Identification of Unbalanced Forces and Foundation Parameters of Rotating Machines from Vibration Measurements

A technique is described to use measured vibration data of a rotating machine and its foundation to identify unbalanced forces, stiffness and damping parameters of the mountings, and the parameters of the foundation. It is based on an idealisation treating the rotor, the machine structure and the foundation as rigid masses supported by springs and dampers. Operational vibration data of the machine and its foundation before andafter the rotating unbalanced forces are perturbed by adding unbalanced mass to the rotor are used in the identification procedure. Once the parameters are identified, dynamic forces transmitted to the foundation can be estimated. The technique is demonstrated using simulated example for a machine with a two bearings rotor

System identification of linear vibrating structures

Methods of dynamic modelling and analysis of structures, for example the finite element method, are well developed. However, it is generally agreed that accurate modelling of complex structures is difficult and for critical applications it is necessary to validate or update the theoretical models using data measured from actual structures. The techniques of identifying the parameters of linear dynamic models using Vibration test data have attracted considerable interest recently. However, no method has received a general acceptance due to a number of difficulties. These difficulties are mainly due to (i) Incomplete number of Vibration modes that can be excited and measured, (ii) Incomplete number of coordinates that can be measured, (iii) Inaccuracy in the experimental data (iv) Inaccuracy in the model structure. This thesis reports on a new approach to update the parameters of a finite element model as well as a lumped parameter model with a diagonal mass matrix. The structure and its theoretical model are equally perturbed by adding mass or stiffness and the incomplete number of eigen-data is measured. The parameters are then identified by an iterative updating of the initial estimates, by sensitivity analysis, using eigenvalues or both eigenvalues and eigenvectors of the structure before and after perturbation. It is shown that with a suitable choice of the perturbing coordinates exact parameters can be identified if the data and the model structure are exact. The theoretical basis of the technique is presented. To cope with measurement errors and possible inaccuracies in the model structure, a well known Bayesian approach is used to minimize the least squares difference between the updated and the initial parameters. The eigen-data of the structure with added mass or stiffness is also determined using the frequency response data of the unmodified structure by a structural modification technique. Thus, mass or stiffness do not have to be added physically. The mass-stiffness addition technique is demonstrated by simulation examples and Laboratory experiments on beams and an H-frame

Development of a Genetic Algorithm Based Search Strategy Suited For Design Optimisation of Internal Combustion Engines

Engine design optimisation is a multi-objective, multi-domain problem in a discontinuous design space. The state of the art of optimisation techniques shows that only methods of direct and adaptive search are appropriate for this type of problem. These include, adaptive random search, simulated annealing, evolution strategies and genetic algorithms. Ofthese methods, the genetic algorithms have been shown to be the most suited for the optimisation of multi-modal response functions in a discontinuous design space. This paper considers the important characteristics of genetic algorithms and their adaptation for use in parametric design optimisation of internal combustion engines. In order to verify the basicfunctionality of the proposed optimisation strategy, a genetic algorithm based, optimisation software was developed and tested on a number of analytical functions, selected from optimisation literature, with satisfactory results

Motivation and Challenges Facing Employers in Recruiting Professional Women in Building Construction Companies in Dar-Es-Salaam, Tanzania

The study intended to assess the motivation and challenges facing employers in recruitment of professional women in building construction companies; by analyzing motivation; examining the challenges encountered; and proposing the possible measures to overcome challenges facing employers in recruiting professional women in building construction companies, in Dar-Es-Salaam, Tanzania. This descriptive designed survey study, engaged large size contractors as a unit of analysis, with building contractors from Class I and II, within Dar-Es-Salaam Tanzania, as a study population and a sample. Moreover, the study involved non-probability sampling; specifically, judgmental sampling, which was used in determining the number of registered building construction firms in Dar-Es-Salaam particularly from Class I and II. Literature review; open and closed ended questionnaires administered to employers and human resources managers in building construction companies in Dar-Es-Salaam, were used in collecting primary and secondary qualitative and quantitative data. In collecting data, total of 56 questionnaire were distributed, whereby only 41 (73%) were returned. Quantitative data were analyzed using Statistical Package for Social Sciences (SPSS), while qualitative data were analyzed thematically. Findings revealed the need to address gender balance; non-discriminatory policy; improved staff retention (you can keep your employees, boost their morale); a better reflection to the customers or clients; encourage organization to change from gender stereotype; different perspective (benefits from different points of view and approaches); enhance collaboration (improve team processed and group collaboration); the perception of women being more multitasked than men, and the need to explore a wide talent pool; women are professionally ethical, committed to their work, and less corrupt, with better listening and soft skills; improve reputation (no gender biasness to your company); and women are loyal, practical innovative, and patience, as the most prevalent motivations that; pushes employers to recruit professional women in building construction companies. Furthermore, the critical challenges revealed were; work-life balance, private life demands, emotions, and non-family friendly working hours; lack of good recruitment practises, procedures and selection plans; lack of good staff development plan; lack of gender policy; lack of confidence and low number of female applicants in the building construction industry; and lack of proper motivation and mentorship policy. The study concluded that; more attention must be made on recruiting more women in building construction industry as a part of the gender equality, in order to increase their participation number in the construction industry, against male, alongside addressing all the challenges and motivation factors revealed in the study. Lastly, the study recommended; incentives (such as training and mentoring); support and encouragement of women participation in construction; enhancement of labour laws and regulations; and mandatory to recruitment of more women in construction industry

The Tanzanian Trauma patients' Prehospital Experience: A Qualitative Interview-based Study.

We sought to characterise the prehospital experience of Tanzanian trauma patients, and identify barriers and facilitators to implement community-based emergency medical systems (EMS). Our study was conducted in the emergency department of an urban national referral hospital in Tanzania. A convenience sample of 34 adult trauma patients, or surrogate family members, presenting or referred to an urban referral emergency department in Tanzania for treatment of injury, participated in the study. Participation in semistructured, iteratively developed interviews until saturation of responses was reached. A grounded theory-based approach to qualitative analysis was used to identify recurrent themes. We characterised numerous deficiencies within the existing clinic-to-hospital referral network, including missed/delayed diagnoses, limited management capabilities at pre-referral facilities and interfacility transfer delays. Potential barriers to EMS implementation include patient financial limitations and lack of insurance, limited public infrastructure and resources, and the credibility of potential first aid responders. Potential facilitators of EMS include communities' tendency to pool resources, individuals' trust of other community members to be first aid responders, and faith in community leaders to organise EMS response. Participants expressed a strong desire to learn first aid. The composite themes generated by the data suggest that there are myriad structural, financial, institutional and cultural barriers to the implementation of a formal prehospital system. However, our analysis also revealed potential facilitators to a first-responder system that takes advantage of close-knit local communities and the trust of recognised leaders in society. The results suggest favourable acceptability for community-based response by trained lay people. There is significant opportunity for care improvements with short trainings and low-cost supply planning. Further research looking at the effects of delay on outcomes in this population is needed

Stimulating Gender Equity Through Female Academic Empowerment: The Case of the CoET, University of Dar es Salaam

Tanzania, like many other countries in Africa, has for a long time suffered from cultural-related gender inequality syndrome where females did not receive the same share of opportunity as males in many aspects of socioeconomic development, notably in education, politics, administration, science and technology. The gender inequality in education, and also in science and technology, are reflected by the low levels of female enrolment science subjects in secondary schools when compared to males, and also in institutions of higher learning. Another reflection is a low number of female professionals in comparison to males in science-based professions. This article presents an overview of the efforts taken by the College of Engineering and Technology at the University of Dar es Salaam in stimulating gender equity through female academic empowerment. The paper highlights situation analysis prior to 2003, before deliberate intervention measures were instituted, motivation for the gender equity intervention at the College, achievements and shortfalls, and chart out scenario for possible improvement and sustainability

System identification of linear vibrating structures

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