Study on Reliability Design of the Domestic Compressor Subjected to Repetitive Internal Stresses by Parametric Accelerated Life Testing

This chapter explains the parametric accelerated life testing (ALT) to recognize design defects in mechanical products. A life-stress model and a sample size formulation are suggested. A compressor is used to demonstrate this method. Compressors were failing in the field. At the first ALT, the compressor failed due to a fractured suction reed valve. The failure modes were similar to those valves returned from the field. The fatigue of the suction reed valves came from an overlap between the suction reed valve and the valve plate. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan performed the heat treatment to the exterior of the crankshaft made of cast iron. After the design modifications, there were no troubles during the third ALT. The lifetime of compressor was secured to have a B1 life 10 years.

Refactoring Techniques for Improving Software Quality: Practitioners’ Perspectives

Refactoring is a critical task in software maintenance and is commonly applied to improve system design or to cope with design defects. There are 68 different types of refactoring techniques and each technique has a particular purpose and effect. However, most prior studies have selected refactoring techniques based on their common use in academic research without obtaining evidence from the software industry. This is a shortcoming that points to the existence of a clear gap between academic research and the corresponding industry practices. Therefore, to bridge this gap, this study identified the most frequently used refactoring techniques, the commonly used programming language, and methods of applying refactoring techniques in the current practices of software refactoring among software practitioners in the industry, by using an online survey. The findings from the survey revealed the most used refactoring techniques, programming language, and the methods of applying the refactoring techniques. This study contributes toward the improvement of software development practices by adding empirical evidence on software refactoring used by software developers. The findings would be beneficial for researchers to develop reference models and software tools to guide the practitioners in using these refactoring techniques based on their effect on software quality attributes to improve the quality of the software systems as a whole.

FORMAL MODELING AND ANALYSIS OF ENTITY FRAMEWORK USING ALLOY

Formal methods provide multiple benefits when applied in the software development process. For instance, they enable engineers to verify and validate models before working on their implementation, leading to earlier detection of design defects. However, most of them lack flexibility to be applied in agile software development projects. Alloy is a lightweight formal modeling language with a friendly tool that facilitates the agile approaches application. Unfortunately, its industrial adoption is hampered by the lack of methods and tools for current software development frameworks, such as Entity Framework. This platform is usually chosen by agile projects following the code-first approach that allows automatic generation of a database from domain classes coded in the C# language. We present a new method and tool for the formal specification and analysis of Entity Framework projects with Alloy. The proposal allows engineers to start the software development using Alloy for modeling, validation and verification, automatically translate Alloy specifications to C# domain classes and then generate the corresponding database with Entity Framework. We validate our approach with a real case study: an application required by a gas supplier company.

Building information modeling as a tool for prevention ofdesign defects

Purpose In recent decades, professionals in the architecture, engineering and construction industry have come to recognize building information modeling (BIM) as one of the most powerful technologies available to ensure successful project outcomes. The purpose of this paper is to explore the benefits of BIM on design defect prevention during the design phase of building projects. Design/methodology/approach The authors qualitatively analyzed 160 design defect leading indicators (LIs) to identify key themes for design defect prevention. Then, by matching appropriate BIM functionalities to each key LI theme, they identified BIM-supported key LI themes. Findings The result of this paper served as the foundation of a BIM-based key design processes framework, which identifies the necessary data, project parties, actions and applicable BIM functions for preventing particular design defects. In addition, the authors found that BIM implementation can benefit 71.2% of the LIs of the design defects associated with problematic deliverables. Originality/value This study establishes the current state of BIM use for design defect prevention and also gives practitioners precisely targeted guidelines for using BIM functions during the design phase for better quality management.

Reliability Design of Mechanical Systems Such as Compressor Subjected to Repetitive Stresses

This study demonstrates the use of parametric accelerated life testing (ALT) as a way to recognize design defects in mechanical products in creating a reliable quantitative (RQ) specification. It covers: (1) a system BX lifetime that X% of a product population fails, created on the parametric ALT scheme, (2) fatigue and redesign, (3) adapted ALTs with design alternations, and (4) an evaluation of whether the system design(s) acquires the objective BX lifetime. A life-stress model and a sample size formulation, therefore, are suggested. A refrigerator compressor is used to demonstrate this method. Compressors subjected to repetitive impact loading were failing in the field. To analyze the pressure loading of the compressor and carry out parametric ALT, a mass/energy balance on the vapor-compression cycle was examined. At the first ALT, the compressor failed due to a cracked or fractured suction reed valve made of Sandvik 20C carbon steel (1 wt% C, 0.25 wt% Si, 0.45 wt% Mn). The failure modes of the suction reed valves were similar to those valves returned from the field. The fatigue failure of the suction reed valves came from an overlap between the suction reed valve and the valve plate in combination with the repeated pressure loading. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan specified to perform the heat treatment to the exterior of the crankshaft made of cast iron (0.45 wt% C, 0.25 wt% Si, 0.8 wt% Mn, 0.03 wt% P). After these design modifications, there were no troubles during the third ALT. The lifetime of the compressor was secured to have a B1 life of 10 years.

System Approach in Complex Integral Design Methodology and Its Application in New Zealand

Many New Zealand houses are energy-inefficient, unhealthy, cold, mouldy, and damp. Therefore, a new approach to building design is imminent. This article proposes a framework for the transformation of housing that integrates construction planning and design, optimization, and control tools at strategic, tactical, and operational levels. The introduced Complex Integral Design New Zealand (CIDNZ) represents a comprehensive and balanced system-based design and delivery process that facilitates and accelerates cross-disciplinary and trans-disciplinary expertise and knowledge. CIDNZ delineates a new way of designing the process based on integral, complex, and systems thinking. The emerging novel understanding of sustainability, which guides the transformation process, might lead to a balance between individuals, groups, society, and existing ecosystems. CIDNZ comprises all stages in the life cycle of buildings and all significant factors in the architecture, engineering, and construction industry, particularly, people, processes, technology, and the environment. Therefore, the entire construction process that implements a system approach to buildings as a vital part of environmental systems, goes from the environment to humans and vice versa and offers unlimited possibilities. The consequent practical application of these principles might eliminate or reduce the design defects and lead accordingly to the reduction of costs involved in their rectification.

Minimum contact stress modification for profile curve design defects in the beam-spring-cone docking mechanism

A minimum contact stress modification method for profile curve design defects in a beam-spring-cone docking mechanism (BSCDM) based on genetic algorithm is presented in this paper, the profile curve and contact position of BSCDM are optimized. Under low-speed conditions, an improved elastic contact model of semi-space elastic bodies is established to modify and optimize the elliptic profile envelope curve based on Hertz contact theory and two kinds of complete elliptic integral, the improved contact model is used to solve elastic contact problems with the geometric characteristics of the ellipse surface, the optimal profile curve of the docking joint and the optimal docking contact point position are obtained. The results of numerical simulation and the experiment demonstrate the feasibility and validity of above models and methods.

Vibration Characteristics and Simulation Verification of the Dual-Rotor System for Aeroengines with Rub-Impact Coupling Faults

To study the rub-impact fault between the dynamic and static parts of the rotor system of aeroengines, the dual-rotor system of a typical aeroengine is introduced and taken as the research object. The analytical kinetic model is established based on the Lagrange equation considering the structural characteristics of the dual-rotor system, the coupling effect of the intermediate bearing, and the rub-impact fault between the high-pressure turbine disc and the casing. The dynamic characteristics of the dual-rotor system under the rub-impact fault are analyzed, and the change rule of the rub-impact shape is obtained. The vibration coupling and transfer among the high-pressure rotor and the low-pressure rotor are revealed. The influence of the unbalanced position and the speed of high and low rotors on the vibration response of the dual rotor is obtained. The sensitivity of the vibration response of the dual rotor at different test points to rub-impact stiffness, clearance, and friction coefficient is compared. The simulation model is established based on the rigid-flexible coupling multibody dynamic simulation platform. The analytical results and simulation results are compared, which have a good consistency. The theoretical research can deepen the understanding of the nature and law of aeroengine rotor operation, expose the possible faults and design defects, greatly improve the development efficiency and quality, reduce repeated physical tests, reduce the development risk and cost, and accelerate the development process. This study can provide a theoretical basis for the monitoring and diagnosis of engine rub-impact faults and provide theoretical and practical reference for the establishment of the vibration fault test and analysis method system.