T. A. Janardhan Reddy

RELIABILITY DESIGN EVALUATION AND OPTIMIZATION OF A NITROGEN GAS BOTTLE USING RESPONSE SURFACE METHOD

Optimization of any aerospace product results in increasing payload capacity of space vehicles. Essentially weight, volume and cost are the main constraints. Design optimization studies for aerospace system are increasingly gaining importance. The problem of optimum design under uncertainty has been formulated as reliability-based design optimization. The reliability based optimization, which includes robustness requirements leads to multi-objective optimization under uncertainty. In this paper Reliability, based design optimization study is carried out under linear constraint optimization to minimize the weight of a nitrogen gas bottle with specified target reliability. Response surface method considering full factorial experiment is used to establish multiple regression equation for induced hoop stress and maximum strain. Necessary data pertaining to design, manufacturing and operating conditions are collected systematically for variability study. Structural reliability is evaluated using Advanced First-Order Second-Moment Method (AFOSM). Finally, optimization formulation established and it has been discussed in this paper.

A robust process optimisation for fused deposition modelling

Rapid Prototyping (RP) technology is being widely used in diverse areas including mould manufacturing. However, the quality of RP parts is significantly affected by the process parameters of the RP machine. This work presents an experimental design technique for determining the optimal quality of a part build by the Fused Deposition Modelling (FDM) process with ABS plastic material. The design investigates (L9 Taguchi array) the effect of the parameters, contour width, raster width, raster angle and air gap on the dimensional accuracy, form features and surface finish. The experimental results are analysed by using the Analysis of Variance (ANOVA) method.

Optimisation of cam-follower motion using B-splines

This paper proposes design of cam-follower velocity curve by using B-spline polynomials. B-spline polynomials are smooth curves defined by control points. Curve shape can be modified by changing the control points. The traditional design method for improving the motion characteristics of the follower is to find an optimum displacement curve for which follower velocity, acceleration curves to be continuous and their peak values as small as possible (i.e. minimum jerk). B-spline polynomials of degree three and six control points are used in design of follower velocity curve. The B-spline curve is used to approximate the various basic curves which have better motion characteristics. A computer-aided design and computer-aided manufacturing (CAD/CAM) system is developed which generates follower motion curves, i.e. displacement, velocity, acceleration, jerk and cam profiles. An analysis is carried out on B-splines with basic curves for maximum accelerations to select the best cam follower motion. It also provides cam profile coordinates to manufacture a cam on computer numerical control (CNC) machines.

Reliability design optimization for aerospace product an integrated approach

The need for continuous improvement in engineering designs of aerospace and automotive products exist in order to optimize cost, weight, volume etc. Due to the inherent uncertainties such as external loading, material properties and manufacturing quality, the prototypes of manufactured product may not satisfy all the requirements. Deterministic approaches cannot take into account all the variabilities that characterize design input properties leading to oversized or undersized structure. The present paper deals with response surface methodology where the performance functions are generated using design of experiments. These simplified linear performance functions are used for design optimization. Further, an outline of the methodology is discussed that could serve as a guideline to develop a more efficient and optimized design process. Here, the product optimization is carried out in stages starting from deterministic optimization, followed by reliability based design optimization using reliability index approach and performance measure approach to meet target reliability requirements.

Parametric modelling and simulation of rapid prototyping

This work proposes a virtual system for parametric modelling and simulation of rapid prototyping (RP) process. The system aims to reduce the manufacturing risks of prototypes early in a product development cycle and, hence, reduce the number of costly design-build-test cycles. It involves modelling and simulation of RP system, which facilitates visualisation and testing the effects of process parameters on the part quality. Modelling of RP is based on qualifying the measures of part quality, which includes accuracy, build-time and efficiency of the selective laser sintering (SLS) process. The model incorporates various process parameters like layer thickness, hatch space, bed temperature, laser power and sinter factor, etc. It has been integrated with the simulation system to provide a testbed to optimise the process parameters.

Structural Reliability Evaluation and Optimization of a Pressure Vessel Using Nonlinear Performance Functions

Structural safety is one of the most important factors of any aerospace product. Until recently, a design is considered to be robust if all the variables that affect its life has been accounted for and brought under control. The meaning of robustness is changing. Designer and engineers have traditionally handled variability with safety factors. In this chapter, in the first phase, a pressure vessel made of titanium alloy is considered for safety index (structural reliability) study. The safety index is evaluated based on the data collected during manufacturing and operation. Various methods like mean value and moment methods are used for safety evaluation and same have been discussed. In the second phase of this chapter, an attempt has been made to carry out multi-objective design analysis taking into account the effect of variation of design parameters. Multiple objective of interests include structural weight, load-induced stress, deflection and structural reliability. The design problem is formulated under nonlinear constrained optimization and has been solved. Nonlinear regression relations are used for various performance functions. Nonlinear regression model is validated and found to be in good agreement with experimental results. Finally, optimum design parameters are suggested for design operating conditions.

A comparative study of probabilistic structural safety analysis

Structural Safety is one of the most important factors of any aerospace product. Until recently, a design is considered to be robust if all the variables that affect its life has been accounted for and brought under control Safety factor cannot, by themselves, guarantee satisfactory performance and they do not provide sufficient information to achieve optimal use of available resources. The meaning of robustness is shifting. Designer and engineers have traditionally handled variability with safety factors. Some safety factors are derived from observation and analysis, and many cases it use to be pure guess work. In those cases, the bigger the guess, the bigger the risk, the bigger the safety factor resulting over designed product. In the present paper, a spherical pressure vessel is identified for structural safety evaluation. Structural Safety Index is evaluated using uncertainty. Various statistical methods like mean value and moment methods are discussed. Simulation techniques for evaluation of probability of failure are also discussed. It is well established that simulation techniques have proven their value especially for problem where the representation of the state function is associated with difficulties. Such cases are e.g when the Limit State function is not differentiable or when several design points contribute to the failure probability. The various simulation methodologies have been discussed in brief for structural safety evaluation, such as Crude Monte Carlo, Importance Sampling, Importance Sampling based on β point and Latin Hyper Cube Sampling. Finally a comparative study of safety evaluation based on these techniques are made in this paper. These methods found to be useful for structural safety and design evaluation.

Structural reliability evaluation of a pressure vessel using response surface method

High Reliability and operational safety are most important requirements of an aerospace product. Many aerospace standard guidelines are followed during design phases and after many iterations the product parameters are established. The conventional design practices do not take variability in to account. Probabilistic structural analysis, unlike traditional methods, provides a means to quantify the inherent risk of a design. In the present paper, Response Surface method is considered to evaluate Structural Reliability and Safety. A Response Surface model generated is validated with actual test data. This model can be used for Safety Index, Sensitivity analysis and Structural optimization with good confidence.