Heave Conditions Research Articles

Impact performance of the marine rotating machinery coupled with floating raft-airbag-limiter under heaving motion

A dynamic model of an asymmetric system is developed with limiter under heave conditions to explore the impact characteristics of a marine rotating machinery coupled airbag-floating raft-limiter systems. The steady-state response of the system is numerically solved using the Runge-Kutta theory. Nonlinear dynamic analysis methods, including energy trajectories and time-averaged energy diagrams, have been introduced to examine the influence of rotor speed, heaving amplitude, limiter clearance, and contact stiffness on the dynamic characteristics of the system. The results show that the amplitude of the heave increases, the system collides with the limiter, resulting in a significant reduction in amplitude. Meanwhile, the dynamic behavior of system transitions from quasi-periodic motion to chaotic state. After the impact, the energy of the system begins to concentrate in the region of impact, and the higher the time-averaged energy value, the more severe the impact of the system. The method proposed in this paper can provides an optimization scheme and theoretical reference for the impact problem of this system.

Charging performance of a novel finned latent heat storage unit under sloshing

Latent heat storage (LHS) on ships using phase change materials (PCMs) is challenged by inefficient heat storage efficiency and susceptibility to sloshing conditions. To address this issue, this paper proposes a shell-and-tube LHS unit using innovative fins. The enthalpy-porosity approach is employed to study the melting characteristics of LHS units under sloshing, focusing on the effects of direction, frequency, and strength of sloshing conditions. An optimal fin configuration to enhance thermal storage performance under sloshing is proposed. The results indicate that the sloshing conditions effectively enhance the temperature uniformity and heat storage capacity of LHS units. Compared with the slosh-free condition, the full melting duration of PCMs in LHS units under roll and heave conditions is reduced by 20.9 % and 23.6 %, respectively. Moreover, the natural convection intensity and heat transfer uniformity under sloshing conditions increase significantly, improving the heat transport capacity in the late melting stage. Additionally, the heat storage capacity of LHS units improves with a decrease in sloshing frequency and an increase in sloshing strength; however, there is a limit to the performance enhancement gains. Interestingly, the arrangement of fins closest to the refractory zone effectively improves the heat transport in the later melting stage, resulting in a further 6.8% increase in the melting rate.

Numerical Simulation Study on the Hydrothermal Characteristics and Dynamic Response of the Embankment–Bridge Transition Zone in Cold Regions

The chain reaction of bridge abutment structure caused by frost heave of the embankment–bridge transition zone filler in cold regions has a great impact on the smoothness of railway lines, which will bring great challenges to the normal operation, safety, and maintenance of rail transit in cold regions under the action of long-term dynamic load. In this paper, the hydrothermal model and dynamic analysis model of the embankment–bridge transition zone are established, and the frost heave deformation rule and dynamic response characteristics of the embankment–bridge transition zone under frost heave conditions are studied. The results show that the effect of the bridge abutment structure on vertical frost heave is mainly concentrated in the range of the bridge abutment, and the vertical frost heave near the abutment is much smaller than other parts away from the abutment. The dynamic response and wheel–rail contact force of the embankment–bridge transition zone are significantly different under non-frost heave and frost heave conditions. Frost heave may cause a higher risk of derailment. This study provides a scientific reference for the design, construction, and safe operation and maintenance of embankment–bridge transition zones in cold regions, and has certain practical engineering significance.

Model Test Investigation of Pipe-Soil Interaction under Frost Heave Conditions of Roadbed

Model Test Investigation of Pipe-Soil Interaction under Frost Heave Conditions of Roadbed

Study on frost heaving force and the propagation of cracks in freezing rocks using the phase field method

In cold regions, the water in rocks expands volumetrically after freezing, leading to the propagation of fractures. In this study, the effective volume expansion coefficient is employed as a substitute for the volume expansion strain after the water in the fracture undergoes freezing and transforms into ice, and the phase field method is used to simulate the propagation of fractures in freezing rocks under various conditions to further explore the law of fracture propagation. The Abaqus software is used to solve the mechanical field control equation and the phase field evolution equation. First, the theoretical calculation of the frost-heaving pressure is compared with that obtained by experimental and numerical calculations. This comparison indicates that the numerical model presented in this study can effectively calculate the frost-heaving pressure during fracture propagation. Subsequently, the propagation of single and double fractures caused by frost heave is simulated based on fracture propagation experiments under frost heave conditions. The simulation results closely resemble the observed morphology of fracture propagation caused by frost heave obtained from the experiments. This confirms the suitability of the proposed model for simulating and predicting the propagation of fractures caused by frost heave. Finally, the influence of volume expansion strain growth path on fracture propagation due to frost heave is discussed. Although the final volume expansion strain value is the same, different growth paths of the volume expansion strain result in different fracture propagation morphologies.

Mechanical Properties of Ballastless Track Considering Freeze–Thaw Deterioration Damage

In order to investigate the stress characteristics of ballastless track under high latitude, and multi-source and multi-field extreme temperature conditions. Based on the finite element theory and the elastic foundation beam–plate principle, a finite element model of the ballastless track considering the limit convex abutment, gel resin, and interlayer bonding is established. The mechanical characteristics of the ballastless track under the slab–CAM layer bonding state, mortar separation, freeze–thaw degradation and forced deformation of the foundation are studied. Considering the deterioration of materials, the bending moment and reinforcement of track structures in cold regions are checked and calculated. The studies show that under the action of negative temperature gradient load, the edge of the track slab is subjected to tension, and structural separation occurs at the edge of the slab. When the interface between the track slab–CAM layer is poorly bonded, the bearing capacity can be improved, and the amount of separation can be reduced by increasing the structural stiffness of the CAM layer. Under the action of freeze–thaw cycles, the material performance deteriorates seriously, the separation between the track structures intensifies, the baseplate is seriously powdered and cracked, and the maximum tensile stress exceeds 6 MPa. The CAM layer and the baseplate are weak structures, and the foundation frost heave occurs at the expansion joint of the baseplate, which is the frost heave condition. Under freeze–thaw deterioration, the original reinforcement design of the substructure structure does not meet the requirements of structural cracks and reinforcement yield stress. In severely cold areas, the structural reinforcement scheme should be reasonably determined.

The mechanics of frost heave with stratigraphic microstructure evolution

Frost heave is a major cause of engineering geology hazards in cold regions, which is mainly the result of frost-heaving pressure due to the non-linear transport-freezing of water in the pore network. However, few studies have fully quantified the contribution of the strata pore-network structure to that pressure and the hazard to cold-region projects under multifactorial effects. Therefore, to address this long-term challenge in cold regions, we pioneered a generic, interdisciplinary, thermal-hydrological-mechanical fractal model for the quantitative study of the effect of strata microstructure on frost heave and hence the assessment of construction risk for engineering geology projects. First, a strata frost heave model based on fractal theory is proposed, with pore fractal dimension, maximum pore diameter, and pore tortuosity fractal dimension used to characterize strata pore density, pore size, and throat complexity, respectively. Secondly, the numerical model is compared with field observations in cold-region projects, and reasonable agreements can be obtained. The results indicate that various fractal parameters have different effects on engineering geology projects in cold regions. The strata displacement changes by 9.7–20.3% as microscopic parameters change. This study contributes to a better understanding of the micro- and macro-interactions of soil in cold regions, as well as a reference for geoengineering stability in cold regions under frost heave conditions.

Experimental study on pressure oscillation phenomenon of vertical upward bubble submerged jet under heave conditions

With the vigorous progress of nuclear industry under marine environment, the ocean motion will exacerbate the pressure oscillation phenomenon caused by the change of the steam-liquid interface during the jet, causing great harm and challenges to the security and steady operation of device related to steam submerged jets. Therefore, the effects of heave motion on the steam bubble morphology and pressure oscillation phenomenon of jets with vertically upward low mass fluxes were experimentally investigated. The experimental results show that when the heave motion is upward, the steam bubble will be stretched obviously in the necking and detachment stages; while when the heave motion is downward, the steam bubble will accumulate at the nozzle outlet during the growth initial stage. Compared with the land environment, the heave motion increases the dominant frequency and pressure pulses average amplitude, and the dominant frequency and pressure pulses average amplitude have a positive correlation with the heave amplitude and a negative correlation with the heave period. In addition, there is a positive correlation between the Strouhal number and the heave maximum acceleration amplitude. An experimental correlation is proposed to predict the dominant frequency in heave motion, and the error is basically within ±30%.

Analytical stress solution for cold region tunnels with unequal ground stress and support delay under different frost heave conditions of surrounding rock

Stress response analysis of tunnels under the frost heave state is a crucial problem in cold region tunnel construction. Hence, in this study, an analytical stress solution for cold region tunnels with unequal ground stress and support delay under different frost heave conditions is presented. The solution simultaneously considers the unequal ground stress along the horizontal and vertical directions, the rock displacement occurring before support installation, and the different frost heave modes of surrounding rock. To resolve the unequal ground stress boundary condition, the complex function method is utilized, and the stress solution is directly acquired by the method under isotropic frost heave (IFH) condition, whereas the solution under transversely isotropic frost heave (TIFH) condition is acquired through combination with the superposition method. In addition, a displacement release coefficient is adopted to depict the support delay. The solution is validated by existing solutions in degenerate cases. Finally, the stress distributions and the influence of key factors for cold region tunnels are discussed with a case study. In the lining, the radial stress increases with the radius and decreases from 0° to 90°, and the maximum of tangential stress occurs at the inner edge. Moreover, the normal contact stress between the lining and surrounding rock is much greater under TIFH condition; however, the tangential contact stress is identical under the two different frost heave modes. The lateral pressure coefficient shows greater impact on the stress in the lining along the vertical direction, whereas the displacement release coefficient exhibits greater effect on the stress along the horizontal direction. The stress in the lining under TIFH condition is much greater than that under IFH condition, and increases significantly as the degree of anisotropy increases, which implies that the TIFH condition is a much severer state.

Numerical Investigation of Pool Boiling Under Ocean Conditions with Lattice Boltzmann Simulation. Part Ⅰ: Heaving Condition

Pool boiling is the heat-transfer mechanism of many heat exchangers inside ocean nuclear power plants working under the complex marine circumstances. Also, ocean conditions will create a new acceleration field other than gravity for the fluid, which induces some unique thermal–hydraulic characteristics. In this study, pool boiling under heaving conditions is numerically simulated using multiple relaxation time phase change lattice Boltzmann method. Firstly, the simulated results under static condition have been validated with recognized empirical equations, such as Rohsenow’s correlation at nucleate boiling, Zuber’s model, and Kandlikar’s model about critical heat flux (CHF). Then, pool boiling patterns, the boiling curve of time-averaged heat flux, transient heat flux, and heaving effects on different pool boiling regions are investigated. The results show that pool boiling curves of time-averaged heat flux between heaving conditions and static conditions with middle superheat degrees are similar. Heat transfer under heaving conditions at low superheat is somewhat enhanced, and it is weakened at high superheat, which leads to a slightly smaller critical heat flux with larger superheat compared with that under static conditions. Moreover, distinct fluctuation of the transient heat flux of pool boiling under heaving conditions is found for all boiling regimes. Furthermore, the heaving condition shows both positive and negative effects on pool boiling heat transfer at high-gravity and low-gravity regions, respectively. Besides, both the larger heaving height and shorter period time bring out more violent heaving motion and make a greater impact on pool boiling heat transfer.

Deformation Law and Control Limit of CRTSIII Slab Track under Subgrade Frost Heave

In order to find out the influence of subgrade frost heave on the deformation of track structure and track irregularity of high-speed railways, a nonlinear damage finite element model for China Railway Track System III (CRTSIII) slab track subgrade was established based on the constitutive theory of concrete plastic damage. The analysis of track structure deformation under different subgrade frost heave conditions was focused on, and amplitude the limit of subgrade frost heave was put forward according to the characteristics of interlayer seams. This work is expected to provide guidance for design and construction. Subgrade frost heave was found to cause cosine-type irregularities of rails and the interlayer seams in the track structure, and the displacement in lower foundation mapping to rail surfaces increased. When frost heave occured in the middle part of the track slab, it caused the greatest amount of track irregularity, resulting in a longer and higher seam. Along with the increase in frost heave amplitude, the length of the seam increased linearly whilst its height increased nonlinearly. When the frost heave amplitude reached 35 mm, cracks appeared along the transverse direction of the upper concrete surface on the base plate due to plastic damage; consequently, the base plate started to bend, which reduced interlayer seams. Based on the critical value of track structures’ interlayer seams under different frost heave conditions, four control limits of subgrade frost heave at different levels of frost heave amplitude/wavelength were obtained.

Two-dimensional numerical study on fluid resonance in the narrow gap between two rigid-connected heave boxes in waves

This paper considers the motion response and hydrodynamic characteristics of two rigid-connected boxes freely heaving in waves. Two numerical models were established for the numerical simulation, namely an in-house Constrained Interpolation Profile (CIP) method-based code and a commercial Computational Fluid Dynamics (CFD) tool STAR-CCM+ combined with the overset mesh approach. Based on the developed numerical models, the motion response and hydrodynamic forces of the rigid-connected boxes were simulated under incident waves of different frequency. The effects of the body draft and the distance between the connected boxes were also discussed. Numerical results demonstrated that the developed two numerical models can accurately predict the motion response and hydrodynamic resonance characteristics of the rigid-connected boxes in waves. A systematic analysis proved that the hydrodynamic characteristics of the rigid-connected boxes are quite different under free heave condition and under motion constrained condition.

Two-phase flow boiling characteristics in plate-fin channels at offshore conditions

In order to optimize the plate-fin heat exchangers for floating liquefied natural gas and avoid the degradation of performance at offshore conditions, the flow boiling characteristics in offset strip fins channels of plate-fin heat exchangers under offshore heaving conditions were investigated experimentally, covering the mass fluxes in the range 64–128 kg/(m2·s) and vapor qualities (vapor mass fractions) in the range 0.1–0.8. The results show that the influence of heaving is stronger for vapor quality equal to 0.6, leading to the increment of the heat transfer coefficients by 8.4%. The heat transfer coefficients under heaving conditions vary with the sloshing motion in a sinusoidal-like way. The enhancement of time-average heat transfer coefficients varies in the range of 98.4–108.4% for different heaving conditions. As the vapor quality increases, the relative fluctuation amplitude Ah and sloshing time-average factor Fh of heat transfer coefficients initially increase and then decrease, showing a maximum at a vapor quality of 0.6; for increasing mass flux, Ah decreases and Fh increases; for decreasing sloshing period and increasing sloshing amplitude, both Ah and Fh decrease. A novel correlation model for the heat transfer coefficients under heaving conditions for flow boiling in offset strip fin channels is proposed, and the predicted deviations within ±10%.

Distribution characteristics of liquid in spiral-wound heat exchanger under sloshing conditions

The maldistribution of working medium restricts the heat transfer performance of the spiral-wound heat exchangers (SWHEs), especially when the heat exchangers are applied in floating production storage and offloading platform. Therefore, the maldistribution in the SWHEs needs to be studied under sloshing conditions. In the investigation, a novel distributor named “disc distributor” is designed and its distribution characteristic is analysed under sloshing conditions experimentally. The impacts of sloshing amplitude, sloshing periods, mass flow rate and structural parameters on flow uniformity are discussed. The results show that based on steady condition the augmentation of the sloshing amplitude makes the liquid uniformity deteriorate by 14.2–56.0%, and the enlargement of the sloshing period improves the liquid flow uniformity by 12.8–28.3%. The elevation of the mass flow rate promotes the flow uniformity by 23.8–27.0% and 13.9–32.4% under steady and sloshing conditions, respectively. The variation of hole diameter exacerbates distribution performance of the distributor by 5.3–18.4% and 2.5–22.3% under steady and sloshing conditions separately. Heave condition always has less influence on the flow uniformity of the distributor than other sloshing conditions.

The sloshing effects on distribution characteristics of gas–liquid mixture in spiral-wound heat exchanger

Spiral-wound heat exchanger (SWHE) is important equipment for industry, and it is suitable for floating production storage off-loading (FPSO). However, two-phase mixture maldistribution always restricts the heat transfer capacity of SWHE in FPSO. Few studies have focused on the maldistribution of SWHE. According to this, an experimental device was fabricated to evaluate the maldistribution of a novel distributor on the sloshing platform. The effects of vapor qualities and mass flow rates were analyzed at the range of 0.106–0.702 and 608.5–1491.6 kg h−1, respectively. The following conclusions are drawn: With the augmentation of vapor quality, the gas–liquid uniformity deteriorates after optimizing under steady and sloshing conditions. Heave condition improves gas and liquid flow uniformity by 2.9–11.0% and 1.7–3.7% separately, and pitch condition improves the gas flow uniformity by 0.5–3.7%, and roll condition lowers the liquid flow uniformity by 2.0–7.2% in the variation of vapor quality. It is also proved that the flow uniformity achieves better performance with the increasing mass flow rate under steady, heave and pitch conditions. Heave condition improves the distribution characteristic by 4.4–8.7% for the gas phase and 2.0–9.5% for the liquid phase, and pitch condition elevates the gas flow uniformity by 3.1–7.7%. Under the roll condition, the distribution performance of the experimental model changes worse after better and obtains the best performance at the mass flow rate of 1183.8 kg/h. At large mass flow rates, gas entering into liquid space under roll condition can bring the structural problem. Increasing the tube diameter and making the upper baffle tilt from shell to center barrel are beneficial to keep the distributor structure safe.

Time Domain Modeling of Propeller Forces due to Ventilation in Static and Dynamic Conditions

This paper presents experimental and theoretical studies on the dynamic effect on the propeller loading due to ventilation by using a simulation model that generates a time domain solution for propeller forces in varying operational conditions. For ventilation modeling, the simulation model applies a formula based on the idea that the change in lift coefficient due to ventilation computes the change in the thrust coefficient. It is discussed how dynamic effects, like hysteresis effects and blade frequency dynamics, can be included in the simulation model. Simulation model validation was completed by comparison with CFD (computational fluid dynamics) calculations and model experiments. Experiments were performed for static and dynamic (heave motion) conditions in the large towing tank at the SINTEF Ocean in Trondheim and in the Marine Cybernetics Laboratories at NTNU (Norwegian University of Science and Technology). The main focus of this paper is to explain and validate the prediction model for thrust loss due to ventilation and out of water effects in static and dynamic heave conditions.

Study on the Control Strategies of Offshore Drilling Crown-Block Heave Compensation System With Compound Cylinders

To overcome the effect of floating platform heave motion on the drilling operation, a new crown-block heave compensation system with compound cylinders is developed. The new heave compensation system has certain advantages, such as low derrick, short hydraulic pipeline, compact structure, easy operation, etc. The numerical calculation functions of the new heave compensation system are established based on the theories of fluid dynamics and theoretical mechanics. The entire model was built using the Simulink module of MATLAB with a hierarchical structure. As the core component of the compensation system, four control strategies are established to improve the compensation performance, including the PID control, fuzzy control, fuzzy PID control, and Terminal Sliding Mode (TSM) control. Laboratory equipment with a ratio of 1:5 to the new compensation system was designed and developed. The simulation and experimental results show that the new compensation system achieves a good compensation rate of more than 90% under different heave conditions. Among these four strategies, the TSM control strategy generates the highest compensation rate and lowest power fluctuation for the compensation cylinders.

DESIGN AND TYPE SELECTION OF CONCRETE‐LINED SMALL CANALS IN CUT AND EXPANSIVE SOIL IN COLD REGIONS

AbstractIn cold regions, deformation because of frost heave in the soil seriously damages the concrete lining of canals, which results in seepage loss and high maintenance costs. Cross‐sectional canal shapes with low‐stress concrete lining are an important aspect of small canal design. Round‐bottom triangular, parabolic and catenary sections are curved and therefore regarded as likely to perform well in conditions in which frost heave occurs. This study provides an objective answer to the question of which section would perform well in frost heave conditions with as large as possible water conveyance efficiency. The design process of small canals was simplified first, and the result shows savings in the land area required for canals. Then, based on two principles, the hydraulic radius and performance of three sections in resisting frost heave damage were compared. In regions without frost heave, the round‐bottom triangular section is better because it has the largest hydraulic radius and design flexibility. In cold regions, if width to depth ratio or depth is a principal constraint, a parabolic (wide section) or catenary (narrow section) is better for big side slopes and curved structures. If side slope (horizontal to vertical) is the principal constraint, the round‐bottom triangular is better. © 2019 John Wiley & Sons, Ltd.

Experimental investigation of flexural behaviour of U-shaped concrete subgrade panel

In pavement design, subgrade condition is one of the criteria to be looked into. Poor subgrade made up of problematic soils could cause the soils to move upwards, known as heaving condition. The U-shaped subgrade concrete panel (USSP) is introduced in this study to help in reducing soil heave condition for low bearing capacity soils. This paper presents a description of the mechanical properties for the USSP flexural strength through experimental works. Flexural strength of USSP for 6 different sizes are compared with the control panel sizes of 150 × 150 × 50 mm, 300 × 300 × 50 mm and 600 × 600 × 70 mm. Modified supports of square-cross section steel blocks with the size of 45 × 45 mm were used in the 3-point flexural strength test to obtain the flexural strength of the control panel. The USSP sustained more flexural load compared to control panel ranging between 7 % to 88 %. The result of the flexural strength test shows that the introduction of the webs to USSP allows the USSP to sustain higher flexural load and induce lower modulus of rupture (MOR) compared to the control panel.

Interaction analysis of waffle slabs supporting houses on expansive soil

Abstract This study investigates the soil–slab interaction for waffle slabs supporting residential structures on highly expansive soils. Interaction modelling techniques are reviewed, and the implications of the modelling assumptions typically employed are discussed. More realistic modelling assumptions are proposed, and their effects are investigated. For this purpose, advanced incremental/inelastic FE models are developed in OpenSees to capture the slab structural response during the history of soil movement in heave condition. Soil profile (mound shape), soil stiffness profile and soil–slab contact are updated corresponding to growing mound. The study provides an insight into the resulting changes in bending moment and deformation demands on such slabs. It is found that the conventional assumption of a constant soft soil stiffness coupled with a stepped transition to that of hard soil is generally unconservative. The analyses also suggest that predefining a critical scenario and disregarding the history of loading is not necessarily conservative.