Micro-FTIR spectroscopy of liptinite macerals in coal

Reflectance FTIR microspectroscopy has been used to investigate the chemical structure of the liptinite macerals, alginite, bituminite, sporinite, cutinite and resinite in bituminous coals of Carboniferous to Tertiary age. In comparison with the spectra of vitrinite in the same coals, the micro-FTIR spectra of liptinite macerals are characterized by stronger aliphatic CH_x absorptions at 3000–2800 and 1460–1450 cm⁻¹, less intense aromatic C=C ring stretching vibration and aromatic CH out of plane deformation at 1610–1560 and 900–700 cm⁻¹ respectively and various intense acid C=O group absorptions at 1740–1700 cm⁻¹. The peaks at 1000–900 cm⁻¹ due to aliphatic CH₂ wagging vibrations in olefins and at 730–720 cm⁻¹ due to CH₂ rocking vibration in long chain aliphatic substances ([CH₂]_n, n≥4), are characteristic of liptinite macerals. Collectively the micro-FTIR spectral characteristics indicate that liptinite is composed of greater numbers of long chain aliphatics, fewer aromatics and a broader range of oxygen-containing groups than other macerals. Marked differences exist in micro-FTIR spectra within the liptinite maceral group. Alginite has the strongest aliphatic and least aromatic absorptions followed by bituminite, resinite, cutinite and sporinite. The aliphatic components in alginite are the longest chained and least branched whereas those in sporinite are the shortest chained and most branched. Bituminite, resinite and cutinite are intermediate. Notable differences in micro-FTIR spectra of individual liptinite macerals, such as intensities and peak locations of aromatic C=C in alginite, C=O groups in bituminite and resinite and substituted aromatic CH and C–O–C groups in cutinite and sporinite, also exist, which are attributed to differences in depositional environments or biotaxonomy.     

Forced transverse vibrations of a simply supported rectangular orthotropic plate in the case where the force acts over a plate subdomain

The present study deals with the exact solution of the title problem in the case where a uniformly distributed p₀ cos ωt-type force acts over a rectangular portion of the plate. The problem is of interest in naval and ocean engineering systems where a motor or an engine mounted on a plate or slab induces a dynamic excitation over a finite area. Mechanical designers commonly consider the problem from the point of view of a concentrated dynamic or static force. On the other hand, modelling the structural system as an orthotropic element is of considerable interest in ocean and naval design in view of the ever-increasing use of composite materials and also of the anisotropic characteristics often induced by metallurgical processes.     

Fatigue damage in randomly vibrating jack-up platforms under non-Gaussian loads

The problem of fatigue damage estimation of ageing jack-up platforms is considered, using theories of random processes. The sea-wave excitations are modelled as stationary, Gaussian random processes, with specified power spectral density function. The loads acting on the structure due to the sea waves is calculated using Morison’s equation and are therefore non-Gaussian whose probabilistic properties are not available in explicit form. Assuming linear structure behaviour, the probabilistic properties of the structure response are determined using theories of random vibrations. The simple peak counting method is adopted for estimating the mean fatigue damage. This requires knowledge of the joint probability density function of the structure response and its first and second time derivatives, at the same time instant. A methodology has been presented for developing analytical expressions for this joint pdf. This requires evaluation of multidimensional integrals. A recently developed computational algorithm is presented to deal with integrals for which derivation of closed form analytical expressions may not be feasible. The methodology proposed in this paper provides an alternative and computationally cheaper technique for estimating the fatigue damage in comparison to the Monte Carlo simulation procedure. Numerical results have been presented for illustration of the proposed methodology.     

Appraisal of ground vibration from civil engineering construction

Amplitude and style of ground vibration from two types of pile driving — vibrodriver (periodic) and drophammer (transient) — are considered for the analysis of deformation in a portal frame structure. It is argued that the three-dimensional character of the vibration should be determined in the form of a resultant vector and this requires the measurement of vibration in three directions at right angles together with information on the sense of the motion along each orthogonal axis of vibration. Such resultant vector data during the period of vibration are best processed and presented in the style of a suite of hemispherical projections that comprise upper and lower hemisphere forms, respectively embodying components of upward and downward vibrational motion. It is shown that analysis for the dynamic stability of a simple block foundation is assisted by reference to the hemispherical projection representation and by the use of ground surface acceleration data.     

Dynamic Response of Footing and Machine with Spring Mounting Base

The effect of the spring mounting cushion inserted in between a machine base and its concrete footing has been examined experimentally by conducting a number of block vibrations tests. The machine was subjected to steady state vertical harmonic loading. Experiments were performed with two different stiffness values of the spring mounting cushion. The employment of the spring mounting cushion, with the stiffness much smaller than that of soil strata, offers a drastic reduction in the resonant displacement amplitudes of the footing. It also results in a significant decrease in the resonant frequency of the foundation. The resonant displacement amplitudes of both the footing and the machine were found to become lower with the smaller stiffness value of the springs. The resonant frequency for the machine base, in all the experiments, was found to be invariably the same as that of the footing.     

Flow induced vibrations of a sharp edge square cylinder in the wake of a circular cylinder

The response of an oscillating circular cylinder at the wake of an upstream fixed circular cylinder was classified by different researchers as galloping, wake induced galloping or wake induced vibration. Furthermore it is already known that a sharp edge square cylinder would undergo galloping if it is subjected to uniform flow. In this study the influence of the wake of a fixed circular cylinder on the response of a downstream square cylinder at different spacing ratios (S/D = 4, 8, 11) is experimentally investigated. The subject appears not to have received previous attention. The lateral displacements, lift forces and the pressure data from gauges mounted in the wake of the oscillating cylinder are recorded and analyzed. The single degree of freedom vibrating system has a low mass-damping parameter and the Reynolds number ranges from 7.7 × 10² to 3.7 × 10⁴.In contrast to that for two circular cylinders in tandem arrangement, the freely mounted downstream square cylinder displays a VIV type of response at all spacing ratios tested. There is no sign of galloping or wake induced galloping with the square cylinder. With increase at the spacing ratio the cross-flow oscillations decrease. It is shown that the vortices arriving from the upstream fixed circular cylinder play a major role on the shedding mechanism behind the downstream square cylinder and cause the square cylinder to shed vortices with frequencies above Strouhal frequency of the fixed square cylinder (St = 0.13). The VIV type of oscillations in the downstream square cylinder is most probably caused by the vortices newly generated behind the square cylinder.     

Prediction of peak particle velocity using multi regression analysis: case studies

Ground vibrations produced from blasting operations cause structural vibrations, which may weaken structure if it occurs at the resonant frequency. Measurable parameters associated with ground vibrations are peak particle velocity (PPV), amplitude and dominant frequency (frequency of highest PPV amongst translational, vertical and horizontal vibrations). In this paper, an attempt is made to correlate measurable parameters associated with ground vibrations with scaled distance. Using the correlated data, it was found that a predictor equation can be determined for the amplitude and PPV, but not for dominant frequency as it is dynamic and depends upon infinitesimal changes that occur within a number of other parameters. Another analysis of the same is made using multiple linear regression analysis. This included predicting the PPV using scaled distance, maximum charge per delay, amplitude as predictors. A considerable improvement is seen in the prediction on adding the interaction of the predictors in multiple regressions. A comparison of different combination of predictors is made so as to assess the best combination giving the best R² value for the given mine. Frequency is also plotted using the aforementioned method. However, it was found that the dominant frequency cannot be predicted with high accuracy even with this method.     

The importance of site-specific characters in prediction models for blast-induced ground vibrations

The aim of this study is to show the effect of geological factors in predicting the level of blast-induced ground vibrations. The site-specific character of ground must be involved in the prediction models especially if the ground conditions have a variable character like in this case. But in a blasting environment, this is only possible by using an empirical way. Towards this aim, an in-situ experimental study in a highly jointed sandstone quarry was carried out to incorporate the variable conditions into the prediction models. Therefore, 60 shots were organized and their ground vibrations monitored in two different directions to compare the results. These shots were normal production shots involving the true technological properties as well as geological properties into the prediction model. Based on these, the empirical relations between particle velocity, the amount of explosive and distance have been developed. The results show that the performances of these estimations depend on the site-specific character of these empirical relations. The best prediction was obtained with only 2.08% error level provided that the true technological and geological properties are involved.     

Simulating fundamental and higher harmonic VIV of slender structures

Vortex-induced vibrations (VIV) of slender marine structures are complicated response processes, where a number of distinct frequency components might be simultaneously active. These are categorized as fundamental and higher harmonics respectively, where the latter can have a tremendous impact on the fatigue life. The present work proposes a method for time domain simulation of such multi-frequency response, by introducing a higher harmonic load term to a pre-existing semi-empirical hydrodynamic force model. Forced motion tests of a circular cylinder were simulated to experimentally and qualitatively validate the fluid-structure energy transfer. Next, the model was used to predict the response of a tension dominated riser in uniform current, for 22 velocities in the range 0.3 m/s to 2.4 m/s. The empirical input was chosen to give an average best fit with respect to the cross-flow strain measurements, which allowed dominating frequencies, fatigue damage, higher harmonics and response variability to be predicted with a high level of realism. Same set of empirical coefficients was subsequently used to predict VIV of three additional flexible pipe experiments in uniform flow, with significant differences in structural properties. The results were satisfactory for all cases, but could be improved by moderate changes to the empirical input.