To address the fuel-air ratio imbalance caused by the turbo lag during the loading process of conventional turbocharged diesel engines,a transient matching method for an electric supercharger was proposed,and the tran-sient performance of a diesel engine was studied with a focus on fuel-air cooperative control.Based on a heavy-duty diesel engine,a one-dimensional simulation model was established.The electric supercharger was arranged upstream of the engine's single-stage turbocharger.During a sudden,constant-speed loading process with a duration of 1.0 s and a speed of 950 r/min(load change:0-90%),an electric supercharger selection scheme was determined through transient calculations using the proposed matching method.The selected motor had a rated power of 8 kW and a rated speed of 50 000 r/min.Subsequently,a test bench of the electric supercharger system was constructed,and transient loading tests were performed for five types of fuel injection schemes and different electric supercharger intervention methods.The results showed that for a fuel injection scheme involving a 0.5 s ramp-up to 70%load,the intervention of the electric supercharger accelerated the intake response speed during the transient process.As the intake mass flow rate was increased,the intake pressure increased and the mixture in the cylinder burned more completely.The peak in-cylinder pressure and peak heat release rate increased by 0.76 MPa and 30.03 J/(℃A),respectively,while the peak in-cylinder average temperature and combustion duration decreased by 49.17 K and 0.91℃A,respectively.Fur-thermore,the combustion center of gravity advanced,indicating an improved combustion effect.The peak equiva-lent ratio decreased to below the critical equivalent ratio of 0.80.The electric supercharger significantly reduced soot emissions while exerting only a minor effect on NOx emissions.The lowest transient soot emission peak of 167.34 mg/m3 was achieved using an injection scheme featuring a step increase to 45%load at 0.1 s coordinated with the electric supercharger.Therefore,the control strategy combining the fuel injection scheme with electric super-charger intervention was an effective means to achieve low emissions.
In the field of engineering research,the creep behavior of soft clay and the evaluation of its long-term strength are crucial issues in geotechnical engineering.In this paper,the influence of drainage conditions on the creep characteristics and long-term strength of Tianjin coastal clay were analyzed through triaxial creep tests conducted un-der various stress levels,confining pressures and drainage conditions.The existing methods for determining the long-term strength of soil were discussed and improved,and a novel approach based on stress-strain isochronous curves was proposed to assess the long-term shear strength indicators of the soil.The proposed method was validated through comparative analysis,demonstrating its effectiveness and rationality in practical applications.Results indicate that under the same confining pressure conditions,the creep amount and deformation stability time increase with an in-crease in the stress level.At the same stress level,the creep amount at each stress level decreases with an increase in the confining pressure.The creep deformation difference is significant under different drainage conditions.During the process of soil creep,the drainage condition is an important factor affecting the shear strength and strength indicators of soil.Under consolidated and undrained creep conditions,the long-term shear strength τ∞ is about 84%to 93%of the instantaneous shear strength τ0,among which the cohesion decreases significantly,and the long-term cohesion c∞ is about 37%of the instantaneous cohesion c0.Meanwhile,the internal friction angle remains relatively unchanged.Under consolidated and drained creep conditions,the long-term shear strength τ∞ is about 106%to 116%of the instan-taneous shear strength τ0,with only a minor reduction in cohesion and a significant increase in the internal friction angle.In addition,the long-term internal friction angle φ∞ is about 110%of the instantaneous internal friction angle φ0.The research results can provide a reference for the long-term stability analysis and engineering design of soil in coastal soft soil areas.
The rapid and accurate detection of moisture content in clayey shield tunnel muck is a key issue for improv-ing the muck disposal efficiency and reducing environmental impact.In this paper,an intelligent identification method based on VIM-OFE was proposed,and experiments were conducted using three clayey muck samples from different geological strata.A dynamic analysis window was applied to Sample 1 to extract the spectral intervals highly correlated with the moisture content,specifically 1 438-1 455 nm and 1 916-1 926 nm.The resulting prediction models achieved high accuracy within these intervals.The study further examined the impact of absorption peak area and depth features on the model performance and compared the proposed method with iPLS,SiPLS and CSMW in terms of predictive accuracy and computational efficiency.Results show that VIM-OFE demonstrated superior predic-tion performance while maintaining a comparable computation time.Both the single-soil and mixed-soil moisture pre-diction models were developed,with the mixed model achieving high accuracy in Samples 1 and 3(R2＞0.890),indicating strong generalization capability.Additionally,the influence of particle size and mineral composition on near-infrared(NIR)spectral response was analyzed,and strategies such as outlier optimization and the development of a regional spectral database were proposed to enhance the model robustness and adaptability.The proposed method offers a reliable technical approach for on-site rapid detection of moisture content in clayey shield tunnel muck and shows promising application potential in engineering practice.
Human body's subjective perception of environmental vibrations can be altered by introducing another vibrational stimulus—the vibration masking effect.Understanding the impacts of the masking effects on human vibra-tion perception is theoretically relevant for optimizing environmental vibrations,regulating vibration perception,and enhancing human-factor ergonomics.A subjective evaluation experiment on human vibration perception was con-ducted,investigating the frequency-domain masking effect of vertical vibration on seated human subjects.A novel evaluation metric—the masking beneficial index(MBI)—and its calculation method were proposed,revealing the influence laws of key variables,such as the amplitude ratio between the masking vibration and the target vibration and their frequency difference,on the masking effect.Results reveal that under constant amplitude ratios,masking efficiency increases with the frequency difference when masking vibrations induce lower discomfort than target vibra-tions,thereby correlating with reduced discomfort perception of target vibrations.Under fixed frequency differences,an optimal amplitude ratio maximizing masking efficiency is observed,which increases with the target signal amplitude,whereas the efficiency at this ratio decreases with the increasing amplitude,demonstrating nonlin-earity in human vibration perception.
As an important in-situ resource for the construction of lunar space stations,the lunar soil geopolymer is vital for promoting deep space exploration.On the Moon,a lunar base is often subjected to extreme temperatures from day to night and meteorite impact shock loads,and the compressive strength,flexural strength and impact re-sistance of traditional simulated lunar soil geopolymers are substandard.Aimed at the extreme environmental condi-tions on the Moon,the impact resistance of simulated lunar soil geopolymers under extreme lunar environments was improved by adding polypropylene fibers(PPFs),and falling hammer impact tests were conducted on cylindrical specimens with two impact energies of 5 J and 10 J.The effects of different temperatures on the impact resistance and fiber crack resistance of simulated lunar soil geopolymers were studied from aspects such as the mechanical strength,number of impacts,energy consumption and damage morphology.Based on mathematical and statistical modeling,the results of impact tests were examined for their reasonableness,and life prediction was also performed.Test results showed that the strengths and impact resistance of the simulated lunar soil geopolymers at high temperatures were significantly improved compared with those at room temperature.With a decrease in temperature,their strengths and impact resistance decreased to some extent,and the compressive strength,flexural strength and impact resistance of each test group reached their lowest values when temperature dropped to-60℃.A fiber length of 6 mm with a doping amount of 0.4%(mass fraction)was the optimal doping combination for fiber-reinforced simulated lunar soil geo-polymers.A Weibull distribution model was used to check the impact resistance test results and predict the life,and the values of correlation coefficient R2 of measured samples were all greater than 0.800.Through a comparison with the measured data,it was found that the trend of damage impact life at different failure probabilities was consistent with those of measured values,indicating that the two-parameter Weibull distribution can reasonably describe the distribution characteristics of the number of times of impact resistance for PPF-reinforced simulated lunar soil geo-polymers.The research results in this paper can provide a scientific basis for the selection of construction materials of lunar research stations in the future.
