impact biomechanics specialists and research scholars at academic institutions. Two intertwining factors and their assumed interpretations have been at the core of these discourses, namely the roof crush strength versus the legislative requirement Federal Motor Vehicle Safety Standard 216 (FMVSS 216) and the real associated injuries in rollovers. The newly updated roof crush standard FMVSS 216 (effective from 2012) seems to answer some of the queries raised in the many debates, which include the increase in the applied force from 1.5 to 3.0 times the vehicle's unloaded weight, the addition to the legislative requirement of heavier vehicles between 2.7 and 4.5 tons and the improved crush procedure that includes the roof testing of both sides at platen combination angles of 5° pitch and 25° roll. From the National Highway Traffic Safety Administration's (NHTSA) own regulatory analysis estimates, the new FMVSS 216 will save 135 lives from the recorded 10,000 yearly rollover fatalities. The interpretation of these survival figures is that the societal cost is still high and can be further reduced by looking at the European rollover analysis and how the European Union (EU) has approached the reconstruction of rollover problems. Through in-depth numerical analysis using finite element model of a passenger vehicle tested at different platen combination of pitch-to-roll angles, this paper demonstrates that using the regulatory requirement of 5° pitch and 25° roll does not constitute the worst loading condition. The roof resisting resultant force and the energy associated therewith depict the force for the 10° pitch and 45° roll angle combination to be, in reality, twice smaller than that for the 5° pitch and 25° roll angle combination. This can be interpreted with conviction that occupants will be put at high risk of injuries because the roof, despite meeting the new FMVSS 216 requirement, will collapse catastrophically. As a result, the new regulation will be rendered inadequate unless the platen angle combination of 10° pitch and 45° roll is adopted.

Should We Commit to Bailing Out?

A commitment to an ex-post inefficient bailout can be ex-ante optimal because it can mitigate rollover problems without an actual bailout. Reinforcement between illiquidity and insolvency create beneficial multiplier effects that overwhelm the adverse effect of moral hazard. Committing to bail out using a rescue fund can be more effective and cheaper than directly injecting liquidity because of the option value of not exercising the rescue later if the economy ends up in a good state. The paper concerns a public agency that bails out a government of a distressed country, but the results can be applied, with minor modifications, to domestic banking crises.

Does the IMF's Official Support Affect Sovereign Bond Maturities?

This paper looks at whether the tendency of some governments to borrow short term is reinforced by financial support from the International Monetary Fund. I first present a model of sovereign debt issuance at various maturities featuring endogenous liquidity crises and maturity mismatches due to financial underdevelopment. I use the model to analyze the impact of IMF lending during debt crises on the sovereign’s optimal maturity structure. Within the model, although IMF assistance is able to catalyze private flows, this provides incentives for government to issue larger amounts of short-term debt, making the roll-over problem larger. I take the model to the data and find support for the hypothesis that IMF lending leads countries to increase their short-term borrowing. Additionally, I do not find any positive effect of IMF lending on countries’ ability to tap international capital markets. These results helps explain why a catalytic effect of IMF lending has proved empirically elusive.

Does the IMF's Official Support Affect Sovereign Bonds Maturities?

This paper looks at whether the tendency of some governments to borrow short term is reinforced by financial support from the International Monetary Fund. I first present a model of sovereign debt issuance at various maturities featuring endogenous liquidity crises and maturity mismatches due to financial under-development. I use the model to analyse the impact of IMF lending during debt crises on the sovereign’s optimal maturity structure. Within the model, although IMF assistance is able to catalyse private flows, this provides incentives for government to issue larger amounts of short-term debt, making the roll-over problem larger. I take the model to the data and find support for the hypothesis that IMF lending leads countries to increase their short-term borrowing. Additionally, I do not find any positive effect of IMF lending on countries’ ability to tap international capital markets. These results help explain why a catalytic effect of IMF lending has proved empirically

An estimation process for vehicle wheel-ground contact normal forces

This paper presents a new methodology for estimating wheel-ground contact normal forces, commonly known as vertical forces. The proposed method uses measurements from currently available standard sensors (accelerometers and relative suspension sensors). The aim of this study is to improve vehicle safety, especially to prevent rollover problems. One particular feature of the method is the separation of the estimation process into three blocks. The first block serves to identify the vehicle's weight, the second block contains a linear observer whose main role is to estimate the one-side lateral transfer load, while the third block calculates the four wheel vertical forces using a nonlinear observer. The different observers are based on the Kalman filter. The estimation process is applied and compared to real experimental data obtained in real conditions. Experimental results validate and prove the feasibility of this approach.

Identifying and Correcting Errors with Odometer Readings from Inspection and Maintenance Data

The analysis of data from state inspection and maintenance (I/M) programs and remote-sensing studies has revealed a number of fundamental insights about vehicle emissions. These include a deterioration effect (emissions increase as vehicles age) and the vintage effect (because of technological improvements, newer model year vehicles are cleaner at any given age than older model year vehicles). As a result, vehicle age and vehicle mileage (from odometer readings) are both important proxies for estimating deterioration and identifying high-emitting vehicles. In this paper, Colorado data are used to demonstrate systematic problems with odometer readings from state I/M data. The paper shows that odometer readings are notoriously poor indicators of actual vehicle miles because of the rollover of five-digit odometers (i.e., from 99,999 to 0) and recording errors. Visual inspection of a distribution of I/M records plotted against odometer readings shows obvious issues with the use of raw odometer readings and implausibly high emissions levels for low-mileage vehicles. A three-part iterative process for identifying and correcting these readings is proposed. After the method is applied, it is found that the rollover problem affects roughly 1 in 20 of the observations in the data set. The problem is particularly acute for older model year vehicles, and negative correlations are observed between miles driven and emissions for certain model years. The results suggest that some results of empirical studies of I/M data need to be reexamined and that emissions improvements resulting from technical change may be overstated.

Improving handling of vehicles with active suspensions

In this paper, an active suspension system which guarantees passenger comfort in normal cruising and rollover prevention in emergencies is proposed. In the control design, the changes in forward velocity, the normalised load transfer, the performance specifications both for rollover and suspension problems, and the model uncertainties are taken into consideration. By selecting scheduling variables, a Linear Parameter Varying model is constructed, which is the basis of the control design. The operation of the active suspension is demonstrated in a cornering manoeuvre.

About the Existence of Common Internal Causes of Recent Latin American Currency Crises

While the currency crises in Asia seem to have been one-of events, Latin America experiences recurring currency crisis. In this paper, we analyse whether common internal factors existed, that contributed to the build-up of the currency crisis. For our sample, we chose the three most recent Latin American currency crisis in Mexico 1994/95, Brazil 1998/99 and Argentina 2001/02. Each one of these three countries adopted a stabilization program with an exchange rate anchor as the central element among other liberal reforms in order to combat inflation. In a quantitative analysis for these stabilization periods, we work us step-by-step along the causalities chains that were started by the reforms. Our main findings include that to a considerable extent, the stabilization programs caused similar reactions in the three economies. Among these were a substantially overvalued currency, which implied considerable current account deficits and an elevation of the debt stock. In Brazil, increasing debt was less driven by the overvalued currency and more by fiscal indiscipline, while Mexican agents in 1994 faced a debt roll-over problem. Argentina suffered from its rigidities in the real sector, particularly the labor market, that did not allow adjustment, when imbalances increasingly built up over time. We conclude that the risk for crisis can be considerably dampened by prudent domestic policy making. However, the solidity of internal determinants alone will not be able to rule out turbulence.