1,720,963 research outputs found
An air suspension cushion to reduce human exposure to vibration
Get PDFThesis (PhD (Industrial Engineering))--University of Stellenbosch, 2007.Off-road working vehicles are subjected to high levels of vibration input on the rough
terrain and irregular roads they work. The human operators are therefore exposed to high
levels of whole body vibration (WBV) and at risk of developing health problems. A
number of international standards address the matter of whole body vibration, and the
European Union issued a directive which limits the exposure of workers in the EU to
WBV. Unfortunately, to date there is no law in South Africa requiring compliance with
any of these EU standards nor guidelines.
There are vehicles which are not fitted with suspension and/or suspension seats. The three
wheeled logger used in forestry is a highly manoeuvrable and effective bulk handler, but
without any form of suspension and no space under the operator’s seat to install a
suspension seat. However, a suspension cushion can be retrofitted to existing vehicles
largely alleviating the problem.
To isolate low frequency vibration large suspension travel is required which makes an air
suspension cushion attractive, as it can fully collapse. Additionally, a Helmholtz resonator
if added to the cushion in the form of a pipe and tank, provides anti-resonance at a specific
frequency. The resonator can be tuned by adjusting the pipe’s length and diameter as well
as the volume of the tank. Larger diameter pipes have less friction and give better
reduction of the transmissibility curve at the anti-resonance frequency.
The SEAT value is a single number used to compare suspension seats for a specific input
vibration. It is calculated from the weighted input acceleration power spectral density
curve and the suspension seat transmissibility curve. The former is obtained from the
vehicle and is vehicle, path and speed dependent. The latter is the only variable that can be
improved by using a better suspension seat/cushion. The input power spectral density
often contains significant energy at frequencies where the human operator is most
sensitive. The cushion resonator could be tuned to position the anti-resonance in the
transmissibility curve at these frequencies. The resultant output vibration would thus be
lower than the input vibration at that frequency.
In this dissertation an analytical model describes the state variables in the cushion, pipe
and tank. A Simulink model predicts the transmissibility curve with a solid mass as well
as with a two degree of freedom seated human model. Initially the prototype was tested
with a solid mass to compare the transmissibility curve produced by the simulation with
the experimental results. It was required to evaluate the contribution of the resonator
without the complexity of the human impedance. Subsequent tests were carried out with
human subjects. Test results showed high inter subject similarity at the anti-resonance
frequencies.
Design guidelines are formulated that can be used by the suspension cushion designer to
specify the pipe diameter and length and the volume of the tank to determine the optimal
transmissibility. Input psd from ISO7096 class EM3 vehicles is used as an example during
the design process.
A prototype air suspension cushion was designed to reduce output vibration on the three
wheeled logger. Laboratory tests with human subjects showed a significant improvement
at the problematic frequencies through the tuning of the resonator. Using a Helmholtz
resonator with the air suspension cushion the overall SEAT value improved by 25%
compared with a 100mm foam cushion. However, the current tank and pipe need to be
reduced in size for practical implementation to the vehicle.
Future work would include finding an alternative mass to replace the air in the pipe. This
should reduce the size of the tank and the pipe required. Additionally the simultaneous
effect of multiple resonators at different frequencies should be investigated. This is
required for vehicles having an input psd with significant energy at more than one
frequency band.Doctora
A decision-making framework for implementing digitalisation in the South African tooling industry
Get PDFCITATION: Dewa, M. T., Van Der Merwe, A. F. & Matope, S. 2018. A decision-making framework for implementing digitalisation in the South African tooling industry. South African Journal of Industrial Engineering, 29(4):245-262, doi:10.7166/29-4-1903.The original publication is available at http://sajie.journals.ac.zaENGLISH ABSTRACT: In this paper, a decision-making framework for implementing the concept of digitalisation within the South African tool, die, and mould-making (TDM) industry context is developed and employed. The purpose of this framework is to answer the following question: “Which digital technologies currently available on the market can be employed to improve the efficiency of shop-floor operations in the South African TDM industry?” An exhaustive literature study of existing digital technologies is conducted. Thereafter, TDM processes requiring digitalisation are identified through knowledge engineering. Based on the system requirements analysis, digital technologies relevant to the South African TDM context are then proposed.AFRIKAANS OPSOMMING: ʼn Besluitnemingsraamwerk vir implementering van die konsep van digitalisering binne die Suid-Afrikaanse matrysmaak industrie is ontwikkel en toegepas. Die doel van hierdie raamwerk is om die volgende vraag te beantwoord: “Watter digitale tegnologieë, wat nou beskikbaar is, kan gebruik word om die rendement van werkswinkel bedrywighede in die Suid-Afrikaanse matrysmaak industrie te verbeter?” ʼn Omvattende literatuurstudie van bestaande digitale tegnologieë is van stapel gestuur. Daarna is matrysmaak prosesse wat kan baat by digitalisering identifiseer. Op grond van die sisteemvereistes analise is digitale tegnologieë relevant tot die Suid-Afrikaanse matrysmaak konteks dan voorgestel.http://sajie.journals.ac.za/pub/article/view/1903Publisher's versio
Digitalisation of shop-floor operations in the south African tool, DIE, and mould-making industry
Get PDFCITATION: Dewa, M. T., Van Der Merwe, A. F. & Matope, S. 2018. Digitalisation of shop-floor operations in the south African tool, DIE, and mould-making industry. South African Journal of Industrial Engineering, 29(2):153-170, doi:10.7166/29-2-1899.The original publication is available at http://sajie.journals.ac.zaENGLISH ABSTRACT: Digitalisation has been advocated as a possible strategy to improve the competitiveness of tool, die, and mould-making (TDM) companies in the 21st century. The recent rise of digital technologies, such as Internet of Things devices, now makes digitalisation an achievable reality. This paper focuses on the digitalisation of shop-floor operations in the South African TDM industry through the development of a novel mobile data collection (MDC) tool known as a shop-floor management system (SMS). The developed SMS was deployed to, and validated in, a selected tooling company for various products. The developed system improved the shop-floor’s real-time data collection.http://sajie.journals.ac.za/pub/article/view/1899Publisher's versio
A conceptual framework for the certification of laser powder bed fusion process quality management systems for aerospace applications
Get PDFCITATION: Gibbons, D. W. & Van Der Merwe, A. F. 2021. A conceptual framework for the certification of laser powder bed fusion process quality management systems for aerospace applications. South African Journal of Industrial Engineering, 32(1):144-156, doi:10.7166/32-1-2342.The original publication is available at http://sajie.journals.ac.zaENGLISH ABSTRACT: This study aims to develop a conceptual framework for the certification of laser powder bed fusion quality management systems for aerospace applications. This research is structured around industry standards and best practices. The developed framework consists of a process map that identifies the required processes and activities for the realisation of parts. Industry standards and best practices are referenced to form standard operating procedures. The framework was presented to subject matter experts within the industry and academia, whose feedback was positive.AFRIKAANSE OPSOMMING: Hierdie studie stel ʼn konseptuele raamwerk voor vir die sertifisering van laserpoeierbed laagvervaardigingsproses kwaliteitsbestuurstelselsvir lug-en ruimtevaarttoepassings. Hierdie navorsing is gestruktureer rondom bedryfstandaarde en beste praktyke. Die ontwikkelde raamwerk bestaan uit ʼn proseskaart wat die vereiste prosesse en aktiwiteite vir die realisering van onderdele identifiseer. Daar word verwys na bedryfstandaarde en beste praktyke in die vorm van standaardprosedures. Die raamwerk was aangebied aanindustrie-en akademie vakkundiges, en die terugvoer was positief.http://sajie.journals.ac.za/pub/article/view/2342Publisher's versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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