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Abstract Large floating raft vibration isolation systems (FRVISs) based on high-static-low-dynamic stiffness (HSLDS) technology offer excellent low frequency vibration isolation performance with broad application prospects. However, the design process for these complex high-dimensional coupled nonlinear systems remains poorly developed, particularly when applied for ocean-going vessels that experience rolling and pitching motions. The present work addresses this issue by establishing a six-degree-of-freedom HSLDS vibration isolation model for FRVISs composed of eight isolators, and the model is applied to fully analyze the swing stability and multidimensional vibration isolation performance of these systems. The influence of nonlinearity on the mechanical properties of the vibration isolators is analyzed more clearly by assuming that each vibration isolator realizes nonlinear HSLDS characteristics in the z direction and linear characteristics in the x and y directions. The results demonstrate that the swing displacement responses of the system are greatly reduced under weak nonlinearity, which reflects the high static stiffness and high static stability characteristics of an HSLDS system. The multidimensional vibration isolation performance of the system is evaluated according to the impacts of nonlinearity, the installation height H z of the isolators, and the relative position D r of the two middle isolators. The results of analysis demonstrate that applying a value of H z = 0 produces the best vibration isolation performance overall under strong nonlinearity by avoiding unnecessary secondary peaks in the force transmission rate under harmonic mechanical excitation and ensuring a maximum high-frequency vibration isolation effect. However, applying a weak nonlinearity is better than a strong nonlinearity if H z is not zero. In contrast, D r has little effect on the vibration isolation effect of the raft in the x, y, and z directions. Therefore, an equidistant installation with D r = 0.5 would be considered ideal from the standpoint of installation stability.

Abstract The bellows structure in an air spring can be constantly reinforced to cope with the complicated work environment, but it exerts a stronger and stronger effect on the stiffness characteristics of the air spring. However, there is not any effective way for the parameterized solution of the bellows stiffness of the air spring. With the precise transfer matrix method, the bellows stiffness characteristics of a cord-reinforced air spring with winding formation under preload conditions were analyzed in this paper. The thin-shell theory was used to solve the bellows pre-stress of the air spring under preload conditions. The pre-stress was introduced into the equilibrium equation for the bellows. Based on the geometrical and physical equations for the bellows with the complex cord winding characteristics, the precise integration method was borrowed to construct a transfer matrix for the bellows of the air spring under preload conditions. The state vector of the bellows in the air spring was solved through boundary conditions. The iteration method was adopted to develop the expression for the bellows stiffness characteristics, and combined with the theoretical model of pneumatic stiffness to solve the stiffness characteristics of the air spring. The comparison with the prototype test results verified the validity and correctness of the theoretical model. On this basis, we explored the influence of preload conditions, geometrical structure, and material characteristics on the stiffness characteristics of the air spring. The research findings will provide significant guidance for the structural design and material selection of cord-reinforced air springs with winding formation.

A precise transfer matrix was employed to analyze the free vibration characteristics of a cord-reinforced air spring with winding formation under preload conditions. The air spring was abstracted as a rotary combined shell structure with variable winding trajectory characteristics. The rotary structure, which consisted of cylindrical and toroidal shells, was analyzed for its shell pre-stress under preload conditions. The shell pre-stress was combined with the theory of thin shells to create the rotary shell vibration control equations under preload effect. The Helmholtz equation was used to analyze the influence of sound pressure inside shells under the fluid–structure coupling boundary conditions. The rotary shell transfer matrix was derived from the variable winding trajectory equation, geometrical equation, and physical equation of shells. Under the continuous conditions of state vector between the cylindrical and toroidal shells, the shells were combined into a rotary combined shell structure to obtain its total free vibration equation. The shell boundary conditions were considered to solve the natural frequency of the air spring. The calculation results were compared with the prototype test and simulation results to verify the effectiveness and accuracy of the theoretical model. On this basis, we explored the influence of axial half wave number, circumferential wave number, geometrical structure, and material characteristics on the free vibration characteristics of the air spring. The research findings would provide important and significant guidance for the structural design of cord-reinforced air springs with winding formation.

In this paper, we investigate the initial-boundary value problem of a diffusive three-species intraguild predation model, in which the variable-carrying capacity is proportional to the biotic resource and the biotic resource follows the logistic law. We mainly discuss the stabilities of the constant equilibrium points at different levels of enrichment, including the linear local, global stability and nonlinear stability. Finally, the non-existence of non-constant positive steady states has been shown. [ABSTRACT FROM AUTHOR]

Internal waves induced by an underwater self-propelled body expose its existence by changing the sea surface roughness. This study employs short-time Fourier transform to perform the time–frequency analysis on the internal wave signal captured in the experiments. Some key characteristics of the underwater self-propelled body are obtained through the spectrum analysis of the internal wave wake signal. Moreover, the influence of the interaction between the momentums induced by the propulsion and drag force is discussed. The results show that the action of the self-propelled body has varying degrees of influence on the symmetry and spatial distribution of the spectrum characteristics of the signal.

Abstract Filament-wound flexible pipes are widely used to transport fluid in pipeline systems, proved extremely useful in marine engineering. The hyperbolic flexible pipes have good vibration suppression performance, but they are easily deformed under internal pressure. This paper focuses on the stability of hyperbolic flexible pipes based on the composite Reissner shell theory and the transfer-matrix method. The nonlinear stretch of the reinforced filament and the fiber bridge effect are considered in the model. The calculation results show that a large winding angle reduces the deformation and the meridional stress. The available initial winding angle is limited by the geometry and the slippage coefficient of flexible pipe. The reinforced filament of high tensile modulus will reduce the deformation of the pipe. Compared with the geodesic winding trajectory, non-geodesic winding trajectories improves the stability of the pipe. The theoretical result is verified by the finite element analysis. The investigation method and results present in this paper will guide the design and optimization of more novel flexible pipes in the future.

As the lifeblood of national energy, oil and gas pipelines are vulnerable to corrosion, third-party damage, and natural disasters. Among these, third-party damage accidents have a high probability and serious consequences. However, China lacks a mature and unified pipeline accident database, making it difficult to assess and manage the risk of such incidents. To address this issue, this paper identifies 20 key risk factors for third-party damage to oil and gas pipelines through literature and case studies. The paper then proposes a multistate probabilistic assessment model using the Decision-Making Trial and Evaluation Laboratory (DEMATEL), interpretative structural modeling method (ISM), Røed method, and Bayesian network (BN). Real case studies demonstrate that the model not only predicts the probability of third-party damage risks but also clearly identifies key influencing factors and causal chains in the risk system. This provides a new approach for assessing third-party damage risks to oil and gas pipelines and offers a scientific basis for decision-making in managing actual pipelines. Practical Applications: The high probability and serious consequences of third-party damage accidents of oil and gas pipelines have caused certain hidden dangers to social security, environment, and economy, and put forward higher requirements for pipeline operation and management. In order to scientifically manage and effectively control the occurrence of third-party damage accidents of oil and gas pipelines, this paper, in the absence of an applicable pipeline failure database. Based on expert knowledge, a model that can be used for the assessment and prediction of third-party damage probability of oil and gas pipelines is constructed. Through the application of real cases, it is shown that the model can be used not only to predict the probability of third-party damage of oil and gas pipelines, but also to identify the key influencing factors and key causal chains leading to third-party damage. The results of the study not only provide theoretical support for pipeline management in reality, but also provide new ideas for risk assessment of oil and gas pipelines that lack actual data. [ABSTRACT FROM AUTHOR]

Quasi-zero-stiffness (QZS) structures offer substantial practical benefits for facilitating the essential support and isolation of vibrational source loads aboard modern marine vessels. In order to design a compact QZS system of high bearing capacity, the article proposes a low stiffness air spring (LSAS) vibration-isolation mounting system composed of both vertical and lateral air springs. The vertical air springs support the load and isolate vibrations in the vertical direction, while the lateral air springs support the load and isolate transversal vibrations. Theoretical analyses based on a simple two-dimensional, single degree of freedom model demonstrate that the proposed novel LSAS design decreases the degree of stiffness in the support structure that would otherwise be induced by introducing lateral air springs and accordingly increases the vibration isolation effect. Moreover, optimization of the air spring parameters enables the lateral air springs to provide negative stiffness and thereby realize QZS characteristics. Experimental testing based on prototypes of a standard air spring mounting system and the proposed LSAS mounting system demonstrates that the stiffness of the proposed system is about 1/5 that of the standard system. Accordingly, the proposed structure design successfully alleviates the undesirable influence of lateral air springs on the stiffness of the mounting system.

The worsening of climate conditions is closely related to the large amount of carbon dioxide produced by human use of fossil fuels. Under the guidance of the goal of "carbon peaking and carbon neutrality goals", with the deepening of the structural reform of the energy supply side, the hybrid energy system coupled with renewable energy has become an important means to solve the energy problem. This paper focuses on the comprehensive evaluation of hybrid energy systems. A complete decision support system is constructed in this study. The system primarily consists of four components: 1) Twelve evaluation criteria from economic, environmental, technological, and socio-political perspectives; 2) A decision information collecting and processing method in uncertain environment combining triangular fuzzy numbers and hesitation fuzzy language term sets; 3) A comprehensive weighting method based on Lagrange optimization theory; 4) Solution ranking based on the fuzzy VIKOR method that considers the risk preferences of decision-makers. Through a case study, it was found that the four most important criteria are investment cost, comprehensive energy efficiency, dynamic payback period and energy supply reliability with weights of 7.21%, 7.17%, 7.17%, and 7.15% respectively. A1 is the scheme with the best comprehensive benefit. The selection of solutions may vary depending on the decision-maker's risk preference. Through the aforementioned research, the decision framework enables the evaluation of the overall performance of the system and provides decision-making references for decision-makers in selecting solutions. [ABSTRACT FROM AUTHOR]

In order to explore the law of ground pressure activity in metal mines and monitor it in a timely manner, a 12 channel high-precision micro seismic monitoring system was designed and arranged with Zhengyuan Iron Mine as the research object. Through comprehensive analysis of multiple parameters, the characteristics of microcosmic activity were clarified, and the law of ground pressure activity was revealed. The active period of ground pressure activity m Zhengyuan Iron Men was obtained through comprehensive analysis of multiple indicators the results show that the deigned microcosmic monitoring system has calibrated the accuracy of monitoring in its speedier area, and the accuracy results n time and space are consistent with the actual situation on sit. The monitoring results are effective and reliability. Based on the location and number of micro seismic events, multiple parameters such as microcosmic activity apparent volume, and energy index were analyzed. It was found that the variation patterns and significant feature distributions of each parameter were basically consistent under the same time axis, and the ground pressure activity was more frequent doing the monitoring pieced. Based on the microcosmic b value and EV value, the active periods of ground pressure activities n Zhengyuan Iron Mine were determined to be from August 28th to 30th, from September 14th to September 17th, and from September 24th to 28th. Observation should be strengthened in order to respond in a timely manner, which provides technical support for monitoring ground pressure activities based on microcosmic monitoring technology. [ABSTRACT FROM AUTHOR]