Compression Pressure Research Articles

Spatial and Temporal Visualization of Polymorphic Transformations in Pharmaceutical Tablets.

X-ray Diffraction Computed Tomography (XRD-CT) represents a cutting-edge method for non-destructive material analysis, offering the unique capability of providing molecular-level information with spatial resolution. In this study, we have applied XRD-CT to investigate pharmaceutically relevant tablets that have been subjected to a range of compression pressures typical in tablet manufacturing. By employing XRD-CT to pharmaceutical tablets, we reveal material changes without tablet destruction, thereby avoiding potential phase transformations during sample preparation that could lead to errors in the interpretation of the processes that have occurred. Utilizing a pressure-sensitive marker, glycolide, we have tracked changes within tablet structures induced by compression, pinpointing locations where glycolide undergoes pressure-induced transformation. Additionally, we conducted a follow-up study with analysis one month later, observing an in-situ hydrolysis reaction of glycolide within the tablets. Through the complementary use of electron diffraction, we have elucidated the structure of the hydrolysis product, further enhancing our understanding of temporal changes in the tablets.

Spatial and Temporal Visualization of Polymorphic Transformations in Pharmaceutical Tablets

X‐ray Diffraction Computed Tomography (XRD‐CT) represents a cutting‐edge method for non‐destructive material analysis, offering the unique capability of providing molecular‐level information with spatial resolution. In this study, we have applied XRD‐CT to investigate pharmaceutically relevant tablets that have been subjected to a range of compression pressures typical in tablet manufacturing. By employing XRD‐CT to pharmaceutical tablets, we reveal material changes without tablet destruction, thereby avoiding potential phase transformations during sample preparation that could lead to errors in the interpretation of the processes that have occurred. Utilizing a pressure‐sensitive marker, glycolide, we have tracked changes within tablet structures induced by compression, pinpointing locations where glycolide undergoes pressure‐induced transformation. Additionally, we conducted a follow‐up study with analysis one month later, observing an in‐situ hydrolysis reaction of glycolide within the tablets. Through the complementary use of electron diffraction, we have elucidated the structure of the hydrolysis product, further enhancing our understanding of temporal changes in the tablets.

Air Excess Coefficient and Irreversibility Value Analysis of Gas Turbines

Gas turbines used in natural gas cycle power plants have been researched in terms of energy efficiency. Gas turbines used in power generation plants have a very complex structure because they contain many components. In order to determine the thermodynamic performance of this system, the efficiency of each component and the increase in entropy of each component were calculated using exergy analysis. Irreversibility was chosen as the main parameter and used for thermodynamic optimization of production. The system consists of many components. An increase in the irreversibility of a single component causes an increase in the irreversibility of other components. The effect of gas turbine pressure ratio and excess air percentage on fuel consumption, fuel exergy, combustion chamber exergy change and irreversibility change was investigated. It was observed that the increase in compressor pressure ratio increased irreversibility. Maximum irreversibility was observed in the combustion chamber. Irreversibility was compared with the excess air used in the combustion chamber. The air excess coefficient was examined as percentages of 100%, 200%, and 300%, respectively. The compression pressure ratio was examined for air excess coefficient percentage values from 3 to 40.

Structure design and ultimate strength envelope of a modular carbon fiber-reinforced polymer (CFRP) laminate tube box on a 5000 ft deep-sea ultra large unmanned underwater vehicle

Deep-sea tube box is a crucial and basic structural component of various deep-sea equipment such as deep-sea submarine and unmanned underwater vehicles. The deep-sea ultra large unmanned underwater vehicle (ULUUV) is the most representative one of them. Tube boxes are the basic modular members on the ULUUV, which are widely used as the load-bearing hull in torpedo launch, load transportation, pipeline protection and etc. Due to the extremely harsh operation condition, deep-sea tube box simultaneously suffers extremely high lateral water pressure and tremendous axial compression induced by water pressure. Considering the strict requirements for lightweight, high strength, and corrosion resistance of deep-sea tube boxes, carbon fiber-reinforced polymers (CFRP) have become the most potential choice for the construction materials of future deep-sea tube box. Thus, the aim of this paper is to make a structure design of a deep-sea CFRP tube box which can operate at the water depth of 5000 ft. In this paper, a detailed design process of the deep-sea CFRP tube box was introduced, including geometrical configuration, critical buckling load prediction method, FE modeling technique and experimental validation. Corresponding to 5 ply schemes, 495 cases of FE analyses were performed to obtain the ultimate strength envelopes of the CFRP tube box subjected to combined axial compression and external lateral water pressure. Based on the obtained results, the best ply scheme for the deep-sea CFRP tube box was figured out. This paper could provide design method and data references for deep-sea CFRP structures which are subjected to combined loads.

Enhancing pressure ulcer prevention through optimized design of a multi-cellular foam mattress

Sustained mechanical loading on skeletal muscle tissue can lead to degeneration and cell damage over time, resulting in the development of pressure ulcers, particularly in hospital mattresses or for wheelchair-bound users. The primary risk factors for this damage are tissue ischemia caused by pressure in the contact area and tissue compressive strain. In this study, a multi-cell, multi-material foam mattress for the upper comfort layer was developed, with the aim of simultaneously minimizing soft tissue compressive strain and maximum surface pressure on the human buttocks zone. The levels of these factors were estimated using the finite element method (FEM). A multi-objective optimization (MOO) approach was employed, coupling the non-dominated sorting genetic algorithm (NSGA-II) with FEM. This algorithm helped determine the required compressive strength and the optimal cell configurations to achieve the desired outcomes. The majority of the optimal solutions exhibited contact pressures (Cpresss) below the recommended threshold to avoid local tissue ischemia. The optimized cellular material configurations resulted in soft tissue compressive strain of 12% and Cpress of 3.4 kPa, indicating longer safety times for supine support on the foam mattress without the need for repositioning. The optimization process utilized 5 softer foam materials out of the 9 firmness levels tested to achieve these results. The proposed multi-cell, multi-material foam mattress model shows promise for the prevention of pressure sores, as suggested by the optimization findings.

Critical current degradation of commercial REBCO coated conductors under thermomechanical loads

Abstract The process to obtain a superconducting joint between Coated Conductors (CCs) involves the simultaneous application of temperature and transverse compressive pressure to promote the joining of the two adjacent REBCO layers. We performed experiments to simulate this procedure by subjecting samples from commercial CCs to different combinations of pressure, and temperature. The objective was to understand the effects of the thermomechanical cycles on the critical current (Ic) and, therefore, determine the upper limit for the achievable current in a superconducting joint between CCs. We observed a reduction of the Ic across the investigated parameter range that is accelerated at higher temperatures and pressures. For instance, the average reduction of Ic measured at 77 K in self-field varied from 45% to 90% when increasing the pressure for samples heated at 820 °C, as compared to samples heated at the same temperature without applied pressure. As a complement to electrical transport measurements, we carried out TEM and EDX investigations to study the relation between the degradation of Ic and alterations in the microstructure of REBCO. These analyses indicate that the concurrent application of temperature and pressure accelerates the decomposition of the REBCO phase. The EDX data suggests that the decomposition products could correspond with a peritectic reaction of the REBCO occurring at lower temperatures, accelerated by the presence of an external pressure. This early decomposition occurs in localized areas of the REBCO layer, constricting the available cross-section for current flow and thereby diminishing the critical current.

Influence of hot pressing temperature of composite copper-titanium billets on the formation of intermetallide layer at the material interface

Billets for drawing of microwires based on Grade 4 titanium and protective sheath of M1 copper have been obtained at different temperatures by hot pressing method with drawing coefficient µ = 16. The influence of the billet heating temperature on the pressing pressure, configuration of the interface of bimetal materials and thickness of the intermetallide layer is shown. The influence of elastic compression pressure of composite copper-titanium billets in the range of 350–1400 MPa on the formation of intermetallide at the interface of materials at 850°C has been analyzed.

Grain disintegration and dynamic recrystallization during impact tests of additively manufactured nickel-based alloy 718

The high-temperature dynamic mechanical response of Alloy 718 produced via laser-powder bed fusion (LPBF) was investigated through compressive Split-Hopkinson Pressure Bar (SHPB) tests. Simulating the typical service conditions of Alloy 718, the tests were conducted at temperatures ranging from 298 K to 773 K and at strain rates of 1000 s−1 to 1500 s−1. Phenomenological material constitutive models, such as the modified versions of Johnson-Cook and Hensel-Spittel models, were developed based on the SHPB test results. Analysis of microstructural evolution under impact conditions highlighted that columnar grains with high Schmid factors tend to undergo preferential activation and dislocation pile-up. This process leads to the formation of adiabatic shear bands, grain disintegration, and intense lattice rotation, particularly at higher strain rates. Furthermore, increasing the dynamic deformation temperature facilitates the activation of discontinuous dynamic recrystallization (DRX), with strain accumulation promoting localized grain nucleation along heavily dislocated dendritic boundaries. Recognizing the limitations of phenomenological material constitutive models in accurately representing the underlying microstructural evolution, an artificial neural network (ANN)-based constitutive model employing a three-layer backpropagation learning algorithm was implemented, reducing the Average Absolute Relative Error (AARE) to 0.17%.

Material-Sparing Approach to Predict Tablet Capping Under Processing Compression Conditions Based on Mechanical and Molecular Properties Derived from Compaction Simulation and Crystal Structural Analysis.

Present study evaluates the usability of compaction simulation-based mechanical models as a material-sparing approach to predict tablet capping under processing compression conditions using Acetaminophen (APAP) and Ibuprofen (IBU). Measured mechanical properties were evaluated using principal component analysis (PCA) and principal component regression (PCR) models. PCR models were then utilized to predict the capping score (CS) from compression pressure (CP). APAP formulations displayed a quadratic correlation between CS and CP, with CS rank order following CP of 200MPa < 300MPa < 100MPa, indicating threshold compression pressure (TCP) limit between 200 and 300 MPa, resulting in higher CS at 300 than 200 MPa regardless of increased CP. IBU formulations displayed a linear correlation between CS and CP, with CS rank order following CP of 100MPa < 200MPa < 300MPa, indicating TCP limit between 100 and 200 MPa, resulting in higher CS at 200 and 300 than 100 MPa regardless of increased CP. Molecular models were developed as validation methods to predict capping from CP. Measured XRPD patterns of compressed tablets were linked with calculated Eatt and d-spacing of slip planes and analyzed using variable component least square methods to predict TCP triggering cleavage in slip planes and leading to capping. In APAP and IBU, TCP values were predicted at 245 and 175 MPa, meaning capped tablets above these TCP limits regardless of increased CP. A similar trend was observed in CS predictions from mechanical assessment, confirming that compaction simulation-based mechanical models can predict capping risk under desired compression conditions rapidly and accurately.

Investigations on the Impacts of Drugs or Excipients with Different Physicochemical and Compaction Properties on the Disintegration Behavior of Kollidon®SR-Based Binary Controlled Release Matrix Tablets.

The objective of this study was to examine the impact of the physicochemical properties of the loaded drug or excipient, the concentration of Kollidon®SR (KSR), and the mechanical characteristics of KSR compacts on their disintegration times. Using disintegration apparatus, a two-hour constraint was chosen as the process's end point. Lactose-KSR compacts subjected to the highest compression pressure and Microcrystalline cellulose-KSR compacts with KSR concentrations exceeding 30% exhibited disintegration times of less than ten minutes. Likewise, compacts containing Diltiazem HCl-KSR demonstrated brief disintegration times across all tested KSR concentrations and compression pressures. Compacts of Modafinil, Metformin HCl, and Ascorbic acid-KSR displayed disintegration times ranging from fast to moderate, contingent upon the levels of KSR and compression pressure applied. Compacts containing KSR with Aspirin, Salicylic acid, or Ibuprofen did not exhibit significant disintegration even at minimal amounts of KSR (0.5%). Theophylline-KSR tablets also showed prolonged dissolution times, even at very low concentrations of KSR. The disintegration times of Dic-KSR tablets were roughly close to an hour and were predominantly unaffected by varying KSR levels and only marginally influenced by compression pressures. It is possible to draw the conclusion that different drugs or excipients have different minimum KSR requirements to resist compacts' disintegration process. Compounds that demonstrate low solubility in water can result in extended disintegration times for KSR compacts. The melting points of these compounds, in conjunction with the Py values of the compacts and their compaction properties, could affect the disintegration process, although a precise evaluation is necessary.

Unveiling the high-pressure behavior of thymol+carvone NADES: A combined experimental-computational approach

this study considers the high-pressure behavior of thymol + carvone Natural Deep Eutectic Solvent using a combined experimental and computational approach. Experimentally, PVT (pressure – volume/density - temperature) measurements were conducted to characterize the fluid volumetric behavior as well as compressibility and internal pressure, which are directly related with hydrogen bonding and nanoscopic structuring. Likewise, these measurements provide crucial insights into the thermodynamic properties of the considered fluid under high pressure, which is pivotal for scaling up and process design for high pressure operations. Computationally, the PC-SAFT equation of state was employed to predict phase equilibria and PVT behavior, Machine Learning for density predictions, while Density Functional Theory and Classical Molecular Dynamics simulations were considered for the structural and dynamic characterization. These simulations provides insights into the electronic structure, intermolecular interactions (hydrogen bonding), liquid structuring and they unveil the pressure's impact on microscopic interactions, structural organization, and transport properties. This comprehensive investigation aims to shed light on the behavior under high pressure, facilitating their optimization for applications in chemical processing, energy storage, and materials science.

Electrochemical behavior and microstructure of diffusion welding of zirconium alloy and super duplex stainless steel

In this study, the effect of welding temperature on interface microstructure, mechanical properties, and electrochemical behavior of diffusion welded joints (DWJs) of zirconium alloy (ZrA, Zr702 grade) and super duplex stainless steel (2205 duplex stainless steel grade) were investigated. Alloys were welded in a vacuum atmosphere at four different temperatures (800, 850, 900, and 925 °C) for 75min under 4MPa compressive pressure. The optical, scanning electron microscopy, electron probe micro-analyzer, and X-ray diffraction techniques were used to characterize the interfacial microstructure of the DWJs. Layers of intermetallics were formed along the welded interface at 850 °C and above welding temperatures. At 850 °C, a single reaction layer (phase mixture of ZrFe2+ZrCr2) was observed; however, bilayers (ZrFe2+ZrCr2 and Fe2Zr+FeZr3 phase mixtures), and triple layers (ZrFe2+ZrCr2, Fe2Zr+FeZr3, and β-Zr+FeZr3 phase mixtures) were observed at the welded interface of the joints processed at 900 and 925 °C, respectively. Width of the reaction layer (phase mixtures) increases with an increase in the welding temperature. The DWJs processed at 900 °C reach the maximum joint strength of ~312MPa along with ~6.4% ductility. For corrosion analysis, studies of the base alloys and DWJs in 0.1mol/L HCl and 0.1mol/L NaOH solutions separately using electrochemical techniques, such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization were undertaken.

Systematic screening of particle engineered polymers for the preparation of multiparticulates embedded orally disintegrating tablets

This paper evaluated polymers' physical and mechanical properties to formulate modified-release multiparticulates to be embedded in orally disintegrating tablets (ODTs). The targeted polymer should have adequate elastic-plastic properties in a multiparticulate system during the manufacturing process, which is affected by its physical properties. The good mechanical properties of the multiparticulate system can effectively aid in retaining the shape of the particles from being affected under applied compression pressure during the formulation process and tablets preparations. Therefore, the formulation should have good mechanical attains. Five polymers (three natural and two synthetic), namely: sodium alginate, polyvinyl alcohol (PVA), methylcellulose (MC), polyacrylic acid (PAA) and Eudragit L100, were evaluated. Polymers in raw form or particle engineered using spray drying were characterised using different analysis techniques: differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), compacts tensile strength, texture analysis, particle size analysis and surface area analysis. The unprocessed PAA exhibited the lowest Young's modulus, measuring at 5.38 MPa, whereas MC displayed the highest value of 14.74 MPa. The polymers were subjected to spray drying at a concentration of 5% w/v. Data of the texture analysis revealed that Young's modulus increased for the spray-dried PAA powder, reaching 13.69 MPa. This suggests an enhanced polymer compressibility subsequent to the spray drying process. Eudragit L100 demonstrated an enhanced tabletability prolife after spray drying. SEM and surface area results showed a correlation with the mechanical findings. Plasticity and elasticity together provide strong, durable tablets with structural integrity. Achieving a balance between these properties is crucial for effective tabletability. The results of this study provide an insight into physical and mechanical properties and changes encountered upon spray drying. A balance between elastic- plastic properties is required for optimal multiparticulate development.

Thermophysical study for Binary mixtures of Dimethyl carbonate with Anisole, Butyl vinyl ether, Diisopropyl ether and Dibutyl ether at 303.15, 308.15 and 313.15 K

Ultrasonic velocity, density and viscosity have been determined for the binary compositions of dimethyl carbonate+ butyl vinyl ether, + diisopropyl ether, + anisole and + dibutyl ether at T= 303.15, 308.15 and 313.15 K. The inventive data is applied to assess the excess molar volume VmE, deviation in viscosity Δη and the acoustical parameters namely isentropic compressibility (Ks), free volume (Vf ), free length (Lf ) and internal pressure (πi). The excess or deviation properties are contoured to the Redlich-Kister polynomials and the outcomes are elucidated in terms of molecular interactions present in compositions.

Experimental and numerical investigations of the octagonal concrete-filled thin-walled tube columns with binding bars (O-CFT-WBB) under compressive pressure and thermal loads

An experimental and theoretical investigation is conducted to evaluate the behavior of CFT columns with a unique geometric cross-section under axial loading and in a thermal environment. In this study, based on previous research on octagonal CFT columns, this geometry was chosen as a favorable option compared to other possible configurations. Additionally, binding bars were employed to enhance these columns' mechanical and thermal behavior. A thermal gradient (temperature changes ranging from 0 to 600 degrees) was applied in the laboratory to replicate extreme environmental conditions. By experimental results, a theoretical investigation was conducted to derive suggested formulas for considering confinement effects in O-CFT-WBB columns, and the results were then compared with experimental results and the closest existing formulas. After examining the experimental results, it was shown that the presented formulas had more accuracy than the existing ones. Additionally, based on the experimental results, the presence of binding bars at different temperatures led to different behaviors in the axial capacity of the columns. According to the results, the binding bars in the O-CFT-WB columns can lead to different behaviors in the axial capacity of the columns. Based on a constitutive model of confined concrete, a method for calculating the maximum strength of L-shaped CFT columns with and without binding bars is proposed. The method is verified with experimental results from this test program and data from other experiments.

Effect of Piston Geometry on Performance Characteristics of VCR Engine with and without EGR when Fueled with Blends of Methyl Ester

The growing population and exhaustion of fossil fuels necessitate our search for new sources of energy. The study for this research encompasses an amalgamation of interest in alternative fuels, advanced engine technology such as variable compression ratio VCR, engine component modification, and a methodical approach to testing for assessing the effects on key performance of the engine. A 3.5 kW compression ignition (CI) engine was fueled with blends of behada, chicken fat, and turmeric oil methyl ester. Engine operating parameters, such as the compression ratio (CR), rate of exhaust gas recirculation (EGR), and piston top geometry, are optimized to maximize engine performance. CI engine was modified by changing the piston head (square and tangential groove top) for methyl ester diesel blend operations. In the study, diesel fuel is designated as B00 and methyl ester as B20. The influence of compression ratio (CR16 and CR18) with exhaust gas re-circulation (EGR 0% and EGR 10%) was evaluated. The key performance indicators: brake thermal efficiency (BTE), brake-specific energy consumption (BSEC), brake-specific fuel consumption (BSFC), air-to-fuel ratio (AFR), and exhaust gas temperature (EGT) are investigated. Results indicate that an increase in BTE accompanies an increase in load, suggesting enhanced thermal efficiency with increased power output. The consequence of VCR is also investigated, and it is determined that a higher CR results in a higher BTE due to an increase in compression pressure and temperature, thereby enhancing combustion. Due to the re-combustion of unburned hydrocarbons with the addition of EGR at a 10% rate, BTE increases further. Utilizing a piston geometry with tangential grooves and methyl ester blends also contributes to increased BTE. BSEC increases with increasing load, with an important rise observed when operating at maximum capacity. However,at CR 18, BSEC decreases as a result of enhanced combustion efficiency. EGR has different effects on BSEC depending on the geometry of the piston and the kind of fuel used. Enhanced air-fuel blending and re-combustion of unburned hydrocarbons reduce the BSEC of the engine. The tangential groove top piston operates with 10% EGR. Similar to BSEC, BSFC decreases with increasing CR and improves with the use of a piston with a tangential groove and 10% EGR operation. AFR decreases as the consumption of fuel increases to meet the power demand, and higher CR values result in a lower AFR. EGT rises with load, and CR18 has a lower EGT than CR16 as a result of a higher compressing temperature and pressure. 10% EGR operation reduces EGT by decreasing the concentration of oxygen in the combustible area.

Stiffness in compression therapy: Analytical estimation of pressure changes beneath textile compression devices

Compression pressure changes in dynamic conditions under textile compression devices have a critical impact on the success of compression therapy. Models exist to predict the level of compression pressure, but not the actual change in pressure. This paper aims to derive a formula to accurately determine the pressure change under textile compression devices, to investigate the factors influencing the pressure change and to verify their effects through theoretical analysis. Firstly, a formula based on Laplace’s law is presented which mathematically describes the dependencies of pressure changes. Secondly, a simulation is carried out to demonstrate the effect of these dependencies on pressure changes using theoretical textile curve functions. Finally, the effect of these dependencies is demonstrated by testing short- and long-stretch bandages in a tensile testing machine and using the recorded material curves to simulate a theoretical application of these bandages to the lower limbs. The results show that the change in pressure is not solely determined by the intrinsic properties of the material, but is influenced by several variables, including the mechanical performance of the textile materials during stretching, the target pressures for application of the textile material, and the body geometries to which the material is applied. Pressure change cannot be a constant for textile compression devices such as bandages. The research increases the understanding of the factors that influence pressure changes in compression device materials. The findings may have implications for the design and selection of compression textiles in clinical applications.

Impact of Extended Intervals on Diesel Engine Performance with 15W-40 DH1 Lubricant Oil

Engine lubricant oil is crucial for minimizing friction between moving components within an engine, directly influencing the engine's reliability and lifespan. Determining the appropriate oil replacement intervals is essential, as extending these intervals necessitates more rigorous monitoring of both oil quality and engine condition. This study investigated the performance of SAKAI 15W-40 DH1 engine oil in the SAKAI Vibrating Roller SV526 over varying operational periods: 125 hours, 250 hours, 375 hours, and 500 hours. The research involved analyzing oil samples for viscosity, metal additives, total base number (TBN), and contaminants using Fourier Transform Infrared Spectroscopy (FTIR). Additionally, key engine performance indicators, including fuel consumption, valve clearance, and compression pressure, were measured. The findings revealed a gradual decrease in oil viscosity from 13.48 cSt to 11.56 cSt, approaching the minimum acceptable threshold of 11.45 cSt. Concurrently, the Fe content in the oil increased to 11 ppm, indicating wear, while the valve clearance in cylinder number three expanded to 0.48 mm, and compression pressure dropped from 31 kg/cm² to 28 kg/cm². Despite these changes, the oil remained within the standard operational limits, and the engine continued to perform adequately. However, based on the observed trends, extending the oil replacement interval to 500 hours cannot be conclusively recommended, as the oil's condition and engine performance may begin to decline beyond this point.

Research on the Vibration Fatigue Characteristics of Ancient Building Wood Materials

In this study, we selected ancient building timber as the research object. A series of static load tests were conducted to analyze the different performances of timber under tensile and compressive loads. After that, vibration fatigue tests on ancient timber samples were carried out under different upper limit stress ratios. Finally, a dynamic constitutive model of ancient timber was established based on the Ramberg–Osgood model. The static load test results show that the tensile strength was approximately 80% of the compressive strength. Meanwhile, the samples that failed under compressive pressure had obvious residual strength, and their failure strains were also much larger than those under tensile stress. In the vibration fatigue tests, the stress–strain curves were analyzed and the results showed that the curves displayed a trend moving to sparse from dense during the loading process. Meanwhile, the curves moved right with the increase in the upper limit stress ratios. The relationship between axial strain and the number of cycles appeared to be characterized by a three-stage form, i.e., damage occurrence, damage expansion, and damage penetration, and this relationship was formulated by a nonlinear function model. Finally, a dynamic constitutive model with high accuracy in describing the vibration fatigue characteristics of ancient timber was established by converting constant parameters to the variable parameters of the Ramberg–Osgood model.

Investigation on the responses of geotechnical materials to unloading and seepage based on the CFD-DEM coupling method

The unloading issue is prevalent in underground engineering and significantly affects construction safety and the operation of surrounding facilities, while research regarding it is still relatively scarce. A novel CFD-DEM coupling method with dynamic fluid meshes is proposed to reproduce the unloading effect and reveal its micro-scale mechanisms. It adopts uniformly distributed point sets to generate/update fluid meshes and solves with a proposed numerical mapping method. The one-dimensional linear unloading modeling method is further established. The numerically obtained excess pore pressure and rebound deformation under the one-way drained condition are compared with the analytical solutions. The coupling method demonstrates considerable reliability in forecasting the pore pressure response and its advantage for predicting rebound deformation is revealed. The evolutions of the fluid velocity field, particle displacement field, and pore pressure distribution profile are described. The influences of fluid compressibility, unloading rate, unloading volume and initial pore pressure on the unloading characteristics are carefully investigated. The results indicate that the pore pressure is obviously influenced by the selected factors. However, the impact of unloading volume on the final rebound deformation is most significant. Finally, influences of frictionless walls, two-way drained conditions, buoyancy and fluid viscosity on the unloading response are further discussed.