Seismic response of liquid-filled tank with baffles

In thispaper, the effects of a rigid baffle on the seismic response of liquid in a rigid cylindrical tank are evaluated. A baffle is an annular plate which supplies a kind of passive control on the effects of ground excitation. The contained liquid is assumed incompressible, inviscid and has irrotational motion. To estimate the seismic response, the method of superposition of modes has been applied. To analyze the rigid tank response, Laplace＆#39;s equation is considered as the governing equation of the fluid domain, in both time and frequency domains. The boundary element method （BEM） is employed to evaluate the natural modes of liquid in a cylindrical tank. To gain this goal, the fluid domain is divided into two upper and lower parts partitioned by the baffle. Linearized kinematic and dynamic boundary conditions of the free surface of the contained liquid have been considered.     

Investigation of pitch motion portion in vertical response at sides of a Tension-Leg Platform

Tendons vertically moor Tension-Leg Platforms (TLPs), thus, a deep understanding of physical tendon stresses requires the determination of the total axial deformation of the tendons, which is a combination of the heave, pitch, and surging responses. The vertical motion of the lateral sides of the TLP is coupled with surge and constitutes a portion of the pitch motion. Tendons are connected to the sides of the TLP; hence, the total displacement of the lateral sides is related to the total deformation of the tendons and the total axial stress. Therefore, investigating the total vertical response at the sides of the TLP is essential. The coupling between various degrees of freedom is not considered in the Response Amplitude Operator (RAO). Therefore, in frequency domain analysis, the estimated vertical RAO is incomplete. Also, in the time domain, only the heave motion at the center of TLP is typically studied; this problem needs to be addressed. In this paper, we investigate the portion of the pitch motion in the vertical response at the sides of the TLP in both the frequency and time domains. Numerical results demonstrate a significant effect of the pitch motion in the vertical motion of the edges of the TLP in some period ranges.     

Geometric stress distribution along the weld toe of the outer brace in two-planar tubular DKT-joints: Parametric study and deriving the SCF design equations

Regarding the research efforts expended so far on the calculation of stress concentration factors (SCFs) in tubular joints, two major shortcomings can be noted: (a) significant effort has been devoted to the study of SCFs in various uni-planar connections. Nevertheless, for multi-planar joints which cover the majority of practical applications, very few investigations have been reported due to the complexity and high cost involved; (b) majority of these research works focused on the study of SCFs at certain positions such as the saddle, crown toe, and crown heel, and they have ignored the hot-spot stress (HSS) at other positions along the weld toe. In the present paper, effects of dimensionless geometrical parameters on the SCF distribution along the weld toe of main (outer) braces in the axially loaded right-angle two-planar tubular DKT-joints are investigated. In order to study the multi-planar effect, SCF distribution in two-planar joints is compared with the distribution in a uni-planar joint having the same geometrical properties. A complete set of SCF database is constructed based on the two-planar DKT-joint Finite element models which are verified against experimental results and the predictions of Lloyd’s Register (LR) equations. The FE models cover a wide range of geometrical parameters. Six new SCF parametric formulae are developed through nonlinear regression analyses for the accurate and reliable fatigue design of two-planar DKT-joints under axial loads. An assessment study of these equations is conducted against the experimental data, the original FEM database and the acceptance criteria recommended by the UK Department of Energy.     

Multi-response optimization of diesel engine performance parameters using thumba biodiesel-diesel blends by applying the Taguchi method and grey relational analysis

This paper presents an experimental study that involves an application of the Taguchi method and grey relational analysis to determine the optimum factor level to obtain optimum multiple-performance characteristics of a diesel engine run with different low-percentage thumba biodiesel-diesel blends. Four factors, namely, low-percentage thumba biodiesel-diesel blend, compression ratio, nozzle opening pressure and injection timing were each considered at three levels. An L₉ orthogonal array was used to collect data for various engine performance- and emission-related responses under different engine loads. The signal-to-noise (S/N) ratio and grey relational analysis were used for data analysis. The results of the study revealed that the combination of a blend consisting of 30% thumba biodiesel (B30), a compression ratio of 14, a nozzle opening pressure of 250 bar and an injection timing of 20° produces maximum multiple performance of a diesel engine with minimum multiple emissions from the engine.     

Mooring Damage Identification of Floating Wind Turbine Using a Non-Probabilistic Approach Under Different Environmental Conditions

This paper discusses the damage identification in the mooring line system of a floating wind turbine (FWT) exposed to various environmental loads. The proposed ...     

Flame propagation model for a rotary Atkinson cycle SI engine

The rotary Atkinson cycle engine includes two modes of combustion: combustion initiation and propagation in ignition chamber and then flame jet entrainment and propagation in expansion chamber. The turbulent flame propagation model is a predictive model for SI engines which could be developed for this type of combustion for the rotary Atkinson engine similar to the congenital engine with pre-chamber; in split combustion chamber SI engines, small amount of fuel is burned in pre-chamber while the fuel burned in ignition chamber of rotary Atkinson cycle is considerable. In this study a mathematical modeling of spherical flame propagation inside ignition chamber and new combined conical flame and spherical flame propagation model of a new two-stroke Atkinson cycle SI engine will be presented. The mathematical modeling is carried out using two-zone combustion analysis and the model also is validated against experimental tests and compared with previous study using non-predictive Weibe function model.     

Path-following in model predictive rollover prevention using front steering and braking

In this paper vehicle path-following in the presence of rollover risk is investigated. Vehicles with high centre of mass are prone to roll instability. Untripped rollover risk is increased in high centre of gravity vehicles and high-friction road condition. Researches introduce strategies to handle the short-duration rollover condition. In these researches, however, trajectory tracking is affected and not thoroughly investigated. This paper puts stress on tracking error from rollover prevention. A lower level model predictive front steering controller is adopted to deal with rollover and tracking error as a priority sequence. A brake control is included in lower level controller which directly obeys an upper level controller (ULC) command. The ULC manages vehicle speed regarding primarily tracking error. Simulation results show that the proposed control framework maintains roll stability while tracking error is confined to predefined error limit.     

Telecommuting Suitability Modeling: An Approach Based on the Concept of Abstract job

A new approach to modeling telecommuting suitability is proposed in this paper. The approach, based on the concept of abstract job, can be employed to assess the level of suitability for telecommuting of the bundle of tasks comprising a job. By abstract job is meant a way of considering jobs on the basis of their elements and tasks, representing the general structure of the job. In this study, the basic tasks a job is composed of, pertaining to telecommuting suitability, are identified. To show the applicability of the approach, discrete choice models are calibrated, based on a sample of 245 employees in Tehran, Iran, indicating that from among the 6 tasks identified, 5 tasks are significantly associated with the level of telecommuting suitability.     

Vehicle trajectory challenge in predictive active steering rollover prevention

High center of mass vehicles are likely to rollover in extreme maneuvers. Available works present control strategies to prevent rollover. In these works, however, other important parameters such as path trajectory tracking are not a main concern. In this paper conflicts between rollover prevention and trajectory tracking is investigated. Model predictive control (MPC) is adopted to predict and avoid rollover while tracking desired trajectory. For this regard a model based future error estimation is introduced. The control framework predicts both rollover and trajectory error simultaneously. It avoids rollover while tries to track the trajectory. Simulation results for two controllers with and without trajectory tracking are presented. The results indicate that the controllers effectively limit rollover as a hard constraint while the trajectory tracking controller also minimizes and recovers the path error.     

采用耦合有限元、边界元方法的矩形储液舱中液体晃荡数值仿真(英文)

Sloshing of liquid can increase the dynamic pressure on the storage sidewalls and bottom in tanker ships and LNG careers. Different geometric shapes were suggested for storage tank to minimize the sloshing pressure on tank perimeter. In this research, a numerical code was developed to model liquid sloshing in a rectangular partially filled tank. Assuming the fluid to be inviscid, Laplace equation and nonlinear free surface boundary conditions are solved using coupled FEM-BEM. The code performance for sloshing modeling is validated against available data. To minimize the sloshing pressure on tank perimeter, rectangular tanks with specific volumes and different aspect ratios were investigated and the best aspect ratios were suggested. The results showed that the rectangular tank with suggested aspect ratios, not only has a maximum surrounded tank volume to the constant available volume, but also reduces the sloshing pressure efficiently.