Search Results

1 - 10 of 18 items :

  • "frequency ratio" x
Clear All
Landslide Susceptibility Assessment in Constantine Region (NE Algeria) By Means of Statistical Models

, the quantitative approaches are the most used. They are based on mathematical expressions of the relationship between conditioning factors and the landslides, usually managed as thematic data within geographic information system (GIS). Their two main branches include deterministic methods, more appropriate for large scale [ 20 ], and statistical methods, valid for small and medium scale, such as weight of evidence (WoE), information value (IV), frequency ratio (FR), fuzzy logic (FL), logistic regression (LR) and artificial neural network (ANN) approaches [ 21 , 22

Open access
Large Amplitude Free Vibration Analysis of Tapered Timoshenko Beams Using Coupled Displacement Field Method

Abstract

Tapered beams are more efficient compared to uniform beams as they provide a better distribution of mass and strength and also meet special functional requirements in many engineering applications. In this paper, the linear and non-linear fundamental frequency parameter values of the tapered Timoshenko beams are evaluated by using the coupled displacement field (CDF) method and closed form expressions are derived in terms of frequency ratio as a function of slenderness ratio, taper ratio and maximum amplitude ratio for hinged-hinged and clamped-clamped beam boundary conditions. The effectiveness of the CDF method is brought out through the solution of the large amplitude free vibrations, in terms of fundamental frequency of tapered Timoshenko beams with axially immovable ends. The results obtained by the present CDF method are validated with the existing literature wherever possible.

Open access
Increased breathing resistance compromises the time course of rhythmical forearm movements—a pilot study

Abstract

Background and Objectives: Skeletal muscle dysfunction is a major problem among the co-morbidities associated with chronic obstructive pulmonary disease (COPD). However, muscle weakness and increased fatigability are not the only limitations of skeletal muscle function. Motor–respiratory coordination (MRC) may occur even during movements at lowest workloads. MRC modifies the temporal pattern of motor actions, thus probably impairing motor performance and movement precision. Little attention has been paid to the question of whether motor functions may be compromised in COPD patients independent of workload and required muscle strength and endurance. The present pilot study was designed to investigate the effects of a simulated obstruction (SO) in healthy subjects on their breathing pattern and the timing of a rhythmical forearm movement.

Methods: Twenty-one subjects performed flexion–extension movements with their right forearm at a self-chosen rate within a range between 0.2 and 0.4 Hz. After a control experiment with normal breathing, a plug with a narrow hole was inserted between face mask and pneumotachograph to simulate obstruction. Subjects were required to repeat the rhythmical forearm movement at the same rate as in the control experiment.

Results: The condition of SO significantly prolonged breath duration but reduced tidal volume and ventilation. In addition, period duration of the forearm movement increased significantly under this condition while the movement-to-breathing frequency ratio remained almost constant. Increased breathing resistance was considered to cause prolonged breath duration accompanied by an increase in movement period duration. The constant near-integer ratio between movement and breathing rates indicates that the change in movement period duration resulted from MRC.

Conclusions: The findings of this pilot study demonstrate that increased breathing resistance may compromise motor performance even at lower workloads. This means that in COPD patients, not only muscle strength and endurance are reduced but, moreover, fine motor skills may be impaired. This aspect has particular importance for many everyday activities as reduced fine motor performance substantially contributes to a progressive inability of the patients to manage their daily life.

Open access
Derivation of Motor Mean Phase Currents in PMSM Drives Operating with Low Switching-to- Fundamental Frequency Ratio

Abstract

Pulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase currents to consist of distinctive ripples. In order to provide suitable feedback for the motor current controllers, the mean value must be extracted from the currents’ waveforms in every PWM cycle. A common solution to derive the mean phase currents is to sample their value at the midpoint of a symmetrical PWM cycle. Using an assumption of linear current changes in steady PWM subintervals, this midpoint sample corresponds to the mean current in the PWM cycle. This way no hardware filtering or high-rate current sampling is required. Nevertheless, the assumption of linear current changes has been recently reported as over simplistic in permanent magnet synchronous motor (PMSM) drives operating with low switching-to-fundamental frequency ratio (SFFR). This, in turn, causes substantial errors in the representation of the mean phase currents by the midpoint sample. This paper proposes a solution for deriving mean phase currents in low SFFR PMSM drives, which does not rely on the linear current change assumption. The method is based on sampling the currents at the start point of a PWM cycle and correcting the sampled value using a model-based formula that reproduces the current waveforms. Effectiveness of the method is verified by simulation for an exemplary setup of high-speed PMSM drive. The results show that the proposed method decreases the error of determining the mean phase currents approximately 10 times when compared to the classical midpoint sampling technique.

Open access
Study of Radial Vibrations in an Infinitely Long Fluid-Filled Transversely Isotropic Thick-Walled Hollow Composite Poroelastic Cylinders

Abstract

In this paper, radial vibrations of an infinitely long fluid-filled transversely isotropic thick-walled hollow composite poroelastic cylinder are investigated in the framework of poroelasticity. The cylinder consists of two concentric cylindrical layers namely, core (inner one) and coating (outer one), each of which retains its own distinctive properties. A comparative study has been made between the thick-walled hollow composite poroelastic cylinder and that of fluid-filled one. Frequency is computed against the ratio between the thickness to inner radius of the composite cylinder at various anisotropic ratios. Another comparative study is made between the results of current case and that of isotropic case by making Young’s modulus and Poisson ratio values of isotropic and that of transversely isotropic in the transverse direction equal. Numerical results are depicted graphically and then discussed.

Open access
Effect of natural frequency modes on sloshing phenomenon in a rectangular tank

Abstract

Liquid sloshing in two-dimensional (2-D) and three-dimensional (3-D) rectangular tanks is simulated by using a level set method based on the finite volume method. In order to examine the effect of natural frequency modes on liquid sloshing, we considered a wide range of frequency ratios (0.5 ≤ fr ≤ 3.2). The frequency ratio is defined by the ratio of the excitation frequency to the natural frequency of the fluid, and covers natural frequency modes from 1 to 5. When fr = 1 which corresponds to the first mode of the natural frequency, strong liquid sloshing reveals roof impact, and significant forces are generated by the liquid in the tank. The liquid flows are mainly unidirectional. Thus, the strong bulk motion of the fluid contributes to a higher elevation of the free surface. However, at fr = 2 the sloshing is considerably suppressed, resulting in a calm wave with relatively lower elevation of the free surface, since the waves undergo destructive interference. At fr = 2 the lower peak of the free surface elevation occurs. At higher modes of fr3, fr4, and fr5 the free surface reveals irregular deformation with nonlinear waves in every case. However, the deformation of the free surface becomes weaker at higher natural frequency modes. Finally, 3-D simulations confirm our 2-D results.

Open access
The Influence of Glycemic Control on Heart Rate Variability and Blood Pressure in Adult Patients with the Type 1 Diabetes

Abstract

Background and aims: to identify heart rate variability (HRV) and blood pressure (BP) in patients with type 1 diabetes depending on the duration of disease and glycemic control.

Materials and methods: 43 patients were examined. All patients were divided into 2 groups according to the level of НвА1с: group 1 (n=21) with НвА1с ≤ 7.5% and group 2 (n=22) with НвА1с > of 7.5%. All patients underwent daily monitoring of electrocardiogram Holter and ambulatory BP monitoring within 24 hours in parallel with long term monitoring of blood glucose.

Results: Hyppoglycemia is characterized by significant decrease root mean square difference between adjacent RR intervals (RMSSD) (r = −0.531; p = 0.003) and number of consecutive RR intervals, the difference between them is more than 50 ms expressed as a percentage of total number of RR-intervals (pNN50%) (r = the −0.503; p = 0.005) and increase of Low Frequency/High Frequency Ratio (LF/HF) (r = 0552; p = 0.002). Patients with hypoglycemia had significantly higher daily diastolic pressure area index (DPAI24) (p = 0.016), and daily diastolic pressure time index DPTI24 (p = 0.025).

Conclusion: our findings demonstrate the need to reduce the frequency of hypoglycemia episodes in patients with T1DM.

Open access
The Influence of Unplanned Technical Services on Aircraft Fleet's Management

The Influence of Unplanned Technical Services on Aircraft Fleet's Management

In this paper the influence of introduced airworthiness directives and bulletin services on in-service process were described. During the in-service time two main states can be distinguished: exploitation and service. An aircraft is an example of technical object in which exists strong relations between these states. The main aim of any airline is to maximize its profits. Such an optimization is affected by several factors. They are mainly connected to the service state (service cost minimization) as well as to the exploitation state (flight interval minimization, frequency ratio maximization, work waiting time minimization, etc.)

Open access
Response of Non-Linear Shock Absorbers-Boundary Value Problem Analysis

Abstract

A nonlinear boundary value problem of two degrees-of-freedom (DOF) untuned vibration damper systems using nonlinear springs and dampers has been numerically studied. As far as untuned damper is concerned, sixteen different combinations of linear and nonlinear springs and dampers have been comprehensively analyzed taking into account transient terms. For different cases, a comparative study is made for response versus time for different spring and damper types at three important frequency ratios: one at r = 1, one at r > 1 and one at r <1. The response of the system is changed because of the spring and damper nonlinearities; the change is different for different cases. Accordingly, an initially stable absorber may become unstable with time and vice versa. The analysis also shows that higher nonlinearity terms make the system more unstable. Numerical simulation includes transient vibrations. Although problems are much more complicated compared to those for a tuned absorber, a comparison of the results generated by the present numerical scheme with the exact one shows quite a reasonable agreement

Open access
An Improved Feature Extraction Method for Rolling Bearing Fault Diagnosis Based on MEMD and PE

Abstract

The health condition of rolling bearing can directly influence to the efficiency and lifecycle of rotating machinery, thus monitoring and diagnosing the faults of rolling bearing is of great importance. Unfortunately, vibration signals of rolling bearing are usually overwhelmed by external noise, so the fault frequencies of rolling bearing cannot be readily obtained. In this paper, an improved feature extraction method called IMFs_PE, which combines the multivariate empirical mode decomposition with the permutation entropy, is proposed to extract fault frequencies from the noisy bearing vibration signals. First, the raw bearing vibration signals are filtered by an optimal band-pass filter determined by SK to remove the irrelative noise which is not in the same frequency band of fault frequencies. Then the filtered signals are processed by the IMFs_PE to get rid of the relative noise which is in the same frequency band of fault frequencies. Finally, a frequency domain condition indicator FFR(Fault Frequency Ratio), which measures the magnitude of fault frequencies in frequency domain, is calculated to compare the effectiveness of the feature extraction methods. The feature extraction method proposed in this paper has advantages of removing both irrelative noise and relative noise over other feature extraction methods. The effectiveness of the proposed method is validated by simulated and experimental bearing signals. And the results are shown that the proposed method outperforms other state of the art algorithms with regards to fault feature extraction of rolling bearing.

Open access