System Dynamic Analysis of the Fleet Availability and Reliability Influence on the Lead Time of the Delivery Order Process

The inventory replenishment process in the warehouse becomes difficult if there is uncertainty. It can cause warehouse performance not to be as expected. The warehouse is an important part of the supply chain subsystem, which smooths the flow of goods from upstream to downstream throughout the system. This paper uses system dynamics modeling to analyze the replenishment of raw materials where there is randomness in availability and reliability and their effects on the delivery lead time of the fleet. The model obtained is much simpler but more robust when compared to the analytical-mathematical model or the discrete-events simulation. Tests on the model show that the model can behave as it should logically. Several experiments were conducted to see how fleet availability's reliability can affect the delay in receiving or delivery lead time. One interesting thing revealed is that reliability does not have to be 100%, but there is a certain minimum threshold for the system to perform well. This is different from availability, which must be 100%

Optimal Ship Maintenance Scheduling Under Restricted Conditions and Constrained Resources

The research presented in this dissertation addresses the application of evolution algorithms, i.e. Genetic Algorithm (GA) and Differential Evolution algorithm (DE) to scheduling problems in the presence of restricted conditions and resource limitations. This research is motivated by the scheduling of engineering design tasks in shop scheduling problems and ship maintenance scheduling problems to minimize total completion time. The thesis consists of two major parts; the first corresponds to the first appended paper and deals with the computational complexity of mixed shop scheduling problems. A modified Genetic algorithm is proposed to solve the problem. Computational experiments, conducted to evaluate its performance against known optimal solutions for different sized problems, show its superiority in computation time and the high applicability in practical mixed shop scheduling problems. The second part considers the major theme in the second appended paper and is related to the ship maintenance scheduling problem and the extended research on the multi-mode resource-constrained ship scheduling problem. A heuristic Differential Evolution is developed and applied to solve these problems. A mathematical optimization model is also formulated for the multi-mode resource-constrained ship scheduling problem. Through the computed results, DE proves its effectiveness and efficiency in addressing both single and multi-objective ship maintenance scheduling problem

Cost and benefits design optimization model for fault tolerant flight control systems

Requirements and specifications for a method of optimizing the design of fault-tolerant flight control systems are provided. Algorithms that could be used for developing new and modifying existing computer programs are also provided, with recommendations for follow-on work

Advanced information processing system: The Army fault tolerant architecture conceptual study. Volume 2: Army fault tolerant architecture design and analysis

Described here is the Army Fault Tolerant Architecture (AFTA) hardware architecture and components and the operating system. The architectural and operational theory of the AFTA Fault Tolerant Data Bus is discussed. The test and maintenance strategy developed for use in fielded AFTA installations is presented. An approach to be used in reducing the probability of AFTA failure due to common mode faults is described. Analytical models for AFTA performance, reliability, availability, life cycle cost, weight, power, and volume are developed. An approach is presented for using VHSIC Hardware Description Language (VHDL) to describe and design AFTA's developmental hardware. A plan is described for verifying and validating key AFTA concepts during the Dem/Val phase. Analytical models and partial mission requirements are used to generate AFTA configurations for the TF/TA/NOE and Ground Vehicle missions

Advanced Manned Launch System (AMLS) study

To assure national leadership in space operations and exploration in the future, NASA must be able to provide cost effective and operationally efficient space transportation. Several NASA studies and the joint NASA/DoD Space Transportation Architecture Studies (STAS) have shown the need for a multi-vehicle space transportation system with designs driven by enhanced operations and low costs. NASA is currently studying an advanced manned launch system (AMLS) approach to transport crew and cargo to the Space Station Freedom. Several single and multiple stage systems from air-breathing to all-rocket concepts are being examined in a series of studies potential replacements for the Space Shuttle launch system in the 2000-2010 time frame. Rockwell International Corporation, under contract to the NASA Langley Research Center, has analyzed a two-stage all-rocket concept to determine whether this class of vehicles is appropriate for the AMLS function. The results of the pre-phase A study are discussed

Robust multi-disciplinary modelling of future re-usable aerospace planes

Practical embodiment of the Single-Stage to Orbit concept has long been held as the key to unlocking a future of rapid, reliable, even scheduled access to space. The full potential of Single-Stage to Orbit will only be realised when this vehicle concept is integrated into an airline-like operational paradigm which has, as its basis, the re-usability of the individual vehicles that comprise the fleet, but in addition, extends to the long-term assuredness of operations through sustained reliability, quick turnaround, and control over recurring costs to the point where the profitability of the enterprise can be assured for its owners and investors. The purpose of this paper is to make some initial steps towards providing some quantitative answers as to how decisions that are made regarding the design of the actual hardware might impact on long-term viability of the technology through influencing the reliability of the system and eventually its cost when incorporated as part of an integrated transportation system. This is achieved through embedding a physics-based simulation of the performance of the vehicle subsystems, under operational conditions, into a Discrete Event Simulation of spaceport operations, allowing the statistical relationship between the various design characteristics of the vehicle, and the metrics that are relevant to its operational cost, to be exposed