Rocketry employs cryogenic refrigeration to increase the density of propellants, such as oxygen, and stores the propellant as a liquid. In addition to propellant liquefaction, cryogenic refrigeration can also conserve propellant and provide propellant subcooling and densification. Previous studies analyzed vapor conditioning of a cryogenic propellant, which occurred by either a heat exchanger positioned in the vapor or by using the vapor as the working fluid in a refrigeration cycle. This study analyzes the refrigeration effects of a heat exchanger located beneath the vapor-liquid interface of liquid oxygen. This study predicts the mass liquefaction rate and heat transfer coefficient for liquid oxygen using two different models, a Kinetic Theory Model and a Cold Plate Model, and compares both models to experimental data. The Kinetic Theory Model overestimated the liquefaction rate and heat transfer coefficient by five to six orders of magnitude, while the Cold Plate Model underestimated the liquefaction rate and heat transfer coefficient by one to two orders of magnitude. This study also suggested a model to predict the densification rate of liquid oxygen, while the system is maintained at constant pressure. The densification rate model is based on transient heat conduction analysis and provides reasonable results when compared to experimental data.

No / It is important to consider the potential instability of the seabed due to the accumulation of wave-induced pore pressure in the design of a composite breakwater as the pore pressure within the seabed can considerably build-up under waves loading and eventually leads to a sharp decrease of the effective stress. Due to the importance in practical engineering, many theoretical models have been developed to evaluate the magnitude and distribution of the residual pore pressure. However, most of these studies treat the soil skeleton as an invariant medium, which ignores the damping of the soil strength due to the reduction of the effective stress. In this study, a two-dimensional poro-elastoplastic model, in which the influence of the reduction of the effective stress on the soil strength has been considered, is proposed to investigate the accumulation of pore water pressure around a composite breakwater and its effect on the soil characteristics. The simulation results show that the liquefaction is likely to occur around the toe of the breakwater due to the accumulation of pore water pressure there. The liquefaction leads to the decrease of soil resistance, which has great effect on the development of the residual pore pressure. Analysis shows that the development of residual pore pressure is also greatly affected by both the wave height and soil permeability. The simulation demonstrates that if the decrease of soil resistance is not considered, the soil liquefaction depth will be overestimated. / National Natural Science Foundation of China (Grant No. 51479053), the 111 Project (Grant No. B12032), the marine renewable energy research project of State Oceanic Administration (GHME2015GC01), the Natural Science Foundation of Jiangsu province (Grant No. BK20150804), Colleges and Universities in Jiangsu Province Plans for Graduate Research and Innovation Projects (Grant No. B1504708) and the Distinguished Visiting Fellowship from the Royal Academy of Engineering

Yes / When ocean waves propagate over porous seabed, they cause variations of the pore pressure within seabed, leading to the possible wave attenuation and soil liquefaction. In order to advance and improve our understanding of the process of wave-induced seabed liquefaction and its impact on wave propagation, systematical experiments are carried out in a wave flume with a soil basin filled with silt. Both the pore pressures and water surface elevations are measured simultaneously, while the seabed liquefaction is videotaped using a high-speed camera. Laboratory measurements show that the pore pressure in surface layer mainly oscillates over time, while the wave period averaged pore pressure has little change. In the deep layer, however, the wave period averaged value of the pore pressure builds up dramatically. The results show that the wave height decreases rapidly along the direction of wave propagation when seabed liquefaction occurs. Such a wave attenuation is greatly enhanced when the liquefaction depth further increases. The experiments also demonstrate that the conditions (wave height and wave period) of incident waves have significant impacts on the wave-induced pore pressures, liquefaction depth and wave attenuation in a silt bed. / National Natural Science Foundation of China (Grant No. 51479053), the 111 Project (Grant No. B12032), the marine renewable energy research project of State Oceanic Administration (GHME2015GC01), the Fundamental Research Funds for the Central University, China (Grant No. 2013B31614), the Colleges and Universities in Jiangsu Province Plans to Graduate Research and Innovation (Grant No. B1504708), and Open Foundation of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University (Grant No: 2016491011).

No description available.

Earthen levees are crucial components of a nation's flood protection system. However, in some regions, these levees face the unique challenge of being subjected to both floods and earthquakes throughout their lifespan, an aspect that is relatively unexplored in the existing literature. The primary aim of this research is to examine earthquakes' and floods' effects on earthen levee failures. Using numerical simulations, the seepage, slope stability, and liquefaction potential of an earthen levee were modeled by considering compound of different floods and earthquakes scenarios. Elkhorn Levee in Sacramento, CA, was used as a representative case study for the simulations. The probability of levee failure and the extent of the breach caused by compound flood-earthquake scenarios are further determined by Fault Tree Method. The findings provide a practical approach to analyzing levee systems under multi-hazard conditions and enhancing levee resilience.

No description available.

When the excess pore water pressure generated during an earthquake dissipates in saturated loose sand, it causes post-liquefaction reconsolidation that can potentially yield substantial damage to the structure. To build resilient infrastructure, it is paramount to estimate these settlements as well as introduce soil reinforcement techniques to mitigate associated risks. Although there are abundant studies on liquefaction triggering assessment, the study of post-liquefaction settlement and the effects of stone columns as soil reinforcement is a relatively less established field. Generally, simplified empirical methods are employed for settlement evaluations. However, they possess several limitations such as the influence of non-liquefiable layers, soil fabric, permeability, and so on. Numerical models can be utilized to capture these effects with proper validation. This study evaluates the performance of stone columns in reducing seismically induced post-liquefaction settlement utilizing the Finite Element Method (FEM) and constitutive relationship, PM4Sand model, as it has been extended to account for reconsolidation settlement. The ability of the numerical framework to capture reconsolidation settlement is validated by replicating a shake table test performed on Ottawa F-55 sand. Results are compared with a previous numerical study inspired by the same experiment. After validation, a generic numerical model is proposed, and the performance of the natural ground and the reinforced ground is compared. A parametric analysis using 12 different ground motions is performed to assess the effect of varying ground motion intensity on the post-liquefaction settlement. The analysis is also performed with the conventional PM4Sand model (without the extension for reconsolidation). Finally, simulations are performed with a footing load above the soil model. The results demonstrate that (a) the presence of stone columns reduces post-liquefaction settlement, and (b) conventional constitutive models can highly underpredict post-liquefaction settlement. Further research is required to assess the effects of (a) 3D, (b) variations in permeability, (c) parametric analysis of stone columns, and (d) densification of stone columns. / Master of Science / When subjected to an earthquake, loose saturated sand may undergo liquefaction and exhibit a reduction in shear strength due to a rise in excess pore water pressure and the corresponding reduction in effective stress. This leads to failures associated with settlements resulting from the gradual dissipation of excess pore pressures. This mechanism results in post-liquefaction settlement. Several authors have investigated the mechanism of the post-liquefaction behavior of sand and proposed methodologies to assess the deformation caused by seismic loads. They mainly conclude that the reconsolidation mechanism is characterized by a decrease in the overall soil stiffness and an increase in permeability. Among different methodologies to quantify this settlement, finite element numerical modeling is the most widely used. The primary task in performing such numerical simulation is to select the best constitutive model (i.e., stress-strain relationships) that can accurately capture post-liquefaction behavior. In this study, the capabilities and limitations of the most common constitutive models are reviewed. Moreover, the efficacy of stone columns is also assessed to mitigate the risk posed by liquefaction. Firstly, the numerical framework is validated against data from a shake table test experiment. Then, a numerical model is proposed and subjected to different seismic motions. The settlement of the ground with and without stone columns is assessed and compared for all motions. In addition, the efficacy of stone columns is also analyzed by simulating the model with a footing load. Thus, this study provides insights into the effectiveness of stone columns under different seismic motions.

Energibolaget Stockholm Exergi (SE) har satt upp målet att driva en klimatpositiv verksamhet till 2025. För att möta miljömålet planerar företaget att bygga en BECCS-anläggning (Bio Energy Carbon Capture and Storage) till kraftvärmeverket KVV8 där biogen koldioxid avskiljs med HPC-absorption (Hot Potasium Carbonates). Den avskilda koldioxiden ska därefter förvätskas, skeppas och lagras i en djuphavsbotten. I anslutning med BECCS-anläggningen byggs därför en kylanläggning för att förvätska och trycksätta den avskilda koldioxiden.  Förvätskningsanläggningen för koldioxid planeras inte vara i drift under sommarmånaderna juni till och med augusti då KVV8 är avstängd. Sommartid är högsäsong för fjärrkylaproduktionen på SE:s fjärrkylanät och under värmetopparna finns ett behov av extra redundans på nätet. Därför studeras möjligheten att nyttja förvätskningsanläggningen till fjärrkylaproduktion.  Utformningen av en förvätskningsanläggning med önskade slutvillkor om 7 bar och -50 ̊C är idag inte framtagen. Studien listar därför hur tre av de anläggningstyper som undersöks mest idag skulle kunna användas för fjärrkylaproduktion; dels en CO2-NH3-kaskadcykel (Fall 1), en NH3-extern cykel (Fall 2) och en CO2-intern cykel (Fall 3). Modellen för kaskadcykeln är framtagen i av Alabdulkarem et al. (2012) samt Dopazo och Fernández-Seara (2010). Modellerna för den NH3-externa och CO2-interna kylcyklerna är framtagna av Adhikari et al. (2014) och Øi et al. (2016). I det här arbetet har anläggningarna simulerats i Chemcad och anpassats till SE:s ingångs och produktvillkor på CO2-gasen. Enhetliga processvillkor har använts för simuleringarna av Fall 1-3. Därefter har förslag på hur Fall 1-3 kan nyttjats för fjärrkylaproduktion tagits fram och simulerats.  För Fall 1,2 och 3 framtogs kopplingsförslag som genererade kyleffekter till fjärrkylanätet om 22,2; 15,6 och 13,1 MW. COP för kylcyklerna beräknades till 4,6; 5,8 och 4,1.  Investeringsbehovet bedöms högt främst till följd av rördragning och markarbete för ett sjövattenledningspar som tillförser fjärrkylaanläggningens kylvattenbehov. Investeringsbehovet för Fall 1, 2 och 3 bedömdes till ungefär 52,7; 50,6 och 54,2 MSEK. Av det totala investeringsbehovet står sjövattenledningen för ungefär halva investeringsbehovet. I den här studien har höga påslagsfaktorer använts för bland annat oförutsedda kostnader eftersom att utredningen är i ett tidigt stadie.  Som alternativ till fjärrkylaproduktion med direkt anslutning mellan förvätskningsanläggningen och fjärrkylanätet diskuteras även användningen av en mellankrets (Fall 4). Ett förslag på hur mellankretsen kan utformas och dimensioneras har tagits fram av Energiingenjörspraktikant Nasim Rafieyan (2020) under handledning av Förbränningsingenjör Hans P. Larsson. Mellankretsen har tagits fram med tre olika köldbärare; etanol, metanol och en metanol/vattenlösning. / The energy company Stockholm Exergy (SE) has set the goal of running a climate positive business by 2025. To meet the environmental goal, the company plans to build a BECCS plant (Bio Energy Carbon Capture and Storage) for the combined heat and power plant KVV8. The carbon dioxide of the plants flue gases will then be separated with HPC absorption (Hot Potassium Carbonates). The separated carbon dioxide is then to be liquefied, shipped and stored in a deep sea bottom. To liquefy the separated carbon dioxide a cooling plant is being built in connection to the BECCS facility.  The liquefaction plant is expected to not be operating between the summer months of June through August. Summer time is also the when the demand on district cooling is at its highest. To increase the redundancy of cooling capacity during high demand periods the possibility of using the liquefaction plant for district cooling production has been investigated.  The design of a liquefaction plant with the final conditions of 7 bar and -50 ̊C is yet to be fully developed. The study therefore investigates how three of the most researched liquefaction types could be used for district cooling production which is a CO2-NH3 cascade cycle (Case 1), an NH3 external cycle (Case 2) and a CO2 internal cycle (Case 3). The model for the cascade cycle is developed in by Alabdulkarem et al. (2012) as well as Dopazo and Fernández-Seara (2010). The models for the NH3 external and CO2 internal cooling cycles has been developed by Adhikari et al. (2014) and Øi et al. (2016). The liquefaction plants have been simulated in Chemcad with uniform process conditions as well as SE’s CO2 input and product conditions. Subsequently, a proposal on how each of the three cases can be used for district cooling production were developed.  For proposals on district cooling production for Case 1-3 are expected to be generating a cooling effect of 22.2, 15.6 and 13.1 MW. The COP for the cooling cycles was calculated to be 4.6, 5.8 and 4.1.  The investment capital is expected to be high, mainly as a result of piping and ground work for a seawater pipeline to supply the district cooling plant with cooling water. The total investment capital for Case 1, 2 and 3 were estimated to be approximately 52.7, 50.6 and 54.2 MSEK. The sea water pipeline accounts for almost half of the total investment capital. Since the investment capital has been reviewed at an early stage typical percentages such as unforeseen costs were set high for the project.  As an alternative to district cooling production where the liquefaction plant and the district cooling network are directly connected, an intermediate circuit has also been reviewed (Case 4). A proposal on how the intermediate circuit could be designed and dimensioned has been developed by Energy Engineering trainee Nasim Rafieyan (2020) under the supervision of Combustion Engineer Hans P. Larsson (SE). The intermediate circuit has been dimensioned using three different refrigerants; ethanol, methanol and a methanol/water solution.

Passive site remediation is a new concept proposed for non-disruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. It is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location using the natural groundwater flow. The purpose of this research was to establish the feasibility of passive site remediation through identification of stabilizing materials, a study of how to design or adapt groundwater flow patterns to deliver the stabilizers to the right place at the right time, and an evaluation of potential time requirements and costs. Stabilizer candidates need to have long, controllable gel times and low viscosities so they can flow into a liquefiable formation slowly over a long period of time. Colloidal silica is a potential stabilizer for passive site remediation because at low concentrations it has a low viscosity and a wide range of controllable gel times of up to about 100 days. Loose Monterey No. 0/30 sand samples (Dr = 22%) treated with colloidal silica grout were tested under cyclic triaxial loading to investigate the influence of colloidal silica grout on the deformation properties. Distinctly different deformation properties were observed between grouted and ungrouted samples. Untreated samples developed very little axial strain after only a few cycles and prior to the onset of liquefaction. Once liquefaction was triggered, large strains occurred rapidly and the samples collapsed within a few additional cycles. In contrast, grouted sand samples experienced very little strain during cyclic loading. What strain accumulated did so uniformly throughout loading and the samples remained intact after cyclic loading. In general, samples stabilized with 20 weight percent colloidal silica experienced very little (less than two percent) strain during cyclic loading. Sands stabilized with 10 weight percent colloidal silica tolerated cyclic loading well, but experienced slightly more (up to eight percent) strain. Treatment with colloidal silica grout significantly increased the deformation resistance of loose sand to cyclic loading. Groundwater and solute transport modeling were done using the codes MODFLOW, MODPATH, and MT3DMS. A "numerical experiment" was done to determine the ranges of hydraulic conductivity and hydraulic gradient where passive site remediation might be feasible. For a treatment are of 200 feet by 200 feet, a stabilizer travel time of 100 days, and a single line of low-head (less than three feet) injection wells, it was found that passive site remediation could be feasible in formations with hydraulic conductivity values of 0.05 cm/s or more and hydraulic gradients of 0.005 and above. Extraction wells will increase the speed of delivery and help control the down gradient extent of stabilizer movement. The results of solute transport modeling indicate that dispersion will play a large role in determining the concentration of stabilizer that will be required to deliver an adequate concentration at the down gradient edge. Consequently, thorough characterization of the hydraulic conductivity throughout the formation will be necessary for successful design and implementation of passive site remediation. The cost of passive site remediation is expected to be competitive with other methods of chemical grouting, i.e. in the range of $60 to $180 per cubic meter of treated soil, depending on the concentration of colloidal silica used. / Ph. D.

In historical, large-magnitude earthquakes, lateral spreading has been a very damaging type of ground failure. When a subsurface soil deposit liquefies, intact blocks of surficial soil can move downslope, or toward a vertical free face, even when the ground surface is nearly level. A lateral spread is defined as the mostly horizontal movement of gently sloping ground (less than 5% surface slope) due to elevated pore pressures or liquefaction in undelying, saturated soils. Here, lateral spreading is defined specifically to exclude liquefaction failures of steeper embankments and retaining walls, which can also produce lateral surface deformations. Lateral spreads commonly occur at waterfront sites underlain by saturated, recent sediments and are particularly threatening to buried utilities and transportation networks. While the occurrence of soil liquefaction and lateral spreading can be predicted at a given site, methods are needed to estimate the magnitude of the resulting deformations. In this research effort, an empirical model was developed for predicting horizontal and vertical surface displacements due to liquefaction-induced lateral spreading. The resulting model is called "EPOLLS" for Empirical Prediction Of Liquefaction-induced Lateral Spreading. Multiple linear regression analyses were used to develop model equations from a compiled database of historical lateral spreads. The complete EPOLLS model is comprised of four components: (1) Regional-EPOLLS for predicting horizontal displacements based on the seismic source and local severity of shaking, (2) Site-EPOLLS for improved predictions with the addition of data on the site topography, (3) Geotechnical-EPOLLS using additional data from soil borings at the site, and (4) Vertical-EPOLLS for predicting vertical displacements. The EPOLLS model is useful in phased liquefaction risk studies: starting with regional risk assessments and minimal site information, more precise predictions of displacements can be made with the addition of detailed site-specific data. In each component of the EPOLLS model, equations are given for predicting the average and standard deviation of displacements. Maximum displacements can be estimated using probabilities and the gamma distribution for horizontal displacements or the normal distribution for vertical displacements. / Ph. D.