Browse Topic: Underbodies
Wind noise is one of the largest sources to interior noise of modern vehicles. This noise is encountered when driving on roads and freeways from medium speed and generates considerable fatigue for passengers on long journeys. Aero-acoustic noise is the result of turbulent and acoustic pressure fluctuations created within the flow. They are transmitted to the passenger compartment via the vibro-acoustic excitation of vehicle surfaces and underbody cavities. Generally, this is the dominant flow-induced source at low frequencies. The transmission mechanism through the vehicle floor and underbody is a complex phenomenon as the paths to the cavity can be both airborne and structure-borne. This study is focused on the simulation of the floor contribution to wind noise of two types of vehicles (SUV and Sports car), whose underbody structure are largely different. Aero-Vibro-acoustic simulations are performed to identify the transmission mechanism of the underbody wind noise and contribution. The external fluctuating pressure fields are simulated using computational fluid dynamics based on the Lattice Boltzmann Method (LBM). The vehicle exterior and interior vibro-acoustic coupling and transmission are simulated using subsystems modeled by the finite-element (FEM), boundary element methods (BEM) and statistical energy analysis (SEA). The analysis results are discussed, and a contribution analysis is proposed to identify potential improvements.
The automotive sector’s growing focus on sustainability has been spurred to investigate the creation of sustainable resources for different parts, emphasizing enhancing efficiency and minimizing environmental harm. For use in automobile flooring trays and underbody shields, this study examines the impact of injection molding on composite materials made of polyvinyl chloride (PVC) and Linum usitatissimum (flax) fibers. As processed organic fiber content was increased, the bending and tensile rigidity initially witnessed an upsurge, peaking at a specific fiber loading. At this optimal loading, the composite exhibited tensile strength, flexural strength, and elastic modulus values of 41.26 MPa, 52.32 MPa, and 2.65 GPa, respectively. Given their deformation resistance and impact absorption attributes, the mechanical properties recorded suggest that such composites can be efficiently utilized for automotive underbody shields and floor trays. The inherent structure of the flax fiber within the PVC matrix constrains molecular movement, leading to superior deformation resistance that enhances impact force absorption. This characteristic is also responsible for the observed decline in impact strength as fiber content increases. The investigation’s results add to the expanding literature on environmentally friendly materials in automobile manufacturing and offer important new information for designing and producing floor trays and underbody shields made of PVC composites with Linum usitatissimum fiber.
ABSTRACT Presented are two designs for compact, low-profile UGVs with high cross-country mobility, intended for underbody operations with heavy manned vehicles. These UGVs are designed to remotely detect and assess combat damage incurred during combat operations, and analyze wear, leaks, and cracks, without the need for a human technician to be exposed to enemy fire, allowing crews to rapidly assess the conditions of their vehicles. Since robots required for underbody inspection would necessarily maintain a low, compact profile, they could also perform effective last-mile resupply in a contested environment, their small size allowing them to hide behind terrain and battlefield debris much more effectively than a heavy logistics robot. Naturally, a robotic vehicle that is capable of rapid underbody inspection of friendly vehicles or last-mile resupply could also be easily adapted as a combat platform to be used against enemy vehicles. Citation: A. Washington, et al., “Expendable Low-Profile Robot for Vehicle Underbody Operation”, in Proceedings of the Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), NDIA, Novi, MI, Aug. 15-17, 2023.
In electrified automobiles, wind noise significantly contributes to the overall noise inside the cabin. In particular, underbody airflow is a dominant noise source at low frequencies (less than 500 Hz). However, the wind noise transmission mechanism through a battery electric vehicle (BEV) underbody is complex because the BEV has a battery under the floor panel. Although various types of underbody structures exist for BEVs, in this study, the focus was on an underbody structure with two surfaces as inputs of wind noise sources: the outer surface exposed to the external underbody flow, such as undercover and suspension, and the floor panel, located above the undercover and battery. In this study, aero-vibro-acoustic simulations were performed to clarify the transmission mechanism of the BEV underbody wind noise. The external flow and acoustic fields were simulated using computational fluid dynamics. The vehicle structural vibration and sound fields of the interior and exterior cabin were analyzed using vibroacoustic models consisting of three subsystems modeled by the finite-element or boundary-element method: The first is an underbody structure finite-element model containing a white body, suspension, battery, and undercover; the second is the interior cabin space boundary-element model; the third is the exterior cabin space finite-element model for analyzing acoustic radiation resulting from vehicle structural vibration for the small space between the floor panel and battery, the motor room and the under-vehicle space between the ground and undercover. The analysis results using the vehicle model reveal that the pressure fluctuations acting on the floor panel are more-dominant inputs for cabin noise than those acting on the outer surface. The pressure fluctuation acting on the floor panel is affected by the acoustic mode of the space between the battery and the floor panel.
ABSTRACT This paper reviews the Army Generic Hull [1-5] as a vital developmental tool for underbody blast modeling and simulation applications. Since 2010, it has been used extensively to help calibrate and validate various numerical software codes and methodologies. These are being used extensively today in the development of underbody armor, as well as mine blast subsystems such as seats, to protect both military vehicles and their occupants. In the absence of easily shareable information in this domain due to data classification, this specially formulated product is a valuable part of any toolset for underbody blast development and product design. Citation: K. Kulkarni, S. Kankanalapalli, V. Babu, J. Ramalingam, R. Thyagarajan, “The Army Generic Hull As A Vital Developmental Tool For Underbody Blast Applications,” In Proceedings of the Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), NDIA, Novi, MI, Aug. 16-18, 2022.
This study numerically investigates the vortex flow that is generated within the underbody diffuser of a bluff body. Previous experimental studies have identified the existence of three main types of trailing vortex structures that correlate with the aerodynamic behavior of an underbody diffuser in ground-effect. The “force enhancement” behavior of the underbody diffuser results in a pair of longitudinal counter-rotating vortices that are generated off of the sidewalls within the upswept section of the underbody diffuser. By comparing the aerodynamic forces with the resulting flow field induced by the trailing vortex pair, this investigation aims to identify a relationship between the circulation of the vortices and the resulting downforce. It is hypothesized that the circulation generation of the vortex pair is directly linked to the generation of the downforce, just as with a wing. The bluff body features an elliptical nose, a straight midsection, and a thin-walled underbody diffuser with an upswept angle of 17 degrees. The flow is simulated using the opensource computational fluid dynamics solver OpenFOAM, which solves the Reynolds Averaged Navier-Stokes equations with a turbulence model and wall functions using the SIMPLE algorithm. The ride height of the bluff body is varied while the flow Reynolds number based on the length of the body is kept constant at 1.68 × 106. It is shown that during the “force enhancement” behavior of the lift curve, the lift coefficient is linearly related to the circulation of the counter-rotating vortex pair. This trend is shown at multiple axial locations within the diffuser flow. Moreover, the circulation of the vortex pair increases with axial position within the diffuser. Downstream of the diffuser exit plane the circulation of the trailing vortex pair begins to decrease.
A multi-year, multi-vehicle study was conducted to quantify the aerodynamic drag changes associated with drag reduction technologies for light-duty vehicles. Various technologies were evaluated through full-scale testing in a large low-blockage closed-circuit wind tunnel equipped with a rolling road, wheel rollers, boundary-layer suction and a system to generate road-representative turbulent winds. The technologies investigated include active grille shutters, production and custom underbody treatments, air dams, wheel curtains, ride height control, side mirror removal and combinations of these. This paper focuses on mean surface-, wake-, and underbody-pressure measurements and their relation to aerodynamic drag. Surface pressures were measured at strategic locations on four sedans and two crossover SUVs. Wake total pressures were mapped using a rake of Pitot probes in two cross-flow planes at up to 0.4 vehicle lengths downstream of the same six vehicles in addition to a minivan and a pick-up truck. A smaller rake was used to map underbody total pressures in one cross-flow plane downstream of the rear axle for three of these vehicles. The results link drag reduction due to various technologies with specific changes in vehicle surface, rear underbody and wake pressures, and provide a database for numerical studies. In particular, the results suggest that existing or idealized prototype technologies such as active grille shutters, sealing the external grille and ride height control reduce drag by redirecting incoming flow from the engine bay or underbody region to smoother surfaces above and around the vehicle. This mechanism can enhance the reduction in wheel drag due to reduced wheel exposure at lowered ride height. Sealing the external grille was found to redirect the flow more efficiently than closing the grille shutters, and resulted in greater drag reduction. Underbody treatments were also found in some cases to redistribute the flow around the vehicle to reduce pressure drag in addition to underbody friction drag. The magnitude and spatial extent of the measured pressure changes due to the various technologies were often consistent with the amount of drag reduction.
During Operation Iraqi Freedom and Operation Enduring Freedom, improvised explosive devices were used strategically and with increasing frequency. To effectively design countermeasures for this environment, the Department of Defense identified the need for an under-body blast-specific Warrior Injury Assessment Manikin (WIAMan). To help with this design, information on Warfighter injuries in mounted under-body blast attacks was obtained from the Joint Trauma Analysis and Prevention of Injury in Combat program through their Request for Information interface. The events selected were evaluated by Department of the Army personnel to confirm they were representative of the loading environment expected for the WIAMan. A military case review was conducted for all AIS 2+ fractures with supporting radiology. In Warfighters whose injuries were reviewed, 79% had a foot, ankle or leg AIS 2+ fracture. Distal tibia, distal fibula, and calcaneus fractures were the most prevalent. The most common injury mechanisms were bending with probable vehicle contact (leg) and compression (foot). The most severe injuries sustained by Warfighters were to the pelvis, lumbar spine, and thoracic spine. These injuries were attributed to a compressive load from the seat pan that directly loaded the pelvis or created flexion in the lumbar spine. Rare types of injuries included severe abdominal organ injury, severe brain injury, and cervical spine injury. These typically occurred in conjunction with other fractures. Mitigating the frequently observed skeletal injuries using the WIAMan would have substantial long-term benefits for Warfighters.
In the last decades it has been constantly debated about the behaviour of the human being towards a better usage of the natural resources through a restructuring of unsustainable processes. Considering the case for road vehicles, it was noticed a potential for improvement by assigning a more “harmonious” configuration to the underbody of the vehicles, in order to contribute to the reduction of aerodynamic drag. This region of the vehicles is often overlooked by the automakers because it is not easily accessible to the eyes of the consumer. The objective of this paper is, therefore, to improve the aerodynamic performance of the underbody region of a compact hatchback car available in the Brazilian market. This project proposes a new underbody configuration that promotes a more harmonious flow under the vehicle, reducing this way the drag coefficient (Cd) hence improving the fuel consumption. A comparative analysis, therefore, was performed between the standard condition of the underbody (baseline) and the experimental configuration by the fluid flow simulation of the tridimensional models using a Computational Fluid Dynamics (CFD) software. Both analysis can be divided in three main stages: the tridimensional geometry modeling in CAD software, the model discretization (the creation of the computational domain and boundary conditions using a mesh generator) and the fluid flow solution in CFD. Based on the analysis of the results obtained for the fluid flow on the baseline, panels (belly pans) were proposed to cover the underbody of the vehicle. This experimental condition presented a reduction on the local drag coefficient, that is, considering only the underbody, of 28,4% and, considering the complete vehicle, of 13%. The total drag coefficient with the proposed panels was reduced from 0.34 to 0.296, which would make the studied model the vehicle with the lowest Cd of its category (compact hatchback) available in the Brazilian market.
A full-system, end-to-end blast modeling and simulation of vehicle underbody buried blast events typically includes detailed modeling of soil, high explosive (HE) charge and air. The complex computations involved in these simulations take days to just capture the initial 50-millisecond blast-off phase, and in some cases, even weeks. The single most intricate step in the buried blast event simulation is in the modeling of the explosive loading on the underbody structure from the blast products; it is also one of the most computationally expensive steps of the simulation. Therefore, there is significant interest in the modeling and simulation community to develop various methodologies for fast running tools to run full simulation events in quicker turnarounds of time. This paper discusses investigation of a fast running blast loading methodology wherein the effects of the soil can be adequately captured without having to employ a highly detailed and computationally intensive soil/explosive model, and the interactions thereof (with each other and with the vehicle), in the simulation. The paper will also present a basis of such methodology utilizing the free air-blast loading data that is readily available and implemented in LS-DYNA, the technical approach for matching the buried blast loading patterns using free-air blast datasets and selection of test cases for evaluation and validation. Test cases include simple flat plate with high deformation and a generic vehicle representative of a military ground vehicle. The results from the development and validation of the methodology are presented along with future technical development strategies.
It is well known that the underbody region of a tractor-trailer is responsible for up to 30% of the aerodynamic drag. This is the highest drag created by any region of a tractor-trailer. There are a number of underbody drag-reduction devices available on the market but they create a few operational issues, such as low ground clearance and ice collection, which inhibit their mass market appeal. In this paper, a novel concept of an underbody aerodynamic device is developed and investigated. The underbody device is a combination of a ramp and a side skirt; which are optimized simultaneously. In addition, the device is made collapsible to facilitate easy storage when not in use (i.e., city driving). NASA’s Generic Conventional Model (GCM); a 1/8th scale model of a generic class-8 tractor-trailer is used to evaluate and optimize the concept. The GCM allows the concept to be applicable to a wider range of tractor-trailers. The studies were conducted using the RANS based turbulence model, k-ω SST in ANSYS Fluent. The simulations were validated with NASA’s experimental data on the GCM model; which include the surface pressure coefficients and a drag coefficient of the model. The results showed that the underbody device decreased the overall drag coefficient by 4.1%. In addition, the adverse negative pressure region in the wake was significantly reduced.
Anthropomorphic test devices (ATDs) have been used in automotive safety research since the 1970s to predict injuries. ATDs must repeatedly perform under a dynamic range of loading rates and reliably distinguish between injuries ranging from minor to severe.
The automotive underbody diffuser is an expansion device which works by speeding up the air flowing underneath a vehicle. This reduces the pressure below the vehicle thereby increasing downforce. When designed properly, it can lead to a massive gain in downforce and even a reduction in drag. However, a majority of the research and development is restricted to motorsport teams and supercar manufacturers and is highly secretive. Most of the publicly available research has been done for very simple shapes (bluff bodies) to study the effects of ground clearance and rake angle. Very little research has been done for complex geometries with vanes, flaps and vortex generators. This paper aims to investigate the effects of the addition of vanes/strakes and flaps, their location as well as angle, on diffuser performance. Computational Fluid Dynamics simulations have been carried out using three dimensional, steady state RANS equations with the k-ε turbulence model on STAR CCM+ V9.06. The simulation methodology has been verified using experimental data first. The diffuser geometry is based on the Formula SAE car developed at the University. Vanes and flaps have been simulated at various positions and angles. The flow features are studied and the performance is quantified in terms of downforce and downforce to drag ratio or efficiency. The vanes increase the downforce by up to 13% and even increase the efficiency. They increase the pumping action of the diffuser and isolate the different channels, minimizing the adverse effects of tire squirt. The addition of a flap above the trailing edge of the diffuser also has a marked effect as it evacuates more air from underneath the car. A maximum improvement in downforce of 25% is seen with the vane and flap used together.
Three laboratory simulated sub-injurious under-body blast (UBB) test conditions were conducted with whole-body Post Mortem Human Surrogates (PMHS) and the Warrior Assessment Injury Manikin (WIAMan) Technology Demonstrator (TD) to establish and assess UBB biofidelity of the WIAMan TD. Test conditions included a rigid floor and rigid seat with independently varied pulses. On the floor, peak velocities of 4 m/s and 6 m/s were applied with a 5 ms time to peak (TTP). The seat peak velocity was 4 m/s with varied TTP of 5 and 10 ms. Tests were conducted with and without personal protective equipment (PPE). PMHS response data was compiled into preliminary biofidelity response corridors (BRCs), which served as evaluation metrics for the WIAMan TD. Each WIAMan TD response was evaluated against the PMHS preliminary BRC for the loading and unloading phase of the signal time history using Correlation Analysis (CORA) software to assign a numerical score between 0 and 1. A weighted average of all responses was calculated to determine body region and whole body biofidelity scores for each test condition. The WIAMan TD received UBB biofidelity scores of 0.62 in Condition A, 0.59 in Condition B, and 0.63 in Condition C, putting it in the fair category (0.44-0.65). Body region responses with scores below a rating of good (0.65-0.84) indicate potential focus areas for the next generation of the WIAMan design.
The present work deals with a computational study of a ‘DrivAer’ car model, the rear-end shape of which corresponds to the Notchback configuration (Heft et al. [1] and Heft [2]). The study investigates the effects of the underbody geometry and wheel rotation on the aerodynamic performance. The configurations with detailed and smooth underbody as well as with stationary and rotating wheels are considered. The computational model applied relies on a VLES (Very Large Eddy Simulation) formulation, Chang et al. [3]. The residual turbulence related to the VLES framework is presently modelled by a RANS-based (Reynolds-Averaged Navier-Stokes), four-equation (D(k,ɛ,ζ, f)/Dt) near-wall eddy-viscosity model, Hanjalic et al. [4]. In addition to the equations governing the kinetic energy of turbulence (kus) and its dissipation rate (ɛus), it solves a transport equation for the quantity , representing a key parameter, as it models the velocity scale in the expression for the corresponding turbulence viscosity. In addition to VLES, all considered flows are simulated within both RANS and Unsteady RANS (URANS) frameworks using the same background model formulation representing the constituent of the VLES method. Whereas the “k-ɛ-ζ-f” model describes fully-modelled turbulence within the RANS/URANS method, it relates to the unresolved sub-scale turbulence within the VLES framework (the relevant quantities are denoted by the subscript ‘us’). Unlike the RANS/URANS method, the VLES method is capable of capturing the spectral dynamics of turbulence to an extent complying with the underlying grid resolution. Accordingly, the superiority of the VLES method is especially visible at the computed evolution of the aerodynamic coefficients, agreeing reasonably well with the experimental database.
Recently, modeling and simulation (M&S) engineers have made impressive strides in improving ground vehicle reliability and soldier safety. This work involved live-fire testing and evaluation (LFT&E) of the effects of underbody improvised explosive device (IED) blasts on moving ground vehicles. A multi-fidelity, multi-temporal M&S methodology was developed and successfully applied towards reconstruction of theater IED events.
A blast buck (Accelerative Loading Fixture, or ALF) was developed for studying underbody blast events in a laboratory-like setting. It was designed to provide a high-magnitude, high-rate, vertical loading environment for cadaver and dummy testing. It consists of a platform with a reinforcing cage that supports adjustable-height rigid seats for two crew positions. The platform has a heavy frame with a deformable floor insert. Fourteen tests were conducted using fourteen PMHS (post mortem human surrogates) and the Hybrid III ATD (Anthropomorphic Test Device). Tests were conducted at two charge levels: enhanced and mild. The surrogates were tested with and without PPE (Personal Protective Equipment), and in two different postures: nominal (knee angle of 90°) and obtuse (knee angle of 120°). The ALF reproduces damage in the PMHS commensurate with injuries experienced in theater, with the most common damage being to the pelvis and ankle. Load is transmitted through the surrogates in a caudal-to-cranial sequential fashion. Damage to the PMHS lower extremities begins within 2 ms after the initiation of foot/floor motion. The Hybrid III cannot assume the posture of the PMHS in rigid seats and exhibits a stiffer overall response compared to the PMHS. The ATD does not mimic the kinematic response of the PMHS lower extremities. Further, the Hybrid III does not have the capability to predict the potential for injury in the high-rate, vertical loading environment. A new ATD dedicated to under-body blast is needed to assist in the effort to mitigate injuries sustained by the mounted soldier.
ABSTRACT For this particular effort, TARDEC Center for Systems Integration (CSI) was tasked to lead an effort to develop an underbody kit that would serve multiple functions. The underbody kit would provide an additional 1,200 lbs of net buoyancy to enhance water mobility per the LAV. This program is in the development and testing phase with a prototype expected to be produced June of 2015. This program is one of multiple efforts to ensure the FOLAV meet all system requirements to keep the vehicle viable to 2035. In addition, the TARDEC concept/prototype must meet the same mine blast protection provided by the underbody D-Kit that was produced for the fleet of vehicles in 2010. This is a unique challenge as a combination of buoyancy, mine blast, and structural requirement on a ground military vehicle is novel idea. Vehicle weight and survivability requirements are difficult challenges on combat vehicles, to include the LAV, so the TARDEC solution would have to reduce the weight of the shell by approximately 60% and still achieve current survivability. Typically 20-30% reductions are considered aggressive, but 60% is usually unattainable. Reference herein to any specific commercial company, product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the Dept. of the Army (DoA). The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government, the DoD, or U.S. Army TACOM Life Cycle Command and shall not be used for advertising or product endorsement purposes.
Vehicle water wading capability refers to vehicle functional part integrity (e.g. engine under-tray, bumper cover, plastic sill cover etc.) when travelling through water. Wade testing involves vehicles being driven through different depths of water at various speeds. The test is repeated and under-body functional parts are inspected afterwards for damage. Lack of CAE capability for wading equates to late detection of failure modes which inevitably leads to expensive design change, and potentially affects program timing. It is thus of paramount importance to have a CAE capability in this area to give design loads to start with. Computational fluid dynamics (CFD) software is used to model a vehicle travelling through water at various speeds. A non-classical CFD approach was deemed necessary to model this. To validate the method, experimental testing with a simplified block was done and then verified with CFD modeling. The simple rectangular block at two different speeds and three immersion depths in water was utilized for the purpose. As a next step a full vehicle test was conducted and was used to validate the simulation method. Fluid structure interaction is also explored.
Electric cars are the future of urban mobility which have very less carbon foot print. Unlike the conventional cars which uses BIW (Body in White), some of the electric cars are made with a space frame architecture, which is light weight and suitable for low volume production. In this architecture, underbody consists of frames, battery pack, electronics housing and electric motor. Underbody drag increases due to air entrapment around these components. Aerodynamic study for baseline model using CFD simulations showed that there was a considerable air resistance due to underbody components. To reduce the underbody drag, different add-ons are used and their effect on drag is studied. A front spoiler (air dam) is used to deflect the incoming air towards sides of the car. A under hood cover for front components, trailing arm cover for trailing arm and rear bumper cover for rear components were used to reduce underbody drag. Finally it is observed that aerodynamic behavior of the car improved drastically due to these add-ons. In the current paper, results of different simulations are discussed in detail with respect to the underbody drag reduction of an electric car. Results of the CFD simulations are validated with wind tunnel measurements. Good correlation is achieved with the test results.
ABSTRACT In order to defeat under body blast events and improve crew survivability, a monocoque aluminum cab structure has been designed as a drop on solution based on the current M1151A1 (HMMWV) chassis. The structure is comprised of all 5083-H131 Aluminum alloy armor plates with various thicknesses. The structure design consists of the following new features: (1) Robust joining design utilizing interlocking ballistic joints and mechanical interlocking features, (2) unique B-pillar gusset design connects roof & floor with B-pillar & tunnel, and (3) “Double V” underbody shaping design. The TARDEC designed, integrated & built vehicle achieved no crew core body injuries for a vehicle of this weight class and demonstrated meeting the crew survivability objective when subjected to a 2X blast during the live fire underbody blast tests. These efforts help to not only baseline light tactical vehicle capabilities, but also validate the possibility of meeting aggressive blast objectives for light tactical vehicles. These results provide government-owned designs that are scalable and actionable solutions for future HMMWV fleet upgrades.
ABSTRACT In this paper a new bolt attachment method was explored, where the attaching bolts were divided into two sets. The first set of bolts was tightened and was used to connect the underbody plate to the hull under ordinary operations. The second set of bolts connecting the plate and the hull were not tightened and had some extra axial freedom. Under blast loading, the first set of bolts would break due to high tensile and shear loads, but the second set of bolts would survive due to extra axial freedom which allows the plate and the hull vibrate and separate from each other to a certain extent. A simulation model was developed to verify this concept. Three underbody plate-hull connection approaches were simulated and analyzed: 1) all tightened bolts, 2) some bolts not fully seated, 3) all bolts not fully seated. The simulation results show that with option 1), 100% of the bolts broke under the blast loading. With option 2) the not fully seated bolts survived and continued to attach the plate to the hull. And with option 3) all the bolts not fully seated also survived. This new concept might provide an improved approach for attaching the underbody armor plate to the vehicle hull which would enhance the occupant and vehicle survivability while reducing engineering complexity and cost.
This work is based on a current project funded by the United States Army Small Business Innovation Research (SBIR) Program and is being conducted with the Tank Automotive Research, Development and Engineering Center (TARDEC) Ground Systems Survivability (GSS) Team and Paradigm Research and Engineering. The focus of this project is to develop an advanced and novel sensing and activation strategy for Pyrotechnic Restraint Systems, Air Bags and other systems that may require activation. The overriding technical challenge is to activate these systems to effectively protect the Soldier during blast events in addition to Crash, Rollover and Other Injury Causing events. These activations of Pyrotechnic systems must occur in fractions of milliseconds as compared to typical automotive crashes. By investigating systems outside of typical accelerometer based applications and activations, the potential exists to exploit systems that require little power, are self-contained and provide the required output for the desired result. As such Constant-Flux Magnetostrictive Sensors shall be evaluated in a self-contained environment to provide the output during these events. By activating the Pyrotechnic Restraint Systems and Air Bag Systems early in Blast Events, the systems can Restrain the Occupant and provide flail protection from surfaces within the vehicle. As the system is developed various test scenarios will be introduced to activate these systems and design a robust sensing and activating strategy.
In today's vehicles underbody parts are absolutely necessary to reach a certain performance level regarding fuel saving, corrosion protection, driving performance and exterior as well as interior noise. With the constant demand for additional parts, which means additional weight on the car, lightweight materials have come more and more into the focus of development work. LWRT (low weight reinforced thermoplastic) is the acronym for this material group. The ongoing success of such materials in underbody applications that compared to compact materials such as GMT (glass mat reinforced thermoplastic) is the weight saving of up to 50 %, or in other words, with LWRT you can cover twice as much surface then with GMT. The production process is compression molding, but with low pressure because LWRT-material needs only partial compact areas, most regions of these parts can have a density even below 0.5 g/cm3. Another advantage coming with the process is the possibility to use multi-cavity tools, so a high volume production becomes very economical. The multilayer structure can be easily tailored to customer specifications regarding stiffness, strength, acoustic performance and other properties. Since LWRT can have an open porous structure, which absorbs noise from both sides of the part (engine side for engine noise and street side for e.g. tire noise), the material has become very interesting to replace existing NVH-solutions such as additional absorbers on the parts.
The Wuling Rongguang is a small van which uses a mid-engine layout where the engine is located underneath the floor panel in-between front and rear wheels. A particular challenge for this kind of layout is the protection of the engine against soiling. Typical protective measures consist of large mudguards in combination with an engine cover. While needed for soiling protection, these parts can have a strongly adverse effect on aerodynamic drag. This paper describes process and the results of the aerodynamic optimization of the underbody of the Wuling Rongguang. Because design changes had to be evaluated for aerodynamics performance as well as for their effect on the soiling, a digital approach was used which allowed to do the soiling analysis as a post processing to the flow simulation. As a first step, a baseline model was built and analyzed. This included the development of a soiling model taking into account wheel spray and splashing effects. The soiling model used available best practices where available and was also calibrated against some road test results to ensure a proper reproduction of the soiling effect. The analysis of the baseline results identified the areas of inefficiencies and the potential for reducing the drag. In an iterative process design changes were made to the front mudguards and the engine cover to improve the flow in the underbody and finally to the rear spoiler for improving the overall wake structure. The soiling performance was evaluated for all design changes and only those changes that gave improved or at least equal soiling patterns compared to the baseline were accepted. As a result of this process, an overall improvement potential of 9.6% in aerodynamic drag was obtained. The final step in this project was the confirmation of the results in the wind tunnels of the Shanghai Automotive Wind Tunnel Center (SAWTC). The tests in the aero-acoustic wind tunnel confirmed an improvement of 7.1 % for drag. Tests for soiling were done in the climatic wind tunnel. These tests in a well-controlled environment also confirmed the results obtained from the CFD simulations.
ABSTRACT Over the course of typical survivability analyses for underbody blast events, a multitude of individual cases are examined where charge size, charge location relative to the vehicle, and vehicle clearance from the ground are varied, so as to arrive at a comprehensive assessment. While multi-physics computational tools have reduced the expense and difficulty of testing each loading case experimentally, these tools still often require significant execution and wall-clock times to perform the simulations. In efforts to greatly reduce the time required to conduct a holistic survivability analysis, Fast Running Models (FRMs) have been implemented and validated to act as a surrogate for the computationally expensive finite element tools in use today. Built using a small set of simulations, FRMs generate loading data in a matter of seconds, representing a significant improvement in survivability analysis turnaround time.
In this paper the effects of a rough underbody on the rear wake structure of a simplified squareback model (the Windsor model) is investigated using balance measurements, base pressure measurements and two and three component planar PIV. The work forms part of a larger study to develop understanding of the mechanisms that influence overall base pressure and hence the resulting aerodynamic drag. In the work reported in this paper the impact of a rough underbody on the base pressure and wake flow structures is quantified at three different ground clearances. The underbody roughness has been created through the addition of five roughness strips to the underbody of the model and the effects on the wake at ground clearances of 10.3%, 17.3% and 24.2% of the model height are assessed. All work has been carried out in the Loughborough University Large Wind Tunnel with a ¼ scale model giving a blockage ratio of 4.4% for a smooth under-body or 4.5% with the maximum thickness roughness strips. The tests are conducted with a fixed ground plane. Results are presented for the base pressure distribution and these are compared against the stream-wise PIV results. This work demonstrates the need for rough underbody structures to be considered during base pressure investigations before any model scale work is conducted due to their influence on the wake structures.
The Selective Catalytic Reduction (SCR) is the main after-treatment solution for high efficient diesel engines under development to cope with future lower fuel consumption and NOx emissions requirements (EU6+ legislation). Exhaust gas temperatures are decreasing too, leading to new after-treatment system developments in a close coupled position. Nevertheless before all vehicle architectures allow it, SCR systems are and will still be installed in underbody position. The current paper deals with an underbody metal SCR after-treatment systems, which is capable of active thermal management, and an ultra-compact SCR dosing system. These technologies are described and emission results obtained on several application examples (from passenger cars to light duty commercial vehicles) are presented and discussed in conjunction with an effective active thermal management of the SCR function. It is shown that the NO2/ NOx ratio as well as the temperature level at SCR system inlet, among all the parameters governing the SCR efficiency play an important role for the feasibility and the acceptance of an underbody SCR solution.
Wind noise has become an important indicator for passenger automobile quality. Several transmission paths can be related to different parts of the vehicle exterior. While the greenhouse (side glasses, windshield, seals & others) often dominates the interior noise level above 500 Hz, the contribution coming from the underbody area usually dominates the interior noise spectrum at lower frequencies. This paper describes a framework of numerical tools which is capable of determining realistic underbody turbulent and acoustic loads being generated for typical driving conditions, as well as performing the noise transmission through underbody panels and the propagation of sound to the drivers ear location. Different numerical tests are performed to demonstrate the ability of a Statistical Energy Analysis model updated with Finite Element Method properties to predict accurately the noise transmission through the underbody of simplified car vehicle in the mid frequency range under aero acoustic excitation. Parameters of the hybrid technique and the use of finite element modeling to estimate them are discussed. Transfer function comparisons between pure FEM and the hybrid technique are performed involving various load types to demonstrate the consistency of these methods. Cabin sound pressure level comparison for a simplified vehicle with wind noise excitation shows good correlation to FEM calculations performed with adequate statistical treatment. In addition, sensitivity analysis for several underbody parameters involving stiffness, mass, damping and geometry design change is applied to show further the utility of the technique for wind noise design.
In this paper, using the facilities offered by the ANSYS CFX, CFD code, the authors investigate numerically the flow around the Ahmed body for the rear slanted upper surface of 35°, fitted with a simple underbody diffuser, without endplates, in order to find the influence of the later one on the main aerodynamic characteristics, drag and lift. Relative motion between body and ground is simulated. The study is performed for different geometrical configurations, length and the angle of the diffuser being the parameters which are varied in ranges which are relevant for hatchback passenger cars. Later, based on a theoretical approach, a coefficient of the equivalent hydraulic resistance of the diffuser is computed, which helps to evaluate the drag due to underbody diffuser.
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