Mathematical Modelling and Dynamic Analysis of an Offshore Drilling Riser

In this paper, a dynamic model of an offshore drilling riser is developed based on the Hamilton principle. The developed dynamic model is transformed into a finite element model by introducing an approximate solution which chooses the Hermite cubic interpolation function of bending beam element as the shape function. Thereafter, the standard Newmark integration is applied to numerically simulate the dynamic responses of offshore drilling risers with varied system parameters, including the length of riser, top tension ratio, and buoyant factor. Based on the results of numerical simulation, under the influences of sea wind, sea current, and the periodic excitation of sea wave, the offshore drilling riser experiences a fast lateral deflection phase in the beginning, a reciprocating deflection phase in the following long duration, and then, a periodic oscillation when it reaches the dynamic stable condition, respectively. The riser system working in deeper water with a higher top tension ratio and a lower buoyant factor shows more controllable vibration and less lateral deflection.

Design of A New Hydraulic Accumulator for Transient Large Flow Compensation

Hydraulic accumulators are widely used in industry due to their ability to store energy and absorb fluid shock. Researchers have designed kinds of novel accumulators with better performance in these specific areas. However, the pressure in these accumulators decreases significantly when the fluid oil is continuously supplied from the accumulator to the hydraulic system. This limitation leads to a transient large pressure drop, especially in a small hydraulic system with varied working frequency. In this research, a combined piston type accumulator is proposed with a relatively steady pressure property. The gas chamber and the fluid chamber are separated by a cam mechanism. By using the nonlinear property of the cam mechanism, the nonlinear relationship between the pressure and the volume of the gas can be offset. Hence, the fluid pressure can be maintained in a relatively steady range. The defect of the traditional accumulator in the frequency varied system is analyzed in detail. Then, the structure of the new accumulator is proposed and modeled based on the traditional piston type accumulator. The mathematical equation of the cam mechanism is built under the assumption that the nitrogen gas works in an adiabatic process. A simulation system based on the Amesim platform is constructed, and mathematic equations of the system are given. Preliminary experiments are conducted to evaluate the performance of the new accumulator. The comparison results show that the adaptability of the new accumulator is obviously larger than that of the traditional accumulator in a frequency varied system.

Demand response-based dynamic dispatch of microgrid system in hybrid electricity market

Purpose Technological development has not only helped in effective integration of renewable sources but also made it possible for consumers to participate in system operation. Different market players are coming up in the electricity market, microgrid being one of them. Thus, this paper aims to investigate consumers’ role in the dispatch of a microgrid system that has a hybrid market structure under varied system conditions. Design/methodology/approach The mathematical model developed has been solved by the CONOPT solver in the GAMS optimization tool. GAMS-MATLAB interfacing is done to obtain solutions. Findings The problem formulated shows the effect of consumers in dispatch and overall operational cost. Consumers’ participation has been proposed through a quadratic cost function. The system operation under pool and bilateral contracts has been investigated. It shows that proper incentives to the consumers can help in reduction and effective management of the demand, carbon emission and overall system operational cost. Originality/value This paper considers the hybrid market structure to find the load dispatch in a microgrid system. The participation of consumers in the microgrid system has been implemented considering variations in wind power, solar power and load. The power exchange between the grid and microgrid system has been modeled showing the contribution of the consumers in system operation.

It takes all kinds: understanding diverse entrepreneurial ecosystems

Purpose This paper aims to explore the dynamics of entrepreneurial ecosystems with both rural and urban features, as well as the varied system requirements of differing types of entrepreneurs within such an ecosystem. Design/methodology/approach Using a mixed-methods case study approach, the study examined the Roanoke–Blacksburg region in western Virginia. Researchers conducted quantitative analysis of entrepreneurial metrics and network relationships, as well as qualitative analysis of data collected through entrepreneur surveys and stakeholder interviews. Findings Findings suggest entrepreneurs of different types faced disparate challenges and uneven access to resources and networks. Innovation-driven “gazelle” enterprises (IDEs) had numerous growth-related resource needs, including angel, venture and scale-up funding; prototyping equipment and facilities; and translational research by local universities. Small- and medium-sized enterprises (SMEs) required more entrepreneurial education programming, subsidized main street office space and clearer pathways through the government regulatory system. A key finding was also concerned with the different ways by which IDEs and SMEs accessed key resources within the ecosystem, illustrated through social network analysis, and supported through qualitative feedback. Research limitations/implications Study findings were limited by a relatively low survey response rate from some entrepreneur demographic segments, particularly minorities. Originality/value The study represents an in-depth, multi-methods approach that offers insight into two under-researched areas in the ecosystem literature: the dynamics of urban – rural ecosystems and the varied system requirements of different entrepreneur types. The paper includes three overarching recommendations for policy and practice: improved collection and sharing of regional metrics; differentiated approaches to entrepreneurial support based on entrepreneur type; and enhanced efforts to advance inclusive entrepreneurship.

Varied System Geometry and Noise Implementation Applied to Nonlinear Model Tracking

The following is a study in nondestructive health monitoring wherein the physical system being studied is excited near resonance and mapped through its transition from health to failure. The system studied is a slender cantilever beam excited near its second natural frequency. For this study, no damage is initiated and so it comes in contrast to the more common techniques where the damage type and location allow for an element of control in instrumentation and analysis. The method implemented allows for health monitoring in situ, so it does not require stopping the event to do system testing, as is the case for many common approaches. Moreover, this method, implements a nonlinear model of the physical system, avoiding false flags that can be problematic for linear-based methods when applied to systems demonstrating healthy nonlinear behavior. The method, known as Nonlinear Model Tracking (NMT) uses a theoretical model of the system that includes a cubic nonlinear stiffness term. Experimentally, stimulus and response data are collected and used in Continuous Time-based system identification to estimate the system’s nonlinear stiffness coefficient. Harmonic fitting to the two recorded data sets allow for robust performance in the presence of noise and variations in the system geometry show that, even in cases where the nonlinear model is not accurate for the system being studied, the method works consistently. In many of the tests the method gives premonition of failure hours in advance, which would in many real world scenarios, gives users time to react safely. This study focusses particularly on varying inputs to the system and attempting to map changes in parameter estimation to stages of damage.

‘THESE ARE THE TONES COMMONLY USED’: THE TONOS DE CANTO DE ÓRGANO IN SPANISH BAROQUE MUSIC THEORY

In the course of the seventeenth and eighteenth centuries, composers and music theorists moved away from the system of the eight ecclesiastical modes that had been elaborated by medieval theorists and was later applied to polyphonic music (including the varied system extended to twelve modes in the sixteenth century) towards modern bimodal tonality. Although several modal systems coexisted within this time period, a distinct variant of the eight modes, often known in modern scholarship as the church keys, developed as a practical solution to problems associated with the performance of psalms and other recited formulas (especially the Magnificat) in alternatim practice between the choir in plainchant and the organ. A scarcity of research on this topic within investigations of Spanish music prompts us to outline an introduction to a matter so crucial to music theory of the baroque period in Spain. Thus we present an overview of the treatment of the church keys or tones in Spanish treatises over a long period of two centuries, and focus briefly on particular contributions made by individual authors.

An attempt to interpret some electrophysiological phenomena in plants in terms of Pflüger's laws

In <i>Lupinus</i> shoots an electrical stimulus (DC) produces a voltage wave identical in character to the action potential wave (AP) in stimulated simple plant cells or in nerves and muscles. This fact served as basis for investigations undertaken to establish whether the dependences, known in neurophysiology as Pflüger's laws of contraction, are also true in the case of plant stimulation. Experiments were performed both in a system analogous to that of Pflüger (Variant I), and in more varied system (Variant II). The validity of these laws in plants has been fully confirmed. Other investigations (Paszewski and Zawadzki 1973a, 1973b, 1974) showed that such laws as the strength-duration relation and the all-or-nothing law prove correct in plants.

Taking Control from Above: The Rationalization of Schooling in the Progressive Era

The progressive era saw a massive rationalization of American schooling; its imprint stretches into the present day. Drawing on the ideas of (then) modern management techniques, a heterogeneous group of elites transformed a localized and highly varied system of schooling into what David Tyack famously called “the one best system.” This movement both created the form and structure of the school system that would profoundly shape later events and, as the benefit of hindsight makes evident, was driven by much the same underlying vision and set of forces that recurred in subsequent eff orts to rationalize schools. What motivated the Progressive Era transformation of schooling was the image of a rationally organized system of production. Whether in the public or private sector, the hallmarks of this approach are distinct organizational categories of work, clear delineation of roles and responsibilities, specialization of labor, and hierarchical control of workers by more powerful superiors. In the case of the school system, this meant a shift from one-room school-houses of age-mixed groups, with instruction and assessment largely decided by the teacher, to larger schools, with grades sorted by age, Carnegie units to measure student progress, and teachers’ work structured and assessed by their administrative superiors. In the larger context, one might say that this is just the story of the shift from preindustrial to industrial society, from small-scale institutions in which social connections and individual discretion were paramount to larger social organizations with systems, roles, and rules. But there are different versions of modernity, and the American school system was decisively shaped by a particularly rationalistic, scientific, and hierarchical approach to social organization. As we will see, the Progressive Era reformers were enthralled by the emerging power of scientific and business techniques that, they were convinced, would make schooling more efficient and effective. In particular, the brand of management techniques they embraced sought to shift power upwards from frontline workers (teachers) to administrative superiors, who would set goals, prescribe desired strategies, and use an early form of assessment to hold teachers accountable for their performance.

Dynamic Analysis of a Motion Transformer Mimicking a Hula Hoop

Hula-hoop motion refers to the spinning of a ring around a human body; it is made possible by the interactive force between the moving ring and the body. Inspired by the generic concept of hula-hoop motion, this study proposes a novel motion transformer design that consists of a main mass sprung in one translational direction and a free-moving mass attached at one end of a rod, the other end of which is hinged onto the center of the main mass. It is expected that the transformer is capable of transforming linear reciprocating motion into rotational motion. In addition, the transformer could be integrated with coils, magnets, and electric circuits to form a portable energy scavenging device. A thorough dynamic analysis of the proposed transformer system is conducted in this study in order to characterize the relationships between the varied system parameters and the chance of hula-hoop motion occurrence. The governing equations are first derived with Lagrange’s method, which is followed by the search for steady-state solutions and the corresponding stability analysis via the homotopy perturbation method and the Floquet theory. Direct numerical simulation is simultaneously performed to verify the correctness of the approximate analysis. In this manner, the feasibility of the proposed design and the occurrence criteria of hula-hoop motion are assessed.