The assessment of mooring line damping for offshore structures

With increasing water depth of oil and gas exploration, greater importance has been attached to the damping force from mooring systems. The effect is significantly important to slow drift motion of the floating structure, and it is also coupled with its motions. Coupled analysis is thus preferred to be applied to estimate the floating structure motions and to calculate the mooring system response, especially for offshore structures in deep-water.;In this study, the aim is to achieve a better understanding of mooring line induced damping estimation. Drag forces normal to the mooring line due to the motion of the mooring line through the water, are the main source of hydrodynamic damping of the mooring line. A method of energy dissipation based on the mooring line dynamic response obtained by Orcaflex is developed. The validation is established through two types of mooring lines in shallow water and deep water.;The present approach shows a good agreement with the published results, but with two exceptions. One is for the mooring line oscillated by a very slow LF motion in shallow water, when the hydrodynamic damping is very small. Another one is for the wire mooring line oscillated by WF motion in deep water, the result shows significant discrepancy with that from the quasi-static method.;Then a non-dimensional analysis is completed, due to the strong complexity of the mooring line induced damping. The effects of the factors can be divided into three groups: first, the effects from pretension and scope are related to the geometry changes of the mooring line; second, the oscillation, current velocity and drag coefficient make contributions to the drag forces of mooring line directly; and the last, the effects of stiffness and seabed friction which, it was found, can be neglected.;In order to experimentally investigate the chain behaviour moving in water, a series model tests for the damping characteristics of a single chain line is implemented through oscillation tests of various parameters. The drag coefficient ( C D ) variations with different Reynold ( Rn ) and KC numbers are investigated. The drag coefficients in this study range from 1.5 to 4.0, which is case-dependent, because both Reynold ( Rn ) and KC number affect them.;With the increase of KC number, the drag coefficient shows a decrease with exceptions occurring in low KC cases. In addition, it is shown that the chain segments near the fairlead and touch down area are most sensitive to the drag coefficient, which is consistent with the velocity distribution along the mooring line.;Finally, the validation is established by comparing the results of experimental tests and numerical simulations. Based on the assessment of drag coefficient from the scaled experimental investigation, numerical simulations of estimated drag coefficient are carried out within Orcaflex. A good agreement is achieved between the numerical calculations and experimental measurements, which illustrates that the present method can be applied for mooring line damping estimation. Meanwhile, the effects of the amplitude and frequency of the oscillation are studied.With increasing water depth of oil and gas exploration, greater importance has been attached to the damping force from mooring systems. The effect is significantly important to slow drift motion of the floating structure, and it is also coupled with its motions. Coupled analysis is thus preferred to be applied to estimate the floating structure motions and to calculate the mooring system response, especially for offshore structures in deep-water.;In this study, the aim is to achieve a better understanding of mooring line induced damping estimation. Drag forces normal to the mooring line due to the motion of the mooring line through the water, are the main source of hydrodynamic damping of the mooring line. A method of energy dissipation based on the mooring line dynamic response obtained by Orcaflex is developed. The validation is established through two types of mooring lines in shallow water and deep water.;The present approach shows a good agreement with the published results, but with two exceptions. One is for the mooring line oscillated by a very slow LF motion in shallow water, when the hydrodynamic damping is very small. Another one is for the wire mooring line oscillated by WF motion in deep water, the result shows significant discrepancy with that from the quasi-static method.;Then a non-dimensional analysis is completed, due to the strong complexity of the mooring line induced damping. The effects of the factors can be divided into three groups: first, the effects from pretension and scope are related to the geometry changes of the mooring line; second, the oscillation, current velocity and drag coefficient make contributions to the drag forces of mooring line directly; and the last, the effects of stiffness and seabed friction which, it was found, can be neglected.;In order to experimentally investigate the chain behaviour moving in water, a series model tests for the damping characteristics of a single chain line is implemented through oscillation tests of various parameters. The drag coefficient ( C D ) variations with different Reynold ( Rn ) and KC numbers are investigated. The drag coefficients in this study range from 1.5 to 4.0, which is case-dependent, because both Reynold ( Rn ) and KC number affect them.;With the increase of KC number, the drag coefficient shows a decrease with exceptions occurring in low KC cases. In addition, it is shown that the chain segments near the fairlead and touch down area are most sensitive to the drag coefficient, which is consistent with the velocity distribution along the mooring line.;Finally, the validation is established by comparing the results of experimental tests and numerical simulations. Based on the assessment of drag coefficient from the scaled experimental investigation, numerical simulations of estimated drag coefficient are carried out within Orcaflex. A good agreement is achieved between the numerical calculations and experimental measurements, which illustrates that the present method can be applied for mooring line damping estimation. Meanwhile, the effects of the amplitude and frequency of the oscillation are studied

Mianyang: The Legacy of State Socialism and Local Construction

This paper provides an account of the development trajectory of Mianyang City, a prefecture-level administration in the Southwest of China, as relevant to the Chinese government’s two major attempts to develop the country’s vast West, i.e. the ‘Third Front Construction Project’ and the ‘Open Up the West’ Campaign. Based on empirical research, the author argues that the past of socialist construction under Mao should not be dismissed when one tries to understand China’s current prosperity. This paper also provides a local perspective to examine the rather under-viewed development scheme—the ‘Third Front Construction Project’. Although seen as a failed endeavour at macro level, the project’s impacts on local development could be positive and constructive

Performance analysis of spatial modulation aided NOMA with full-duplex relay

A spatial modulation aided non-orthogonal multiple access with full-duplex relay (SM-NOMA-FDR) scheme is proposed for the coordinated direct and relay transmission in this paper. Specifically, the signal of the near user is mapped to an M-ary modulated symbol and the signal of the far user is mapped to an SM symbol. The base station first transmits signals to the near user and relay via SM-NOMA, and then the relay decodes and retransmits the signal of the far user. An SM-assisted FDR is used in this scheme to improve the spectral efficiency while reducing energy consumption and making full use of the antenna resources at the relay, since SM only activates one antenna in each transmission. We derive the ergodic capacity and bit error rate of the proposed scheme over independent Rayleigh fading channels. Numerical results validate the accuracy of the theoretical analysis and show the superior performance of the proposed SM-NOMA-FDR scheme

Artificial noise assisted secure interference networks with wireless power transfer

Interference alignment (IA) is a remarkable technique to manage interference, and artificial noise (AN) can be utilized to combat one main threat of security, passive eavesdropping. Nevertheless, in the existing schemes AN is only eliminated at each legitimate receiver, which is a waste of energy. In this paper, we propose an AN assisted IA scheme with wireless power transfer (WPT). In the proposed scheme, AN is generated by each transmitter along with data streams, which can disrupt the eavesdropping without introducing any additional interference. Due to the fact that the transmit power of AN should be high enough to ensure the security, energy harvesting (EH) is also performed in the scheme. A power splitter is equipped at each receiver, which can divide the received signal, including desired signal, interference and AN, into two parts: one for information decoding (ID) and the other for EH. To optimize the antieavesdropping performance, the total transmit power of AN is maximized by jointly optimizing the information transmit power and the coefficient of power splitting, with the requirements of signal-to-interference-plus-noise ratio (SINR) and harvested power satisfied. Due to the non-convex nature of the problem, a suboptimal solution is also derived to calculate the closed-form solutions with extremely low computational complexity. Extensive simulation results are presented to show the effectiveness of the proposed scheme

Privacy preservation via beamforming for NOMA

Non-orthogonal multiple access (NOMA) has been proposed as a promising multiple access approach for 5G mobile systems because of its superior spectrum efficiency. However, the privacy between the NOMA users may be compromised due to the transmission of a superposition of all users’ signals to successive interference cancellation (SIC) receivers. In this paper, we propose two schemes based on beamforming optimization for NOMA that can enhance the security of a specific private user while guaranteeing the other users’ quality of service (QoS). Specifically, in the first scheme, when the transmit antennas are inadequate, we intend to maximize the secrecy rate of the private user, under the constraint that the other users’ QoS is satisfied. In the second scheme, the private user’s signal is zero-forced at the other users when redundant antennas are available. In this case, the transmission rate of the private user is also maximized while satisfying the QoS of the other users. Due to the nonconvexity of optimization in these two schemes, we first convert them into convex forms and then, an iterative algorithm based on the ConCave-Convex Procedure is proposed to obtain their solutions. Extensive simulation results are presented to evaluate the effectiveness of the proposed scheme

Wave-riding and wave-passing by ducklings in formation swimming

It has been commonly observed on open waters that ducklings/goslings follow their mothers in a highly organized formation. The questions arise: (1) why are they swimming in formation? (2) what is the best swimming formation? (3) how much energy can be preserved by each individual in formation swimming? To address these questions, we established a simplified mathematical and numerical model and calculated the wave drag on a group of waterfowl in a swimming formation. We observed two new and interesting findings: wave-riding and wave-passing. By riding the waves generated by a mother duck, a trailing duckling can obtain a significant wave-drag reduction. When a duckling swims at the ‘sweet point’ behind its mother, a destructive wave interference phenomenon occurs and the wave drag of the duckling turns positive, pushing the duckling forward. More interestingly, this wave-riding benefit could be sustained by the rest of the ducklings in a single-file line formation. Starting from the third one in a queue, the wave drag of individuals gradually tended towards zero, and a delicate dynamic equilibrium was achieved. Each individual under that equilibrium acted as a wave passer, passing the waves’ energy to its trailing one without any energy losses. Wave-riding and wave-passing are probably the principal reasons for the evolution of swimming formation by waterfowl. This study is the first to reveal the reasons why the formation movement of waterfowl can preserve individuals’ energy expenditure. Our calculations provide new insights into the mechanisms of formation swimming

Dauricine Attenuates Vascular Endothelial Inflammation Through Inhibiting NF-κB Pathway

Endothelial cells are the fundamental components of blood vessels that regulate several physiological processes including immune responses, angiogenesis, and vascular tone. Endothelial dysfunction contributes to the development of various diseases such as acute lung injury, and endothelial inflammation is a vital part of endothelial dysfunction. Dauricine is an extract isolated from Menispermum dauricum DC, a traditional Chinese medical plant that can be used for pharyngitis. In this work, we found that IL-1β-induced overexpression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin was inhibited by dauricine in primary human umbilical vein endothelial cells (HUVECs). Correspondingly, adhesion of human acute monocytic leukemia cell line (THP-1) to HUVECs was decreased by dauricine. Further studies showed that dauricine inhibited the activation of nuclear factor-κB (NF-κB) pathway in HUVECs stimulated with IL-1β. In vivo, dauricine protected mice from lipopolysaccharide (LPS)-induced acute lung injury. In lung tissues, the activation of NF-κB pathway and the expression of its downstream genes (ICAM-1, VCAM-1, and E-selectin) were decreased by dauricine, consistent with what was found in vitro. In summary, we concluded that dauricine could alleviate endothelial inflammation by suppressing NF-κB pathway, which might serve as an effective candidate for diseases related with endothelial inflammation

Systematic analysis and case series of the diagnosis and management of trichilemmal carcinoma

BackgroundTrichilemmal carcinoma (TLC) is a rare malignant cutaneous adnexal neoplasm, with no relatively comprehensive research.ObjectiveThe aim of this study is to perform an updated statistical analysis so as to better understand TLC’s epidemiology, clinical features, diagnosis, and treatment.MethodsThe diagnosis and treatment of three TLC cases in our department were summarized. Then, all TLC cases published in the literature were retrieved for a comprehensive analysis, followed by the analysis of global trends and regional distribution, demographic characteristics, clinical features, pathogenesis, histopathological features, and treatment and prognosis of TLC.ResultsOf the 231 cases, the incidence of TLC has shown an upward trend recently, especially in China, in Asia. The susceptible population is men aged 60–80 and women over 80, and the most prone location is head and neck. The phenotype of TLC is not always typical and may be misdiagnosed because of the coexistence of other diseases. There is a linear relationship between the diameter and its duration or thickness. UV, locally present skin lesions, trauma, scarring, organ transplantation, and genetic disorders may trigger the occurrence of TLC. Periodic acid–Schiff staining and CD34, but not Epithelial Membrane Antigen (EMA), were helpful in the diagnosis of TLC. Although effective, surgical excision and Mohs micrographic surgery need further improvement to reduce recurrence of TLC. Carcinoma history is an independent risk factor for TLC recurrence.LimitationsThe limitation of this study is the lack of randomized controlled trial on TLC treatment and recurrence.ConclusionTLC has the possibility of invasive growth and recurrence, especially in patients with longer duration and carcinoma history