The accidents of heavy vehicles due to stability problems are not so frequent, but when this type of accident occurs, its results are often fatal, which is why the analysis of stability of heavy ...vehicles allows us to predict their limit of speed to safely travel on road or perform certain maneuvers that involve rollover risk. Additionally, when these vehicles transport liquids, the stability problems may be greater. Taking into account that one of the main factors to determine the risk of accident due to rollover is the Static Rollover Threshold, this article develops this factor for road tankers and it is determined by a case study such as these loads depending on the filling of the tank; they affect the stability of this type of vehicles and a comparison is made with respect to the improvement of the stability if the movement of this load is avoided.
•A novel algorithm is proposed for enhancing the roll stability of fuel tank.•Fluid c.g. height and overturning moment are considered as two objective functions.•B-spline function is employed to ...optimize the tank cross section.•The presented optimal shape is approximately 6% higher than the conventional one.•The Pareto solution presents the fast converged results.
In this paper, a novel tank design algorithm is proposed for enhancing roll stability of fuel tank shape considering the multi-objective genetic algorithm, sum of weighted cost function and Pareto solution. Two conflicting objective functions, fluid c.g. height and overturning moment, are well thought out in the present optimization processing. The proposed novel algorithm is presented based on using b-spline function to optimize tank cross section. This algorithm receives tank capacity as an input, and then a modified cross-section is proposed with the aid of third order b-spline functions using 8 control points, initially. Consequently, with averaging and optimizing, range of control points are modified and the numbers of control points as well as the order of b-spline functions are enhanced into fourth order with 10 control points. The optimized results of Pareto solution are compared with sum of weighted cost functions to explore the best method for fuel tank design. The comparison indicates that both solutions are in a good agreement although the Pareto solution indicates a faster convergence. In this respect, investigation of certain operators such as selection, crossover, mutation and elitism has been carried out to provide a proper design. The results show that, the mutation rate seems to be taken in the range of 4–6% and the number of individuals in each generation should be at least 60. Comparing the GA results with conventional method, demonstrates that the optimized tank shape reveals more roll stability while its rollover threshold is approximately 6% higher than conventional tanks.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Rollover is a potential risk to the safety of LNG storage tanks during the LNG storage process, so study of its prevention method is very important. In this paper, rollover phenomenon in a liquefied ...natural gas (LNG) storage tank is modeled physically and mathematically. Its evolution is simulated using FLUENT™ software from the breakdown of stratification to the occurrence of rollover. Results show that the evolution consists of three phases: the initial phase where rollover occurs near the side wall of the storage tank; the turbulent phase where rollover transfers to the center of the tank; and the final phase where new layers evolve. Based on these phases, rollovers in 160,000, 30,000, and 5000 m3 LNG storage tanks are simulated at varying initial density differences, and a rollover coefficient is defined to describe rollover intensity. The simulations show that the rollover coefficient initially increases within a small scope and then increases rapidly with the increment of initial density difference. This turning point is chosen to be the rollover threshold, which is regarded as the critical density difference in this study. The critical density differences obtained from the simulation results of the 160,000, 30,000, and 5000 m3 LNG storage tanks are 3, 5, and 7 kg/m3, respectively, which can be used as their rollover criteria to ensure the safety of LNG storage tanks.
•The rollover evolution is modeled and simulated, the results show that the evolution consists of three phases.•A rollover coefficient is defined to describe rollover intensity and confirm the rollover threshold.•Critical density difference 3, 5and 7 kg/m3are proposed to be rollover thresholds of the 160,000, 30,000and 5000 m3 tank.•Critical density difference is not influenced by small diameter changes but increases with the increasing layer depth.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
An efficient methodology is proposed for simulation of roll dynamics of a tank vehicle system coupled with transient hydrodynamic forces due to fluid slosh. The transient fluid slosh in a horizontal ...cylindrical tank is analytically modeled considering simultaneous lateral, vertical and roll excitations assuming potential flows and a linearized free-surface boundary condition. For this purpose, the fluid domain in the Cartesian coordinate system is transformed to the bipolar coordinates, where the Laplace equation could be solved using separation of variables. The resulting hydrodynamic pressure, free-surface elevation and slosh force and roll moment are formulated in the tank-fixed coordinate system. The transient fluid slosh model is subsequently integrated to a dynamic roll plane model of a tank vehicle combination to investigate the effect of transient liquid slosh on the roll stability of the vehicle during steady-turning as well as path-change maneuvers. The analyses are performed for different fluid fill heights considering both variable and constant cargo load conditions. The results suggest that the roll stability of tank vehicles can be efficiently analyzed using the coupled linear slosh and multi-body vehicle models with significantly lower computational effort than the methods employing computational fluid dynamic fluid slosh models.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
En el presente trabajo se realiza elanálisis de la estabilidad de vehículos pesados tipo carro-tanque. Para dicho propósito se utiliza el factor denominado umbral de vuelco estático (Static Rollover ...Threshold, por las siglas eninglés SRT), el cual permite evaluar la máxima fuerza inercial aplicada lateralmente que puede soportar el vehículo antes de iniciar el proceso de vuelco. Adicionalmente, este factor permite determinar la máxima velocidad que el vehículo puede desarrollar al recorrer una curva, dando de esta manera mayor seguridad para los usuarios de la vía. Teniendo en cuenta estos aspectos, se estudia la estabilidad de un carro-tanque de sección transversal circular, ya que para vehículos que transportan líquidos la estabilidad es más crítica, debido a que se debe tener en cuenta el movimiento del fluido transportado cuando es sometido a una aceleración lateral, lo cual puede disminuir el factor de estabilidad. Por consiguiente, para determinar el factor de estabilidad se realiza un análisis detallado del movimiento del fluido como función de la aceleración y el llenado del tanque y se utiliza el método de Davies para el análisis cuasi-estático de la estabilidad del vehículo.
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An analytical model of a partly-filled tank of arbitrary cross-section is developed for predicting transient lateral slosh force and overturning moment using linear slosh theory. Slosh frequencies ...and mode shapes are initially estimated using the variational method, which is applied to the linearized free-surface boundary condition. The resulting truncated system of linear ordinary differential equations is subsequently solved numerically to determine the fluid velocity potentials followed by hydrodynamic force and moment. The validity of the model is examined through comparisons with available analytical solutions and experimental data. The slosh force and roll moment are obtained for four different tank cross-sections, namely, circular, elliptical, modified-oval and Reuleaux-triangle. It is shown that the magnitudes of the slosh force and overturning moment are strongly dependent upon the tank cross-section. The slosh model is subsequently integrated to a roll plane model of an articulated tank-semitrailer vehicle to study the effect of dynamic liquid slosh as well as the tank cross-section on the steady-turning roll stability limit of the vehicle under constant and variable cargo load conditions. The results suggest that a tank cross-section with lower overall center of mass and lower critical slosh length yields an enhanced roll stability limit under medium- and high-fill conditions.
•An analytical model of lateral slosh is developed using the linear slosh theory.•The model is applicable to tanks with arbitrary cross-sections and liquid depths.•Effectiveness of Reuleaux-triangle tank in suppressing the liquid slosh is shown.•Rollover limits are much lower than those of the widely-used quasi-static analysis.•Highest rollover limits are obtained for vehicle with the Reuleaux-triangle tank.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The objective of this article is to investigate the rollover threshold of a heavy-duty vehicle during cornering. Based on the multi-body dynamics theory, a high-fidelity model is established, which ...takes account of the chassis flexibility, the suspension nonlinear characteristics, the tire handling model, and Ackermann steering strategy. Furthermore, by the inverse fast Fourier transform method, a three-dimensional stochastic road in space domain is employed in the model to improve the accuracy. A full-size heavy-duty vehicle test was carried out to validate the model. Based on the validated model, the rollover stability and rollover threshold of the heavy-duty vehicle during cornering are investigated. Lateral acceleration, yaw rate, roll angle, and vehicle torsional deflection in different cornering conditions are analyzed. The rollover threshold is summarized by the response surface methodology for the safe cornering purpose. The result shows the practical meaning of improving transportation safety of heavy-duty vehicles and also provides useful insights for developing the rollover warning system.
From the perspective of heavy vehicles stability, some criteria of stability should be adhered to highway designs. In particular, the relationship between minimum radius, superelevation, slope angle, ...side friction, and design speed should be re-evaluated. In this regard, the static rollover threshold (SRT) is one of the most important factors used to define the stability of vehicles. This factor is highly dependent on the maximum lateral acceleration (ay) of a vehicle until it reaches the rollover threshold. This acceleration in turn is dependent on the vehicle speed and the radius of curvature. Taking into account the stability of vehicles, in this study the highways design is evaluated and compared with the classic design criterion. This study also suggests that in order to ensure driving safety, the State Highway Agencies should make a reevaluation of existing speed limits and the design of highway curves.
In this paper, the influence of load distribution on the stability of heavy articulated vehicles is analyzed. In general, heavy articulated vehicles have low performance with respect to stability ...analysis, being the focus of many studies in literature. Several characteristics of the vehicles have been analyzed to determine their influence on the vehicle stability calculation; however, load distribution is rarely analyzed. To conduct this research, the Davies method is used to obtain the static of the mechanism that represent the last trailer of the vehicle. Using this method, the longitudinal, lateral and vertical displacements of the center of gravity (CG) are investigated, and a sensitivity analysis is made. Finally, a numerical case study is showed and the results of this study demonstrate that the load distribution has important role on the static rollover threshold (SRT) calculation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
The directional dynamic analyses of partly-filled tank vehicles have been limited to quasi-static fluid motion due to computational complexities associated with dynamic fluid slosh analyses. The ...dynamic fluid slosh causes significantly higher magnitudes of slosh forces and moments in the transient state that cannot be characterized through quasi-static approach, which provides reasonably good estimates of the mean responses. In this study, a three-dimensional nonlinear model of a partly-filled cylindrical tank with and without baffles is developed to investigate the significance of resulting destabilizing forces and moments caused by the transient fluid slosh, and the effects of baffles. The baffles and the end caps are modeled with curved shapes. The analyses are performed under varying magnitudes of steady lateral, longitudinal and combinations of lateral and longitudinal accelerations of the tank, and two different fill volumes using the FLUENT software. The results of the study are presented in terms of mean and peak slosh forces and moments, and variations in the mass moments of inertia of the fluid cargo within a clean bore and a baffled tank, for two different fill volumes and different magnitudes of acceleration excitations. The ratios of transient responses to the mean responses, termed as amplification factors, are further described to emphasize the significance of dynamic fluid slosh on the forces and moments induced on the vehicle. The results in general suggest that the mean responses attained from dynamic fluid slosh analyses correlate well with those attained from the quasi-static analyses for a clean bore tank. The amplification ratios of the resulting forces and moments could approach as high as 2. The results clearly show that the presence of baffles helps to suppress the peak as well as mean slosh forces and moments significantly.
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