This study presents a free vibration analysis of a laminated composite beam, based on the Euler-Bernoulli beam theory. A numerical model of the laminated composite beam was obtained for various boundary conditions based on different length-to-thickness ratios for a number of layers, using the finite element method. A planar beam bending element with two nodes, each having two degrees of freedom, was chosen according to Euler-Bernoulli beam theory. The natural frequencies of the laminated composite beam were obtained for each case, and presented in such a way as to display the effect of these changes on the natural frequencies. Eight natural frequencies of clamped-free, clamped-clamped (CC) and simple-simple (SS) composite beams were first obtained for different length-to-thickness ratios (L x /h), numbers of layers, layer angles and for their different positions. It can be seen that natural frequencies decrease for all modes with increasing length-to-thickness ratio in all cases.
Viscous friction occurs between the roller guide shoes and guide rail because of the grease layer.This friction causes to vibration on the cage. This study's aim is an investigation and active control of that vibration for passengers. Initially, the passenger elevator's dynamics modeling is carried out by Linear Graph Method. The DC motor and AC motor parameters are used in the system modeling separately. Then, vibrations occurred on the elevator cabin are observed. Finally, the effect of vibrations is reduced with the aid of an active controller. The time and frequency responses are compared for two kinds of the motor.
Bu çalışmada, simetrik ve farklı oryantasyon açılarına sahip iki tabakalı kompozit kirişlerin dinamik analizi numerik olarak incelenmiştir. İlk kısımda gerçek boyutlara sahip tabakalı kirişin sonlu elemanlar metodu ile analitik çözümü yapılmıştır. Analitik çözümde kiriş Euler-Bernoulli kiriş teorisi kirişi kabul edilmiştir. İkinci kısımda ise sistem sönümsüz serbest titreşime maruz bırakılarak dinamik analizi yapılmıştır. Sistemin numerik analizi için matematik analiz programı olan MATLAB program dili kullanılmıştır. İki tabakalı çeşitli sınır şartlarına sahip kirişlerin; farklı açılarda ve uzunluk-kalınlık oranlarında doğal frekansları elde edilmiştir. Tabakalı kompozit kirişlerde büyük genlikli titreşimler oldukça etkilidir. Bu sebeple frekanslar ilk sekiz mod için tablo haline getirilip yorumlanmıştır.
Ülkemizde madencilik iş gücü kapasitesinin büyük olduğu sektörlerden birisidir. İşçiler sektörde zaman ve ekonomik değerlerin ön planda olması, aynı zamanda çalışma şartlarının ağırlığı yeraltı madenciliğinde güçlü iş makine ve ekipmanlarının da işçiler ile aynı iş sahasında olmasını zorunlu kılmaktadır. Günümüz madencilik sektöründe kullanılan maden makinelerinin aşırı seviyede gürültü kirliliği oluşturduğu ve işçilerin bu gürültüyle maruz kalmaları en sık karşılaşılan meslek hastalıklardan birisi olan işitme kaybı riskini doğurmaktadır. Yeraltı maden ocakları işçilerinin etkisi altında kaldıkları gürültü seviyesini, seviyenin yaşam kalitesi üzerindeki olumsuz etkilerini ve gürültü etki seviyesinin standartlara uygunluğunu değerlendiren çalışmalar ülkemizde yok denecek kadar azdır. Bu çalışmada yeraltı madenciliğinde gürültü kaynaklarının şiddeti her bir frekans değeri için ayrı ayrı belirlenmiş ve işçi sağlığı ve güvenliği için ele alınmıştır.
In the mining sector, which requires a lot of attention, excessive noise pollution is encountered during the works due to the use of mining machines, and this is observed as one of the most important factors causing various problems for the personnel working in underground mining. The study investigated the neurological effects of instantaneous noise exposure and exposure to noise on workers' health in the underground mining sector using electroencephalography (EEG) device. Firstly, the noises that underground workers are exposed to in different working areas were determined. The brain’s electrical activities were measured at periodic intervals under the noise of one hundred people who work or will work in the mining industry. Their relationship with occupational noise exposure was analyzed statistically. As a result of these measurements, the values collected in noise-free and noisy environments were compared.
The free vibration of stepped nanobeams embedded in the elastic foundation was investigated using Eringen's nonlocal elasticity theory. It is fixed at the system ends with a simple-simple support. The stepped nanbeam’s equations of motion are obtained by using Hamilton's principle. Multi-time scale, which is the perturbation methods, was used for the analytical solution of the equations. To observe the effects of nano size effect, elastic basis coefficient and step location, natural frequencies of the first three modes of the system were obtained for different non-local parameter values, elastic foundation coefficients, step rates and step positions. In the results, it was seen that the non-local parameter had a negative effect on the natural frequency. The elastic foundation coefficient has been shown to reduce vibration amplitudes.
It is known that the problems created by noise cause numerous psychological, social, and various health consequences in many environments. One of the environments where noise exposure is observed most effectively is work areas. Recently, the number of studies on the effects of occupational noise exposure on worker performance and health has increased globally. In this study, it was aimed to determine the effect of exposure to noise on the cardiovascular system. The effects of the noise in the working environment of 100 workers who work or will work in the underground mining sector were examined. Physiological signals such as blood pressure, oxygen saturation, heart rate, respiratory rate, and electrical activity of individuals were measured. The obtained data were analyzed statistically. Our study statistically suggests that noise is a cardiovascular risk factor. It can be assumed that cardiovascular changes are related to noise levels and exposure time, and these effects may also be due to individual susceptibility. In conclusion, the results obtained from this study show the existence of cardiovascular problems in workers working in underground mines and the usefulness of cardiology screening for workers working in this sector.
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