Research Article
Robust H∞ Control Approach for Neutral Time-delay Systems Under Uncertainty Consideration: A Case Study on Permanent Magnet Synchronous Generators
Mohammad Karimi*
Issue:
Volume 9, Issue 1, June 2025
Pages:
1-9
Received:
11 April 2025
Accepted:
22 April 2025
Published:
29 May 2025
Abstract: Time-delay in many systems and applications is often a source of instability and reduced system performance where among them Neutral time delay systems are a class of functional differential equations where the derivatives of the state not only depend on the current and past states but also explicitly on delay derivatives. These systems arise naturally in various engineering, biological and economic models where delays affect both the state and its rate of change. Also, the presence of uncertainties such as parameter variations, unmodeled dynamics and external disturbances further complicates the analysis and control of such systems. so, this paper deals with the robust H_∞ state-feedback control design for a class of uncertain systems subject to neutral Time-delay varying with multiple state and state derivatives delays is investigated in this paper. The parametric uncertainties are time varying and unknown but norm bounded. The main motivation of the paper is to develop a robust H∞ controller, which ensures robust asymptotic stability of the system as well as a desired H∞ performance and satisfy a prescribed γ performance level for all admissible uncertainties. By constructing a Lyapunov-Krasovskii functional, some sufficient conditions for the existence of the H∞ state-feedback controller is derived in terms of linear matrix inequalities (LMI). Finally Numerical examples are provided to illustrate the effectiveness of the proposed method.
Abstract: Time-delay in many systems and applications is often a source of instability and reduced system performance where among them Neutral time delay systems are a class of functional differential equations where the derivatives of the state not only depend on the current and past states but also explicitly on delay derivatives. These systems arise natur...
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Research Article
Evaluating the Safety Practices in Sewerage Projects in Addis Ababa
Ebisa Bayisa Hunde*,
Habtamu Hailu Kebede
Issue:
Volume 9, Issue 1, June 2025
Pages:
10-18
Received:
15 May 2025
Accepted:
23 July 2025
Published:
28 August 2025
DOI:
10.11648/j.cse.20250901.12
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Abstract: This study evaluated safety practices in sewerage projects in Addis Ababa using a descriptive survey design. A sample of 132 participants was selected through purposive sampling, focusing on individuals with firsthand experience in sewage projects. Data collection included primary and secondary sources. A quantitative approach was employed, utilizing closed-ended questionnaires on a Likert scale distributed to contractors, consultants, and clients. SPSS 26 was used for data analysis, and the Relative Importance Index was used to rank strategies for enhancing safety practices based on perceived importance. The survey results indicated that 76% of respondents disagree with the provision of mandatory safety training programs for all workers before starting sewerage project work. About 24.8% of respondents believe that the supply of Personal Protective Equipment (PPE) is adequate, pointing to a widespread concern regarding insufficient availability of essential safety gear on-site. Access to first aid kits and emergency medical assistance is reported, yet concerns remain about risk assessments and confined space protocols. Although training for handling hazardous materials exists, there is inconsistent agreement on safety audits and air quality monitoring. Workers in sewerage projects face significant health hazards, including exposure to toxic gases like hydrogen sulfide, lack of vaccinations for diseases such as hepatitis and tetanus, and risks from biological hazards in sewage. Additional concerns include potential hearing loss, ergonomic injuries, slips, trips, and falls, as well as musculoskeletal disorders from heavy lifting and psychological stress from working conditions. Risks related to confined spaces and inadequate training to identify health hazards complicate their challenges. The top five strategies identified to enhance safety practices in sewerage projects include the allocation of additional funding for better quality Personal Protective Equipment (RII=0.924), implementation of advanced monitoring technologies, such as gas detectors and air quality monitors (RII=0.921), regular training programs for workers on safety procedures (RII=0.92), establishment of regular safety audits (RII=0.908), and creation of a dedicated safety management team (RII=0.907). Stakeholders, including government agencies and contractors, must collaborate to implement these strategies effectively to mitigate health risks and enhance safety in sewerage projects.
Abstract: This study evaluated safety practices in sewerage projects in Addis Ababa using a descriptive survey design. A sample of 132 participants was selected through purposive sampling, focusing on individuals with firsthand experience in sewage projects. Data collection included primary and secondary sources. A quantitative approach was employed, utilizi...
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