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In this paper an improved mathematical model of a hydro-pneumatic tensioner (HPT) system for top tensioned riser (TTR) is derived by consideration of friction, mass of piston and piston rod, tension loss in hydraulic oil piping, and compressibility of hydraulic oil. The vertical motion of the riser string is also considered. Subsequently, the proposed detailed model and the conventional simplified model are comparatively studied. Finally, the tension characteristic and performance parameters of the HPT are analyzed based on the proposed model. Results show that the conventional simplified model indeed overestimates the tension of tensioner as it neglects some performance parameters resulting in tension loss. The diameters of piston and piston rod and the initial pressure of high pressure (HP) gas have the most significant influence on the tension of the tensioner. The initial volume of HP gas and the initial pressure of low pressure (LP) gas also have some impact. The influence of the initial volume of LP gas and the inner diameter and length of the piping is relatively small. The research has some reference value for HPT and TTR design.

A three-dimensional (3D) finite element analysis (FEA) model of top-tensioned riser (TTR) with hydropneumatic tensioner is proposed in this work. First, the tension calculation equation of the hydropneumatic system is derived, and the kinematic relationship of the platform–tensioner–riser system is established. Second, a 3D FEA model is established based on the FEA code ABAQUS, considering the actual riser string configuration and the Christmas tree. At last, four kinds of tensioner models, i.e., a constant vertical tension model, a conventional simplified model, a linear spring–damper model, and a nonlinear spring–damper model, are compared and analyzed in this study. Results show that the constant vertical tension model is not recommended as it cannot reflect the actual tension in the tensioner and the response of the TTR. The conventional simplified model indeed overestimates the tension of tensioner and may lead to inaccurate estimation results of the TTR response. The linear model is applicable when the environmental condition is relatively mild, but it is strongly recommended to use the nonlinear model especially in harsher environmental conditions.

Attempts on the preparation of elastic sorbents from waste rubber tyres, for removal of biobutanol from ferment liquor extracts, using low-distribution apolar solvent like n-heptane have been discussed. The main factors in preparation of useful sorbents are the type of the waste tyre, the type of the sulphonating agent, and the reaction conditions. The waste tyres containing large amount of styrene proved to be useful base material for preparation of elastic sorbent with concentrated sulphuric acid as sulphonation agent. The common mixed waste tyres resulted in elastic sorbents with lower absorbing capacities. Therefore, the styrene containing ones were studied over a wide range of the sulphonation conditions., European Chemical Bulletin, Vol 5, No 9 (2016): European Chemical Bulletin

Biobutanol (n-C4H9OH, available as fermentation product of various carbohydrate derivatives obtained from different resources of agricultural production such as crops and wastes) is one of the most promising biofuels in the near future. It can be produced by the so-called ABE (acetone-butanol-ethanol) type anaerobic fermentation discovered by Pasteur [1, 2] and industrialized by Weizmann [3]. Main problems associated with industrial production of biobutanol include high energy demand for processing of dilute ferment liquors and high volume of wastewater. A bioreactor with a volume of 100 m3 produces at 90% filling ratio 1053 kg of butanol, 526 kg of acetone and 175 kg of ethanol together with 2900 kg of carbon dioxide, 117 kg of hydrogen and 84150 kg of wastewater. Efforts to increase productivity and decrease production costs resulted in many new methods. This chapter summarizes some selected results on methods of biobutanol production.

A method to evaluate the probability of failure of a failure path leading to fatigue collapse of an offshore structure is presented. The failure path is modeled by a number of failure elements, which represent the fatigue-sensitive joints in the structure, connecting in parallel and failing in sequence. The probability of failure of the parallel system is calculated by using first-order second-moment method. The formulation is further improved by considering the probability of occurrence of a specified sequence in which the failure elements fail. The method can be employed both in searching for important failure paths and in evaluating the probability of failure of the whole structure in systems fatigue reliability analysis of offshore structures.